U.S. patent number RE37,852 [Application Number 09/172,024] was granted by the patent office on 2002-09-17 for blood pressure monitoring system.
This patent grant is currently assigned to Nihon Kohden Corporation. Invention is credited to Shigeru Aso, Hidehiro Hosaka, Hiroshi Sakata, Yoshihiro Sugo.
United States Patent |
RE37,852 |
Aso , et al. |
September 17, 2002 |
Blood pressure monitoring system
Abstract
A blood pressure monitoring system includes a blood pressure
measurement device for measuring blood pressure using a cuff, a
memory for storing an externally inputted pulse wave propagation
time fluctuation threshold, a time interval detection reference
point detection section for detecting a time interval detection
reference point in a pulse wave on the side of aortae of a living
organism, a pulse wave detection section for detecting a pulse wave
on the side of peripheral blood vessels appearing with a time lag
with respect to the pulse wave on the side of aortae, a pulse wave
propagation time measurement section for measuring a pulse wave
propagation time based on respective detected outputs from the time
interval detection reference point detection section and the pulse
wave detection section, an operation device for calculating a pulse
wave propagation fluctuation from two measured pulse wave
propagation times, a judgment device for judging whether or not the
calculated pulse wave propagation time fluctuation exceeds the
pulse wave propagation time fluctuation threshold read from the
memory, and a control device for controlling the blood pressure
measurement device based on an output of the judgment device so
that the blood pressure of a subject is measured using the
cuff.
Inventors: |
Aso; Shigeru (Tokyo,
JP), Sakata; Hiroshi (Tokyo, JP), Sugo;
Yoshihiro (Tokyo, JP), Hosaka; Hidehiro (Tokyo,
JP) |
Assignee: |
Nihon Kohden Corporation
(Tokyo, JP)
|
Family
ID: |
26397947 |
Appl.
No.: |
09/172,024 |
Filed: |
October 14, 1998 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
413850 |
Mar 30, 1995 |
05564427 |
Oct 15, 1996 |
|
|
Foreign Application Priority Data
|
|
|
|
|
Mar 30, 1994 [JP] |
|
|
6-061409 |
Mar 16, 1995 [JP] |
|
|
7-056940 |
|
Current U.S.
Class: |
600/485; 600/493;
600/494; 600/500 |
Current CPC
Class: |
A61B
5/02255 (20130101); A61B 5/0285 (20130101) |
Current International
Class: |
A61B
5/026 (20060101); A61B 5/0285 (20060101); A61B
5/0225 (20060101); A61B 005/00 () |
Field of
Search: |
;600/485,493-6,500 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Nasser; Robert L.
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
What is claimed is:
1. A blood pressure monitoring system comprising: blood pressure
measurement means for measuring blood pressure using a cuff; a
memory for storing an externally inputted pulse wave propagation
time fluctuation threshold; time interval detection reference point
detection means for detecting a time interval detection reference
point in an aortic pulse wave of a subject; pulse wave detection
means for detecting a pulse wave in peripheral blood vessels
appearing with a time lag with respect to the aortic pulse wave;
pulse wave propagation time measurement section for measuring a
pulse wave propagation time based on respective detected outputs
from the time interval detection reference point detection means
and the pulse wave detection means; first operation means for
calculating a pulse wave propagation fluctuation from two measured
pulse wave propagation times; judgment means for judging whether or
not the calculated pulse wave propagation time fluctuation exceeds
the pulse wave propagation time fluctuation threshold read from the
memory; and control means for controlling the blood pressure
measurement means based on an output of the judgment means so that
the blood pressure of a subject is measured using the cuff.
2. The blood pressure monitoring system according to the claim 1,
wherein the memory stores a blood pressure fluctuation threshold,
and further comprising: second operation means for calculating
constants inherent in the subject by dividing a difference between
two blood pressure values obtained by the blood pressure
measurement means by a difference between the two measured pulse
wave propagation times; third operation means for updating the
pulse wave propagation time fluctuation threshold within the memory
by dividing the blood pressure fluctuation threshold read from the
memory by the at least on of said calculated constants inherent in
the subject; and auxiliary control means for controlling the
operation of updating the pulse wave propagation time fluctuation
threshold.
