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Claims  |
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What is claimed is:
1. A pulse-wave propagation time basis blood pressure monitor comprising:
a memory for storing information representing a relationship between pulse
wave propagation times and values of a parameter .alpha., each of said
pulse wave propagation times being derived from data gathered from a
number of subjects;
input means for inputting a blood pressure value of a subject, for
calibration;
time-interval detect reference point detecting means for detecting a time
of occurrence of a pulse wave in the aorta of a subject;
pulse wave detecting means for detecting a pulse wave which appears in a
peripheral blood vessel after said pulse wave appears in the aorta;
pulse-wave propagation time measuring means for measuring pulse wave
propagation time from signals output from said time-interval detect
reference point detecting means and said pulse wave detecting means,
wherein a first measured pulse wave propagation time is used for
calibration;
first computing means for determining the parameter .alpha. which
corresponds to said pulse wave propagation time used for calibration based
upon the information stored in said memory;
second computing means for determining a parameter .beta. by using said
blood pressure value input for calibration, said pulse wave propagation
time measured for calibration, and said parameter .alpha. determined by
said first computing means;
third computing means for computing a blood pressure value in accordance
with another pulse wave propagation time measured by said pulse-wave
propagation time measuring means, and the parameters .alpha. and .beta.;
and
measured data output means for outputting at least one of said blood
pressure value and said parameter .alpha..
2. The pulse-wave propagation time basis blood pressure monitor according
to claim 1, wherein said information includes one of a predetermined
equation and a table describing the relationship between said pulse wave
propagation times and said values of said parameter .alpha. stored in said
memory.
3. A pulse-wave propagation time basis blood pressure monitor comprising:
a memory for storing information representing a relationship between pulse
pressure values and values of a parameter .alpha., said pulse pressure
values being derived from data gathered from a number of subjects;
input means for inputting a blood pressure value of a subject, for
calibration;
pulse pressure computing means for computing a pulse pressure for
calibration using said blood pressure value received from said input
means;
time-interval detect reference point detecting means for detecting a time
of occurrence of a pulse wave in the aorta of the subject;
pulse wave detecting means for detecting a pulse wave which appears in a
peripheral blood vessel after said pulse wave appears in the aorta;
pulse-wave propagation time measuring means for measuring pulse wave
propagation time from output signals of said time-interval detect
reference point detecting means and said pulse wave detecting means,
wherein a first measured pulse wave propagation time is used for
calibration;
first computing means for determining the parameter .alpha. which
corresponds to said pulse pressure for calibration computed for the
subject based upon the information stored in said memory;
second computing means for determining a parameter .beta. by using said
blood pressure value input for calibration, said pulse wave propagation
time used for calibration, and the parameter .alpha. determined by said
first computing means;
third computing means for computing a blood pressure value by using another
pulse wave propagation time measured by said pulse-wave propagation
measuring means, and the parameters .alpha. and .beta.; and
measured data output means for outputting at least one of said blood
pressure value and said parameter .alpha..
4. The pulse-wave propagation time basis blood pressure monitor according
to claim 3, wherein said information includes one of a predetermined
equation and a table describing the relationship between said blood
pressure values and said values of said parameter .alpha. stored in said
memory.
5. A pulse-wave propagation time basis blood pressure monitor comprising:
first input means for inputting at least a patient's height value as
patient information;
second input means for inputting a blood pressure value for calibration;
time-interval detect reference point detecting means for detecting a time
of occurrence of a pulse wave in the aorta of the patient;
pulse wave detecting means for detecting a pulse wave which appears in a
peripheral blood vessel after said pulse wave appears in the aorta;
pulse-wave propagation time measuring means for measuring pulse wave
propagation time, at a supine position and at one of a sitting and
standing position, from output signals of said time-interval detect
reference point detecting means and said pulse wave detecting means,
wherein a first measured pulse wave propagation time in one of said supine
position, said sitting position and said standing position is used for
calibration;
first computing means for computing a change .DELTA.T of said pulse wave
propagation time at a time of postural change by using a pulse wave
propagation time for calibration measured at said supine position and a
pulse wave propagation time for calibration measured at said one of a
sitting position and a standing position;
second computing means for computing a change .DELTA.P of a hydrostatic
pressure between the heart and a pulse wave measuring position at the time
of postural change, by using the patient's height as patient information;
third computing means for determining a parameter .alpha. by using said
change .DELTA.T of said pulse wave propagation time and said change
.DELTA.P of the hydrostatic pressure;
fourth computing means for determining a parameter .beta. by using said
blood pressure value input for calibration, said pulse wave propagation
time used for calibration, and the parameter .alpha. determined by said
third computing means;
fifth computing means for computing a blood pressure value by using another
pulse wave propagation time measured by said pulse-wave propagation time
measuring means, and the parameters .alpha. and .beta.; and
measured data output means for outputting at least one of said blood
pressure value, said parameter .alpha. and said parameter .beta..
