System and method for evaluating the circulatory system of a living subject

Claims

What is claimed is:

1. A device for evaluating a circulatory system of a living subject, comprising:

a blood-pressure changing device that changes a blood pressure of the living subject;

a blood-pressure measuring device that measures the blood pressure of the living subject while the living subject's blood pressure is changing;

an oscillatory pressure-pulse wave detector that detects oscillatory pressure-pulse waves of the living subject while the living subject's blood pressure is changing, the oscillatory pressure-pulse waves produced by a cardiac muscle of the living subject propagating along an artery of the living subject;

an electrocardiographic waveform detector that detects an electrocardiographic waveform of the living subject;

a time-difference determining circuit that determines time differences between predetermined periodic points on the electrocardiographic waveform of the living subject and predetermined periodic points on corresponding oscillatory pressure-pulse waves of the living subject; and

a circulatory-system evaluation circuit that evaluates the living subject's circulatory system based on a relationship between changes in the living subject's blood pressure and changes in the corresponding time differences determined by the time-difference determining circuit.

2. The device of claim 1, wherein the blood-pressure changing device comprises a strain application device that applies a strain to the living subject for a predetermined period of time, the subject's blood pressure increasing from an initial value in response to the strain and decreasing back to the initial value when the strain is removed.

3. The device of claim 2, wherein the strain application device comprises:

a pressure gauge that measures an air pressure;

a mouthpiece; and

a hollow tube connecting the mouthpiece to the pressure gauge, wherein the living subject begins a strain operation by blowing into the mouthpiece with a force sufficient to register a predetermined air pressure value on the pressure gauge.

4. The device of claim 3, wherein the pressure gauge comprises a mercury pressure gauge.

5. The device of claim 2, further comprising a signaling device that signals the living subject to begin a strain operation with the strain application device.

6. The device of claim 5, wherein the signaling device comprises a lamp.

7. The device of claim 1, wherein the blood-pressure measuring device comprises:

a blood-pressure measuring circuit that determines a systolic blood pressure and a diastolic blood pressure of the living subject;

a relationship determining circuit that determines a first relationship between the blood pressure values determined by the blood-pressure measuring circuit and magnitudes of corresponding oscillatory pressure-pulse waves detected by the oscillatory pressure-pulse-wave detector; and

a monitor-blood-pressure determining circuit that determines monitor-blood-pressure values based on the first relationship determined by the relationship determining circuit and magnitudes of the oscillatory pressure-pulse wave.

8. The device of claim 7, wherein the monitor-blood-pressure determining circuit determines systolic monitor-blood-pressure values and diastolic monitor-blood-pressure values.

9. The device of claim 7, wherein the circulatory-system evaluation circuit determines a second relationship between the monitor-blood-pressure values determined by the monitor-blood-pressure determining circuit and corresponding time differences determined by the time-difference determining circuit.

10. The device of claim 9, wherein the circulatory-system evaluation circuit evaluates the living subject's circulatory system based on an amount of hysteresis present in the second relationship.

11. The device of claim 1, wherein the oscillatory pressure-pulse wave detector comprises:

a housing having an opening;

a diaphragm attached to the housing;

a sensor capable of sensing the oscillatory pressure-pulse wave and supported by the diaphragm so that the sensor is movable relative to the housing and is advanceable through the opening of the housing; and

an attachment mechanism capable of attaching the oscillatory pressure-pulse wave detector to a portion of the living subject;

the housing, the diaphragm and the sensor defining a pressure chamber capable of receiving pressurized air, the pressurized air applying a pressing force to the sensor to press the sensor against the living subject when the oscillatory pressure-pulse wave detector is attached to the living subject.

12. The device of claim 1, wherein the electrocardiographic waveform detector comprises:

a plurality of electrocardio electrodes, the electrocardio electrodes capable of sensing an electrocardiographic signal from the living subject when the electrocardio electrodes are in electrical contact with the living subject; and

an electrocardiographic-waveform detection circuit that detects the living subject's electrocardiographic waveform based on the electrocardiographic signals sensed by the electrocardio electrodes.

