U.S. patent application number 09/977343 was filed with the patent office on 2002-06-27 for superior-and-inferior-limb blood-pressure index measuring apparatus.
This patent application is currently assigned to COLIN CORPORATION. Invention is credited to Honda, Takashi, Ogura, Toshihiko, Tsuda, Hideichi.
Application Number | 20020082508 09/977343 |
Document ID | / |
Family ID | 18813339 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020082508 |
Kind Code |
A1 |
Ogura, Toshihiko ; et
al. |
June 27, 2002 |
Superior-and-inferior-limb blood-pressure index measuring
apparatus
Abstract
An apparatus for measuring a superior-and-inferior-limb
blood-pressure index of a living subject, including a first
measuring device which measures a first blood pressure of an
inferior limb; a second measuring device which measures a second
blood pressure of a superior limb; an information obtaining device
for iteratively obtaining information changing in relation with
change of blood pressure of the subject; a change-value determining
device for determining a change value of blood pressure of the
subject between a first time when the first blood pressure is
measured and a second time when the second blood pressure is
measured, based on a first piece of information obtained by the
information obtaining device at the first time and a second piece
of information obtained by the information obtaining device at the
second time; a corrected-blood-pressure determining device for
determining, based on the determined change value, one of the first
and second blood pressures to a corrected blood pressure that would
have been measured at one of the first and second times that
corresponds to the other of the first and second blood pressures;
and an index determining device for determining the
superior-and-inferior-limb blood-pressure index, based on the
determined corrected blood pressure and the other of the first and
second blood pressures that has not been corrected by the
corrected-blood-pressure determining device.
Inventors: |
Ogura, Toshihiko;
(Komaki-shi, JP) ; Honda, Takashi; (Komaki-shi,
JP) ; Tsuda, Hideichi; (Komaki-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
COLIN CORPORATION
Komaki-shi
JP
|
Family ID: |
18813339 |
Appl. No.: |
09/977343 |
Filed: |
October 16, 2001 |
Current U.S.
Class: |
600/490 |
Current CPC
Class: |
A61B 7/04 20130101; A61B
5/02125 20130101; A61B 5/02225 20130101; A61B 5/0225 20130101 |
Class at
Publication: |
600/490 |
International
Class: |
A61B 005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 2000 |
JP |
2000-338060 |
Claims
What is claimed is:
1. An apparatus for measuring a superior-and-inferior-limb
blood-pressure index of a living subject, comprising: a first
blood-pressure measuring device which includes at least one first
inflatable cuff adapted to be wound around an inferior limb of the
subject and measures a first blood pressure of the inferior limb; a
second blood-pressure measuring device which includes a second
inflatable cuff adapted to be wound around a superior limb of the
subject and measures a second blood pressure of the superior limb;
a blood-pressure-relating-information obtaining device which
iteratively obtains, from the subject, a piece of
blood-pressure-relating information changing in relation with a
change of a blood pressure of the subject; a
blood-pressure-change-value determining means for determining a
change value of the blood pressure of the subject between a first
time when the first blood pressure is measured by the first
blood-pressure measuring device and a second time when the second
blood pressure is measured by the second blood-pressure measuring
device, based on a first piece of blood-pressure-relating
information obtained by the blood-pressure-relating-information
obtaining device at the first time and a second piece of
blood-pressure-relating information obtained by the
blood-pressure-relating-information obtaining device at the second
time; a corrected-blood-pressure determining means for determining,
based on the change value determined by the
blood-pressure-change-value determining means, one of the first and
second blood pressures to a corrected blood pressure that would
have been measured at one of the first and second times that
corresponds to the other of the first and second blood pressures;
and a blood-pressure-index determining means for determining the
superior-and-inferior-limb blood-pressure index, based on the
corrected blood pressure determined by the corrected-blood-pressure
determining means and said other of the first and second blood
pressures that has not been corrected by the
corrected-blood-pressure determining means.
2. An apparatus according to claim 1, wherein the
blood-pressure-relating-- information obtaining device comprises a
pulse-wave-propagation-velocity-r- elating-information obtaining
device which iteratively obtains, as the piece of
blood-pressure-relating information, a piece of
pulse-wave-propagation-velocity-relating information relating to a
velocity at which a pulse wave propagates through an artery of the
subject.
3. An apparatus according to claim 1, wherein the first
blood-pressure measuring device includes a right-ankle first
inflatable cuff adapted to be wound around a right ankle of the
subject, and a left-ankle first inflatable cuff adapted to be wound
around a left ankle of the subject, and measures a right-ankle
first blood pressure of the right ankle and a left-ankle first
blood pressure of the left ankle, wherein the
blood-pressure-change-value determining means determines a
right-ankle first change value of the blood pressure of the subject
between a right-ankle first time when the right-ankle first blood
pressure is measured by the first blood-pressure measuring device
and the second time when the second blood pressure is measured by
the second blood-pressure measuring device, based on a right-ankle
first piece of blood-pressure-relating information obtained by the
blood-pressure-relating-information obtaining device at the
right-ankle first time and the second piece of
blood-pressure-relating information obtained by the
blood-pressure-relating-information obtaining device at the second
time, and additionally determines a left-ankle first change value
of the blood pressure of the subject between a left-ankle first
time when the left-ankle first blood pressure is measured by the
first blood-pressure measuring device and the second time, based on
a left-ankle first piece of blood-pressure-relating information
obtained by the blood-pressure-relating-information obtaining
device at the left-ankle first time and the second piece of
blood-pressure-relating information obtained by the
blood-pressure-relating-information obtaining device at the second
time, wherein the corrected-blood-pressure determining means
corrects, based on the right-ankle change value determined by the
blood-pressure-change-value determining means, one of the
right-ankle first blood pressure and the second blood pressure to a
corrected blood pressure that would have been measured at one of
the right-ankle first time and the second time that corresponds to
the other of the right-ankle first blood pressure and the second
blood pressure, and additionally corrects, based on the left-ankle
change value determined by the blood-pressure-change-value
determining means, one of the left-ankle first blood pressure and
the second blood pressure to a corrected blood pressure that would
have been measured at one of the left-ankle first time and the
second time that corresponds to the other of the left-ankle first
blood pressure and the second blood pressure, and wherein the
blood-pressure-index determining means determines a right-side
blood-pressure index, based on the corrected blood pressure
determined by the corrected-blood-pressure determining means and
said other of the right-ankle first blood pressure and the second
blood pressure that has not been corrected by the
corrected-blood-pressure determining means, and additionally
determines a left-side blood-pressure index, based on the corrected
blood pressure determined by the corrected-blood-pressure
determining means and said other of the left-ankle first blood
pressure and the second blood pressure that has not been corrected
by the corrected-blood-pressure determining means.
4. An apparatus according to claim 1, further comprising a display
device which displays at least one of the
superior-and-inferior-limb blood-pressure index determined by the
blood-pressure-index determining means and the piece of
blood-pressure-relating information obtained by the
blood-pressure-relating-information obtaining device.
5. An apparatus according to claim 1, wherein the
blood-pressure-index determining means comprises means for
determining, as the superior-and-inferior-limb blood-pressure
index, at least one of a ratio of the first blood pressure to the
second blood pressure, and a ratio of the second blood pressure to
the first blood pressure.
6. An apparatus according to claim 1, wherein the
blood-pressure-relating-- information obtaining device comprises
two pulse-wave sensors which are worn on two different portions of
the subject, respectively, and each of which detects a pulse wave
at a corresponding one of the two portions.
