JP2003505180A - Metabolic calorimeter using respiratory gas analysis - Google Patents

Abstract

(57) SUMMARY An indirect calorimeter is provided for measuring a subject's metabolic rate. This includes a respiratory calorimeter (10) that is configured to contact and be supported by the subject and to pass inspiration and expiration as the patient breathes. The flow path (22) is operative to receive and pass inspired and exhaled gas, a first end in fluid communication with the respiratory connector (20), and a first end in fluid communication with a source and sink of respiratory gas. It has two ends. The flow meter generates an electrical signal as a function of the instantaneous volumetric flow of inspiration and expiration through the flow path. The component gas concentration sensor (84) generates an electric signal as an instantaneous ratio of a predetermined component gas during exhalation when the exhalation passes through the flow path. As the subject breathes through the calorimeter (10), the computing unit (96) receives the electrical signals from the flow meter and the component gas concentration sensor (84) and calculates at least one respiratory parameter.

Description

Detailed Description of the Invention

TECHNICAL FIELD The present invention relates to a respiratory device for measuring metabolic and related respiratory parameters by indirect calorimetric analysis. (Background Art) Granted to Mault, co-inventor of the present invention, US Pat. Nos. 4,917,108, 5,038,792, 5,178,155, 5,179,958, and 5,836,300 are incorporated herein by reference. These patents disclose a system for measuring metabolic and related respiratory parameters through an indirect calorimeter.
These devices typically use a flow meter that passes both the inspiration and expiration of the user through the device and integrate the resulting instantaneous flow signal to determine the total total volumetric flow. In one embodiment, the gas exhaled by the user is passed through the carbon dioxide scrubber before it is passed through the flow meter, so that the difference between inspiratory volume and expiratory volume is
It is a measure of the oxygen substantially consumed by the lungs. In another embodiment, the concentration of carbon dioxide exhaled by the user is measured by passing the exhalation volume through a capnometer and integrating the signal with the expiratory flow rate. The oxygen consumption can then be calculated as the difference between the inspiratory volume and the expiratory volume minus the exhaled carbon dioxide volume.

Scrubbers used with these certain systems are relatively bulky and require replenishment after extended use. The capnometer used with the instrument to measure carbon dioxide concentration is highly precise, as any error in measuring carbon dioxide concentration will result in a significantly higher error in the determination of the resulting exhaled oxygen concentration. Must be and therefore expensive.

An additional approach for monitoring indirect heat and cardiac output is Maul.
Co-pending application No. 09 / 008,435, 09 / 191,782, PCT / US99 / 17553, PCT / US99 /
No. 27297, PCT / US00 / 12745, which are incorporated herein by reference.

DISCLOSURE OF THE INVENTION The present invention provides an indirect calorimeter for measuring the metabolic rate of a subject. The calorimeter includes a respiratory connector supported in contact with the subject and configured to allow inspiratory and expiratory gases to pass as the subject breathes. The flow path serves to receive and pass inspiratory and expiratory gases. A first end of the flow path is in communication with a respiratory connector and a second end is in communication with a source and sink of respiratory gas, the respiratory gas being atmospheric, ventilator, or other gas. It can be a mixture source. The flow meter produces an electrical signal as a function of the instantaneous volumetric flow of inspiratory and expiratory gases passing through the flow path. The constituent gas concentration sensor produces an electrical signal as the gas passes through the flow path as a function of the instantaneous ratio of a predetermined constituent gas in the inspiratory gas and / or the expiratory gas. The calculation unit receives electrical signals from the flow meter and the constituent gas concentration sensor as the subject breathes through the calorimeter and calculates at least one respiratory parameter for the subject.

In some embodiments, the flow passage comprises a flow tube through which inspiratory gas and expiratory gas pass, and a chamber disposed between the first end of the flow passage and the flow tube. Contains. The chamber surrounds one end of the flow tube to form a concentric chamber.

In another embodiment, the flow tube forms part of the channel and is located between the two ends of the channel. The first end of the flow path takes the form of an inlet conduit extending orthogonal to the flow tube.

In some embodiments, the flow path comprises an elongated flow tube through which inspiratory and expiratory gases pass. Omni-Flowmeter is an ultrasonic flowmeter and contains two spaced ultrasonic transducers. Each of these transducers is aligned with the elongated flow tube such that the ultrasonic pulses transmitted between the transducers generally travel in a path parallel to the fluid flow within the flow tube. There is.

Further embodiments of the present invention are also disclosed in the following description and the accompanying drawings. Other advantages and applications of the invention will become apparent from the detailed description of the preferred embodiment of the invention, given below with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION Basic Configuration of Calorimeter Referring to FIGS. 1 and 2, a respiratory calorimeter according to the present invention is shown generally at 10. The calorimeter 10 includes a body 12 and a respiratory connector, such as a mask 14, extending from the body 12. In use, the body 12 is grasped by the user's hand and, as best shown in FIG. 1, the mask 14 is brought into contact with the user's face so as to surround the mouth and nose. An optional pair of straps 15 is shown in FIG. This strap provides another means for holding the body 12 of the calorimeter 10 by hand. Alternatively, the strap can support the mask and calorimeter in contact with the user's face.

With the mask 14 in contact with the face, the user normally breathes through the calorimeter 10 for a certain period of time. Calorimeter 10 measures various factors and calculates one or more respiratory parameters such as oxygen consumption and metabolic rate. A power button 16 is located on the top side of the calorimeter 10 to allow the user to control the calorimeter functions. Another light is located below the power button 16, which acts as a light pipe so that when the light is turned on, the button is illuminated. This light is
It is preferably used to indicate the status of the calorimeter before, during and after the test. A display screen is arranged behind the lens 18 on the calorimeter main body 12 on the side opposite to the mask 14. The test result is displayed on the screen after the test.

Referring now to FIG. 8, there is shown another respiratory calorimeter and calorimeter with a mouthpiece 20 rather than the mask 14 of FIG. Mouthpiece 20 is preferably sized and shaped to be inserted into a user's mouth and through which breaths can pass. This mouthpiece may be made of various materials including silicone. Depending on the preference of the user, the calorimeter according to the invention may be used with either a mask or a mouthpiece. Mouthpiece 20 may be needed for certain users, such as users with facial hair. To obtain accurate results, substantially all of the user's inspiration and expiration must pass through the calorimeter. Therefore, when the mouthpiece 20 is used as a breathing connector, it is preferable to use a nose clip (not shown) to close the user's nostril.

As best shown in FIG. 8, the calorimeter body 12 preferably includes a disposable flow tube portion 22 and a reusable main portion 24. Mouthpiece 20
A breathing connector such as is connected to the side of the disposable flow tube section 22. In use, each user is provided with a fresh disposable part 22 with an appropriate breathing connector 14 or 20. The reusable main part may be used by multiple users. The reusable main part 24 has a recess 26 formed on one side to accommodate the disposable part 22.

<Basic Mechanical Configuration> Next, the mechanical configuration of the calorimeter 10 will be described in more detail with reference to FIGS. 3 and 4. FIG. 3 shows all the parts of the calorimeter in exploded form, with the disposable part 22 removed from the recess 26 of the main part 24. FIG. 4 is a vertical cross-sectional view of the calorimeter showing the disposable part 22 assembled in the main part 24 and assembled. However, since the calorimeter can be described in other positions, the description in these orientations is merely used for convenience and is optional.

The disposable portion 22 of the calorimeter 10 is generally elongated in the longitudinal direction, and the disposable portion 22 is a concave portion.
It may be said to have a generally vertical outward facing surface 28 that remains exposed when housed in 26. In the preferred embodiment, this outward facing surface has a height of about 75 mm and a width of about 28 mm. The inlet conduit 30 extends outwardly perpendicularly from this outward facing surface 28. In the preferred embodiment, the conduit 30 extends from the outward surface 28 about 2 mm,
It has an inner diameter of 19 mm. As best shown in FIG. 4, a radial mounting flange 32 is provided adjacent the outer end of the inlet conduit 30 to provide attachment of a respiratory connector such as a mask. The breathing connector is securely attached and sealed to the mounting flange 32, preferably by ultrasonic welding.

Disposable portion 22 generally comprises an outer shell 34 within which is generally provided vertical sidewalls and vertical flow tubes 36. The flow tube 36
It is preferably cylindrical with open upper and lower ends. In the preferred embodiment, the flow tube has a length of about 63 mm and an inner diameter of about 12 mm.
For purposes of definition, flow tube 36 may be said to have an inner surface 38 on the inside of tube 36 and an outer surface 40 on the outside of tube 36. Similarly, the outer shell
34 can be said to have an inner surface 42 inside the shell and an outer surface 44 outside the shell. As shown in FIG. 4, the outer surface 40 of the flow tube 36 is spaced from the inner surface 42 of the outer shell 34 so that a concentric gap is formed between the two components of the disposable portion 22. The width of this gap is somewhat different at different locations around the tube. However, the width of this gap is generally at least 5 mm at the top of the flow tube 36, and the outer surface 40 of the tube 36 and the inner surface of the shell 34 are interdigitated as the gap extends downward for purposes of molding. It is slightly tapered.

The flow tube 36 and the outer shell 34 are interconnected by an annular flange extending between an inner surface 42 of the outer shell 34 and an outer surface 40 of the flow tube 36. An annular flange 46 joins the flow tube 36 and the outer shell and is located closer to the bottom of the flow tube than to the top. In the preferred embodiment, the flange 46 is located approximately 43 mm from the top of the tube 36. Above the flange 46,
And, the flange 46 completely connects the outer surface of the flow tube 36 to the inner surface of the outer shell 34 so that a concentric chamber 48 is formed between the outer surface of the flow tube 36 and the inner surface of the outer shell 34. It is sealed.

As best shown in FIG. 4, the inlet conduit 30 intersects and penetrates the outer surface 28 of the outer shell 34 above the flange 46 so that the conduit is concentric chambers. In fluid communication with 48. In the preferred embodiment, the center of the inlet conduit 30 is approximately 25 mm from the top of the outer surface.

Referring again to FIG. 3, the upper end of the outer shell 34 has a pair of generally horizontal engaging rails 50 that project laterally. The recess 26 of the reusable portion 24 of the calorimeter has a corresponding pair of engagement slots 52 (only one of which is shown). When the disposable portion 22 is docked in the recess 26 of the reusable portion 24, the engagement rail
The 50 is slid into the engagement slot 52 to stably secure the disposable portion and the rest of the calorimeter 10. The spring 54 forms part of the engagement slot 52 and pushes upward on the underside of the engagement rail 50. As will be appreciated by those skilled in the art, the disposable portion may be made of a variety of materials. In the preferred embodiment, the disposable portion is made of ABS plastic.

According to one embodiment of the invention, the disposable part 22 and the reusable part 24 are designed so that only specially designed genuine disposable parts cooperate with the reusable part. Various approaches to achieving this will be apparent to those of skill in the art. For example, the disposable part may include a genuine device, such as a chip or magnetic chip recognized by the reusable main part. Preferably, the calorimeter is
It only works when the genuine disposable part is docked to the reusable part.
Also, the main part is some kind of physical "recognition" that the correct disposable part has been fully docked, so that it does not have to be tested for accidentally or incompletely docked disposable parts. May include an interlock of.
Alternatively, the reusable part may recognize, record and / or transmit some sort of identification code associated with each disposable part. This allows accurate record keeping. Also, a particular code may be given to a particular user to allow the reusable portion to recognize the particular user.

Referring now to FIGS. 3 and 4, the recess 26 in the reusable main portion 34
The upper end of is determined by the upper wall 56. Outer shell 34 on disposable portion 22
The upper edge of is fitted into this upper wall 56 and is held in place by the spring 54. The bottom ledge 58 generally defines the lower end of the recess 26. The lower end of the outer shell 28 in the disposable portion 22 fits against this bottom shelf 58. Therefore, the upper wall 56 of the recess 26 is
When the disposable part 22 is docked with the reusable part, it seals the upper end of the outer shell 34 of the disposable part. Alternatively, a seal may be provided on the upper edge or upper wall 56 of the outer shell 28 to improve sealing performance. Preferably, the sides of the disposable portion 22 are also snugly fitted to the sides of the recess 26. When docking the disposable part 22 to the reusable part, it is preferred that little or no leakage gas passing through the disposable part leaks through the connection between the disposable part 22 and the rest of the calorimeter 10.

The bottom of the recess 22 is only partially defined by the bottom ledge 58. An outlet channel 60 is formed behind the shelf 58 between the rear edge of the shelf 58 and the back wall 62 of the recess 26.

The flow tube 36 does not extend upward or downward like the outer shell 34 of the disposable portion 22. When the disposable part 22 is docked to the reusable part, the upper end of the flow tube 36 stops without reaching the upper end of the outer housing and also does not reach the upper wall 56 of the recess 26. In the preferred embodiment, a gap of about 6 mm is left between the upper end of the flow tube and the upper wall 56. Thus, when the disposable portion 22 is docked to the reusable portion 24, the interior of the flow tube 36 is in fluid communication with the concentric chamber 48. The bottom end of the flow tube 36 also stops without reaching the bottom ledge 58 of the recess 26. In the preferred embodiment, a gap of about 6 mm is left between the flow tube and the ledge 58. Therefore, the bottom end of the flow tube 36 is not blocked by the ledge 58, and the interior of the flow tube 36 is in fluid communication with the outlet channel 60 behind the ledge 58.

