Abstrict
A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: pulse-wave-propagation-velocity-relating
information obtaining means for successively obtaining pulse-wave-propagation-velocity-relating
information which relates to a pulse-wave propagation velocity at
which a pulse wave propagates in an artery of the subject; pulse-period-relating
information obtaining means for successively obtaining pulse-period-relating
information which relates to a pulse period of the subject; peripheral-blood-volume-relating
information obtaining means for successively obtaining peripheral-blood-volume-relating
information which relates to a volume of blood which flows in a
peripheral body portion of the subject; and abnormality judging
means for judging that the blood pressure of the subject is abnormal
when at least one of the pulse-wave-propagation-velocity-relating
information, pulse-period-relating information, and peripheral-blood-volume-relating
information does not fall within a corresponding one of a first,
a second and a third reference range.
Claims
What is claimed is:
1. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: pulse-wave-propagation-velocity-relating
information obtaining means for successively obtaining pulse-wave-propagation-velocity-relating
information which relates to a pulse-wave propagation velocity at
which a pulse wave propagates in an artery of the subject; pulse-period-relating
information obtaining means for successively obtaining pulse-period-relating
information which relates to a pulse period of the subject; peripheral-blood-volume-relating
information obtaining means for successively obtaining peripheral-blood-volume-relating
information which relates to a volume of blood which flows in a
peripheral body portion of the subject; and abnormality judging
means for judging that said blood pressure of the subject is abnormal
when at least one of said pulse-wave-propagation-velocity-relating
information, said pulse-period-relating information, and said peripheral-blood-volume-relating
information does not fall within a corresponding one of a first,
a second and a third reference range, wherein said first, second,
and third reference ranges have a first, a second, and a third upper
limit value, respectively, each of said first, second, and third
upper limit values being a common value.
2. A blood pressure monitor apparatus according to claim 1, further
comprising blood pressure measuring means which includes a cuff
and which measures a blood pressure of the subject by changing a
pressing pressure of said cuff applied to a body portion of the
subject, wherein said abnormality judging means starts a blood pressure
measurement of said blood pressure measuring means when a said blood
pressure of the subject is judged to be abnormal.
3. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: pulse-wave-propagation-velocity-relating
information obtaining means for successively obtaining pulse-wave-propagation-velocity-relating
information which relates to a pulse-wave propagation velocity at
which a pulse wave propagates in an artery of the subject; pulse-period-relating
information obtaining means for successively obtaining pulse-period-relating
information which relates to a pulse period of the subject; peripheral-blood-volume-relating
information obtaining means for successively obtaining peripheral-blood-volume-relating
information which relates to a volume of blood which flows in a
peripheral body portion of the subject; and abnormality judging
means for judging that said blood pressure of the subject is abnormal
when at least one of said pulse-wave-propagation-velocity-relating
information, and pulse-period-relating information, and said peripheral-blood-volume-relating
information does not fall within a corresponding one of a first,
a second and a third reference range, wherein said first, second,
and third reference ranges have a first, a second, and a third lower
limit value, respectively each of said first, second, and third
lower limit values being a common value.
4. A blood pressure monitor apparatus according to claim 3, further
comprising blood pressure measuring means which includes a cuff
and which measures a blood pressure of the subject by changing a
pressing pressure of said cuff applied to a body portion of the
subject, wherein said abnormality judging means starts a blood pressure
measurement of said blood pressure measuring means when a said blood
pressure of the subject is judged to be abnormal.
5. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: pulse-wave-propagation-velocity-relating
information obtaining means for successively obtaining pulse-wave-propagation-velocity-relating
information which relates to a pulse-wave propagation velocity at
which a pulse wave propagates in an artery of the subject; pulse-period-relating
information obtaining means for successively obtaining pulse-period-relating
information which relates to a pulse period of the subject; peripheral-blood-volume-relating
information obtaining means for successively obtaining peripheral-blood-volume-relating
information which relates to a volume of blood which flows in a
peripheral body portion of the subject; and abnormality judging
means for judging that said blood pressure of the subject is abnormal
when at least one of said pulse-wave-propagation-velocity-relating
information, and pulse-period-relating information, and said peripheral-blood-volume-relating
information does not fall within a corresponding one of a first,
a second and a third reference range, wherein said first, second,
and third reference ranges have a first, a second, and a third lower
limit value, respectively each of said first, second, and third
lower limit values and each of said first, second, and third upper
limit values being a common value being a common value.
6. A blood pressure monitor apparatus according to claim 5, further
comprising blood pressure measuring means which includes a cuff
and which measures a blood pressure of the subject by changing a
pressing pressure of said cuff applied to a body portion of the
subject, wherein said abnormality judging means starts a blood pressure
measurement of said blood pressure measuring means when a said blood
pressure of the subject is judged to be abnormal.
Description The present application is based on Japanese Patent Application
No. 10-337697 filed Nov. 27, 1998, the contents of which are incorporated
hereinto by reference.
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 pulse-wave-propagation-velocity-relating
information which relates to a propagation velocity of a pulse wave
which propagates through an artery of a subject, pulse-period-relating
information which relates to a period of a pulse of a subject, and
peripheral-blood-volume-relating information which relates to a
volume of blood which flows in a peripheral body portion of a subject.