7. An apparatus according to claim 1, wherein the
blood-pressure-change-va- lue determining means comprises: a
relationship determining means for determining a relationship
between estimated blood pressure and blood-pressure-relating
information, based on at least one of the first and second blood
pressures measured by the first and second blood-pressure measuring
devices and at least one piece of blood-pressure-relating
information obtained by the blood-pressure-relating-information
obtaining device; an estimated-blood-pressure determining means for
determining, according to the determined relationship between
estimated blood pressure and blood-pressure-relating information, a
first estimated blood pressure of the subject based on the first
piece of blood-pressure-relating information obtained by the
blood-pressure-relating-information obtaining device at the first
time, and a second estimated blood pressure of the subject based on
the second piece of blood-pressure-relating information obtained by
the blood-pressure-relating-information obtaining device at the
second time, and determining the change value between the first and
second estimated blood pressures of the subject.
8. An apparatus according to claim 1, further comprising: a
heart-contraction-relating-information obtaining device which
iteratively obtains a piece of heart-contraction-relating
information changing in relation with a change of a contraction
period of a heart of the subject; an abnormality judging means for
judging, based on the pieces of heart-contraction-relating
information iteratively obtained by the
heart-contraction-relating-information obtaining device, whether
each of the first and second pieces of blood-pressure-relating
information obtained by the blood-pressure-relating-information
obtaining device at the first and second times is abnormal; and a
correct-blood-pressure-rela- ting-information producing means for
producing, when the abnormality judging means judges that said each
of the first and second pieces of blood-pressure-relating
information is abnormal, a correct piece of blood-pressure-relating
information based on the iteratively obtained pieces of
blood-pressure-relating information other than said each of the
first and second pieces of blood-pressure-relating information
judged as being abnormal, wherein the blood-pressure-change-value
determining means determines, when the abnormality judging means
judges that said each of the first and second pieces of
blood-pressure-relating information is abnormal, the change value
based on the correct piece of blood-pressure-relating information
produced by the correct-blood-pressure-relating-information
producing means.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an apparatus for measuring
a superior-and-inferior-limb blood-pressure index of a living
subject (e.g., a ratio of an inferior-limb blood pressure to a
superior-limb blood pressure, or a ratio of a superior-limb blood
pressure to an inferior-limb blood pressure).
[0003] 2. Related Art Statement
[0004] Arteriosclerotic cardiovascular disease is one of major
death causes of aged women, e.g., not younger than sixty-five-year
old, but there is no easy method of finding latent
arteriosclerosis. However, it is known that since measurement of
superior-and-inferior-limb blood-pressure index can be used as a
simple and repeatable method to find inferior-limb arterial disease
and can be used to check quickly and easily the condition of whole
cardiovascular system, the index is useful to identify individuals
who need special treatments to reduce their death rate or incidence
rate.
[0005] Generally, the above-mentioned superior-and-inferior-limb
blood-pressure ("BP") index is obtained as the ratio of a systolic
blood pressure of an ankle as the inferior-limb to a systolic blood
pressure of an upper arm as the superior-limb, that is,
ankle/upper-arm BP index (abbreviated to "ABI"). If the measured
ankle/upper-arm BP index of a living subject is smaller than a
prescribed value, e.g., about 0.9, abnormality may be diagnosed on
the subject. Thus, a small change of the systolic blood pressure of
the inferior limb such as ankle or a small change of the systolic
blood pressure of the superior limb such as upper arm largely
influences the diagnosis made on the subject. On the other hand,
since blood pressure of each living subject may change in a short
time, a conventional super-and-inferior-limb BP index measuring
apparatus simultaneously starts increasing respective pressures of
two cuffs respectively wound around the superior and inferior limbs
to measure respective systolic BP values of the superior and
inferior limbs.
[0006] However, even if the respective increasing of respective
pressures of the two cuffs may be simultaneously started, there
exist a certain amount of difference between the respective
systolic BP values of the superior and inferior limbs. Therefore,
there exists a certain time difference between respective times
when the respective systolic BP values of the superior and inferior
limbs are determined. The time difference corresponds to a few
heartbeats of the subject. Meanwhile, the blood pressure of the
subject contains a respiratory change corresponding to his or her
respiration period. Thus, the blood pressure of the subject may
change between the respective times of determination of the
respective systolic BP values of the superior and inferior limbs.
Thus, the superior-and-inferior-limb BP index determined by the
conventional apparatus cannot enjoy a sufficiently high
accuracy.
SUMMARY OF THE INVENTION
[0007] It is therefore an object of the present invention to
provide a superior-and-inferior-limb blood-pressure index measuring
apparatus which can measure a highly accurate superior-and-inferior
blood-pressure index.
[0008] The Inventors have carried out extensive studies and found
that if blood-pressure-relating information changing with blood
pressure is iteratively obtained when inferior-limb and
superior-limb blood pressures (systolic, mean, or diastolic blood
pressures) are measured, a change of the blood pressure between
respective times of measurement of the inferior-limb and
superior-limb blood pressures is determined based on the
iteratively obtained pieces of blood-pressure-relating information,
and one of the inferior-limb and superior-limb blood pressures is
corrected based on the thus determined blood-pressure change, then
a highly accurate superior-and-inferior-limb blood-pressure index
is obtained. The present invention has been developed based on this
finding.
[0009] The above object has been achieved by the present invention.
According to the present invention, there is provided an apparatus
for measuring a superior-and-inferior-limb blood-pressure index of
a living subject, comprising a first blood-pressure measuring
device which includes at least one first inflatable cuff adapted to
be wound around an inferior limb of the subject and measures a
first blood pressure of the inferior limb; a second blood-pressure
measuring device which includes a second inflatable cuff adapted to
be wound around a superior limb of the subject and measures a
second blood pressure of the superior limb; a
blood-pressure-relating-information obtaining device for
iteratively obtaining, from the subject, a piece of
blood-pressure-relating information changing in relation with a
change of a blood pressure of the subject; a
blood-pressure-change-value determining means for determining a
change value of the blood pressure of the subject between a first
time when the first blood pressure is measured by the first
blood-pressure measuring device and a second time when the second
blood pressure is measured by the second blood-pressure measuring
device, based on a first piece of blood-pressure-relating
information obtained by the blood-pressure-relating-information
obtaining device at the first time and a second piece of
blood-pressure-relating information obtained by the
blood-pressure-relating-information obtaining device at the second
time; a corrected-blood-pressure determining means for determining,
based on the change value determined by the
blood-pressure-change-value determining means, one of the first and
second blood pressures to a corrected blood pressure that would
have been measured at one of the first and second times that
corresponds to the other of the first and second blood pressures;
and a blood-pressure-index determining means for determining the
superior-and-inferior-limb blood-pressure index, based on the
corrected blood pressure determined by the corrected-blood-pressure
determining means and said other of the first and second blood
pressures that has not been corrected by the
corrected-blood-pressure determining means.
[0010] According to this invention, the blood-pressure-change-value
determining means determines the change value of the blood pressure
of the subject between the first time when the first blood pressure
is measured by the first blood-pressure measuring device and the
second time when the second blood pressure is measured by the
second blood-pressure measuring device, based on the first piece of
blood-pressure-relating information obtained by the
blood-pressure-relating-information obtaining device at the first
time and the second piece of blood-pressure-relating information
obtained by the blood-pressure-relating-information obtaining
device at the second time, and the corrected-blood-pressure
determining means determines, based on the change value determined
by the blood-pressure-change-value determining means, one of the
first and second blood pressures to a corrected blood pressure that
would have been measured at one of the first and second times that
corresponds to the other of the first and second blood pressures.
