JP2002505923A - Metabolic gas exchange and non-invasive cardiac output monitor - Google Patents

Abstract

(57) [Summary] The present invention is a respiratory gas analyzer (10) for measuring a subject's metabolic activity or cardiac output. The respiratory gas analyzer (10) includes a bidirectional flow meter (40), a capnometer sensor (16) connected to the mouthpiece (12) by a conduit, a penetrating carbon dioxide scrubber (34) for absorbing carbon dioxide, It has a computer (18) for calculating the cardiac output of the patient.

Description

DETAILED DESCRIPTION OF THE INVENTION

FIELD OF THE INVENTION The present invention relates to a flowmeter and a capnometer that can be interconnected to a first configuration for measuring a patient's metabolic activity or a second configuration for measuring a patient's cardiac output. The present invention relates to a respiratory gas analyzer using the same.

BACKGROUND OF THE INVENTION Inventor's US Pat. No. 5,179,958 and related US Pat. No. 5,038.
U.S. Pat. No. 4,792,708 and U.S. Pat. No. 4,917,708, which are connected to a mouthpiece, measure the amount of gas inhaled by a patient over a period of time, exhale gas to a carbon dioxide scrubber, and then to a flow meter. Discloses a calorimeter or a calorimeter. In a broad sense, the integrated value of the difference between the inspiratory flow and the exhaled air flow excluding carbon dioxide is a measure of the patient's oxygen consumption and the patient's metabolic activity. These instruments may incorporate a capnometer that measures the concentration of exhaled air, or exhaled carbon dioxide. The computer that receives the signals from the flow meter and the capnometer calculates the respiratory quotient (RQ) and the Weir equat in addition to the patient's oxygen consumption.
Resting Energy Expenditure: R
EE) can be calculated.

[0003] A patient's cardiac output, ie, the amount of blood pumped out of the heart per hour, is another important measured parameter of an inpatient. Currently, cardiac output is measured regularly in a non-invasive manner. Such non-invasive techniques include thermal dilution using an indwelling pulmonary artery catheter. This method has several disadvantages, including high morbidity and mortality due to the placement of invasive intracardiac catheters, the potential for infections, considerable expense, And the measurement by such a method is not continuous but intermittent. Non-invasive, reusable, continuous cardiac output measurement substantially improves patient care and substantially reduces hospital costs.

[0004] The partial rebreathing method is a known cardiac output measurement method. Papers by Kapek and Roy, “The Noninvasive Measurement of Cardiac Output Using Partial CO2 Re
As described in “breathing” (Biomedical Engineering, Vol. 35, No. 9, pp. 653-659, published in September 1988),
This method uses the well-known Fick procedure (Fick procedeures), uses carbon dioxide instead of oxygen, and uses a sufficiently short measurement period to measure intravenous carbon dioxide levels and cardiac output. It can be regarded as being substantially constant.
The Fick method of measuring cardiac output, in its original form, requires the gas or oxygen content of the mixed arterial and arteriovenous blood as described below.

C. [0005] O. In _{= VO 2 / (CaO 2 -C} v O 2) above equation, C. O. The cardiac output, VO _2, the oxygen consumption, CaO ₂ is the arterial oxygen content, C _v O ₂ is a venous oxygen content. By using carbon dioxide instead of oxygen in the Fick equation, the use of partial rebreathing allows the calculation of cardiac output as follows without using invasive blood gas measurement.

C. O. _{= VCO 2 / (CaCO 2 -C} v CO 2) portion rebreathing method, CO ₂ generation amount that is responsive to changes in a short time during ventilation (VCO ₂₎ and end-tidal (hereinafter, abbreviated as "et" In some cases) changes in CO ₂ are used. The value obtained by dividing the change in the amount of CO ₂ production estimated from the end-tidal CO ₂ by the CO ₂ content (CaCO ₂ ) of arterial blood is equal to the blood flow in the pulmonary artery capillary as follows.

C. O. = ΔVCO ₂ / ΔetCO ₂ Clinical trials have shown that this partial rebreathing method was more accurate than the older invasive method. Despite the benefits of partial rebreathing, this is not widespread.

[0008] With a slight redesign of the calorimeter we have developed, we can not only use the partial carbon dioxide rebreathing method, but also relate to the metabolism described in our US patent. It has been found that a cardiac output measurement method can be implemented that performs a suitable measurement method.

