U.S. patent application number 10/639463 was filed with the patent office on 2004-04-01 for heart-sound detecting apparatus and heart-sound detecting method.
This patent application is currently assigned to COLIN CORPORATION. Invention is credited to Ogura, Toshihiko.
Application Number | 20040064056 10/639463 |
Document ID | / |
Family ID | 32032099 |
Filed Date | 2004-04-01 |
United States Patent
Application |
20040064056 |
Kind Code |
A1 |
Ogura, Toshihiko |
April 1, 2004 |
Heart-sound detecting apparatus and heart-sound detecting
method
Abstract
An apparatus for detecting a heart sound of a living subject,
including a pressure-pulse-wave sensor which is adapted to be worn
on a body portion of the subject that is distant from a chest of
the subject, detects a pressure pulse wave produced by an artery of
the body portion, and generates a pressure-pulse-wave signal
representing the detected pressure pulse wave; and a heart-sound
extracting device for extracting, from the pressure-pulse-wave
signal generated by the pressure-pulse-wave sensor, a heart-sound
component representing the heart sound of the subject.
Inventors: |
Ogura, Toshihiko;
(Komaki-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
COLIN CORPORATION
Komaki-shi
JP
|
Family ID: |
32032099 |
Appl. No.: |
10/639463 |
Filed: |
August 13, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10639463 |
Aug 13, 2003 |
|
|
|
09942865 |
Aug 31, 2001 |
|
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Current U.S.
Class: |
600/490 |
Current CPC
Class: |
A61B 2562/043 20130101;
A61B 5/6843 20130101; A61B 5/02233 20130101; A61B 5/0285 20130101;
A61B 7/00 20130101; A61B 2562/0247 20130101 |
Class at
Publication: |
600/490 |
International
Class: |
A61B 005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 7, 2001 |
JP |
2001-030879 |
Claims
What is claimed is:
1. An apparatus for detecting a heart sound of a living subject,
comprising: a pressure-pulse-wave sensor which has a press surface
adapted to be pressed on a body portion of the subject that is
distant from a chest of the subject, without intervention of an air
between the press surface of the sensor and the body portion,
detects a pressure pulse wave produced by an artery of the body
portion, and generates a pressure-pulse-wave signal representing
the detected pressure pulse wave; a pressing device which presses
the pressure-pulse-wave sensor so that the press surface of the
sensor is pressed on the body portion of the subject; and a
heart-sound extracting means for extracting, from the
pressure-pulse-wave signal generated by the pressure-pulse-wave
sensor, a heart-sound component representing the heart sound of the
subject, and having frequencies in a prescribed frequency range of
above 30 Hz to 600 Hz.
2. An apparatus for detecting a heart sound of a living subject,
comprising: a pressure-pulse-wave sensor which has a press surface
adapted to be pressed on a body portion of the subject that is
distant from a chest of the subject, without intervention of an air
between the press surface of the sensor and the body portion, and
includes a plurality of pressure sensing elements provided in the
press surface and arranged in a widthwise direction of an artery of
the body portion, each of the pressure sensing elements detecting a
pressure pulse wave produced by the artery of the body portion, and
generating a pressure-pulse-wave signal representing the detected
pressure pulse wave; a pressing device which presses the
pressure-pulse-wave sensor so that the press surface of the sensor
is pressed on the body portion of the subject and accordingly each
of the pressure sensing elements provided in the press surface is
pressed on the body portion without intervention of the air between
the press surface and the body portion; an optimum-element
selecting means for selecting one of the pressure sensing elements
provided in the press surface, as an optimum pressure sensing
element, based on respective magnitudes of the respective
pressure-pulse-wave signals generated by the pressure sensing
elements; and a heart-sound extracting means for extracting, from
the pressure-pulse-wave signal generated by the optimum pressure
sensing element, a heart-sound component representing the heart
sound of the subject, and having frequencies in a prescribed
frequency range of above 30 Hz to 600 Hz.
3. An apparatus for obtaining information relating to a velocity at
which a pulse wave propagates through an artery of a body portion
of a living subject, the apparatus comprising: a heart-sound
detecting apparatus comprising a pressure-pulse-wave sensor which
is adapted to be worn on the body portion of the subject that is
distant from a chest of the subject, detects a pressure pulse wave
produced by the artery of the body portion, and generates a
pressure-pulse-wave signal representing the detected pressure pulse
wave, and a heart-sound extracting means for extracting, from the
pressure-pulse-wave signal generated by the pressure-pulse-wave
sensor, a heart-sound component representing a heart sound of the
subject; and an information obtaining means for obtaining said
information based on a first timing at which the
pressure-pulse-wave sensor of the heart-sound detecting apparatus
detects a prescribed periodic portion of the heart sound, and a
second timing at which the pressure-pulse-wave sensor detects a
prescribed periodic portion of the pressure pulse wave.
4. An apparatus according to claim 3, wherein the information
obtaining means comprises means for obtaining, as said information,
a time difference between the first and second timings.