And, the blood-pressure-index determining means determines the
superior-and-inferior-limb blood-pressure index, based on the
corrected blood pressure determined by the corrected-blood-pressure
determining means and the other of the first and second blood
pressures that has not been corrected by the
corrected-blood-pressure determining means. Since the
superior-and-inferior-limb blood-pressure index is determined based
on the two blood-pressure values measured at the same time, it
enjoys a high accuracy.
[0011] Preferably, the blood-pressure-relating-information
obtaining device comprises a
pulse-wave-propagation-velocity-relating-information obtaining
device which iteratively obtains, as the piece of
blood-pressure-relating information, a piece of
pulse-wave-propagation-ve- locity-relating information relating to
a velocity at which a pulse wave propagates through an artery of
the subject.
[0012] Since the pulse-wave-propagation-velocity-relating
information is one of those sorts of blood-pressure-relating
information that change most faithfully corresponding to the change
of blood pressure, each of the change value determined by the
blood-pressure-change-value determining means, the corrected blood
pressure obtained based on the change value, and the
superior-and-inferior-limb blood-pressure index determined based on
the corrected blood pressure enjoys a high accuracy.
[0013] Preferably, the first blood-pressure measuring device
includes a right-ankle first inflatable cuff adapted to be wound
around a right ankle of the subject, and a left-ankle first
inflatable cuff adapted to be wound around a left ankle of the
subject, and measures a right-ankle first blood pressure of the
right ankle and a left-ankle first blood pressure of the left
ankle, the blood-pressure-change-value determining means determines
a right-ankle first change value of the blood pressure of the
subject between a right-ankle first time when the right-ankle first
blood pressure is measured by the first blood-pressure measuring
device and the second time when the second blood pressure is
measured by the second blood-pressure measuring device, based on a
right-ankle first piece of blood-pressure-relating information
obtained by the blood-pressure-relating-information obtaining
device at the right-ankle first time and the second piece of
blood-pressure-relating information obtained by the
blood-pressure-relating-information obtaining device at the second
time, and additionally determines a left-ankle first change value
of the blood pressure of the subject between a left-ankle first
time when the left-ankle first blood pressure is measured by the
first blood-pressure measuring device and the second time, based on
a left-ankle first piece of blood-pressure-relating information
obtained by the blood-pressure-relating-information obtaining
device at the left-ankle first time and the second piece of
blood-pressure-relating information obtained by the
blood-pressure-relating-information obtaining device at the second
time, the corrected-blood-pressure determining means corrects,
based on the right-ankle change value determined by the
blood-pressure-change-value determining means, one of the
right-ankle first blood pressure and the second blood pressure to a
corrected blood pressure that would have been measured at one of
the right-ankle first time and the second time that corresponds to
the other of the right-ankle first blood pressure and the second
blood pressure, and additionally corrects, based on the left-ankle
change value determined by the blood-pressure- change-value
determining means, one of the left-ankle first blood pressure and
the second blood pressure to a corrected blood pressure that would
have been measured at one of the left-ankle first time and the
second time that corresponds to the other of the left-ankle first
blood pressure and the second blood pressure, and the
blood-pressure-index determining means determines a right-side
blood-pressure index, based on the corrected blood pressure
determined by the corrected-blood-pressure determining means and
the other of the right-ankle first blood pressure and the second
blood pressure that has not been corrected by the
corrected-blood-pressure determining means, and additionally
determines a left-side blood-pressure index, based on the corrected
blood pressure determined by the corrected-blood-pressure
determining means and said other of the left-ankle first blood
pressure and the second blood pressure that has not been corrected
by the corrected-blood-pressure determining means.
[0014] According to this feature, the blood-pressure-index
determining means determines both the right-side blood-pressure
index and the left-side blood-pressure index. Since the lower one
of the two blood-pressure index values can be used to make a
diagnosis on the subject, the diagnosis enjoys a higher accuracy.
In some cases, a blood pressure of an ankle may not be accurately
measured because a tibia or a fibula prevents a posterior tibial
artery from being sufficiently pressed, that is, a higher blood
pressure than an accurate blood pressure may be measured. In those
cases, an accurate diagnosis may not be expected. However,
according to this feature, at least one of the right-side
blood-pressure index and the left-side blood-pressure index is
expected to be accurate. Thus, a more accurate diagnosis may be
made based on the lower one of the two blood-pressure index
values.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] 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:
[0016] FIG. 1 is a diagrammatic view of a construction of an
ankle/upper-arm blood-pressure index measuring apparatus to which
the present invention is applied;
[0017] FIG. 2 is a graph showing respective examples of a
phonocardiogram detected by a microphone of the apparatus of FIG.
1, and a carotid-artery pulse wave detected by a carotid-artery
pulse-wave sensor of the same apparatus;
[0018] FIG. 3 is a diagrammatic view for explaining essential
functions of a control device of the apparatus of FIG. 1;
[0019] FIG. 4 is a flow chart representing a control program
according to which the control device of the apparatus of FIG. 1 is
operated;
[0020] FIG. 5 is a diagrammatic view for explaining additional
functions that are employed by the control device of the apparatus
of FIG. 1 in another embodiment of the present invention; and
[0021] FIG. 6 is a graph showing respective examples of
pulse-wave-propagation velocities, and ejection times, that are
iteratively determined in the embodiment shown in FIG. 5.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0022] Hereinafter, there will be described an embodiment of the
present invention in detail by reference to the drawings. FIG. 1
shows a diagrammatic view for explaining a construction of an
ankle/upper-arm blood-pressure ("BP") index measuring apparatus 10
to which the present invention is applied. The ankle/upper-arm BP
index measuring apparatus 10 is a sort of
superior-and-inferior-limb BP index measuring apparatus, since the
apparatus 10 measures, as an inferior-limb BP value, a BP value
from an ankle of a patient as a living person and measures, as a
superior-limb BP value, a BP value from an upper arm of the
patient. The present apparatus 10 carries out measurements on the
patient who takes a face-down, lateral, or face-up position so that
the upper arm and the ankle are substantially level with each
other.
[0023] In FIG. 1, the ankle/upper-arm BP index measuring apparatus
10 includes a right-leg first BP measuring device 14 which measures
a BP value from a right ankle 12 of the patient, a left-leg first
BP measuring device 18 which measures a BP value from a left ankle
16 of the patient, and a second BP measuring device 22 which
measures a BP value from an upper arm 20 of the patient.
[0024] The right-leg first BP measuring device 14 includes an
inflatable cuff 24 which includes a belt-like cloth bag and a
rubber bag accommodated in the cloth bag and which is wound around
the right ankle 12 of the patient; a piping 26; and a pressure
sensor 28, a switch valve 30, and an air pump 32 which are
connected to the cuff 24 via the piping 26. The switch valve 30 is
selectively placed in one of three positions, that is, (a) a
pressure-supply position in which the switch valve 30 allows
pressurized air to be supplied from the air pump 32 to the cuff 24,
(b) a slow-deflation position in which the valve 30 allows the
pressurized air to be slowly discharged from the cuff 24, and (c) a
quick-deflation position in which the valve 30 allows the
pressurized air to be quickly discharged from the cuff 24.
[0025] The pressure sensor 28 detects an air pressure in the cuff
24, and supplies a pressure signal, SP.sub.1, representing the
detected air pressure, to a static-pressure filter circuit 34 and a
pulse-wave filter circuit 36. The static-pressure filter circuit 34
includes a low-pass filter which extracts, from the pressure signal
SP.sub.1, a cuff-pressure signal, SK.sub.1, representing a cuff
pressure, P.sub.C1, as a static component of the detected air
pressure. The filter circuit 34 supplies the cuff-pressure signal
SK.sub.1 to a control device 38 via an analog-to-digital ("A/D")
converter, not shown.