13. A device for evaluating a circulatory system of a living subject, comprising:

a blood-pressure changing device that changes a blood pressure of the living subject;

a blood-pressure measuring device that measures the blood pressure of the living subject while the living subject's blood pressure is changing;

an electrocardiographic waveform detector that detects an electrocardiographic waveform of the living subject;

an oscillatory pressure-pulse wave detector that detects oscillatory pressure-pulse waves of the living subject while the living subject's blood pressure is changing, that oscillatory pressure-pulse wave produced by a cardiac muscle of the living subject and propagating along an artery of the living subject;

an oscillatory pressure-pulse wave velocity determining device that determines propagation velocities of the oscillatory pressure-pulse waves; and

a circulatory-system evaluation circuit that evaluates the living subject's circulatory system based on a relationship between changes in the living subject's blood pressure and changes in the propagation velocities of corresponding oscillatory pressure-pulse waves.

14. The device of claim 13, wherein the blood-pressure changing device comprises a strain application device that applies a strain to the living subject for a predetermined period of time, the subject's blood pressure increasing from an initial value in response to the strain and decreasing back to the initial value when the strain is removed.

15. The device of claim 14, wherein the strain application device comprises:

a pressure gauge that measures an air pressure;

a mouthpiece; and

a hollow tube connecting the mouthpiece to the pressure gauge, wherein the living subject begins a strain operation by blowing into the mouthpiece with a force sufficient to register a predetermined air pressure value on the pressure gauge.

16. The device of claim 15, wherein the pressure gauge comprises a mercury pressure gauge.

17. The device of claim 14, further comprising a signaling device that signals the living subject to begin a strain operation with the strain application device.

18. The device of claim 17, wherein the signaling device comprises a lamp.

19. The device of claim 13, wherein the blood-pressure measuring device comprises:

a blood-pressure measuring circuit that determines a systolic blood pressure and a diastolic blood pressure of the living subject;

a relationship determining circuit that determines a first relationship between the blood pressure values determined by the blood-pressure measuring circuit and magnitudes of corresponding oscillatory pressure-pulse waves detected by the oscillatory pressure-pulse wave detector; and

a monitor-blood-pressure determining circuit that determines monitor-blood-pressure values based on the first relationship determined by the relationship determining circuit and magnitudes of the oscillatory pressure waves.

20. The device of claim 19, wherein the monitor-blood-pressure determining circuit determines systolic monitor-blood-pressure values and diastolic monitor-blood-pressure values.

21. The device of claim 19, wherein the circulatory-system evaluation circuit determines a second relationship between the monitor-blood-pressure values determined by the monitor-blood-pressure determining circuit and propagation velocities of corresponding oscillatory pressure-pulse waves determined by the oscillatory pressure-pulse wave velocity determining device.

22. The device of claim 21, wherein the circulatory-system evaluation circuit evaluates the living subject's circulatory system based on an amount of hysteresis present in the second relationship.

23. The device of claim 13, wherein the oscillatory pressure-pulse wave detector comprises:

a housing having an opening;

a diaphragm attached to the housing;

a sensor capable of sensing the pressure-pulse-wave and supported by the diaphragm so that the sensor is movable relative to the housing and is advanceable through the opening of the housing; and

an attachment mechanism capable of attaching the oscillatory pressure-pulse wave detector to a portion of the living subject;

the housing, the diaphragm and the sensor defining a pressure chamber capable of receiving pressurized air, the pressurized air applying a pressing force to the sensor to press the sensor against the living subject when the oscillatory pressure-pulse wave detector is attached to the living subject.

24. The device of claim 13, wherein the oscillatory pressure-pulse wave velocity determining device comprises:

a time-difference determining device that determines time differences between predetermined periodic points on the electrocardiographic waveform of the living subject and predetermined periodic points on the oscillatory pressure-pulse waves of the living subject; and

a oscillatory pressure-pulse wave velocity determining circuit that determines a propagation velocity of the oscillatory pressure-pulse waves based on the time differences determined by the time-difference determining device.

25. The device of claim 24, wherein the electrocardiographic waveform detector comprises:

a plurality of electrocardio electrodes, the electrocardio electrodes capable of sensing an electrocardiographic signal from the living subject when the electrocardio electrodes are in electrical contact with the living subject; and

an electrocardiographic-waveform detection circuit that detects the living subject's electrocardiographic waveform based on the electrocardiographic signals sensed by the electrocardio electrodes.

