Abstrict
A blood pressure monitor apparatus including a blood pressure measuring
device which includes a cuff and measures a blood pressure value
of the subject by changing a pressing pressure of the cuff, a volume
pulse wave detecting device which detects a volume pulse wave of
the subject, a normalized pulse-wave area calculating device for
successively calculating an area which is defined by a waveform
of each of heartbeat-synchronous pulses of the volume pulse wave
and is normalized based on a period and an amplitude of the each
pulse of the volume pulse wave, a pulse wave area-blood pressure
relationship determining device for determining a relationship between
pulse-wave area and blood pressure, based on a normalized pulse-wave
area value and a blood pressure value, when the blood pressure value
is measured; and a monitor blood pressure determining device for
successively determining a monitor blood-pressure value of the subject,
based on each of normalized pulse-wave area values, according to
the pulse wave area-blood pressure relationship.
Claims
What is claimed is:
1. A blood pressure monitor apparatus comprising:
a blood pressure measuring device which includes a cuff adapted
to be pressed on an artery of a living subject and measures a blood
pressure value of the subject by changing a pressing pressure of
the cuff;
a volume pulse wave detecting device which detects a volume pulse
wave of the subject;
normalized pulse-wave area calculating means for successively calculating
an area which is defined by a waveform of each of heartbeat-synchronous
pulses of the volume pulse wave detected by said volume pulse wave
detecting device and is normalized based on a period and an amplitude
of said each pulse of the volume pulse wave;
pulse wave area-blood pressure relationship determining means for
determining a relationship between pulse-wave area and blood pressure,
based on a normalized pulse-wave area value calculated by said normalized
pulse-wave area calculating means and a blood pressure value measured
by said blood pressure measuring device, when said blood pressure
value is measured; and
monitor blood pressure determining means for successively determining
a monitor blood-pressure value of the subject, based on each of
normalized pulse-wave area values successively calculated by said
normalized pulse-wave area calculating means, according to the pulse
wave area-blood pressure relationship determined by said pulse wave
area-blood pressure relationship determining means.
2. A blood pressure monitor apparatus according to claim 1, further
comprising monitor-blood-pressure abnormality judging means for
judging whether each of the monitor blood-pressure values successively
determined by said monitor blood pressure determining means does
not fall in a reference range, and controlling, when a negative
judgment is made, said blood pressure measuring device to start
a blood pressure measuring operation.
3. A blood pressure monitor apparatus according to claim 2, further
comprising an indicating device which indicates a trend graph of
the monitor blood-pressure values successively determined by said
monitor blood pressure determining means.
4. A blood pressure monitor apparatus according to claim 3, wherein
said indicating device comprises means for indicating that said
negative judgment is made by said monitor-blood-pressure abnormality
judging means.
5. A blood pressure monitor apparatus according to claim 1, wherein
said volume pulse wave detecting device comprises a photoelectric
pulse-wave sensor including a light-emitting and a light-receiving
element, the light-emitting element adapted to emit, toward a skin
of the subject, a light having a wavelength which can be reflected
by hemoglobin present in blood of the skin, the light-receiving
element adapted to receive the light scattered by the hemoglobin
from the skin, said photoelectric pulse-wave sensor outputting a
photoelectric pulse wave signal representing an instantaneous blood
volume in capillaries of the skin.
6. A blood pressure monitor apparatus according to claim 1, wherein
said volume pulse wave detecting device comprises an impedance pulse-wave
sensor including at least two electrodes adapted to be set on different
locations of a skin of the subject at a predetermined interval,
said impedance pulse-wave sensor outputting an impedance pulse-wave
signal representing an instantaneous blood volume in a tissue of
the skin located between said two electrodes.
7. A blood pressure monitor apparatus including a blood pressure
measuring device which includes a cuff being set on a body portion
of a living subject and periodically measures a blood pressure value
of the subject, based on a variation of a pulse wave produced while
a pressing pressure of the cuff is changed, the blood pressure monitor
apparatus comprising:
a volume pulse wave detecting device which detects a volume pulse
wave of the subject;
normalized pulse-wave area calculating means for successively calculating
an area which is defined by a waveform of each of heartbeat-synchronous
pulses of the volume pulse wave detected by said volume pulse wave
detecting device and is normalized based on a period and an amplitude
of said each pulse of the volume pulse wave;
pulse-wave area change calculating means for calculating a change
of the normalized pulse-wave area values successively calculated
by said normalized pulse-wave area calculating means; and
blood-pressure change identifying means for identifying an abnormal
blood-pressure change of the subject when the change of the normalized
pulse-wave area values is greater than a reference value.
8. A blood pressure monitor apparatus according to claim 7, wherein
said blood-pressure change identifying means comprises means for
controlling said blood pressure measuring device to start a blood
pressure measuring operation upon identification of the abnormal
blood-pressure change.
9. A blood pressure monitor apparatus according to claim 7, further
comprising an indicating device which indicates the abnormal blood-pressure
change of the subject upon identification of the abnormal blood-pressure
change.
10. A blood pressure monitor apparatus according to claim 7, wherein
said volume pulse wave detecting device comprises a photoelectric
pulse-wave sensor including a light-emitting and a light-receiving
element, the light-emitting element adapted to emit, toward a skin
of the subject, a light having a wavelength which can be reflected
by hemoglobin present in blood of the skin, the light-receiving
element adapted to receive the light scattered by the hemoglobin
from the skin, said photoelectric pulse-wave sensor outputting a
photoelectric pulse wave signal representing an instantaneous blood
volume in capillaries of the skin.
11. A blood pressure monitor apparatus according to claim 7, wherein
said volume pulse wave detecting device comprises an impedance pulse-wave
sensor including at least two electrodes adapted to be set on different
locations of a skin of the subject at a predetermined interval,
said impedance pulse-wave sensor outputting an impedance pulse-wave
signal representing an instantaneous blood volume in a tissue of
the skin located between said two electrodes.
Description BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a blood pressure monitor apparatus
which monitors a blood pressure of a living subject based on each
of heartbeat-synchronous pulses.
2. Related art statement
Generally, a blood pressure monitor apparatus which monitors a
blood pressure of a living subject for a considerably long time
includes a cuff being worn on a body portion of the subject and
a blood pressure measuring device which periodically measures a
blood pressure value of the subject by changing a pressing pressure
of the cuff. The blood pressure values measured by the blood pressure
measuring device enjoy high reliability.
However, in the above blood pressure monitor apparatus, if the
interval between successive blood pressure measurements is shortened
for improving the accuracy of blood pressure monitoring, the frequency
of pressing of the cuff is increased and the subject feels more
discomfort. In the case where the frequency of pressing of the cuff
is excessively high, congestion occurs to the body portion of the
subject, and accurate blood pressure values are not obtained.