5. An apparatus according to claim 4, wherein the information
obtaining means comprises means for obtaining, as said information,
said velocity by dividing, by said time difference, a distance
between a heart of the subject and the body portion thereof distant
from the chest thereof.
6. An apparatus for measuring a blood pressure of a living subject,
comprising: an inflatable cuff which is adapted to be wound around
an upper arm of the subject; a blood-pressure determining means for
determining the blood pressure of the subject based on a signal
which is produced in the cuff while a pressing pressure of the cuff
is gradually changed; a pressure-pulse-wave sensor which is
provided in an inner surface of the cuff, has a press surface
adapted to be pressed on the upper arm of the subject without
intervention of an air between the press surface and the upper arm,
detects a pressure pulse wave produced by an artery of the upper
arm, and generates a pressure-pulse-wave signal representing the
detected pressure pulse wave; a pressing device which presses the
pressure-pulse-wave sensor so that the press surface of the sensor
is pressed on the upper arm; and a heart-sound extracting means for
extracting, from the pressure-pulse-wave signal generated by the
pressure-pulse-wave sensor, a heart-sound component representing
the heart sound of the subject, and having frequencies in a
prescribed frequency range of above 30 Hz to 600 Hz.
7. A method of detecting a heart sound of a living subject,
comprising the steps of pressing a pressure-pulse-wave sensor on a
body portion of the subject that is distant from a chest of the
subject, without intervention of an air between the press surface
and the upper arm, so that the pressure-pulse-wave sensor detects a
pressure pulse wave produced by an artery of the body portion, and
generates a pressure-pulse-wave signal representing the detected
pressure pulse wave, pressing the pressure-pulse-wave sensor so
that the press surface of the sensor is pressed on the body portion
of the subject; and extracting, from the pressure-pulse-wave signal
generated by the pressure-pulse-wave sensor, a heart-sound
component representing the heart sound of the subject, and having
frequencies in a prescribed frequency range of above 30 Hz to 600
Hz.
8. An apparatus according to claim 1, further comprising a noise
removing means for removing, from the pressure-pulse-wave signal
generated by the pressure-pulse-wave sensor, a component having
frequencies not lower than 50 Hz.
9. An apparatus according to claim 1, wherein the
pressure-pulse-wave sensor comprises no inflatable portion.
10. An apparatus according to claim 2, further comprising a noise
removing means for removing, from the pressure-pulse-wave signal
generated by the optimum pressure sensing element, a component
having frequencies not lower than 50 Hz.
11. An apparatus according to claim 2, wherein each of the pressure
sensing elements provided in the press surface comprises no
inflatable portion.
12. An apparatus according to claim 6, further comprising a noise
removing means for removing, from the pressure-pulse-wave signal
generated by the pressure-pulse-wave sensor, a component having
frequencies not lower than 50 Hz.
13. An apparatus according to claim 6, wherein the
pressure-pulse-wave sensor comprises no inflatable portion.
14. A method according to claim 7, further comprising a step of
removing, from the pressure-pulse-wave signal generated by the
pressure-pulse-wave sensor, a component having frequencies not
lower than 50 Hz.
15. A method according to claim 7, wherein the pressure-pulse-wave
sensor comprises no inflatable portion.
Description
This is a Continuation-In-Part application of application Ser. No.
09/942,865, filed on Aug. 31, 2001 now abandoned.
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an apparatus and a method
for detecting a heart sound of a living subject, at a position
distant from a chest of the subject.
[0003] 2. Related Art Statement
[0004] Heart sounds are used to make a diagnosis of heart-valve
disease or congenital heart disease. In addition, heart sounds may
be used to obtain pulse-wave-propagation-velocity-relating
information such as a pulse-wave propagation needed for a pulse
wave to propagate through an artery between two body portions of a
living subject, or a pulse-wave propagation velocity at which a
pulse wave propagates through an artery.
[0005] It has been a conventional manner to detect heart sounds
using a microphone. Since heart sounds are vibrations, blood-flow
sounds, etc. produced when the valves of the heart open and close,
the heart-sound microphone is usually put on the skin of the chest
(in particular, the skin right above the heart).
[0006] Therefore, when the heart-sound microphone is put on, it is
needed to take off cloths to expose the chest. Thus, putting on the
heart-sound microphone is more cumbersome than putting on a sensor
on an arm or a neck.
[0007] Meanwhile, obtaining
pulse-wave-propagation-velocity-relating information needs
detecting respective heartbeat-synchronous signals at two body
portions of a living subject. Therefore, in the case where the
heart sound detected by the microphone put on the chest is used as
one of the two heartbeat-synchronous signals needed to obtain the
pulse-wave-propagation-velocity-relating information, it is
disadvantageously needed to put on another sensor on the subject so
as to detect the other heartbeat-synchronous signal.