SUMMARY OF THE INVENTION Accordingly, the present invention relates to a respiratory gas analyzer that can measure either metabolic activity or cardiac output of a subject. The configuration of the preferred embodiment of the breathing gas analyzer is similar to the indirect calorimeter disclosed in the inventor's U.S. Patent in that it includes a bidirectional flow meter, a capnometer and a carbon dioxide scrubber. A conduit connects the flow meter between a source of respiratory gas (which is typically atmospheric) and a mouthpiece such that the flow meter measures the amount of gas being inspired. During exhalation, gas flows through a capnometer to a carbon dioxide scrubber, and the output of the scrubber is returned to the atmosphere through a flow meter. In this form, the computer connected to receive the electrical output of the flow meter and the capnometer, alone or in conjunction with one or more of the differential measures of respiratory quotient and dormant energy expenditure, allows the patient to consume oxygen. Calculate the amount.

In order to measure the cardiac output of a patient using partial CO ₂ rebreathing, the system does not allow exhaled gas to pass through a carbon dioxide scrubber but directly to a flow meter or flow meter. Accumulation of a portion of the exhaled gas that was later mixed with additional air that passed through the flow meter during the next inhalation, resulting in a higher carbon dioxide content in the subsequent inspiration Can be converted to a form that is flowed into a volume in the analyzer that allows for The analyzer is completely removable for the purpose of making the cardiac output measurement by the carbon dioxide scrubber,
Alternatively, the scrubber may be configured such that the flow path is kept in place on the redesigned analyzer so that exhaled air does not flow through the scrubber.

[0011] The analyzer further comprises a valve device coupled to the circuit to shift the circuit configuration between the two alternative forms. In the first configuration, the exhaled gas flows through the capnometer and then directly to the flow meter. On the next inspiration,
Fresh breathing gas is drawn into the flow meter. In a second alternative, after the valve shifts, exhaled gas flows through the capnometer and then into a conduit leading to a flow meter. Thus, the volume of the conduit serves as dead space or dead volume. Then, when the subject inhales, a significant portion of the inspired gas becomes rebreathing gas from the dead space in the conduit with a high carbon dioxide content. Preferably, 20 of inspired air
７０70% will be rebreathing air and the remainder will be composed of air inhaled through the flow meter by inspiration.

[0012] Measurements relating to metabolism are performed by connecting the scrubber to an operating configuration such that exhaled gas flows through a carbon dioxide scrubber and then through a flow meter. A computer connected to the flow meter integrates the inspiratory and expiratory flow signals. The difference between these signals is a function of the patient's metabolic rate. To calculate cardiac output using the Analyzer, remove the scrubber or shut off its input so that the computer receives signals from the flow meter and capnometer while the subject is breathing. ,
During this time, the valve is in a first configuration in which exhaled gas flows through the capnometer and then directly through the flow meter. The computer integrates the capnometer readings over the entire flow volume to determine the exhaled carbon dioxide content and to determine the end-tidal expiratory carbon dioxide content, i.e., end-tidal carbon dioxide measurement. . An alternative configuration in which the valve is then shifted to introduce the circuitry into the dead space volume inside the circuitry so that only a portion of the exhaled gas for each exhalation flows through the flow sensor To The inspired gas for each inspiration becomes part of the rebreathing air with increased carbon dioxide content. The measurement is made for about 30 seconds, during which time the computer again measures end-tidal carbon dioxide. This measurement is used in measurements taken while the valve is in the first configuration to calculate cardiac output.

Alternatively, the volume of the flow chamber containing the rebreathing air is made and / or computer-controlled to adjust the dead space to match the user's breathing volume.

[0014] Other objects, advantages and uses of the present invention will become apparent upon reading the following detailed description of the preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention, shown generally at 10 in FIG. 1, is in a form that can be used to measure a patient's metabolic activity. The analyzer employs a mouthpiece 12 adapted to engage an inner surface of a user's mouth to form a unique passage for breathing gas into and out of the mouth. A nasal clamp of conventional construction (not shown) may be used in conjunction with mouthpiece 12 to allow all breathing gas to pass through the mouthpiece. Alternatively, a mask that engages the mouth as well as the nose may be used, or an endotracheal tube may be used.