3. A blood pressure monitoring method comprising the steps of:
measuring blood pressure using a cuff; storing an externally
inputted pulse wave propagation time fluctuation threshold in a
memory; detecting a time interval detection reference point in an
aortic pulse wave of aortae of a living organism; detecting a pulse
wave in peripheral blood vessels appearing with a time lag with
respect to the aortic pulse wave; measuring a pulse wave
propagation time based on respective detected outputs from the time
interval detection reference point detection means and the pulse
wave detection means; calculating a pulse wave propagation
fluctuation from two measured pulse wave propagation times; judging
whether or not the calculated pulse wave propagation time
fluctuation exceeds the pulse wave propagation time fluctuation
threshold read from the memory; and controlling the blood pressure
measurement means based on an output of the judgment means so that
the blood pressure of a subject is measured using the cuff.
4. A blood pressure monitoring method comprising the steps of:
measuring blood pressure using a cuff; storing a pulse wave
propagation time fluctuation threshold and a blood pressure
fluctuation threshold in a memory, the thresholds being inputted
from an external means; detecting a time interval detection
reference point in an aortic pulse wave of a living organism;
detecting a pulse wave in peripheral blood vessels appearing with a
time lag with respect to the aortic pulse wave; measuring a pulse
wave propagation time based on respective detected outputs from the
time interval detection reference point detection means and the
pulse wave detection means; calculating a pulse wave propagation
time fluctuation from two measured pulse wave propagation times;
calculating constants inherent in said living organism by dividing
a difference between two blood pressure values obtained by the
blood pressure measurement means by a difference between the two
measured pulse wave propagation times; updating the pulse wave
propagation time fluctuation threshold within the memory by
dividing the blood pressure fluctuation threshold read from the
memory by the at least on of said calculated constants inherent in
the subject; controlling the operation of updating the pulse wave
propagation time fluctuation threshold; judging whether or not the
calculated pulse wave propagation time fluctuation exceeds the
pulse wave propagation time fluctuation threshold read from the
memory; and controlling the blood pressure measurement means based
on an output of the judgment means so that the blood pressure of
the subject is measured using the cuff. .Iadd.
5. A blood pressure monitoring apparatus comprising: blood pressure
measurement means for measuring blood pressure using a cuff; pulse
wave propagation time measurement means for measuring pulse wave
propagation time; control means for controlling said blood pressure
measurement means substantially on the basis of the pulse wave
propagation time measured by said pulse wave propagation time
measurement means, so that the blood pressure of a subject is
measured using the cuff..Iaddend..Iadd.
6. The blood pressure monitoring apparatus according to claim 5,
wherein said control means controls the blood pressure measurement
means based on the judgement whether or not pulse wave propagation
time fluctuation exceeds a predetermined threshold, so that the
blood pressure of the subject is measured using the
cuff..Iaddend..Iadd.
7. The blood pressure monitoring apparatus according to claim 6,
further comprising: updating means for updating said predetermined
threshold..Iaddend..Iadd.
8. The blood pressure monitoring apparatus according to claim 7,
wherein said updating means updates said predetermined threshold by
modifying a constant inherent in the subject which is represented
in the relationship between blood pressure and pulse wave
propagation time..Iaddend..Iadd.
9. The blood pressure monitoring apparatus according to claim 7,
wherein said updating means updates on the basis of at least two
pairs of information of blood pressure values, obtained by said
blood pressure measurement means, and pulse wave propagation times,
obtained by said pulse wave propagation time measurement
means..Iaddend..Iadd.
10. The blood pressure monitoring apparatus according to claim 7,
wherein said updating means comprises: first operation means for
calculating a constant inherent in the subject by dividing a
difference between two blood pressure values obtained by the blood
pressure measurement means by a difference between the two measured
pulse wave propagation times; second operation means for updating
said predetermined threshold by dividing a second predetermined
threshold by said calculated constant inherent in the subject; and
auxiliary control means for controlling the operation of updating
said predetermined threshold..Iaddend..Iadd.
11. The blood pressure monitoring apparatus according to claim 5,
wherein said pulse wave propagation time measuring means includes
an electrode to be attached to the subject, and senses an
electrocardiographic wave for detecting a time interval detection
reference point..Iaddend..Iadd.
12. The blood pressure monitoring apparatus according to claim 5,
wherein said pulse wave propagation time measuring means includes
at least one of a photoelectric pulse wave sensor and a pressure
pulse wave sensor for detecting a time interval detection reference
point in an aortic pulse wave of a subject..Iaddend..Iadd.