[0026] The pulse-wave filter circuit 36 includes a band-pass filter
which extracts, from the pressure signal SP.sub.1, a pulse-wave
signal, SM.sub.1, representing a pulse wave as an oscillatory
component of the detected air pressure that has prescribed
frequencies. The filter circuit 36 supplies the pulse-wave signal
SM.sub.1 to the control device 38 via an A/D converter, not
shown.
[0027] The left-leg first BP measuring device 18 includes an
inflatable cuff 40, a piping 42, a pressure sensor 44, and a switch
valve 46 which have respective constructions identical with those
of the counterparts 24, 26, 28, 30 of the right-leg first BP
measuring device 14. The switch valve 46 is connected to the air
pump 32. The pressure sensor 44 detects an air pressure in the cuff
40, and supplies a pressure signal, SP.sub.2, representing the
detected air pressure, to a static-pressure filter circuit 48 and a
pulse-wave filter circuit 50 which have respective constructions
identical with those of the counterparts 34, 36 of the right-leg
first BP measuring device 14. The static-pressure filter circuit 48
extracts, from the pressure signal SP.sub.2, a cuff-pressure
signal, SK.sub.2, representing a cuff pressure, P.sub.C2, as a
static component of the detected air pressure, and supplies the
cuff-pressure signal SK.sub.2 to the control device 38 via an A/D
converter, not shown. The pulse-wave filter circuit 50 extracts,
from the pressure signal SP.sub.2, a pulse-wave signal, SM.sub.2,
representing a pulse wave as an oscillatory component of the
detected air pressure that has prescribed frequencies, and supplies
the pulse-wave signal SM.sub.2 to the control device 38 via an AID
converter, not shown.
[0028] The second BP measuring device 22 includes an inflatable
cuff 52 which has a construction identical with the cuff 24 or 40
and which is wound around an upper arm 20 (e.g., a right upper arm)
of the patient; and a piping 54, a pressure sensor 56, and a switch
valve 58 which have respective constructions identical with those
of the counterparts 26, 28, 30 of the right-leg first BP measuring
device 14. The switch valve 58 is connected to the air pump 32. The
pressure sensor 56 detects an air pressure in the cuff 52, and
supplies a pressure signal, SP.sub.3, representing the detected air
pressure, to a static-pressure filter circuit 60 and a pulse-wave
filter circuit 62 which have respective constructions identical
with those of the counterparts 34, 36 of the right-leg first BP
measuring device 14. The static-pressure filter circuit 60
extracts, from the pressure signal SP.sub.3, a cuff-pressure
signal, SK.sub.3, representing a cuff pressure, P.sub.C3, as a
static component of the detected air pressure, and supplies the
cuff-pressure signal SK.sub.3 to the control device 38 via an A/D
converter, not shown. The pulse-wave filter circuit 62 extracts,
from the pressure signal SP.sub.3, a pulse-wave signal, SM.sub.3,
representing a pulse wave as an oscillatory component of the
detected air pressure that has prescribed frequencies, and supplies
the pulse-wave signal SM.sub.3 to the control device 38 via an A/D
converter, not shown.
[0029] The control device 38 is essentially provided by a
microcomputer including a central processing unit ("CPU") 64, a
read only memory ("ROM") 66, a random access memory ("RAM") 68, and
an input-and-output ("I/O") port, not shown, and processes input
signals according to the control programs pre-stored in the ROM 66,
while utilizing the temporary-storage function of the RAM 68. The
control device 38 outputs, from the I/O port, drive signals to the
air pump 32 and the three switch valves 30, 46, 58 to control the
respective operations thereof, and additionally outputs display
signals to a display device 70 to control the contents displayed
thereby.
[0030] A microphone 72 is attached, with an adhesive tape, not
shown, to the skin of central portion of the chest of the patient,
more specifically described, a prescribed heart-sound-detect
position right above the apex cordis, the left end of the fourth
intercostal sternum, the left end of the second intercostal
sternum, the right end of the second intercostal sternum, or the
right end of the fourth intercostal sternum. The microphone 72
detects heart sounds which are transmitted from the heart to the
skin of the prescribed heart-sound-detect position. The heart
sounds are produced when the heart starts outputting blood to the
aorta, and when the heart ends outputting blood to the aorta. Thus,
the heart sounds provide a pulse wave which is produced from the
most upstream portion of the aorta. The microphone 72 functions as
a first pulse-wave detecting device.
[0031] The microphone 72 includes a piezoelectric element, not
shown, which converts the sounds detected thereby into an electric
signal, i.e., a heart-sound signal, SH, and outputs the heart-sound
signal SH, which subsequently is amplified by a preamplifier, not
shown, and is supplied to a filter device 74. Then, the signal SH
is supplied to the control device 38 via a main amplifier and an
A/D converter, both not shown. The filter device 74 includes four
sorts of filters, not shown, which can be so selected and used that
the low-pitched-sound components of the heart-sound signal SH are
attenuated and the high-pitched-sound components thereof are
exaggerated and accordingly the heart sounds can be heard by the
auditory sense of a human being. An upper half portion of FIG. 2
shows an example of phonocardiogram detected by the microphone 72.
The phonocardiogram includes a first sound I corresponding to the
closing of the mitral valve and the opening of the aortic valve,
and a second sound II corresponding to the closing of the aortic
valve.
[0032] A carotid-artery pulse-wave sensor 76 functions as a second
pulse-wave detecting device which is worn on a portion of the
patient that is located on a downstream side of the microphone 72
as the first pulse-wave detecting device, as seen in the direction
of flowing of blood in the body of the patient, and which detects a
pulse wave propagating through an artery running in that portion of
the patient. The pulse-wave sensor 76 includes a contact member,
and a vibration sensor, not shown, which detects vibration of the
contact member. The pulse-wave sensor 76 is attached to the neck of
the patient such that the contact member is held in pressed contact
with the skin right above a carotid artery 78 and detects a
carotid-artery pulse wave produced from the carotid artery 78. The
pulse-wave sensor 76 supplies a signal, SM.sub.4, representing the
detected carotid-artery pulse wave, to the control device 38 via an
A/D converter, not shown. A lower half portion of FIG. 2 shows an
example of the carotid-artery pulse wave detected by the pulse-wave
sensor 76. Since the carotid artery 78 has a considerably great
diameter and is directly connected to the aorta, the waveform of
the carotid-artery pulse wave is substantially identical with that
of aortic pulse wave.
[0033] FIG. 3 is a diagrammatic view for explaining essential
control functions of the control device 38. A cuff-pressure
regulating means 80 controls the air pump 32 and the three switch
valves 30, 46, 58, such that the respective pressing pressures of
the three cuffs 24, 40, 52 are quickly increased up to a
predetermined target pressure value, P.sub.CM, (e.g., about 180
mmHg) and then are slowly decreased at a rate of about 3
mmHg/sec.