The mouthpiece 12 communicates with a capnometer type sensor 16 through a short passageway 14. Capnometer 16 outputs an electrical signal that is a function of the instantaneous carbon dioxide concentration of the gas passing through mouthpiece 12. Capnometers are conventional, such as U.S. Pat. Nos. 4,859,858, 4,859,859, 4,914,71.
No. 0 or 4,958,075. The capnometer produces an electrical output signal to a computer processing unit 18 having a suitably programmed microprocessor (not shown), a display 20 and a keypad 22.

The capnometer is connected by a short passage 24 to a two-position three-way valve, generally designated 26. The valve has a single input flow channel from a one-way valve 28 leading to a gas flow conduit 30. The valve has a first position shown in FIG. 1 where the output is provided to a second one-way valve 32 connected to the input of a carbon dioxide scrubber 34.
In the second position, shown schematically in FIG. 3, the valve is shifted to prevent gas flow to the valve 32 and thus to the scrubber and divert flow to the air passage 34 leading to the gas conduit volume 30.

The carbon dioxide scrubber 34 is a vessel with a central gas passage filled with a carbon dioxide absorbing material, for example, sodium hydroxide or calcium hydroxide. Such absorbent materials may include sodium hydroxide and / or calcium hydroxide mixed with silica in a form called "Soda Lime (R)". Another absorbent material that can be used is "Bara," which comprises a mixture of barium hydroxide and calcium hydroxide.
lyme® ". The carbon dioxide scrubber has an internal baffle 36 which creates a labyrinthine flow of gas.

The output 38 of the scrubber is located adjacent to a bi-directional volumetric flow sensor 40 provided at the end of the volume 30 opposite the valve 26. The flow sensor is preferably of the differential pressure type manufactured, for example, by Medical Graphics Corporation of St. Paul, Minn., Under the general trademark "Medgraphics" described in U.S. Pat. No. 5,038,773. Alternatively, other types of flow transducers may be used, for example, pneumatic or a spirameter. The other end of the flow sensor is connected via line 42 to a sink-type source of breathing gas. The sink source is typically air, but may alternatively be a suitable type of positive pressure vent. The electrical output of the bi-directional volumetric flow sensor is connected to a computer processing unit 18.

When the valve 26 is in the first position shown schematically in FIG. 1, the system operates in the same manner as the unit described in the inventor's US Pat. No. 5,179,958. Various respiratory parameters of the patient, such as oxygen consumption per hour, respiratory quotient (RQ
(This is equal to VCO ₂ divided by VO ₂ ) and preferably the dormant energy expenditure (REE) calculated from the Weir equation.

In this operation mode, assuming that the room air is being inhaled, the room air passes through the air inlet 42 and flows through the flow meter 4 by the inhalation of the subject wearing the mouthpiece 12.
0 and generate an electrical signal to the computer processing unit 18. The inspired air then passes through the volume 30, through the one-way valve 28, and into the passage 24 leading to the capnometer-type sensor 16. Sensor 16 generates an electrical signal that is sent to a computer processing unit 18. The inspired air then flows to the patient through mouthpiece 12 through passageway 14. When the patient exhales, the exhaled gas flows through the capnometer 16 in the opposite direction, and then through the one-way valve 32 to the input of the carbon dioxide scrubber 34. Scrubber absorbs carbon dioxide in exhaled gas,
The output is sent into the volume 30 located immediately adjacent to the bi-directional volumetric flow sensor 40 in the opposite direction to the inspired gas.

The amount of exhaled air that has passed through flow sensor 40 will be less than the amount of inspired air due to the absorption of carbon dioxide by scrubber 34. The difference in this amount is a function of the oxygen absorbed from the inspired air by the patient's lungs. Computer processing unit 18 converts the signals from capnometer 16 and flow sensor 40 to digital form if the signals are in analog form as used in the preferred embodiment of the present invention. Otherwise, the computer processing unit 18 operates as disclosed in U.S. Pat. No. 4,917,718 and integrates a signal representing the difference between inspiratory volume and expiratory volume over the duration of the test. And multiply them by a constant to get an indication of kilocalories per hour. Energy consumption during sleep (REE
) And respiratory quotient (RQ) are calculated similarly. The keyboard 22 associated with the computer processing unit 18 allows the storage and display of various factors in the same manner as the system of the inventor's US patent.

