Abstrict
A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, by changing a pressing pressure of an inflatable
cuff being wound around a body portion of a living subject, including
a cuff-pressure regulating device which iteratively changes the
pressure of the cuff within a predetermined range whose upper limit
is lower than a mean blood pressure of the subject, a pulse-wave
sensor which detects an amplitude of each of a plurality of heartbeat-synchronous
pulses of a pulse wave which is produced in the cuff when the pressure
of the cuff is changed within the predetermined range by the regulating
device, a characteristic determining device for determining a characteristic
value relating to an envelope of the pulse amplitudes detected by
the pulse-wave sensor during each of the iterative cuff-pressure
changes within the predetermined range, and a identifying device
for identifying an abnormal decrease of the blood pressure of the
subject based on the characteristic value determined by the characteristic
determining device.
Claims
What is claimed is:
1. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, by changing a pressing pressure of an inflatable
cuff being wound around a body portion of a living subject, comprising:
a cuff-pressure regulating device which iteratively changes the
pressure of said cuff within a predetermined range whose upper limit
is lower than a diastolic blood pressure of the subject;
a pulse-wave sensor which detects an amplitude of each of a plurality
of heartbeat-synchronous pulses of a pulse wave which is produced
in said cuff when said pressure of the cuff is changed within said
predetermined range by said regulating device;
characteristic determining means for determining a characteristic
value relating to an envelope of the pulse amplitudes detected by
said pulse-wave sensor during each of the iterative changes of the
pressure of said cuff by said regulating device within said predetermined
range; and
identifying means for identifying an abnormal decrease of said
blood pressure of the subject based on the characteristic value
determined by said characteristic determining means.
2. A blood pressure monitor apparatus according to claim 1, wherein
said characteristic determining means comprises area-using characteristic
determining means for determining said characteristic value based
on an area defined by said envelope of said pulse amplitudes and
a base line connecting a plurality of cuff pressures corresponding
to said pulse amplitudes, respectively.
3. A blood pressure monitor apparatus according to claim 2, wherein
said area-using characteristic determining means comprises means
for determining, as said characteristic value, a ratio of said area
to the pulse amplitude corresponding to a lower limit of said predetermined
range.
4. A blood pressure monitor apparatus according to claim 2, wherein
said area-using characteristic determining means comprises means
for determining, as said characteristic value, an area defined by
said base line and an envelope of respective normalized values of
said pulse amplitudes.
5. A blood pressure monitor apparatus according to claim 1, wherein
said characteristic determining means comprises amplitude-using
characteristic determining means for determining said characteristic
value based on at least two of said pulse amplitudes.
6. A blood pressure monitor apparatus according to claim 5, wherein
said amplitude-using characteristic determining means comprises
means for determining, as said characteristic value, a ratio of
the pulse amplitude corresponding to said upper limit of said predetermined
range to the pulse amplitude corresponding to a lower limit of the
predetermined range.
7. A blood pressure monitor apparatus according to claim 5, wherein
said amplitude-using characteristic determining means comprises
means for determining, as said characteristic value, a difference
between the pulse amplitude corresponding to said upper limit of
said predetermined range and the pulse amplitude corresponding to
a lower limit of the predetermined range.
8. A blood pressure monitor apparatus according to claim 1, further
comprising a blood pressure measuring device which automatically
carries out, when said identifying means identifies said abnormal
decrease of said blood pressure of the subject, a blood pressure
measurement on the subject according to a series of predetermined
steps.
9. A blood pressure monitor apparatus according to claim 1, further
comprising a pulse-rate sensor which detects a pulse rate of the
subject when said pressure of the cuff is changed within said predetermined
range by said regulating device.
10. A blood pressure monitor apparatus according to claim 9, wherein
said pulse-rate sensor comprises pulse-rate determining means for
determining said pulse rate based on at least two pulses of said
heartbeat-synchronous pulses of said pulse wave detected by said
pulse-wave sensor from said cuff when said pressure of the cuff
is changed within said predetermined range by said regulating device.
11. A blood pressure monitor apparatus according to claim 9, further
comprising pulse-rate-change determining means for determining a
change of a current pulse-rate value detected by said pulse-rate
sensor, from at least one prior pulse-rate value detected by said
pulse-rate sensor before said current pulse-rate value is detected.
12. A blood pressure monitor apparatus according to claim 11, wherein
said pulse-rate-change determining means comprises means for determining
said change of said current pulse-rate value from a moving average
of a plurality of prior pulse-rate values detected by said pulse-rate
sensor before said current pulse-rate value is detected.
13. A blood pressure monitor apparatus according to claim 11, further
comprising reference-value determining means for determining a reference
value, R*, based on the pulse-rate change, .DELTA. PR, determined
by said pulse-rate-change determining means, according to a following
predetermined expression:
where k.sub.1 and k.sub.2 are a first and a second constant, respectively,
wherein said identifying means identifies said abnormal decrease
of said blood pressure of the subject when said characteristic value
determined by said characteristic determining means is greater than
said reference value R*.
14. A blood pressure monitor apparatus according to claim 13, further
comprising a memory which stores data indicative of said predetermined
expression.
15. A blood pressure monitor apparatus according to claim 1, wherein
said cuff-pressure regulating device comprises means for changing
the pressure of said cuff to a predetermined first hold value equal
to a lower limit of said predetermined range and holding the cuff
pressure at said first hold value and changing said cuff pressure
to a predetermined second hold value higher than said first hold
value and equal to said upper limit of the predetermined range and
holding said cuff pressure at said second hold value, and wherein
said characteristic determining means determines said characteristic
value based on the pulse amplitude detected by said pulse-wave sensor
when said cuff pressure is held at said first hold value and the
pulse amplitude detected by said pulse-wave sensor when said cuff
pressure is held at said second hold value.
16. A blood pressure monitor apparatus according to claim 15, wherein
said pulse-wave sensor comprises means for detecting an identical
amplitude of two heartbeat-synchronous pulses of said pulse wave
when the pressure of said cuff pressure is held at each of said
first and second hold values, and wherein said characteristic determining
means determines said characteristic value based on the identical
pulse amplitude detected by said pulse-wave sensor when said cuff
pressure is held at said first hold value and the identical pulse
amplitude detected by said pulse-wave sensor when said cuff pressure
is held at said second hold value.
17. A blood pressure monitor apparatus according to claim 1, further
comprising a blood pressure measuring device which automatically
carries out a blood pressure measurement on the subject at a predetermined
period, wherein said cuff-pressure regulating device automatically
changes the pressure of said cuff at a predetermined period which
is shorter than the predetermined period of operation of said blood
pressure measuring device.