13. The blood pressure monitoring apparatus according to claim 5,
wherein said pulse wave propagation time measuring means includes a
photoelectric pulse wave sensor for measuring a pulse wave at a
peripheral blood vessel..Iaddend..Iadd.
14. The blood pressure monitoring apparatus according to claim 11,
wherein said electrocardiographic wave is an R
wave..Iaddend..Iadd.
15. A blood pressure monitoring system comprising: blood pressure
measurement means for measuring blood pressure using a cuff; pulse
wave propagation time measurement means for measuring a pulse wave
propagation time; first operation means for calculating a pulse
wave propagation fluctuation from two measured pulse wave
propagation times; judgment means for judging whether or not the
calculated pulse wave propagation time fluctuation exceeds a first
predetermined threshold; and control means for controlling the
blood pressure measurement means based on an output of the judgment
means so that the blood pressure of a subject is measured using the
cuff..Iaddend..Iadd.
16. The blood pressure monitoring system according to the claim 15,
further comprising: second operation means for calculating
constants inherent in a subject by dividing a difference between
two blood pressure values obtained by the blood pressure
measurement means by a difference between the two measured pulse
wave propagation times; third operation means for updating said
first predetermined threshold by dividing a second predetermined
threshold by the at least one of said calculated constants inherent
in the subject; and auxiliary control means for controlling the
operation of updating said first predetermined
threshold..Iaddend..Iadd.
17. A blood pressure monitoring method comprising the steps of:
measuring blood pressure using a cuff; measuring a pulse wave
propagation time; calculating a pulse wave propagation time
fluctuation from two measured pulse wave propagation times; judging
whether or not the calculated pulse wave propagation time
fluctuation exceeds a predetermined threshold; and controlling
measurement of blood pressure in the measuring step based on a
result of the judging step so that the blood pressure of a subject
is measured using the cuff..Iaddend..Iadd.
18. A blood pressure monitoring method comprising the steps of:
measuring blood pressure using a cuff; measuring a pulse wave
propagation time; calculating a pulse wave propagation time
fluctuation from two measured pulse wave propagation times;
calculating constants inherent in said living organism by dividing
a difference between two blood pressure values obtained by the
blood pressure measurement means by a difference between the two
measured pulse wave propagation times; updating a first
predetermined threshold by dividing a second predetermined
threshold by at least one of said calculated constants inherent in
the subject; judging whether or not the calculated pulse wave
propagation time fluctuation exceeds said first predetermined
threshold; and controlling the measuring step based on a result of
the judging step so that the blood pressure of a subject is
measured using the cuff..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a blood pressure monitoring system in
fields requiring continuous blood pressure monitoring of a patient
in an operating room, an intensive care unit, a first-aid room, an
extracorporeal dialysis room, and the like. More particularly, the
invention is directed to a blood pressure monitoring system
utilizing pulse wave propagation time.
2. Related Art
To monitor the blood pressure of a subject by continuously
measuring his or her blood pressure, the following methods have
heretofore been available. An oscillometric, noninvasive method is
designed to measure blood pressure by wrapping a cuff to the upper
part of an arm of the subject. A direct, invasive method is
designed to measure blood pressure by puncturing an artery of the
subject.
By the way, the noninvasive blood pressure measuring method using
the cuff may, in some cases, overlook a drastic change in blood
pressure due to a shock when the measuring cycle in fixed time
measurement is long (e.g., when the measuring cycle is set to 5
minutes or more).
If the measuring cycle is reduced to, e.g., 1 minute to overcome
this problem, the blood vessel around which the cuff is wrapped is
burdened, which in turn imposes the problem of causing internal
hemorrhage.
Further, in the case of fixed time measurement, frequently applied
cuff wrapping force that is more than necessary burdens the
patient, and therefore causes somnipathy and the like.
On the other hand, the direct, invasive blood pressure measurement
not only gives the subject a mental burden due to invasion or
brings about the problem of infection, but also gives too much work
to the medical staff by involving more labor than in noninvasive
blood pressure measurement.
SUMMARY OF THE INVENTION
The invention has been proposed to overcome these problems
encountered by the conventional art. Accordingly, the object of the
invention is to provide a blood pressure monitoring system capable
of monitoring the blood pressure of a subject continuously in
safety without burdening the subject.