Referring to FIGS. 3 and 4, the reusable main portion 24 of the calorimeter 10 has an outer housing 64 constructed in multiple pieces. A semi-cylindrical main housing member 66 defines the side wall of the reusable portion and the recess 26. A top cap 68 closes the top of the main housing member 66 and houses the power button 16. Vented button cap
70 closes the bottom of the main housing member 66. The button cap 70 includes an open grill 72 in fluid communication with the outlet channel 60 in the housing. Thus, breathing gas and atmosphere can flow between the area outside the calorimeter 10 and the area inside the calorimeter by flowing through the grill 72. The front cap 74 closes the front of the main housing member 66. The front side here is defined as the side of the calorimeter facing away from the mask. The front cap 74 contains the lens 19 and has an oval opening 76 formed therein to allow viewing of the display screen 18 behind the lens 19. . As shown, the main housing member 66, top cap 68, bottom cap and front cap 74 are joined using various fasteners. Alternatively, they may be designed to snap fit together and may be glued together or otherwise joined together. Those skilled in the art will appreciate that the components forming outer housing 64 can be made of a variety of materials. In the preferred embodiment, these parts are molded from ABA plastic.

<Flow Path> With reference to FIG. 4, a flow path of respiratory gas passing through the calorimeter 10 will be described. In use, when the user exhales, the exhaled air passes through the respiratory connector and out through the calorimeter 10 into the atmosphere. When inhaled, ambient air is drawn into the calorimeter, through it, and through the respiratory connector to the user. This flow of breathing gas is illustrated by arrows AG. It will be appreciated that the calorimeter may be connected to a mechanical ventilator or another gas source instead of the surrounding atmosphere.

Arrow A indicates the flow to and from the user, and the flow to and from the inlet conduit 30. The inlet conduit 30 is a concentric chamber so that the breath flowing from the inlet conduit encounters the outer surface 40 of the flow tube 36.
It must be connected to 48, and therefore must run the outer surface of the flow tube 36 up, down, or around its side, as shown by arrow B. This abrupt change in flow direction has several effects. First, the lower end of the concentric chamber 48 acts as a saliva trap. That is, excess water in the user's exhaled air is easily removed from the exhaled air stream and easily falls to the lower end of the concentric chamber 48. Second, exhaled gas can take various paths and can be redirected to assist in introducing vortices into the flow tube. Vortex flow through the flow tube 36 is preferred for flow measurement purposes. Most importantly, the concentric chambers 48 act to introduce respiratory gas into the flow tube 36 from all radial directions as uniformly as possible. This helps make the flow in the flow tube linearly measurable over a wide range of flow rates.

The gas flowing from the concentric chambers during exhalation is represented by arrows C and D.
As shown in, the flow encounters the upper wall 56 of the recess 26 and changes the flow by approximately 180 °,
Flows down through the interior of 6. The flow through the flow tube 36 is indicated by arrow E. As mentioned above, the bottom end of the flow tube 36 has stopped without reaching the bottom ledge 58. Thus, during exhalation, gas flowing down the flow tube 36 encounters the bottom ledge 58, diverges around the ledge as indicated by arrow F, and is directed to the outlet flow path 60. From there, the exhaled gas passes through the grill 72 and into the atmosphere, as indicated by arrow G.

Upon inhalation, gas flows from the atmosphere through the grill 72 and into the outlet channel 60, as indicated by arrow G. From there, the intake air flows around the bottom ledge 58 towards the bottom end of the flow tube 36, as indicated by arrow F. As shown, an additional concentric chamber 78 is formed between the outer surface of the flow tube 36 and the inner surface 42 of the outer shell 34 and below the flange 46. When inhaled, this concentric chamber 78 creates a vortex in the flow that acts to introduce gas from all radial positions into the flow tube as uniformly as possible. The intake air then flows as indicated by arrow E.
Flow through 36 and turn 180 ° as indicated by arrows C and D and into concentric chamber 48. From here, the intake air enters the inlet conduit 30 as indicated by arrow B.
Into the breathing connector as indicated by arrow A.

The physical configuration of the calorimeter 10 described above allows for a number of, and often the opposite, factors. Inspiration and expiration are preferably unrestricted as they flow through the calorimeter. Experiments have shown that when the inspiratory and expiratory flows encounter some significant resistance, breathing becomes more difficult and metabolic rate increases.
The calorimeter preferably measures the actual metabolic rate rather than the metabolic rate artificially enhanced by flow resistance. Flow resistance also leads to a pressure drop through the calorimeter.
The pressure drop through the calorimeter is preferably less than 3 cm water column at a flow rate of 1 liter / sec (1 L / s). As an opposite factor, the accuracy with which an ultrasonic velocimetry system can measure the flow rate through the flow tube 36 increases as the flow rate increases. However, flow resistance increases with flow velocity. Therefore, there is a tradeoff between flow velocity measurement accuracy and flow resistance. Also, longer flow paths allow better measurement accuracy. Increasing the flow path length increases the calorimeter size and may also increase flow resistance. The configuration described above provides an excellent combination of low flow resistance, accurate flow rate measurement, saliva removal and compact packaging.

Electronic Components Referring to FIGS. 3 and 4, the circuit board 88 is mounted vertically inside the front cap 74 in the reusable main portion 24 of the calorimeter 10. The circuit board supports or connects to each of the electronic components of the calorimeter. The oxygen sensor 84 is mounted near the lower edge of the circuit board and extends forward so as to be located immediately behind the rear wall 62 of the recess 26. An opening 86 in the back wall 62 allows gas in the flow path 60 to contact the oxygen sensor 84. To prevent leakage of breathing gas that has passed through the oxygen sensor, the oxygen sensor
A gasket 87 is placed around the opening 86 between the 84 and the back of the wall 62. Temperature sensor 90, ambient pressure sensor 92, and relative humidity sensor 94 are all mounted on circuit board 88 at the positions shown. Obviously, these various sensors may be placed in other locations if desired. As will be appreciated by those skilled in the art, various types of sensors may be used to measure temperature, pressure and humidity. In one embodiment of the present invention,
Temperature sensor is part number RL1005-5744-10 available from Keystone Thermometrics
It is a thermistor such as 3-SA, and the pressure sensor is a Motorola sensor (part number MPX4115A)
And the relative humidity sensor is a Honeywell sensor (part number HIH3605A). A calorimeter central processing unit 96 and a speaker are also mounted on the circuit board, along with an application specific integrated circuit (ASIC) 98 that forms part of the ultrasonic flow sensing system. The display screen 18 and its associated circuitry are mounted behind the lens 19 on the front side of the circuit board and aligned with the holes 76 in the front cap 74 to allow viewing of the display screen 18.

The upper ultrasonic transducer 80 is located on the upper wall of the recess 26 in the reusable main part 24 of the calorimeter 10. This is connected to the circuit board 88 by wiring not shown. The lower ultrasonic transducer 82 is arranged on the bottom shelf 58 and is also connected to the circuit board 88 by wiring not shown. Ultrasonic transducers 80 and 82 form part of an ultrasonic flow sensing system, which are described in further detail below.

In the embodiment shown in FIGS. 3 and 4, the power connector 102 is provided on the circuit board 88 and is aligned with the hole 104 on the reusable portion 24 side of the calorimeter 10. In this embodiment, a power cord (not shown) is connected to the power connector 102 and extends to a plug-in power supply for powering the calorimeter. Alternatively, the calorimeter may include a rechargeable or replaceable internal battery instead of or in addition to the power connector. A communication connector 106 is also mounted on the circuit board 88 to allow the calorimeter 88 to be connected to an external device such as a computer. This communication connector can take several forms. Alternatively or additionally, the calorimeter may include infrared (IR) transmitters and receivers, radio frequency transceivers (such as Bluetooth), or one or more wireless communication devices such as cell phone or modem devices. it can. The inclusion of a wireless communication device allows the calorimeter to send and / or receive data to / from local / remote computing devices, including over the Internet. Cordless phones may also be incorporated into communications, physiological monitoring and data processing. This and other approaches are disclosed in Mault's Provisional Patent Application No. 60 / 165,166, filed on 11/12/99, which is incorporated herein by reference. As a further alternative, the calorimeter may include a slot for receiving a removable memory card. The data measured or calculated by the calorimeter can be stored in or retrieved from this removable memory card. This card can later be removed and inserted into another computer for data transfer and / or further processing.

Approaches for Indirect Calorimetric Analysis As will be appreciated by those skilled in the art, the calorimeters described above offer significant packaging, airflow, and moisture removal advantages over the prior art. Again, as will be apparent to those skilled in the art, the actual measurements and calculations required to determine various respiratory and metabolic parameters can be made in a number of ways. A calorimeter constructed in accordance with the above description and accompanying drawings may be configured for use with some of these approaches, as described in further detail below. Therefore, it should be understood that the following description of the preferred measurement and calculation approaches is not exhaustive of the possible approaches of the described calorimeter physical configuration.

According to a first preferred embodiment of the present invention, ambient temperature, relative humidity and pressure as well as inspiratory volume, expiratory volume and oxygen concentration are measured. The remaining factors may be calculated or hypothesized as needed. As one of ordinary skill in the art will appreciate, each of these factors can be measured in various ways.

Flow Sensing In accordance with the first preferred embodiment of the present invention, inspiratory volume and expiratory volume are measured by instantaneously measuring the flow rate of gas through the flow tube 36. All inspiration and expiration pass through this tube. Moreover, since the inner diameter of the tube is known, the volumetric flow rate can be calculated by measuring the flow velocity in the tube. According to the present invention, the flow velocity in flow tube 36 is measured using two spaced ultrasonic transducers.

Referring to FIG. 4, the upper ultrasonic transducer 80 is supported by the upper wall 56 of the recess 26. The lower ultrasonic transducer 82 is supported on the bottom shelf 58 at the bottom of the recess 26. As shown, these transducers are arranged such that the ultrasonic pulses traveling between transducers 30 and 82 travel parallel to the flow in the flow tube indicated by arrow E.
As will be apparent to those skilled in the art, ultrasonic pulses propagating in a direction parallel to the fluid flow provide advantages in measurement accuracy.

Flow velocity measurements using ultrasonic pulses are all made in US Pat. Nos. 5,419,326, 5,503,151, 5,645,071 and 5,647,370 issued to Hamoncourt et al.
, Which are incorporated herein by reference. these
In the Hamoncourt patent, an ultrasonic transducer is arranged such that pulses are transmitted through a fluid flowing in a direction, which direction has a component in said flow direction. That is, while flowing the fluid through the tube, the transducer is positioned on the sidewall of the tube at an angle such that the ultrasonic pulses are transmitted at an angle to the fluid flow. The flow velocity may be calculated based on the fact that the ultrasonic pulse propagating with the flow travels rapidly, while the ultrasonic pulse propagating against the flow travels slowly. A mathematical correction is made for the fact that the ultrasonic pulse travels at an angle to the flow.
Preferably, the pulses are transmitted alternately in the same direction as the flow and in the opposite direction so that the time difference can be calculated.

The present invention can use a transducer that includes a metallized polymer film and a perforated metal sheet. In one preferred embodiment, the ultrasonic flow measurement system comprises an NDD company of Zurich, Switzerland and a C of Massachusetts.
Supplied by hemsford. This embodiment combines the use of ultrasonic transducers with a coaxial flow path in a new and improved configuration.

The ultrasonic pulse is transmitted in the direction along the flow or in the direction opposite to the flow,
Passage times are measured in the upstream and downstream directions. If the gas flow rate is zero, the transit time in either direction through the gas is the same, which is related to the velocity of the sound wave and the distance traveled. However, if there is a gas flow, the transit time upstream will be different from the transit time downstream. For a given flow, the transit times upstream and downstream are directly related to the gas flow rate.

The flow velocity is measured using a pair of ultrasonic transducers 80 and 82 mounted at opposite ends of the flow channel formed generally by the flow tube 36. A high voltage (approx. 200 V) is applied to one transducer, for example 80, in order to deliver an ultrasonic pulse, and then this voltage is rapidly removed. This causes transducer 80 to resonate at its original frequency and function as a sound wave transmitter. A voltage of approximately 100V is applied to the other transducer 82, allowing it to act as a sound wave receiver (sound wave detector). A DC bias must be applied to the receiving transducer 82 so that it produces the maximum electrical signal. Transit time is
The time between the transmission of a pulse from the converter 80 and the detection of the pulse by the converter 82. The roles of transmitter and detector are then reversed in order to measure the transit times of the pulses traveling in opposite directions.