6. A method for measuring blood pressure using a pulse-wave propagation
time basis blood pressure monitor comprising the steps of:
storing information describing the relationship between pulse wave
propagation times and values of a parameter .alpha. in a memory, each of
said pulse wave propagation times being derived from data gathered from a
number of subjects;
inputting a blood pressure value of a subject for calibration;
detecting a reference point for detecting a time of occurrence of a pulse
wave in the aorta of the subject;
detecting a pulse wave which appears in a peripheral blood vessel after
said pulse wave appears in the aorta;
measuring a pulse wave propagation time from said reference point and said
pulse wave which appears in the peripheral blood vessel for calibration;
determining the parameter .alpha. proper to the subject based upon the
information stored in said memory corresponding to said pulse wave
propagation time for calibration gathered from the subject;
determining a parameter .beta. by using said blood pressure value input for
calibration, said pulse wave propagation time for calibration, and the
parameter .alpha.;
measuring a second propagation time of another pulse wave into the
peripheral blood vessel;
computing a blood pressure value in accordance with said second pulse wave
propagation time, and the parameters .alpha. and .beta.; and
outputting at least one of said blood pressure value, said parameter
.alpha. and said parameter .beta..
7. A method for measuring blood pressure using a pulse-wave propagation
time basis blood pressure monitor, comprising the steps of:
storing information describing the relationship between pulse pressure
values and values of a parameter .alpha. in a memory, said pulse pressure
values being derived from data gathered from a number of subjects;
inputting a blood pressure value of the subject for calibration;
computing a pulse pressure for calibration using said blood pressure value;
detecting a reference point for detecting a time of occurrence of a pulse
wave in the aorta of the subject;
detecting a pulse wave which appears in a peripheral blood vessel after
said pulse wave appears in the aorta;
measuring a pulse wave propagation time from said time of occurrence of
said pulse wave in the aorta of the subject and said pulse wave of said
peripheral blood vessel;
determining the parameter .alpha. proper to the subject based upon the
information stored in said memory corresponding to said pulse pressure for
calibration gathered from the subject;
determining a parameter .beta. by using said blood pressure value input for
calibration, said pulse wave propagation time and the parameter .alpha.;
measuring a second propagation time of another pulse wave into the
peripheral blood vessel;
computing a blood pressure value by using said second pulse wave
propagation time, and the parameters .alpha. and .beta.; and
outputting at least one of said blood pressure value, said parameter
.alpha. and said parameter .beta.. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pulse-wave propagation time basis blood
pressure monitor suitable for a stress test blood pressure monitor, a
blood pressure monitor of the Holter type, and a blood pressure monitor
used in a care room, which are used in a field where a non-restrictive,
successive and noninvasive blood pressure measurement is required for a
subject. More particularly, the present invention relates to a blood
pressure monitor for measuring parameter values used when blood pressure
is measured by using the pulse wave propagation time without greatly
varying blood pressure in a stress test, for example.
2. Related art
A blood pressure monitor using a cuff has been known as a noninvasive blood
pressure monitor which is capable of measuring a blood pressure in a
successive and noninvasive fashion.
In this type of blood pressure monitor, the cuff must be wound on the upper
part of an arm. Accordingly, the arm is restricted by the cuff wound
thereon, the weight of the cuff is for the subject to bear, and the
subject's sleep will be disturbed by squeezing the arm by the cuff or
noise generated when the cuff is handled.
