JP2002523122A - Apparatus and method for measuring pulse transit time - Google Patents

Abstract

(57) [Summary] In a method of measuring a pulse transmission time of a living body, first and second pulse wave signals are generated by detecting pulses at first and second pulse points spaced from each other. . The first and second pulse wave signals are differentiated, and corresponding points of the first and second pulse wave signals (e.g., points with the maximum gradient) are selected based on the results. A delay time between the selected points is detected, thereby obtaining a pulse transit time. A preferred device measures pulse transit time using at least one fiber optic pulse sensor that includes a fused fiber coupling region, the fused fiber coupling region being tensioned in the coupling region. Deflectable at least in part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Cross Reference of Related Applications]

This application is based on US Provisional Application 60 / 097,1 filed August 24, 1998.
8 and US Provisional Application 60 / 126,33 filed March 26, 1999.
Enjoy the benefits of Publication No. 9. Both of these applications are incorporated herein by reference.

[0002]

BACKGROUND OF THE INVENTION

The present invention relates to a method and an apparatus for measuring the transmission of a pulse wave, and more particularly to a method and an apparatus for measuring the pulse time of a human or mammal body.

[0003] The pulse of a person (or mammal) is a disturbance of the waves transmitted from the heart and travels through the arterial system. Since the speed of propagation of the pulse in the fluid is directly proportional to the fluid pressure, the blood pressure can be detected by measuring the propagation speed of the pulse wave. The pulse wave propagation velocity can be measured by detecting the pulse transit time. The pulse transit time is the period of time required for a pulse wave to travel between two spaced apart arterial points.

[0004] An example of a blood pressure monitoring system that utilizes pulse transit time is the Trimmer
) Etc. can be found in US Pat. No. 4,245,648. This system is closely spaced (approximately 3c) along the arm artery to detect transmitted pulse waves.
m) Including a pair of piezoelectric sensors. The pulse transmission speed is determined as the difference between the arrival times of the pulse waves at the two sensors. The use of piezoelectric sensors as described in the above-mentioned patent publications has some significant practical limitations. For example, piezoelectric sensors exhibit limited sensitivity at frequencies below about 2 Hz. Adult pulse rates are typically 60 beats per minute, or 1 Hz. Infant pulse rates are typically 120-180 beats per minute, or 2-3 Hz. As a result, systems that use piezoelectric sensors to monitor the human body may be practically demanded to raise or even limit the capabilities of such sensors. Piezoelectric sensors also have other practical limitations due to the fact that conductive materials (such as electrodes and leads) are required at the sensor location on the test object. As a result, the system cannot be used in environments where the presence of such materials would be problematic. For example, MR
Conductive materials are known that cause severe burns to patients undergoing MRI examinations due to the presence of strong radio frequency fields emitted by I-devices. Yet another limitation is imposed by placing the sensors close to each other along the same artery. Placing the sensors in close proximity to each other means that the pulse transit time to be measured is very short and inherently difficult to measure accurately. The shorter the measurement time interval, the greater the predetermined amount of error.

[0005]

Summary of the Invention

In one of the above aspects, the present invention provides a particularly useful method of measuring pulse transit time with pulse sensors disposed at substantially spaced pulse points (although there is no limit in use). I will provide a. For example, one of the sensors may be placed over the artery of the arm on or near the upper arm. And another of the sensors may be placed on the wrist-shaped radial artery. The method requires the difference between each pulse signal from the sensor to determine the corresponding point of the two signals, such as the point of maximum slope. The time delay between these points is then determined. The result is a pulse transit time. Recognizing the derivative of the two pulse wave signals, even if the pulse waveforms can be somewhat different when the sensors are substantially spaced from each other as described above,
It facilitates identification of corresponding points of these signals. Further, to base the calculation of the transit time from one pulse wave to the next, a precise time marker can be selected here at that point (eg, the maximum slope point). This is particularly beneficial because the pulse waveform usually changes from one heart beat to the next.

[0006] In another of these aspects, the present invention provides an apparatus for performing the above method. The apparatus includes a signal processing unit for processing each pulse wave signal of the pulse sensor and a pair of pulse sensors according to the method.

In another of the above aspects, the present invention is directed to at least one pulse sensor, preferably comprising a variable coupler fiber optic sensor having an improved design as will be described herein. Provides an apparatus for measuring pulse transit time including at least two pulse sensors. The device may further include a signal processor (signal processing device) and may be used to implement the method described above or other methods of measuring pulse transit time.