A blood pressure monitoring system based on the aforementioned
measurement principle of the invention includes: a blood pressure
measurement means for measuring blood pressure using a cuff, a
memory for storing an externally inputted pulse wave propagation
time fluctuation threshold; a time interval detection reference
point detection means for detecting a time interval detection
reference point in a pulse wave on the side of aortae of a living
organism; a pulse wave detection means for detecting a pulse wave
on the side of peripheral blood vessels appearing with a time lag
with respect to the pulse wave on the side of aortae; a pulse wave
propagation time measurement section for measuring a pulse wave
propagation time based on respective detected outputs from the time
interval detection reference point detection means and the pulse
wave detection means; an operation means for calculating a pulse
wave propagation fluctuation from two measured pulse wave
propagation times; a judgment means for judging whether or not the
calculated pulse wave propagation time fluctuation exceeds the
pulse wave propagation time fluctuation threshold read from the
memory; and a control means for controlling the blood pressure
measurement means based on an output of the judgment means so that
the blood pressure of a subject is measured using the cuff.
Further, a blood pressure monitoring system of the invention
includes: a blood pressure measurement means for measuring blood
pressure using a cuff; a memory for storing a pulse wave
propagation time fluctuation threshold and a blood pressure
fluctuation threshold, the thresholds being inputted from an
external means; a time interval detection reference point detection
means for detecting a time interval detection reference point in a
pulse wave on the side of aortae of a living organism; a pulse wave
detection means for detecting a pulse wave on the side of
peripheral blood vessels appearing with a time lag with respect to
the pulse wave on the side of aortae; a pulse wave propagation time
measurement section for measuring a pulse wave propagation time
based on respective detected outputs from the time interval
detection reference point detection means and the pulse wave
detection means; a first operation means for calculating a pulse
wave propagation time fluctuation from two measured pulse wave
propagation times; a second operation means for calculating
constants inherent in a subject by dividing a difference between
two blood pressure values obtained by the blood pressure
measurement means by a difference between the two measured pulse
wave propagation times; a third operation means for updating the
pulse wave propagation time fluctuation threshold within the memory
by dividing the blood pressure fluctuation threshold read from the
memory by the calculated constants inherent in the subject; a first
control means for controlling the operation of updating the pulse
wave propagation time fluctuation threshold; a judgment means for
judging whether or not the calculated pulse wave propagation time
fluctuation exceeds the pulse wave propagation time fluctuation
threshold read from the memory; and a second control means for
controlling the blood pressure measurement means based on an output
of the judgment means so that the blood pressure of the subject is
measured using the cuff.
According to the present invention, the blood pressure of a subject
can be measured by measuring a pulse wave propagation time
fluctuation and consecutively judging whether or not the measured
pulse wave propagation time fluctuation exceeds a pulse wave
propagation time fluctuation threshold. As long as the blood
pressure is measured correctly using the cuff when the pulse wave
propagation time fluctuation has exceeded the pulse wave
propagation time fluctuation threshold, burdens given to the
subject can be minimized.
Further, according to the present invention, the pulse wave
propagation time fluctuation threshold is updated. Therefore, the
operation of monitoring the blood pressure of the subject can be
performed more accurately.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a blood pressure monitoring
system, which is an embodiment of the invention;
FIG. 2 is a flowchart illustrative of an operation of the blood
pressure monitoring system of FIG. 1;
FIG. 3 is a flowchart illustrative of an operation of another
embodiment of the invention; and
FIG. 4 is a waveform diagram illustrative of a pulse wave
propagation time.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the invention will now be described in detail with
reference to the drawings.
The basic concept of the invention will now be described below.
A blood pressure measuring apparatus that measures blood pressure
from pulse wave propagation speed (the time required for a pulse
wave to be propagated a predetermined distance) is known as a
noninvasive blood pressure measuring apparatus.
The principle of blood pressure measurement based on the pulse wave
propagation speed can be explained in the following way.
The pulse wave propagation time will be described first. As shown
in FIG. 4, a specific point of a pulse wave on the side of
peripheral blood vessels such as a finger or a ear appears with a
time lag with respect to a specific point of an aortic pulse wave.
This time lag is the pulse wave propagation time.
The pulse wave propagation speed corresponding to the time required
for a pulse wave to be propagated a predetermined distance is
expressed in the form of a function of the modulus of volumetric
elasticity of a blood vessel. When the blood pressure increases,
the modulus of volumetric elasticity of the blood vessel is
increased; the blood vessel wall hardens; and the propagation speed
is increased. Therefore, a blood pressure fluctuation can be found
from the pulse wave propagation speed.