18. A blood pressure monitor apparatus according to claim 1, further
comprising an output device which outputs information indicating
that said identifying means identifies said abnormal decrease of
said blood pressure of the subject.
19. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, by changing a pressing pressure of an inflatable
cuff being wound around a body portion of a living subject, comprising;
a cuff-pressure regulating device which iteratively changes the
pressure of said cuff within a predetermined range whose upper limit
is lower than a mean blood pressure of the subject;
a pulse-wave sensor which detects an amplitude of each of a plurality
of heartbeat-synchronous pulses of a pulse wave which is produced
in said cuff when said pressure of the cuff is changed within said
predetermined range by said regulating device;
characteristic determining means for determining a characteristic
value relating to an envelope of the pulse amplitudes detected by
said pulse-wave sensor during each of the iterative changes of the
pressure of said cuff by said regulating device within said predetermined
range; and
identifying means for identifying an abnormal decrease of said
blood pressure of the subject based on the characteristic value
determined by said characteristic determining means,
wherein said characteristic determining means comprises area-using
characteristic determining means for determining said characteristic
value based on an area defined by said envelope of said pulse amplitudes
and a base line connecting a plurality of cuff pressures corresponding
to said pulse amplitudes, respectively.
20. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, by changing a pressing pressure of an inflatable
cuff being wound around a body portion of a living subject, comprising:
a cuff-pressure regulating device which iteratively changes the
pressure of said cuff within a predetermined range whose upper limit
is lower than a mean blood pressure of the subject;
a pulse-wave sensor which detects an amplitude of each of a plurality
of heartbeat-synchronous pulses of a pulse wave which is produced
in said cuff when said pressure of the cuff is changed within said
predetermined range by said regulating device;
characteristic determining means for determining a characteristic
value relating to an envelope of the pulse amplitudes detected by
said pulse-wave sensor during each of the iterative changes of the
pressure of said cuff by said regulating device within said predetermined
range; and
identifying means for identifying an abnormal decrease of said
blood pressure of the subject based on the characteristic value
determined by said characteristic determining means,
wherein said cuff-pressure regulating device comprises means for
changing the pressure of said cuff to a predetermined first hold
value equal to a lower limit of said predetermined range and holding
the cuff pressure at said first hold value and changing said cuff
pressure to a predetermined second hold value higher than said first
hold value and equal to said upper limit of the predetermined range
and holding said cuff pressure at said second hold value, and
wherein said characteristic determining means determines said characteristic
value based on the pulse amplitude detected by said pulse-wave sensor
when said cuff pressure is held at said first hold value and the
pulse amplitude detected by said pulse-wave sensor when said cuff
pressure is held at said second hold value.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a blood-pressure monitor apparatus
which monitors the blood pressure of a living subject.
2. Related Art Statement
The blood pressure of a living subject such as a patient may continuously
be monitored by using an automatic blood-pressure (BP) measuring
device including an inflatable cuff adapted to be wound around a
body portion (e.g., upper arm) of the subject. In this case, the
BP measuring device periodically carries out BP measuring operations
at a regular interval of time. However, if this interval is shortened
to improve the reliability of the BP monitoring, then the frequency
of pressing of the cuff against the subject's body portion increases,
thereby causing the subject to feel even serious discomfort.
In contrast, a different BP monitoring method is disclosed in Japanese
Patent Applications laid open for inspection under Publication Nos.
61-103432 and 60-241422. In this method, an inflatable cuff is wound
around a body portion of a living subject and is inflated to apply
an appropriate pressing pressure to the body portion, and a pulse-wave
sensor continuously detects heartbeat-synchronous pulses produced
as pressure oscillations in the cuff. The disclosed BP monitor device
continuously estimates the BP values of the subject based on the
respective amplitudes of the continuous pulses.
However, in the above-described BP monitor device, the pressing
pressure of the cuff cannot be decreased to sufficiently low levels
to be able to reduce the physical and/or psychological load to the
subject, because the changing of the pulse amplitudes at such low
levels does not accurately correspond to the changing of the subject's
blood pressure. A curve indicated at solid line in FIG. 35 represents
the envelope of the pulse amplitudes which are obtained from the
cuff as the cuff pressure P.sub.c is changed. If the blood pressure
of the subject decreases from a normal level represented by the
solid-line curve, the solid-line curve is changed into a curve indicated
at one-dot chain line in the same graph. In the case where the pulse
amplitudes are detected at a low cuff pressure P.sub.K, the amount
of changing of the pulse amplitudes is significantly smaller than
that of the subject's blood pressure, thereby lowering the accuracy
of monitoring of the prior BP monitor device.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
blood-pressure monitor apparatus which monitors the blood pressure
of a living subject with high accuracy and without causing the subject
to feel discomfort.
The above object has been achieved by the present invention, which
provides a blood pressure monitor apparatus for monitoring a blood
pressure of a living subject, by changing a pressing pressure of
an inflatable cuff being wound around a body portion of a living
subject, comprising a cuff-pressure regulating device which iteratively
changes the pressure of the cuff within a predetermined range whose
upper limit is lower than a mean blood pressure of the subject;
a pulse-wave sensor which detects an amplitude of each of a plurality
of heartbeat-synchronous pulses of a pulse wave which is produced
in the cuff when the pressure of the cuff is changed within the
predetermined range by the regulating device; characteristic determining
means for determining a characteristic value relating to an envelope
of the pulse amplitudes detected by the pulse-wave sensor during
each of the iterative cuff-pressure changes within the predetermined
range; and identifying means for identifying an abnormal decrease
of the blood pressure of the subject based on the characteristic
value determined by the characteristic determining means.
In the blood pressure (BP) monitor apparatus constructed as described
above, the blood pressure of a living subject is monitored by utilizing
the finding that the slope of the envelope of pulse amplitudes detected
while the cuff pressure is changed within a predetermined range
under a mean BP value of the subject changes in response to a change
of the blood pressure of the subject. Thus, the blood pressure of
the subject is monitored with high accuracy. In addition, since
the slope of the envelope is obtained by changing the cuff pressure
within a low pressure range whose upper limit is lower than the
mean BP value of the subject, the subject does not feel discomfort
due to the pressing of the cuff.
In a preferred embodiment of the present invention, the characteristic
determining means comprises area-using characteristic determining
means for determining the characteristic value based on an area
defined by the envelope of the pulse amplitudes and a base line
connecting a plurality of cuff pressures corresponding to the pulse
amplitudes, respectively. The area may be calculated by integration,
or by approximation.