The computer processing unit may have an artificial nose and / or bacterial filter as described in the above-mentioned applicant's US patent, or may take measurements as a function of breathing and external air temperature. It may have a temperature sensor that sends a signal to the computer processing unit 18 to adjust the temperature.

In order for the analyzer to measure the cardiac output of the patient non-invasively, the connection between the scrubber 34 and the body of the computer processing unit is blocked. Physically removing the scrubber from the main unit, or the scrubber shuts off the scrubber while it is measuring
It may remain supported on the computer processing unit with the appropriate valve position (not shown) shifted to an inoperative state.

FIG. 2 shows the computer processing unit with the scrubber 34 physically removed and the wall portions 50, 52 closing the ports of the body through which the input and output connections of the scrubber 34 communicate. I have. This creates a relatively narrow, small volume passage 54 that connects the output of the one-way valve 32 to the area adjacent the flow meter 40.

In this position, as the patient inhales, air or breathing gas is drawn into inlet 42, through bi-directional sensor 40, through volume 30 and one-way valve 28, through capnometer 16, and through mouthpiece 12. Flows to As the patient exhales, gas exits the mouthpiece 12 through passage 14, through the capnometer 16, through the one-way valve 32 and passage 54, and out of the bi-directional sensor 40.

The computer processing unit 18 controls the two-position valve 26 to move it to a second position, shown schematically in FIG. 3, in which the flow passage to the one-way valve 32 is Blocked, passageway 34 opens to flow volume 24 adjacent to capnometer 16. The shifted valve prevents exhaled gas from entering passage 56, but instead causes exhaled gas to return through conduit volume 30 toward flow sensor 40. As a result, the dead space temporarily increases, and when the patient inhales, re-breathing of air rich in carbon dioxide from the volume 30 is performed, and the expiration VC
The carbon dioxide content of O2 and end-tidal carbon dioxide (not shown) change, thus allowing the computer processing unit 18 to output a signal that is a function of cardiac output.

The measurement order is as follows.

[0029] 1. With the valve 26 in the position shown in FIG. 2, VCO ₂ and etCO ₂ are recorded for 3 minutes. The amount of VCO ₂ is calculated by integrating the instantaneous measurement of the capnometer sensor over the flow volume as indicated by sensor 40. this
etCO ₂ is calculated for each breath using a peak detection algorithm that stores the maximum of the transient CO ₂ signal from the capnometer 16 for each breath. The inspired air does not mix much with the previously exhaled air.

[0030] 2. Next, the computer processing unit 18 switches the valve 26 to the position shown in FIG. The volume of the conduit 30 is filled with exhaled air, and overflow overflows through the bi-directional flow sensor 40. The volume of passage 30 is preferably about 15-25% of the subject's tidal volume. Typical tidal volumes range from 600 ml to 1000 ml, and the volume of passage 30 is preferably about 150 ml. Thus, the subject rebreaths carbon dioxide from the temporary dead space chamber for about 30 seconds. This 30
During the second, the end-tidal carbon dioxide between breaths and the total cumulative amount of carbon dioxide are recorded.

[0031] 3. Next, the collected data is processed by the computer processing unit 18 and the result is displayed or printed.

Thus, the computer processing unit can determine the following parameters: oxygen consumption (VO ₂ ), energy consumption measurement (MEE), carbon dioxide production (VCO ₂ ),
Cardiac output (CO), respiratory exchange ratio (RER), can be displayed by calculating the minute ventilation (V) and end-tidal carbon dioxide (ETCO _2).

In the cardiac output mode, the computer processing unit 18 may use a calculation algorithm of the type described in the above-mentioned paper by Kapek and Roy.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a preferred embodiment of the present invention in the form of measuring metabolic activity.

2 is a schematic diagram of the system of FIG. 1 shown in a form for performing a first measurement required to measure a patient's cardiac output.

FIG. 3 is a schematic diagram of the system of FIG. 1 shown in a form for performing a second measurement required to measure cardiac output.