The blood pressure measuring apparatus based on the pulse wave
propagation time measures blood pressure by using a cuff or the
like and must make a calibration with reference to the measured
blood pressure data.
For the calibration, blood pressures and pulse wave propagation
times are measured when a subject is at rest and when the subject
is in exercise.
Here, let it be assumed that the blood pressure and the pulse wave
propagation time when the subject is at rest are P1, T1; the blood
pressure and the pulse wave propagation time when the subject is in
exercise are P2, T2; and constants inherent in the subject are
.alpha., .beta.. Then, the blood pressures P1, P2 are given as
Therefore, by measuring P1, T1, P2, T2, the constants .alpha.,
.beta. can be calculated from the above two equations. Once the
constants .alpha., .beta. have been calculated, the blood pressure
of the subject can be measured only by measuring the pulse wave
propagation time from then on.
To measure two different blood pressures, measurement may be made
at any timings at which two different blood pressures appear;
measurement may not necessarily be made when the subject is at rest
and in exercise.
On the other hand, the blood pressure fluctuation of the subject
could be monitored simply by measuring the pulse wave propagation
time consecutively. In this case, the procedure to be taken is as
follows. First, it is judged that a drastic change has occurred in
the blood pressure fluctuation of the subject when a pulse wave
propagation time fluctuation .DELTA.T has exceeded a preset pulse
wave propagation time fluctuation threshold .DELTA.T.sub.s. Then,
the blood pressure is non-invasively measured correctly using the
cuff at such timing of drastic change.
Since this procedure frees the subject from burdens accompanied in
the case where the blood pressure is measured continuously at a
predetermined cycle using the cuff, the burdens borne by the
subject can be remarkably alleviated.
FIG. 1 shows a blood pressure monitoring system, which is an
embodiment of the invention, in the form of a block diagram. In
FIG. 1, a cuff 2 is designed to be put on the upper part of an arm
or a finger of a subject. An exhaust valve 3 of opens and closes
the cuff with respect to the atmosphere. The air is supplied to the
cuff 2 by a pressuring pump 4. A pressure sensor 5 is attached to
the cuff main body, and a sensor output is detected by a cuff
pressure detection section 6. The output of the cuff pressure
detection section 6 is converted into a digital signal by an A/D
converter 7, and inputted to a CPU (Central Processing Unit) 1.
A time interval detection reference point detection section 8 is
designed to detect a timing at which the aortic pressure hits the
bottom value substantially simultaneously with the generation of an
R wave in an electrocardiogram. The output of this detection
section is converted into a digital signal by an A/D converter 9,
and inputted to the CPU 1. The time interval detection reference
point detection section 8 may include an electrode attached to the
chest of a subject, and an electrocardiographic R wave detection
section to which the electrode is connected. Further, the time
interval detection reference point detection section 8 may,
instead, include a photoelectric pulse wave sensor or pressure
pulse wave sensor for detecting the pulse wave of the aorta, and a
pulse wave detection section to which either one of these sensors
is connected.
On the other hand, the photoelectric pulse wave sensor 10 is
attached to, e.g., a finger of a subject to measure the pulse wave
on the side of peripheral blood vessels. The output of this sensor
10 is applied to the pulse wave detection section 11, so that the
pulse wave at the position of the subject to which the sensor 10 is
attached can be detected. The output of the pulse wave detection
section 11 is inputted to the CPU 1 after converted into a digital
signal by an A/D converter 12.
A key 14 is pressed either to manually measure blood pressure with
the cuff 2 or to update a pulse wave propagation time fluctuation
threshold .DELTA.T.sub.s.
An initial pulse wave propagation time fluctuation threshold
.DELTA.T.sub.s and a blood pressure fluctuation threshold
.DELTA.BP.sub.s are inputted from an input means 13.
The CPU 1 executes a processing program based on signals inputted
from the A/D converters 7, 9, 12 and the key 14 to not only output
necessary signals to the exhaust valve 3, the pressuring pump 4,
and the like, but also output processed results to a display 15. A
memory (ROM) 16 that is connected to the CPU 1 stores the
processing program, and a memory (RAM) 17 that is also connected to
the CPU 1 stores in-process data.