In another embodiment of the present invention, the area-using
characteristic determining means comprises means for determining,
as the characteristic value, a ratio of the area to the pulse amplitude
corresponding to a lower limit of the predetermined range. Alternatively,
the characteristic value may be determined as a ratio of the area
to the pulse amplitude corresponding to an upper limit of the predetermined
range.
In another embodiment of the present invention, the area-using
characteristic determining means comprises means for determining,
as the characteristic value, an area defined by the base line and
an envelope of respective normalized values of the pulse amplitudes.
In another embodiment of the present invention, the characteristic
determining means comprises amplitude-using characteristic determining
means for determining the characteristic value based on at least
two of the pulse amplitudes.
In another embodiment of the present invention, the amplitude-using
characteristic determining means comprises means for determining,
as the characteristic value, a ratio of the pulse amplitude corresponding
to the upper limit of the predetermined range to the pulse amplitude
corresponding to a lower limit of the predetermined range Alternatively,
the characteristic value may be determined as a ratio of the pulse
amplitude corresponding to a lower limit of the predetermined range
to the pulse amplitude corresponding to the upper limit of the same
range.
In another embodiment of the present invention, the amplitude-using
characteristic determining means comprises means for determining,
as the characteristic value, a difference between the pulse amplitude
corresponding to the upper limit of the predetermined range and
the pulse amplitude corresponding to a lower limit of the predetermined
range.
In another embodiment of the present invention, the blood pressure
monitor apparatus further comprises a blood pressure measuring device
which automatically carries out, when the identifying means identifies
the abnormal decrease of the blood pressure of the subject, a blood
pressure measurement on the subject according to a series of predetermined
steps. In this embodiment, since the blood pressure measuring device
automatically measures a BP value or values of a patient at the
time when an abnormal BP decrease of the patient is identified,
a doctor or a nurse can quickly read the BP values of the patient
and do appropriate treatments on the subject.
In another embodiment of the present invention, the blood pressure
monitor apparatus further comprises a pulse-rate sensor which detects
a pulse rate of the subject when the pressure of the cuff is changed
within the predetermined range by the regulating device.
In another embodiment of the present invention, the pulse-rate
sensor comprises pulse-rate determining means for determining the
pulse rate based on at least two pulses of the heartbeat-synchronous
pulses of the pulse wave detected by the pulse-wave sensor from
the cuff when the pressure of the cuff is changed within the predetermined
range by the regulating device.
In another embodiment of the present invention, the blood pressure
monitor apparatus further comprises pulse-rate-change determining
means for determining a change of a current pulse-rate value detected
by the pulse-rate sensor, from at least one prior pulse-rate value
detected by the pulse-rate sensor before the current pulse-rate
value is detected.
In another embodiment of the present invention, the pulse-rate-change
determining means comprises means for determining the change of
the current pulse-rate value from a moving average of a plurality
of prior pulse-rate values detected by the pulse-rate sensor before
the current pulse-rate value is detected. In this embodiment, the
change of pulse rate is prevented from being adversely influenced
by noise, and accordingly the accuracy of determination of the pulse-rate
change is improved.
In another embodiment of the present invention, the blood pressure
monitor apparatus further comprises reference-value determining
means for determining a reference value, R*, based on the pulse-rate
change, .DELTA. PR, determined by the pulse-rate-change determining
means, according to a following predetermined expression:
where k.sub.1 and k.sub.2 are a first and a second constant, respectively,
wherein the identifying means identifies the abnormal decrease
of the blood pressure of the subject when the characteristic value
determined by the characteristic determining means is greater than
the reference value R*. In the case where the blood pressure of
a patient abnormally decreases because of falling in shock, the
envelope of pulse amplitudes detected from the patient in shock
becomes flat or level. In this case, it is not easy to identify
the shock of the patient based on only the slope of the pulse amplitudes
with respect to the cuff pressure. In the present embodiment, however,
the reference value R* is determined depending upon the pulse-rate
change .DELTA.PR that decreases as the blood pressure of the patient
decreases. Thus, the blood pressure of the patient, i.e., the characteristic
value that increases as the blood pressure of the patient decreases
is monitored in association with the pulse rate of the patient,
i.e., reference value R*. Accordingly, the present BP monitor can
immediately identify, with high accuracy, that the patient has fallen
in shock.
In another embodiment of the present invention, the blood pressure
monitor apparatus further comprises a memory which stores data indicative
of the predetermined expression.
In another embodiment of the present invention, the cuff-pressure
regulating device comprises means for changing the pressure of the
cuff to a predetermined first hold value equal to a lower limit
of the predetermined range and holding the cuff pressure at the
first hold value and changing the cuff pressure to a predetermined
second hold value higher than the first hold value and equal to
the upper limit of the predetermined range and holding the cuff
pressure at the second hold value, and the characteristic determining
means determines the characteristic value based on the pulse amplitude
detected by the pulse-wave sensor when the cuff pressure is held
at the first hold value and the pulse amplitude detected by the
pulse-wave sensor when the cuff pressure is held at the second hold
value. Since the pulses detected when the cuff pressure is held
at the first and second hold values are free from distortion, the
characteristic determining means determines, with high accuracy,
the characteristic value based on the respective amplitudes of those
pulses. Therefore, the blood pressure of the subject can be monitored
with high accuracy.
In another embodiment of the present invention, the pulse-wave
sensor comprises means for detecting an identical amplitude of two
heartbeat-synchronous pulses of the pulse wave when the pressure
of the cuff pressure is held at each of the first and second hold
values, wherein the characteristic determining means determines
the characteristic value based on the identical pulse amplitude
detected by the pulse-wave sensor when the cuff pressure is held
at the first hold value and the identical pulse amplitude detected
by the pulse-wave sensor when the cuff pressure is held at the second
hold value.
In another embodiment of the present invention, the blood pressure
monitor apparatus further comprises a blood pressure measuring device
which automatically carries out a blood pressure measurement on
the subject at a predetermined period, wherein the cuff-pressure
regulating device automatically changes the pressure of the cuff
at a predetermined period which is shorter than the predetermined
period of operation of the blood pressure measuring device.
In another embodiment of the present invention, the blood pressure
monitor apparatus further comprises an output device which outputs
information indicating that the identifying means identifies the
abnormal decrease of the blood pressure of the subject.