SUMMARY OF THE INVENTION
[0008] It is therefore an object of the present invention to
provide a heart-sound detecting apparatus for detecting a heart
sound at a position distant from a chest of a living subject; a
heart-sound detecting method of detecting a heart sound at a
position distant from a chest of a living subject; a
pulse-wave-propagation-velocity-relating-information obtaining
apparatus including the heart-sound detecting apparatus which
allows a sensor thereof to be easily worn; and a blood-pressure
measuring apparatus capable of detecting a heart sound.
[0009] The above object has been achieved by the present invention.
According to a first feature of the present invention, there is
provided an apparatus for an apparatus for detecting a heart sound
of a living subject, comprising a pressure-pulse-wave sensor which
is adapted to be worn on a body portion of the subject that is
distant from a chest of the subject, detects a pressure pulse wave
produced by an artery of the body portion, and generates a
pressure-pulse-wave signal representing the detected pressure pulse
wave; and a heart-sound extracting means for extracting, from the
pressure-pulse-wave signal generated by the pressure-pulse-wave
sensor, a heart-sound component representing the heart sound of the
subject.
[0010] According to this feature, the heart-sound extracting means
extracts, from the pressure-pulse-wave signal generated by the
pressure-pulse-wave sensor worn on the body portion distant from
the chest, the heart-sound component representing the heart sound.
Thus, the present apparatus can detect a heart sound at a position
distant from a chest of a living subject.
[0011] According to a second feature of the present invention,
there is provided an apparatus for detecting a heart sound of a
living subject, comprising a pressure-pulse-wave sensor which is
adapted to be worn on a body portion of the subject that is distant
from a chest of the subject, and includes a plurality of pressure
sensing elements arranged in a widthwise direction of an artery of
the body portion, each of the pressure sensing elements detecting a
pressure pulse wave produced by the artery of the body portion, and
generating a pressure-pulse-wave signal representing the detected
pressure pulse wave; an optimum-element selecting means for
selecting one of the pressure sensing elements, as an optimum
pressure sensing element, based on respective magnitudes of the
respective pressure-pulse-wave signals generated by the pressure
sensing elements; and a heart-sound extracting means for
extracting, from the pressure-pulse-wave signal generated by the
optimum pressure sensing element, a heart-sound component
representing the heart sound of the subject.
[0012] According to this feature, the optimum-element selecting
means selects, from the pressure sensing elements, the optimum
pressure sensing element that can detect, with high sensitivity,
the pressure pulse wave, and the heart-sound extracting means
extracts, from the pressure-pulse-wave signal generated by the
optimum pressure sensing element, the heart-sound component
representing the heart sound of the subject. Thus, the present
apparatus can detect a heart sound having a clear waveform. In
order to detect a heart sound having a clear waveform, it is needed
to position a pressing sensing element right above a target artery.
However, since the artery is present under the skin and accordingly
is not visible, and additionally, since the artery may move because
of the pressing of the pressure-pulse-wave sensor and/or the motion
of the body, it is difficult to accurately position a single
pressure sensing element right above, or in the vicinity of, a
target artery. If the pressure sensing element is not positioned
right above, or in the vicinity of, the target artery, the heart
sound extracted from the pressure-pulse-wave signal supplied from
the pressure sensing element may not have a clear waveform.
[0013] According to a third feature of the present invention, there
is provided an apparatus for obtaining information relating to a
velocity at which a pulse wave propagates through an artery of a
living subject, the apparatus comprising a heart-sound detecting
apparatus according to the first or second feature; and an
information obtaining means for obtaining the information based on
a first timing at which the pressure-pulse-wave sensor of the
heart-sound detecting apparatus detects a prescribed periodic
portion of the heart sound, and a second timing at which the
pressure-pulse-wave sensor detects a prescribed periodic portion of
the pressure pulse wave.
[0014] According to this feature, the pressure-pulse-wave sensor of
the heart-sound detecting apparatus detects two
heartbeat-synchronous signals, i.e., the heart sound and the
pressure pulse wave, and the information obtaining means obtains
the information based on the heart sound and the pressure pulse
wave. Thus, the single pressure-pulse-wave sensor suffices for
obtaining the pulse-wave-propagation-velocity-relatin- g
information. The single sensor is easily worn on the subject.
[0015] According to a fourth feature of the present invention,
there is provided an apparatus for measuring a blood pressure of a
living subject, comprising an inflatable cuff which is adapted to
be wound around an upper arm of the subject; a blood-pressure
determining means for determining the blood pressure of the subject
based on a signal which is produced in the cuff while a pressing
pressure of the cuff is gradually changed; a pressure-pulse-wave
sensor which is provided in an inner surface of the cuff, detects a
pressure pulse wave produced by an artery of the upper arm, and
generates a pressure-pulse-wave signal representing the detected
pressure pulse wave; and a heart-sound extracting means for
extracting, from the pressure-pulse-wave signal generated by the
pressure-pulse-wave sensor, a heart-sound component representing
the heart sound of the subject.