To continuously monitor blood pressure values of a subject, when the
measurement interval is 5 minutes or longer, an abrupt change of a blood
pressure by a shock is possibly passed unmarked.
One of the possible ways to solve this problem is to reduce the measuring
interval to about one minute. In this case, the tightening of the arm by
the cuff is frequently repeated, to thereby increase a load to the subject
and to the blood vessels in the portion wound by the cuff. In the extreme
case, inner hemorrhage may be caused in the subject.
For the noninvasive blood pressure monitor which succeeds in solving the
problems of the above-mentioned blood pressure monitor, there is known a
blood pressure monitor for measuring a blood pressure by making use of a
pulse wave propagation velocity (pulse wave propagation time for a fixed
time).
The principle of measuring a blood pressure on the basis of a pulse wave
propagation velocity will be described.
The pulse wave propagation time will first be described. As shown in FIG.
9, a specific point of a pulse wave appears in the peripheral blood vessel
of the finger or the ear later than in the aorta. This delay time is a
pulse wave propagation time.
A pulse wave propagation velocity corresponding to a pulse wave propagation
time for a fixed distance is expressed as the function of a volumetric
elasticity of the vessel. When a blood pressure rises, the volumetric
elasticity of the vessel increases, the wall of the vessel becomes hard,
and the pulse wave propagation velocity increases.
As a consequence, a variation of the blood pressure can be obtained from
the pulse wave propagation velocity.
The blood pressure monitor based on the pulse wave propagation time must be
calibrated by the values of the blood pressure measured by a blood
pressure measuring method which uses the cuff or other suitable means.
For the calibration, the blood pressure and the pulse wave propagation time
are measured at rest and at excercise stress, for example.
Assuming that the blood pressure and the pulse wave propagation times at
rest are P1 and T1, the blood pressure and the pulse wave propagation
times at excercise stress are P2 and T2, and constants (parameters) proper
to subjects are .alpha. and .beta., then the blood pressure P1 and P2 are
expressed by
P1=.alpha.T1+.beta.
P2=.alpha.T2+.beta.
As seen from these equations, if P1, T1, P2, and T2 are determined by
measurement, the parameters .alpha. and .beta. can be calculated. If these
parameters are determined, a blood pressure of a subject can be obtained
by merely measuring the pulse wave propagation time.
Thus, in the blood pressure monitor using the pulse wave propagation time,
the calibration for determining the parameters .alpha. and .beta. is
inevitably required. For the calibration, a stress test must be carried
out on the subject. The test puts a strain on the subject, and much time
is taken for the calibration.
Additionally, a stress test device or a blood pressure monitor exclusively
used for the stress test must used, thereby increasing the device cost.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a pulse-wave
propagation time basis blood pressure monitor which can measure a blood
pressure on the basis of the pulse wave propagation time without
increasing the time for the calibration to determine the parameters
.alpha. and .beta. and putting a strain to the subject.
According to an aspect of the present invenion, there is provided a
pulse-wave propagation time basis blood pressure monitor comprising:
a memory for storing a general equation describing the relationship between
the pulse wave propagation time and the parameter .alpha., in computing
blood pressure values from the pulse wave propagation time, the pulse wave
propagation time being derived from data gathered from a number of
subjects in order to determine the parameter .alpha. that is proper to
each subject and to be multiplied by the pulse wave propagation time;
input means for inputting blood pressure values of subjects that are for
calibration;
time-interval detect reference point detecting means for detecting a
reference point for detecting the time interval of a pulse wave in the
aorta of a subject;
pulse wave detecting means for detecting a pulse wave which appears in the
peripheral blood vessel after it appears in the aorta;
pulse-wave propagation time measuring means for measuring a pulse wave
propagation time from the output signals of the time-interval detect
reference point detecting means and the pulse wave detecting means;
first computing means for determining the parameter .alpha. proper to the
subject on the basis of the general equation stored in the memory by using
the pulse wave propagation time for calibration gathered from the subject;
second computing means for determining the parameter .beta. to be added in
computing a blood pressure value by using the pulse wave propagation time,
by using the blood pressure value inputted for calibration, the pulse wave
propagation time measured for calibration, and the parameter .alpha.
determined by the first computing means;
third computing means for computing a blood pressure value by using the
measured pulse wave propagation time, and the parameters .alpha. and
.beta.; and
measured data output means for outputting data of the computed blood
pressure value.