In another embodiment of the present invention, the cuff-pressure
regulating device comprises means for changing the pressure of the
cuff within the predetermined range whose upper limit is lower than
a diastolic blood pressure of the subject.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and optional objects, features, and advantages of the
present invention will better be understood by reading the following
detailed description of the preferred embodiments of the invention
when considered in conjunction with the accompanying drawings, in
which:
FIG. 1 is a diagrammatic view of a blood-pressure (BP) monitor
apparatus embodying the present invention;
FIG. 2 is a block diagram for illustrating various functions of
a control device of the apparatus of FIG. 1;
FIG. 3 is a flow chart representing a portion of a control program
according to which the control device of the apparatus of FIG. 1
functions as illustrated in FIG. 2;
FIG. 4 is a flow chart representing another portion of the control
program according to which the control device of the apparatus of
FIG. 1 functions as illustrated in FIG. 2;
FIG. 5 is a graph representing a relationship used by the apparatus
of FIG. 1 at a step of the control program represented by the flow
chart of FIG. 4;
FIG. 6 is a time chart showing the time-wise change of cuff pressure
P.sub.c regulated by the apparatus of FIG. 1;
FIG. 7 is a graph for illustrating an area calculated by the apparatus
of FIG. 1 at a step of the control program represented by the flow
chart of FIG. 4;
FIG. 8 is a graph for illustrating the manner in which the envelope
of pulse amplitudes detected from an inflatable cuff is changed
because of a decrease of the blood pressure of a living subject;
FIG. 9 is a flow chart corresponding to FIG. 4, representing a
portion of a control program according to which a control device
of another BP monitor apparatus as a second embodiment of the invention
functions; and
FIG. 10 is a time chart showing the time-wise change of cuff pressure
P.sub.c regulated by the apparatus of FIG. 9.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is shown a blood pressure monitor apparatus
embodying the present invention (hereinafter, referred to as the
"BP monitor").
In FIG. 1, reference numeral 10 designates an inflatable cuff 10
adapted to be wound around, e.g., an upper arm of a living subject,
such as a patient, so as to press the arm. The cuff 10 includes
an inflatable bag 10a formed of an elastic sheet such as a rubber
sheet or a vinyl sheet. The inflatable bag 10a is accommodated in
an arm belt 10b formed of a non-stretchable sheet. The bag 10a of
the cuff 10 is connected to a pressure sensor 12, an air pump 14,
and a pressure regulator valve 16 via air piping 18. The pressure
regulator valve 16 controls the pressing pressure (i.e., air pressure)
of the cuff 10 applied to the upper arm of the subject. Thus, the
regulator valve 16 provides part of a cuff-pressure regulating device
54 (FIG. 2) which will be described later.
The pressure sensor 12 includes a semiconductor pressure-sensing
element, detects the air pressure in the cuff 10, and supplies a
pressure signal, SP, representative of the detected cuff pressure,
to a low-pass filter 20 and a band-pass filter 22. The low-pass
filter 20 permits only a direct-current component of the pressure
signal SP to pass therethrough, thereby supplying a cuff-pressure
signal, SK, representative of a cuff pressure (i.e., static pressure),
P.sub.c, to an analog-to-digital (A/D) converter 24. The low-pass
filter provides part of a blood-pressure (BP) measuring device 52
(FIG. 2) which will be described later.
The band-pass filter 22 permits only a 1 to 10 Hz frequency-band
component of the pressure signal SP to pass therethrough, thereby
supplying, to the A/D converter 24, a pulse-wave signal, SM.sub.1,
representative of a pulse wave including heartbeat-synchronous pulses
that are pressure oscillations or changes produced in the cuff 10
because of the pulsation of arterial vessels (e.g., brachial artery)
running in the subject's arm. The band-pass filter 22 has a narrow
frequency-band characteristic to extract, from the pressure signal
SP, pulse amplitudes, i.e., pressure oscillations which are produced
in the cuff 10 in synchronism with the subject's heartbeats while
the cuff pressure P.sub.c is slowly changed (e.g., decreased) at
the rate of, e.g., 2 to 3 mmHg/sec. Thus, the pulse-wave signal
SM.sub.1 is free from noise such as motion-induced artifact noise.
The A/D converter 24 includes a multiplexer for concurrently dealing
with the two input signals, SK and SM.sub.1, by time sharing. The
band-pass filter 22 provides part of a pulse-wave sensor 50 which
will be described later.
The present BP monitor has a control device 26 which is provided
by a microcomputer including a central processing unit (CPU) 28,
a random access memory (RAM) 30, a read only memory (ROM) 32, an
output interface 34, and a display interface 36. The CPU 28 processes
the signals SK, SM.sub.1 received from the A/D converter 24, by
utilizing a temporary-storage function of the RAM 30, according
to a control program pre-stored in the ROM 32. In addition, the
CPU 28 drives and controls the air pump 14 and the pressure regulator
valve 16 via the output interface 34, and drives and controls a
display 38 via the display interface 36. The display 38 includes
a display panel for displaying an image which consists of a multiplicity
of picture elements and represents numerals and/or waveforms, and
a printer for recording the image with an ink on a recording sheet.
In the present embodiment, the display 38 corresponds to an output
device 68 (FIG. 2).
A mode-selection switch 40 is operable for switching the BP monitor
between a single-measurement mode and a BP-monitor mode. The mode
switch 40 supplies, to the CPU 28, a mode signal representing a
selected mode. A start/stop switch 42 is operable for alternately
supplying, to the CPU 28, an ON signal to start the BP monitor and
an OFF signal to stop the same, each time the switch 42 is operated.
FIG. 2 illustrates various functions of the control device 26 of
the present BP monitor. The BP monitor includes a pulse-wave sensor
50 which detects a pulse wave including heartbeat-synchronous pulses
that are pressure oscillations produced in the cuff 10 in synchronism
with subject's heartbeats when the cuff pressure P.sub.c is changed.
The BP monitor also includes a blood-pressure (BP) measuring device
52 which determines, according to a known oscillometric method,
two cuff pressures at which the rate of change of pulse amplitudes
A.sub.m obtained during the changing of the cuff pressure P.sub.c
becomes maximal, as a systolic (P.sub.SYS) and a diastolic (P.sub.DIA)
blood pressure of the subject, and determines a cuff pressure at
which the greatest pulse amplitude is obtained, as a mean (P.sub.MEAN)
blood pressure of the subject. The BP measuring device 52 carries
out a BP measurement not only when the start/stop switch 42 is operated
to start the BP monitor, but also when an abnormal-decrease identifying
means 58 identifies an abnormal decrease of the blood pressure of
the subject, in a manner described later, with the mode switch 40
being placed in the BP-monitor mode.