Thus, a series of transit time measurements in the form of U1-D1-U2-D2-U3-D3 are obtained. Here, U and D refer to the transit times for the pulses traveling up and down the flow tube, respectively, and the numbers refer to the order of measurement. (The terms upper and lower are appropriate for the configuration shown in FIG. 10, but in other embodiments the flow direction may be horizontal, diagonal, etc.). By averaging U1 and U2, we obtain by linear interpolation the upper time estimated at the time D1 was measured. To obtain the difference in transit times at the time D1 is measured, and thus the flow velocity, we use D1
Is compared to the average of U1 and U2. Similarly, to get the flow rate at the time U2 was measured, we compare U2 to the average of D1 and D2. This is just one simple way of processing the measured data. Other approaches will be apparent to those of skill in the art.

A schematic of the electronic device is shown in FIG. The ultrasonic transducers 80 and 82 are preferably controlled by an ASIC (application specific integrated circuit) 98 using the transducer control circuit 110. The ASIC 98 controls the transmission and detection of ultrasonic pulses and also uses a serial UART (universal asynchronous receiver transmitter) operating at 19.2 Kbaud to communicate with the calorimeter CPU (Central Processing Unit) 96. Used for. ASIC1
Using a conventional boost converter 112 regulated by 98, 190-230V (DC
) Range high voltage is generated from a low voltage (5V) power supply 114. This high voltage
Required to operate the ultrasonic transducer. Low voltage source 114 also supplies power to other device elements. Other electronic control schemes with similar functionality may be used.

A command is sent from the CPU 96 to the ASIC 98 to start the flow measurement. The ASIC applies 200V to one converter (eg, 80) through the control circuit 110. The voltage is then discharged and a pulse of approximately 35 kHz (resonant frequency of the transducer) is emitted. At the same time, 100V is applied to the other converter 82. A 10 MHz clock in ASIC 98 controlled by a crystal 116 associated with the ASIC drives a 100 MHz counter,
The counter counts in 10 ns increments starting from the time the pulse was sent.
Upon receiving the 35 kHz signal from the detecting transducer 82, the counter is stopped and the transit time value (in the form of a number of 10 ns time intervals) is sent to the CPU 96 using a serial connection. The roles of the sound wave transmitter and the sound wave receiver are switched every 5 ms, and the ultrasonic pulse is transmitted in the opposite direction along the flow path.

A typical transit time in this example is 220 μs, or 220 × 10 ns time sense, in which case the number 2200 will be sent to the CPU as a data byte.
The transit time data is sent from the ASIC to the CPU on the UART. An interrupt service routine is used to capture the serial byte when it is received by the CPU.

The transit times (upper and lower times) of the pulse traveling up and down the flow tube, and the difference between successive measurements are stored in three separate buffers. Use a different buffer to zero the device so that the flow reading is zero when there is no actual flow. Different buffers are also used to detect inspiratory, expiratory, and no flow conditions. There is an additional instrument delay time in the transit time measurement process, typically around 20 μs. These can be different for the upper and lower time measurements and can be compensated for by subtracting this delay from the transit time data.

A software process is used to calculate the flow value using an averaging method, eg, a method of comparing the average of two upper times with an intervening lower time (as described in more detail above). It To obtain the flow velocity as well as the linearization constant, this flow value is
Combined with the cross-sectional area of the tube (113 mm ² in the presently preferred embodiment), the path length (transducer feel distance, 76 mm in the presently preferred embodiment), and the calibration factors for upflow and downflow. The flow velocity is summed over the expiration time and the inspiration time to obtain the volumetric flow rate.

In the preferred embodiment, the CPU's interrupt service routine is used to form an accumulation of the upper and lower times stored in separate buffers.
The software process samples them periodically, eg every 100 ms (20 samples). This effectively averages the flow rate measurements, leading to high resolution in the calculated volumetric flow rate. In the presently preferred embodiment, the measured volumetric flow resolution is approximately 0.9 ml / s per individual measurement, or approximately 0.045 ml / s for an average of 20 readings.

Other embodiments are possible. For example, the ultrasonic flow sensor may be obtained from other sources. Some sensors use the sing-around method of flow velocity determination. The ultrasonic pulse is transmitted along the flow path from one transducer to the other, and a new pulse is delivered when the previous pulse is received. The frequency of the pulse transmitted is related to the transit time along the tube. The role of transmitter and detector is reversed after a certain time or after a certain number of pulses, the pulse train being sent in opposite directions along the flow path,
A new pulse is sent when the previous pulse is detected. The new frequency of the transmitted pulse is measured. Therefore, equivalent upper and lower times are determined from the frequency measurements and can be processed as described above.

Microfabricated ultrasonic transducer arrays are available from Sensant, Inc. of San Jose, Calif. These sensors have the advantages of low noise, high frequency range, potentially low drive voltage, and can be used in the present invention. For example,
The pulse repetition rate can be increased, allowing the instantaneous flow rate to be measured more frequently (ie with higher resolution), giving a more accurate integrated volumetric flow rate. Microfabricated temperature, pressure, and humidity sensors may be incorporated into the ultrasonic array to compensate for the effects of these environmental factors on the properties of the ultrasonic transducer. For example, distortion of microfabricated structures due to environmental effects can be monitored using electrical capacitance. One or many arrays may be used to measure (cross-section flow imaging) and integrate variations in transit time across the lateral dimension of the flow tube (orthogonal to the flow direction). Different sensors on the array may be used simultaneously as transmitters and detectors to allow simultaneous measurement of upstream and downstream transit times so that averaging is not required.

As will be appreciated by those skilled in the art, other approaches to flow sensing may be used instead of, or in addition to, ultrasonic sensing in the preferred embodiment. For example, the flow velocity may be measured by using fine rotors, hot wire based mass flow meters, and pressure differential type flow meters in the flow path. As will be apparent to those skilled in the art, the presently preferred embodiment could be adapted to use these or other approaches for flow measurement.

<Oxygen Sensor> As described above, in the present invention, the oxygen concentration in the expiratory flow is also measured. That is, the instantaneous oxygen concentration is measured simultaneously with the measurement of the flow velocity. The term "instantaneous" means that oxygen sensing has a very fast response time. Preferably, the response time of oxygen sensors for use with the present invention is 100 msec or less. In some embodiments, this response time is 30-40 msec or less.

The oxygen concentration may be measured by various methods. In the presently preferred embodiment of the present invention, a fluorescence-based oxygen sensor is used to measure oxygen partial pressure in exhaled breath.

As best shown in FIGS. 4 and 5, oxygen sensor 84 is mounted adjacent window 86 in the rear wall of recess 26. This brings the oxygen sensor 84 into contact with the inspiratory and expiratory gases passing through the outlet channel 60. This arrangement also exposes the oxygen sensor to a swirl of gas, which is preferred.

Fluorescence-based oxygen sensors are known in the art and have been described, for example, by Colvin (US Pat. No. 5,517,313, all incorporated by reference herein).
Nos. 5,894,351, 5,910,661, 5,917,605, and PCT International Publication
WO 00/13003). The sensor typically includes an oxygen permeable membrane in which oxygen indicator fluorescent molecules are embedded. In U.S. Pat.Nos. 5,517,313 and 5,894,351, Colvin describes a sensor that uses a silicone polymer membrane, wherein the oxygen indicator fluorophore molecule is the ruthenium complex tris (4,7-diphenyl-perchlorate). The use of 1,10-phenanthroline) ruthenium (II) is suggested. The orange / red fluorescence of this ruthenium complex is quenched by the local presence of oxygen. Oxygen diffuses from the gas flowing over the oxygen permeable membrane into the membrane, inducing fluorescence quenching. The time response of the quenching effect to changes in oxygen concentration in the gas outside the membrane is related to the thickness of the membrane. As described in U.S. Pat.No. 5,517,313,
Thin membranes are preferred for rapid response.

Referring now to FIGS. 6 and 7, the fluorescence-based oxygen sensor used in this embodiment is shown generally at 120. 6 is an exploded view, and FIG. 7 is a cross-sectional view. Presently preferred sensors are Se based on the technology described in the Colvin patent.
Supplied by nsors for Medicine and Science, Inc. Circuit board 144,
It has a plurality of downwardly extending pins 149 for mechanically and electrically connecting the sensor 120 to the main circuit board 88 of the calorimeter. An LED 132 is typically mounted in the top center of the circuit board. In addition, the pair of photodiodes 134 and 136 are connected to the circuit board 14
Mounted on top of 4. The photodiodes 134 and 136 are mounted on the opposite side of the LED 132 and at a short distance from the LED. An optical fiber is mounted on top of each photodiode. The filter 138 is mounted on the photodiode 134 and the filter 140 is mounted on the photodiode 136. The optical fiber is bonded to the photodiode with an optically clear adhesive.

A heat dissipator 142, ie a thin copper sheet, preferably with a downwardly bent edge, is mounted on top of the circuit board. This heat dissipator has legs 143 extending downward at its four corners, each of which engages with a hole 145 in the circuit board 144. Heat dissipator 142
The legs 143 and the downwardly bent edges of the heatsink dissipate the central portion of the heat dissipator 142 on the circuit board 14.
Support a short distance above 4 and form a gap between them. The LED 132, photodiodes 134 and 136, filters 138 and 140 are located in this gap between the circuit board 144 and the dissipator 142. Two circular holes 146 are drilled in the heat dissipator, one hole being located directly above each of the photodiodes 134 and 136. Two glass substrates 128
And 130 are mounted on top of the heat dissipator 142 and one glass substrate is mounted just above the top of each hole 146. As shown, these glass substrates 128 and 130 are rectangular. A circular phosphor film is formed on top of each glass substrate. That is, the circular film 122 is formed on the glass substrate 128, and the circular film 124 is formed on the glass substrate 130. A gas impermeable glass cover 126 is placed over the circular membrane 124 and bonded to the glass substrate 130 with epoxy resin 125. Therefore, the circular membrane 124 is internally sealed by the upper cover 126 and the edge epoxy resin 125. This allows one circular membrane 1
While the 22 is exposed to the atmosphere, the other circular membrane 124 is sealed and unexposed. Therefore, the circular film 122 does not react to the change in oxygen concentration, whereas the circular film 122 does. Circular membrane 122 is referred to as the sensing area and circular membrane 124 is referred to as the reference area.

Referring again to FIG. 7, the gap between the circuit board 144 and the heat spreader 142, and the hole 14
The 6 is filled with an optically transparent waveguiding material 141. The waveguiding material 141 serves to optically couple the LED 132 to the glass substrates 128 and 130, making the glass substrate an integral part of the waveguide. The waveguiding material also optically couples the sensing region 122 and the reference region 124 to the filters 138 and 140 and the photodiodes 134 and 136. The result is a continuous optical waveguide that optically couples these components. Suitable waveguiding materials are manufactured by Norland Products of New Brunswick, NJ and Epoxy Technoloty of Bilerica, MA,
The latter is sold as EPOTEK®.

To avoid the problem of agglomeration formed on the sensing area 122 and the reference area 124,
Preferably, heat dissipator 142 is used to warm both of these areas. For this purpose, a small heater 148 including a resistor is mounted on the circuit board 144 adjacent to each leg mounting hole 145. The heat dissipator legs 143 are soldered into the holes 45 and to the heater 148 so that heat is transferred to the heat dissipator. The thermistor 147 is mounted on the circuit board 144 in a position such that it contacts one of the downward bent edges of the heat spreader 142 when the sensor is assembled. A thermistor may be soldered to the edge to improve heat transfer. Then, using the thermistor 147, the heat dissipator 142
Temperature is monitored and the heater 148 is controlled to maintain a generally constant temperature. EEPROM 155 containing calibration data for oxygen sensor on circuit board
It is attached to the bottom surface of 144.

Fluorescent films 122 and 124 are formed by oxygen permeable films containing oxygen indicator fluorescent molecules such as ruthenium complexes. In the presently preferred embodiment, the oxygen permeable membrane is a porous glass such as a sol / gel.

Light radiation from an LED 132, preferably a diode (LED) that emits blue light, is transmitted by a light guiding material 141 to a sensing region 122 and a reference region 124. The emission wavelength of LED 132 is selected to induce fluorescence from regions 122 and 124 of the phosphor film.
Other wavelengths may be used for other fluorophores. The orange / red fluorescence emission from the detection area and the reference area is detected by two photodiodes. The photodiode 134 detects the fluorescence from the reference region 124, and the photodiode 136 detects the fluorescence from the detection region 122. The output of the photodiode is provided to a high speed transconductance amplifier as described below. Optical filters 138 and 140
Overlies the photodiode and passes orange / red fluorescent radiation while rejecting other wavelengths, especially blue radiation from the LED. Optical filter 128 and
140 may be made of epoxy coating, glass filter, or polymer-based sheet material. Preferably, prefabricated polymer-based sheet material is used. Emissions from the LED 132 and fluorescent emissions from the membranes 122 and 124 pass through holes 146 in the plate 142. Preferably circular membranes 122 and 124,
The hole 146 and the active areas of the photodiodes 134 and 136 are all circular with the same diameter.