26. A device for evaluating a circulatory system of a living subject, comprising:

a blood-pressure measuring device that successively measures the blood pressure of the living subject while the living subject is subjected to a physical load;

a means for creating the physical load;

a pressure-pulse wave propagation velocity information obtaining device that, while the living subject is subjected to the physical load, successively obtains pressure-pulse wave propagation velocity information relating to a propagation velocity of a pressure-pulse wave through an artery of the living subject; and

a circulatory-system evaluation circuit that evaluates the circulatory system of the living subject based on a relationship between changes in the blood pressure of the living subject and changes in the pressure-pulse wave propagation velocity information.

27. The device of claim 26, wherein the pressure-pulse wave propagation velocity information obtaining device comprises:

a first pulse wave detection circuit that detects first pulse waves from a first portion of the subject;

a second pulse wave detection circuit that detects second pulse waves from a second portion of the subject; and

a time-difference determining circuit that determines, as the pressure-pulse wave propagation velocity information, time differences between predetermined periodic points on the first pulse waves and predetermined periodic points on the corresponding second pulse waves.

28. The device of claim 27, wherein the circulatory-system evaluation circuit comprises evaluating means for evaluating the circulatory system of the subject based on a relationship between changes in the blood pressure of the subject and changes in the time differences determined by the time-difference determining circuit.

29. The device of claim 28, wherein the pressure-pulse wave propagation velocity information obtaining device further comprises a propagation-velocity determining circuit that determines the propagation velocity of the pulse wave based on each of the time differences determined by the time-difference determining circuit, and wherein the circulatory-system evaluation circuit comprises evaluating means for evaluating the circulatory system of the subject based on a relationship between changes in the blood pressure of the subject and changes in the propagation velocities determined by the propagation-velocity determining circuit.

30. The device of claim 26, wherein the circulatory-system evaluation circuit comprises hysteresis determining means for determining an amount of hysteresis present in the relationship between the changes in the blood pressure of the subject and the changes in the pressure-pulse wave propagation velocity information.

31. The device of claim 30, wherein the hysteresis determining means comprises area-calculating means for calculating, as the amount of hysteresis, an area defined by a closed line representing the relationship between the changes in the blood pressure of the subject and the changes in the pressure-pulse wave propagation velocity information.

32. A method of evaluating a circulatory system of a living subject, comprising:

changing a blood pressure of the living subject over a predetermined period of time;

measuring the subject's blood pressure while the subject's blood pressure is changing;

measuring oscillatory pressure-pulse waves of the living subject while the living subject's blood pressure is changing, the oscillatory pressure-pulse waves produced by a cardiac muscle of the living subject and propagating along an artery of the living subject;

measuring an electrocardiographic waveform of the living subject while the living subject's blood pressure is changing;

determining time differences between predetermined periodic points on the electrocardiographic waveform of the living subject and predetermined periodic points on corresponding oscillatory pressure-pulse waves of the living subject; and

evaluating the living subject's circulatory system based on a relationship between changes in the living subject's blood pressure and changes in corresponding time differences.

33. The method of claim 32, changing the blood pressure of the living subject comprises:

applying a strain on the living subject for a predetermined period of time to raise a blood pressure of the living subject from an initial value; and

removing the strain applied to the living subject to lower the subject's blood pressure back to the initial value.

34. The method of claim 33, wherein applying a strain on the living subject comprises causing the living subject to blow into a mouthpiece of an air pressure gauge with a predetermined force for a predetermined period of time.

35. The method of claim 32, wherein measuring the subject's blood pressure comprises:

determining a systolic blood pressure value of the subject and a diastolic blood pressure value of the subject;

determining a first relationship between the blood pressure values and magnitudes of corresponding oscillatory pressure-pulse waves; and

determining systolic and diastolic monitor-blood-pressure values based on the first relationship.

36. The method of claim 35, wherein evaluating the living subject's circulatory system comprises determining a second relationship between the monitor-blood-pressure values and corresponding time differences between predetermined periodic points on the electrocardiographic waveform of the living subject and predetermined periodic points on corresponding oscillatory pressure-pulse waves of the living subject.

37. The method of claim 36, wherein the subject's circulatory system is evaluated based on an amount of hysteresis present in the second relationship.

38. The method of claim 35, wherein propagation velocities of the oscillatory pressure-pulse waves are determined based on the time differences between predetermined periodic points on the electrocardiographic waveform of the living subject and predetermined periodic points on the oscillatory pressure-pulse waves of the living subject.

39. The method of claim 35, evaluating the living subject's circulatory system comprises determining a second relationship between the monitor-blood-pressure values and the propagation velocities of corresponding oscillatory pressure-pulse waves.