As shown in FIG. 6, in each BP-measuring period of the BP measuring
device 52, a cuff-pressure regulating device 54 quickly increases
the cuff pressure P.sub.c up to a first target value, P.sub.CM,
which is pre-determined to be higher than a systolic BP value of
the subject, and subsequently slowly decreases the cuff pressure
P.sub.c at the rate of 2 to 3 mmHg/sec. In each non-BP-measuring
period, T.sub.2M, in which the BP measuring device 52 does not work,
the cuff-pressure regulating device 54 iteratively increases and
decreases the cuff pressure P.sub.c to and from a second target
value, P.sub.CH, which is pre-determined to be lower than a mean
BP value of the subject, while inserting a predetermined rest period,
T.sub.1M, between successive two cuff-pressure regulating periods.
The control device 26 functions as a characteristic determining
means 56 which determines a characteristic value relating to an
envelope, H, (FIG. 7) of the pulse amplitudes Am detected by the
pulse-wave sensor 50 during each of the iterative cuff-pressure
changing periods of the cuff-pressure regulating device 54 within
a predetermined range whose upper limit is lower than a mean BP
value of the subject. For example, the characteristic determining
means 56 determines the characteristic value of the envelope H based
on an area, indicated at inclined lines in FIG. 7, which is defined
by (i) the envelope H of the pulse amplitudes A.sub.m and (ii) a
base line connecting the cuff-pressure values P.sub.C corresponding
to the pulse amplitudes A.sub.m, respectively, i.e., axis of abscissa
indicative of the cuff pressure P.sub.c in the graph of FIG. 7.
More specifically described, the characteristic determining means
56 determines, as the characteristic value of the envelope H, a
ratio, R.sub.AREA, of the area to a pulse amplitude corresponding
to a lower limit of the predetermined range.
The control device 26 also functions as an abnormal-decrease identifying
means 58 which identifies an abnormal decrease of the blood pressure
of the subject based on the characteristic value determined by the
characteristic determining means 56. The control device 26 further
functions as a pulse-rate-change determining means 60 which determines
a change, .DELTA. PR, of a current pulse-rate value, PR.sub.n, determined
by a pulse-rate determining means 64, from a prior pulse-rate value,
PR.sub.n-1, determined by the pulse-rate determining means 64 or
a moving average, PR.sub.ave (=(PR.sub.n-1 + . . . +PR.sub.n-m)/m
), of a predetermined number, m, of prior pulse-rate values determined
by the pulse-rate determining means 64 before the current pulse-rate
value PR.sub.n is determined. The pulse-rate determining means 64
determines the pulse rate PR.sub.n based on a time interval between
two successive heartbeat-synchronous pulses of the pulse-wave signal
SM.sub.1 which is detected by the pulse-wave sensor 50 each time
the cuff pressure P.sub.c is increased to, or decreased from, the
second target value P.sub.CH lower than the mean BP value of the
subject by the cuff-pressure regulating device 54 during the non-BP-measuring
period T.sub.2M. The pulse-rate-change determining means 60 includes
the pulse-rate determining means 64, and a moving-average determining
means for determining the above-indicated moving average PR.sub.ave.
In the case where the blood pressure of the subject is normal,
the envelope (indicated at solid line in FIG. 8) of the pulse amplitudes
A.sub.m obtained when the cuff pressure P.sub.c is changed under
the mean BP value of the patient, exhibits a small angle, .alpha..
On the other hand, when the blood pressure of the subject decreases,
the upper-peak point of the envelope (indicated at one-dot chain
line) of the pulse amplitudes A.sub.m obtained under the same conditions,
decreases and moves left in FIG. 8, therefore exhibits a greater
angle, .beta.. Accordingly, in the latter case, the ratio R.sub.AREA
increases. The present invention has been developed based on this
finding. For example, the abnormal-decrease identifying means 58
identifies an abnormal decrease of the blood pressure of the subject,
when a ratio R.sub.AREA determined by the characteristic determining
means 56 exceeds a reference value R*. The BP monitor includes an
output device 68 which outputs information indicating that the abnormal-decrease
identifying means 58 has identified an abnormal decrease of the
blood pressure of the subject.
The reference value R* may be a predetermined constant value. However,
in the present embodiment, the control device 26 functions as a
reference-value determining means 62 which determines a reference
value R* based on the pulse-rate change APR determined by the pulse-rate-change
determining means 60, according to the following predetermined expression
(1) pre-stored in the ROM 32 and illustrated in FIG. 5:
where k.sub.1 and k.sub.2 are a first and a second constant, respectively.
Next, there will be described the operation of the control device
26 of the BP monitor by reference to the flow charts of FIGS. 3
and 4 which represent the control program pre-stored in the ROM
32.
First, at Step S1 of FIG. 3, the CPU 28 of the control device 26
judges whether the start/stop switch 42 has been operated to start
the present BP monitor, based on the signal supplied from the switch
42. If a negative judgment is made at Step S1, Step S1 is repeated.
Meanwhile, a positive judgment is made at Step S1, the control of
the CPU 28 proceeds with Step S2 to operate the air pump 14 and
the pressure regulator valve 16 to increase quickly the pressure
P.sub.c of the cuff 10.
Step S2 is followed by Step S3 to judge whether the cuff pressure
P.sub.c has been increased up to a first predetermined target value
PCM, e.g., 180 mmHg. If a negative judgment is made at Step S3,
Steps S2 and S3 are repeated. Meanwhile, if a positive judgment
is made at Step S3, the control of the CPU 28 proceeds with Step
S4 to stop the air pump 14 and change the degree of opening of the
regulator valve 16 to start decreasing the cuff pressure P.sub.c
at the low rate of 2 to 3 mmHg/sec suitable for blood pressure measurements.
Step S4 is followed by Step S5 to judge whether the CPU 28 has read
in one heartbeat-synchronous pulse of the pulse-wave signal SM.sub.1
from the band-pass filter 22. If a negative judgment is made at
Step S5, Steps S4 and S5 are repeated. Meanwhile, if a positive
judgment is made at Step S5, the control of the CPU 28 goes to Step
S6, i.e., oscillometric BP-value determining routine. As shown in
FIG. 7, a cuff pressure at which the pulse amplitudes A.sub.m largely
increase during the slow decreasing of the cuff pressure P.sub.c,
is determined as a systolic blood pressure P.sub.SYS of the subject;
a cuff pressure at which the pulse amplitudes A.sub.m largely decrease
is determined as a diastolic blood pressure P.sub.DIA of the subject;
and a cuff pressure at which the greatest pulse amplitude is detected
is determined as a mean blood pressure P.sub.MEAN Of the subject.