[0008] Other aspects of the invention will become apparent from a reading of the following description of a preferred embodiment with reference to the drawings.

[0009]

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a block diagram of an apparatus for measuring a pulse transit time according to the present invention. The device includes two arterial sensors S1 and S2, which may be in any suitable manner. For example, these sensors use a piezoelectric, optical fiber and have a pulse (
Any known design capable of converting the displacement of the skin due to pressure) into a corresponding output signal representing the pulse waveform is sufficient. However, at least one of these sensors,
Preferably, both are embodied in an embodiment of a variable coupler fiber optic sensor configured according to the improved design described below.

[0010] These pulse sensors S1 and S2 are connected to a signal processing unit SPU which processes the output signals from these sensors in order to determine the pulse transit time. The signal processing unit may be of either a digital or analog design as desired.
Of course, if digital processing is used, the outputs of these sensors can be supplied to the signal processing unit via an A / D converter, or the processing unit can have such a converter therein.

With reference to FIG. 2, the operation of the signal processing unit SPU according to the present invention will be described below.

First, in step 1, the signal processing unit inputs a pulse wave signal from the sensors S1 and S2. Next, in step 2, the signal processing unit differentiates each pulse wave signal (obtains a differential coefficient). The differential coefficient, of course, indicates the instantaneous gradient of the pulse wave signal. Next, in step 3, the signal processing unit uses the result of step 2 to select a point having a corresponding curve characteristic from the two pulse wave signals. For example, the processing unit may select each point of the maximum slope of the curve in the two pulse wave signals. Finally, in step 4, the signal processing unit calculates the time delay between these two selected points. The calculated time delay constitutes the pulse transit time.

[0013] Since the corresponding points of the two pulse wave signals can be easily identified from the differential waveform, the above-described method is applied to the sensor S even if the pulse waveform is somewhat different at the two sensor positions.
1 and S2 easily correspond to a substantial separation. Furthermore, as already mentioned, by differential calculation, based on the calculation of the transmission time from one pulse wave to the next,
An accurate time marker on a point (such as the maximum slope point) can now be selected. This is particularly beneficial because the pulse waveform usually changes from one heart beat to the next.

FIG. 3 shows another apparatus of the present invention. The device includes a pair of variable coupler fiber optic sensors S1 and S2 of an improved design to be described herein. However, it will be helpful first to provide some background on variable coupler fiber optic sensors in order to fully understand the benefits provided by the present device.

The variable coupler optical fiber sensor is a so-called biconical fused tap coupler conventionally manufactured by a drawing process and a melting process.
ered couplers). In the above process, the plurality of optical fibers are stretched (drawn) and fused at a high temperature. The plastic sheath is first removed from each of the optical fibers, exposing the portions that will form the fused region. These parts are internally twisted, juxtaposed and stretched once or several times, usually while maintaining the softening temperature above an electric furnace or the like.

As the exposed portions of the fiber are stretched, the portions fuse together to form a narrow body region—ie, a fused region—that can couple light between the fibers. During the stretching process, light is incident on one input of the fiber and monitored at the respective output of the fiber to determine the coupling ratio. This coupling ratio varies with the length of the trunk region. The fiber is then typically stretched by the same amount of fiber light output until the desired coupling ratio is achieved. The coupler is withdrawn to such an extent that in the barrel portion each fiber core has effectively disappeared and the cladding can reach a diameter close to the diameter of the former core. The cladding becomes a new "core" and a field of propagating light momentarily is created outside of this new core. Here, this field wraps both fibers simultaneously, creating a heat exchange between the fibers. Bicone fused-tapered couplers are available from Applied Optics (Journal of the Optical Society
of America), Vol. 22, No. 12, June 15, 1983, pp. 1918-1922
lyse d'un coupler Bidirecitional a Fibers Optiques Monomodes Fusionnes "
The title was published by J. Bures.

[0017] Bicone fused-tapered couplers have the particular advantage that the power ratio can be varied by bending the melting region. Since the power ratio varies with the amount of bending, such couplers can be used in almost any sensor application that involves movement that can couple to the melting zone.

