Abstrict
A blood pressure monitor apparatus including a blood pressure measuring
device which includes a cuff and measures a blood pressure value
of a living subject by changing a pressing pressure of the cuff
applied to a body portion of the subject, an estimated blood pressure
determining device for successively determining an estimated blood
pressure value of the subject, based on each of successive sets
of actual pulse-wave propagation information, according to a predetermined
relationship between blood pressure and pulse-wave propagation information,
a pulse period measuring device which successively measures a period
of a pulse of the subject, a peripheral pulse wave detecting device
which detects a peripheral pulse wave from a peripheral body portion
of the subject, a pulse-wave area calculating device for successively
calculating an area defined by a waveform of a pulse of the peripheral
pulse wave detected by the peripheral pulse wave detecting device,
and a blood pressure measurement starting device for starting a
blood pressure measurement of the blood pressure measuring device,
when an amount of change of the estimated blood pressure values
is greater than a first reference value and at least one of an amount
of change of the measured pulse periods and an amount of change
of the calculated pulse-wave areas is greater than a corresponding
one of a second and a third reference value.
Claims
What is claimed is:
1. A blood pressure monitor apparatus comprising:
a blood pressure measuring device which includes a cuff and measures
a blood pressure value of a living subject by changing a pressing
pressure of said cuff applied to a body portion of the subject;
pulse-wave propagation information obtaining means for obtaining
successive sets of actual pulse-wave propagation information;
blood pressure-pulse information relationship determining means
for determining a relationship between blood pressure and pulse-wave
propagation information, based on a blood pressure value measured
by said blood pressure measuring device and a set of pulse-wave
propagation information obtained by said pulse-wave propagation
information obtaining means;
estimated blood pressure determining means for successively determining
an estimated blood pressure value of the subject, based on each
of the successive sets of actual pulse-wave propagation information
obtained by said pulse wave propagation information obtaining means,
according to the relationship between blood pressure and pulse-wave
propagation information determined by said blood pressure-pulse
wave propagation information relationship determining means;
a pulse period measuring device which successively measures a period
of a pulse of the subject;
a peripheral pulse wave detecting device which detects a peripheral
pulse wave from a peripheral body portion of the subject;
pulse-wave area calculating means for successively calculating
an area defined by a waveform of a pulse of the peripheral pulse
wave detected by said peripheral pulse wave detecting device; and
blood pressure measurement starting means for starting a blood
pressure measurement of said blood pressure measuring device, when
an amount of change of the successively estimated blood pressure
values is greater than a first reference value and at least one
of an amount of change of the successively measured pulse periods
and an amount of change of the successively calculated pulse-wave
areas is greater than a corresponding one of a second and third
reference value.
2. A blood pressure monitor apparatus according to claim 1, wherein
said pulse-wave propagation information obtaining means comprises
means for calculating, as said each set of pulse-wave propagation
information, at least one of a propagation time and a propagation
velocity, based on a time difference between a predetermined point
of an electrocardiographic waveform and a predetermined point of
a waveform of a pressure pulse wave or a volume pulse wave detected
from the peripheral body portion of the subject.
3. A blood pressure monitor apparatus according to claim 1, further
comprising an electrocardiographic waveform detecting device which
includes a plurality of electrodes adapted to be put on a body surface
of the subject and detects an electrocardiographic waveform through
the electrodes, wherein said pulse period measuring device comprises
means for measuring, as said period of pulse, an interval between
two successive R-waves of the electrocardiographic waveform.
4. A blood pressure monitor apparatus according to claim 1, wherein
said peripheral 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 body surface
of the subject, a light including a wavelength which can be reflected
by hemoglobin present in blood of the subject, the light-receiving
element receiving the light scattered by the hemoglobin from the
body surface of the subject.
5. A blood pressure monitor apparatus according to claim 1, wherein
said pulse-wave area calculating means comprises means for calculating
the pulse-wave area which is normalized based on a period and an
amplitude of said pulse of the peripheral pulse wave.
6. A blood pressure monitor apparatus according to claim 1, further
comprising a display device which concurrently displays respective
trend graphs of the estimated blood pressure values successively
determined by said estimated blood pressure determining means, the
pulse period values successively measured by said pulse period measuring
device and the pulse-wave area values successively calculated by
said pulse-wave area calculating means.
7. A blood pressure monitor apparatus comprising:
a blood pressure measuring device which includes a cuff and measures
a blood pressure value of a living subject by changing a pressing
pressure of said cuff applied to a body portion of the subject;
pulse-wave propagation information obtaining means for obtaining
successive sets of actual pulse-wave propagation information;
blood pressure-pulse information relationship determining means
for determining a relationship between blood pressure and pulse-wave
propagation information, based on a blood pressure value measured
by said blood pressure measuring device and a set of pulse-wave
propagation information obtained by said pulse-wave propagation
information obtaining means;
estimated blood pressure determining means for successively determining
an estimated blood pressure value of the subject, based on each
of the successive sets of actual pulse-wave propagation information
obtained by said pulse wave propagation information obtaining means,
according to the relationship between blood pressure and pulse-wave
propagation information determined by said blood pressure-pulse
wave propagation information relationship determining means;
a heart rate measuring device which measures a heart rate of the
subject; and
relationship correcting means for correcting said relationship
between blood pressure and pulse-wave propagation information, based
on the heart rate measured by said heart rate measuring device.
8. A blood pressure monitor apparatus according to claim 7, wherein
said relationship comprises a relationship between estimated blood
pressure (EBP) and pulse-wave propagation time (DT) which is represented
by an expression: EBP=.alpha.DT+.beta., and wherein said relationship
correcting means corrects said expression by decreasing an absolute
value of the negative coefficient .alpha. for the pulse-wave propagation
time DT, with the increasing of the heart rate.
9. A blood pressure monitor apparatus according to claim 7, wherein
said relationship comprises a relationship between estimated blood
pressure (EBP) and pulse-wave propagation velocity (V.sub.M) which
is represented by an expression: EBP=.alpha.V.sub.M +.beta., and
wherein said relationship correcting means corrects said expression
by increasing an absolute value of the positive coefficient .alpha.
for the pulse-wave propagation velocity V.sub.M, with the increasing
of the heart rate.
10. A blood pressure monitor apparatus according to claim 9, wherein
said pulse-wave propagation information obtaining means comprises
means for calculating, as said each set of pulse-wave propagation
information, at least one of a propagation time and a propagation
velocity, based on a time difference between a predetermined point
of an electrocardiographic waveform and a predetermined point of
a waveform of a pressure pulse wave or a volume pulse wave detected
from a peripheral body portion of the subject.