Further, there has been proposed a blood pressure monitor apparatus
including a blood pressure measuring device for measuring a blood
pressure value of a living subject based on a variation of a pulse-synchronous
wave obtained while a pressing pressure of a cuff is changed, a
pressure pulse-wave sensor adapted to be pressed on an artery of
the subject for detecting a pressure pulse wave produced from the
artery of the subject, a pressure pulse wave-blood pressure relationship
determining means for determining, at a predetermined period, a
pressure pulse wave-blood pressure relationship between magnitude
of pressure pulse wave and blood pressure, based on the pressure
pulse wave detected by the pulse wave sensor and the blood pressure
value measured by the blood pressure measuring device, by starting
the blood pressure measuring device at the predetermined period,
and a monitor blood pressure determining means for successively
determining a monitor blood-pressure value based on an actual pressure
pulse wave detected by the pressure pulse-wave sensor, according
to the pressure pulse wave-blood pressure relationship. An example
of the blood pressure monitor apparatus is disclosed in Laid-Open
Publication No. 2-177937 of unexamined Japanese patent application.
The blood pressure monitor apparatus is capable of determining a
monitor blood-pressure value based on each of heartbeat-synchronous
pulses, thereby performing the blood pressure monitor without any
delay.
However, in the blood pressure monitor apparatus, it is needed
to press the pressure pulse-wave sensor on the artery of the subject
for detecting the pressure pulse-wave produced from the artery of
the subject. To this end, the sensor has to be set on the skin of
the subject right above the artery, such as the skin of a wrist.
Therefore, the use of the sensor may be limited depending on the
affected part of the subject. Further, in the case where the pressure
pulse wave sensor is set with the help of a band, the pressure pulse-wave
signal may be changed because the pressing state of the sensor may
be changed due to, e.g., the body movement of the subject and accordingly
an accurate blood pressure monitor may not be performed.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
blood pressure monitor apparatus which accurately monitors a blood
pressure of a living subject, without the problem of discomfort
felt by the subject.
The inventors of the present invention have continued their study
in the background of the above-described situation. They have found
that a volume-pulse-wave area, e.g., photoelectric-pulse-wave area,
indicative of a periodical change of blood volume in a peripheral
portion of the subject changes in a close relation with a change
of the blood-pressure values of the subject. The photoelectric pulse
wave is obtained from a light reflected by, or transmitted through,
a tissue of the subject when the light which has a wavelength capable
of being reflected by hemoglobin present in blood of the tissue
is emitted toward the tissue. The present invention has been developed
based on this finding, whereby unnecessary blood pressure measurements
using the cuff are avoided by monitoring the change of blood pressure
based on the volume pulse-wave area.
The above object has been achieved by the present invention. According
to a first aspect of the present invention, there is provided a
blood pressure monitor apparatus comprising: (a) a blood pressure
measuring device which includes a cuff adapted to be pressed on
an artery of a living subject and measures a blood pressure value
of the subject by changing a pressing pressure of the cuff; (b)
a volume pulse wave detecting device which detects a volume pulse
wave of the subject; (c) normalized pulse-wave area calculating
means for successively calculating an area which is defined by a
waveform of each of heartbeat-synchronous pulses of the volume pulse
wave detected by the volume pulse wave detecting device and is normalized
based on a period and an amplitude of the each pulse of the volume
pulse wave; (d) pulse wave area-blood pressure relationship determining
means for determining a relationship between pulse-wave area and
blood pressure, based on a normalized pulse-wave area value calculated
by the normalized pulse-wave area calculating means and a blood
pressure value measured by the blood pressure measuring device,
when the blood pressure value is measured; and (e) monitor blood
pressure determining means for successively determining a monitor
blood-pressure value of the subject, based on each of normalized
pulse-wave area values successively calculated by the normalized
pulse-wave area calculating means, according to the pulse wave area-blood
pressure relationship determined by the pulse wave area-blood pressure
relationship determining means.
In the above described blood pressure monitor apparatus, the pulse
wave area-blood pressure relationship determining means determines
a relationship between pulse-wave area and blood pressure, based
on a normalized pulse-wave area value calculated by the normalized
pulse-wave area calculating means and a blood pressure value measured
by the blood pressure measuring device, when the blood pressure
value is measured. The monitor blood pressure determining means
successively determines a monitor blood-pressure value of the subject,
based on each of normalized pulse-wave area values successively
calculated by the normalized pulse-wave area calculating means,
according to the pulse wave area-blood pressure relationship determined
by the pulse wave area-blood pressure relationship determining means.
Thus, the blood pressure monitor apparatus according to the present
invention can obtain a monitor blood-pressure value based on each
of heartbeat-synchronous pulses, so that the apparatus need not
carry out the blood pressure measurements at an unnecessarily short
interval for improving the accuracy of the blood pressure monitor
operation. Thus, the frequency of pressing of the cuff is decreased
and the distress of the subject is minimized. Additionally, the
volume pulse-wave sensor can be easily worn on the subject. Since
the signal detected by the sensor is not affected by the body movement
of the subject or the like, the blood pressure monitor apparatus
can continue the blood pressure monitor operation with accuracy.
According to a preferred feature of the first aspect of the invention,
the monitor blood pressure apparatus further comprises monitor-blood-pressure
abnormality judging means for judging whether each of the monitor-blood-pressure
values successively determined by the monitor blood pressure determining
means does not fall in a reference range, and controlling, when
a negative judgment is made, the blood pressure measuring device
to start a blood pressure measuring operation. In this case, when
the negative judgment is made, the blood pressure measuring device
starts a blood pressure measuring operation so as to update the
pulse wave area-blood pressure relationship. Accordingly, the blood
pressure monitor apparatus can automatically obtain the blood pressure
value measured with higher reliability upon detection of the blood
pressure abnormality and can raise the reliability of the monitor
blood-pressure values obtained after the detection of the abnormality.
According to another feature of the first aspect of the invention,
the blood pressure monitor apparatus further comprises an indicating
device which indicates a trend graph of the monitor-blood-pressure
values successively determined by the monitor blood pressure determining
means. In this case, a medical person can easily recognize the change
of the blood pressure and can accurately diagnose the blood pressure.
According to another feature of the first aspect of the invention,
the indicating device comprises means for indicating that the negative
judgement is made by the monitor-blood-pressure abnormality judging
means. In this case, the medical person can easily recognize the
monitor-blood-pressure abnormality and accurately grasp the condition
of the subject or the operating state of the blood pressure monitor
apparatus.
According to another feature of the first aspect of the invention,
the volume pulse wave detecting device comprises a photoelectric
pulse-wave sensor including a light-emitting and a light-receiving
element, the light-emitting element emitting, toward a skin of the
subject, a light having a wavelength which can be reflected by hemoglobin
present in blood of the skin, the light-receiving element receiving
the light scattered by the hemoglobin from the skin, the photoelectric
pulse-wave sensor outputting a photoelectric pulse wave signal representing
an instantaneous blood volume in capillaries of the skin. In this
case, the light emitted from the light-emitting element may be a
red or an infrared light.
According to another feature of the first aspect of the invention,
the volume pulse wave detecting device comprises an impedance pulse-wave
sensor including at least two electrodes being set on different
locations of the skin of the subject at a predetermined interval,
the impedance pulse-wave sensor outputting an impedance pulse-wave
signal representing an instantaneous blood volume in a tissue of
the skin located between said two electrodes.