Since the optical fiber sensor of the variable coupler can be made entirely from a dielectric material and can be optically coupled to a remote electronic device (electronic component), the sensor is electrically conductive at the sensor installation location. The presence of the element is particularly beneficial for applications where the risk of electrical shock, burn, fire, or explosion is present. In the medical field, for example, variable coupler fiber optic sensors have been recommended for monitoring a patient's heart rate during MRI examinations. Gerdt
See U.S. Pat. No. 5,074,309 to U.S. Pat. This publication is
The use of such sensors to monitor cardiovascular, including audible and quasi-audible sounds from the patient's heart, pulse, and circulatory system is disclosed. Other uses for variable coupler fiber optic sensors include U.S. Pat. No. 4,634,858 to Gerdt et al. (Disclose application to accelerometers) and U.S. Pat. No. 5,671,191 to Gerdt.
Publication (discloses application to hydrophones) and other fields in the art.

A conventional variable coupler fiber optic sensor is such that the fiber coupler is pulled straight out and fixed under certain tension to a plastic support member, so that in this pre-tensioned linear form, They have relied on designs that are housed in a pod of elastic material, such as silicone rubber. This pod structure forms a sensing membrane that can be deflected by an external force to bend the coupler in the fusion zone. Due to the bending of the melted region, a measurable change is observed in the output ratio of the coupler. This displacement of the membrane can be sensitive to movements of less than 1 micron in the range of a few millimeters.

FIG. 23 of the accompanying drawings shows the basic principle of a sensor device including the variable coupler optical fiber sensor 10 as described above. In the embodiment shown, the sensor 10 includes a 2 × 2 biconical fused tapered coupler 11 made by drawing and fusing two optical fibers to form a barrel or fusing region 13. . The portion where the original fiber (the first fiber) is merged at one end of the fusion zone becomes the input fiber 12 of the sensor. The original fiber section emerging from the opposite end of the fusion zone becomes the output fiber 14 of the sensor. Reference numeral 18 indicates the core of the optical fiber. The molten portion 13 is housed in a sheath of the plastic medium 15. This part constitutes a sensing membrane. The support member is not shown in FIG.

In practice, one of the input fibers 12 is illuminated by a light energy source 16. This light energy source 16 may be, for example, an LED or a semiconductor laser. The light energy is split by the coupler 11 at a rate that varies according to the amount of bending in the melted area as a result of the external force applied on the sensing membrane and is coupled to the optical fiber. The change in the division of the light energy between the optical fibers 14 can be measured by two photodetectors 17 that supply an electrical input to a differential amplifier 19. As a result, the output signal of the differential amplifier 19 is representative of the force exerted on the medium 15. It will be appreciated that if only one of the input fibers 12 directs light to the sensor, the other input fibers may be cut short. On the other hand, it can be kept as a backup in case the initial input fiber fails. Note that for simplicity, the coupler 11 is shown without the fiber twisted in the fusion zone. Such a twist is usually preferred, but reduces the sensitivity of the lead associated with changes in the splitting of the output light in response to movement of the input fiber.

Despite the above advantages, conventional variable coupler fiber optic sensors have been bound by certain limitations inherent in conventional pretensioned linear coupler design structures. Such a conventional design structure introduces particularly large geometric constraints. In particular, the size of the sensor must be sufficient to fit the optical fiber leads at both ends of the sensor. In addition, optical fiber lead structures require the use of a clear space around both ends of the sensor in use. Particularly in medical applications, for example, where sensors on the patient's body are to be placed in a continuous monitoring period, both sensor size and lead position are important. Another constraint stems from the fact that any displacement of the fusion zone necessarily places the fusion zone under increased tension. At some point of displacement, the tension in the melt zone becomes excessive, at which point the coupler malfunctions and cracks or fractures occur.

Returning now to the description of the present invention, the apparatus of FIG. 3 is an improved variable coupler light designed to overcome one or more disadvantages of a conventional pretensioned linear sensor design. Utilizes fiber sensors. More particularly, the sensors used in the present invention may have an improved design that allows deflection of the coupler melt zone without the attendant tension. The coupler melting region is preferably arranged in a generally U-shape, but is incorporated by reference into co-pending U.S. application Ser. No. 09/316, filed May 21, 1999, which is hereby incorporated by reference. 143 may be configured. The use of a generally U-shaped structure allows the optical fiber leads of the sensor to be positioned adjacent to each other rather than at both ends of the sensor. This avoids the previously discussed geometric constraints inherent in conventional variable coupler fiber optic sensors.

By using two such sensors, the apparatus of FIG. 3 fully embodies the benefits of the improved sensor design. However, the use of sensors, such as conventional variable coupler fiber optic sensors, or even piezoelectric sensors, in combination with other pulse sensors that do not utilize the improved design described above is within the scope of the present invention. It can be acceptable.