The first technical idea may also be realized by a pulse-wave propagation
time basis blood pressure monitor comprising:
a memory for storing a table describing the relationship between the pulse
wave propagation time and the parameter .alpha., in computing blood
pressure values from the pulse wave propagation time, the pulse wave
propagation time being derived from data gathered from a number of
subjects in order to determine the parameter .alpha. that is proper to
each subject and to be multiplied by the pulse wave propagation time;
input means for inputting blood pressure values of subjects that are for
calibration;
time-interval detect reference point detecting means for detecting a
reference point for detecting the time interval of a pulse wave in the
aorta of a subject;
pulse wave detecting means for detecting a pulse wave which appears in the
peripheral blood vessel after it appears in the aorta;
pulse-wave propagation time measuring means for measuring a pulse wave
propagation time from the output signals of the time-interval detect
reference point detecting means and the pulse wave detecting means;
first computing means for determining the parameter .alpha. on the basis of
the contents of the table stored in the memory by using the pulse wave
propagation time for calibration gathered from the subject;
second computing means for determining the parameter .beta. to be added in
computing a blood pressure value by using the pulse wave propagation time,
by using the blood pressure value inputted for calibration, the pulse wave
propagation time measured for calibration, and the parameter .alpha.
determined by the first computing means;
third computing means for computing a blood pressure value by using the
measured pulse wave propagation time, and the parameters .alpha. and
.beta.; and
measured data output means for outputting data of the computed blood
pressure value.
According to another aspect of the present invention, there is provided a
pulse-wave propagation time basis blood pressure monitor comprising:
a memory for storing a general equation describing the relationship between
the pulse pressure and the parameter .alpha., in computing blood pressure
values from the pulse wave propagation time, the pulse wave propagation
time being derived from data gathered from a number of subjects in order
to determine the parameter .alpha. that is proper to each subject and to
be multiplied by the pulse wave propagation time;
input means for inputting blood pressure values of subjects that are for
calibration;
pulse pressure computing means for computing a pulse pressure for
calibration using a blood pressure valve received from the input means;
time-interval detect reference point detecting means for detecting a
reference point for detecting the time interval of a pulse wave in the
aorta of a subject;
pulse wave detecting means for detecting a pulse wave which appears in the
peripheral blood vessel after it appears in the aorta;
pulse-wave propagation time measuring means for measuring a pulse wave
propagation time from the output signals of the time-interval detect
reference point detecting means and the pulse wave detecting means;
first computing means for determining the parameter .alpha. proper to the
subject on the basis of the general equation stored in the memory by using
the pulse pressure for calibration gathered from the subject;
second computing means for determining the parameter .beta. to be added in
computing a blood pressure value by using the pulse wave propagation time,
by using the blood pressure value inputted for calibration, the pulse wave
propagation time measured for calibration, and the parameter .alpha.
determined by the first computing means;
third computing means for computing a blood pressure value by using the
measured pulse wave propagation time, and the parameters .alpha. and
.beta.; and
measured data output means for outputting data of the computed blood
pressure value.
The second technical idea may also be realized by a pulse-wave propagation
time basis blood pressure monitor comprising:
a memory for storing a table describing the relationship between the pulse
pressure and the parameter .alpha., in computing blood pressure values
from the pulse wave propagation time, the pulse wave propagation time
being derived from data gathered from a number of subjects in order to
determine the parameter .alpha. that is proper to each subject and to be
multiplied by the pulse wave propagation time;
input means for inputting blood pressure values of subjects that are for
calibration;
pulse pressure computing means for computing a pulse pressure for
calibration using a blood pressure value received from the input means;
time-interval detect reference point detecting means for detecting a
reference point for detecting the time interval of a pulse wave in the
aorta of a subject;
pulse wave detecting means for detecting a pulse wave which appears in the
peripheral blood vessel after it appears in the aorta;
pulse-wave propagation time measuring means for measuring a pulse wave
propagation time from the output signals of the time-interval detect
reference point detecting means and the pulse wave detecting means;
first computing means for determining the parameter .alpha. proper to the
subject on the basis of the table stored in the memory by using the pulse
pressure for calibration gathered from the subject;
second computing means for determining the parameter .beta. to be added in
computing a blood pressure value by using the pulse wave propagation time,
by using the blood pressure value inputted for calibration, the pulse wave
propagation time measured for calibration, and the parameter .alpha.