[0034] A first BP determining means 82 determines right-leg first
BP values, BP1.sub.R, that is, BP values of the right ankle 12,
according to well-known oscillometric method, based on the change
of respective amplitudes of the heartbeat-synchronous pulses of the
pulse-wave signal SM.sub.1 detected one by one during the slow
deflation of the cuff 24 wound around the right ankle 12 under the
control of the cuff-pressure regulating means 80. In addition, the
first BP determining means 82 determines left-leg first BP values,
BP1.sub.L, that is, BP values of the left ankle 16, according to
the oscillometric method, based on the change of respective
amplitudes of the heartbeat-synchronous pulses of the pulse-wave
signal SM.sub.2 detected one by one during the slow deflation of
the cuff 40 wound around the left ankle 16 under the control of the
cuff-pressure regulating means 80. The right-leg first BP values
BP1.sub.R include a systolic BP value BP1.sub.RSYS and a diastolic
BP value BP1.sub.RDIA, and the left-leg first BP values BP1.sub.L
include a systolic BP value BP1.sub.LSYS and a diastolic BP value
BP1.sub.LDIA. Hereinafter, when it is not needed to distinguish the
right-leg first BP values BR1.sub.R and the left-leg first BP
values BP1.sub.L from each other, those BP values will be wholly
referred to as the first BP values BP1.
[0035] A second BP determining means 88 determines second BP
values, BP2, (systolic BP value BP2.sub.SYS and diastolic BP value
BP2.sub.DIA), that is, BP values of the upper arm 20, according to
the well-known oscillometric method, based on the change of
respective amplitudes of the heartbeat-synchronous pulses of the
pulse-wave signal SM.sub.3 detected one by one during the slow
deflation of the cuff 52 wound around the upper arm 20 under the
control of the cuff-pressure regulating means 80.
[0036] A pulse-wave-propagation-velocity-relating-information
obtaining means 86 iteratively obtains a piece of
pulse-wave-propagation-velocity-r- elating-information, such as a
time difference between a periodic point on each of the
heartbeat-synchronous pulses of the first pulse wave detected by
the microphone 72 as the first pulse-wave detecting device, and a
periodic point on a corresponding one of the heartbeat-synchronous
pulses of the second pulse wave detected by the sensor 76 as the
second pulse-wave detecting device. For example, the information
obtaining means 86 includes a time-difference determining means
which iteratively determines a time difference (i.e., a pulse-wave
propagation time), DT, shown in FIG. 2, that is, a time difference
between a time point at which the microphone 72 detects the
commencement of second heart sound II (this point corresponds to a
notch of the aortic pulse wave where the amplitude ends quick
decreasing and then starts increasing), and a time point at which
the sensor 76 detects the notch of the carotid-artery pulse wave.
The information obtaining means 86 iteratively determines, based on
the time difference DT iteratively determined by the
time-difference determining means for each of the
heartbeat-synchronous pulses, a velocity PWV (m/sec) at which the
pulse wave propagates through the artery of the patient, according
to the following expression (1) pre-stored in the ROM 66:
PWV=L/DT (1)
[0037] where L (m) is the distance from the left ventricle of the
heart, via the aorta, to the position where the sensor 76 is worn,
and is replaced with a constant value which is experimentally
obtained in advance.
[0038] Each of the pulse-wave propagation time DT and the
pulse-wave propagation velocity PWV changes in relation with the
blood pressure of the living subject, and accordingly is a sort of
blood-pressure-relating information. Thus, the
pulse-wave-propagation-velocity-relating-informati- on obtaining
means 86 is a sort of blood-pressure-relating-information obtaining
means.
[0039] A relationship determining means 88 determines a
relationship between blood pressure and blood-pressure-relating
information, based on the systolic blood pressure values BP.sub.SYS
determined by one of the first and second BP determining means 82,
84 and the pieces of blood-pressure-relating information obtained
by the blood-pressure-relating-information obtaining means. For
example, either the pulse-wave propagation time values DT or the
pulse-wave propagation velocity values PWV that are obtained
during, or immediately before or after, the BP measuring operation
in which the systolic blood pressure values BP.sub.SYS are
determined by one of the first and second BP determining means 82,
84, are employed as the pieces of blood-pressure-relating
information, and respective coefficients .alpha. and .beta. of
either one of two relationships each between estimated blood
pressure EBP and time DT or velocity PWV that are represented by
the following two expressions (2) and (3), respectively, are
determined, in advance, based on the employed time values DT or
velocity values PWV:
EBP=.alpha.(DT)+.beta. (2)
[0040] where .alpha. is a negative constant and .beta. is a
positive constant.
EBP=.alpha.(PWV)+.beta. (3)
[0041] where .alpha. is a positive constant and .beta. is a
positive constant.
[0042] For example, the coefficients .alpha. and .beta. of the
above expression (2) are determined based on a pair of a second
systolic blood pressure BP.sub.SYS determined by the second BP
determining means 84 and a pulse-wave propagation time DT
determined based on a pulse of the pulse wave detected at the time
of determination of the pressure BP.sub.SYS, and another pair of
another second systolic blood pressure BP.sub.SYS determined by the
means 84 and another pulse-wave propagation time DT determined
based on another pulse of the pulse wave detected at the time of
determination of the latter pressure BP.sub.SYS.
[0043] A blood-pressure-change-value determining means 90
determines a change value .DELTA.BP of blood pressure of the
patient between respective times of determination of the first and
second BP values BP1, BP2, from an estimated BP value EBP
determined according to the relationship determined by the
relationship determining means 88 based on a piece of
pulse-wave-propagation-velocity-relating information obtained by
the information obtaining means 86 at the time of determination of
the first BP value BP1 (i.e., one of the first systolic BP value
BP1.sub.SYS, the first mean BP value BP1.sub.MEAN, and the first
diastolic BP value BP1.sub.DIA) by the first BP determining means
82, and another estimated BP value EBP determined according to the
relationship based on another piece of
pulse-wave-propagation-velocity-relating information obtained by
the information obtaining means 86 at the time of determination of
the second BP value BP2 (i.e., a corresponding one of the second
systolic BP value BP2.sub.SYS, the second mean BP value
BP2.sub.MEAN, and the second diastolic BP value BP2.sub.DIA) by the
second BP determining means 84. For example, supposing that EBP(1)
is an estimated BP value EBP determined according to the
above-indicated expression (2) or (3) based on a pulse-wave
propagation time DT or a pulse-wave propagation velocity PWV
obtained at the time of determination of the first systolic BP
value BP1.sub.SYS, and EBP(2) is another estimated BP value EBP
determined according to the expression (2) or (3) based on another
pulse-wave propagation time DT or another pulse-wave propagation
velocity PWV obtained at the time of determination of the second
systolic BP value BP2.sub.SYS, the blood-pressure change value
.DELTA.BP can be defined by the following expression (4) or
(5):
1 .DELTA.BP.sub.1-2 = EBP(1) - EBP(2) (4) .DELTA.BP.sub.2-1 =
EBP(2) - EBP(1) (5)
[0044] The blood-pressure change value .alpha.BP means an amount of
change of blood pressure of the patient after one of the first and
second BP values BP1, BP2 is measured and before the other of the
first and second BP values BP1, BP2 is measured.
[0045] A corrected-blood-pressure determining means 92 corrects,
based on the blood-pressure change value .DELTA.BP determined by
the blood-pressure-change-value determining means 90, one of the
first and second BP values BP1, BP2 to a corrected BP value CBP
that would have been determined at the time of determination of the
other of the first and second BP values BP1, BP2. For example, the
change value .DELTA.BP determined according to the expression (5)
is added to the first systolic BP value BP.sub.SYS, to determine a
corrected systolic BP value CBP.sub.SYS. The corrected systolic BP
value CBP.sub.SYS means a systolic BP value of the ankle at the
time of determination of the second systolic BP value
BP2.sub.SYS.