[0016] According to this feature, when the cuff is wound around the
upper arm to measure a blood pressure of the subject, the
pressure-pulse-wave sensor to detect the heart sound is naturally
worn on the subject. In addition, since the cuff is wound around
the upper arm such that the cuff closely contacts the arm, that the
cuff is wound around the upper arm means that the
pressure-pulse-wave sensor is appropriately worn on the arm.
[0017] According to a fifth feature of the present invention, there
is provided a method of detecting a heart sound of a living
subject, comprising the steps of wearing the pressure-pulse-wave
sensor of the heart-sound detecting apparatus according to the
first or second feature, on a body portion of the subject that is
distant from a chest of the subject, so that the
pressure-pulse-wave sensor detects a pressure pulse wave produced
by an artery of the body portion, and generates a
pressure-pulse-wave signal representing the detected pressure pulse
wave, and extracting, from the pressure-pulse-wave signal generated
by the pressure-pulse-wave sensor, a heart-sound component
representing the heart sound of the subject.
[0018] According to this feature, the heart-sound component
representing the heart sound is extracted from the
pressure-pulse-wave signal generated by the pressure-pulse-wave
sensor worn on the body portion distant from the chest. Therefore,
the heart sound can be detected at a position distant from the
chest.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The above and optional objects, features, and advantages of
the present invention will be better understood by reading the
following detailed description of the preferred embodiments of the
invention when considered in conjunction with the accompanying
drawings, in which:
[0020] FIG. 1 is a diagrammatic view for explaining a construction
of a physical-information obtaining apparatus functioning as a
heart-sound detecting apparatus, a blood-pressure measuring
apparatus, and a
pulse-wave-propagation-velocity-relating-information obtaining
apparatus, to which the present invention is applied;
[0021] FIG. 2 is a development view of an inflatable cuff of the
apparatus of FIG. 1;
[0022] FIG. 3 is a plan view of a pressure-pulse-wave sensor of the
apparatus of FIG. 1;
[0023] FIG. 4 is a block diagram for explaining essential functions
of a control device of the apparatus of FIG. 1;
[0024] FIG. 5 is a cross-section view for explaining a state in
which the cuff is wound around an upper arm of a living
subject;
[0025] FIG. 6 is a graph showing a relationship between individual
pressure-sensing semiconductor elements and respective amplitudes
of respective pressure-pulse-wave signals SM generated by the
individual pressure-sensing elements;
[0026] FIG. 7 is a graph showing heart sounds extracted by a
heart-sound extracting means, and a pressure pulse wave BAP from
which noise has been extracted by a noise removing means; and
[0027] FIG. 8 is a flow chart representing a control program
according to which the control device of FIG. 4 operates for
determining a pulse-wave propagation velocity PWV.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0028] Hereinafter, there will be described a preferred embodiment
of the present invention in detail by reference to the accompanying
drawings. FIG. 1 shows a diagrammatic view for explaining a
construction of a physical-information obtaining apparatus 10
functioning as a heart-sound detecting apparatus, a blood-pressure
measuring apparatus, and a
pulse-wave-propagation-velocity-relating-information obtaining
apparatus, to which the present invention is applied.
[0029] In FIG. 1, reference numeral 12 designates an inflatable
cuff which is adapted to be wound around a right upper arm 14 of a
patient. FIG. 2 is a development view of the cuff 12. As shown in
FIG. 2, the cuff 12 includes a belt-like cover bag 16 which is
formed of a non-stretchable and considerably rigid cloth and has
substantially the same length as that of a common inflatable cuff
which is used to measure a blood pressure of an upper arm of a
patient. However, a width of the cuff 12 is longer than that of the
common cuff by a length corresponding to a width of a small cuff
20, described below.
[0030] In the cover bag 16, there are provided a large cuff 18 and
the small cuff 20 each of which has substantially the same length
(e.g., 24 cm) as that of a circumferential length of the upper arm
14 and is formed of rubber. The large cuff 18 has substantially the
same width as that of a rubber bag employed in the common cuff. The
width of the small cuff 20 is smaller than that of the large cuff
18 and is, for example, 2 cm. The large cuff 18 and the small cuff
20 are provided such that respective one long sides thereof are
adjacent to each other. In a state in which the cuff 12 is wound
around the upper arm 14, the small cuff 20 is positioned at a
distal-side end of the cuff 12. The large cuff 18 and the small
cuff 20 are connected to respective pipings 22, 24 for supplying
pressurized air thereto.
[0031] A flexible support plate 26 which has substantially the same
width as that of the small cuff 20 is fixed to an inner surface of
the cuff 12 that contacts the upper arm 14 when the cuff 12 is
wound around the same 14. More specifically described, the support
plate 26 is fixed to a portion of the inner surface of the cuff 12
that corresponds to the small cuff 20, so that when the cuff 12 is
wound around the upper arm 14, the support plate 26 is pressed by
the small cuff 20. The support plate 26 supports four
pressure-pulse-wave sensors 28 such that the four sensors 28 are
arranged along a straight line in a lengthwise direction of the
plate 26. Between each pair of adjacent sensors 28, there is
provided a considerably small space of 0.9 mm length.