2. Discussion of the Related Art
As pulse-wave-propagation-velocity-relating information, there
is known a propagation time DT during which a pulse wave propagates
between predetermined two portions of an artery, or a propagation
velocity V.sub.M (m/s) at which a pulse wave propagates through
an artery. It is generally known that such pulse-wave-propagation-velocity-relating
information is substantially proportional to a blood pressure BP
(mmHg) of a living subject within a predetermined range. In view
of this, there is proposed a blood pressure monitor apparatus which
monitors a change or fluctuation of the blood pressure of the subject
by monitoring whether or not successively obtained pulse-wave-propagation-velocity-relating
information is greater than a predetermined upper reference value
or smaller than a predetermined lower reference value, and judges
that the blood pressure has changed and starts a blood pressure
measurement using a cuff when the obtained pulse-wave-propagation-velocity-relating
information is greater than the predetermined upper reference value
or smaller than the predetermined lower reference value.
However, the pulse-wave-propagation-velocity-relating information
is not proportional to the blood pressure in an entire blood pressure
range. Namely, the correlation between the pulse-wave-propagation-velocity-relating
information and the blood pressure is considerably low in a considerably
low blood pressure range and a considerably high blood pressure
range. Accordingly, the conventional blood pressure monitor apparatus
which monitors the change of the blood pressure based on the pulse-wave-propagation-velocity-relating
information is not capable of accurately detecting the change of
the blood pressure in the entire blood pressure range.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
blood pressure monitor apparatus which is capable of accurately
detecting a change or fluctuation of the blood pressure of a living
subject in the entire blood pressure range.
As a result of an extensive study by the inventors of the present
invention, it has been found that the change of the blood pressure
can be detected with high accuracy in the entire blood pressure
range if other information which is correlative with the blood pressure
is used to monitor the blood pressure, in addition to the pulse-wave-propagation-velocity-relating
information. Such information includes pulse-period-relating information
which relates to a period of a pulse of the subject, such as a pulse
period and a heart rate, and peripheral-blood-volume-relating information
which relates to a volume of blood flowing in a peripheral body
portion of the subject, such as an amplitude and an area of a pulse
wave detected from the peripheral body portion of the subject.
The above-indicated object of the present invention may be attained
according to a principle of the invention, which provides a blood
pressure monitor apparatus for monitoring a blood pressure of a
living subject, comprising: pulse-wave-propagation-velocity-relating
information obtaining means for successively obtaining pulse-wave-propagation-velocity-relating
information which relates to a pulse-wave propagation velocity at
which a pulse wave propagates in an artery of the subject; pulse-period-relating
information obtaining means for successively obtaining pulse-period-relating
information which relates to a pulse period of the subject; peripheral-blood-volume-relating
information obtaining means for successively obtaining peripheral-blood-volume-relating
information which relates to a volume of blood which flows in a
peripheral body portion of the subject; and abnormality judging
means for judging that the blood pressure of the subject is abnormal
when at least one of the pulse-wave-propagation-velocity-relating
information, pulse-period-relating information, and peripheral-blood-volume-relating
information does not fall within a corresponding one of a first,
a second and a third reference range.
In the blood pressure monitor apparatus constructed as described
above, the change of the blood pressure of the subject can be detected
with high accuracy in the entire blood pressure range since the
blood pressure of the subject is judged to be abnormal when at least
one of the pulse-period-relating information and the peripheral-blood-volume-relating
information does not fall within a corresponding one of the second
and third reference ranges, even if the pulse-wave-propagation-velocity-relating
information may fall within the corresponding first reference range.
In a preferred form of the present invention, the first, second,
and third reference ranges have a first, a second, and a third upper
limit value, respectively. The first, second, and third reference
ranges may or may not have a lower limit value.
In a preferred form of the present invention, the first, second,
and third reference ranges have a first, a second, and a third lower
limit value, respectively. The first, second, and third reference
ranges may or may not have an upper limit value.
In a preferred form of the present invention, the first, second,
and third reference ranges have a first, a second, and a third upper
limit value, respectively, and a first, a second, and a third lower
limit value, respectively.
In a preferred form of the present invention, the first, second,
and third upper limit values are a common value. The first, second,
and third upper limit values may be different from one another.
In a preferred form of the present invention, the first, second,
and third lower limit values are a common value. The first, second,
and third lower limit values may be different from one another.
In a preferred form of the present invention, the blood pressure
monitor apparatus further comprises blood pressure measuring means
which includes a cuff and which measures a blood pressure of the
subject by changing a pressing pressure of the cuff applied to a
body portion of the subject, and the abnormality judging means starts
a blood pressure measurement of the blood pressure measuring means
when the blood pressure of the subject is judged to be abnormal.
The blood pressure monitor apparatus constructed according to the
above arrangement starts the blood pressure measurement of the blood
pressure measuring means when at least one of the pulse-period-relating
information and the peripheral-blood-volume-relating information
does not fall within a corresponding one of the second and third
reference ranges, even if the pulse-wave-propagation-velocity-relating
information may fall within the corresponding first reference range.
Accordingly, the present blood pressure monitor apparatus is capable
of quickly obtaining the blood pressure of the subject with high
reliability in the entire blood pressure range when the blood pressure
of the subject has changed.