11. A blood pressure monitor apparatus according to claim 7, further
comprising:
a pulse period measuring device which successively measures a period
of a pulse of the subject;
a peripheral pulse wave detecting device which detects a peripheral
pulse wave from the peripheral body portion of the subject;
pulse-wave area calculating means for successively calculating
an area defined by a waveform of a pulse of the peripheral pulse
wave detected by said peripheral pulse wave detecting device; and
blood pressure measurement starting means for starting a blood
pressure measurement of said blood pressure measuring device, when
an amount of change of the successively estimated blood pressure
values is greater than a first reference value and at least one
of an amount of change of the successively measured pulse periods
and an amount of change of the successively calculated pulse-wave
areas is greater than a corresponding one of a second and a third
reference value.
12. A blood pressure monitor apparatus according to claim 11, wherein
said peripheral 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 body surface
of the subject, a light including a wavelength which can be reflected
by hemoglobin present in blood of the subject, the light-receiving
element receiving the light scattered by the hemoglobin from the
body surface of the subject.
13. A blood pressure monitor apparatus according to claim 11, wherein
said pulse-wave area calculating means comprises means for calculating
the pulse-wave area which is normalized based on a period and an
amplitude of said pulse of the peripheral pulse wave.
14. A blood pressure monitor apparatus according to claim 11, further
comprising a display device which concurrently displays respective
trend graphs of the estimated blood pressure values successively
determined by said estimated blood pressure determining means, the
pulse period values successively measured by said pulse period measuring
device and the pulse-wave area values successively calculated by
said pulse-wave area calculating means.
15. A blood pressure monitor apparatus according to claim 11, further
comprising an electrocardiographic waveform detecting device which
includes a plurality of electrodes adapted to be put on a body surface
of the subject and detects an electrocardiographic waveform through
the electrodes, wherein said pulse period measuring device comprises
means for measuring, as said period of pulse, an interval between
two successive R-waves of the electrocardiographic waveform.
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 information
on a pulse wave which propagates through an artery of the subject.
2. Related Art Statement
There is known, as information on a pulse wave which propagates
through an artery of a living subject, a pulse-wave propagation
time DT or a pulse-wave propagation velocity V.sub.M (m/s). The
pulse-wave propagation time DT represents a time in which a pulse
wave propagates between predetermined two different locations of
the subject. Additionally, there is known that the pulse-wave propagation
information is, within a predetermined range, substantially proportional
to a blood pressure BP (mmHg) of the subject. Therefore, there has
been proposed a blood pressure monitor apparatus which determines,
in advance, coefficients .alpha., .beta. in an expression: EBP=.alpha.(DT)+.beta.
(where .alpha. is a negative value) or EBP=.alpha.(V.sub.M)+.beta.
(where .alpha. is a positive value), based on a measured blood pressure
value BP of the subject and an obtained pulse-wave propagation time
(DT) or an obtained pulse-wave propagation velocity (V.sub.M), determines
an estimated blood pressure value EBP of the subject, based on each
set of subsequently obtained pulse-wave propagation information,
according to the above mentioned expression, and starts a blood
pressure measurement using a cuff upon detection of abnormality
of the estimated blood pressure value EBP.
However, for the purpose of improving the reliability of the estimated-blood-pressure
abnormality judgment, the above described blood pressure monitor
apparatus employs a large reference range for finding an abnormality
of the estimated blood pressure value EBP, because the relationship
between the blood pressure and the pulse-wave propagation information
changes due to the conditions of a central organ of the subject
(e.g., conditions of cardiac muscle), and/or the conditions of a
peripheral organ of the subject (e.g., hardness of blood vessels
and/or resistance of the same to blood flow). Therefore, in the
blood pressure monitor apparatus, the starting of blood pressure
measuring operation may be delayed in spite of occurrence of abrupt
blood pressure change or the like, so that the accuracy of operation
of the blood pressure monitor is deteriorated.
SUMMERY OF THE INVENTION
It is therefore an object of the present invention to provide a
blood pressure monitor apparatus which monitors, with high accuracy,
a blood pressure of a living subject, based on information on a
pulse wave which propagates through an artery of the subject.
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 and measures a blood pressure
value of a living subject by changing a pressing pressure of the
cuff applied to a body portion of the subject; (b) estimated blood
pressure determining means for successively determining an estimated
blood pressure value of the subject, based on each of successive
sets of actual pulse-wave propagation information, according to
a predetermined relationship between blood pressure and pulse-wave
propagation information; (c) a pulse period measuring device which
successively measures a period of a pulse of the subject; (d) a
peripheral pulse wave detecting device which detects a peripheral
pulse wave from a peripheral body portion of the subject; (e) pulse-wave
area calculating means for successively calculating an area defined
by a waveform of a pulse of the peripheral pulse wave detected by
the peripheral pulse wave detecting device; and (f) blood pressure
measurement starting means for starting a blood pressure measurement
of the blood pressure measuring device, when an amount of change
of the estimated blood pressure values is greater than a first reference
value and at least one of an amount of change of the measured pulse
periods and an amount of change of the calculated pulse-wave areas
is greater than a corresponding one of a second and a third reference
value. The inventors of the present invention have continued their
study in the background of the above described situation, and they
have found that, when either one of the pulse period obtained as
information on the central organ of subject's circulatory system
and the pulse-wave area obtained as information on the peripheral
organ of the circulatory system is employed as a criterion of the
estimated-blood-pressure abnormality judgment, it is possible to
improve greatly the reliability of blood-pressure abnormality judgment.
In the blood pressure monitor apparatus in accordance with the
first aspect of the present invention, the blood pressure measurement
starting means starts a blood pressure measurement of the blood
pressure measuring device, when an amount of change of the estimated
blood pressure values determined by the estimated blood pressure
determining means is greater than the first reference value and
at least one of an amount of change of the measured pulse periods
and an amount of change of the calculated pulse-wave areas is greater
than a corresponding one of the second and the third reference value.
Thus, the present blood pressure monitor apparatus can employ as
small as possible reference values for finding abnormalities and
accordingly identify, without any delay, abrupt blood pressure changes,
in comparison with a conventional blood pressure monitor apparatus
which starts a blood pressure measuring operation, based on only
the judgment of abnormality of estimated blood pressure values.
The reliability of the present blood pressure monitor apparatus
is thus improved.
According to a preferred feature of the first aspect of the invention,
the blood pressure monitor apparatus further comprises pulse-wave
propagation information obtaining means for obtaining the each set
of pulse-wave propagation information.
According to another feature of the first aspect of the invention,
the blood pressure monitor apparatus further comprises blood pressure-pulse
wave propagation information relationship determining means for
determining the relationship between blood pressure and pulse-wave
propagation information, based on a blood pressure value measured
by the blood pressure measuring device and a set of pulse-wave propagation
information obtained by the pulse-wave propagation information obtaining
means.
According to another feature of the first aspect of the invention,
the pulse-wave propagation information obtaining means comprises
means for calculating, as the each set of pulse-wave propagation
information, at least one of a propagation time and a propagation
velocity, based on a time difference between a predetermined point
of an electrocardiographic waveform and a predetermined point of
a waveform of a pressure pulse wave or a volume pulse wave detected
from the peripheral body portion of the subject. In this particular
case, the present monitor apparatus can obtain a large time difference
in comparison with that obtained in the case where two pressure
pulse wave sensors are set on different locations above on an artery
of the subject. Thus, the accuracy of the pulse-wave propagation
time and/or the pulse-wave propagation velocity improves.