[0032] FIG. 3 is a plan view of one of the four pressure-pulse-wave
sensors 28. The sensor 28 has a press surface 30 which is defined
by a semiconductor chip such as monocrystalline silicon and has a
length of about 13 mm in a lengthwise direction of the cuff 12
(i.e., in a left-right direction in FIG. 3). In the press surface
30, there are provided a number of semiconductor-based pressure
sensing elements (or pressure detecting elements) 32 at a regular
interval of distance along a straight line in the lengthwise
direction of the cuff 12. In the present embodiment, each
pressure-pulse-wave sensor 28 has fifteen pressure sensing elements
32 which are arranged at a regular spacing interval of 0.2 mm.
[0033] Back to FIG. 1, the large cuff 18 is connected to a pressure
sensor 34, a deflation control valve 36, and an air pump 38 via the
piping 22. The deflation control valve 36 is selectively placed in
a pressure-supply position in which the control valve 36 permits a
pressurized air to be supplied from the air pump 38 to the large
cuff 18, a slow-deflation position in which the control valve 18
permits the pressurized air to be slowly discharged from the large
cuff 18, and a quick-deflation position in which the control valve
36 permits the pressurized air to be quickly discharged from the
large cuff 18.
[0034] The pressure sensor 34 detects an air pressure P.sub.K1 in
the large cuff 18, and supplies a first pressure signal SP.sub.1
representing the detected pressure P.sub.K1, to each of a low-pass
filter 40 and a high-pass filter 42 via an amplifier, not shown.
The low-pass filter 40 extracts, from the pressure signal SP.sub.1,
a static-pressure component contained in the signal SP.sub.1, i.e.,
a cuff-pressure signal SK representing the pressing pressure of the
large cuff 18. The cuff-pressure signal SK is supplied to a control
device 46 via an A/D (analog-to-digital) converter 44. The
high-pass filter 42 extracts, from the pressure signal SP.sub.1, an
alternating component having frequencies not lower than 0.8 Hz, and
supplies the thus extracted alternating-component signal to a
low-pass filter 48 via an amplifier, not shown. The low-pass filter
48 extracts, from the alternating-component signal supplied from
the high-pass filter 42, an alternating component having
frequencies not higher than 10.8 Hz. This alternating-component
signal provides a cuff-pulse-wave signal SW representing the
alternating component of the pressure signal SP.sub.1. The
cuff-pulse-wave signal SW is supplied to the control device 46 via
an A/D converter 50.
[0035] The small cuff 20 is connected to a pressure sensor 52, a
pressure control valve 54, and an air pump 56 via the piping 24.
The pressure sensor 52 detects an air pressure P.sub.K2 in the
small cuff 20, and supplies a second pressure signal SP.sub.2
representing the detected pressure P.sub.K2, to the control device
46 via an A/D converter 50. The pressure control valve 54 changes
the pressure of the pressurized air supplied from the air pump 56,
and supplies the pressurized air having the thus changed pressure
to the small cuff 20.
[0036] A multiplexer 60 sequentially supplies, according to a
switch signal SC supplied from the control device 46, the
respective pressure-pulse-wave signals SM supplied from the sixty
pressure sensing elements 32 of the four pressure-pulse-wave
sensors 28, each signal SM for a prescribed time duration, to an
amplifier 62. An EPROM (erasable programmable ROM) 64 stores, for
the sixty pressure sensing elements 32, respective correction
signals for eliminating respective individual sensitivity
differences among the pressure sensing elements 32, and
sequentially supplies, according to the switch signal SC supplied
from the control device 46, i.e., in synchronism with the
respective switching operations of the multiplexer 60, the
respective correction signals, to a D/A (digital-to-analog)
converter 68, in such a manner that the respective correction
signals sequentially correspond to the respective pressure sensing
elements 32 supplying the respective pressure-pulse-wave signals SM
being currently dealt with by the multiplexer 60.
[0037] Each of the sixty pressure-pulse-wave signals SM that have
been amplified by the amplifier 62, and a corresponding one of the
sixty correction signals that have been converted to respective
analog signals by the D/A converter 68 are supplied to an amplifier
70. Thus, the sixty corrected pressure-pulse-wave signals SM
supplied to the amplifier 70 have a uniform sensitivity. Each of
the sixty corrected pressure-pulse-wave signals SM is supplied to
an I/O (input-and-output) port of the control device 46 via an A/D
converter 72.
[0038] The control device 46 is provided by a so-called
microcomputer including a CPU (central processing unit) 74, a ROM
(read only memory) 76, and a RAM (random access memory) 78. The CPU
29 processes signals according to the control programs pre-stored
in the ROM 76 by utilizing the temporary-storage function of the
RAW 78, and controls the deflation control valve 36 and the air
pump 38 to carry out a blood-measure measurement, controls the
pressure control valve 54 and the air pump 56 to carry out a
heart-sound detection, determines a blood-pressure value BP,
extracts a heart sound, determines a pulse-wave-propagation
velocity PWV, and controls a display device 80 to display the thus
determined blood-pressure value BP and pulse-wave-propagation
velocity PWV.