In a preferred form of the present invention, the pulse-wave-propagation-velocity-relating
information obtaining means comprises first estimated blood pressure
determining means for successively determining, as the pulse-wave-propagation-velocity-relating
information, a first estimated blood pressure value EBP.sub.1, based
on a pulse-wave propagation time, by utilizing a predetermined relationship
between first estimated blood pressure value EBP.sub.1 and pulse-wave
propagation time DT.sub.RP, the relationship being represented by
an equation:EBP.sub.1 =.alpha..sub.1 (1/DT.sub.RP)+.beta..sub.1,
wherein .alpha..sub.1 and .beta..sub.1 represent coefficients, the
pulse-period-relating information obtaining means comprises second
estimated blood pressure determining means for successively determining,
as the pulse-period-relating information, a second estimated blood
pressure value EBP.sub.2, based on a pulse period of the subject,
by utilizing a predetermined relationship between second estimated
blood pressure value EBP.sub.2 and pulse period RR, the relationship
being represented by an equation:EBP.sub.2 =.alpha..sub.2 RR+.beta..sub.2,
wherein .alpha..sub.2 and .beta..sub.2 represent coefficients, and
the peripheral-blood-volume-relating information obtaining means
comprises third estimated blood pressure determining means for successively
determining, as the peripheral-blood-volume-relating information,
a third estimated blood pressure value EBP.sub.3, based on a pulse-wave
area, by utilizing a predetermined relationship between third estimated
blood pressure value EBP.sub.3 and pulse-wave area VR, the relationship
being represented by an equation:EBP.sub.3 =.alpha..sub.3 VR+.beta..sub.3,
wherein .alpha..sub.3 and .beta..sub.3 represent coefficients.
In a preferred form of the present invention, pulse-wave-propagation-velocity-relating
information obtaining means comprises an electrocardiographic-waveform
detecting device which includes a plurality of electrodes adapted
to be attached to a body portion of the subject and detects an electrocardiographic
waveform indicative of an action potential of a cardiac muscle of
the subject through the electrodes, and a photoelectric-pulse-wave
detecting device which includes a plurality of light-emitting elements
and a light-receiving element, each of the light-emitting elements
emitting, toward a body surface of the subject, a light having a
wavelength which is reflected by hemoglobin present in the blood
of the subject, the light-receiving element receiving the light
scattered by the hemoglobin from the body surface of the subject,
the photoelectric-pulse-wave detecting device detecting a photoelectric
pulse wave indicative of the volume of the blood flowing in the
body surface, the pulse-wave propagation time (DT.sub.RP) representing
a time difference between a predetermined point of a pulse of the
electrocardiographic waveform detected by the electrocardiographic-waveform
detecting device, and a predetermined point of a waveform of a corresponding
pulse of the photoelectric pulse wave detected by the photoelectric-pulse-wave
detecting device.
In a preferred form of the present invention, the pulse-period-relating
information obtaining means comprises an electrocardiographic-waveform
detecting device which includes a plurality of electrodes adapted
to be attached to a body portion of the subject and detects an electrocardiographic
waveform indicative of an action potential of a cardiac muscle of
the subject through the electrodes, the pulse period (RR) representing
an interval between successive two R-waves of the electrocardiographic
waveform detected by the electrocardiographic-waveform detecting
device.
In a preferred form of the present invention, the peripheral-blood-volume-relating
information obtaining means comprises a photoelectric-pulse-wave
detecting device which includes a plurality of light-emitting elements
and a light-receiving element, each of the light-emitting elements
emitting, toward a body surface of the subject, a light having a
wavelength which is reflected by hemoglobin present in the blood
of the subject, the light-receiving element receiving the light
scattered by the hemoglobin from the body surface of the subject,
the photoelectric-pulse-wave detecting device detecting a photoelectric
pulse wave indicative of the volume of the blood flowing in the
body surface, the pulse-wave area (VR) representing an area defined
by a waveform of a pulse of the photoelectric pulse wave detected
by the photoelectric-pulse-wave detecting device.
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 embodiment 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
constructed according to one embodiment of 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 view showing a pulse-wave propagation time DT.sub.RP
obtained by the operation of the electronic control device of the
blood pressure monitor apparatus of FIG. 1;
FIG. 4 is a view for explaining normalization to obtain a normalized
pulse-wave area VR;
FIG. 5 is a flow chart representing a control routine for determining
a relationship between the blood pressure and the pulse-wave propagation
time DT.sub.RP, pulse period RR, or normalized pulse-wave area VR,
which control routine is executed by the electronic control device
of the apparatus of FIG. 1; and
FIG. 6 is a flow chart representing a control routine for monitoring
a blood pressure of the subject executed by the electronic control
device of the apparatus of FIG. 1;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1, there is shown a blood pressure (BP)
monitor apparatus 8 constructed according to one embodiment of the
present invention. The BP monitor apparatus 8 of FIG. 1 includes
an inflatable cuff 10 which has an elongate fabric bag and a rubber
bag accommodated in the elongate fabric bag and which is to be wound
around an upper arm 12 of a patient, for instance. A pressure sensor
14, a selector valve 16, and an air pump 18 are connected to the
cuff 10 via a conduit 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
from the pump 18 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 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 transmits a static component of the signal SP as a cuff-pressure
signal SK representative of a static cuff pressure Pc to an electronic
control device 28 via a first analog-to-digital (A/D) converter
26.
The pulse-wave filter circuit 24 has a band-pass filter and transmits
an oscillating component of the pressure signal SP as a pulse-wave
signal SM.sub.1 to the electronic control device 28 via a second
analog-to-digital (A/D) converter 30. The pulse-wave signal SM.sub.1
represents a pulse wave, i.e., 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 transmitted
to the cuff 10.
The electronic control device 28 is constituted by a so-called
microcomputer which includes 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 performs signal
processing operations according to control programs stored in the
ROM 31 by utilizing a temporary data storage function of the RAM
33, generates drive signals through the I/O port for controlling
the selector valve 16 and the air pump 18, and outputs a display
signal to a display device 32 through the I/O port.