During oxygen sensing measurements, substrates 128 and 130, as well as sensing area 122 and reference area 124.
Is maintained at approximately 45 ° C. to reduce problems with water aggregation. Heating of the substrate is accomplished by passing current through four surface mounted resistors 148. Copper plate to allow to adjust the heating current and temperature through the resistor
The temperature of 142 is monitored by thermistor 147. Moisture is removed from the gas stream by several means, such as chemical drying, water absorbing / adsorbing materials, membranes, filters, foam sheets, or some type of surface treatment (oxygen permeable hydrophobic membranes or other approaches). It is not necessary to heat the oxygen sensor as long as the agglomeration on the phosphor screen is prevented by). Heating improves temperature stability, but oxygen sensitivity is better at low temperatures.

The emission output of the LED is preferably regulated using an electrically regulated drive current. In the presently preferred embodiment, a regulation frequency of 2 kHz is used. Other tuning frequencies may be used, such as 1-10 kHz. In the present example, the oxygen partial pressure is measured based on fluorescence intensity measurement, where the decrease in fluorescence intensity due to quenching of oxygen is measured. The less oxygen present, the greater the fluorescence detected, and the more oxygen present, the less fluorescence. There is a fluorescent response each time the LED 132 is illuminated and its intensity varies depending on the amount of oxygen present. As is known to those skilled in the art, the fluorescent response is not immediate, and there is a time delay before the fluorescent material fluoresces in response to illumination by LED 132. Similarly, there is a delay between when the LED 32 is turned off and when the fluorescence is stopped. This is known as the decay time. Preferably, the time of adjustment applied is selected to be significantly greater than the fluorescence decay time. Figure 1
2 is the applied radiant intensity along with the possible fluorescence response signal (rounded signal 152)
A possible example of a vs. time signal (square wave signal 150) is schematically shown. In the present example, the square wave time is about 0.50 msec, while the fluorescence decay time is about 3 msec.
It is μsec (0.003 msec). Another approach to measuring oxygen concentration is based on detecting changes in fluorescence decay time, for example using the measurement of the phase delay of the fluorescence signal relative to the excitation signal. For example, in FIG. 12, the measurement may be performed such that the phase delay of fluorescence decay corresponds to the period indicated by “a”. This phase delay changes with oxygen concentration and can therefore be used as an indicator of oxygen concentration. Higher tuning frequencies are used in such fluorescence decay measurements. led
The intensity adjustment of the output may also be sinusoidal. The thickness and porosity of the phosphor film may be adjusted to control the diffusion limited fluorescence signal response time.

A signal from the photodiode 136 (detection area signal) and the photodiode 134
Signal (reference region signal) is passed through similar amplification, filtering and demodulation stages to obtain a DC signal corresponding to the fluorescence intensity from both regions. If the reference signal and the detection signal are at different levels at zero oxygen concentration, their respective gains in the amplification stage may be adjusted to compensate. After amplification and conversion to DC, the sense region signal and the reference region signal are compared to theoretically obtain a signal independent of error sources such as temperature changes, LED intensity changes, etc. In the current example, this comparison takes the form:

Signal = Detection Area−K ^* (Reference Area−Reference Baseline) Here, K is a constant determined experimentally. Alternatively, the ratio of the two signals may be taken.

FIG. 13 shows a schematic diagram of signal processing from the photodiode 136. The signal entering 156 is passed through a high pass filter 158 to remove signals generated by DC and low frequency ambient light (eg, low frequency stray light from a lamp) and also an inverted AC amplification stage. Passed through 160. This AC signal is another high pass filter 1
It is passed through 62 and through another amplification stage 164. The amplified AC signal is then based on the analog switch 166 (based on the analog device chip ADG71BRM,
Other devices may be used). This switch is between the signal when the signal LED is on and a constant reference voltage when the LED is off (used as a virtual ground for the amplification stage, showing the input at 168). Alternate with. The following amplification stage 170 alternates between gains of 0.5 and -0.5 to demodulate the signal. This signal is then passed through a further amplification stage 172 and a low pass filter 174. The use of such a scheme, sometimes referred to as a synchronous amplifier, or lock-in amplifier, significantly improves the signal / noise ratio. This is conventional technology and other schemes may be used.

To calculate the actual signal from the oxygen sensor, a baseline measurement with the LED off is first taken. The signal obtained with the LED turned on (conditioned) is read and subtracted from the baseline to determine the final oxygen sensor signal.

Electrical Circuits and Components FIG. 14 shows a simplified scheme of the calorimeter for electrical configuration.
The calorimeter has a central processing unit (CPU) 96 that controls the overall operation of the device.

The oxygen sensor, generally designated 120, comprises a blue LED 132, a fluorescence quenching oxygen sensing area 122, a fluorescence reference area 124, a thermistor 147, a heater 148, and an EEPROM 155 containing calibration data for the sensor 120. . LED 132 is an oscillator / modulator 1
Receives drive current controlled by 53.

The ultrasonic transducers 80 and 82 use the control circuit 110 to direct high voltage from the signal and high voltage source 112 to the sensor and pass detected ultrasonic pulses to the ASIC 98.
Controlled by IC 98. ASIC 98 and CPU 96 are connected by a serial UART.

When the device is turned on, by pressing the switch 178, the CPU commands the heater 148 to heat the fluorescent region to approximately 45 ° C. The indicator light 176 indicates a warm-up state. The temperature of the oxygen sensor is monitored by the thermistor 147. During this period, the unit calibrates the oxygen sensor and a zero flow test is performed as described below. From the thermistor reading, the CPU indicates that the sensor temperature has stabilized.
, The light 176 indicates that the device is ready.

When the device is ready to begin a respiratory analysis, a human breathes through the device and the inspiratory and expiratory gas flows are monitored by ultrasonic transducers 80 and 82. Flow through the unit triggers data recording. The volumetric flow rate is calculated by the CPU from the serial data received from the ASIC. The ASIC determines the time between transmitting a pulse from one transducer and receiving with the other transducer.

The oxygen sensor provides two electrical signals from photodiodes 134 and 136, both tuned at the same frequency as LED 132. The signal from the photodiode 134 depends on the partial pressure of oxygen in the gas flowing over the reference region due to the fluorescence from the reference region 124. The signal from the photodiode 136 by the oxygen sensing area 122 is reduced in intensity (quenched) by the presence of oxygen in the sensing area. The signals from the two photodiodes have similar filter, amplification and demodulation stages.
It is passed through 0 and 182 to give two respective DC voltage values, which are passed through the analog / digital converter (ADC) to the CPU. The comparison of the two signals eliminates environmental effects (eg temperature, LED intensity) and is used by the CPU to determine oxygen concentration.

Using the calculated volumetric flow rate and oxygen concentration, the human oxygen consumption rate is calculated by the CPU. From this the human metabolic rate is calculated in Kcal / day form and displayed on the liquid crystal display 18 using the LCD control circuit 184.

The CPU also retrieves voltage signals from environmental sensors, namely temperature sensor 90, pressure sensor 92, and temperature sensor 94. These signals are also used in the calculations, as described below.

Calculation of Metabolic Parameters As will be apparent to those skilled in the art, there are many methods for determining metabolic parameters such as VO ₂ (volume of oxygen consumed) and RMR (quiescent metabolic rate). As mentioned previously, the presently preferred approach for measuring metabolic parameters uses ambient temperature, pressure and humidity measurements, as well as inspiratory volume, expiratory volume, and oxygen concentration in exhaled breath.

Initial consideration: VO ₂ , ie the amount of oxygen consumed, is the difference between the amount of oxygen inhaled and the amount of oxygen expelled. It is also desirable to determine VCO ₂ . VCO ₂ is the volume of carbon dioxide produced by the body and is the difference between the amount of carbon dioxide exhaled and the amount of carbon dioxide inhaled. Once VO ₂ and VCO ₂ are known, the RMR can be calculated. Alternatively, certain assumptions are made regarding the ratio of VO ₂ and VCO ₂ , allowing calculation of RMR from VO ₂ alone. Therefore, the main purpose of the present invention is to determine VO ₂ . This requires determining both the amount of oxygen drawn and the amount of oxygen expelled. Determining VCO ₂ is also preferred as it allows the determination of other metabolic parameters. To determine VCO ₂ , it is necessary to measure or calculate both the amount of carbon dioxide inhaled and the amount of carbon dioxide exhaled. The methods and calculations used in the first preferred embodiment of the present invention are schematically represented in FIGS.

Inspiration: The volume of oxygen drawn in, V _i O ₂ , may be calculated by multiplying the volume of air drawn in by the oxygen fraction of air. The oxygen fraction of dry air varies only slightly with position and can therefore be assumed to be 20.946. However, the actual air we breathe is not dry air, but contains various water vapor moieties. In order to determine the oxygen portion of the inhaled air, the intake volume attributable to water vapor must be determined and subtracted to obtain a dry air reading. As mentioned above, the temperature sensor 90, the relative humidity sensor 94, and the atmospheric pressure sensor 92 are all mounted on a circular board 88 in the case of the reusable main part 24 of the calorimeter 10. Theoretically, these should provide values for the temperature, pressure and humidity of the air inhaled by the user. However, under some conditions, the temperature within the case of the reusable main portion 24 may differ from ambient temperature. This may be due to the heating of the case by the user's hand, the heating by internal electronic components, and the heat absorbed from the exhaled breath. Therefore, it is preferable to correct the temperature value received from the ambient temperature sensor 90. If the relative humidity sensor 96 were actually placed in ambient air,
The output will reflect the relative humidity in the ambient air instead of inside the case. Since the relative humidity sensor 94 may be at an elevated temperature, its output does not indicate true ambient conditions, but rather the relative humidity at this elevated temperature. Since the case is not weld-sealed, the water pressure inside the case is the same as the water pressure in the surrounding atmosphere. The partial pressure of water vapor, ppH ₂ O, can be calculated from the following relational expression.

PpH ₂ O = RH × VpH ₂ O (t) (a) where RH is the relative humidity in percent, VpH ₂ O is the vapor pressure of water,
t is the temperature. VpH ₂ O is a function of temperature and can be obtained from a look-up table or using empirical fitting curves. Therefore, the partial pressure of atmospheric water vapor ppH ₂ O
Can be calculated from the known relative humidity and temperature inside the case.

Referring to FIG. 16, a typical total exhaled volume of 750 mL is shown on the far left of the chart. This volume contains water vapor. The water vapor volume in intake air may be determined according to the following formula.

VH ₂ O = (ppH ₂ O / Pamb) × Vtotal (b) where VH ₂ O is the volume of water vapor, ppH ₂ O is the partial pressure of water vapor, Pamb is the ambient pressure, Vtotal is the total volume of intake air. In the example shown in FIG. 16, the ambient temperature, pressure and humidity (ATP) are 23 ° C. temperature, 755 mmHg pressure, and 35% relative humidity. Using the above equation, the total volume of water vapor may be checked in a table,
Alternatively, 7.28 mL may be calculated from the total inhaled volume of 750 mL. The amount of water vapor in the inspiration is then subtracted from the total volume to give a dry volume of 742.72 mL.

The percentage of dry air, attributed to CO ₂ , O ₂ , nitrogen and other gases, is known from various sources, examples of which are given in the chart below. By multiplying the total volume of dry air% Others _{(argon) 0.937 CO 2 0.033 O 2 20.946} N 2 78.084 These percentages Ingredients dry air, to calculate the volume of each of the component gases, the left bar of FIG. 16 The values shown in are obtained.

As shown in the example of FIG. 16, the volume of oxygen taken in under atmospheric conditions is 155.57 mL. However, this is at atmospheric conditions and varies with location and time. Therefore, it is necessary to convert the volume of each component gas to standard temperature, pressure and humidity, STPD (standard temperature and pressure, drying). The calculations typically used for RMR assume 0 ° C, 760 mmHg STPD, and 0 percent relative humidity.

As is known to those skilled in the art, the conversion between one atmospheric pressure condition and another condition is a simple ratio problem based on temperature and pressure. However, in this case, the actual atmospheric pressure is not known because the temperature sensor is at an elevated temperature. As known to those skilled in the art, the speed of sound waves is a function of ambient temperature, water vapor mole fraction, ambient pressure and CO ₂ mole fraction. This relationship is related to The Journal of the Acoustical Society of America, Vo
l.93, No. 5, May 1993, pp. 2510-2516, the contents of which are incorporated herein by reference. Its expression takes the form of the _{following: c = a 0 + a 1} t + a 2 t 2 + (a 3 + a 4 t + a 5 t 2) x w + (a 6 + a 7 t + a 8 t 2) p + (a 9 + a 10 t + a ₁₁ t ² ) x _c + a ₁₂ x _w ² + a ₁₃ p ² + a ₁₄ x _c ² + a ₁₅ x _w px _c (c) where the counts are defined in the table below.