[0046] An ankle/upper-arm BP index determining means 96,
functioning as the superior-and-inferior-limb BP index determining
means, determines an ankle/upper-arm BP index value (hereinafter,
referred as the "ABI value") based on the corrected blood pressure
CBP determined by the corrected-blood-pressure determining means 92
and the non-corrected, other of the first and second BP values BP1,
BP2. An index ABI is obtained by dividing an ankle blood pressure
by an upper-arm blood pressure, or dividing an upper-arm blood
pressure by an ankle blood pressure. Therefore, in the case where
the corrected-blood-pressure determining means 92 corrects the
first BP value BP1 to a corrected BP value CBP, the index ABI is
obtained by dividing the corrected BP value CBP by the second BP
value BP2, or dividing the second BP value BP2 by the corrected BP
value CBP; and in the case where the corrected-blood-pressure
determining means 92 corrects the second BP value BP2 to a
corrected BP value CBP, the index ABI is obtained by dividing the
first BP value BP1 by the corrected BP value CBP, or dividing the
corrected BP value CBP by the first BP value BP1.
[0047] FIG. 4 is a flow chart representing a control program
according to which the control device 38 is operated. In the flow
chart of FIG. 4, first, the control device 38 carries out Steps S1,
S2, and S3 (hereinafter, "Step(s)" is omitted, if appropriate)
corresponding to the cuff-pressure regulating means 80. At S1, the
three switch valves 30, 46, 58 are switched to their
pressure-supply positions and the air pump 32 is operated, so that
the respective air pressures of the three cuffs 24, 40, 52 are
quickly increased. At S2, it is judged whether all the air
pressures P.sub.C of the three cuffs 24, 40, 52 have reached the
predetermined target pressure value P.sub.CM (about 180 mmHg). If a
negative judgment is made at S2, Steps S1 and S2 are repeated to
continue increasing the air pressures P.sub.C of the cuffs 24, 40,
52.
[0048] If a positive judgment is made at S2, the control goes to S3
to stop the operation of the air pump 32 and switch the three
switch valves 30, 46, 58 to their slow-deflation positions, so that
the respective air pressures P.sub.C of the three cuffs 24, 40, 52
are decreased slowly at a predetermined low rate of about 3
mmHg/sec.
[0049] Then, at S4 corresponding to the
pulse-wave-propagation-velocity-re- lating-information obtaining
means 86, the control device 38 determines, as illustrated in FIG.
2, a time difference between a time when the microphone 72 detects
the commencement of second heart sound II and a time when the
carotid-artery pulse-wave sensor 76 detects the notch of
carotid-artery pulse wave, i.e., a pulse-wave propagation time DT
that is a time needed for a pulse wave to propagate from the heart
to the position where the sensor 76 is worn. The control device 38
determines a pulse-wave propagation velocity PWV based on the thus
determined pulse-wave propagation time DT according to the
above-indicated expression (1): PWV=L/DT.
[0050] Then, the control goes to S5, the BP-determining routine
corresponding to the first BP determining means 82 and the second
BP determining means 84. More specifically described, the control
device 38 determines an amplitude of each of successive
heartbeat-synchronous pulses of the cuff pulse wave represented by
the pulse-wave signal SM.sub.1 continuously supplied from the
pulse-wave filter circuit 36, and determines a right-ankle first
systolic BP value BP1.sub.RSYS based on the time-wise change of the
thus determined amplitudes according to well-known oscillometric
BP-determining algorithm. Similarly, the control device 38
determines an amplitude of each of successive heartbeat-synchronous
pulses of the cuff pulse wave represented by the pulse-wave signal
SM.sub.2 continuously supplied from the pulse-wave filter circuit
50, and determines a left-ankle first systolic BP value
BP1.sub.LSYS based on the time-wise change of the thus determined
amplitudes according to the oscillometric BP-determining algorithm.
In addition, the control device 38 determines an amplitude of each
of successive heartbeat-synchronous pulses of the cuff pulse wave
represented by the pulse-wave signal SM.sub.3 continuously supplied
from the pulse-wave filter circuit 62, and determines a second
systolic BP value BP2.sub.SYS, based on the time-wise change of the
thus determined amplitudes according to the oscillometric
BP-determining algorithm.
[0051] At Steps S6 to S11, the control device 38 judges whether
each of the above-indicated three systolic BP values (i.e., three
maximal BP values) BP1.sub.RSYS, BP1.sub.LSYS, BP2.sub.SYS of the
patient has been determined. When each one of the three systolic BP
values is determined, the each one systolic BP value is stored, in
the RAM 68, together with a pulse-wave-propagation velocity PWV
obtained at the time of determination of the each one systolic BP
value.
[0052] More specifically described, at S6, the control device 38
judges whether the right-ankle first systolic BP value BPL.sub.RSYS
of the patient has been determined. If a negative judgment is made
at S6, the control directly goes to S8 but, if a positive judgment
is made at S6, the control goes to S7 to store, in a prescribed
memory area of the RAM 68, the determined right-ankle first
systolic BP value BR1.sub.RSYS and the pulse-wave-propagation
velocity PWV determined at S4 immediately before the positive
judgment is made at S6. At S8, the control device 38 judges whether
the left-ankle first systolic BP value BP1.sub.LSYS of the patient
has been determined. If a negative judgment is made at S8, the
control directly goes to S10 but, if a positive judgment is made at
S8, the control goes to S9 to store, in the prescribed memory area
of the RAM 68, the determined left-ankle first systolic BP value
BP1.sub.LSYS and the pulse-wave-propagation velocity PWV determined
at S4 immediately before the positive judgment is made at S8. At
S10, the control device 38 judges whether the second systolic BP
value BP2.sub.SYS of the patient has been determined. If a negative
judgment is made at S10, the control directly goes to S12 but, if a
positive judgment is made at S10, the control goes to S11 to store,
in the prescribed memory area of the RAM 68, the determined second
systolic BP value BP2.sub.SYS and the pulse-wave-propagation
velocity PWV determined at S4 immediately before the positive
judgment is made at S10.
[0053] At S12, the control device 38 judges whether all the
blood-pressure values have been determined, that is, whether the
right-ankle first systolic blood pressure BP1.sub.RSYS, the
left-ankle first systolic BP value BP1.sub.LSYS and the second
systolic BP value BP2.sub.SYS have been determined and additionally
the respective diastolic blood-pressure values (i.e., respective
minimal values) of the right ankle 12, the left ankle 16, and the
upper arm 20 have been determined. If a negative judgment is made
at S12, Step S4 and the following steps are repeated while the
pulse-wave-propagation velocity values PWV are successively
determined and the blood-pressure determining routine is
continuously carried out.
[0054] Meanwhile, if a positive judgment is made at S12, the
control goes to S13 corresponding to the cuff-pressure regulating
means 80. At S13, the three switch valves 30, 46, 58 are switched
to their quick-deflation positions, so that the respective
pressures of the three cuffs 24, 40, 52 are quickly lowered.
[0055] Then, the control goes to S14 corresponding to the
relationship determining means 88. At S14, the control device 38
determines, based on a first combination of the second systolic
blood pressure BP2.sub.SYS, i.e., the maximal blood pressure of the
upper arm 20, determined by the blood-pressure determining routine
at S5, and the pulse-wave-propagation velocity PWV stored therewith
at S7, and a second combination of another second systolic blood
pressure BP2.sub.SYS measured in advance from the same patient and
another pulse-wave-propagation velocity PWV measured in advance
from the same patient at the time of measurement of the latter
second systolic blood pressure BP2.sub.SYS, the coefficients
.alpha., .beta. of the expression (3) that is used to determine an
estimated blood pressure EBP based on a pulse-wave-propagation
velocity PWV.