As shown in FIG. 3, each of the sensors S 1 ′ and S 2 ′ has a corresponding light source 40 (eg, a laser) and a corresponding photodetector / differential amplifier circuit 4 as described above.
To 2. Each of these circuits has an output connected to a corresponding input of a digital signal processor (DSP) 44 via an AD converter 43. These sensors S1 'and S2' can be combined by placing the fiber optic elements of the sensors S1 'and S2' close to each other on a common support structure. However, as described above, by arranging the pulse sensors close to each other, there is almost no margin for errors. This is because the measured pulse transit time is short.

Digital signal processor 44 can be programmed to determine pulse transit time in any desired manner, including but not limited to the method described in connection with FIG.

FIGS. 4 and 5 are specific examples of an improved tunable fiber optic sensor 20 useful in the apparatus of the present invention. The sensor is configured for placement on a human body, such as a chest, arm, or wrist, to sense skin displacement by pulse. The sensor is more generally capable of sensing both audible and semi-audible cardiovascular breathing sounds manifested by skin displacement.

The sensor 20 has a support member 22 having a generally circular head 24. This head 2
4 comprises a central well or through-hole 26 and an extension 28 such as a handle. A two-cone melt-tapered coupler 30 is placed in space 26 and
At least a part (here, the whole) of the fusion coupling region 32 arranged in the mold
It is attached to the support member using. The input fiber lead 34 and the output fiber lead 36 of the coupler are disposed close to each other in a channel 29 formed by the extension 28. These leads are manipulated to bend coupling region 32 180 degrees into the desired shape and are secured within the channel by a suitable adhesive, such as an epoxy-based glue. The untensioned coupling area is manufactured to form a pot by filling the space 26 with a plastic material (pot manufacturing) to form the sensing membrane 38 in a known manner (not shown in FIG. 4). I do. This known method is, for example, a method of filling with silicone rubber such as GE RTV12. On the other hand, as will be understood from the following description, the coupling region is coated with a layer of a coating material such as GESS 4004 (polydimethylsiloxane with methyl silsesquioxanes). ,
Eliminates the need for manufacturing processes such as making pots. This material is commonly used as a primer to bond room temperature sulfurized (RTV) materials to surfaces that would otherwise form weak bonds. The advantage of omitting the manufacturing process of making this pot is that the sensitivity is improved. This is because the pot manufacturing process tends to be less sensitive no matter how thinly it is applied. The support member 22 is made of, for example, Plexiglass (registered trademark), polyvinyl chloride (PVC: p).
olyvinyl chloride) or other suitable material known to those skilled in the art.

As shown in FIG. 5, the upper portion of the membrane 38 has a convex surface 39 protruding from the surface of the support structure to make contact with the human body. The convex structure of the contact surface allows the sensor of the point probe (probe) to find the location of the observed cardiovascular disease satisfactorily. In a specific embodiment of this sensor,
The maximum diameter of the membrane can be about the same as a nickel coin if the contact surface protrudes by about half of that amount, but the membrane is smaller to fit a particular application. Can be larger or smaller. The dimensions of the support plate can be of any convenient size as long as the coupler fusion region and the fiber portion near this fusion region are securely supported. The sensitivity of the device depends on the stiffness of the membrane, as in previous devices.

When the contact surface 39 is located at a pulse point on the human arm, such as on the brachial or radial artery, the membrane 38 will apply the pulse-dependent skin displacement to the coupling area of the fiber optic coupler 30. 32. This allows
This coupling region will be deflected or deflected, causing the light output ratio of the output fiber 36 to change depending on the sound being observed.

FIGS. 6 and 7 schematically show a comparison between the deflection of a conventional pretensioned linear fiber optic coupler and the deflection of the U-shaped coupler of the sensors of FIGS. 4 and 5. FIG. I have. 6a and 6c are a top view and a side view, respectively, showing the melting region of the conventional coupler in its normal state. 6b and 6d show the downward force F
FIG. 4 is a corresponding view of the melting region being deflected by the. 7a to 7d are:
6 corresponds to the corresponding figures in FIG. 6, but shows a U-shaped coupler used in the present invention.

As can be seen from FIG. 7 d, the deflection of the fusion zone in a conventional coupler causes a bend that extends and increases the tension in the fusion zone. By contrast, the deflection of the U-shaped fusion zone in FIG. 7d is expected to occur along a direction perpendicular to the U-shaped surface, and tensions the fusion zone. Instead, it only produces a U-shaped bend along its height (horizontal direction in FIG. 7d). Therefore, no crack or rupture occurs even with a considerably large displacement of the fusion zone.