[0083] count value _{a 0 331.5024 a 1 0.603055 a 2} -0.000528 a 3 51.471935 a 4 0.1495874 a 5 -0.000782 a 6 -1.82 × 10 -7 a 7 3.73 × 10 -8 a 8 -2.9.3 × 10 -10 a ₉ -85.20931 a ₁₀ -0.228525 a ₁₁ 5.91 × 10 ^-5 a ₁₂ -2.835149 a ₁₃ -2.15 × 10 ^-13 a ₁₄ 29.179762 a ₁₅ 0.000486 Also, c is the velocity of the sound wave, t is the ambient temperature, x _w is the water vapor mole fraction, p is the ambient pressure, and x _c is the CO ₂ mole fraction. Some of these variables have known values. The CO ₂ mole fraction in ambient air can be assumed, as its standard value is known and changes only slightly with position. The ambient pressure may be measured with high accuracy by an ambient pressure sensor inside the calorimeter case. Further, the velocity of the sound wave may be measured by a flow meter during inspiration.

Preferably, the ultrasonic flowmeter used with the present invention transmits ultrasonic pulses in both the upstream and downstream directions so that the transit time in ambient air is the upstream transit time during the intake of ambient air. By averaging time and downstream transit time, it can be measured independently of flow rate. Then, the speed of the sound wave may be calculated according to the following equation.

[0085]

[Equation 1] Where c is the velocity of the sound wave, L is the distance between the transducers, t _u is the transit time in the upward direction and t _d is the transit time in the downward direction. This leaves essentially two variables: ambient temperature and water vapor content. Relative humidity and ambient temperature are correlated by equation (a). By transforming and solving for relative humidity, the following equation is obtained.

[0086]

[Equation 2] At this point, the partial pressure of water, ppH ₂ O, is known based on the output of the humidity sensor 94 and the assumption that the partial pressure is the same inside and outside the case. However, the equation (c) is expressed by the water vapor mole fraction x _w , not the relative humidity. Therefore, three additional equations are needed. The water vapor mole fraction may be calculated by the following equation.

[0087]

[Equation 3] Where RH is the relative humidity in fractions, f is the enhancement factor, and p _sv is the saturated vapor pressure of water vapor in the air:

[0088]

[Equation 4] and

[0089]

[Equation 5] Combining equations (c) (e) (f) (g) and (h), this leaves two unknown variables: temperature and relative humidity. As known to those skilled in the art, these equations can be solved in various ways for the two remaining variables. According to one presently preferred approach, these equations can be solved by an iterative process.

First, initial temperature prediction is performed. The temperature indicated by the temperature sensor may be used as a starting point. Next, the relative humidity is determined according to equation (e). The temperature is then calculated using the just calculated relative humidity in equation (c). The calculated temperature is returned to the equation (e) to calculate a new relative humidity. This process is repeated until the calculated values converge, but typically after a few iterations convergence occurs.

At the end of this process, the actual ambient temperature of the air being drawn is known. The ambient conditions are now known along with the ambient pressure measurements. Then, each volume of the component gas is converted to STPD. Alternatively or in addition to the above approaches, the ambient temperature or the temperature in the flow tube may be measured directly using any type of suitable temperature sensor. As an example, the temperature sensor may be mounted inside the case of the calorimeter, and a small fan may be used to continuously move ambient air through the sensor to ensure accurate readings. Good. Other approaches will be apparent to those of skill in the art.

When converted to STPD, the volume of gas drawn in has the value shown in the second bar of FIG. As shown, the corrected volume of absorbed oxygen, V _i O _2, is 143.48 mL, and the corrected volume of drawn carbon dioxide, V _i CO _2, is 0.23 mL.

Calibration of Oxygen Sensor As mentioned above, the percentage of oxygen in the inhaled air is measured or assumed. In the above description, oxygen concentrations or percentages are assumed. This is because this value only changes slightly with position. However, oxygen sensor 84 responds to the presence of oxygen in the inspiratory air. Therefore, the oxygen sensor output at the time of suction may be used to calibrate the oxygen sensor for each suction. In theory, an ideal oxygen sensor would change its output only in response to changes in oxygen concentration and not changes in other parameters such as temperature, humidity and total pressure. However, real oxygen sensors are not completely immune to changes in other parameters.

FIG. 17 shows a series of curved surfaces representing changes in the oxygen sensor voltage output with changes in oxygen partial pressure and any second factor. This figure is for illustration purposes only, and thus the second factor can be considered to represent any or all of the other parameters to which the sensor actually responds. Since the concentration of oxygen and the values of other parameters such as humidity, temperature and pressure are known during inspiration, point 190 can be plotted to represent a known combination of oxygen partial pressure and other factors. it can. It will be seen that extending upwards from this point, the theoretical output or tested output curve 192 for the oxygen sensor predicts the output voltage corresponding to point 194. If the actual voltage output of the oxygen sensor under these known conditions is different from this value, a correction may be added to the output curve to correct the difference. For example, if the oxygen sensor actually outputs a voltage corresponding to point 196, the gain factor is applied to the main output curve 192, which "moves" it to the curve shown at 198. This allows for continuous fine tuning of the oxygen sensor output to improve accuracy in subsequent breath measurements.

Expiration During exhalation, total volume and oxygen partial pressure are measured using a flow meter and an oxygen sensor, respectively. As known to those skilled in the art, the temperature and humidity of exhaled breath are reasonably constant without individual differences. That is, for most healthy individuals, the temperature of breath exhalation averages 34.5 degrees. Also, the exhaled breath is saturated with 100% steam, giving 100% relative humidity. Experiments with the present invention show that the flow tube 36
It was established that the exhaled breath temperature at the midpoint of the was about 32.5 ° C on average. The pressure in the flow tube is substantially the same as ambient pressure due to the low resistance present in the calorimeter. The exhaled breath condition is called the saturated expiratory temperature pressure (ETPS). ET
The following equation is used to determine the volume of oxygen at PS.

[0096]

[Equation 6] Where V _E O ₂ is the volume of exhaled oxygen, ppO ₂ is the partial pressure of oxygen, Pamb is the ambient pressure, and Vtotal is the total expiratory volume. In the example shown in FIG. 16, the total expiratory volume is 800 mL, the partial pressure of oxygen is 121.6 mmHg, and the ambient pressure is 755 mmHg. This is 12
Give an expiratory oxygen volume at 8.05 mL ETPS. This value is ST
Need to convert to PD.

Exhaled O ₂ volume at ETPS may be converted to STPD by scaling for differences in temperature and pressure. This gives an O ₂ volume in STPD of 114.43 mL. The O ₂ volume consumed by the user during a single breath is calculated by subtracting the exhaled oxygen volume from the inhaled oxygen volume. Multiplying the number of breaths per minute gives the amount of oxygen consumed per minute.

Preferably CO ₂ production is also determined. Additional calculations are needed to do this. First, certain assumptions are made regarding the temperature and humidity of exhaled breath.
The volume of water vapor in the exhaled breath may be determined from the assumed relative humidity and temperature and the measured volumetric flow rate. By removing water vapor and converting it to dry air,
A total volume of 761.68 mL is obtained. Also assume that nitrogen (N ₂ ) and trace gases are retained in the lungs. Therefore, the nitrogen and trace gases inhaled are equal to the volume of nitrogen and other gases expelled in the STPD. This assumption improves as the data is summed over many breaths.

As shown in FIG. 16, the nitrogen and trace gas volumes are converted from STPD to ETPS, giving a volume of 605.74 mL. In this regard, the volumes of water vapor, oxygen, nitrogen, and trace gases are known in ETPS. The total volume is also known. Therefore, the volume not occupied by water vapor, oxygen, nitrogen, and trace gases should be attributed to CO ₂ . This gives a CO ₂ volume of 27.89 mL at ETPS. This value is then converted to STPD to give a breath carbon dioxide volume of 24.92 mL at STPD. User-generated CO ₂ during a single breath is calculated by subtracting the volume of carbon dioxide during inspiration from the volume of carbon dioxide during expiration. Multiplying the number of breaths per minute gives the amount of carbon dioxide produced per minute.

<Calculation of Resting Metabolic Rate> As is known to those skilled in the art, the resting metabolic rate (RMR) can be calculated by various methods. One known and accepted approach is given by the de Weir equation, which takes the form:

[0102] _{RMR = 1.44 (3.581 × VO 2} + 1.448 × VCO 2) - 17.73 where, VO ₂ is oxygen consumed volume in mL / min, VCO ₂ was produced in mL / min It is the amount of CO ₂ , and RMR is the quiescent metabolic rate at Kcal / day. That is, the respiratory quotient is given by the following equation.

RQ = VCO ₂ / VO ₂ where RQ represents the respiratory quotient. The respiratory quotient typically ranges from 0.7 to 1.1, depending on the type of stored energy source metabolized by the user's body. In calculating resting metabolic rate, RQ is assumed to be 0.85 for a typical user. Therefore,
Using this ratio, substituting VCO ₂ , the following equation is obtained.

RMR = 6.929 × VO ₂ −17.73 where RMR is the quiescent metabolic rate in Kcal / day, and VO ₂ is consumed by the user.
Oxygen volume in mL / min. Preferably, summing or averaging the various parameters measured by the calorimeter over multiple breaths provides improved accuracy.

Alternatively, the CO ₂ sensor may be incorporated into the calorimeter so that the CO ₂ concentration is measured directly rather than calculated. This allows the calculation of RMR as well as the more accurate calculation of RQ.

<Use of Calorimeter> When the calorimeter is first turned on, the unit goes through the warm-up and calibration period. Meanwhile, the oxygen sensor heater is turned on, and the oxygen sensor is warmed up to the steady state value. When the oxygen sensor reaches steady state, a zero flow test is performed. During the zero flow test, the flow sensor measures the flow rate through the flow tube. Since no calorimeter was used at this stage, there should be zero flow through the flow meter. However, if the flow meter shows a slight flow in either direction, it is offset to reestablish zero. Various approaches can be used for this zeroing, but it is preferable to take multiple readings before applying the offset factor. Also, during actual testing, the flowmeter may be dynamically rezeroed for a known period of zero flow.

To calculate a subject's resting metabolic rate (RMR) using a calorimeter, the subject sits or relaxes in a comfortable position, then turns on the calorimeter and warms up as described above. And after self-calibration, wear the respiratory connector on its face or mouth. The subject then breathes normally through the calorimeter for a few minutes. Typically, the user takes some time for the breathing and measured metabolic rate to stabilize. Therefore, the initial data is preferably not used as an indication of quiescent metabolic rate. As will be apparent to those skilled in the art, there are various approaches that allow calorimeters to measure accurate quiescent metabolic rates. According to one preferred approach, if the calorimeter detects a breath flow through the calorimeter, wait 30 seconds before recording. However, this time may increase or decrease. Once recording is initiated, the calorimeter makes measurements of flow, oxygen concentration, and sonic velocity. The oxygen partial pressure is measured every 1/10 second, and the flow velocity and sonic velocity are measured 200 times per second.
Flow rate and sonic velocity measurements are averaged to obtain 1 / 10th second values for volume calculation. The calorimeter integrates this data to calculate inspiratory volume, expiratory volume, inspiratory oxygen concentration (for calibration purposes), expiratory oxygen concentration, ambient temperature, ambient humidity, and ambient pressure. Then 10 breaths are averaged to obtain one breath block. At the end of the breath block, calculate VO _{2 for} that block. To determine the steady state, check the three blocks to see if they are within a certain percentage of each other. For example, if both of the previous two blocks are within 7 percent of the current block, the block is flagged as steady state. It is determined that a steady state has been reached when a steady number of consecutive blocks, for example 4 or 5 breathing blocks, are flagged as steady state,
The RMR is then calculated using VO ₂ and VCO ₂ and displayed on the display 18. Typically, 8-10 breaths per minute are used, so the length of one breath block is approximately 1 minute. Obviously, the data may be processed in other ways. Also, a constant error condition may be indicated. For example, an error signal may indicate when breathing is too fast or too slow. Also, if the flow velocity is too high, it will be out of the allowable range.
It may indicate an RMR, a hardware error, or an error for other reasons.

As mentioned above, most users need some time to stabilize their breathing and exhibit a quiescent metabolic rate. However, according to another aspect of the invention, the data during the "settling down period" may be used to predict the data during the steady state period.

Humans should be completely relaxed because the metabolic rate measured is a resting metabolic rate. However, a person's breathing will often be affected by the presence of a mouthpiece or mask, especially immediately after placing the mask over the nose and mouth. Accurate measurements are taken for a period of time after the mouthpiece is placed in the proper position,
For example, it may be delayed by 2 minutes and then return to normal after that period. However, if the mouse is worn for a long time, the person may not feel comfortable.