According to another feature of the first aspect of the invention,
the blood pressure monitor apparatus further comprises an electrocardiographic
waveform detecting device which includes a plurality of electrodes
adapted to be put on a body surface of the subject and detects an
electrocardiographic waveform through the electrodes. In this case,
the pulse period measuring device may measure, as a pulse period,
a time difference between respective predetermined points (e.g.,
R-waves) of successive two pulses of the electrocardiographic waveform
detected by the electrocardiographic waveform detecting device.
According to another feature of the first aspect of the invention,
the peripheral 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 body surface
of the subject, a light including a wavelength which can be reflected
by hemoglobin present in blood of the subject, the light-receiving
element receiving the light scattered by the hemoglobin from the
body surface of the subject. In this case, the present apparatus
can easily obtain a photoelectric pulse wave representative of the
pulse-synchronous change of blood volume, that is, a volume pulse
wave.
According to another feature of the first aspect of the invention,
the pulse-wave area calculating means comprises means for calculating
the pulse-wave area which is normalized based on a period and an
amplitude of the pulse of the peripheral pulse wave. In this case,
the blood pressure monitor apparatus can obtain a pulse-wave area
value free from timewise changes or individual differences.
According to another feature of the first aspect of the invention,
the blood pressure monitor apparatus further comprises a display
device which concurrently displays respective trend graphs of the
estimated blood pressure values successively determined by the estimated
blood pressure determining means, the pulse period values successively
measured by the pulse period measuring device and the pulse-wave
area values successively calculated by the pulse-wave area calculating
means. Since the three trend graphs are concurrently displayed on
the display device, it is possible for a medical person to ascertain
the reason of the starting of the blood pressure measurement by
the blood pressure measurement starting means and to easily monitor
the dynamic condition of the circulatory organ of the subject while
the blood pressure measurements of the blood pressure measuring
device are not carried out.
According to a second aspect of the present invention, there is
provided a blood pressure monitor apparatus comprising: (a) a blood
pressure measuring device which includes a cuff and measures a blood
pressure value of a living subject by changing a pressing pressure
of the cuff applied to a body portion of the subject; (b) estimated
blood pressure determining means for successively determining an
estimated blood pressure value of the subject, based on each of
successive sets of actual pulse-wave propagation information, according
to a predetermined relationship between blood pressure and pulse-wave
propagation information; (g) a heart rate measuring device which
measures a heart rate of the subject; and (f) relationship correcting
means for correcting the predetermined relationship between blood
pressure and pulse-wave propagation information, based on the heart
rate measured by the heart rate measuring device. The present inventors
have found that, when the relationship between blood pressure and
pulse-wave propagation information is corrected by utilizing the
heart rate obtained as information on the central organ of the circulatory
system, it is possible to improve greatly the reliability of the
blood pressure monitor apparatus.
In the blood pressure monitor apparatus in accordance with the
second aspect of the invention, the relationship correcting means
corrects the predetermined relationship between blood pressure and
pulse-wave propagation information, based on the heart rate measured
by the heart rate measuring device. Therefore, the accuracy of the
estimated blood pressure values is improved, whereby the reliability
of the blood pressure monitor increases.
According to a preferred feature of the second aspect of the invention,
the predetermined relationship comprises a relationship between
estimated blood pressure (EBP) and pulse-wave propagation time (DT)
which is represented by an expression: EBP=.alpha.DT+.beta., and
the relationship correcting means corrects the expression by decreasing
an absolute value of the negative coefficient a for the pulse-wave
propagation time DT, with the increasing of the heart rate.
According to another feature of the second aspect of the invention,
the predetermined relationship comprises a relationship between
estimated blood pressure (EBP) and pulse-wave propagation velocity
(V.sub.M) which is represented by an expression: EBP=.alpha.V.sub.M
+.beta., and the relationship correcting means corrects the expression
by increasing an absolute value of the positive coefficient .alpha.
for the pulse-wave propagation velocity V.sub.M, with the increasing
of the heart rate.
In each of the above two cases, the relationship correcting means
corrects the relationship so that the estimated blood pressure value
increases with the increasing of the heart rate HR, whereby the
accuracy of the estimated blood pressures and the reliability of
the blood pressure monitor are raised.
According to another feature of the second aspect of the invention,
the blood pressure monitor apparatus further comprising: (c) a pulse
period measuring device which successively measures a period of
a pulse of the subject; (d) a peripheral pulse wave detecting device
which detects a peripheral pulse wave from the peripheral body portion
of the subject; (e) pulse-wave area calculating means for successively
calculating an area defined by a waveform of a pulse of the peripheral
pulse wave detected by the peripheral pulse wave detecting device;
and (f) blood pressure measurement starting means for starting a
blood pressure measurement of the blood pressure measuring device,
when an amount of change of the estimated blood pressure values
is greater than a first reference value and at least one of an amount
of change of the measured pulse periods and an amount of change
of the calculated pulse-wave areas is greater than a corresponding
one of a second and a third reference value.
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 monitor apparatus
embodying the present invention;
FIG. 2 is a block diagram for illustrating essential functions
of an electronic control device 28 of the apparatus of FIG. 1;
FIG. 3 is a view to show a time difference DT.sub.RP obtained by
the operation of the electronic control device 28;
FIG. 4 is a view to show respective trend graphs of estimated blood
pressure values EBP, pulse period values RR and pulse-wave area
values VR obtained on the apparatus of FIG. 1, which are concurrently
displayed on a display device;
FIG. 5 is a view for explaining a normalization of the pulse-wave
area VR;
FIG. 6 is a flow chart representing a control program according
to which the apparatus of FIG. 1 is operated;
FIG. 7 is a flow chart representing a blood pressure measurement
starting judgment routine carried out at Step SA10 of FIG. 6;
FIG. 8 is a block diagram for explaining essential functions of
an electronic control device of a blood pressure monitor apparatus
according to another embodiment of the invention;
FIG. 9 is a view for illustrating changes of a coefficient for
a pulse-wave propagation time DT.sub.RP in the relationship between
estimated blood pressure EBP and pulse-wave propagation time DT.sub.RP
;
FIG. 10 is a view for illustrating changes of a coefficient for
a pulse-wave propagation velocity V.sub.M in the relationship between
estimated blood pressure EBP and pulse-wave propagation velocity
V.sub.M ;
FIG. 11 is a flow chart representing a relationship correcting
routine carried out by the electronic control device 28 of the blood
pressure monitor apparatus shown in FIG. 8; and
FIG. 12 is a time chart representing the operation of the electronic
control device 28 of the blood pressure monitor apparatus shown
in FIG. 8.