The BP monitor apparatus 8 further includes an electronic cardiographic-waveform
(ECG-waveform) detecting device 34, and a photoelectric-pulse-wave
detecting probe 38 (hereinafter simply referred to as "probe")
which is employed as a pulse oximeter. The ECG-waveform detecting
device 34 detects an ECG waveform, i.e., electrocardiogram, representative
of an action potential of a cardiac muscle of the subject, through
a plurality of electrodes 36 attached to 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 an R wave of the ECG waveform corresponding to a time point when
the output of the blood from the heart to the aorta of the subject
is started. The ECG-waveform detecting device 34 functions as a
first pulse wave detecting device.
The probe 38 functions as a second pulse wave detecting device
or a peripheral pulse-wave detecting device for detecting a pulse
wave which propagates to a peripheral artery including blood capillaries.
The probe 38 is worn on a skin or a body surface 40 of the subject
such as an end portion of a finger of the subject by means of a
band (not shown), such that the probe 38 is held in close contact
with the body surface 40. The probe 38 includes a container-like
housing 42 which opens in a certain direction, first and second
light-emitting elements 44a, 44b provided by light-emitting diodes
(LED), for instance, and disposed on an outer peripheral portion
of an inner bottom surface of the housing 42 (hereinafter simply
referred to as "light-emitting elements 44 in the case where
the first and second light-emitting elements 44a, 44b need not be
distinguished from each other), a light-receiving element 46 provided
by a photodiode or a phototransister and 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 from the light-emitting elements 44 toward the body surface
40 and reflected by the body surface 40, from being received by
the light-receiving element 46.
The first light-emitting elements 44a emit a red light having a
wavelength of about 660 nm while the second light-emitting elements
44b emit an infrared light having a wavelength of about 800 nm.
The first and second light-emitting elements 44a, 44b alternately
emit the red light and the infrared light at a predetermined frequency
for a predetermined time period. The lights emitted from the light-emitting
elements 44 toward the body surface 40 are reflected from a body
portion of the subject where blood capillaries are densely located,
and the reflected lights are received by the common light-receiving
element 46. The wavelength values of the lights respectively emitted
by the first and second light-emitting elements 44a, 44b are not
limited to those described above. The first light-emitting elements
44a emit a light having a wavelength at which the absorption coefficients
of the light with respect to the oxygenerated hemoglobin and the
reduced hemoglobin are considerably different from each other, while
the second light-emitting elements 44b emit a light having a wavelength
at which the absorption coefficients of the light with respect to
the oxygenated hemoglobin and the reduced hemoglobin are substantially
the same with each other. In other words, the second light-emitting
elements 44b emit a light having a wavelength at which the light
is reflected by both of the oxygenerated hemoglobin and the reduced
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, for instance.
The low-pass filer 52 eliminates, from the photoelectric pulse-wave
signal SM.sub.3 input thereto, a noise having a frequency higher
than that of the 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 is a volume pulse
wave produced in synchronism with a pulse of the patient, and corresponds
to 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. 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 respectively
hold the current electric signals SM.sub.R, SM.sub.IR input thereto
until the previous electric signals SM.sub.R, SM.sub.IR have been
converted by the respective A/D converters 58, 62.
In the electronic control device 28, the CPU 29 effects a measuring
operation according to control programs stored in the ROM 31 by
utilizing a temporary-storage function of the RAM 33. More specifically
described, the CPU 29 outputs a control signal SLV to a drive circuit
64 for causing the light-emitting elements 44a, 44b to alternately
emit the red and infrared lights at a predetermined frequency for
a predetermined time period. The CPU 29 also outputs a switch signal
SC in synchronism with the light emissions of the light-emitting
elements 44a, 44b, so that the demultiplexer 54 is alternately switched
to supply the electric signal SM.sub.R to the first sample-and-hold
circuit 56 and the electric signal SM.sub.IR to the second sample-and-hold
circuit 60. 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 mathematical expression.
The blood oxygen saturation is determined according to a method
disclosed in U.S. Pat. No. 5,131,400 assigned to the assignee of
the present invention.
As illustrated in FIG. 2 showing essential functions of the electronic
control device 28 of the BP monitor apparatus 8 of the present embodiment,
the BP monitor apparatus 8 includes blood-pressure (BP) measuring
means 70, cuff-pressure regulating means 72, pulse-wave-propagation-velocity-relating
information obtaining means 74, pulse-period-relating information
obtaining means 76, peripheral-blood-volume-relating information
obtaining means 78, first estimated blood pressure determining means
80, second estimated blood pressure determining means 82, third
estimated blood pressure determining means 84, relationship determining
means 86, and abnormality judging means 88.
The BP measuring means 70 measures a systolic blood pressure BP.sub.SYS,
a mean blood pressure BP.sub.MEAN, and a diastolic blood pressure
BP.sub.DIA of the subject according to a known oscillometric method.
Described in detail, after the pressure in the cuff 10 wound around
on the upper arm of the subject is quickly increased up to a predetermined
target value P.sub.CM (e.g., about 180 mmHg) by the cuff pressure
regulating means 72, the pressure in the cuff 10 is slowly lowered
at a rate of about 3 mmHg/sec. The blood pressure values BP.sub.SYS,
BP.sub.MEAN, BP.sub.DIA are determined on the basis of the change
of respective amplitudes of successive pulses of the pulse-wave
signal SM.sub.1, obtained while the cuff pressure is slowly lowered.
The determined blood pressure values BP.sub.SYS, BP.sub.MEAN, BP.sub.DIA
are indicated on the display 32.