FIG. 8 shows another variable coupler fiber optic sensor 20 ′ that can be used in the apparatus of the present invention. The sensor is about 30 mm such that the support member 22 'conforms to the anatomy of the human arm / wrist and facilitates the patient wearing the sensor, such as by tying the sensor to the arm / wrist. It has the same basic structure as that of the previous embodiment except that it is formed as a substantially rectangular plate angled at ゜. When applied to a particular application, the support member may include a light source 40, a photodetection / differential amplifier circuit 42, and a wireless transmitter coupled to the circuit 42 for making remote observations (
(Not shown) can be accommodated. Indeed, any of the sensor configurations described herein may provide such equipment.

FIG. 9 shows a wrist heart / respiration signal obtained from a human subject using the sensor 20 ′ of FIG. The data stream of FIG. 9 was obtained at a sampling rate of 128 samples per second. It can be seen that the pulse waveform read by this sensor is a more complex phenomenon than a standard pulse reading. This pulse waveform
The amplitude structure of the pulse is shown as a function of time. The pulse amplitude structure does not correspond to what is felt by the finger as an impulse function (if any) at a certain pulse point. Within such an amplitude structure is information about not only all of the heart sounds, but also indicators of respiration and other physical conditions. The sensitivity achieved by the improved sensor described herein allows such sensors to detect complex heartbeat waveforms.

FIG. 10 shows another wrist pulse / respiration signal obtained from a human subject by the sensor 20 ′. The data stream here has been digitized using a 12-bit A / D converter at a sampling rate of 64 samples per second.
This heartbeat signal is well resolved as the inserted graph shows. Also, the modulation induced by the breathing cycle is clearly visible over a duration of 84 seconds.

FIGS. 11 and 12 show another arm / wrist sensor 50 that can be used in the device of the present invention. In this sensor, the fused region 62 of the fiber optic coupler is not contained (as in a container) but is coated as described above.
The fusion zone 62 is joined to the arm / wrist pulsation (indicated by arrow P) by a resilient pillow 68 filled with fluid or gel. 8 except that the support plate 52 is flat and not bent (the passages of the input / output leads 64 and 66 are omitted for simplicity). An optical fiber coupler is mounted. Such a support plate is attached to the top side of the pillow 68, and a cover 69 is attached to the top side of the support plate to protect the melting area 62 of the coupler 60 at the hole 56. Due to the contact between the melting area and the upper surface of the pillow 68 which projects into the hole 56 by its own elasticity and comes into contact with the coupler melting area, the water pressure of the activation of the pulse presses and deflects the melting area It is allowed to be. A strap 57 attached to the support plate 52 with an adhesive or the like allows the sensor to be worn on the arm / wrist. Reference numbers 64 and 66
Indicates an input fiber and an output fiber, respectively.

The unaccommodated sensor configuration of FIGS. 11 and 12 is advantageous over the accommodated configuration described above because the lack of a sensing membrane increases sensitivity. Also, unlike the bent configuration of FIG. 8, the planar structure of the support plate does not require a bend that deviates from the plane of the coupler lead, causing a reduction in light intensity. Instead, the coupler is maintained in a planar configuration to optimize light intensity in the system.

FIG. 13 shows yet another sensor 70 that can be used in the device of the present invention, and is shown in cross-section such that the sensor is worn on the wrist. The sensor includes a frame member 72 having an internal structure that is generally adapted to the wrist as shown.
The frame member may be composed of a suitable material, preferably a plastic such as Delrin®, PVC, acrylic, Lucite®, Plexiglass®, styrene or other polymer. Good.

The upper part of the frame provides a chamber 77 for receiving the fiber optic coupler 80 and its support plate 81. Because the coupler is housed by the frame member, the support plate is provided with an opening (e.g., a well or through-hole) formed with a passageway to receive the input / output leads and accommodating the fused region 82 of the coupler, such as the sensor described above. Holes). The melt zone is coated rather than encased, as described above. The support plate 81 can be of the same material as the frame 72, but the coupler and the coupler are combined as a single module and mounted in place in the chamber 77. This chamber is closed by a protective cover plate (not shown).