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 10 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, 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. 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 30. 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 electronic control device 28 is provided by a so-called microcomputer
including a central processing unit (CPU) 29, a read only memory
(ROM) 31, a random access memory (RAM) 33 and an input-and-output
(I/O) port (not shown). The CPU 29 processes signals according to
control programs pre-stored in the ROM 31 by utilizing a temporary-storage
function of the RAM 33, and supplies drive signals to the selector
valve 16 and the air pump 18 through the I/O port.
The BP monitor apparatus 8 further includes an electrocardiographic
(ECG) waveform detecting device 34 which continuously detects an
ECG waveform representative of an action potential of a cardiac
muscle of a living subject, through a plurality of electrodes 36
being put on predetermined portions of the subject, and supplies
an ECG waveform signal SM.sub.2 representative of the detected ECG
waveform to the electronic control device 28. The ECG waveform detecting
device 34 is used for detecting a Q-wave or a R-wave of the ECG
waveform which corresponds to a time point when the output of blood
from the heart of the subject toward the aorta of the subject is
started. Thus, the ECG waveform detecting device 34 functions as
a first pulse wave detecting device.
The BP monitor apparatus 8 still further includes a photoelectric
pulse wave detecting probe 38 (hereinafter, referred to as the "probe")
which is employed as part of a pulse oximeter. The probe 38 may
function as a second pulse wave detecting device or a peripheral
pulse wave detecting device for detecting a pulse wave propagated
to a peripheral artery including capillaries. The probe 38 is adapted
to be set on a skin or a body surface 40 of the subject, e.g., an
end portion of a finger of the patient, with the help of a band
(not shown) such that the probe 38 closely contacts the body surface
40. The probe 38 includes a container-like housing 42 which opens
in a certain direction, a first and a second group of light emitting
elements 44a, 44b, such as LEDs (light emitting diodes), which are
disposed on an outer peripheral portion of an inner bottom surface
of the housing 42 (hereinafter, referred to as the light emitting
elements 44 in the case where the first and second group of light
emitting elements 44a, 44b need not be discriminated from each other),
a light receiving element 46, such as a photodiode or a phototransister,
which is disposed on a central portion of the inner bottom surface
of the housing 42, a transparent resin 48 which is integrally disposed
in the housing 42 to cover the light emitting elements 44 and the
light receiving element 46, and an annular shade member 50 which
is disposed between the light emitting elements 44 and the light
receiving element 46, for preventing the lights emitted toward the
body surface 40 by the light emitting elements 44 and reflected
from the body surface 40, from being received by the light receiving
element 46.
The first and second groups of light emitting elements 44a, 44b
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 44a, 44b alternately emit the red
and infrared lights at a predetermined frequency. The lights emitted
toward the body surface 40 by the light emitting elements 44 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 46. In place of the 660 nm and 800 nm wavelengths
lights, the first and second light emitting elements 44a, 44b may
employ various pairs of lights each pair of which have different
wavelengths, so long as one light of each pair exhibits significantly
different absorption factors with respect to oxygenated hemoglobin
and reduced hemoglobin, respectively, and the other light exhibits
substantially same absorption factors with respect to the two sorts
of hemoglobin, i.e., has a wavelength which is reflected by each
of the two sorts of hemoglobin.
The light receiving element 46 outputs, through a low-pass filter
52, a photoelectric pulse-wave signal SM.sub.3 representative of
an amount of the received light. The light receiving element 46
is connected to the low-pass filter 52 via an amplifier or the like.
The low-pass filter 52 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 54. The photoelectric pulse wave represented
by the photoelectric pulse-wave signal SM.sub.3 can be said as a
volume pulse wave produced in synchronism with a pulse of the patient.
That is, the photoelectric pulse wave is a pulse-synchronous wave.
The demultiplexer 54 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
elements 44a, 44b. Thus, the demultiplexer 54 successively supplies,
to the I/O port (not shown) of the electronic control device 28,
an electric signal SM.sub.R representative of the red light through
a first sample-and-hold circuit 56 and an A/D converter 58, and
an electric signal SM.sub.IR representative of the infrared light
through a second sample-and-hold circuit 60 and an A/D converter
62. The first and second sample-and-hold circuits 56, 60 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 58,
62, before the prior signals SM.sub.R, SM.sub.IR are completely
converted by the two A/D converters 58, 62, respectively.
In the electronic control device 28, the CPU 29 carries out a measuring
operation according to control programs pre-stored in the ROM 31
by utilizing a temporary-storage function of the RAM 33. More specifically,
the CPU 29 generates a light emit signal SLV to a drive circuit
64 so that the first and second light emitting elements 44a, 44b
alternately emit the red and infrared lights at a predetermined
frequency, respectively, such that each light emission lasts for
a predetermined period. In synchronism with the alternate light
emissions by the first and second light emitting elements 44a, 44b,
the CPU 29 generates a switch signal SC to the demultiplexer 54
so as to correspondingly place the demultiplexer 54 in a first or
a second position. Thus, the signals SM.sub.R, SM.sub.IR are separated
from each other by the demultiplexer 54 such that the signal SM.sub.R
is supplied to the first sample-and-hold circuit 56 while the signal
SM.sub.IR is supplied to the second sample-and-hold circuit 60.
Further, the CPU 29 determines an oxygen saturation in the blood
of the subject, based on respective amplitudes of the signals SM.sub.R,
SM.sub.IR, according to a predetermined expression pre-stored in
the ROM 31. The blood oxygen saturation determining method is disclosed
in U.S. Pat. No. 5,131,391.
FIG. 2 illustrates essential functions of the electronic control
device 28 of the present BP monitor apparatus 8. In the figure,
a 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 subject, according to a well-known oscillometric method,
based on variation of respective magnitudes of pulses of the pulse
wave represented by the pulse-wave signal SM.sub.1 obtained while
the cuff pressure which is quickly increased, by a cuff pressure
regulating means 72, to a target value P.sub.CM (e.g., 180 mmHg),
is slowly decreased at the rate of about 3 mmHg/sec.
A pulse-wave propagation information obtaining means 74 includes
a time-difference calculating means for calculating, as a pulse-wave
propagation time DT.sub.RP, a time difference between a predetermined
point (e.g., R-wave) of the ECG waveform of each of periodic pulses
successively detected by the ECG waveform detecting device 34 and
a predetermined point (e.g., rising point or minimum point) of the
waveform of a corresponding one of periodic pulses of the photoelectric
pulse wave detected by the probe 38, as shown in FIG. 3. The pulse-wave
propagation information obtaining means 74 further calculates a
pulse-wave propagation velocity V.sub.M (m/sec) of the pulse wave
propagated through the artery of the patient, based on the calculated
pulse-wave propagation time DT.sub.RP, according to the following
expression (1) pre-stored in the ROM 31:
where L (m) is a length of the artery as measured from the left
ventricle to the position at which the probe 38 is set, via the
aorta; and T.sup.PEP (sec) is a pre-ejection period between the
R-wave of the ECG waveform of each pulse and the minimum point of
the waveform of a corresponding pulse of the photoelectric pulse
wave. The values L and T.sub.PEP are constants, respectively, and
are experimentally obtained in advance.