According to a second aspect of the present invention, there is
provided a blood pressure monitor apparatus including a blood pressure
measuring device which includes a cuff being set on a body portion
of a living subject and periodically measures a blood pressure value
of the subject, based on a variation of a pulse wave produced while
a pressing pressure of the cuff is changed, the blood pressure monitor
apparatus comprising: (a) a volume pulse wave detecting device which
detects a volume pulse wave of the subject; (b) normalized pulse-wave
area calculating means for successively calculating an area which
is defined by a waveform of each of heartbeat-synchronous pulses
of the volume pulse wave detected by the volume pulse wave detecting
device and is normalized based on a period and an amplitude of the
each pulse of the volume pulse wave; (c) pulse-wave area change
calculating means for calculating a change of the normalized pulse-wave
area values successively calculated by the normalized pulse-wave
area calculating means; and (d) blood-pressure change identifying
means for identifying an abnormal blood-pressure change of the subject
when the change of the normalized pulse-wave area values is greater
than a reference value.
In the blood pressure monitor apparatus in accordance with the
second aspect of the invention, the pulse-wave area change calculating
means calculates a change of the normalized pulse-wave area values
successively calculated by the normalized pulse-wave area calculating
means. The blood-pressure change identifying means identifies an
abnormal blood-pressure change of the subject when the change of
the normalized pulse-wave area values is greater than the reference
value. Thus, the blood pressure monitor apparatus can identify an
abnormal blood-pressure change of the subject based on a change
of the normalized pulse-wave area value calculated based on each
of heartbeat-synchronous pulses, so that the apparatus need not
carry out the blood pressure measurements at an unnecessarily short
interval for improving the accuracy of the blood pressure monitor
operation. Thus, the frequency of pressing of the cuff is decreased
and the distress of the subject is minimized. Additionally, the
volume pulse-wave sensor can be easily worn on the subject. Since
the signal detected by the sensor is not affected by the body movement
of the subject or the like, the blood pressure monitor apparatus
can continue the blood pressure monitor operation with accuracy.
According to another feature of the second aspect of the invention,
the blood-pressure change identifying means comprises means for
controlling the blood pressure measuring device to start a blood
pressure measuring operation upon identification of the abnormal
blood-pressure change. In this case, when the abnormal blood-pressure
change of the subject is identified, the blood pressure measuring
device starts a blood pressure measuring operation using the cuff.
Accordingly, the blood pressure monitor apparatus can automatically
obtain the blood pressure value measured with higher reliability
upon identification of the abnormal blood-pressure change.
BRIEF DESCRIPTION OF THE DRAWINGS
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:
FIG. 1 is a diagrammatic view of a blood pressure monitor apparatus
embodying the present invention;
FIG. 2 is a block diagram for illustrating essential functions
of an electronic control device of the apparatus of FIG. 1;
FIG. 3 is a graph showing a relationship between normalized pulse-wave
area and monitor blood pressure, which is used on the apparatus
of FIG. 1;
FIG. 4 is a view for illustrating a heartbeat-synchronous pulse
of a photoelectric pulse wave detected by a photoelectric pulse-wave
sensor of the apparatus of FIG. 1;
FIG. 5 is a flow chart representing the operation of the electronic
control device of the apparatus of FIG. 1;
FIG. 6 is a view showing respective trend graphs of a monitor blood
pressure VRBP estimated based on a normalized pulse-wave area S.sub.F
by the apparatus of FIG. 1, a systolic blood pressure SBP measured
by a A-LINE direct method and a monitor blood pressure AMPBP estimated
based on an amplitude AMP of each pulse of the photoelectric pulse
wave;
FIG. 7 is a view showing a correlation between the monitor blood
pressure values VRBP and the systolic blood pressure values SBP;
FIG. 8 is a view showing a correlation between the monitor blood
pressure values AMPBP and the systolic blood pressure values SBP;
FIG. 9 is a block diagram for illustrating essential functions
of an electronic control device of a blood pressure monitor apparatus
according to a second embodiment of the present invention;
FIG. 10 is a flow chart representing the operation of the electronic
control device of the apparatus of FIG. 9;
FIG. 11 is a block diagram for illustrating essential functions
of an electronic control device of a blood pressure monitor apparatus
according to a third embodiment of the present invention;
FIG. 12 is a flow chart representing the operation of the electronic
control device of the apparatus of FIG. 11; and
FIG. 13 is a diagrammatic view of a blood pressure monitor apparatus
according to a fourth embodiment of the present invention, which
includes, as a volume pulse-wave sensor, a photoelectric pulse wave
detecting probe of a pulse oximeter.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there will be described a blood pressure (BP)
monitor apparatus 8 embodying the present invention.
In FIG. 1, the BP monitor apparatus 8 includes a cuff which has
a belt-like cloth bag and a rubber bag accommodated in the cloth
bag and which is adapted to be wound around an upper arm 12 of a
patient, for example, and a pressure sensor 14, a selector valve
16 and an air pump 18 each of which is connected to the cuff 10
via a piping 20. The selector valve 16 is selectively placed in
an inflation position in which the selector valve 16 permits a pressurized
air to be supplied to the cuff 10, a slow-deflation position in
which the selector valve 16 permits the pressurized air to be slowly
discharged from the cuff 10, and a quick-deflation position in which
the selector valve 16 permits the pressurized air to be quickly
discharged from the cuff 10.
The pressure sensor 14 detects an air pressure in the cuff 10,
and supplies a pressure signal SP representative of the detected
pressure to each of a static pressure filter circuit 22 and a pulse-wave
filter circuit 24. The static pressure filter circuit 22 includes
a low-pass filter and extracts, from the pressure signal SP, a static
component contained in the signal SP, i.e., cuff pressure signal
SK representative of the static cuff pressure P.sub.C. The cuff
pressure signal SK is supplied to an electronic control device 28
via an analog-to-digital (A/D) converter 26.
The pulse-wave filter circuit 24 includes a band-pass filter and
extracts, from the pressure signal SP, an oscillating component
having predetermined frequencies, i.e., pulse-wave signal SM.sub.1.
The pulse-wave signal SM.sub.1 is supplied to the electronic control
device 28 via an A/D converter 29. The pulse-wave signal SM.sub.1
represents an oscillatory pressure wave which is produced from a
brachial artery (not shown) of the patient in synchronism with the
heartbeat of the patient and is propagated to the cuff 10. The cuff
10, the pressure sensor 14, and the pulse-wave filter circuit 24
cooperate with one another to function as a cuff pulse-wave sensor.
The electronic control device 28 is provided by a so-called microcomputer
including a central processing unit (CPU) 30, a read only memory
(ROM) 32, a random access memory (RAM) 34 and an input-and-output
(I/O) port (not shown). The CPU 30 processes signals according to
control programs pre-stored in the ROM 32 by utilizing a temporary-storage
function of the RAM 34, supplies drive signals to the selector valve
16 and the air pump 18 through the I/O port, and outputs a display
signal to a display device 36 through the I/O port.