The pulse-wave-propagation-velocity-relating information obtaining
means 74 includes time-difference calculating means for successively
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 lowest 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-velocity-relating
information obtaining means 74 successively determines a pulse-wave
propagation velocity V.sub.M (m/sec) of the pulse wave which propagates
in the artery of the subject 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 attached via
the aorta, T.sub.PEP (sec) is a pre-ejection period between the
R-wave of ECG waveform of each pulse and the lowest 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
empirically obtained in advance.
The pulse-period-relating information obtaining means 76 successively
obtains information relating to a pulse period of the subject, such
as a pulse period RR, by measuring an interval between predetermined
points (e.g., R-waves) of successive two pulses of the ECG waveform
detected by the ECG-waveform detecting device 34. The peripheral-blood-volume-relating
information obtaining means 78 successively obtains information
relating to a volume of the blood flowing in the peripheral body
portion of the subject. For instance, the peripheral-blood-volume-relating
information obtaining means 78 determines an area VR which is defined
by a waveform of each of successive pulses of the photoelectric
pulse-wave signal SM.sub.2 and is normalized based on a period W
and an amplitude L of the each pulse of the photoelectric pulse-wave
signal SM.sub.2. As shown in the graph of FIG. 4, the waveform of
each pulse of the photoelectric pulse-wave signal SM.sub.2 is defined
by a series of data points indicative of respective instantaneous
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 (=S.sub.1 +S.sub.2) is obtained by integrating, in the period
W of the pulse of the photoelectric pulse-wave signal SM.sub.2,
the respective magnitudes of the pulse of the signal SM.sub.2, and
then the normalized pulse-wave area VR is calculated according to
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 S to an area defined by the period W and the amplitude of L
of the each pulse of the photoelectric pulse wave. The normalized
pulse-wave area represents a volume of blood flowing in the peripheral
body portion of the subject. A symbol % MAP may be used in place
of the symbol VR.
The first estimated blood pressure determining means 80 successively
determines a first estimated blood pressure EBP1 based on the pulse-wave-propagation-velocity-relating
information such as the pulse-wave propagation time value DT.sub.RP
successively obtained by the pulse-wave propagation-velocity-relating
information obtaining means 74, according to a predetermined relationship
between first estimated blood pressure EBP1 and pulse-wave-propagation-velocity-relating
information DT.sub.RP, which relationship is represented by the
following expression (2):
Since the pulse-wave propagation time DT.sub.RP decreases with
an increase of the blood pressure, in other words, the value (1/DT.sub.RP)
in the above expression (2) increases with an increase of the blood
pressure, the coefficient .alpha..sub.1, in the expression (2) is
a positive value.
The second estimated blood pressure determining means 82 successively
determines a second estimated blood pressure EBP2 based on the pulse-period-relating
information such as the pulse period value RR successively obtained
by the pulse-period-relating information obtaining means 76, according
to a predetermined relationship between second estimated blood pressure
EBP2 and pulse-period-relating information RR, which relationship
is determined according to the following expression (3):
Since the pulse period RR decreases with an increase of the blood
pressure, the coefficient .alpha..sub.2 in the above expression
(3) is a negative value.
The third estimated blood pressure determining means 84 successively
determines a third estimated blood pressure EBP3 based on the peripheral
blood-volume-relating information such as the normalized pulse-wave
area value VR successively obtained by the peripheral-blood-volume-relating
information obtaining means 78, according to a predetermined relationship
between third estimated blood pressure EBP3 and peripheral-blood-volume-relating
information VR, which relationship is represented by the following
expression(4):
Since the normalized pulse-wave area VR increases with an increase
of the blood pressure, the coefficient .alpha..sub.3 in the above
expression (4) is a positive value.
The relationship determining means 86 determines the coefficients
.alpha..sub.1, .beta..sub.1 in the expression (2), the coefficients
.alpha..sub.2, .beta..sub.2 in the expression (3), and the coefficients
.alpha..sub.3, .beta..sub.3 in the expression (4), respectively,
based on the systolic blood pressure value BP.sub.SYS measured by
the blood pressure measuring means 70 and the corresponding one
of the pulse-wave-propagation-velocity-relating information, the
pulse-period-relating information, and the peripheral-blood-volume-relating
information obtained during each blood pressure measurement. For
instance, the relationship determining means 86 determines the coefficients
.alpha..sub.1, .beta..sub.1 in the above expression (2) based on
the pulse-wave propagation time DT.sub.RP obtained by the pulse-wave-propagation-velocity-relating
information obtaining means 74 in the current blood pressure measurement.
Described in detail, either one of the coefficients .alpha..sub.1
and .beta..sub.1 in the above expression (2) is determined or changed
in advance based on the systolic blood pressure value BP.sub.SYS
measured by the blood pressure measuring means 70 and the pulse-wave
propagation time DT.sub.RP obtained during the current blood pressure
measurement. Alternatively, the coefficients .alpha..sub.1, .beta..sub.1
in the expression (2) may be predetermined such that the coefficients
.alpha..sub.1, .beta..sub.1 satisfy a relationship between one set
of data consisting of the systolic blood pressure value BP.sub.SYS
currently measured by the blood pressure measuring means 70 and
the pulse-wave propagation time DT.sub.RP obtained in the current
blood pressure measurement and another set of data consisting of
the systolic blood pressure value BP.sub.SYS and the pulse-wave
propagation time DT.sub.RP which have been obtained in the prior
blood pressure measurement. In place of the systolic blood pressure
BP.sub.SYS, the mean blood pressure BP.sub.MEAN or the diastolic
blood pressure BP.sub.DIA may be employed in determining the coefficients.