A blood pressure-pulse wave propagation information relationship
determining means 76 determines, in advance, two coefficients .alpha.,
.beta. in the following expressions (2) and (3), based on the systolic
blood pressure value BP.sub.SYS measured by the blood pressure measuring
device 70 and either one of the pulse-wave propagation time DT.sub.RP
and the pulse-wave propagation velocity V.sub.M (e.g., either one
of respective average values of the pulse-wave propagation time
values DT.sub.RP and the pulse-wave propagation velocity values
V.sub.M obtained during each blood pressure measurement). The expressions
(2) and (3) respectively show a relationship between systolic blood
pressure BP.sub.SYS and pulse-wave propagation time DT.sub.RP, and
a relationship between systolic blood pressure BP.sub.SYS and pulse-wave
propagation velocity V.sub.M. In place of the relationship between
systolic blood pressure BP.sub.SYS and either one of the pulse-wave
propagation time DT.sub.RP and the pulse-wave velocity V.sub.M,
a relationship between a mean or a diastolic blood pressure measured
by the blood pressure measuring device 70 and either one of the
pulse-wave propagation time DT.sub.RP and the pulse-wave velocity
V.sub.M may be employed. In short, the blood pressure-pulse wave
propagation information relationship may be determined depending
upon which one of the systolic, mean and diastolic blood pressure
value is selected as a monitor (estimated) blood pressure value
EBP.
where .alpha. is a negative constant and .beta. is a positive constant.
where .alpha. is a positive constant and .beta. is a positive constant.
An estimated blood pressure determining means 78 successively determines
the estimated blood pressure value EBP of the subject, based on
either one of the actual pulse-wave propagation time DT.sub.RP and
pulse-wave propagation velocity V.sub.M successively obtained by
the pulse-wave propagation information obtaining means 74, according
to the blood pressure-pulse wave propagation information relationship
(represented by the expression (2) or (3)). The control device 28
controls a display device 32 to concurrently display the thus determined
estimated blood pressure values EBP together with pulse period values
RR and pulse-wave area values VR (which will be described below)
in respective trend graphs along the common axis representative
of time, as shown in FIG. 4.
A pulse period measuring device 82 measures a pulse period RR by
measuring a time difference between respective predetermined points
(e.g., R-waves) of successive two pulses of the ECG waveform detected
by the ECG waveform detecting device 34. A pulse-wave area calculating
means 84 calculates a pulse-wave area VR by normalizing an area
S defined by a waveform of each pulse of the photoelectric pulse
wave which is detected by the probe 38, based on a period W and
an amplitude L of the pulse of the photoelectric pulse wave. More
specifically, as shown in FIG. 5, the waveform of each pulse of
the photoelectric pulse wave is defined by a series of data points
indicative of respective magnitudes which are input at a predetermined
interval such as several milliseconds to several tens of milliseconds.
The 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 being input at the
predetermined interval, and then the normalized pulse-wave area
VR is obtained by calculating the following expression: VR=S/(W.times.L).
The normalized pulse-wave area VR is a dimensionless value indicative
of a ratio of the pulse-wave area 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
VR.
A blood-pressure measurement starting means 86 starts a blood-pressure
measurement of the blood pressure measuring device 70, when an amount
of change of the estimated blood pressure value EBP is greater than
a first reference value and at least one of an amount of change
of the measured pulse period RR and an amount of change of the calculated
pulse-wave area VR is greater than a corresponding one of a second
and a third reference value. For instance, the blood-pressure measurement
starting means 86 includes an estimated-blood-pressure-abnormality
judging means 87 for judging that an estimated blood pressure EBP
determined by the estimated blood pressure determining means 78
is abnormal when the estimated blood pressure value EBP is, by not
less than a predetermined first value or a predetermined first ratio,
greater or smaller than an actual blood pressure value determined
in the prior blood pressure measurement using the cuff 10, a pulse-period-abnormality
judging means 88 for judging that a pulse period RR measured by
the pulse period measuring device 82 is abnormal when the pulse
period RR is, by not less than a predetermined second value or a
predetermined second ratio, greater or smaller than a pulse period
measured in the prior blood pressure measurement using the cuff
10, and a pulse-wave-area-abnormality judging means 89 for judging
that a pulse-wave area VR calculated by the pulse-wave area calculating
means 84 is abnormal when the pulse-wave area VR is, by not less
than a predetermined third value or a predetermined third ratio,
greater or smaller than a pulse-wave area calculated in the prior
blood pressure measurement using the cuff 10. Each of the first,
second, and third ratios is predetermined based on a corresponding
one of the blood pressure value, pulse period, and pulse-wave area
obtained in the prior blood pressure measurement. Thus, when the
estimated-blood-pressure-abnormality judging means 87 judges that
an estimated blood-pressure value EBP is abnormal and at least one
of the pulse-period-abnormality judging means 88 and the pulse-wave-area-abnormality
judging means 89 judges that a corresponding one of a pulse period
RR and a pulse-wave area VR is abnormal, the blood-pressure measurement
starting means 86 starts a blood-pressure measurement of the blood
pressure measuring device 70.
Next, there will be described the operation of the control device
28 of the BP monitor apparatus 8 by reference to the flow charts
of FIGS. 6 and 7.
The control of the CPU 29 begins with Step SA1 of the flow chart
of FIG. 6, where flags, a counter and a register (which are not
shown) are reset. Step SA1 is followed by Step SA2 to calculate,
as a pulse-wave propagation time DT.sub.RP, a time difference between
a R-wave of the ECG waveform of a pulse and a rising point of the
waveform of a corresponding pulse of the photoelectric pulse wave
obtained before the increasing of the cuff pressure, and then calculate
a pulse-wave propagation velocity V.sub.M (m/sec) based on the calculated
pulse-wave propagation time DT.sub.RP according to the expression
(1) before the increasing of the cuff pressure. Step SA2 corresponds
to the pulse-wave propagation information obtaining means 74.
The control of the CPU 29 goes to Steps SA3 and SA4 corresponding
to the cuff pressure regulating means 72. At Step SA3, the CPU 29
starts 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 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 judgement is made at Step SA4, the control
of the CPU 29 goes back to Step SA2 so as to continue to increase
the cuff pressure P.sub.C.
If a positive judgement is made at Step SA4, the control of the
CPU 29 goes to Step SA5 to carry out a blood pressure measuring
algorithm. More specifically, the air pump 18 is stopped and the
selector value 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 value 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 the 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 about 3 mmHg/sec,
and a pulse rate is determined based on the interval of successive
two pulses of the pulse wave. The thus measured blood pressure values
and pulse rate are displayed on the display device 32, and 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.
Next, Step SA5 is followed by Step SA6 to determine a blood pressure-pulse
wave propagation information relationship between one of the blood
pressure values BP.sub.SYS, BP.sub.MEAN, BP.sub.DIA measured at
Step SA5 and one of the pulse-wave propagation time DT.sub.RP and
the pulse-wave propagation velocity V.sub.M calculated at Step SA2.