40. The method of claim 39, wherein the subject's circulatory system is evaluated based on an amount of hysteresis present in the second relationship.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to medical diagnostic devices. More specifically, this invention is directed to a system and method for evaluating the circulatory system of a living subject.

2. Description of Related Art

Some circulatory ailments that cause high blood pressure, such as arteriosclerosis, are discovered by measuring the subject's blood pressure with a blood pressure measurement apparatus. One such blood pressure measurement apparatus is disclosed in Japanese Laid-Open Application No. 6-292660.

The blood-pressure measurement device measures the blood pressure of a living subject using a cuff that is wrapped around a portion of the living subject. The cuff applies pressure to the living subject. The living subject's blood pressure is measured using a well-known oscillometric method, which is based on detecting changes in the amplitude of a synchronous wave pulsation as the pressure applied by the cuff is gradually released.

Although a blood pressure measurement is effective in discovering the existence of high blood pressure in a living subject, it is not an effective method for evaluating improvement in the underlying cause of the living subject's high blood pressure brought about by dietary treatments. Blood pressure measurement is not effective in evaluating the effects of dietary treatment on the circulatory ailment because high-blood-pressure patients typically take blood-pressure-reducing medication. Thus, because the living subject's blood pressure is kept at normal levels by medication, a blood pressure measurement will not reveal if the underlying condition causing the living subject's high blood pressure is improving.

SUMMARY OF THE INVENTION

This invention provides a device that accurately evaluates a living subject's circulatory system, even if the living subject is taking high-blood-pressure medication. The device provides a time-difference determining device that determines a time difference between predetermined periodic points on a subject's electrocardiographic waveform and predetermined periodic points on corresponding oscillatory pressure-pulse waves of the living subject. A strain application device applies a physical strain to the subject's body for a predetermined period of time so that the subject's blood pressure changes. A blood-pressure measurement device measures the subject's blood pressure while the subject's blood pressure is changing. A circulatory-system evaluation device determines a relationship between changes in the subject's blood pressure and corresponding time differences determined by the time-difference determining device. The circulatory-system evaluation device evaluates the subject's circulatory system based on the hysteresis present in the determined relationship.

The inventors have discovered, as a result of extended study, that the relationship between changes in a subject's blood pressure and changes in the corresponding time differences between predetermined periodic points on the subject's electrocardiographic waveform and predetermined periodic points on corresponding oscillatory pressure-pulse waves of the living subject exhibits little or no hysteresis if the subject's circulatory system is healthy. Furthermore, the relationship exhibits hysteresis if the subject's circulatory system is not healthy.

In a preferred embodiment, a propagation velocity determining device is used to determine the propagation velocities of a subject's oscillatory pressure-pulse waves based on the time difference determination by the time-difference determining device. In this embodiment, the circulatory-system evaluation device determines a relationship between changes in the subject's blood pressure and changes in the propagation velocities of corresponding oscillatory pressure-pulse waves. The circulatory-system evaluation device evaluates the subject's circulatory system based on the hysteresis present in the determined relationship. The amount of hysteresis present is an indicator of the relative health of the subject's circulatory system.

These and other features and advantages are described in or are apparent from the following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments of this invention will be described in detail, with reference to the following Fig.s, wherein:

FIG. 1 is a combined schematic and block diagram of the circulatory-system evaluation device of this invention;

FIG. 2 is a perspective view of a thoracic-cavity pressure applicator and measurement device used in the circulatory-system evaluation device of FIG. 1;

FIG. 3 is a block diagram of an electronic control device of the circulatory-system evaluation device of FIG. 1;

FIG. 4 shows a relationship between a subject's oscillatory pressure-pulse wave and a subject's blood pressure;

FIG. 5 is a timing chart of the circulatory-system evaluation device of FIG. 1;

FIG. 6 is a relationship determined by the circulatory-system evaluation device of FIGS. 1 and 3;

FIGS. 7A and 7B show a flowchart of a preferred control routine for the circulatory-system evaluation device of FIGS. 1 and 3;

FIG. 8 is a block diagram of a second preferred embodiment of an electronic control device of the circulatory-system evaluation device of FIG. 1;

FIGS. 9A and 9B show a flowchart of a preferred control routine for the circulatory-system evaluation device of FIGS. 1 and 8; and

FIG. 10 shows a relationship determined by the circulatory-system evaluation device of FIGS. 1 and 8.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the circulatory-system evaluation device 8 of this invention. The device 8 comprises an inflatable cuff 10 which is preferably formed by a rubber bag that is positioned inside a flexible cloth bag. The inflatable cuff 10 is wrappable around a portion of a living subject, e.g., an upper arm 12 of a subject.