The BP monitor apparatus 8 further includes a photoelectric pulse-wave
sensor 40 which has a known construction. The photoelectric pulse-wave
sensor 40 functions as a volume pulse-wave sensor. The sensor 40
includes a housing 42 which is capable of accommodating a body portion
(e.g., finger) of a living subject therein. The housing 42 is provided
with a light-emitting element 44 and a light-receiving element 46
which are opposed to each other on predetermined locations of an
inner surface of the housing. The light-emitting element 44 emits,
toward the finger of the subject, a red or an infrared light having
a wavelength which can be reflected by hemoglobin present in blood
of the finger, and the light-receiving element 46 receives the light
transmitted through the finger. The sensor 40 outputs a photoelectric
pulse wave signal SM.sub.2 representative of an instantaneous amount
of the hemoglobin, that is, instantaneous blood volume in the finger.
The signal SM.sub.2 oscillates or pulsates in synchronism with the
heartbeat of the subject. The signal SM.sub.2 is supplied to the
control device 28 via an A/D converter 48.
FIG. 2 illustrates essential functions of the electronic control
device 28 of the present BP monitor apparatus 8. In the figure,
a cuff pressure regulating means 72 changes a pressing pressure
of the cuff 10 according to a well-known blood pressure measuring
method during a blood pressure measurement of a blood pressure measuring
device 70, which periodically starts a blood pressure measuring
operation for calibrating pulse wave area-blood pressure relationship
shown in FIG. 3. For example, the cuff pressure regulating means
72 increases the cuff pressure to a target value (e.g., 180 mmHg)
which is greater than a systolic blood pressure value of the subject,
and then slowly decreases it at the rate of about 3 mmHg/sec while
a blood pressure measuring algorithm is carried out. Upon termination
of the blood pressure measurement, the cuff pressure regulating
means 72 releases the pressure of the cuff 10. The blood pressure
measuring device 70 measures a systolic, a mean and a diastolic
blood pressure value, BP.sub.SYS, BP.sub.MEAN, BP.sub.DIA, of the
patient, according to a well-known oscillometric method, based on
a variation of respective magnitudes of heartbeat-synchronous pulses
of the pulse-wave signal SM.sub.1 obtained while the cuff pressure
is slowly changed, and controls the display device 36 so as to indicate
the measured blood pressure values.
The photoelectric pulse-wave sensor 40 detects a photoelectric
pulse wave from the finger of the subject which is accommodated
in the housing 42 thereof and outputs the photoelectric pulse wave
signal SM.sub.2 representative of the detected photoelectric pulse
wave. The photoelectric pulse-wave sensor 40 corresponds to the
volume pulse-wave sensor. A normalized pulse-wave area calculating
means 74 successively calculates an area S.sub.F which is defined
by a waveform of each of heartbeat-synchronous pulses of the photoelectric
pulse wave (or signal SM.sub.2) and is normalized based on a period
and an amplitude of the each pulse of the photoelectric pulse wave.
More specifically, as shown in FIG. 4, the waveform of each pulse
of the photoelectric pulse wave is defined by a series of data points
indicative of respective magnitudes of the photoelectric pulse-wave
signal SM.sub.2 which are input to the control device 28 at a predetermined
interval such as several milliseconds to several tens of milliseconds.
A pulse-wave area S is obtained by integrating, in the period W
of the pulse of the photoelectric pulse wave, the respective magnitudes
of the pulse of the photoelectric pulse wave, and then the normalized
pulse-wave area S.sub.F is calculated according to the following
expression: S.sub.F =S/(W.times.L). The normalized pulse-wave area
S.sub.F is a dimensionless value indicative of a ratio of the pulse-wave
area S to an area defined by the period W and the amplitude L of
each pulse of the photoelectric pulse wave. In other cases, a symbol
%MAP may be used in place of the symbol S.sub.F.
A pulse wave area-blood pressure relationship determining means
76 determines, in advance, a relationship between pulse-wave area
and blood pressure, based on a normalized pulse-wave area value
S.sub.F calculated by the normalized pulse-wave area calculating
means 74 and a blood pressure value (one of a systolic, a mean,
and a diastolic blood pressure value, BP.sub.SYS, BP.sub.MEAN, BP.sub.DIA)
measured by the blood pressure measuring device 70, when the blood
pressure value is measured by the device 70. As shown in FIG. 3,
the pulse wave area-blood pressure relationship is represented by,
for example, an expression: VRBP=.alpha..multidot.S.sub.F +.beta.,
where .alpha.is a constant indicative of the slope, .beta. is a
constant indicative of the intercept, and VRBP is a monitor blood-pressure
value. The above expression VRBP=f(S.sub.F) may be determined based
on one set of blood pressure value BP and normalized pulse-wave
area value S.sub.F, and a statistically obtained constant .alpha.
or .beta. which is selected depending upon the sexuality and age
of the subject. Alternatively, the expression VRBP=f(S.sub.F) may
be determined based on at least two sets of blood pressure value
BP and normalized pulse-wave area value S.sub.F. In the latter case,
the constants .alpha., .beta. in the expression are both determined
as values for the specific subject. The one or two constants .alpha.,
.beta. in the expression is or are corrected each time a blood pressure
measurement is carried out by the blood pressure measuring device
70.
A monitor blood pressure determining means 78 successively determines
a monitor blood-pressure value VRBP of the subject, based on each
of the normalized pulse-wave area values S.sub.F successively calculated
by the normalized pulse-wave area calculating means 74, according
to the expression VRBP=f(S.sub.F) determined by the pulse wave area-blood
pressure relationship determining means 76, and controls the display
device 36 to indicate a trend graph of the determined monitor blood-pressure
values VRBP. In the case where one or more systolic blood pressure
values BP.sub.SYS of the subject are used to determine the expression
VRBP=f(S.sub.F), systolic monitor blood-pressure values are successively
determined. Meanwhile, in the case where one or more mean blood
pressure values BP.sub.MEAN are used to determine the expression,
mean monitor blood-pressure values are successively determined;
and in the case where one or more diastolic blood pressure values
BP.sub.DIA are used to determine the expression, diastolic monitor
blood-pressure values are successively determined.
FIG. 5 is a flow chart representing an operation of the electronic
control device 28 of the BP monitor apparatus 8. The control of
the CPU 30 begins with Step SA1 of the flow chart of FIG. 5, where
counters and registers (not shown) are reset. Step SA1 is followed
by Step SA2 to quickly increase the cuff pressure for a blood pressure
measurement, by switching the selector valve 16 to the inflation
position and operating the air pump 18. Step SA2 corresponds to
the cuff pressure regulating means 72.
The control of the CPU 30 goes to Step SA3 corresponding to the
normalized pulse-wave area calculating means 74. At Step SA3, the
CPU 30 successively obtains, based on the photoelectric pulse-wave
signal SM.sub.2 (shown in FIG. 4) detected by the photoelectric
pulse-wave sensor 40, a pulse-wave area S (=S.sub.1 +S.sub.2) defined
by a waveform of each of heartbeat-synchronous pulses of the photoelectric
pulse wave, and calculates a normalized pulse-wave area S.sub.F
based on a period W and an amplitude L of the each pulse of the
photoelectric pulse wave, according to the expression S.sub.F =S/(W.times.L).