More specifically, when at Step SA5 the blood pressure values BP.sub.SYS,
BP.sub.MEAN, BP.sub.DIA are measured, then at Step SA6 the relationship
(the expression (2) or (3)) between estimated blood pressure EBP
and one of the pulse-wave propagation time DT.sub.RP and the pulse-wave
propagation velocity V.sub.M is determined, based on one of the
blood pressure values BP.sub.SYS, BP.sub.MEAN, BP.sub.DIA and one
of the pulse-wave propagation time DT.sub.RP and propagation velocity
V.sub.M. Step SA6 corresponds to the pulse wave propagation information-blood
pressure relationship determining means 76.
Step SA6 is followed by Step SA7 to judge whether or not the R-wave
of the ECG waveform of a pulse and the waveform of a corresponding
pulse of the photoelectric pulse wave have been read in. If a negative
judgment is made at Step SA7, the control of the CPU 29 waits until
a positive judgment is made at Step SA7. If a positive judgment
is made at Step SA7, the control of the CPU 29 goes to Step SA8
corresponding to the pulse-wave propagation information obtaining
means 74. At Step SA8, the CPU 29 calculates a pulse-wave propagation
time DT.sub.RP and a pulse-wave propagation velocity V.sub.M based
on the R-wave of the ECG waveform and the waveform of the photoelectric
pulse wave read in at Step SA7 in the same manner as carried out
at Step SA2.
Step SA8 is followed by Step SA9 corresponding to the estimated
blood pressure determining means 78. At Step SA9, the CPU 29 determines
an estimated blood pressure value EBP (a systolic, a mean or a diastolic
blood pressure value), based on one of the pulse-wave propagation
time DT.sub.RP and the pulse-wave propagation velocity V.sub.M calculated
at Step SA8, according to the blood pressure-pulse wave propagation
information relationship determined at Step SA6. Further, the CPU
29 displays, on the display device 32, a trend graph of the estimated
blood pressure values EBP determined for respective pulses of the
ECG waveform and the photoelectric pulse wave.
Step SA9 is followed by Step SA10 to start a blood pressure measurement
of the blood pressure measuring device 70, when the estimated blood
pressure value EBP is greater than the first reference value and
at least one of the measured pulse period RR and the calculated
pulse-wave area VR is greater than a corresponding one of the second
and the third reference value, as a result of the execution of a
blood pressure measurement starting judgment routine shown in FIG.
7. Step SA10 corresponds to the blood-pressure measurement starting
means 86.
At Step SA101 of the flow chart of FIG. 7, the CPU 29 measures
the pulse period RR from the ECG waveform detected by the ECG waveform
detecting device 34. Step SA101 corresponds to the pulse period
measuring device 82. Step SA101 is followed by Step SA102 corresponding
to the pulse-period-abnormality judging means 88. At Step SA102,
the CPU 29 judges whether or not the measured pulse period RR is
abnormal. For instance, the CPU 29 judges that the pulse period
is abnormal when a state in which the pulse period RR measured at
Step SA101 is, by not less than a predetermined value or a predetermined
ratio (e.g., .+-.5%), greater or smaller than a pulse period measured
in the prior blood pressure measurement using the cuff 10 continues
during a time period corresponding to more than a predetermined
number of pulses (e.g., 20 pulses). If a negative judgment is made
at Step SA102, the control of the CPU 29 goes to Step SA104. If
a positive judgment is made at Step SA102, the control goes to Step
SA103 where a RR flag is set "ON" so as to indicate the
abnormality of the pulse period RR.
Step SA103 is followed by Step SA104 to calculate the normalized
pulse-wave area VR from the photoelectric pulse wave detected by
the probe 38. Step SA104 corresponds to the pulse-wave area calculating
means 84. Step SA104 is followed by Step SA105 to judge whether
or not the photoelectric pulse wave detected from the peripheral
portion (i.e., finger) of the subject is normal. At Step SA105,
the CPU 29 eliminates an abnormal waveform of the photoelectric
pulse wave. In any rate, the CPU 29 eliminates the waveform of the
photoelectric pulse wave when an inclination of a base line of the
waveform is greater than a predetermined value, or the waveform
changes due to a calibration of the present monitor 8. If a negative
judgment is made at Step SA105, the control of the CPU 29 goes to
Step SA110. On the other hand, if a positive judgement is made at
Step SA105, the control of the CPU 29 goes to Step SA106.
At Step SA106 corresponding to the pulse-wave-area-abnormality
judging means 89, the CPU 29 judges whether or not the normalized
pulse-wave area VR calculated at Step SA104 is abnormal. For instance,
the CPU 29 judges the pulse-wave area is abnormal when a state in
which the pulse-wave area VR is, by not less than a predetermined
value or a predetermined ratio (e.g., .+-.3%), greater or smaller
than a pulse-wave area calculated in the prior blood pressure measurement
continues during a time period corresponding to more than a predetermined
number of pulses (e.g., 20 pulses). If a negative judgment is made
at Step SA106, the control of CPU 29 goes to Step SA108. If a positive
judgment is made at Step SA106, the control of the CPU 29 goes to
Step SA107 where a VR flag is set "ON" so as to indicate
the abnormality of the pulse-wave area VR.
Next, Step SA107 is followed by Step SA108 corresponding to the
estimated-blood-pressure-abnormality judging means 87. At Step SA107,
the CPU 29 judges whether or not the estimated blood pressure value
EBP determined at Step SA9 is abnormal. For instance, the CPU 29
judges that the estimated blood pressure is abnormal when a state
in which the estimated blood pressure value EBP is, by not less
than a predetermined value or a predetermined ratio (e.g., .+-.30%),
greater or smaller than an actual blood pressure value determined
in the prior blood pressure measurement continues during a time
period corresponding to more than a predetermined number of pulses
(e.g., 20 pulses). If a negative judgment is made at Step SA108,
the control of the CPU 29 goes to Step SA11O. If a positive judgment
is made at Step SA108, the control of the CPU 29 goes to Step SA109
where an EBP flag is set "ON" so as to indicate the abnormality
of the estimated blood pressure value.
Step SA109 is followed by Step SA110 to judge whether or not the
EBP flag is "ON" and at least one of the RR flag and the
VR flag is "ON". If a negative judgment is made at Step
SA110, the control of the CPU 29 goes to Step SA11. At the Step
SA 11, the CPU 29 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. If a negative judgment is
made at Step SA11, the control of the CPU 29 goes back to Step SA7
and the following steps so as to carry out the blood pressure monitor
routine, that is, determine an estimated blood pressure value EBP
for each pulse, and timewise display, on the display device 32,
the trend graph of the determined estimated blood pressures EBP.
On the other hand, if a positive judgment is made at Step SA11,
the control of the CPU 29 goes back to Step SA2 and the following
steps so as to determine a new blood pressure-pulse wave propagation
information relationship between blood pressure and pulse-wave propagation
information.