In other words, when the mean blood pressure BP.sub.MEAN is used
to determine the coefficients in the above expressions (2)-(4),
the value EBP indicates mean blood pressure, while the value EBP
indicates the diastolic blood pressure when the diastolic blood
pressure BP.sub.DIA is used to determine the coefficients.
The abnormality judging means 88 functioning as blood pressure
measurement starting means judges that the blood pressure of the
subject is abnormal when at least one of the pulse-wave-propagation-velocity-relating
information obtained by the pulse-wave-propagation-velocity-relating
information obtaining means 74, the pulse-period-relating information
obtained by the pulse-period-relating information obtaining means
76, and the peripheral-blood-volume-relating information obtained
by the peripheral-blood-volume-relating information obtaining means
78 does not fall within a predetermined common reference range.
When the blood pressure of the subject is judged to be abnormal,
the abnormality judging means 88 starts a blood pressure measurement
of the blood pressure measuring means 70 and indicates, on the display
32, the abnormality of the blood pressure of the subject. Namely,
the abnormality judging means 88 starts a blood pressure measurement
of the blood pressure measuring means 70 when at least one of the
first estimated blood pressure value EBP.sub.1 which corresponds,
one to one, to the pulse-wave-propagation-velocity-relating information,
the second estimated blood pressure value EBP.sub.2 which corresponds,
one to one, to the pulse-period-relating information, and the third
estimated blood pressure value EBP.sub.3 which corresponds, one
to one, to the peripheral-blood-volume-relating information, is
smaller than a predetermined lower limit value EBP.sub.L or greater
than a predetermined upper limit value EBP.sub.U of the common reference
range.
There will be described the operation of the electronic control
device 28 referring to the flow chart of FIG. 5. A control routine
of FIG. 5 is effected for determining the relationship between the
blood pressure and the pulse-wave propagation time for determining
the first estimated blood pressure EBP.sub.1, represented by the
above expression (2), the relationship between the blood pressure
and the pulse period for determining the second estimated blood
pressure EBP.sub.2, represented by the above expression (3), and
the relationship between the blood pressure and the normalized pulse-wave
area for determining the third estimated blood pressure EBP.sub.3,
represented by the above expression (4).
The control routine of FIG. 5 is initiated with Step SA1 in which
counters and registers (not shown) are reset. Step SA1 is followed
by Step SA2 corresponding to the cuff pressure regulating means
72 to quickly increase the cuff pressure for effecting a blood pressure
measurement, by placing the selector valve 16 to its inflation position
and actuating the air pump 18.
Step SA2 is followed by Step SA3 corresponding to the pulse-wave-propagation-velocity-relating
information obtaining means 74 to obtain, as the pulse-wave propagation
time DT.sub.RP, a time difference between an 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 detected by the probe 38.
Step SA3 is followed by Step SA4 corresponding to the pulse-period-relating
information obtaining means 76 to obtain the pulse period RR by
measuring an interval between the R-waves of successive two pulses
of the ECG waveform. Step SA4 is followed by Step SA5 corresponding
to the peripheral-blood-volume-relating information obtaining means
78 to obtain a pulse-wave area S, a period W, an amplitude L of
a pulse of the photoelectric pulse wave obtained based on the photoelectric
pulse-wave signal SM.sub.2 (shown in the graph of FIG. 4) detected
by the probe 38. On the basis of the obtained pulse-wave area S,
period W, and amplitude L of one pulse of the photoelectric pulse
wave, a normalized pulse-wave area VR is calculated according to
the expression VR=S/(W.times.L).
The control flow then goes to Step SA6 to judge whether or not
the cuff pressure P.sub.C is increased up to or higher than a predetermined
target value P.sub.CM (e.g., 180 mmHg) If a negative decision is
made in Step SA6, the control flow goes back to Step SA2 so as to
continue the increasing of the cuff pressure P.sub.C. If the cuff
pressure P.sub.C is equal to or higher than the target value P.sub.CM,
an affirmative decision is made in Step SA6 and the control flow
goes to Step SA7 corresponding to the blood pressure measuring means
70 to perform a blood pressure measuring algorithm. Described in
detail, the air pump 18 is turned off and the selector valve 16
is switched from the inflation position to its slow-deflation position
where the selector valve 16 permits the pressurized air to be slowly
discharged from the cuff 10, so that the pressure in the cuff 10
is slowly decreased at a predetermined rate of 3 mmHg/sec. A systolic
blood pressure BP.sub.SYS, a mean blood pressure BP.sub.MEAN, and
a diastolic blood pressure are determined based on the variation
of amplitudes of successive pulses of the pulse wave represented
by the pulse-wave signal SM.sub.1 obtained during the slow decreasing
of the cuff pressure, according to a well-known oscillometric blood
pressure determining algorithm. The thus determined blood pressure
values BP.sub.SYS, BP.sub.MEAN, BP.sub.DIA are indicated on the
display device 32, and the selector valve 16 is switched from the
slow-deflation position to its rapid-deflation position, whereby
the pressure in the cuff 10 is rapidly lowered.