Step SA3 is followed by Step SA4 to judge whether or not the cuff
pressure P.sub.C is equal to or greater than a predetermined target
value P.sub.CM (e.g., 180 mmHg). If a negative judgment is made
at Step SA4, the control of the CPU 30 goes back to Step SA2 so
as to continue the increasing of the cuff pressure P.sub.C On the
other hand, if a positive judgment is made at Step SA4, the control
of the CPU 30 goes to Step SA5 to carry out a blood pressure measuring
algorithm. More specifically, the air pump 18 is stopped and the
selector valve 16 is switched to the slow-deflation position where
the selector valve 16 permits the pressurized air to be slowly discharged
from the cuff 10. A systolic blood pressure BP.sub.SYS, a mean blood
pressure value BP.sub.MEAN, and a diastolic blood pressure value
BP.sub.DIA are determined, according to a well known oscillometric
type blood pressure determining algorithm, based on a variation
of respective amplitudes of pulses of the pulse wave represented
by the pulse-wave signal SM.sub.1 obtained while the cuff pressure
is slowly decreased at a predetermined rate of 3 mmHg/sec, and a
pulse rate is determined based on an interval of successive two
pulses of the pulse wave. The thus measured blood pressure values
and pulse rate are indicated on the display device 36, and then
the selector valve 16 is switched to the quick-deflation position
where the selector valve 16 permits the pressurized air to be quickly
discharged from the cuff 10. Step SA5 corresponds to part of the
blood pressure measuring device 70.
Step SA5 is followed by Step SA6 to determine a relationship between
pulse-wave area and blood pressure, based on a normalized pulse-wave
area values successively calculated at Step SA3 and a blood pressure
value measured at Step SA5. More specifically, at Step SA6, the
CPU 30 determines the relationship (the expression: VRBP=.alpha..multidot.S.sub.F
+.beta.) between pulse-wave area and blood pressure, based on an
average of the normalized blood pressure values S.sub.F successively
calculated at Step SA3 and one of the systolic, mean and diastolic
blood pressure values, BP.sub.SYS, BP.sub.MEAN, BP.sub.DIA measured
at Step SA5. Step SA6 corresponds to the pulse wave area-blood pressure
relationship determining means 76.
Step SA6 is followed by Step SA7 to judge whether or not one pulse
of the photoelectric pulse wave has been read in. If a negative
judgment is made at Step SA7, the control of the CPU 30 waits until
a positive judgment is made at Step SA7. If a positive judgment
is made at Step SA7, the control of the CPU 30 goes to Step SA8
corresponding to the normalized pulse-wave area calculating means
74. At Step SA8, the CPU 30 calculates a normalized pulse-wave area
S.sub.F based on the waveform of the one pulse of the photoelectric
pulse wave read in at Step SA7 in the same manner as carried out
at Step SA3.
Step SA8 is followed by Step SA9 to determine a monitor blood-pressure
value VRBP based on the normalized pulse-wave area value S.sub.F
calculated at Step SA8, according the pulse wave area-blood pressure
relationship (VRBP=.alpha..multidot.S.sub.F +.beta.) determined
at Step SA6, and then output the determined monitor blood-pressure
value VRBP to the display device 36 so as to indicate a trend graph
of the monitor blood-pressure values. Step SA9 corresponds to the
monitor blood pressure determining means 78.
Then, the control of CPU 30 goes to Step SA10. At Step SA10, the
CPU 30 judges whether or not a predetermined period (e.g., 15 to
20 minutes), that is, a calibration period, has passed after the
prior blood pressure measurement was carried out at Step SA5. If
a negative judgment is made at Step SA10, the control of the CPU
30 goes back to Step SA7 and the following steps so as to carry
out one or more blood pressure monitor cycles, that is, successively
determine a monitor blood-pressure value VRBP for each of heartbeat-synchronous
pulses, and timewise indicate, on the display device 36, the trend
graph of the determined monitor blood-pressure values VRBP as indicated
at solid line in FIG. 6. On the other hand, if a positive judgment
is made at Step SA10, the control of the CPU 30 goes back to Step
SA2 and the following steps so as to determine a new pulse wave
area-blood pressure relationship (VRBP=.alpha..multidot.S.sub.F
+.beta.).
In the above described embodiment, the pulse wave area-blood pressure
relationship (VRBP=.alpha.S.sub.F +.beta.) between pulse-wave area
and blood pressure is determined by the pulse wave area-blood pressure
relationship determining means 76 (Step SA6), based on a normalized
pulse-wave area S.sub.F calculated by the normalized pulse-wave
area calculating means 74 (Step SA3) and one of blood pressure values
BP.sub.SYS, BP.sub.MEAN , BP.sub.DIA, measured by the blood pressure
measuring device 70 (Step SA5), when the blood pressure values BP.sub.SYS,
BP.sub.MEAN, BP.sub.DIA are measured. The monitor blood-pressure
values VRBP are successively determined by the monitor blood pressure
determining means 78 (Step SA9), based on the normalized pulse-wave
area values S.sub.F successively obtained from the respective waveforms
of heartbeat-synchronous pulses of the photoelectric pulse wave
detected by the photoelectric pulse-wave sensor 40, according to
the pulse wave area-blood pressure relationship determined by the
pulse wave area-blood pressure relationship determining means 76.
Thus, the BP monitor apparatus 8 can obtain a monitor blood-pressure
value from each of heartbeat-synchronous pulses of the signal SM.sub.2,
so that the apparatus need not carry out the blood pressure measurements
at an unnecessarily short interval for improving the accuracy of
the blood pressure monitor operation. Thus, the frequency of pressing
of the cuff is decreased and the distress of the subject is minimized.
Additionally, the photoelectric pulse-wave sensor 40 can be easily
worn on the subject. Since the signal SM.sub.2 detected by the sensor
40 is not affected by the body movement of the subject or the like,
the BP monitor apparatus 8 can continue the blood pressure monitor
operation with accuracy.
In the above described embodiment, the normalized pulse-wave area
S.sub.F is obtained by normalizing the pulse-wave area S defined
by the waveform of each pulse of the photoelectric pulse wave, based
on the period W and the amplitude L of the waveform of the pulse
of the photoelectric pulse wave. Accordingly, the normalized pulse-wave
area S.sub.F is not influenced by the change of the heart rate,
body temperature, or the like, of the subject, whereby the BP monitor
apparatus 8 can obtain reliable monitor blood-pressure values VRBP.
FIG. 6 shows respective trend graphs of the monitor blood pressure
VRBP (systolic blood pressure), a blood pressure SBP (systolic blood
pressure) and another monitor blood pressure AMPBP (systolic blood
pressure), which are indicated at solid line, one-dot chain line
and broken line, respectively. The monitor blood-pressure values
VRBP are determined or estimated based on the normalized pulse-wave
area values S.sub.F. The blood pressure values SBP are measured
by an A-LINE method in which a pressure in a blood vessel of the
subject is directly measured by utilizing a catheter. The monitor
blood-pressure values AMPBP are determined or estimated based on
respective amplitudes AMP of heartbeat-synchronous pulses of the
photoelectric pulse wave, according to a predetermined relationship
between pulse amplitude and blood pressure. FIG. 7 shows a correlation
between monitor blood pressure VRBP and blood pressure SBP. FIG.