It may be noted that the CPU 1 constitutes a pulse wave propagation
time measurement section, an operation means, a judgment means, and
a control means, and further constitutes first to third operation
means, and first and second control means.
An operation of the thus constructed blood pressure monitoring
system will be described with reference to a flowchart shown in
FIG. 2.
First, the pulse wave propagation time fluctuation threshold
.DELTA.T.sub.s is inputted from the input means 13, and written to
the memory 17 in Step S1.
Then, whether or not the key 14 has been pressed is judged in Step
S2. If the key has been pressed, the exhaust valve 3 and the
pressuring pump 4 are controlled by the CPU 1 to start measuring
the blood pressure of a subject using the cuff 2 in Step S3. At
this instance, the data supplied from the A/D converter 7 is
processed within the CPU 1, and a blood pressure value BP1 measured
by an oscillometric method is written to the memory 17.
Then, a pulse wave propagation time T1 is measured based on the
data inputted to the CPU 1 from the A/D converters 9, 12, and the
measured value is written to the memory 17 in Step S4. The pulse
wave propagation time T1 is equivalent to a time from a timing at
which the aortic pressure hits the bottom value substantially
simultaneously with the generation of an R wave in an
electrocardiogram to a timing at which the pulse wave hits the
bottom value on the side of peripheral blood vessels.
Subsequently, the previously measured blood pressure value BP1 is
displayed on the display 15 in Step S5. The system then returns to
Step S2.
In Step S2, whether or not the key has been pressed is judged
again. If the key has not been pressed, a pulse wave propagation
time T.sub.2 is measured based on the data from the A/D converters
9, 12, and the measured value is written to the memory 17 in Step
S6.
Then, in Step S7, whether or not the previously measured pulse wave
propagation time T1 data is present is judged. If the data is
present, a pulse wave propagation time fluctuation .DELTA.T is
calculated based on the following equation using T1, T2 in Step
S8.
Then, in Step S9, whether or not the pulse wave propagation time
fluctuation .DELTA.T calculated in Step S8 exceeds the pulse wave
propagation time fluctuation threshold .DELTA.T.sub.s inputted in
advance is judged; i.e., whether or not .DELTA.T satisfies an
inequality .DELTA.T>.DELTA.T.sub.s is judged. If
.DELTA.T>.DELTA.T.sub.s is not satisfied, the system returns to
Step S2 to repeat a series of processing.
On the other hand, if it is judged that .DELTA.T>.DELTA.T.sub.s
is satisfied in Step S9, the system deems that a drastic change
such as a shock has occurred in the blood pressure fluctuation of
the subject, and therefore proceeds to Step S3.
In Step S3, to handle the drastic change in the blood pressure
fluctuation of the subject, blood pressure is measured with the
cuff 2, and the measured value BP1 is written to the memory 17.
Successively, the pulse wave propagation time T1 is measured based
on the data from the A/D converters 9, 12 again, and the measured
value is written to the memory 17 in Step S4.
In Step S5, the blood pressure measured in Step S3 is displayed on
the display 15. The system then returns to Step S2.
By judging whether or not the pulse wave propagation time
fluctuation .DELTA.T exceeds the pulse wave propagation time
fluctuation threshold .DELTA.T.sub.s while measuring the pulse wave
propagation time at all times in this way, a drastic change in the
blood pressure fluctuation of a subject is monitored. In addition,
blood pressure is measured correctly using the cuff 2 when a
drastic change in the blood pressure fluctuation has been
monitored. Therefore, the burden conventionally given to the
subject can be reduced significantly.
An operation of another embodiment in the case of correcting the
pulse wave propagation time fluctuation threshold .DELTA.T.sub.s,
will be described next with reference to a flowchart shown in FIG.
3.
First, the initial pulse wave propagation time fluctuation
threshold .DELTA.T.sub.s and a blood pressure fluctuation threshold
.DELTA.BP.sub.s, are inputted from the input means 13, and written
to the memory 17 in Step S11.
Then, whether or not the key 14 has been pressed is judged in Step
S12. If the key has been pressed, blood pressure is made with the
cuff 2, and the measured value BP1 is written to the memory 17 in
Step S13.
Then, the pulse wave propagation time T1 is measured based on the
data from the A/D converters 9, 12, and written to the memory 17 in
Step S14.