Step SA7 is followed by Steps SA8 through Step SA10 corresponding
to the relationship determining means 86. In Step SA8, the control
device 28 determines a relationship between the pulse-wave propagation
time and the blood pressure. Namely, the coefficients .alpha..sub.1,
.beta..sub.1 in the above expression (2) are determined based on
one set of data consisting of the pulse-wave propagation time value
DT.sub.RP calculated in Step SA3 and the systolic blood pressure
value BP.sub.SYS determined in Step SA7 which are obtained in the
current control cycle, and another set of data consisting of the
pulse-wave propagation time value DT.sub.RP and the systolic blood
pressure value BP.sub.DIA respectively obtained in Step SA7 and
Step SA3 of the prior control cycle. Step SA8 is followed by Step
SA9 to determine a relationship between the pulse period and the
blood pressure, i.e., the coefficients .alpha..sub.2, .beta..sub.2
in the above expression (3) based on one set of data consisting
of the pulse period value RR and the systolic blood pressure value
BP.sub.SYS respectively obtained in Step SA4 and Step SA7 of the
current control cycle, and another set of data consisting of the
pulse period value RR and the systolic blood pressure value BP.sub.SYS
respectively obtained in Step SA4 and Step SA7 of the prior control
cycle. SA9 is followed by Step SA10 to determine a relationship
between the normalized pulse-wave area and the blood pressure, i.e.,
the coefficients .alpha..sub.3, .beta..sub.3 in the above expression
(4) based on one set of data consisting of the normalized pulse-wave
area value VR and the systolic blood pressure value BP.sub.SYS respectively
obtained in Step SA5 and Step SA7 of the current control cycle,
and another set of data consisting of the normalized pulse-wave
area value VR and the systolic blood pressure value BP.sub.SYS respectively
obtained in Step SA5 and Step SA7 of the prior control cycle.
After the coefficients in the above expressions (2)-(4) are determined
as described above, the electronic control device 28 executes a
blood pressure monitor routine as indicated by a flow chat of FIG.
6. The control routine of FIG. 6 is initiated with Step SB1 to judge
whether or not the R-wave of the ECG waveform and the photoelectric
pulse wave have been detected. As long as a negative judgment is
made in Step SB1, this step is repeatedly implemented. If an affirmative
judgment is made in Step SB1, the control flow goes to Step SB2
corresponding to the pulse-wave-propagation-velocity-relating information
obtaining means 74 to obtain a pulse-wave propagation time DT.sub.RP
with respect to the R-wave of the ECG waveform and the photoelectric
pulse wave which have been read in Step SB1, in the same manner
as carried out in Step SA3 of the control routine of FIG. 5.
Step SB2 is followed by Step SB3 corresponding to the pulse-period-relating
information obtaining means 76 to obtain a pulse period RR based
on the interval between the R-waves of successive two pulses of
the ECG waveform detected in Step SB1. SB3 is followed by Step SB4
corresponding to the peripheral-blood-volume-relating information
obtaining means 78 to obtain a normalized pulse-wave area VR based
on the photoelectric pulse wave read in Step SB1, in the same manner
as carried out in Step SA5 of FIG. 5.
The control flow then goes to Step SB5 corresponding to the first
estimated blood pressure determining means 80 to determine a first
estimated blood pressure EBP.sub.1 based on the pulse-wave propagation
time DT.sub.RP calculated in Step SB2, according to the relationship
which is represented by the above expression (2) and determined
in Step SA8 of the control routine of FIG. 5. Step SB5 is followed
by Step SB6 corresponding to the second estimated blood pressure
determining means 82 to determine a second estimated blood pressure
EBP.sub.2 based on the pulse period RR obtained in Step SB3, according
to the relationship which is represented by the above expression
(3) and determined in Step SA9 of the control routine of FIG. 5.
Step SB6 is followed by Step SB7 corresponding to the third estimated
blood pressure determining means 84 to determine a third estimated
blood pressure EBP.sub.3 based on the normalized pulse-wave area
VR obtained in Step SB4, according to the relationship which is
represented by the above expression (4) and determined in Sep SA10
of the control routine of FIG. 5.
The control flow then goes to Step SB8 corresponding to the abnormality
judging means 88 to judge whether or not at least one of the estimated
blood pressure values EBP.sub.1, EBP.sub.2, EBP.sub.3 is greater
than an upper limit value EBP.sub.H or smaller than a lower limit
value EBP.sub.L of a predetermined reference range. If a negative
judgment is made in Step SB8, step SB9 is implemented to judge whether
or not a predetermined period (e.g., 15 to 20 minutes), that is,
a calibration period, has passed after the control routine of FIG.
5 for determining the relationships represented by the expressions
(2)-(4) was implemented. If a negative judgment is made in Step
SB9, the control flow goes back to Step SB1 and the following steps
so as to repeat the blood pressure monitor routine.
On the other hand, if an affirmative judgment is made in Step SB9,
the relationship determining routine of FIG. 5 is implemented to
update the coefficients in the above expressions (2)-(4). If an
affirmative judgment is made in Step SB8, the control flow goes
to Step SB10 to indicate abnormality of the blood pressure on the
display 32, and implement the relationship determining routine of
FIG. 5 for effecting a reliable blood pressure measurement using
the cuff 10 and updating the coefficients in the expressions (2)-(4).