8 shows a correlation between monitor blood pressure AMPBP and blood
pressure BP.
As is apparent from FIG. 6, the monitor blood pressure VRBP estimated
based on the normalized pulse-wave area S.sub.F faithfully follows
the blood pressure SBP measured by the A-LINE method, in comparison
with the monitor blood pressure AMPBP estimated based on the pulse
amplitude AMP. That is, the monitor blood pressure VRBP enjoys a
higher correlation with the true blood pressure SBP, than the monitor
blood pressure AMPBP, and done not change so largely as time passes.
Accordingly, in the BP monitor apparatus 8 which determines the
monitor blood pressure VRBP based on the normalized pulse-wave area
S.sub.F, the need to update the pulse wave area-blood pressure relationship
by operating the blood pressure measuring device 70 is minimized.
In FIG. 7, data points indicative of the correlation between the
monitor blood pressure VRBP and the blood pressure SBP are more
normally distributed on the upper and lower side of the straight
line (indicated at solid line) representative of the correlation
coefficient, in comparison with those of FIG. 8 which shows the
correlation between the monitor blood pressure AMPBP and the blood
pressure SBP. Thus, in a wider pressure range, a blood pressure
of the subject can be estimated with high accuracy. That is, the
BP monitor apparatus 8 can obtain monitor blood-pressure values
VRBP with high reliability.
In the above described embodiment, the trend graph of the monitor
blood-pressure values VRBP successively determined by the monitor
blood pressure determining means 78 (Step SA9) is indicated on the
display device 36, so that a doctor can easily recognize any change
of the blood-pressure values and can accurately diagnose the patient.
Next, there will be described another embodiment according to the
present invention. Hereinafter, the same parts as those of the prior
embodiment will be denoted by the same reference numerals and the
description thereof is omitted.
FIG. 9 is a block diagram for explaining essential functions of
an electronic control device 28 of a BP monitor apparatus to which
the second embodiment is applied and which has the same hardware
construction as that of the prior embodiment shown in FIG. 1. FIG.
10 is a flow chart representing a control program according to which
the apparatus of FIG. 9 is operated. The electronic control device
28 shown in FIG. 9 is different from the electronic control device
28 shown in FIG. 2 in that the former device 28 additionally includes
a monitor-blood-pressure abnormality judging means 80 and Steps
SA11 and SA12.
In FIG. 9, the monitor-blood-pressure abnormality judging means
80 judges whether each of the monitor blood-pressure values successively
determined by the monitor blood pressure determining means 78 does
not fall in a predetermined reference range, and controls, when
a negative judgment is made, the blood pressure measuring device
70 to start a blood pressure measuring operation for determining
a new pulse wave area-blood pressure relationship (VRBP=.alpha..multidot.S.sub.F
+.beta.), and the display device 36 to indicate that the negative
judgment is made. The reference range is a criterion for judging
that the blood pressure of the subject has been abnormally changed.
For example, in the case where systolic blood pressure values are
determined as the monitor blood-pressure values VRBP, the reference
range may be the range of 90 to 180 mmHg.
In the flow chart of FIG. 10, at Step SA11, the CPU 30 judges whether
the monitor blood-pressure value VRBP determined at Step SA9 is
abnormal, i.e., does not fall in the reference range. If a negative
judgment is made at Step SA11, the control of the CPU 30 goes to
Step SA10 to judge whether or not the predetermined period has passed
in the same manner as carried out in the prior embodiment. If a
positive judgment is made at Step SA11, the control of the CPU 30
goes to Step SA12 to control the display device 36 to indicate that
the abnormal blood pressure value has been detected. Then, the control
of the CPU 30 goes back to Step SA2 to determine a new pulse wave
area-blood pressure relationship (VRBP=.alpha..multidot.S.sub.F
+.beta.).
In the above described embodiment, the photoelectric pulse-wave
sensor 40 is employed, so that the apparatus 8 can monitor the blood
pressure of the subject without any delay, based on the monitor
blood-pressure value VRBP determined for each of heartbeat-synchronous
pulses, whereby the same effects as those of the prior embodiment
are obtained. Additionally, when the judgment that the monitor blood-pressure
value does not fall in the reference range is made by the monitor-blood-pressure
abnormality judging means 80 (Steps SA11 and SA12), a blood pressure
measuring operation of the blood pressure measuring device 70 (Step
SA5) is started and a new pulse wave area-blood pressure relationship
(VRBP=.alpha..multidot.S.sub.F +.beta.) is determined by the pulse
wave area-blood pressure relationship determining means 76 (Step
SA6). Thus, the BP monitor apparatus can automatically obtain a
blood pressure value with higher reliability upon detection of the
blood pressure abnormality, and the reliability of the monitor blood-pressure
values obtained after the detection of the abnormality is raised.
Next, there will be described still another embodiment according
to the present invention. Hereinafter, the same parts as those of
the prior embodiments will be denoted by the same reference numerals
and the description thereof is omitted.
FIG. 11 is a block diagram for explaining essential functions of
an electronic control device 28 of a BP monitor apparatus to which
the third embodiment is applied and which has the same hardware
construction as that of the first embodiment shown in FIG. 1. FIG.
12 is a flow chart representing a control program according to which
the apparatus of FIG. 11 is operated. The electronic control device
28 shown in FIG. 11 is different from the electronic device 28 shown
in FIG. 2 in that the former device 28 carries out a blood pressure
monitor method different from that carried out by the latter device
28. More specifically, the BP monitor apparatus according to the
third embodiment identifies an abnormal blood-pressure change of
the subject, when a change .DELTA.D of the normalized pulse-wave
area values S.sub.F exceeds a reference value .gamma. while the
blood pressure measurement using the cuff 10 is not carried out.
When the change .DELTA.D of the normalized pulse-wave area values
exceeds the reference value .gamma., the apparatus starts a blood
pressure measuring operation using the cuff 10.
In FIG. 11, a blood pressure measuring device 82 starts, at a predetermined
period T.sub.B, a blood pressure measuring operation using the cuff
10 in the same manner as that in which the BP measuring device 70
does in the prior embodiments, and indicates the measured blood
pressure values on the display device 36. A pulse-wave area change
calculating means 84 calculates a change .DELTA.D of the normalized
pulse-wave area values S.sub.F successively calculated by the normalized
pulse-wave area calculating means 74. The change .DELTA.D may be
a rate or amount of change of the current normalized pulse-wave
area value S.sub.F from a moving average of the normalized pulse-wave
area values S.sub.F, or the normalized pulse-wave area value S.sub.F
calculated in the prior blood pressure measurement of the blood
pressure measuring device 82. A blood-pressure change identifying
means 86 identifies an abnormal blood-pressure change of the subject
when the change .DELTA.D of the normalized pulse-wave area values
S.sub.F is greater than the reference value .gamma.. Upon identification
of the abnormal blood-pressure change, the blood pressure change
identifying means 86 controls the display device 36 to indicate
the abnormal blood-pressure change, and controls the pressure measuring
device 82 to start a blood pressure measuring operation. Thus, the
blood-pressure change identifying means 86 functions as a blood
pressure measurement starting means for starting a blood pressure
measuring operation when the change .DELTA.D of the normalized pulse-wave
area values S.sub.F is greater than the reference value .gamma..