In order to reduce the time required to determine the exact value of human metabolic rate,
An algorithm may be used to extract quiescent level VO ₂ from data heading for the quiescent value. FIG. 18 illustrates a possible data set of VO ₂ measurement (and thus exit rate measured) vs. time obtained using an indirect calorimeter.
Oxygen consumption is measured as a function of time, for example as a function of breaths or a fixed number (eg 10) of blocks of breathing. In FIG. 18, the measured oxygen consumption shown by the solid line approaches the value corresponding to the true quiescent metabolic rate shown by the broken line as time passes. The person's actual metabolic rate is initially high due to respiratory abnormalities but can be constant during the measurement, in other cases the metabolic rate itself tends towards the true resting metabolic rate value. May gradually decrease. It can be modeled for both cases. The data obtained is applied to mathematical equations (eg polynomials, exponentials, logarithms, other functions, etc.) in the form of many parameters, including quiescent metabolic rate. The resting metabolic rate is determined from the fit to the data and the error in this measurement is evaluated from the quality of the fit to the data. This process can be performed continuously in real time as the breath analysis progresses, so when accurate measurements are taken, stop the measurements,
The mouthpiece can be removed. Alternatively, the data can be saved and the numerical analysis performed after the test is complete.

The exact form of data fitting used depends on the human response to the mouthpiece and other test conditions. In this example, for the case illustrated in FIG. 18, the data may be fit into: VO ₂ = A + B exp (-t / C) where A is the volume of VO ₂ corresponding to the true quiescent metabolic rate, B is the measure of respiratory abnormality at the start of the test, and C is after the start of the test. It is a measure of how quickly breathing returns to normal. After a number of initial tests have been performed on a person, an appropriate equation can be selected that models the respiratory response to that person's test. Alternatively, the model may be selected based on age or other demographic data about the person. The first breath or the first few breaths may be subtracted from the data to improve fit. Subsequent respiratory analysis may be shortened using this analysis, eg, the method described below or other methods.

(A) After the initial test, the time for hypopnea to approach normal can be determined and used to determine the length of the test. The data from the first part of the test can be excluded and the remaining measurements averaged. For example, if the above equation is applicable, data obtained before several multiples (integer or fraction) of C may pass (eg, C = 10 seconds, the first The data taken during 30 seconds can be discarded and the remaining data can be averaged).

(B) If the data from the test is analyzed in real time, the test can be terminated when an acceptable fit to the data is obtained.

(C) The data may be examined by an expert while the test is in progress, and the test may be stopped when the expert determines that data of sufficient quality has been measured. This decision will be empirical.

For a person breathing through the calorimeter of the present invention, the data is stored by calorimeter time and then sent to another electronic device for display, analysis, etc. The data may also be sent to another electronic device while the test is in progress (ie, "real time"). Data transfer from the calorimeter to another device may be done using flash card (memory card), wireless transmission (eg Bluetooth), cable, IR transmission, or other electromagnetic or electrical methods. , Or by inserting the calorimeter into another device. The use of flash cards
Details are disclosed in Mault's provisional patent application No. 60 / 177,009, filed January 19, 2000. Furthermore, the calorimeter may be equipped with calculation means for performing data analysis.

Under certain circumstances, the user cannot reach steady state during the test. Under these circumstances, the calorimeter indicates that it is not readable and that steady state values can be estimated. According to one approach, when the user appears to be near steady state, the blocks towards the end of the test may be given some additional weighting to average out the respiratory blocks during the test. Clearly, the detailed data recorded by the calorimeter may be observed by an experienced professional to determine the reliability of the data. For example, the calorimeter may be connected to a desktop computer, which records and / or displays data on a per-measurement or on a breath-by-breath basis. In this way, the expert can observe that the subject has a problem to reach a steady state, consult on how to better interact with the device and give a difference. Also, detailed data is
Other valuable instructions about the subject can be provided.

Example of a Calorimeter with Improved Hygiene The calorimeter according to the present invention can be safely used by multiple users without the undue risk of transmitting the pathogen from one user to another. It is possible.
In the preferred embodiment of the invention described above, each user is provided with their own disposable part along with their breathing connector. The fitness facility or doctor owns the reusable part. Alternatively, each individual user may own a complete calorimeter and only replace the disposable part for cleaning purposes. However, the calorimeter is preferably designed so that the pathogen is not easily transmitted from one user to another. Some improved sanitary versions of the present invention are disclosed in Figures 19-26, and another configuration of the oxygen sensor is shown in Figure 9.

Referring first to FIG. 19, a calorimeter according to the present invention is shown generally at 210.
The calorimeter has a reusable main portion 212 similar to the reusable main portion 24 described above. However, in the case of the embodiment shown in FIGS. 3 and 4, the user's inspiration and expiration is due to the ultrasonic transducers 80 and 82, the oxygen sensor 84, and the outlet flow path.
It comes in contact with 60 surfaces. They form part of the reusable part and are therefore not disposable or changed from user to user. The embodiment of FIG. 19 has been modified to prevent the user's breath from contacting the transducer and oxygen sensor. The disposable portion 214 has a ceiling 216 closing the upper end of the outer shell and a floor 220 closing the lower end of the outer shell 218. A hole 222 in the ceiling 216 is aligned with the ultrasonic transducer 224 above and has a piece of bacterial barrier material disposed in the hole 222. The barrier material may be any type of material that blocks the passage of pathogens but allows the passage of ultrasonic pulses. Similarly, a hole 228 aligned with the lower ultrasonic transducer is formed in the floor 220. Also in this hole 228 is a piece of bacterial barrier material 232
Are arranged. The oxygen sensor 234 in this embodiment has been moved somewhat upwards as compared to the previously disclosed embodiment. An opening 238 is formed in the rear wall 236 of the recess in the main portion 21 and is aligned with the front sensing surface of the oxygen sensor. The outer shell 218 of the disposable portion 214 has a rear wall 240 extending downwardly through the opening 238 and coupled to the floor 220 of the disposable portion 214. This high part 2
An opening 242 is formed in 40, and a membrane 244 is disposed across the opening. This membrane allows oxygen to pass freely, but not pathogens. Disposable part
The floor 220 of 214 has a passage 246 cut into it to allow flow into the outlet passage formed in the reusable portion. The passage 248 is large and has smooth sides to facilitate inspiratory and expiratory flow. The sides of the passageway 248 may be coated with an antimicrobial and / or high viral material to prevent contamination. Alternatively, this passage may be cleaned between uses. As a further alternative, a disposable sleeve that engages a floor opening in the disposable portion may be inserted into this passage. The sleeve may be removed and discarded after each use.

Referring to FIG. 20, another improved sanitary version of a calorimeter according to the present invention is shown generally at 250. Similar to the version described above, the disposable portion 252 of the calorimeter 250 includes a ceiling 254 that closes the top of the outer shell and a floor 258 that closes most of the bottom. In this version, a thin micromachined ultrasonic transducer 260 is mounted beneath the ceiling 254 of the disposable portion 252, just above the upper end of the flow tube 262 forming part of the disposable portion. This thin ultrasonic transducer replaces the large ultrasonic transducer described in the previous embodiment. The transducer may be a micromachined ultrasonic transducer array, such as that manufactured by Sensant, Inc. of San Jose, CA.

Electrical contacts 264 are located on the rear wall 266 of the disposable portion immediately behind the converter 260 and are electrically connected to the converter 260 by, for example, wiring 268. A corresponding electrical contact 270 is located on the back wall of the recess in the reusable portion 274 of the calorimeter 250 and is aligned with the contact 264 of the disposable portion 252. The contact point 270 of the reusable part is
It is connected to the main circuit board by wiring. Thus, the thin ultrasonic transducer 260 is in electrical communication with the main circuit board 276 when the disposable portion 252 is docked to the reusable portion of the calorimeter. However, since the thin transducer 260 and its associated wiring are mounted on the disposable portion 252, the entire transducer may be placed with the rest of the disposable portion. This prevents any problems with the contact of the user's breath with the transducer. Alternatively, the disposable part may be designed to be cleaned according to a special cleaning method that does not damage the transducer.

The lower thin ultrasonic transducer 278 is located on the upper surface of the floor 258 of the disposable part 252,
Aligned with the flow tube 262 and cooperates with the upper transducer 260 to measure the flow through the flow tube. Similar to upper transducer 260, lower transducer 278 is wired to electrical contact 280 adjacent electrical contact 282 located on the rear wall 272 of the recess.
A passageway 284 is formed in the floor 258 of the disposable portion 252 to allow inspiration and expiration to flow to and from the disposable portion. This passage communicates with the large flow area at the bottom of the reusable portion 274 of the calorimeter. Alternatively, the entire lower portion of the reusable portion may be moved so that the passageway in the floor of the disposable portion does not have a portion of the reusable portion beneath it. In this way, inspiratory and expiratory air flowing through the passages will flow directly into or out of the ambient atmosphere without contacting any of the reusable portions.

This embodiment of the calorimeter also uses another version of the oxygen sensor 288. In this version, the LED and photodiode portions of the oxygen sensor are incorporated into a sensor package 290 located on the back wall of the recess, approximately midway between the top and bottom of the recess. The remainder of the oxygen sensor 288 forms part of the disposable portion 252 and is referred to as the fluorescent portion 292. The fluorescent portion 292 comprises a light pipe 294 extending from the rear surface of the outer shell 256 adjacent the sensor package 290 into the wall 298 of the flow tube 262. Fluorescent material 300 is placed at the end of light pipe 294 so that it is in contact with the gas flowing through flow tube 262. The light pipe 294 conducts light traveling to and from the fluorescent material 300. This configuration is an oxygen sensor that comes into contact with the user's area.
Allows a portion of the 288 to be disposable. As shown, the fluorescent material 300 is a flow tube.
It is arranged substantially in the middle of 262. This provides the advantage that the flow section sensed by the oxygen sensor is approximately at the midpoint of the flow section being measured for flow rate.
This allows for better time correlation of flow and oximetry measurements.

Referring to FIG. 9, another version of oxygen sensor 302 is disclosed. In this version, the sensor package 304 is connected to the circular board 304. The sensor package 304 includes a light emitting diode LED and the photodiode of the previously described embodiment. A piece of fluorescent material 308 is placed in the wall of the flow tube 312, a portion of which is shown. The light travels across the small gap between the sensor package 304 and the fluorescent material 308. Clearly, this configuration requires a different construction of the flow tube. However, it allows a simple and compact construction of the oxygen sensor with a disposable part.

An important factor for the disclosed oxygen sensor with a disposable part is calibration. Fluorescence quenching oxygen sensors of the type described herein typically require careful calibration of the chemistry used. However, the highly accurate and repeatable application of fluorescent materials reduces the need for personalized calibration. Alternatively, the sensor package can include a mathematical model of the fluorescent material so that accurate oxygen concentration measurements can be made using the disposable fluorescent material. As mentioned earlier, calibration of the oxygen sensor during inspiration further improves accuracy.

Referring now to FIG. 21, another approach for improving hygiene for use with a calorimeter according to the present invention is illustrated. A calorimeter body according to any embodiment of the present invention is shown generally at 320. A sterilization filter module 322 connects between the inlet conduit 324 of the calorimeter 320 and a respiratory connector, shown here as a mouthpiece 326. With reference to FIGS. 21 and 22, the module 322 has a filter housing 328 with a calorimeter port 330 formed on one side and a breathing port 332 formed on the other side. The calorimeter port 330 mates with the calorimeter inlet conduit 324, while the respiratory port 332 mates with the respiratory connector. housing
328 may have a variety of shapes, including the generally rectangular shape shown in FIG. Three
A piece of biological filter material 334, such as Filtrete® available from Company M, extends within the housing 328, and air flowing between the breathing port 332 and the calorimeter port 330 allows the filter material to pass through the filter material. You have to go through. This filter material acts to remove pathogens, thus preventing them from flowing from the respiratory connector into the calorimeter. In this way, the calorimeter remains hygienic during use. Each subsequent user has a new filter module
322 is used and the used module is either retained by the user or discarded.

Referring again to FIG. 22, the module 322 includes an outer peripheral edge that joins the sidewalls 336 together.
It can be seen that it has two generally parallel and spaced side walls 336 with 338.
The filter material is generally parallel to the sidewalls 336 and extends between the outer perimeter edges 338. Figure 2
2, the saliva retaining wall 340 extends upwardly from the bottom edge adjacent the filter material 334, on the side of the filter material closest to the respiratory connector 326. In particular, while using a calorimeter with a mouthpiece, saliva is entrained in the exhaled breath, but preferably not introduced into the calorimeter. Much of the entrained saliva will run down the inside of the sidewall 336 along the lower edge of the breathing port 332 and collect in the area between the saliva retaining wall 340 and the sidewall 336 as shown. Also, some entrained saliva contacts the filter material and falls down and is collected in the saliva trap. This configuration avoids the previously mentioned need for a saliva trap in the disposable part of the calorimeter, but it may be retained for other purposes.

Referring now to FIGS. 23 and 24, another sanitary barrier configuration is illustrated. In the configurations of FIGS. 23 and 24, a mask 342 is provided instead of the mouthpiece. In this case, the mask 432 consists of a semi-rigid outer shell 344 that couples to the inlet conduit 346 of the calorimeter 348. Mask shell 344 may be made of any of a variety of materials, including polystyrene. The mask shell 344 is preferably ultrasonically coupled to the inlet conduit 346 of the disposable portion of the calorimeter to provide a hermetic seal. The disposable mask liner 350 is inserted into the mask shell 344. The mask liner 350 includes a liner shell 352 and a mask 342 that overlap a portion of the mask shell 344.
Includes a face seal 354 to seal the to the user's face, and a sanitary barrier 356 to filter all gases in and out of the calorimeter.
Again, the sanitary barrier 356 is a material such as 3M's Eltrete®.
Face seal 354 is preferably an inflatable seal membrane that is easily molded into the user's facial shape to provide a secure seal. The face seal 354 is securely attached to the liner shell 352, which is preferably vacuum formed plastic, such as by cement bonding. The sanitary barrier 356 is bonded to the liner shell 352, for example, by ultrasonic bonding.