Meanwhile, if a positive judgment is made at Step SA110, the control
of the CPU 29 goes to Step SA12 shown in FIG. 6. At Step SA12, the
CPU 29 displays the estimated-blood-pressure abnormality on the
display device 32. Then, the control of the CPU 29 goes back to
Step SA2 to start a blood pressure measurement using the cuff 10
so as to determine a new blood pressure-pulse wave propagation information
relationship between blood pressure and pulse-wave propagation information.
In the above described embodiment, the blood pressure measurement
of the blood pressure measuring device 70 is started by the blood
pressure measurement starting means 86 (Steps SA101 to SA110), when
the amount of change of the estimated blood pressure value EBP determined
by the estimated blood pressure determining means 78 (Step SA9)
is greater than the first reference value and at least one of the
amount of change of the pulse period RR measured by the pulse period
measuring device 82 (Step SA101) and the amount of change of the
pulse-wave area VR calculated by the pulse-wave area calculating
means 84 (Step SA104) is greater than a corresponding one of the
second and third reference values. Thus, the BP monitor apparatus
can employ as small as possible reference values for finding abnormalities,
and can identify, without any delay, an unexpected blood pressure
change and find an abnormality of the blood pressure. Thus, the
reliability of the blood pressure monitor 8 improves, in comparison
with a conventional BP monitor apparatus which starts a blood pressure
measurement of a blood pressure measuring device, based on only
the abnormality of an estimated blood pressure.
In the above described embodiment, the pulse-wave area calculating
means 84 (Step SA104) calculates the normalized pulse-wave area
VR, by normalizing the area S defined by 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 BP
monitor apparatus 8 can obtain values VR free from timewise changes
or individual differences.
In the above described embodiment, the estimated blood pressure
values EBP successively determined by the estimated blood pressure
determining means 78 (Step SA9), the pulse period values RR successively
measured by the pulse period measuring device 82 and the pulse-wave
area values VR successively calculated by the pulse-wave area calculating
means 84 are concurrently displayed, on the display device 32, as
the respective trend graphs. Since the respective values EBP, RR,
VR are concurrently displayed, it is possible to ascertain the reason
of the start of the blood pressure measurement by the blood pressure
measurement starting means 86 and to easily monitor the dynamic
condition of the circulatory organ of the subject while the blood
pressure measurement of the blood pressure measuring device 70 is
not carried out.
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. 8 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. The
electronic control device 28 shown in FIG. 8 is different from the
electronic control device 28 shown in FIG. 2 in that the former
device 28 additionally includes a heart rate measuring device 90
and a relationship correcting means 92.
The heart rate measuring device 90 calculates a heart rate HR (1/min)
of a living subject, based on a pulse period RR (sec) measured by
the pulse-period measuring device 82, according to a predetermined
relationship (e.g., HR=60/RR) pre-stored in a ROM 31.
The relationship correcting means 92 corrects the relationship
(the expression (2) or (3)) determined by the blood pressure-pulse
wave propagation information relationship determining means 76,
based on the heart rate HR of the subject. For instance, when the
relationship represented by the expression (2) (EBP=.alpha.DT.sub.RP
+.beta.) between estimated blood pressure EBP and pulse-wave propagation
time DT.sub.RP is employed, the relationship correcting means 92
corrects the expression (2) by decreasing an absolute value of the
coefficient .alpha. (negative value) for the pulse-wave propagation
time DT.sub.RP in the expression (2), with the increasing of the
heart rate HR. As shown in FIG. 9, when the heart rate HR is increased,
the relationship correcting means 92 corrects the relationship so
that the estimated blood pressure value EBP increases, because,
when the absolute value of the coefficient .alpha. for the pulse-wave
propagation time DT.sub.RP is decreased, the slope of the straight
line representative of the relationship or expression (2) is decreased
and the estimated blood pressure value EBP for the same pulse-wave
propagation time value DT.sub.RP is increased.
Meanwhile, when the relationship represented by the expression
(3) (EBP=.alpha.V.sub.M +.beta.) between estimated blood pressure
EBP and pulse-wave propagation velocity V.sub.M is employed, the
relationship correcting means 92 corrects the expression (3) by
increasing the coefficient .alpha. (positive value) for the pulse-wave
propagation velocity V.sub.M in the expression (3), with the increasing
of the heart rate HR. As shown in FIG. 10, when the heart rate HR
is increased, the relationship correcting means 92 corrects the
relationship so that the estimated blood pressure value EBP increases,
because, when the coefficient .alpha. for the pulse-wave propagation
velocity V.sub.M is increased, the slope of the straight line representative
of the relationship or expression (3) is increased and the estimated
blood pressure value EBP for the same pulse-wave propagation velocity
value V.sub.M is increased.
FIG. 11 is a flow chart representing a relationship correcting
routine which is carried out by the electronic control device 28,
independent of the flow charts of FIGS. 6 and 7, in the manner of
an interruption handling or a time sharing.
In FIG. 11, at Step SB1, the CPU 29 calculates a heart rate HR
of the subject based on the pulse period RR measured at Step SA101
of FIG. 7. Step SB1 corresponds to the heart rate measuring device
90. Step SB1 is followed by Step SB2 to judge whether or not the
heart rate HR is greater than a predetermined upper limit value
HR.sub.UL. If a negative judgement is made at Step SB2, the control
of the CPU 29 goes to Step SB3 to judge whether or not the pulse
rate HR is smaller than a predetermined lower limit value HR.sub.LL.
Those limit values HR.sub.UL, HR.sub.LL are predetermined based
on a heart rate HR which is obtained when the blood pressure-pulse
wave propagation information relationship is determined by the blood
pressure-pulse wave propagation information relationship determined
means 76 in the prior blood pressure measurement of the blood pressure
measuring device 70 is employed. Preferably, the upper and lower
limit values, HR.sub.UL, HR.sub.LL, are respectively set at 120%
and 80% values of an average value of the ten heart rate values
HR calculated for the ten pulses obtained in the prior blood pressure
measurement. The upper and lower limit values are, in advance, experimentally
set at values suitable for correcting the relationship (the expression
(2) or (3)) so as to maintain the accuracy of the estimated blood
pressure values EBP. There is known a phenomenon that, when the
blood pressure BP of the subject changes, the pulse-wave propagation
information (DT, V.sub.M) does not change, but the heart rate HR
changes.
If a positive judgment is made at Step SB2, the control of the
CPU 29 goes to Step SB4. At Step SB4, in the case where the relationship
represented by the expression (2) (EBP=.alpha.DT.sub.RP +.beta.)
between estimated blood pressure EBP and pulse-wave propagation
time DT.sub.RP is employed, the CPU 29 decreases the absolute value
of the coefficient .alpha. (negative value) for the pulse-wave propagation
time DT.sub.RP in the expression (2). For example, the coefficient
.alpha. is changed from -1.2 to -0.8. In the case where the relationship
represented by the expression (3) (EBP=.alpha.V.sub.M +.beta.) between
estimated blood pressure EBP and pulse-wave propagation velocity
V.sub.M is employed, the CPU 29 increases the coefficient .alpha.