[0039] FIG. 4 is a block diagram for explaining essential functions
of the control device 46. In the figure, a large-cuff-pressure
control means 90 controls the deflation control valve 36 and the
air pump 38 to quickly increase the pressing pressure of the large
cuff 18 up to a prescribed target pressure PM.sub.1, e.g., 180 mmHg
and then slowly decrease the pressing pressure at a rate of from 2
to 3 mmHg/sec. After a blood-pressure determining means 92
determines a blood pressure BP of the patient, the
large-cuff-pressure control means 90 releases the pressing pressure
into the atmosphere, i.e., decreases the pressing pressure down to
the atmospheric pressure.
[0040] The blood-pressure determining means 92 determines, based on
the change of the cuff-pulse-wave signal SW obtained during the
slow deflation of the pressing pressure of the large cuff 18 by the
large-cuff-pressure control means 90, a systolic blood pressure
BP(SYS), a mean blood pressure BP(MEAN), and a diastolic blood
pressure BP (DIS) of the patient, according to well-known
oscillometric method, and controls the display device 80 to display
the thus determined blood pressure values.
[0041] A small-cuff-pressure control means 94 controls, based on
the second pressure signal SP.sub.2 supplied from the pressure
sensor 52, the pressure control valve 54 and the air pump 56 to
increase the air pressure PK.sub.2 in the small cuff 20 up to a
prescribed target pressure PM.sub.2 and then keep the pressure
PK.sub.2 at the target pressure PM.sub.2. The target pressure
PM.sub.2 is prescribed at such a value which assures that the press
surface 30 which is provided on the inner surface of the cuff 12
and to which the pressure-pulse-wave sensors 28 are fixed, is
pressed against the upper arm 14, but does not occlude the flow of
blood through a brachial artery 98 of the upper arm 14.
[0042] An optimum-element selecting means 96 selects, from the
sixty pressure-sensing semiconductor elements 32 of the four
pressure-pulse-wave sensors 28, an optimum pressure-sensing element
32 that is the most appropriate to detect heart sounds
(hereinafter, referred to as the optimum element A). FIG. 5 is a
cross-section view showing the state in which the cuff 12 is wound
around the upper arm 14. As shown in FIG. 5, the pressure-sensing
elements 32 provided on the press surfaces 30 of the
pressure-pulse-wave sensors 28 have respective different distances
from the brachial artery 98 of the upper arm 14. Therefore, it is
desirable that one of the pressure-sensing elements 32 that is
located right above, or in the vicinity of, the brachial artery 98
be selected as the optimum element A that can detect, with the
highest sensitivity, the pressure pulse wave. FIG. 6 shows a
relationship between the pressure-sensing elements 32 and
respective amplitudes of the pressure-pulse-wave signals SM
detected by the elements 32. In the figure, the sequential numbers
of the pressure-sensing elements 32 start with one of opposite ends
of the array of elements 32 provided on the press surfaces 30.
Respective amplitudes of pressure-pulse-wave signals SM detected by
nearer pressure-sensing elements 32 to the brachial artery 98 are
greater than those detected by remoter elements 32 from the artery
98. Therefore, the optimum-element selecting means 96 selects, as
the optimum element A, one of the pressure-sensing elements 32 that
provides a pressure-pulse-wave signal SM having a greater amplitude
in the relationship shown in FIG. 6, most preferably, the element
32 that provides the signal SM having the greatest amplitude.
[0043] A heart-sound extracting means 100 subjects the
pressure-pulse-wave signal SM supplied from the optimum element A,
to a digital filter, and thereby extracts, from the signal SM, a
heart-sound component having frequencies in a prescribed frequency
band corresponding to a frequency band generally possessed by heart
sounds. The thus extracted heart sounds are displayed on the
display device 80. The prescribed frequency band may range from
above 30 to 600 Hz. A main component of the pressure-pulse-wave
signal SM is the pressure pulse wave BAP produced from the brachial
artery 98. However, heart sounds which are produced when the valves
of the heart are opened and closed, propagate through the blood
vessels. Therefore, the pressure-pulse-wave signal SM contains the
heart-sound component. Thus, the heart sounds can be detected at
the upper arm 14 by extracting, from the pressure-pulse-wave signal
SM, a signal having frequencies in the frequency band generally had
by heart sounds.
[0044] A noise removing means 102 subjects the pressure-pulse-wave
signal SM supplied from the optimum element A, to a digital filter,
and thereby removes noise from the signal SM, so as to extract the
pressure pulse wave BAP produced when the brachial artery 98
pulsates. The signal SM from which noise has been removed is
displayed on the display device 80. Since the pressure pulse wave
BAP is a heartbeat-synchronous wave, the noise removing means 102
removes, from the signal SM, a component having frequencies not
lower than 50 Hz. FIG. 7 shows heart sounds extracted by the
heart-sound extracting means 100, and a pressure pulse wave BAP
freed of noise by the noise removing means 102.