Then, the previously measured blood pressure value BP1 is displayed
on the display 15 in Step S15.
Successively, whether or not measured blood pressure value data BP3
is present is judged in Step S16. If the data is not present, not
only the blood pressure value BP1 is written to the memory 17 as
BP3, but also the pulse wave propagation time T1 is written to the
memory 17 as T3 in Step S19. The system then returns to Step
S12.
If it is judged that the measured blood pressure value data BP3 is
present in Step S16, values .alpha., .beta., and .DELTA.T.sub.s are
calculated based on the following equations.
The calculated constants .alpha., .beta. inherent in a subject are
written to the memory 17, and used thereafter to calculate a blood
pressure using the pulse wave propagation time T2.
Further, the pulse wave propagation time fluctuation threshold
.DELTA.T.sub.s is updated to the calculated value, and written to
the memory 17 in Step S18.
Successively, not only the blood pressure value BP1 is written to
the memory 17 as BP3, but also the pulse wave propagation time T1
is written to the memory 17 as T3 in Step S19. The system then
returns to Step S12.
In Step S12, whether or not the key has been pressed is judged
again. If the key has not been pressed, the pulse wave propagation
time T2 is measured based on the data from the A/D converters 9,
12, and the measured value is written to the memory 17 in Step
S20.
Then, in Step S21, a blood pressure value P is calculated from the
following equation using both the measured pulse wave propagation
time T2 and the constants .alpha., .beta. calculated in Step S17,
and the calculated value is written to the memory 17.
P=.alpha.T2+.beta.
In Step S22, the calculated blood pressure value P is displayed on
the display 15.
Successively, in Step S23, whether or not the previously measured
pulse wave propagation time data T3 is present is judged. If the
data is present, a pulse wave propagation time fluctuation .DELTA.T
is calculated from the following equation using T2, T3 in Step
S24.
Then, in Step S25, whether or not the pulse wave propagation time
fluctuation .DELTA.T calculated in Step S24 exceeds the pulse wave
propagation time fluctuation threshold .DELTA.T.sub.s inputted in
advance is judged; i.e., whether or not .DELTA.T satisfies an
inequality .DELTA.T>.DELTA.T.sub.s is judged. If
.DELTA.T>.DELTA.T.sub.s is not satisfied, the system returns to
Step S12 to repeat a series of processing.
On the other hand, if it is judged that .DELTA.T>.DELTA.T.sub.s
is satisfied in Step S25, the system deems that a drastic change
such as a shock has occurred in the blood pressure fluctuation of
the subject, and therefore proceeds to Step S13.
In Step S13, to handle the drastic change in the blood pressure
fluctuation of the subject, blood pressure is measured using the
cuff 2, and the measured value BP1 is written to the memory 17.
Successively, the pulse wave propagation time T1 is measured based
on the data from the A/D converters 9, 12 again, and the measured
value is written to the memory 17 in Step S14.
In Step S15, the blood pressure correctly measured in Step S13 is
displayed on the display 15. The system then moves to Step S16 to
repeat similar processing.
As described above, this embodiment is characterized as allowing a
drastic change in the blood pressure fluctuation of a subject to be
monitored more correctly by updating the pulse wave propagation
time fluctuation threshold .DELTA.T.sub.s.
Moreover, a pulse wave propagation time measurement is made on a
single pulse basis, or such measurements may be made at a
predetermined time interval or predetermined number of pulses and
the measured values may thereafter be averaged. The averaging
operation contributes to more accurate measurement free from
irregularly generated noise.
As described in the foregoing, the present invention is provided as
not only judging whether or not a drastic change in the blood
pressure fluctuation of a subject has occurred by judging whether
or not the pulse wave propagation time fluctuation has exceeded the
pulse wave propagation time fluctuation threshold while
consecutively measuring the pulse wave propagation time, but also
correctly measuring the blood pressure of the subject using a cuff
when the blood pressure changes drastically. Therefore, pains such
as those to which the subject is exposed when the blood pressure is
measured using the cuff at a short interval or in the case of the
direct, invasive blood pressure measurement in the conventional
blood pressure measurement are not accompanied, so that the burden
to be borne by the subject can be reduced significantly.
Further, the present invention is provided as updating the pulse
wave propagation time fluctuation threshold. Therefore, the
invention can provide the advantage that a drastic change in the
blood pressure fluctuation of a subject can be monitored more
correctly.
* * * * *