Referring now to FIGS. 25 and 26, another filter mask design 360 is disclosed. Similar to the previous version, the semi-rigid mask shell 362 has a calorimeter 368.
Is coupled to the inlet conduit 364 in the disposable portion 366 of the. The mask liner 370 is inserted into the shell and is disposable. Mask Liner 370 is Fitre
It includes a piece of sanitary barrier material 372, such as te®, which is bonded to the liner shell 374 by, for example, insert molding and then molded with an injection molded face seal 376 of elastomeric material. The face seal 376 prevents leakage by firmly sealing the face of the user.

Because the user's face varies in size and shape, mask shells and / or mask liners are provided in different sizes and shapes to suit different users. Also, masks and filter housings of other breath-filtering designs may be used, as will be apparent to those skilled in the art. According to the invention, a relatively large piece of sanitary barrier material is used so as to prevent a pressure drop across the piece of sanitary barrier material. In this way, the barrier material does not significantly increase the resistance of the flow through the calorimeter, thereby causing no additional energy consumption when using the calorimeter.

Alternatively, a mask according to the present invention may include a nostril dilator to open the user's nostrils to reduce the effort associated with breathing through the mask. As one approach, an adhesive pad may be provided inside the nose of the mask. The pad presses against the user's nose and when opened, the mask opens the nostril passage.

Other Alternative Designs The embodiments of the invention described above may be modified in various ways without departing from the scope or teaching of the invention. The following description is of many alternative designs and modifications to the preferred embodiment.

Although the preferred embodiment of the present invention utilizes a fluorescence-based oxygen sensor, other approaches may be used. Other possible oxygen sensing methods include solid oxide sensors using zirconium oxide or other electrochemical sensors if adapted for rapid response. Molecular fluorescence, such as laser induced fluorescence, may be used. For example, sending laser radiation along the flow path, using a sensor on the side of the flow path to detect the fluorescence, or using a light guide to detect the fluorescence in the reusable body of the device. Can be transmitted to. Similarly, Raman spectrometers, including non-linear Raman spectrometers, may be used. The laser beam passes along the flow path and is detected at an angle to the beam. As with phase sensitive detection, a narrow band filter that rejects laser radiation will aid in detection. Other oxygen detection techniques include laser absorption; chromatographic methods; sensors based on diffusion rates through membranes; or fast response calorimetric sensors, such as light absorption or reflection of membranes such as transition metal complexes in the presence of oxygen. Changes in IR emissions from vibrationally excited molecules may be detected. Laser radiation may be used to selectively vibrate or vibronicly excite molecules. Also, for example, A. Mills, Platinum Metals Review, June 1997;
Fluorescent compounds (eg, platinum and gold complexes) are useful for oxygen detection, as described in US Pat. No. 5,119,463 and the like. Selective (eg, laser) photoionization of molecules followed by detection of photoions and electrons can provide a photocurrent that is proportional to molecule concentration. Also, the ultrasonic spectrum of the discharged gas is
It may contain molecular information about concentration, especially when using microfabricated ultrasonic transducers with broad spectrum response (10 MHz and below and higher frequencies).

As mentioned previously, the preferred oxygen sensing capabilities of the present invention can be augmented by the addition of carbon dioxide sensors. Other gases may be detected as well. The oxygen sensor, the carbon dioxide sensor, and other gas sensors are collectively referred to as a component gas concentration sensor here. Carbon dioxide sensing may be accomplished in various ways. Carbon dioxide concentration can be measured by using a carbon dioxide scrubber in combination with volumetric measurements, as described in some of Mault's previous patents and applications. Also, as described in Mault's earlier patents and applications, metabolic calculations based on carbon dioxide measurements may be performed without oxygen measurements. The calorimeter according to the invention can be constructed without any oxygen sensor and with any of a variety of carbon dioxide such as capnometers. Carbon dioxide may be measured using IR absorption with strong carbonyl absorption or other analytical techniques listed above for oxygen.
The carbon dioxide sensor and the oxygen sensor may be combined in the same package for a combined fluorescence quenching sensor, for example using selectively permeable membranes or fluorescent compounds.

As an alternative approach to indirect calorimetry, the approach disclosed in Mault's PCT WO 00/07498, incorporated herein by reference, may be incorporated into a calorimeter constructed in accordance with the present invention. Good. That is, the oxygen sensor could be omitted and the mass flow determined based on any of the approaches in WO 00/07498. This avoids the costs associated with oxygen sensors. Alternatively, a mass flow based approach may be used as a reinforcement for one or more gas concentration sensors.

Yet another approach to indirect calorimetry is to use a carbon dioxide scrubber to remove substantially all carbon dioxide from the inspiratory and / or expiratory flow and measure the difference in volumetric flow. May determine the amount of carbon dioxide produced. From this the metabolic rate may be determined. This avoids the need for component gas concentration sensors. Instead, only a scrubber and a two-way flow meter are needed.
This approach is further disclosed in Mault US Pat. No. 5,179,958. The above embodiments of the present invention can be readily configured to utilize this approach. For example, a scrubber module may be inserted as part of, or instead of, the sanitary filter module of Figure 21 in the flow path between the disposable portion and the respiratory connector. Alternatively, the disposable portion may be designed to include the scrubber material within the extended flow path.

Other flow sensing methods are possible, for example using the cooling rate or heat dissipation of objects in the flow path. Thermal wire mass sensors are known in the art, as well as analog devices using semiconductors (eg silicon), ceramics etc., eg thermal thin film semiconductor sensors. Other methods include turbines or impellers; noise levels of gas flow around obstacles or through holes; can be monitored with high precision, eg using laser reflection, eg holes or membranes due to pressure differences on each side. Strain; or other structures placed in the flow path, such as micromachined rod strain; and thermoelectric gas flow sensors. For example, direct pressure differential measurements may be used by using microfabricated pressure sensors at both ends of the flow path. Other configurations of ultrasonic transducers are possible.
For example, three transducers may be mounted at the edges of the gas flow path to form a V-shaped configuration. This V-centered transducer will transmit to two other transducers mounted equidistantly on opposite sides of the flow path on either side of the central transducer. The difference between the two transmission times is related to the gas flow rate. Other flow measurement techniques include thermal imaging followed by image analysis; Doppler shift of the transmitted ultrasonic signal; or absorption or emission of molecules or atoms as measured using, for example, laser radiation. Includes Doppler shift or spread of the band.

Moisture problems can be reduced by protecting the oxygen sensor from moisture or removing moisture from the air stream. For example, moisture removal may include exhaled gas, foam sheets (manufactured to include a drying mechanism); zeolites; molecular sieves;
Membrane; may include passing through a chemical desiccant (eg, silica gel). These moisture removal means may be mounted in the removable part for easy replacement. The oxygen sensor can be protected from the effects of moisture using a water impermeable and oxygen permeable membrane placed over the oxygen sensor or a hydrophobic membrane placed over the sensor. .

Other methods for measuring the temperature of the gas stream use optical or electrical methods to detect the thermal strain of microfabricated structures (eg multilayers) in the flow path. Or monitoring temperature-dependent molecular or atomic properties (eg emission or absorption wavelengths). Computer modeling of breathed air as it passes through the device may be combined with spot temperature measurements to obtain a detailed temperature distribution. Thermoelectric sensors, thermistors, pyroelectric sensors, thermopiles and the like may be used. The temperature dependence of the inspiratory ultrasound spectrum may be monitored. Thermal imaging of the flow channel may also be useful.

In addition to the current embodiments, there are many other adaptations of the invention (sometimes referred to below as “the device”) that may be useful. For example, the vent of the device may be replaced with a connector adapted to direct exhaled breath to another analysis device for further analysis. Other gas sensors may be included in the flow path. Respiratory components of interest include oxygen and carbon dioxide (as described above), nitrogen oxides, other radicals, ketones (eg acetone), aldehydes (eg acetaldehyde), alkanes (
For example pentane), other hydrocarbons, esters, hydrogen sulphide, indicators of lung disease or cancer, other volatile organic compounds, gases produced by bacteria (eg sulphides). Inert gas (eg xenon) for quantitative lung function tests
A detector for radioactive isotopes may be included.

The embodiments of the present invention described so far assume the intake of atmospheric gas.
However, the invention is equally applicable to the inhalation of other gas mixtures from respiratory gas sources. For example, a connector may be provided on the bottom of the calorimeter in addition to, or instead of, the vent so that the calorimeter may be connected to a source and / or sink of respiratory gas other than atmospheric. One application of such an approach is the use of the calorimeter according to the invention in anesthesia or respiratory assistance devices. Flow through the calorimeter can be assisted in any direction and at pressures other than atmospheric. It is clear that the sensors are used to monitor these non-atmospheric conditions so that appropriate calculations of metabolic rate and other respiratory factors can be made. Additional aspects relating to the use of a calorimeter according to the present invention as part of a mechanical ventilator are described in Mault's Provisional Patent Application No. 60 / 179,906, filed February 2, 2000, which is incorporated by reference herein. And will be apparent from the review of 60 / 179,961 submitted on February 3, 2000.

Respiratory profile analysis can be used, for example, to accurately determine terminal ventilation, or to examine respiratory abnormalities due to, for example, obstruction. The device is
It may communicate with other physiological sensors and / or with other electronic devices, eg, for data transmission, data analysis, display, feedback, or other use. The data from spirometry / joint calorimetry obtained using the present invention may be combined with other physiological or environmental data for analysis. The device emits electromagnetic radiation to provide energy to a physiological sensor implanted in the human body under test, such as a micromachined ultrasonic flow sensor located near the lungs, arteries or veins. May be generated. The calorimeter according to the invention may also include other sensors or physiological monitors. For example, positioning devices based on GPS, telemetry, mobile phone signals, etc. may be incorporated to provide information regarding the user's location. The calorimeter can then be used during exercise sessions that require locomotion, while the calorimeter will provide metabolic information while the location system will provide location information to enable correlation and analysis.

Although the present invention is preferably directed to measuring respiratory parameters such as metabolic rate, the simple flow meter version of the present invention also has advantages. Eliminating the oxygen sensor and otherwise simplifying it, the present invention provides an excellent flow meter for measuring flow rate and volume in, for example, lung volume testing. Also, the flow meter could be used for other applications.

A calorimeter according to the present invention may be incorporated into a weight or health care system, which system includes a personal digital assistant (PDA) for data entry, communication,
It may include physiological monitoring, feedback, and data processing. This and other uses of the present invention are described in Mault's provisional application filed November 17, 1999.
No. 0/165988, 60 / 167,276 filed November 24, 1999, and 60 / 177,016 filed January 19, 2000.

Other physical configurations are possible without departing from the scope or teachings of the invention.
For example, the position of the display for displaying metabolic parameters may be repositioned, reconfigured, or supplemented. The display could be moved to a position that allows the subject to set the display during the test. Alternatively, a separate display may be provided that receives data from the calorimeter, either hard-wired or wirelessly, allowing the display to be placed where the user can easily see it during the test. Additionally or alternatively, another person, such as a health professional, may view the display. Viewing the display during the test allows the user to witness metabolic changes due to changes in their activity level, relaxation level, or for other reasons. For example, the calorimeter and display, or other feedback device, could use biofeedback to help a person reach a certain level of relaxation. The calorimeter could also be used to provide respiratory therapy and training to monitor respiratory rate, volume and other factors.

As yet another alternative, an artificial "nose" may be provided for use with or as part of the calorimeter. An artificial "nose" regulates inhalation and / or exhalation to control humidity or temperature. This can be an advantage for some applications.

[Brief description of drawings]

FIG. 1 is a perspective view of a respiratory calorimeter according to a first embodiment of the present invention including a calorimeter, shown in use by a user.

[Fig. 2]   FIG. 2 is a perspective view showing the first embodiment of the present invention.

[Figure 3]   FIG. 3 is an exploded perspective view showing the first embodiment of the present invention.

[Figure 4]   FIG. 4 is a sectional view of the first embodiment of the present invention taken along line 4-4 of FIG.

[Figure 5]   FIG. 5 is a sectional view of the first embodiment of the present invention taken along the line 5-5 of FIG.

FIG. 6 is an exploded perspective view of one embodiment of an oxygen sensor for use with the present invention.

FIG. 7 is a cross-sectional view showing an assembled oxygen sensor for use with the present invention.

FIG. 8 is a perspective view of the present invention with another mouthpiece showing the disposable part removed from the reusable part.