In FIG. 12, at Step SB1, the CPU 30 carries out an initializing
operation in the same manner as carried out at Step SA1. Step SB1
is followed by Step SB2 to judge whether or not a photoelectric
pulse wave has been detected. If a negative judgment is made at
Step SB2, the control of the CPU 30 goes to Step SB3. At Step SB3,
the CPU 30 judges whether or not the predetermined period T.sub.B
has passed after the prior blood pressure measurement was carried
out at Step SB8. For example, the period T.sub.B may be a relatively
long period such as ten and several minutes to several tens of minutes.
If a negative judgment is made at Step SB3, the present routine
is terminated and the control of the CPU 30 goes back to Step SB1.
If a positive judgment is made at Step SB3, the control of the CPU
goes to Step SB8 to carry out a blood pressure measurement using
the cuff 10 according to an oscillometric method, output the measured
systolic and diastolic blood pressure values BP.sub.SYS, BP.sub.DIA,
and terminate the present routine.
If a positive judgment is made at Step SB2, the control of the
CPU 30 goes to Step SB4 to read in the photoelectric pulse wave
detected by the photoelectric pulse-wave sensor 40. Step SB4 is
followed by Step SB5 to calculate a normalized pulse-wave area S.sub.F
in the same manner as carried out at Step SA8. Step SB5 corresponds
to the pulse-wave area calculating means 74. Step SB5 is followed
by Step SB6 to calculate a change .DELTA.D of the normalized pulse-wave
area value S.sub.F. The change .DELTA.D of the normalized pulse-wave
area value S.sub.F may be an absolute value of an amount, S.sub.Fi
-S.sub.FAV, or a rate, (S.sub.Fi -S.sub.FAV)/S.sub.FAV, of change
of the normalized pulse-wave area value S.sub.F to a moving average
S.sub.FAV [=(S.sub.Fi-n + . . . +S.sub.Fi-1 +S.sub.Fi)/(n+1)] of
the normalized pulse-wave area values, or an amount, S.sub.F -S.sub.Fm,
or a rate, (S.sub.F -S.sub.Fm)/S.sub.Fm, of change of the normalized
pulse-wave area value S.sub.F from the normalized pulse-wave area
value S.sub.Fm calculated in the prior blood pressure measurement.
Step SB6 corresponds to the pulse-wave area change calculating means
84.
Step SB6 is followed by Step SB7 to judge whether or not the change
.DELTA.D of the normalized pulse-wave area value S.sub.F is equal
to or greater than the reference value .gamma.. Step SB7 corresponds
to the blood-pressure change identifying means 86. The reference
value .gamma. is experimentally obtained in advance as a criterion
for identifying an abnormal blood-pressure change of the subject.
If a negative judgment is made at Step SB7, the control of the
CPU 30 goes to Step SB3. If a positive judgment is made at Step
SB7, the control of the CPU 30 goes to Step SB8. At Step SB8, the
CPU 30 starts a blood pressure measuring operation and controls
the display device 36 to indicate the abnormal blood-pressure change
in characters or symbols together with the measured blood pressure
value.
In the above described embodiment, the normalized pulse-wave area
value S.sub.F is calculated by the normalized pulse-wave area calculating
meals 74 (Step SB5). A change .DELTA.D of the normalized pulse-wave
area values S.sub.F is calculated by the pulse-wave area change
calculating means 84 (Step SB6). The abnormal blood-pressure change
of the subject is identified by the blood-pressure change identifying
means 86 (Step SB7), when the change .DELTA.D of the normalized
pulse-wave area value S.sub.F is greater than the reference value
.gamma.. Thus, the BP monitor apparatus can identify the abnormal
blood-pressure change of the subject based on the change of the
normalized pulse-wave area value S.sub.F calculated for each pulse
of the photoelectric pulse wave. Accordingly, the present apparatus
need not carry out the blood pressure measurements at an unnecessarily
short interval for improving the accuracy of the blood pressure
monitor operation, whereby the frequency of pressing of the cuff
10 is decreased and the distress of the subject is minimized. Additionally,
the photoelectric pulse-wave sensor 40 can be easily worn on the
body portion of the subject. Since the signal detected by the sensor
40 is not changed by the body movement of the subject or the like,
the BP monitor apparatus can continue the blood pressure monitor
operation with accuracy.
In the above described embodiment, the blood-pressure change identifying
means 86 (Step SB7) controls the blood pressure measuring device
82 to start a blood pressure measuring operation upon identification
of the abnormal blood-pressure change of the subject. Thus, when
the abnormal blood-pressure change of the subject is identified
by the blood-pressure change identifying means 86, the blood pressure
measurement of the blood pressure measuring device 82 is carried
out, so that the BP monitor apparatus can automatically obtain a
blood pressure value with high reliability.
FIG. 13 shows a BP monitor apparatus which employs a photoelectric
pulse wave detecting probe 90 (hereinafter, referred to as the "probe")
as part of a pulse oximeter 88 for measuring an oxygen saturation
in blood of a living subject. The probe 90 functions as the volume
pulse-wave sensor. The probe 90 is adapted to be set on a body surface
38 of the subject, e.g., a forehead of a patient, with the help
of a band (not shown) such that the probe 90 closely contacts the
body surface 38. The probe 90 includes a container-like housing
92 which opens in a certain direction, a first and a second group
of light emitting elements 94a, 94b, such as LEDs (light emitting
diodes), which are disposed on an outer peripheral portion of an
inner bottom surface of the housing 92 (hereinafter, referred to
as the light emitting elements 94 in the case where the first and
second groups of light emitting elements 94a, 94b need not be discriminated
from each other), a light receiving element 96, such as a photodiode
or a phototransister, which is disposed on a central portion of
the inner bottom surface of the housing 92, a transparent resin
98 which is integrally disposed in the housing 92 to cover the light
emitting elements 94 and the light receiving element 96, and an
annular shade member 100 which is disposed between the light emitting
elements 94 and the light receiving element 96, for preventing the
lights emitted toward the body surface 38 by the light emitting
elements 94 and reflected from the body surface 38, from being received
by the light receiving element 96.
The first and second groups of light emitting elements 94a, 94b
emit a red light having about 660 nm wavelength and an infrared
light having about 800 nm wavelength, respectively. The first and
second light emitting elements 94a, 94b alternately emit the red
and infrared lights at a predetermined frequency, according to a
drive current supplied from a drive circuit 101. The lights emitted
toward the body surface 38 by the light emitting elements 94 are
reflected from a body tissue of the subject where a dense capillaries
occur, and the reflected lights are received by the common light
receiving element 96.