(positive value) for the pulse-wave propagation velocity V.sub.M
in the expression (3). For example, the coefficient .alpha. is changed
from 0.8 to 1.2.
If a positive judgment is made at Step SB3, the control of the
CPU 29 goes to Step SB5. At Step SB5, in the case where the relationship
represented by the expression (2) (EBP=.alpha.DT.sub.RP +.beta.)
between estimated blood pressure EBP and pulse-wave propagation
time DT.sub.RP is employed, the CPU 29 increases the absolute value
of the coefficient .alpha. (negative value) for the pulse-wave propagation
time DT.sub.RP in the expression (2). For example, the coefficient
.alpha. is changed from -0.8 to -1.2. In the case where the relationship
represented by the expression (3) (EBP=.alpha.V.sub.M +.beta.) between
estimated blood pressure EBP and pulse-wave propagation velocity
V.sub.M is employed, the CPU 29 decreases the coefficient .alpha.
(positive value) for the pulse-wave propagation velocity V.sub.M
in the expression (3). For example, the coefficient .alpha. is changed
from 1.2 to 0.8. Steps SB2 to SB5 correspond to the relationship
correcting means 92.
In the above described second embodiment, the relationship correcting
means 92 (Steps SB2 to SB5) corrects the predetermined relationship
(the expression (2) or (3)) between estimated blood pressure EBP
and pulse-wave propagation information (DT or V.sub.M), based on
the heart rate HR measured by the heart rate measuring device 90
(Step SB1), so that the estimated blood pressure value EBP increases
with the increasing of the heart rate HR. Thus, the accuracy of
the estimated blood pressure value EBP is increased and accordingly
the reliability of the present blood pressure monitor is improved.
More specifically, in the case where the relationship represented
by the expression (2) (EBP=.alpha.DT.sub.RP +.beta.) between estimated
blood pressure EBP and pulse-wave propagation time DT.sub.RP is
employed, the relationship correcting means 92 corrects the expression
(2) by decreasing the absolute value of the coefficient .alpha.
(negative value) for the pulse-wave propagation time DT.sub.RP in
the expression (2), with the increasing of the heart rate HR. When
the relationship represented by the expression (3) (EBP=.alpha.V.sub.M
+.beta.) between estimated blood pressure EBP and pulse-wave propagation
velocity V.sub.M is employed, the relationship correcting means
92 corrects the expression (3) by increasing the coefficient .alpha.
(positive value) for the pulse-wave propagation velocity V.sub.M
in the expression (3), with the increasing of the heart rate HR.
In short, the relationship correcting means 92 corrects the relationship
(the expression (2) or (3)) so that the estimated blood pressure
value EBP increases, with the increasing of the heart rate HR, whereby
the accuracy of the estimated blood pressure and the reliability
of the blood pressure monitor is raised.
FIG. 12 shows respective trend graphs of actual blood pressure
values BP, the estimated blood pressure values EBP and the pulse
rate values HR. In FIG. 12, it is recognized that, after a time
point t.sub.a, the heart rate HR increases at the same rate as that
of the increasing of the blood pressure BP, but the estimated blood
pressure EBP does not increase at the same rate as that of the increasing
of the blood pressure BP of the subject. When the relationship is
corrected at a time point t.sub.b, the estimated blood pressure
values EBP are determined so as to be greater than the blood pressure
values BP by just small amounts. To this end, the relationship correcting
means 92 corrects the coefficient .alpha.. Accordingly, the accuracy
of judging of a blood-pressure abnormality is improved, whereby
the reliability of the blood pressure monitor are raised.
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 each of the illustrated embodiments the blood pressure
measuring device 70 employs the so-called oscillometric method,
it is possible to employ a so-called Korotokoff-sound method which
determines, as a systolic and a diastolic blood pressure value,
respective cuff pressures at the time of occurrence and disappearance
of Korotokoff-sounds.
While in each of the illustrated embodiments the photoelectric
pulse wave detecting probe 38 is used as the peripheral pulse wave
detecting device, an impedance sensor being set on a finger of a
living subject for detecting the change of impedance of the subject,
a pressure pulse wave measuring device being adapted to be pressed
on a radial artery of a subject for measuring a pressure in the
radial artery of the subject, or the like may be used. In short,
any pulse wave representative of circulation dynamics of a peripheral
body portion of a subject may be detected and utilized.
While in each of the illustrated embodiments the pulse-wave propagation
time DT.sub.RP or the pulse-wave propagation velocity V.sub.M is
calculated, based on the time difference between the predetermined
point of the ECG waveform detected by the ECG waveform detecting
device 34 and the predetermined point of the waveform of the photoelectric
pulse wave detected by the photoelectric pulse wave probe 38, the
pulse-wave propagation time DT.sub.RP or the pulse-wave propagation
velocity V.sub.M may be calculated using a First pulse wave detecting
device being set on a carotid artery or a brachial artery of the
subject and a second pulse wave detecting device being set on a
wrist or a finger of the subject, in place of the ECG waveform detecting
device 34 and the photoelectric pulse wave probe 38.
While in each of the illustrated embodiments the photoelectric
pulse wave detecting probe 38 is used as the second pulse wave detecting
device, it is possible to employ a cuff pulse wave sensor which
detects a cuff pulse wave from the cuff 10 being held at a predetermined
cuff pressure, a pressure pulse-wave sensor which is adapted to
be pressed on a radial artery of a subject and detects a pressure
pulse wave from the artery, an impedance pulse-wave sensor which
detects, through electrodes, an impedance pulse wave from an arm
or an end portion of a finger of a subject, a light-transmission
type photoelectric pulse wave sensor which is adapted to be set
on a finger of a subject and detects a photoelectric pulse wave
from the finger, or the like.
In each of the illustrated embodiments, the pulse-wave propagation
velocity V.sub.M is calculated based on the time difference between
the R-wave of the ECG waveform and the rising point of the waveform
of the photoelectric pulse wave. However, the pulse-wave propagation
velocity V.sub.M may be calculated based on a time difference between
a Q-wave of the ECG waveform of each pulse and the rising point
of the waveform of a corresponding pulse of the photoelectric pulse
wave.
In each of the illustrated embodiments, an estimated blood pressure
EBP is determined based on the R-wave of the ECG waveform of each
pulse or the waveform of each pulse of the photoelectric pulse wave.
However, an estimated blood pressure EBP may be determined based
on every second pulse, or so on, of the ECG waveform or the photoelectric
pulse wave.
In each of the illustrated embodiments, the pulse period RR (SEC)
and the heart rate HR (1/min) may be employed in place of each other,
because the pulse period RR corresponds to the heart rate HR, one
to one (HR=60/RR).
In the above described second embodiment, the blood pressure measurement
starting means 86 may be omitted because it is possible to monitor
the blood pressure of the subject by just displaying, on the display
device 32, the trend graph of the estimated blood pressure values
EBP.
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. |