Step S6 is followed by Step S7 to judge whether the BP-value determination
at Step S6 has been completed. If a negative judgment is made at
Step S7, Steps S4 to S7 are repeated. Meanwhile, if a positive judgment
is made at Step S7, the control of the CPU 28 goes to Step S8 to
store the determined BP values P.sub.SYS, P.sub.MEAN, P.sub.DIA
in the RAM 30 and command the display 38 to display numerals indicative
of the determined BP values P.sub.SYS, P.sub.MEAN, P.sub.DIA. Step
S8 is followed by Step S9 to decrease quickly the cuff pressure
P.sub.c, thereby releasing the subject's arm from the pressing of
the cuff 10. In the present embodiment, Steps S2 to S9 correspond
to the BP measuring device 52.
At Step S10, the CPU 28 judges whether the mode switch 40 indicates
that the BP-monitor mode has been selected, based on the signal
supplied from the switch 40. A negative judgment made at Step S10
indicates that the present BP monitor is now in the single-measurement
mode. In this case, the control of the CPU 28 returns to Step S1.
On the other hand, a positive judgment made at Step S10 indicates
that the present BP monitor is now in the BP-monitor mode. In the
latter case, the control of the CPU 28 goes to Step S11 and the
following steps, i.e., BP monitoring routine.
At Step S11, a second timer or counter, T.sub.2, is reset to zero
and, at Step S12, a first timer or counter, T.sub.1, is reset to
zero. At Step S13, one is added to each of the respective contents
of the first and second timers T.sub.1, T.sub.2 and, at Step S14,
the CPU 28 judges whether the content or time counted or measured
by the first timer T.sub.1 has increased up to a first predetermined
reference value, T.sub.1M, of, e.g., 1 to 5 minutes. The first reference
value T.sub.1M corresponds to a time interval between successive
two cuff-pressure regulating periods in each of which the cuff pressure
P.sub.c is increased up to a second predetermined target value P.sub.CH
of, e.g., 60 mmHg during a second predetermined time interval, T.sub.2M,
between two successive BP-measuring periods, as illustrated in FIG.
6.
Initially, negative judgments are made at Step S14, and Steps S13
and S14 are repeated. Meanwhile, if a positive judgment is made
at Step S14, the control of the CPU 28 goes to Step S15 to operate
the air pump 14 and the pressure regulator valve 16 to increase
the cuff pressure P.sub.c at a predetermined low rate. This low
rate is predetermined such that four or more heartbeat-synchronous
pulses of the pulse-wave signal SM.sub.1 are obtained through the
band-pass filter 22 while the cuff pressure P.sub.c is increased
from atmospheric pressure up to the second target value P.sub.CH.
The low rate is, e.g., 10 mmHg/sec. At Step S16, the CPU 28 reads
in each heartbeat-synchronous pulse of the signal SM.sub.1, determines
the amplitude A.sub.m of each pulse, the time when that pulse is
read in, and the cuff pressure P.sub.c at the time of reading of
that pulse, and store the thus obtained data in the RAM 30.
Step S16 is followed by Step S17 to judge whether the cuff pressure
P.sub.c has been increased up to the second target value P.sub.CH.
The second target value P.sub.CH is predetermined to be sufficiently
lower than a mean BP value of the subject, and allows the CPU 28
or the control device 26 to identify a significant change of the
pulse amplitudes A.sub.m. As described above, the target value P.sub.CH
may be 60 mmHg. If a negative judgment is made at Step S17, Steps
S15, S16, and S17 are repeated. Meanwhile, if a positive judgment
is made at Step S17, the control of the CPU 28 goes to Step S18
to stop the low-rate increasing of the cuff pressure P.sub.c and
cause the cuff pressure P.sub.c to be quickly decreased down to
atmospheric pressure.
Step S18 is followed by Step S19 to produce, based on the pulse
amplitudes A.sub.m and the cuff pressures P.sub.c determined and
stored at Step S16, an envelope H of the pulse amplitudes A.sub.m
in a two-dimensional coordinate system defined by an axis of abscissa
indicative of the cuff pressure P.sub.c (mmHg) and an axis of ordinate
indicative of the pulse amplitude A.sub.m (mmHg), as illustrated
in FIG. 7. The axis of abscissa corresponds to a base line which
connects the cuff pressures P.sub.c corresponding to the pulse amplitudes
A.sub.m, respectively. Subsequently, the CPU 28 determines an area,
S, defined or bounded by the envelope H and the base line, within
a predetermined pressure range between, e.g., 30 mmHg and 60 mmHg.
The area S may be calculated by integration. In the present embodiment,
however, the area S is obtained by approximation. For example, in
the case where the CPU 28 obtains, at Step S16, a pulse amplitude,
A.sub.m30, corresponding to a cuff pressure P.sub.c of 30 mmHg,
a pulse amplitude, A.sub.m40, corresponding to a cuff pressure P.sub.c
of 40 mmHg, a pulse amplitude, A.sub.m50, corresponding to a cuff
pressure P.sub.c of 50 mmHg, and a pulse amplitude, A.sub.m60, corresponding
to a cuff pressure P.sub.c of 60 mmHg, when the cuff pressure P.sub.c
is increased from atmospheric pressure up to the target value P.sub.CH
of 60 mmHg at Step S15, the CPU 28 approximates the area S by the
sum of the four amplitudes, i.e., S=A.sub.m30 +A.sub.m40 +A.sub.m50
+A.sub.m60. Finally, the CPU 28 determines a characteristic, R.sub.AREA,
of the envelope H by the following expression (2):
Thus, Step S19 corresponds to the characteristic determining means
56.
Step S19 is followed by Step S20 to determine a current pulse rate,
PR.sub.n, from a time interval between the respective times of occurrence
of two successive heartbeat-synchronous pulses of the pulse-wave
signal SM.sub.1 determined and stored at Step S16. Step S20 corresponds
to the pulse-rate determining means 64. Step S20 is followed by
Step S21 to calculate a moving average, PR.sub.ave (=(PR.sub.n-1
+PR.sub.n-2 + . . . +PR.sub.n-m)/m), of a predetermined number,
m, of prior pulse rates, PR.sub.n-1, PR.sub.n-2, . . . , PR.sub.n-m,
determined at Step S19 in the same number m of prior control cycles
before the current control cycle. Step S21 corresponds to the moving-average
calculating means 66. Step S21 is followed by Step S22 to determine
a change, .DELTA.PR (=PR.sub.n -PR.sub.ave), of the current pulse
rate PR.sub.n determined at Step 20 from the moving average PR.sub.ave
determined at Step S21. Step S22 corresponds to the pulse-rate-change
determining means 60.