[0056] Then, the control goes to S15 corresponding to the
blood-pressure-change-value determining means 90. At S15, the
control device 38 determines, according to the expression (3) the
coefficients .alpha., .beta. of which have been determined at S14,
an estimated blood pressure EBP(2) at the time of determination of
the second systolic blood pressure BP2.sub.SYS, based on the
pulse-wave-propagation velocity PWV stored at S11, i.e., determined
at the time of determination of the second systolic blood pressure
BP2.sub.SYS. Similarly, the control device 38 determines, according
to the expression (3), an estimated blood pressure EBP(1R) at the
time of determination of the right-ankle first systolic blood
pressure BR1.sub.RSYS, based on the pulse-wave-propagation velocity
PWV stored at S7, and subtracts, according to the expression (5),
the estimated blood pressure EBP(1R) from the estimated blood
pressure EBP(2), to determine a change value .DELTA.BP.sub.2-1R of
blood pressure of the patient from the time of determination of the
right-ankle first systolic blood pressure BP1.sub.RSYS to the time
of determination of the second systolic blood pressure
BP2.sub.SYS.
[0057] Then, the control goes to S16 corresponding to the
corrected-blood-pressure determining means 92. At S16, the control
device 38 adds, to the right-ankle first systolic blood pressure
BR1.sub.RSYS stored at S7, the change value .DELTA.BP.sub.2-1R
determined at S15, to determine a corrected systolic blood pressure
CBP.sub.SYS of the right ankle 12 indicating a systolic blood
pressure at the time of determination of the second systolic blood
pressure BP2.sub.SYS.
[0058] Steps S17 and S18 for the right-ankle first systolic blood
pressure BR1.sub.RSYS are similar to Steps S15 and 16 for the
left-ankle first systolic blood pressure BP1.sub.LSYS. More
specifically described, first, at S17 corresponding to the
blood-pressure-change-value determining means 90, the control
device 38 determines, according to the expression (3) the
coefficients .alpha., .beta. of which have been determined at S14,
an estimated blood pressure EBP(1L) at the time of determination of
the left-ankle first systolic blood pressure BP1.sub.LSYS, based on
the pulse-wave-propagation velocity PWV stored at S9, and
subtracts, according to the expression (5), the estimated blood
pressure EBP(1L) from the estimated blood pressure EBP(2), to
determine a change value .DELTA.BP.sub.2-1R of blood pressure of
the patient from the time of determination of the left-ankle first
systolic blood pressure BP1.sub.LSYS to the time of determination
of the second systolic blood pressure BP2.sub.SYS. Then, at S18
corresponding to the corrected-blood-pressure determining means 92,
the control device 38 adds, to the left-ankle first systolic blood
pressure BP1.sub.LSYS stored at S9, the change value
.DELTA.BP.sub.2-1R determined at S17, to determine a corrected
systolic blood pressure CBP.sub.SYS indicating a systolic blood
pressure of the left ankle 12 at the time of determination of the
second systolic blood pressure BP2.sub.SYS.
[0059] Then, the control goes to S19 corresponding to the
ankle/upper-arm BP index determining means 94. At S19, the control
device 38 calculates a right-leg index ABI.sub.R by dividing, by
the second systolic BP value BP2.sub.SYS stored at S11, the
corrected systolic blood pressure CPB.sub.SYS determined at S16 by
correcting the right-ankle first systolic BP value BR1.sub.RSYS,
and calculates a left-leg index ABI.sub.L by dividing, by the
second systolic BP value BP2.sub.SYS stored at S11, the corrected
systolic BP value CBP1.sub.SYS determined at Step S18 by correcting
the left-ankle first systolic BP value BP1.sub.LSYS.
[0060] Then, at S20, the control device 38 controls the display
device 70 to display the right-leg and left-leg index values
ABI.sub.R, ABI.sub.L determined at Step S19.
[0061] As is apparent from the foregoing description of the
illustrated embodiment, the blood-pressure-change-value determining
means 90 (S15, S17) determines, based on the pulse-wave-propagation
velocity PWV determined by the
pulse-wave-propagation-velocity-relating-information obtaining
means 86 (S4) when the first systolic blood pressure BP1.sub.SYS is
determined by the first blood-pressure determining means 82 (S5),
and the pulse-wave-propagation velocity PWV determined by the
wave-propagation-velocity-relating-information obtaining means 86
(S4) when the second systolic blood pressure BP2.sub.SYS is
determined by the second blood-pressure determining means 84 (S5),
the change value .DELTA.BP of blood pressure of the patient from
the time of determination of the first systolic blood pressure
BP1.sub.SYS to the time of determination of the second systolic
blood pressure BP2.sub.SYS; and the corrected-blood-pressure
determining means 92 (S16, S18) corrects, based on the change value
.DELTA.BP determined by the blood-pressure-change-val- ue
determining means 90 (S15, S17), the first systolic blood pressure
BP1.sub.SYS into the corrected blood pressure CBP.sub.SYS that
would have been determined at the time of determination of the
second systolic blood pressure BP2.sub.SYS. And, the
ankle/upper-arm BP index determining means 94 (S19) determines the
index ABI by dividing the corrected blood pressure-CBP.sub.SYS
determined by the corrected-blood-pressure determining means 92
(S16, S18), by the second systolic blood pressure BP2.sub.SYS that
has not been corrected by the corrected-blood-pressure determining
means 92 (S16, S18). Since the index ABI is determined based on the
two systolic blood-pressure values obtained at the same time, the
index can enjoy a high accuracy.
[0062] Also, in the illustrated embodiment, the
blood-pressure-relating-in- formation obtaining means is provided
by the pulse-wave-propagation-veloci- ty-relating-information
obtaining means 86 (S4) that successively obtains
pulse-wave-propagation-velocity-relating information as one of
those sorts of blood-pressure-relating information that change most
faithfully corresponding to the change of blood pressure of a
living subject. Therefore, each of the change value .DELTA.BP
determined by the blood-pressure-change-value determining means 90
(S15, S17), the corrected blood pressure CBP.sub.SYS obtained based
on the change value .DELTA.BP, and the index ABI determined based
on the corrected blood pressure CBP.sub.SYS, can enjoy a high
accuracy.
[0063] In addition, in the illustrated embodiment, the
ankle/upper-arm BP index determining means 94 (S19) determines the
index ABI.sub.R and the index ABI.sub.L. Since the lower one of the
two index values can be used, a more accurate diagnosis can be made
on the patient.
[0064] 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.
[0065] For example, in the illustrated embodiment, the
pulse-wave-propagation-velocity-relating information is used as the
blood-pressure-relating information. However,
heart-contraction-relating information that relates to contraction
of heart, such as ejection time or period ET, pre-ejection period
PEP, Q-II period, or time from closing of mitral valve to opening
of aortic valve, changes in relation with change of blood pressure.
Therefore, the heart-contraction-relating information may be used
as the blood-pressure-relating information. Otherwise, heart rate,
pulse period, or area of pulse wave that propagates through artery
of living subject may be employed as the blood-pressure-relating
information.
[0066] In the illustrated embodiment, each of the right-leg first
BP measuring device 14, the left-leg first BP measuring device 16,
and the second BP measuring device 22 employs the oscillometric
blood-pressure measuring method. However, each device 14, 16, 22
may employ so-called Korotkoff-sound method in which blood-pressure
values are determined based on respective values of a cuff pressure
when Korotkoff sounds are first and last detected. Otherwise, each
device 14, 16, 22 may employ a supersonic Doppler method in which
supersonic transmitter and receiver are placed right above an
artery to detect the opening and closing of the artery when the
pressing force applied to the artery is changed, and thereby
determine a blood pressure.