[0045] A pulse-wave-propagation-velocity-relating-information
obtaining means 104 includes a time-difference determining means
106, and a pulse-wave-propagation-velocity determining means 108.
The time-difference determining means 106 determines a timing when
a prescribed periodic point of the heart sounds extracted by the
heart-sound extracting means 100 is detected, and a timing when a
prescribed periodic point of the pressure pulse wave BAP is
detected, and determines a time difference DT (sec) between the two
timings (i.e., a pulse-wave propagation time). The prescribed
periodic point of the heart sounds may be a starting point (i.e., a
rising point) of a first heart sound I, a peak point of a first
heart sound I, a starting point of a second heart sound II, or a
peak point of the second heart sound II. The prescribed periodic
point of the pressure pulse wave BAP may be a rising point or a
peak point of a heartbeat-synchronous pulse of the wave BAP. FIG. 7
shows a time difference DT between a rising point of a first heart
sound I and a rising point of a corresponding heartbeat-synchronous
pulse of a pressure pulse wave BAP.
[0046] The pulse-wave-propagation-velocity determining means 108
determines, based on the pulse-wave propagation time DT determined
by the time-difference determining means 106, a pulse-wave
propagation velocity PWV (m/sec), according to the following
expression (1), pre-stored in the ROM 76:
PWV=L/DT (1)
[0047] The thus determined pulse-wave propagation velocity PWV is
displayed on the display device 80. In the above expression (1), L
is a length of an artery from an initial end of the aorta to a
portion thereof located right below the optimum element A, and is
obtained in advance by experiments.
[0048] FIG. 8 is a flow chart representing a control program
according to which the control device 46 is operated, as shown in
FIG. 4, to determine a pulse-wave propagation velocity PWV. The
determination of pulse-wave propagation velocity PWV is carried out
in a state in which the upper arm 14 is not pressed by the large
cuff 18.
[0049] In FIG. 8, first, at Step S1 (hereinafter, "Step" is
omitted) corresponding to the small-cuff-pressure control means 94,
the control device 46 starts the air pump 56 and operates the
pressure control valve 54, so that the pressing pressure P.sub.K2
of the small cuff 20 is kept at a considerably low pressure of,
e.g., 40 mmHg.
[0050] Next, at S2, a content of a timer t is replaced with "0", so
that the timer t is reset to zero and, at S3, the control device 46
outputs the switch signal SC to switch the multiplexer 60 and the
EPROM 64 at a period sufficiently shorter than an average pulse
period. Then, at S4, the control device 46 reads in the
pressure-pulse-wave signal SM supplied from the multiplexer 60.
[0051] Next, at S5, the control device 46 judges whether a time
indicated by a number counted by the timer t has reached a
prescribed reading-in period T. The reading-in period T may be
equal to an average pulse period, i.e., a length of one average
heartbeat-synchronous pulse. Each time one switch signal SC is
supplied to the multiplexer 60 at S3, one of the respective
pressure-pulse-wave signals SM detected by the sixty
pressure-sensing elements 32 is supplied from the multiplexer 60 to
the control device 46. While S3, S4 and S5 are repeated sixty
times, all the signals SM detected by the sixty elements 32 are
supplied from the multiplexer 60 to the control device 46.
[0052] Next, the control goes to S6 and S7 corresponding to the
optimum-element selecting means 96. First, at S6, the control
device 46 determines respective amplitudes of the respective
pressure-pulse-wave signals SM which have been read in while S3, S4
and S5 are repeated. At S7, the control device 46 determines the
greatest one of the respective amplitudes determined at S6, and
determines, as the optimum element A, one of the pressure sensing
elements 32 that provides the greatest amplitude.
[0053] Next, the control goes to S8 corresponding to the
heart-sound extracting means 100. More specifically described, at
S8, the control device 46 subjects the pressure-pulse-wave signal
SM detected by the optimum element A selected at S7, to a digital
filter, so as to extract a component having frequencies of above 30
to 600 Hz. Thus, the heart-sound component is extracted from the
pressure-pulse-wave signal SM.
[0054] At S9, the control device 46 processes a waveform of the
heart-sound component extracted at S8, so as to determine a
prescribed periodic point on the waveform as one of two reference
points to determine a pulse-wave propagation time DT. More
specifically described, the waveform of the heart-sound component
is subjected to a smoothing or differentiating process which is
known as a useful technique to process a physical signal, and the
thus processed waveform is further subjected to a squaring process.
Thus, the amplitude of the waveform of heart sounds, measured from
a baseline representing a signal level when no heart sounds are
detected, is squared.