determined by the first computing means;
third computing means for computing a blood pressure value by using the
measured pulse wave propagation time, and the parameters .alpha. and
.beta.; and
measured data output means for outputting data of the computed blood
pressure value.
According to another aspect of the present invention, there is provided a
pulse-wave propagation time basis blood pressure monitor comprising:
first input means for inputting at least a patient's height value as
patient information;
second input means for inputting a blood pressure value for calibration;
time-interval detect reference point detecting means for detecting a
reference point for detecting the time interval of a pulse wave in the
aorta of a subject;
pulse wave detecting means for detecting a pulse wave which appears in the
peripheral blood vessel after it appears in the aorta;
pulse-wave propagation time measuring means for measuring a pulse wave
propagation time from the output signals of the time-interval detect
reference point detecting means and the pulse wave detecting means;
first computing means for computing a change .DELTA.T of the pulse wave
propagation time at the time of postural change by using the pulse wave
propagation time for calibration measured at the supine position and the
pulse wave propagation time for calibration measured at the sitting or
standing position;
second computing means for computing a change .DELTA.P of a hydrostatic
pressure between the heart and a pulse wave measuring position at the time
of postural change, by using a patient's height as patient information;
third computing means for determining the parameter .alpha. to be
multiplied by the pulse wave propagation time in computing blood pressure
values from the pulse wave propagation time, by using the change .DELTA.T
of the pulse wave propagation time and the change .DELTA.P of the
hydrostatic pressure;
fourth computing means for determining the parameter .beta. to be
multiplied by the pulse wave propagation time in computing blood pressure
values from the pulse wave propagation time, by using the blood pressure
value inputted for calibration, the pulse wave propagation time inputted
for calibration, and the parameter .alpha. determined by the third
computing means;
fifth computing means for computing a blood pressure value by using the
measured pulse wave propagation time, and the parameters .alpha. and
.beta.;and
measured data output means for outputting data of the computed blood
pressure value.
As described above, the pulse-wave propagation time basis blood pressure
monitor can determine the parameter .alpha. by using the pulse wave
propagation time measured for calibration while using the general equation
stored in the memory or referring to the table also stored in the memory.
After the parameter .alpha. is determined, the parameter .beta. can be
determined by using the parameter .alpha., the blood pressure value
inputted for calibration, and the pulse wave propagation time measured for
calibration.
In the process of calibration for determining the parameters .alpha. and
.beta., all one has to do is to measure a blood pressure one time.
After the parameters .alpha. and .beta., a blood pressure of a patient can
be measured by using these parameters .alpha. and .beta. and the pulse
wave propagation time subsequently measured.
The pulse-wave propagation time basis blood pressure monitor can determine
the parameter .alpha. by using the blood pressure value input for
calibration while using the general equation stored in the memory or
referring to the table also stored in the memory.
After the parameter .alpha. is determined the parameter .beta. can be
determined by using the parameter .alpha., the blood pressure value input
for calibration, and the pulse wave propagation time measured for
calibration.
In the process, of calibration for determining the parameters .alpha. and
.beta., all one has to do is to measure a blood pressure one time.
The pulse-wave propagation time basis blood pressure monitor can compute a
change .DELTA.P of a hydrostatic pressure between the heart and a pulse
wave measuring position at the time of postural change, by using a
patient's height as patient information, and determines the parameter
.alpha. by using the change .DELTA.P of the hydrostatic pressure and the
change .DELTA.T of the pulse wave propagation time at the time of postural
change.