A fluid column 74 is provided to couple the fusion zone to the pulsation of the radial artery. The column has a pair of elastic membranes 73 and 75 provided on its inner and outer portions, respectively, and extends across the thickness of the frame 72 between the chamber 77 and the inner surface of the frame. The coupler module is equipped with a coupler melting region 82 in contact with the outer membrane 75 of the fluid column. The outer membrane is attached to an annular boss 76 to increase the height of the fluid column for contact with the coupler melt zone. Due to the contact with the outer membrane, a slight preload can be applied to the melting zone. The coupler can be manufactured to provide a substantially equal splitting of the light between the output fibers by pre-loading the fusion zone, thereby providing a wide linear dynamic range. Inside of the fluid column (Fig. 1
3, the lower part) is stepped as shown to increase the diameter of the coupling area at the wrist.

[0041] Such a membrane constitutes an important part of the fluid column. Because the arterial pulsation is weak, the membrane should be light, thin, and low durometer and highly extensible for optimal performance. At the same time, at least the inner membrane should be rough enough to eliminate sustained contact with the skin.
Materials found to have very good properties for this membrane include Fl
exChem, an FDA-certified long-lasting vinyl-based material available from Colorite in the form of globules. FlexChem is also thermoformable, providing a maximum sensing area with the radial artery and forming the inner sensing membrane 73 to protrude from the inner surface of the frame member 72 for good connection with the wrist. Allow. Fl
Fluids compatible with exChem membranes include the medical MDM silicon fluids available from Applied Silicone. Incidentally, water is not preferred for use with FlexChem membranes. This is because such a membrane is permeable to water vapor.

Tests have been performed on some of the sizes of the inner membrane to determine the effect of sensor responsiveness. In particular, the diameters of the 4 mm, 7 mm and 10 mm diameter membranes were tested for response to oscillations of the excited oscillator as measured using a commercial acceleration (meter). The responsiveness was tested over a frequency range of 0 to about 11 Hz (cardiovascular disease and respiratory signals are in the range of about 0.1-4 Hz). Each of the membranes has obtained acceptable responsiveness, with the 10 mm membrane having the best responsiveness.

Returning to FIG. 13, this configuration also shows how auxiliary components such as light sources and output circuits (eg, photodetectors and differential amplifier circuits) can be incorporated into the sensor unit. . More specifically, such components may be housed in one or more chambers 79 (as shown) of frame 72.

FIGS. 14 to 16 show another sensor 80 configured for carotid artery applications. This sensor uses a planar, passage-formed support plate 82 and a coupler configuration similar to that of FIG. 11 except that the melted area is contained to form the sensor membrane. This membrane area may be made large enough (eg, on the order of 25 cents silver) to allow for the addition of a spherical cap 99 'over the convex projecting surface of the sensing membrane 98. The addition of such a spherical cap reduces the sensitivity of the sensor to any tightening movements made by hand when the sensor is manually pressed against the neck. This coupler has a plastic cover plate 9
7 protects the rear side of the sensor (the lower side in FIGS. 14 and 15). The sensor may be attached to the neck by any suitable means such as an adhesive tape.

The input and output fibers are paired and have respective protective sheaths 102 and 10.
4 and further into an outer protective sheath 106.
A fiber optic connector 108 is provided at the end of the lead to interface the sensor with external components.

FIGS. 17 to 21 show the brachial and radial artery pulse waveforms and the corresponding pulse transit times obtained with the device according to FIG. 3 using the improved two variable coupler fiber optic sensors described herein. It is a plot. The digital signal processor is programmed according to the method described with reference to FIG. It should be understood that the devices of FIGS. 1 and 3 are not mutually exclusive. For example, when programmed according to FIG. 2, the device of FIG. 3 will constitute a particular form of the configuration generally shown in FIG. Conversely, if provided with an improved variable coupler fiber optic sensor of the type described, the device of FIG. 1 would constitute a particular form of the configuration schematically illustrated in FIG.

FIG. 17 shows normal breathing data for an adult male on the spine. It can be seen that the pulse transit time is on average about 50 msec long.

FIG. 18 is a similar plot except that the breathing pattern was changed to simulate a sleep inhaling for 2 seconds and exhaling for 3 seconds. This pulse transmission time lasts about 35 msec on average.

FIG. 19 uses a breathing pattern similar to that just described, but with the nose sandwiched, breathing is constricted. Blood pressure will drop under these circumstances because the chest cavity is placed under more negative pressure (azygous pulse). This is evidenced by an increase in pulse transit time on average to about 50 msec.

FIG. 20 also uses a similar breathing pattern, but with complete obstruction of airflow. To simulate apnea, air was not allowed to enter the lungs for a total of 16 seconds of testing. It can be seen that the pulse transit time is significantly increased, indicating that the blood pressure is further reduced compared to FIG.