The inflatable cuff 10 is connected via piping 20 to a pressure sensor 14, a switch valve 16 and a first air pump 18.

The switch valve 16 is selectively placeable in either an inflation position, a slow-deflation position or a quick-deflation position. In the inflation position, the switch valve 16 allows pressurized air from the first air pump 18 to be supplied to the inflatable cuff 10. In the slow-deflation position, the switch valve 16 allows the pressurized air in the inflatable cuff 10 to be slowly discharged. In the quick-deflation position, the switch valve 16 allows the pressurized air in the inflatable cuff 10 to be quickly discharged.

The pressure sensor 14 detects an air pressure in the inflatable cuff 10 and supplies a pressure signal SP, representing the detected pressure, to a static-pressure discrimination circuit 22 and a pressure-pulse-wave discrimination circuit 24. The static-pressure discrimination circuit 22 includes a low-pass filter that extracts a static component contained in the pressure signal SP, i.e., a cuff pressure signal SK that represents the static cuff pressure. The cuff pressure signal SK is supplied to an electronic control device 28 via a first A/D converter 26.

The pressure-pulse-wave discrimination circuit 24 includes a band-pass filter that extracts an oscillatory component of the pressure signal SP falling within a predetermined frequency range. The oscillatory component is supplied as a cuff pressure signal SM.sub.1 to the electronic control device 28 via a second A/D converter 30. The cuff pressure signal SM.sub.1 represents an oscillatory pressure wave that is produced from a brachial artery of the subject and that propagates to the area on the subject's right arm 12 in contact with the inflatable cuff 10.

The electronic control device 28 preferably includes a central processing unit (CPU) 29, a read-only memory (ROM) 31, a random-access memory (RAM) 33 and an input-output (I/O) port (not shown). The CPU 29 processes input signals according to control programs pre-stored in the ROM 31 using the RAM 33 as temporary storage. In addition, the CPU 29 outputs display signals to a display device 32.

When a measurement is initiated, the CPU 29 supplies a control signal to the switch valve 16 to place it in the inflation position and a drive signal to the first air pump 18 to inflate the inflatable cuff 10, thus compressing the upper portion of the subject's right arm 12. The CPU 29 then supplies a control signal to the switch valve 16 to place it in the slow-deflation position, thus gradually reducing the air pressure in the inflatable cuff 10.

While the air pressure in the inflatable cuff 10 is gradually reduced, the CPU 29 obtains the cuff pressure signal SM.sub.1 and the cuff pressure signal SK from the pressure sensor 14 via the pressure-pulse-wave discrimination circuit 24 and the static-pressure discrimination circuit 22, respectively. The CPU 29 then determines the subject's systolic blood pressure value SBP, the subject's diastolic blood pressure value DBP and the subject's mean blood pressure value BP based on the obtained signals SM.sub.1 and SK using well-known oscillometric blood pressure measuring techniques. These techniques are based on the variation of the amplitudes of the heartbeat-synchronous pulses of the oscillatory pressure-pulse wave (i.e., the cuff pressure pulse signal SM.sub.1).

The circulatory-system evaluation device 8 further includes a oscillatory pressure-pulse-wave detection probe 34. The oscillatory pressure-pulse-wave detection probe 34 has a container-like housing 36 that is detachably worn, using attachment bands 40, on a body surface 38 of a subject's wrist 42 downstream of an upper arm. The oscillatory pressure-pulse-wave detection probe 34 is preferably worn on the other than the arm 12 around which the inflatable cuff 10 is worn. However, the oscillatory pressure-pulse-wave detection probe 34 may also be worn downstream of the upper arm 12 around which the inflatable cuff 10 is worn.

The oscillatory pressure-pulse-wave detection probe 34 is positioned on the subject's wrist 42 such that an opening of the housing 36 is opposed to the body surface 38. A pressure-pulse-wave sensor 46 is supported by the housing 36 via a diaphragm 44 such that the pressure-pulse-wave sensor 46 is movable relative to the housing 36 and is advanceable through the opening of the housing 36.