Subsequently, the control of the CPU 28 goes to Step S23 to determine
a reference value R* based on the pulse-rate change .DELTA.PR determined
at Step S22, according to the pre-stored expression (1), i.e., relationship
shown in FIG. 5. Step S23 corresponds to the reference-value determining
means 62. The research of the Applicant has found that as the blood
pressure P of a living subject decreases, the characteristic R.sub.AREA
of the subject increases and the pulse rate PR decreases. Based
on this finding, the reference value R* is modified depending upon
the pulse-rate change .DELTA.PR. Thus, the accuracy of identification
of an abnormal BP decrease of the subject is improved.
Step S23 is followed by Step S24 to judge whether the characteristic
value R.sub.AREA determined at Step S19 is greater than the reference
value R* determined at Step S23. Step S24 corresponds to the abnormal-decrease
identifying means 58. If a positive judgment is made at Step S24,
the control of the CPU 28 goes to Step S25 to operate the display
38 to output a message to inform the operator of the identification
of the abnormal BP decrease of the subject, and subsequently to
Step S2 and the following steps corresponding to part of the BP
measuring device 52 to measure a BP value or values of the subject
immediately after the identification of the abnormal BP decrease.
On the other hand, if a negative judgment is made at Step S24,
the control of the CPU 28 goes to Step S26 to decrease the cuff
pressure P.sub.c down to atmospheric pressure and subsequently to
Step S27 to judge whether the content or time counted or measured
by the second timer T.sub.2 has increased up to a second predetermined
reference value T.sub.2M of, e.g., 10 to 30 minutes. The second
reference value T.sub.2M corresponds the time interval between two
BP-measuring periods, as shown in FIG. 6. Thus, the BP measuring
device 52 periodically carries out a BP measuring operation at Steps
S2 through S9. Initially, negative judgments are made at Step S27,
and Steps S12 and the following steps are repeated. Meanwhile, if
a positive judgment is made at Step S27, the control of the CPU
28 goes back to Step S2 and the following steps.
Thus, according to the flow charts of FIGS. 3 and 4, the cuff pressure
P.sub.c is changed as time elapses, as shown in FIG. 6. That is,
after the initial BP-measuring operation is carried out in response
to the operation of the start/stop switch 42 and the first time
interval T.sub.1M elapses, the cuff pressure P.sub.c is periodically
increased up to the second target pressure P.sub.CH lower than a
mean BP value of the subject, during the non-BP-measuring period,
i.e., BP-monitoring period. The control device 26 of the present
BP monitor determines a characteristic value R.sub.AREA based on
the pulse amplitudes A.sub.m and the corresponding cuff pressures
P.sub.c that are obtained during each cuff-pressure regulating period,
and identifies a possible abnormal BP decrease of the subject based
on the thus determined characteristic value R.sub.AREA.
As is apparent from the foregoing description relating to the first
embodiment of the present invention, each time the air pump 14 and
the pressure regulator valve 16 are operated to increase the cuff
pressure P.sub.c to the second target pressure P.sub.CH lower than
a mean BP value of a living subject, the CPU 28 calculates the characteristic
value R.sub.AREA at Step S29, and identifies an abnormal BP decrease
of the subject based on the determined characteristic value R.sub.AREA
at Step S24. Thus, the present BP monitor monitors, with high accuracy,
the blood pressure of the subject by utilizing the finding that
the slope of the envelope H of the pulse amplitudes A.sub.m detected
while the cuff pressure P.sub.C is changed within the predetermined
range whose upper limit is lower than the mean BP value of the subject
changes when the blood pressure of the subject changes. In addition,
since the slope of the envelope H is obtained when the cuff pressure
P.sub.c is changed under the mean BP value of the subject, the subject
does not feel discomfort due to the pressing of the cuff 10.
Also, in the present embodiment, if an abnormal BP decrease of
the subject is identified at Step S24, the BP measuring device 52
automatically carries out a BP measuring operation according to
a series of predetermined steps. Thus, an actual BP value or values
of the subject at the time of identification of the abnormal BP
decrease is promptly measured by the BP measuring device 52. Therefore,
a medical staff such as a doctor or a nurse can quickly take an
appropriate action for the subject.
Moreover, at Step S23, the CPU 28 determines, according to the
pre-stored expression (1), the reference value R* based on the pulse-rate
change .DELTA. PR of the current pulse rate PR.sub.n that is determined
based on the same pulse-wave signal SM.sub.1 as that used to determine
the characteristic value R.sub.AREA and, at Step S24, the CPU 28
identifies an abnormal BP decrease of the subject if the characteristic
value R.sub.AREA is greater than the reference value R*. For example,
in the case where the blood pressure of a patient abnormally decreases
because of falling in shock, the envelope H of pulse amplitudes
A.sub.m detected from the patient in shock becomes flat or level.
In this case, therefore, it is not easy to identify the shock of
the patient based on only the slope of the pulse amplitudes A.sub.m
with respect to the cuff pressure P.sub.c. In the present embodiment,
however, the reference value R* is determined depending upon the
pulse-rate change .DELTA. PR that decreases as the blood pressure
of the patient decreases. Thus, the blood pressure of the patient,
i.e., the characteristic value R.sub.AREA is monitored in association
with the pulse rate PR of the patient, i.e., the reference value
R*. Accordingly, the present BP monitor can immediately identify,
with high accuracy, that the patient has fallen in shock.
Next, there will be described a second embodiment of the present
invention by reference to FIGS. 9 and 10. The second embodiment
relates to a BP monitor which has the same hardware construction
as that of the first embodiment shown in FIG. 1 and which operates
according to the control program represented by the flow charts
of FIGS. 3 and 4 except that in the second embodiment, Steps S17-1
to S17-6 of FIG. 9 replace Steps S15, S16, and S17 of FIG. 4. The
same reference numerals as used in the first embodiment are used
to designate the corresponding elements or parts of the second embodiment
and the description thereof is omitted.
In the second embodiment, a control device 26 of the BP monitor
functions as part of a blood pressure regulating device 54 which
increases a cuff pressure P.sub.c up to a first predetermined hold
value, P.sub.CH1, and holds the cuff pressure P.sub.c at the first
hold value P.sub.CH1 for a predetermined duration, and subsequently
increases the cuff pressure P.sub.c up to a second predetermined
hold value, P.sub.CH2, higher than the first hold value P.sub.CH1
and holds the cuff pressure P.sub.c at the second hold value P.sub.CH1
for the same duration. The control device 26 also functions as a
characteristic determining means 56 which determines a characteristic,
R.sub.ENV, relating to an envelope of two pulse amplitudes A.sub.m1,
A.sub.m2 which are detected when the cuff pressure P.sub.c is held
at the first and second hold values P.sub.CH1, P.sub.CH2, respectively.