The light receiving element 96 outputs, through a low-pass filter
102, a photoelectric pulse-wave signal SM.sub.3 representative of
an amount of the received light. The light receiving element 96
is connected to the low-pass filter 102 via an amplifier or the
like. The low-pass filter 102 eliminates, from the photoelectric
pulse-wave signal SM.sub.3 input thereto, noise having frequencies
higher than that of a pulse wave, and outputs the noise-free signal
SM.sub.3, to a demultiplexer 104. The demultiplexer 104 is alternately
switched according to signals supplied thereto from the electronic
control device 28 in synchronism with the light emissions of the
first and second light emitting element 94a, 94b. Thus, the demultiplexer
104 successively supplies, to an I/O port (not shown) of an electronic
control device 112 of the pulse oximeter 88, an electric signal
SM.sub.R representative of the red light through a sample-and-hold
circuit 106 and an A/D converter 109, and an electric signal SM.sub.IR
representative of the infrared light through a sample-and-hold circuit
108 and an A/D converter 110. The two sample-and-hold circuits 106,
108 hold the electric signals SM.sub.R, SM.sub.IR input thereto,
respectively, and do not output those current signals to the A/D
converters 109, 110, before the prior signals SM.sub.R, SM.sub.IR
are completely converted by the A/D converters 109, 110, respectively.
The electronic control device 112 is connected to a display device
(not shown) so as to display the measured blood oxygen saturation.
The electronic control device 112 is provided by a microcomputer
including a central processing unit (CPU) 114, a random access memory
(RAM) 116 and a read only memory (ROM) 118. The electronic control
device 112 mutually communicate information with the electronic
control device 28. The CPU 114 performs a blood oxygen saturation
measurement, by utilizing the temporary storage function of the
RAM 116 according to the programs pre-stored in the ROM 118, calculates
an oxygen saturation based on the electric signals SM.sub.R, SM.sub.IR,
controls the display device to indicate the measured oxygen saturation,
and outputs, as the volume pulse wave, the electric signal SM.sub.R
or SM.sub.IR representative of a waveform similar to that shown
in FIG. 4 to the electronic control device 28.
The blood oxygen saturation is determined based on an actual ratio
{(V.sub.dR -V.sub.SR)/(V.sub.dR +V.sub.SR)}/{(V.sub.dIR -V.sub.SIR)/(V.sub.dIR
+V.sub.SIR)}, according to a predetermined relationship between
ratio {(V.sub.dR -V.sub.SR)/(V.sub.dR +V.sub.SR }/{(V.sub.dIR -V.sub.SIR)/(V.sub.dIR
+V.sub.SIR)} and blood oxygen saturation. The blood oxygen saturation
determining method is disclosed in U.S. Pat. No. 5,131,391. In the
ratio {(V.sub.dR -V.sub.SR)/(V.sub.dR +V.sub.SR)}/{(V.sub.dIR -V.sub.SIR)/(V.sub.dIR
+V.sub.SIR)} the values V.sub.dR, V.sub.SR respectively represent
an upper and a lower peak value of a waveform of one pulse of the
photoelectric pulse wave obtained from the red light, and the values
V.sub.dIR, V.sub.SIR respectively represent an upper and a lower
peak value of a waveform of one pulse of the photoelectric pulse
wave obtained from the infrared light. The values, V.sub.dR, V.sub.SR
V.sub.dIR -V.sub.SIR, respectively represent amplitudes of alternating
current components of the respective photoelectric pulse waves obtained
from the red and the infrared lights. The values, V.sub.dR +V.sub.SR,
V.sub.dIR +V.sub.SIR, respectively represent double the respective
amplitudes of direct current components of the respective photoelectric
pulse waves obtained from the red and the infrared lights.
While the present invention has been described in its preferred
embodiments by reference to the drawings, it is to be understood
that the invention may otherwise be embodied.
While in the illustrated embodiments the photoelectric pulse-wave
sensor 40 or the blood oxygen saturation detecting probe 90 which
output the electric signals SM.sub.R, SM.sub.lR are employed as
the volume pulse-wave sensor, an impedance pulse-wave sensor which
outputs an impedance pulse-wave signal may be employed. The impedance
pulse-wave sensor includes at least two electrodes being set on
different locations of a skin of a living subject at a predetermined
interval, and outputs the impedance pulse-wave signal representing
an instantaneous blood volume in a tissue of the skin located between
the two electrodes.
In each of the illustrated embodiments shown in FIGS. 2, 9 and
11, a blood pressure of a living subject is monitored based on a
normalized pulse-wave area value SM.sub.F successively calculated
for each pulse of the photoelectric pulse wave. However, the blood
pressure of the subject may be monitored, based on a normalized
pulse-wave area value SM.sub.F calculated every second pulse of
the photoelectric pulse wave, or at an interval such as several
seconds to several tens of seconds.
In each of the illustrated embodiments, a blood pressure of a living
subject is monitored based on a normalized pulse-wave area value
S.sub.F. However, in place of the normalized pulse-wave area value
S.sub.F, one of normalized first and second pulse-wave area values
may be employed. The normalized first pulse-wave area value is calculated
by normalizing a first pulse-wave area S.sub.1 defined by the waveform
of a pulse of the photoelectric pulse wave between a rising point
and an upper peak point of the waveform shown in FIG. 4. The normalized
second pulse-wave area is calculated by normalizing a second pulse-wave
area S.sub.2 which corresponds to the rest that the first pulse-wave
area S.sub.1 is taken away from the pulse-wave area S. Otherwise,
for example, a normalized value I/W which is obtained by normalizing
a width I between two points on the waveform which correspond to
L.multidot.(2/3) may be employed. In short, the BP monitor apparatus
according to the present invention may calculate a value relating
to an area defined by a waveform of each of heartbeat-synchronous
pulses of the volume pulse wave, or a value representative of a
sharpness of an upper peak of the waveform of each pulse of the
volume pulse wave.
In the above described first and second embodiments, the pulse
wave area-blood pressure relationship determining means 76 (Step
SA6) employs, as the relationship between pulse-wave area and blood
pressure, the liner expression (VRBP=.alpha..multidot.S.sub.F +.beta.).
However, a quadratic or higher polynomial expression may be employed,
and one or more correcting terms may be added if necessary.
In each of the above described embodiments, the blood pressure
measuring devices 70, 82 measure a blood pressure value of a living
subject based on a variation of the pulse wave produced while the
cuff pressure P.sub.C is slowly decreased. However, the blood pressure
measuring devices may measure a blood pressure value of the subject
based on a variation of a pulse wave produced while the cuff pressure
P.sub.C is slowly increased.
In each of the above described embodiments, the blood pressure
measuring devices 70, 82 employ the so-called oscillometric method
to measure a blood pressure value of a living subject based on a
variation of a pressure pulse wave produced while the cuff pressure
P.sub.C is changed. However, the blood pressure measuring devices
may employ a so-called Korotokoff-sound method to determine a blood
pressure value of the subject based on the pressing pressure of
the cuff 10 at the time of occurrence or disappearance of Korotokoff-sounds.
It is to be understood that the present invention may be embodied
with other changes and modifications that may occur to those skilled
in the art without departing from the scope of the invention. |