FIG. 9 is a cross-sectional view showing another approach for constructing an oxygen sensor for use with the present invention.

FIG. 10 is a diagram showing a general configuration of a flow tube and an ultrasonic sensor according to the present invention.

FIG. 11 is a schematic diagram of an electrical circuit for use with one aspect of an ultrasonic flow sensing system that can be used with the present invention.

FIG. 12 is a diagram schematically showing a drive signal and a fluorescence response signal for the fluorescence-based oxygen sensor used in the present invention.

FIG. 13 is a schematic diagram showing the electrical configuration of a fluorescence-based oxygen sensing system for use with the present invention.

FIG. 14   FIG. 14 is a schematic diagram showing an electronic component according to a preferred embodiment of the present invention.

FIG. 15 is a diagram generally illustrating a preferred approach to respiratory parameter determination and metabolic rate calculation.

FIG. 16 is a bar graph showing an example of gas exchange for one inspiration and one exhalation.

FIG. 17 is a graph showing a series of curved surfaces representing changes in the oxygen sensor voltage output with respect to changes in oxygen partial pressure and any second factor.

FIG. 18 is a graph showing an example of how the calculated metabolic rate for a subject changes during the study.

FIG. 19 is a cross-sectional view showing a second embodiment of the present invention configured to improve hygiene.

FIG. 20 is a cross-sectional view showing a second embodiment of the present invention having another configuration for improving hygiene.

FIG. 21 is a partial exploded perspective view of a respiratory calorimeter according to the present invention and a hygienic filter module for use with the calorimeter.

FIG. 22   22 is a cross-sectional view of the filter module of FIG.

FIG. 23 is a partially exploded perspective view of a respiratory calorimeter according to the present invention with another aspect of a mask incorporating a hygiene barrier.

FIG. 24   24 is an exploded perspective view showing a disposable portion of the mask of FIG. 23.

FIG. 25 is a partially exploded perspective view of a respiratory calorimeter according to the present invention with a second embodiment of a mask incorporating a hygiene barrier.

FIG. 26   FIG. 26 is a partially exploded perspective view showing a disposable part of the mask of FIG. 25.

─────────────────────────────────────────────────── ─── Continued front page    (31) Priority claim number 60 / 218,863 (32) Priority date July 18, 2000 (July 18, 2000) (33) Priority claiming countries United States (US) (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE), OA (BF, BJ , CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, K E, LS, MW, MZ, SD, SL, SZ, TZ, UG , ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, BZ, C A, CH, CN, CR, CU, CZ, DE, DK, DM , DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, K E, KG, KP, KR, KZ, LC, LK, LR, LS , LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, PT, RO, R U, SD, SE, SG, SI, SK, SL, TJ, TM , TR, TT, TZ, UA, UG, UZ, VN, YU, ZA, ZW (72) Inventor Barber Theodore W             United States California             94002 Belmont Valley View             Avenue 1716 (72) Inventor Lawrence Craig M             United States California             94025 Menlo Park East Oki             Super Street 165 # 22 (72) Inventor Pracha Timothy Jay             United States California             94301 Palo Alto Addison Av             521 (72) Inventor Wayne Trough Jeffrey C             United States California             95110 San Jose Hawthorne Way               42 (72) Inventor Nason Kevin S             United States California             94041 Mountain View Rainbow               Drive 600 # 222 F term (reference) 2G045 CB22 DB30 FA33 FA34 GC18                       JA01                 4C038 SS04 SU01 SU18 SU19 SX01

Claims (23)

[Claims] 1. An indirect calorimeter for measuring a subject's metabolic rate, wherein the subject is in contact with and supported by inspiratory and expiratory gases as they breathe. A respiratory connector configured to receive and pass inspiratory gas and expiratory gas, the first end being in fluid communication with the respiratory connector, and the fluid communication with a source and sink of respiratory gas. Has a second end, the flow path including a flow tube through which inhalation and exhalation pass, and a chamber disposed between the flow tube and the first end, the chamber comprising the flow tube. A flow path that is a concentric chamber surrounding one end of the tube; a flow meter configured to generate an electrical signal as a function of the instantaneous volume flow of inspiratory and expiratory air passing through the flow path; A component gas concentration sensor operable to generate an electrical signal as an instantaneous fraction of a predetermined component gas in exhaled air as it passes through the flow path; A computing unit operable to receive the electrical signal from the subject and which is operable to compute at least one respiratory parameter for the subject as the subject breathes through the calorimeter.
An indirect calorimeter equipped with. 2. The calorimeter of claim 1, wherein the flow path further comprises an outer housing surrounding the flow tube, and the concentric chamber is between the flow tube and the outer housing. Calorimeter formed on the. 3. The calorimeter of claim 2, wherein a first end of the flow path extends from the outer housing and is in fluid communication with the concentric chambers. 4. The calorimeter of claim 3, wherein the inlet conduit extends generally orthogonal to the flow tube. 5. An indirect calorimeter for measuring a subject's metabolic rate, which is in contact with and supported by the subject to allow inspiratory and expiratory gases to pass as the subject breathes. A breathing connector configured; a flow path operative to receive and pass inspiratory gas and expiratory gas, the first end in fluid communication with said respiratory connector, in fluid communication with a source of breathing gas and a sink Having a second end, and a flow tube disposed between these ends,
A first end of the flow path, the flow path including an inlet conduit extending perpendicular to the flow tube; and generating an electrical signal as a function of the instantaneous volumetric flow of inspiration and expiration through the flow path. A flow meter configured to: a constituent gas concentration operable to generate an electrical signal as an instantaneous fraction of a predetermined constituent gas in the exhaled air as the exhaled air passes through the flow path. A sensor; operable to receive the electrical signal from the flow meter and the concentration sensor, and to calculate at least one respiratory parameter for the subject as the subject breathes through the calorimeter. A working computing unit,
An indirect calorimeter equipped with. 6. The calorimeter according to claim 5, wherein the flow meter measures a volumetric flow rate in the flow tube. 7. The calorimeter of claim 5, wherein the flow meter comprises an ultrasonic flow meter having two spaced ultrasonic transducers. 8. The calorimeter of claim 5, wherein the flow path further comprises an outer housing surrounding the flow tube and a concentric chamber formed between the flow tube and the outer housing. A calorimeter wherein the concentric chamber is in fluid communication with the flow tube and the inlet conduit extends from the outer housing and is in fluid communication with the concentric chamber. 9. An indirect calorimeter for measuring a subject's metabolic rate, wherein the subject is in contact with and supported by inspiratory and expiratory gases as they breathe. A respiratory connector configured to receive and pass inspiratory gas and expiratory gas, the first end being in fluid communication with the respiratory connector, and the fluid communication with a source and sink of respiratory gas. A flow path having an elongated flow tube through which the gas passes; and an electrical signal as a function of instantaneous inspiratory and expiratory volumetric flow rates through the flow path. A configured ultrasonic flow meter comprising a pair of spaced ultrasonic transducers, each of which is aligned with the elongated flow tube, wherein ultrasonic pulses transmitted between the transducers are coupled to the flow tube. An ultrasonic flow meter adapted to follow a path generally parallel to the flow of fluid in the chamber; a moment of a predetermined constituent gas in the exhaled gas as it passes through the flow path. A component gas concentration sensor operable to generate an electrical signal as a percentage; and a subject breathing through the calorimeter operable to receive the electrical signal from the flow meter and the concentration sensor. A computing unit operative to compute at least one respiratory parameter for the subject,
An indirect calorimeter equipped with. 10. The calorimeter according to claim 9, wherein the flow path further comprises an outer housing surrounding the flow tube, and a concentric chamber formed between the flow tube and the outer housing. A calorimeter including a concentric chamber in fluid communication with the first end of the flow path and the flow tube. 11. The calorimeter of claim 10, wherein the first end of the flow path includes an inlet conduit extending from the outer housing and in fluid communication with the concentric chambers. . 12. The calorimeter of claim 11, wherein the inlet conduit extends substantially orthogonal to the flow tube. 13. An indirect calorimeter for measuring a subject's metabolic rate comprising: a disposable portion and a reusable portion including a housing having a recess formed to accommodate the disposable portion. A disposable connector configured to contact and support the subject so as to pass inspiratory gas and expiratory gas when the subject breathes; receiving the inspiratory gas and expiratory gas; A flow path operative to pass through, the flow path having a first end in fluid communication with the respiratory connector and a second end in fluid communication with a source and sink of respiratory gas; The reusable portion further comprises a flow meter configured to generate an electrical signal as a function of the instantaneous volumetric flow of inspiratory and expiratory air passing through the flow path; A component gas concentration sensor operable to generate an electrical signal as a momentary fraction of a predetermined component gas in exhaled air when passing through the flowmeter and the electrical signal from the concentration sensor. And a computing unit operative to receive at least one breath parameter through the calorimeter and calculating at least one respiratory parameter for the subject. 14. The calorimeter of claim 13, wherein the flow path includes an elongated flow tube through which the gas flows, the disposable portion being in the recess in an orientation orthogonal to the flow tube. Calorimeter housed in. 15. An indirect calorimeter for measuring a subject's metabolic rate: for supporting and supporting inspiratory and expiratory gases as they breathe. A respiratory connector configured to receive and pass inspiratory gas and expiratory gas, the first end being in fluid communication with the respiratory connector, and the fluid communication with a source and sink of respiratory gas. A second flow path having a second end, the flow path including a flow tube through which inhalation and exhalation pass, and an outlet passage disposed between the flow tube and the second end; A flow meter configured to generate an electrical signal as a function of instantaneous inspiratory and expiratory volumetric flow rates through the flow passage; Ingredients A component gas concentration sensor operable to generate an electrical signal as a momentary fraction of the flow rate and in fluid communication with the outlet passage; and to receive the electrical signal from the flow meter and the concentration sensor. A computing unit operable and operable to compute at least one respiratory parameter for the subject as the subject breathes through the calorimeter;
An indirect calorimeter equipped with. 16. An indirect calorimeter for measuring a subject's metabolic rate: for supporting and supporting inspiratory and expiratory gases as they breathe. A respiratory connector configured to include a sanitary barrier arranged to pass substantially all of the inspiratory and expiratory gases, the barrier passing the inspiratory and expiratory gases and A respiratory connector for blocking at least some pathogens; a first end in fluid communication with the respiratory connector for receiving and passing inspiratory and expiratory gases, and a source of respiratory gas And a flow path having a second end in fluid communication with the sink; to generate an electrical signal as a function of the instantaneous volumetric flow of inspiratory and expiratory air passing through the flow path. A configured flow meter; and a constituent gas concentration sensor operable to generate an electrical signal as an instantaneous fraction of a predetermined constituent gas in the exhaled gas as the exhaled gas passes through the flow path. Operative to receive the electrical signal from the flow meter and the concentration sensor and to calculate at least one breathing parameter for the subject as the subject breathes through the calorimeter A calculation unit,
An indirect calorimeter equipped with. 17. The calorimeter of claim 16, wherein the breathing connector includes a mask and the sanitary barrier is disposed within the mask. 18. The calorimeter of claim 17, wherein the sanitary barrier comprises a piece of filter material. 19. The calorimeter of claim 16, wherein the sanitary barrier comprises:
A calorimeter including a housing having inlets and outlets and pieces of sanitary barrier material disposed therebetween. 20. The calorimeter of claim 19, wherein the sanitary barrier comprises a piece of filter material. 21. An indirect calorimeter for measuring a subject's metabolic rate: for supporting and supporting inspiratory and expiratory gases as they breathe. A respiratory connector configured; and a flow path that serves to receive and pass inspiratory and expiratory gases,
A disposable portion including a flow path having a first end in fluid communication with the breathing connector and a second end in fluid communication with a source of breathing gas and a sink; and a disposable portion formed to accommodate the disposable portion. A reusable portion including a housing with a recess, the flow meter being configured to generate an electrical signal as a function of instantaneous volumetric flow of inspiratory and expiratory air passing through the flow path, the flowmeter comprising: A flow meter comprising an ultrasonic flow meter including a pair of spaced ultrasonic transducers disposed in the flow path in the disposable portion; a predetermined in exhalation gas as the expiratory gas passes through the flow path A component gas concentration sensor operable to generate an electrical signal as an instantaneous fraction of the component gas; a computing unit arranged in the reusable part, the flow meter and the concentration A computing unit operative to receive the electrical signal from a sensor and operable to compute at least one respiratory parameter for the subject as the subject breathes through the calorimeter. Indirect calorimeter. 22. A flow measurement device for measuring the flow of fluid through the device: an elongated flow tube having a first end and a second end; a first end of the flow tube. A concentric mixing chamber surrounding a portion and in fluid communication with the first end; another inlet conduit in fluid communication with the concentric mixing chamber whereby the fluid passes through the inlet conduit An inlet conduit for flowing into a cylindrical chamber and then through the flow tube to a first end of the flow tube and out the second end; measuring a volumetric flow rate through the flow tube And a flow meter configured to. 23. The flowmeter of claim 22, wherein the inlet conduit extends orthogonally to the elongated flow tube.