FIG. 21 shows another plot for an apnea period of 16 seconds, but for the whole lung. The value of the pulse transmission time here decreases to about 30 msec on average, indicating a high blood pressure.

The results of FIGS. 17-21 are consistent with the well-known fact that negative pulmonary pressure lowers blood pressure, but that gradually increasing positive pressure increases blood pressure.

FIG. 23 depicts an actual configuration using a variable coupler fiber optic sensor implementing the device according to FIG. 1 or FIG. In the form shown here, the sensors S1, S
2 (S1 ', S2') are tied to the arm with a string at the pulse points of the upper arm and the radial artery, respectively. The light source and the signal processing electronics (equipment) are stored in the module M, which is also strapped to the arm. The sensor and module M are connected by a corresponding set of fiber optic leads 34,36. Module M is a wireless transmission device (
(Not shown) to communicate with an external electronic circuit (equipment).

It is to be noted that an optical fiber used for the above-described sensor is very preferably of very high quality. This includes C which exhibits an optical loss of about 0.18 dB per km.
or SMF28. Photo detector is 900n
Gallium-aluminum-arsenic or germanium detectors for light wavelengths above m and silicon detectors for shorter wavelengths.

Such a photodetector can be connected in a photovoltaic mode or a photoconductive mode. In photovoltaic mode, a transimpedance amplifier (which converts current to voltage) can be used to couple the detector to the input of a differential amplifier. The output of such a transimpedance amplifier also
Filtering may be performed to eliminate broadband noise. In the photoconductive mode, the detector output can be connected to a conventional voltage amplifier. This approach creates a lot of noise, but can be used in applications where the concern is cost and not low noise levels.

It should be noted that the above-described embodiment according to the present invention has been described by way of example only.
Of course, many variations of the present invention are possible, as are the ones described broadly herein.

[Brief description of the drawings]

FIG. 1 is a block diagram of a method for measuring a pulse transit time according to the present invention.

FIG. 2 is a flowchart illustrating the operation of the system in FIG. 1;

FIG. 3 is a block diagram showing another apparatus of the present invention.

FIG. 4 is a top view of a variable coupler optical fiber sensor useful in the apparatus of FIGS. 1 and 3;

FIG. 5 is a sectional side view of the sensor of FIG. 4;

FIG. 6 is an explanatory view (6a to 6B) of a normal deflection state of a fusion region of a conventional linear coupler which is pre-tensioned.

FIG. 7 is a corresponding explanatory view (7a to 7d) for a U-shaped molten region.

FIG. 8 is a diagram of a variable coupler fiber optic sensor useful in an apparatus according to the present invention.

FIG. 9 is a graph depicting the response of the sensor of FIG. 8 to a wrist pulse.

FIG. 10 is another graph depicting the response of the sensor to wrist pulse.

FIG. 11 is an exploded view of another variable coupler fiber optic sensor useful for the device according to the present invention.

FIG. 12 is an end view of the sensor of FIG. 9 in an assembled configuration.

FIG. 13 shows another variable coupler optical fiber useful in a device according to the invention shown in cross section as worn on a wrist.

FIG. 14 is a perspective view of a carotid artery useful for the device according to the invention.

FIG. 15 is a fragmentary side elevational view of FIG. 14;

FIG. 16 is a perspective view showing an optical fiber conduit with the sensor of FIG. 14 and an integrated connector.

FIG. 17 is a plot showing pulse waveforms and corresponding pulse transit times obtained using an apparatus as shown in FIG. 3 for performing the method shown in FIG. 2;

FIG. 18 is a plot showing pulse waveforms and corresponding pulse transit times obtained using an apparatus as shown in FIG. 3 for performing the method shown in FIG.

FIG. 19 is a plot showing pulse waveforms and corresponding pulse transit times obtained using an apparatus as shown in FIG. 3 for performing the method shown in FIG.

FIG. 20 is a plot showing pulse waveforms and corresponding pulse transit times obtained using an apparatus as shown in FIG. 3 for performing the method shown in FIG.

FIG. 21 is a plot showing pulse waveforms and corresponding pulse transit times obtained using an apparatus as shown in FIG. 3 for performing the method shown in FIG.

FIG. 22 is a schematic diagram illustrating a practical configuration of the device according to FIG. 1 or FIG.