Claims (5)

[Claims] 1. A respiratory gas analyzer for measuring a metabolic activity or a cardiac output of a subject, the respiratory gas being capable of supporting the subject in contact with the subject to pass inhalation gas and exhalation gas when the subject breathes. Connector, means for connection to a respiratory gas source, a bi-directional flow meter that outputs an electrical signal as a function of the amount of gas passed in either direction, and a through-type that absorbs carbon dioxide from the passing gas. A carbon dioxide scrubber, a capnometer, a valve that can be shifted between a first configuration and a second configuration, the respiratory connector as a component, connection means to the respiratory gas source, the scrubber, the flow meter ,
A conduit for interconnecting the capnometer and the valve, a computer for receiving the outputs of the flowmeter and the capnometer, and means for controlling the position of the valve, the computer comprising: Substantially from the source of respiratory gas flows through the flow meter to the subject, and upon exhalation by the subject, substantially all of the exhaled gas passes through the flow meter in the opposite direction to the inspired gas. In the first configuration, which flows through and during inspiration by the subject, only a portion of the inspired gas flows from the source of the respiratory gas through the flow meter, and the remainder is exhaled earlier than is stored in the conduit. During exhalation by the subject, only a portion of the exhaled gas flows through the flow meter in the opposite direction to the inspired gas and the remainder is stored in the second conduit. The valve position to connect the components together in any of the configurations Connected to the control means, the computer is configured to determine the difference between the carbon dioxide content of the exhaled gas between the time the valve is in the first configuration and the time the second configuration is, and the time the valve is in the first configuration. And the cardiac output of the subject can be calculated based on the difference between the end-tidal carbon dioxide content of the exhaled gas at the time in the second mode and the second mode, wherein the respiratory gas analyzer has a valve in the first mode. The device further comprises means for operating at one time, wherein upon exhalation by the subject, the exhaled gas first passes through the scrubber and then through the flow meter in a direction opposite to the inspired gas, and the computer communicates with the subject. A respiratory gas analyzer capable of outputting a signal proportional to an integrated value of a difference between an inspired gas amount and an expired gas amount over a certain period for calculating a metabolic rate. 2. The scrubber is connected to a conduit such that upon exhalation by the subject, the exhaled gas first passes through the scrubber and then flows through the flow meter in a direction opposite to the inspired gas, or The scrubber is characterized in that, upon exhalation by the subject, the exhaled gas flowing through the flow meter in the opposite direction to the inspired gas is removed from the conduit such that it does not first flow through the scrubber. The respiratory gas analyzer according to claim 1, wherein 3. A respiratory gas analyzer useful for calculating oxygen consumption or cardiac output by breathing per hour of a subject, wherein the breathing gas and exhalation gas are passed during breathing of the subject. A breathing connector supported in contact with the subject's mouth, connecting means to an exhaled gas source, and a through-type bidirectional flow meter, wherein the through-type bidirectional flow meter is connected to any of the Adapted to output an electrical signal as a function of the amount of gas flowing in the direction, the respiratory gas analyzer comprising a penetrating carbon dioxide scrubber for absorbing carbon dioxide from passing gas, a capnometer, and a flow rate. A computer for receiving electrical signals output from the meter and the capnometer, the respiratory connector, means for connecting to the respiratory gas source, a conduit for interconnecting the capnometer and the flow meter, and a scrubber for connecting the A connector removably attached to the tube and connected to the conduit, wherein the breathing gas analyzer is configured to allow the gas to flow from the breathing gas source through the flow meter to the subject upon inspiration by the subject; A first configuration in which substantially all of the gas flows through the flow meter; and, when inhaled by the subject, a portion of the inspired gas is stored in the conduit and the previously exhaled gas. And a valve device coupled to the conduit to configure in any of the second configurations obtained from a respiratory gas source through a flow meter, the computer comprising: Between the carbon dioxide content in the exhaled gas when the valve is in the second mode and the breathing gas when the valve is in the first mode and the second mode when the valve is in the second mode Of subject's cardiac output based on differences in terminal CO2 content Operable to calculate an electrical signal that is a number, the respiratory gas analyzer further connects the scrubber to the conduit when the valve is in the first configuration, and the exhaled gas first activates the scrubber. And then flow through the flow meter in the opposite direction to the inspired gas, which is referred to as the inspired gas volume over a period of time to calculate the metabolic activity of the subject. A respiratory gas analyzer characterized in that it outputs a signal proportional to the integrated value of the difference in the amount of breath gas. 4. The respiratory gas analyzer according to claim 3, wherein the respiratory gas source is the atmosphere. 5. The respiratory gas analyzer according to claim 3, wherein the part of the inspired gas obtained from the previously exhaled gas occupies about 10 to 60% of the entire inspired gas. .