The housing 36, the diaphragm 44 and the pressure-pulse-wave sensor 46 cooperate with one another to define a pressure chamber 48. Pressurized air is supplied to the pressure chamber 48 from a second air pump 50 via a pressure regulator valve 52. Thus, the pressure-pulse-wave sensor 46 is pressed against a radial artery 56 of the subject via the body surface or skin 38 with a pressing force P.sub.HD. The pressing force P.sub.HD corresponds to the air pressure in the pressure chamber 48.

The pressure-pulse-wave sensor 46 includes a number of semiconductor pressure-sensing elements (not shown) which are arranged along a pressing surface 54 of a semiconductor chip. The semiconductor chip is suitably formed from monocrystalline silicon.

The pressure-pulse-wave sensor 46 is pressed against the subject's radial artery 56 via the body surface 38 of the subject's wrist 42 to detect oscillatory pressure-pulse waves of the subject. The oscillatory pressure-pulse waves are produced by the subject's cardiac muscle and propagate along the radial artery 56. They are transmitted to the pressure-pulse-wave sensor 46 via the body surface 38. The pressure-pulse-wave sensor 46 generates an oscillatory pressure-pulse-wave signal SM.sub.2 representing the detected oscillatory pressure-pulse wave. The oscillatory pressure-pulse-wave signal SM.sub.2 is input to the electronic control device 28 via a third A/D converter 58. Thus, the pressure-pulse-wave sensor 46 detects an oscillatory pressure-pulse wave propagating through the subject's radial artery 56.

The CPU 29 of the electronic control device 28 supplies drive signals to the second air pump 50 and control signals to the pressure regulator valve 52 to regulate the air pressure in the pressure chamber 48. By regulating the air pressure in the pressure chamber 48, the CPU 29 regulates the magnitude of the pressing force P.sub.HD applied by the pressure-pulse-wave sensor 46 to the subject's radial artery 56 via the body surface 38.

The CPU 29 determines an optimum value for the pressing force P.sub.HD for the pressure-pulse-wave sensor 46 based on the respective magnitudes of heartbeat-synchronous pulses of the oscillatory pressure-pulse wave detected by the pressure-pulse-wave sensor 46 while the air pressure of the chamber 48 is changed. The CPU 29 then controls the pressure regulator valve 52 to maintain the optimum pressing force P.sub.HD.

The circulatory-system evaluation device 8 also includes an electrocardiographic-waveform detection circuit 60. The electrocardiographic-waveform detection circuit 60 continuously detects an electrocardiographic waveform that indicates the change in electric potential of the subject's cardiac muscle. The electrocardiographic-waveform detection circuit 60 determines the electrocardiographic waveform from signals supplied by multiple electrodes 62. The electrodes 62 are placed at predetermined positions on the subject. The electrocardiographic-waveform detection circuit 60 is suitably an electrocardiograph, and the electrocardiographic waveform is suitably an electrocardiogram detected by the electrocardiograph.

The electrocardiographic-waveform detection circuit 60 supplies the electrocardiographic waveform to the electronic control device 28. The display device 32 may optionally record the electrocardiographic waveform on a recording sheet (not shown).

The circulatory-system evaluation device 8 also includes an indicator lamp 67. The indicator lamp 67 is used to signal the living subject being evaluated to begin a strain operation, as is described in more detail below.

FIG. 2 shows a thoracic-cavity pressure applicator and measurement device 63. The pressure applicator and measurement device 63 includes a mouthpiece 66 that is connected to a pressure gauge 64 via a hollow rubber tube 65. The pressure gauge 64 is suitably a mercury pressure gauge.

When a circulatory-system evaluation measurement is initiated, the CPU 29 illuminates an indicator lamp 67. When the indicator lamp 67 is illuminated, the subject being evaluated executes the well-known Valsalva's operation. During the Valsalva's operation, the subject bites down on, and blows into, the mouthpiece 66. The subject blows into the mouthpiece with a force sufficient to maintain a predetermined pressure reading on the pressure gauge 64 for a predetermined period of time. As an example, the subject being evaluated blows into the mouthpiece 66 with a force sufficient to maintain a pressure value of approximately 40 mmHg for a period of approximately 15 seconds. After the predetermined period of time has expired, the subject removes the mouthpiece and resumes normal breathing.

During the predetermined period of time during which the subject is blowing into the mouthpiece 66, the pressure inside the subject's thoracic cavity is maintained at an elevated level, resu