FIG. 23 illustrates a basic structure of a conventional variable coupler optical fiber sensor.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY , CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP , KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, US, UZ, VN, YU, ZW (71) Applicant Jart, David W. United States 22906 Virginia, Charlottesville, P.E. Oh. Box 8175, within Empirical Technologies Corporation (72) Inventor Barack, Martin C. United States 22906 Virginia, Charlottesville, P.E. Oh. Box 8175, within Empirical Technologies Corporation (72) Inventor Adkins, Charles USA 22906 Virginia, Charlottesville, P.E. Oh. Box 8175, within Empirical Technologies Corporation (72) Inventor Jart, David W .; United States 22906 Virginia, Charlottesville, P.E. Oh. Box 8175, F-term in MEPICAL TECHNOLOGIES CORPORATION (reference) 4C017 AA09 AB01 AC03 AC26 FF15

Claims (19)

[Claims] 1. A method for measuring the transit time of a pulse of a living body, comprising detecting a pulse at a first and a second pulse point spaced from each other to generate first and second pulse wave signals, respectively. Generating, differentiating the first and second pulse wave signals, selecting corresponding points of the first and second pulse wave signals based on a result of the differentiation, and delaying between the selected points How to detect time. 2. The method according to claim 1, wherein the selecting process includes the first process.
And selecting a point of a predetermined slope characteristic from each of the second pulse wave signals. 3. The method according to claim 2, wherein the selection processing is performed by the first processing.
And selecting a point of maximum slope from each of the second pulse wave signals. 4. The method according to claim 1, wherein the first and second pulse points are located in a first artery and a second artery, respectively. 5. The method according to claim 4, wherein the first artery is a brachial artery and the second artery is a radial artery. 6. The method of claim 1, wherein a pulse at at least one of the first and second pulse points is detected by a fiber optic sensor having a fused fiber coupling region. 7. The method of claim 6, wherein at least a portion of the fused fiber coupling region is deflected to change the output of the fiber optic sensor without tensioning the coupling region. A method that is configured to be able to 8. The method of claim 6, wherein said fused fiber coupling region is substantially U-shaped. 9. Apparatus configured to perform the method according to any one of claims 1 to 8. 10. An apparatus for measuring a pulse transmission time of a living body, comprising: first and second pulse sensors arranged at first and second pulse points spaced from each other; At least one of the first and second sensors is a fiber optic sensor that includes a fused coupling region, the fused coupling region configured to deflect without tension being applied to the coupling region. A signal processing unit connected to the first and second pulse sensors and operable to measure a pulse transit time based on the outputs of the first and second sensors. 11. The apparatus of claim 10, wherein each of the first and second sensors is a fiber optic sensor having a fused fiber coupling region having a portion configured as described above. apparatus. 12. The apparatus according to claim 10, further comprising an electro-optic circuit optically coupled to a plurality of output optical fibers of said one sensor, wherein said optical fiber receives light received from said output fiber. A device adapted to convert to an electrical output having a level based on the amount of deflection of said portion of the coupling region. 13. The apparatus according to claim 12, wherein the electro-optical circuit comprises:
An apparatus comprising: a plurality of photodetectors optically coupled to the plurality of output fibers; and a differential amplifier circuit to which an output of the photodetector is connected. 14. The apparatus according to claim 10, wherein said one sensor comprises:
A device having a support structure configured to fit widely on a portion of a human arm. 15. An apparatus for measuring a pulse transmission time of a living body, comprising: a first pulse sensor and a second pulse sensor arranged at a first pulse point and a second pulse point which are spaced apart from each other. At least one of the sensors is an optical fiber sensor including a substantially U-shaped fused fiber coupling region, and the first and second sensors are connected to the first and second pulse sensors. The apparatus further comprising a signal processing unit operable to measure a pulse transit time based on the output of the pulse generator. 16. The apparatus according to claim 15, wherein each of said first and second sensors is a fiber optic sensor having a substantially U-shaped fused fiber coupling region. 17. The apparatus according to claim 15, further comprising an electro-optical circuit optically coupled to a plurality of output optical fibers of said one sensor, wherein the light received from said output fiber is transmitted to said one of said sensors. An apparatus for converting an electrical output having a level based on the amount of deflection of the coupling region. 18. The apparatus according to claim 17, wherein the electro-optical circuit comprises:
An apparatus comprising: a plurality of photodetectors optically coupled to the plurality of output fibers; and a differential amplifier circuit to which outputs of the photodetectors are connected. 19. The apparatus according to claim 15, wherein said one sensor comprises:
A device having a support structure configured to fit widely on a portion of a human arm.