In the present embodiment, after a positive judgment is made at
Step S14, the control of a CPU 28 of the control device 26 goes
to Step S17-1 to increase the cuff pressure P.sub.c up to a first
predetermined hold value P.sub.CH1 and holds the cuff pressure P.sub.c
at the first hold value P.sub.CH1 for a predetermined duration.
The first hold value P.sub.CH1 is, e.g., 30 mmHg. Subsequently,
at Step S17-2, the CPU 28 judges whether two successive heartbeat-synchronous
pulses detected with the cuff pressure P.sub.c being held at the
first hold value P.sub.CH1 have an identical amplitude. This step
is provided for avoiding reading noise as a heartbeat-synchronous
pulse. Since a band-pass filter 22 of the present BP monitor provides
pulses when the cuff pressure P.sub.c is held at a certain value,
i.e., the first hold value P.sub.CH1 at Step S17-1 (or a second
hold value P.sub.CH2 at Step S17-4), those pulses have a more accurate
waveform than the pulses provided by the band-pass filter 22 in
the first embodiment while the cuff pressure P.sub.c is changed.
If a negative judgment is made at Step S17-2, Steps S17-1 and S17-2
are repeated. On the other hand, if a positive judgment is made
at Step S17-2, the control of the CPU 28 goes to Step S17-3 to store
the identical amplitude of the two pulses as a first pulse amplitude
A.sub.m1 in a RAM 30.
Step S17-3 is followed by Step S17-4 to increase the cuff pressure
P.sub.c up to a second predetermined hold value P.sub.CH2 and holds
the cuff pressure P.sub.c at the second hold value P.sub.CH2 for
the same duration. The second hold value P.sub.CH2 is, e.g., 60
mmHg. The second hold value P.sub.CH2 is so pre-determined as to
obtain a greater pulse amplitude than that obtained at the first
hold pressure P.sub.CH1. Subsequently, at Step S17-5, the CPU 28
judges whether two successive heartbeat-synchronous pulses detected
with the cuff pressure P.sub.c being held at the second hold value
P.sub.CH2 have an identical amplitude. If a negative judgment is
made at Step S17-5, Steps S17-4 and S17-5 are repeated. On the other
hand, if a positive judgment is made at Step S17-5, the control
of the CPU 28 goes to Step S17-6 to store the identical amplitude
of the two pulses as a second pulse amplitude A.sub.m2 in the RAM
30. The cuff pressure P.sub.c is changed as time elapses, as illustrated
in FIG. 10.
After the cuff pressure P.sub.c is decreased down to atmospheric
pressure at Step S18, the control of the CPU 28 goes to Step S19
to determine a characteristic value, R.sub.ENV, of the envelope
of the two pulse amplitudes A.sub.m1, A.sub.m2 determined and stored
at Steps S17-3 and S17-6, according to the following expression
(3):
The BP monitor as the second embodiment enjoys the same advantages
as those of the BP monitor as the first embodiment. In addition,
the characteristic value R.sub.ENV is easily calculated from the
two pulse amplitudes A.sub.m1, A.sub.m2.
Moreover, noise is effectively removed from the pulse-wave signal
SM.sub.1 supplied from the band-pass filter 22, because the cuff
pressure P.sub.c is held at the first or second hold pressure P.sub.CH1,
P.sub.CH2 until two successive pulses having an identical amplitude
are detected.
Furthermore, since pulses are detected when the cuff pressure P.sub.c
is held at the first or second hold pressure P.sub.CH1, P.sub.CH2,
those pulses enjoy an accurate waveform free from distortion due
to the changing of the cuff pressure P.sub.c and accordingly provide
an accurate amplitude A.sub.m1, A.sub.m2. Therefore, the characteristic
value R.sub.ENV is determined with accuracy, and the blood pressure
of the subject is monitored with reliability.
While the present invention has been described in its preferred
embodiments, the present invention may otherwise be embodied.
While in each of the first and second embodiments the control device
28 determines the characteristic value R.sub.AREA, R.sub.ENV based
on the pulse amplitudes A.sub.m, A.sub.m1, A.sub.m2 detected when
the cuff-pressure regulating device 54 increases the cuff pressure
P.sub.c within the predetermined pressure range whose lower and
upper limits are 30 and 60 mmHg, respectively, it is possible to
determine a characteristic value R.sub.AREA, R.sub.ENV based on
pulse amplitudes A.sub.m, A.sub.m1, A.sub.m2 detected when the cuff
pressure P.sub.c is decreased within a predetermined pressure range.
Although in the first and second embodiments the control device
26 determines the characteristic value R.sub.AREA, R.sub.ENV according
to the expression (2) or (3), it is possible to determine, as a
characteristic of the envelope H of pulse amplitudes, an area defined
by the envelope of normalized pulse amplitudes A.sub.m1, or a difference
between the two pulse amplitudes A.sub.m1, A.sub.m2. The normalization
of the pulse amplitudes A.sub.m is effected by regarding, as one,
the greatest one of the pulse amplitudes A.sub.m.
While in the first and second embodiments the second target pressure
P.sub.CH or the second hold pressure P.sub.CH2 is 60 mmHg, it is
possible to employ, as the second target or hold pressure P.sub.CH,
P.sub.CH2, a different pressure which is lower than a mean BP value
of a living subject.
However, it is more preferable to employ, as the second target
or hold pressure P.sub.CH, P.sub.CH2, a pressure lower than a diastolic
BP value of a living subject, because the low pressure does not
stop the blood flow through the arteries under the cuff 10.
While in each of the first and second embodiments the control device
26 determines, at Step S20, the pulse rate PR of the subject based
on the pulse wave (i.e., signal SM.sub.1) which is the pressure
oscillation produced in the cuff 10 employed for the blood pressure
measurements, it is possible to employ a different sort of pulse-wave
sensor which detects a different sort of pulse wave, such as a photoelectric
pulse wave, a volumetric pulse wave, an impedance pulse wave, or
an electrocardiograph which produces an electrocardiogram signal,
and determine a pulse rate based on the different pulse wave or
signal.
It is to be understood that the present invention may be embodied
with other changes, improvements, and modifications that may occur
to those skilled in the art without departing from the spirit and
scope of the invention defined in the appended claims. |