In the present embodiment, the abnormality judging means 88 judges
that the blood pressure of the subject is abnormal when at least
one of the first estimated blood pressure value EBP1 determined
by the first estimated blood pressure determining means 80 (Step
SB5), the second estimated blood pressure value EBP2 determined
by the second estimated blood pressure determining means (Step SB6),
and the third estimated blood pressure value EBP3 determined by
the third blood pressure determining means (Step SB7) is smaller
than the lower limit value EBP.sub.L or greater than the upper limit
value EBP.sub.H of the common reference range. According to this
arrangement, even if the first estimated blood pressure value EBP1
determined based on the pulse-wave propagation time DT.sub.RP may
fall within the reference range having the lower limit value EBP.sub.L
and the upper limit value EBP.sub.H, the abnormality judging means
88 judges that the blood pressure of the subject is abnormal when
the second estimated blood pressure value EBP2 determined based
on the pulse period RR or the third estimated blood pressure value
EBP3 determined based on the normalized pulse-wave area VR does
not fall within the reference range. Accordingly, the present arrangement
is capable of accurately detecting the change of the blood pressure
over the entire blood pressure range.
In the present embodiment, when the abnormality judging means 88
(Step SB8) judges that the blood pressure of the subject is abnormal,
the abnormality judging means 88 starts the blood pressure measurement
of the blood pressure measuring means 70 (Step SA7). In the present
arrangement, even if the first estimated blood pressure value EBP1
determined based on the pulse-wave propagation time DT.sub.RP may
fall within the reference range having the lower limit value EBP.sub.L
and the upper limit value EBP.sub.H, the blood pressure measurement
of the measuring means 70 (Step SA7) is executed when the second
estimated blood pressure value EBP2 determined based on the pulse
period RR or the third estimated blood pressure value EBP3 determined
based on the normalized pulse-wave area VR does not fall within
the reference range. Accordingly, the present arrangement is capable
of quickly and accurately obtaining reliable blood pressure values
when the blood pressure of the subject has changed.
While the present invention has been described in its presently
preferred embodiment, it is to be understood that the invention
may be otherwise modified.
Each of the coefficients .alpha..sub.1, .alpha..sub.2, .alpha..sub.3
in the above expressions (2)-(4) may be changed based on a predetermined
relationship between a difference of a blood pressure BP measured
by the blood pressure measuring means 70 and an estimated blood
pressure EBP determined immediately after the blood pressure BP
has measured, and an amount of change of each coefficient .alpha..sub.1,
.alpha..sub.2, .alpha..sub.3. The following Table 1 shows one example
of the relationship, i.e., a relationship used in changing the coefficient
.alpha..sub.1 in the above expression (2).
TABLE 1 BP - EBP1 (mmHg) .alpha..sub.1 not less than +30 .alpha..sub.1
- 0.2 not less than +15 and less than +30 .alpha..sub.1 - 0.1 not
less than -15 and less than +15 (not changed) not less than -30
and less than -15 .alpha..sub.1 + 0.1 less than -30 .alpha..sub.1
+ 0.2
The coefficients in the above formulas (2)-(4) may be determined
by utilizing a pre-established neural network, or a fuzzy theory.
For instance, the coefficient .alpha..sub.1, in the above expression
(2) is determined by utilizing a pre-established neural network
into which other sorts of blood pressure-relating information, such
as pulse-period-relating information, peripheral-blood-pressure-volume-relating
information, arterial sclerosis degree, and pulse pressure, are
input.
In the illustrated embodiment, the peripheral-blood-volume-relating
information 78 obtains, as the peripheral-blood-volume-relating
information, the normalized pulse-wave area VR which is obtained
by normalizing a pulse-wave area S defined by a waveform of a pulse
of the photoelectric pulse wave. The pulse-wave area S of the waveform
of one pulse of the photoelectric pulse wave may be used, as the
peripheral- blood-volume-relating information, without being normalized.
Alternatively, the amplitude of one pulse of the photoelectric pulse
wave may be used as the peripheral-blood-volume-relating information.
In the illustrated embodiment, the abnormality judging means 88
judges whether or not at least one of the first estimated blood
pressure value EBP1 determined based on the pulse-wave propagation
time DT.sub.RP, the second estimated blood pressure value EBP2 determined
based on the pulse period RR, and the third estimated blood pressure
value EBP3 determined based on the normalized pulse-wave area VR
falls within the common reference range having the lower limit value
EBP.sub.L and the upper limit value EBP.sub.H. The abnormality judging
means 88 may be arranged to judge whether or not at least one of
the pulse-wave-propagation-velocity-relating information, the pulse-period-relating
information, and the peripheral-blood-volume-relating information
falls within a corresponding one of a first, a second, and a third
reference range, respectively, which are different from one another.
The BP monitor apparatus of the illustrated embodiment is arranged
to control the display device 32 to indicate abnormality of the
blood pressure of the subject, and to effect the blood pressure
measurement by the blood pressure measuring means 70 when the abnormality
judging means 88 judges abnormality of the blood pressure. The BP
monitor apparatus may be arranged to effect only one of the indication
of abnormality of the blood pressure on the display device 32 and
the blood pressure measurement by the blood pressure measuring means
70.
In the illustrated embodiment, the abnormality judging means 88
judges whether or not at least one of the estimated blood pressure
EBP1, EBP2, EBP3 falls within the reference range having a predetermined
upper limit value and a predetermined lower limit value. However,
the abnormality judging means 88 may be modified to determine upper
and lower limit values of a reference range based on a blood pressure
value BP obtained in the prior blood pressure measurement using
the cuff 10, or a moving average of blood pressure values BP obtained
during a predetermined time period.
While the reference range in the illustrated embodiment has the
lower limit value EBP.sub.L and the upper limit value EBP.sub.H,
the reference range may have only one of the lower and upper limit
values EBP.sub.L, EBP.sub.H.
It is to be understood that the present invention may be embodied
with other changes, modifications, and improvements that may occur
to those skilled in the art without departing from the scope of
the invention defined in the attached claims. |