[0067] In addition, in the illustrated embodiment, both the
right-ankle first systolic blood pressure BR1.sub.RSYS of the right
ankle 12 and the left-ankle first systolic blood pressure
BP1.sub.LSYS of the left ankle 16 are determined. However, it is
possible to determine either one of the two blood-pressure values
BP1.sub.RSYS, BP1.sub.LSYS.
[0068] In addition, in the illustrated embodiment, the microphone
72 that is worn on chest of a living subject is employed as the
first pulse-wave detecting device to obtain the
pulse-wave-propagation-velocity-relating information. However, it
is possible to employ, as the as the first pulse-wave detecting
device, an electrocardiograph that includes a plurality of
electrodes adapted to be worn on a plurality of prescribed portions
of a living subject, and continuously detects an electrocardiogram
representing action potential of cardiac muscle of the subject
through the electrodes.
[0069] In addition, in the illustrated embodiment, the respective
pulse-wave-propagation velocity values PWV themselves determined by
the pulse-wave-propagation-velocity-relating-information obtaining
means 86 at the respective times of determination of the first
systolic blood pressure BP1.sub.SYS and the second systolic blood
pressure BP2.sub.SYS are used to determine the respective estimated
blood-pressure values EBP.sub.SYS. However, it is possible to
improve the accuracy of pulse-wave-propagation-velocity-relating
information used to determine an estimated blood-pressure EBP, in a
manner described below.
[0070] FIG. 5 is a block diagram for explaining additional
functions of the control device 38 that may be employed to improve
the accuracy of pulse-wave-propagation-velocity-relating
information. In FIG. 5, some of the other functions of the control
device 38 that are not relevant to the additional functions thereof
are omitted.
[0071] An ejection-time determining means 96 iteratively and
non-invasively determines an ejection period or time ET in which
blood is ejected from the left ventricle of the heart of a living
subject. Since the ejection time ET is a sort of
heart-contraction-relating information that changes in relation
with change of contraction period or time of the heart of the
subject, the ejection-time determining means 96 functions as
heart-contraction-relating-information obtaining means. For
example, the ejection-time determining means 96 determines, as the
ejection time ET, a time period from a rising point (i.e., a
minimal point) of one heartbeat-synchronous pulse of the
carotid-artery pulse wave continuously detected by the
carotid-artery pulse-wave sensor 76, to a notch of the one pulse.
Since, as described above, the shape of the carotid-artery pulse
wave is substantially identical with that of the aortic pulse wave,
the time period from the rising point to the notch indicates a time
period in which the aortic valve is open, that is, an ejection time
ET.
[0072] An abnormality judging means 98 judges whether the
pulse-wave-propagation-velocity-relating information obtained by
the pulse-wave-propagation-velocity-relating-information obtaining
means 86 at the time of determination of the first or second blood
pressure BP1 or BP2, is sufficiently accurate, by comparing a
tendency of change of the ejection-time values ET determined by the
ejection-time determining means 96 with a tendency of change of the
pieces of pulse-wave-propagation-velo- city-relating information
obtained by the pulse-wave-propagation-velocity--
relating-information obtaining means 86. More specifically
described, the judging means 98 determines a rate of change (i.e.,
pulse-wave-propagation-velocity-relating-information change rate)
of the current piece of pulse-wave-propagation-velocity-relating
information obtained by the
pulse-wave-propagation-velocity-relating-information obtaining
means 86 from one heartbeat-synchronous pulse of the carotid-artery
pulse wave detected at the time of determination of each of the
first and second blood pressure values BP1, BP2, from the preceding
piece of pulse-wave-propagation-velocity-relating information
obtained from the pulse preceding the one pulse, or a rate of
change of the following piece of
pulse-wave-propagation-velocity-relating information obtained from
the pulse following the one pulse, from the current piece of
pulse-wave-propagation-velocity-relating information. Similarly,
the judging means 98 determines a rate of change (i.e.,
ejection-time change rate) of the current ejection time ET
determined by the ejection-time determining means 98 from one
heartbeat-synchronous pulse of the carotid-artery pulse wave
detected at the time of determination of each of the first and
second blood pressure values BP1, BP2, from the preceding ejection
time ET determined from the pulse preceding the one pulse, or a
rate of change of the following ejection time ET determined from
the pulse following the one pulse, from the current ejection time
ET. If the thus determined pulse-wave-propagation-v-
elocity-relating-information change rate falls within a range that
has, as its central value, the ejection-time change rate and a
length that is experimentally determined in advance and is equally
divided by the central value, the judging means 98 judges that the
pulse-wave-propagation-velocity-relating information obtained at
the time of determination of the each of the first and second
blood-pressure values BP1, BP2 is sufficiently accurate.
[0073] Since both the pulse-wave-propagation-velocity-relating
information and the heart-contraction-relating information, such as
the ejection time ET, change in relation with the blood pressure,
the pulse-wave-propagation-velocity-relating-information change
rate should be substantially equal to the ejection-time change
rate. That is, in FIG. 6, the tendency of change of the iteratively
determined pulse-wave-propagation velocity values PWV (or the
iteratively determined pulse-wave-propagation time values DT)
should be substantially identical with that of the iteratively
determined ejection time values ET. However, the iteratively
determined pulse-wave-propagation velocity values PWV may contain
measurement errors. If the pulse-wave-propagation velocity PWV
determined at the time of determination of the first or second
blood pressure BP1, BP2 contains a great measurement error, the
blood-pressure-change-value determining means 90 would provide an
inaccurate change value .DELTA.BP, which would lead to providing an
accurate index ABI. To solve this problem, the abnormality judging
means 98 compares the tendency of change of
pulse-wave-propagation-velocity-rel- ating information and the
tendency of change of heart-contraction-relating information,
obtained at the time of determination of each blood pressure, with
each other, and thereby judges whether the
pulse-wave-propagation-velocity-relating information obtained at
the time of determination of the each blood pressure is
sufficiently accurate.
[0074] A
correct-pulse-wave-propagation-velocity-relating-information
producing means 100 produces, if the current piece of
pulse-wave-propagation-velocity-relating information obtained at
the time of determination of each of the first and second
blood-pressure values BP1, BP2 is judged as being abnormal by the
abnormality judging means 98, a correct piece of
pulse-wave-propagation-velocity-relating information based on at
least one preceding piece of pulse-wave-propagation-velocity--
relating information obtained immediately before the current piece
of information and at least one following piece of information
obtained immediately after the current piece of information. For
example, if, as shown in FIG. 6, the pulse-wave-propagation
velocity PWV determined at the time of determination of the second
systolic blood pressure BP2.sub.SYS is judged as being abnormal,
the producing means 100 provides, as the correct
pulse-wave-propagation velocity PWVa, an average of the preceding
pulse-wave-propagation velocity PWV and the following
pulse-wave-propagation velocity PWV. In this case, since the
blood-pressure-change-value determining means 90 determines a
change value .DELTA.BP based on the thus produced correct
pulse-wave-propagation velocity PWVa, the accuracy of the change
value .DELTA.BP is prevented from being lowered in spite of the
large measurement error contained in the piece of
pulse-wave-propagation-velocity-relating information obtained at
the time of determination of the second systolic blood pressure
BP2.sub.SYS, and accordingly the accuracy of the index ABI is
prevented from being lowered.
[0075] In addition, the illustrated ankle/upper-arm BP index
measuring apparatus 10 is a sort of superior-and-inferior-limb BP
index measuring apparatus in which an ankle is used as a portion of
an inferior limb and an upper arm is used as a portion of a
superior limb. However, it is possible to use, as a portion of an
inferior limb, a femur or a toe or use, as a portion of a superior
limb, a wrist or a finger.
[0076] 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.
* * * * *