[0055] Next, at S10, the control device 46 determines, based on the
waveform whose amplitude has been squared at S9, a starting point
of a first heart sound I as the first reference point to determine
the pulse-wave propagation time DT. Then, at S11 corresponding to
the noise removing means 102, the control device 46 subjects the
pressure-pulse-wave signal SM detected by the optimum element A, to
a digital filter to remove a component having frequencies not lower
than 50 Hz. Thus, a pressure pulse wave BAP free of noise is
extracted from the pressure-pulse-wave sensor SM.
[0056] Subsequently, at S12, the control device 46 determines,
based on the pressure pulse wave BAP extracted at S11, a rising
point of the wave BAP that corresponds to the starting point of the
first heart sound I. The rising point of the wave BAP is the second
reference point to determine the pulse-wave propagation time DT.
Next, at S13 corresponding to the time-difference determining means
104, the control device 46 determines a time difference DT between
the time when the starting point of the first heart sound I
determined at S10 was detected, and the time when the rising point
of the pressure pulse wave BAP determined at S12 was detected.
[0057] Then, at S14 corresponding to the
pulse-wave-propagation-velocity determining means 106, the control
device 46 determines a pulse-wave propagation velocity PWV by
replacing the parameter DT of the expression (1) with the time
difference DT determined at S13. Next, at S15, the thus determined
pulse-wave propagation velocity PWV is displayed on the display
device 80. After S15, the control goes back to S2. Thus, heart
sounds are continuously detected and pulse-wave propagation
velocities PWV are continuously determined.
[0058] In the illustrated embodiment, the heart-sound extracting
means 100 (S8) extracts the heart-sound component representing the
heart sounds, from the pressure-pulse-wave signal SM provided by
the pressure-pulse-wave sensor 28 worn on the upper arm 14. Thus,
the heart sounds can be detected at a position distant from the
chest.
[0059] In the illustrated embodiment, the optimum-element selecting
means 96 (S7) selects, from the plurality of pressure-sensing
semiconductor elements 32, the optimum element A that can detect,
with the highest sensitivity, the pressure pulse wave BAP, and the
heart-sound component is extracted from the pressure-pulse-wave
signal SM provided by the optimum element A. Thus, heart sounds
having a clear waveform can be detected.
[0060] In the illustrated embodiment, the pressure-pulse-wave 28
detects two sorts of heartbeat-synchronous signals, i.e., the heart
sounds and the pressure pulse wave BAP, and the
pulse-wave-propagation-velocity determining means 106 (S14)
determines the pulse-wave propagation velocity PWV based on the
heart sounds and the pressure pulse wave BAP. Thus, the single
pressure-pulse-wave sensor 28 suffices for determining the
pulse-wave propagation velocity PWV, and accordingly it can be
easily worn on the patient.
[0061] In the illustrated embodiment, when the cuff 12 is wound
around the upper arm 14 to measure a blood pressure of a living
subject, simultaneously the pressure-pulse-wave sensor 28 to detect
the heart sounds is worn on the subject. Since the cuff 12 is
adapted to be closely wound around a body portion of a living
subject, that the cuff 12 is wound around the upper arm 14 means
that the pressure-pulse-wave sensor 28 is appropriately worn on the
upper arm 14.
[0062] While the present invention has been described in its
preferred embodiment by reference to the drawings, it is to be
understood that the invention may otherwise be embodied.
[0063] For example, in the illustrated physical-information
obtaining apparatus 10, the pressure-pulse-wave sensor 28 is
adapted to be worn on the upper arm 14. However, the sensor 28 may
be adapted to be worn on a neck or a wrist.
[0064] In the illustrated physical-information obtaining apparatus
10, the heart-sound extracting means 100 comprises the digital
filter, i.e., software. However, the extracting means 100 may
comprise an analog filter which is provided by resistors,
capacitors, etc.
[0065] The illustrated physical-information obtaining apparatus 10
employs the four pressure-pulse-wave sensors 28 each of which
includes the fifteen pressure-sensing semiconductor elements 32,
i.e., the sixty pressure-sensing elements 32, in total, to detect
the respective pressure-pulse-wave signals SM. However, the number
of the pressure-sensing elements 32 is not limited to sixty, but
may be one only.
[0066] Each of the pressure-pulse-wave sensors 28 includes the
pressure-sensing semiconductor elements 32 to detect the respective
pressure pulse waves. However, it is possible to employ a different
type of pressure sensor, e.g., a diaphragm-type pressure sensor
that utilizes the change of resistance of a strain gauge, formed in
a diaphragm, when the gauge is displaced by a pressure exerted
thereto. In addition, the cuff-pulse-wave signal SW extracted by
the high-pass filter 42 and the low-pass filter 48 from the first
pressure signal SP.sub.1 provided by the pressure sensor 34, also
represents a pressure pulse wave BAP produced from the brachial
artery 98. Therefore, the pressure sensor 34, the high-pass filter
42, and the low-pass filter 48 may be used as a pressure-pulse-wave
sensor.
[0067] It is to be understood that the present invention may be
embodied with other changes, improvements and modifications that
may occur to a person skilled in the art without departing from the
spirit and scope of the invention defined in the appended
claims.
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