After the parameter .alpha. is determined, the parameter .beta. can be
determined by using the parameter .alpha., the blood pressure value
inputted for calibration, and the pulse wave propagation time measured for
calibration.
Thus, also in this invention, in the process of calibration for determining
the parameters .alpha. and .beta., all one has to do is to measure a blood
pressure one time.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a pulse-wave propagation time basis blood
pressure monitor according to an embodiment of the present invention;
FIG. 2 is a table showing the relationship between the pulse wave
propagation time and the parameter .alpha., the table being stored into a
ROM of the blood pressure monitor of FIG. 1;
FIG. 3 is another table showing the relationship between the pulse wave
propagation time and the parameter .alpha., the table being stored into a
ROM of the blood pressure monitor.
FIG. 4 is a flowchart showing the operation of a pulse-wave propagation
time basis blood pressure monitor according to a first embodiment of the
present invention;
FIG. 5 is a flowchart showing the operation of a pulse-wave propagation
time basis blood pressure monitor according to a second embodiment of the
present invention;
FIG. 6 is a flowchart showing the operation of a pulse-wave propagation
time basis blood pressure monitor according to a third embodiment of the
present invention;
FIG. 7 is a graph showing the relationship between the pulse wave
propagation time and the parameter .alpha., both being actually measured;
FIG. 8 is a graph showing the relationship between the pulse pressure and
the parameter .alpha., both being actually measured; and
FIG. 9 is a diagram showing waveforms for explaining the pulse wave
propagation time.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiments of the present invention will be described with
reference to the accompanying drawings.
First Embodiment
The basic idea of a first embodiment of the present invention will first be
described.
There is a correlation between the volumetric elasticity of the vessel and
the parameter .alpha.. Further, there is a correlation between the
volumetric elasticity of the vessel and the propagation time of the pulse
wave in the blood pressure at the same blood pressure value.
Hence, there is a correlation between the parameter .alpha. and the pulse
wave propagation time.
The present invention is based on this knowledge.
The relationship between the pulse wave propagation time and the parameter
.alpha. at rest was measured. The measurement was carried out on a total
of 46 subjects including men of health and patients of 22 to 80 years old.
The results of the measurement are as shown in FIG. 7.
As seen from the graph of FIG. 7, the pulse wave propagation time To and
the parameter .alpha. can be expressed by the following equations
To=-25.alpha.+162
.alpha.=-(To-162)/25 (1)
The relationship between pulse wave propagation time To and the parameter
.alpha. may approximately be described by a table TB1 as shown in FIG. 2
on the basis of the equation (1), In the table TB1, the pulse wave
propagation time To is segmented every 15 msec.
As shown, in the table TB1, .alpha. (parameter) is -0.7 for 140 msec or
longer of To (pulse wave propagation time); .alpha. is -1.0 for 125 to 139
msec of To; .alpha. is -1.5 for 110 to 124 msec of To; .alpha. is -2.0 for
95 to 109 msec of To; .alpha. is -3.0 for 94 msec or shorter.
The general equation (1) or the table TB1 shows that one can calculate the
parameter .alpha. by measuring the pulse wave propagation time To at rest.
To be more specific, a program of the equation (1) or the table TB1 (FIG.
2) is stored in a memory (ROM) 10 in a system shown in FIG. 1. To obtain
the parameter .alpha. corresponding to the measured pulse wave propagation
time To, a CPU 1 reads the program of the equation (1) from the ROM 10 and
executes the program or carries out the related process while referring to
the contents of the table TB1 .
After the parameter .alpha. is obtained, the parameter .beta. can be
calculated by the following equation (2), using the blood pressure Po and
the pulse wave propagation time To.
Po=.alpha.To+.beta.
.beta.=Po-.alpha.To (2)
After the parameters .alpha. and .beta. are determined, the pulse wave
propagation time T is successively measured, and then blood pressure P can
successively be calculated by the following equation
P=.alpha.T+.beta. (3)
A pulse-wave propagation time basis blood pressure monitor according to the
present invention is based on the above-mentioned technical idea.
FIG. 1 is a block diagram showing a pulse-wave propagation time basis blood
pressure monitor according to the present invention.
The arrangement of the pulse-wave propagation time basis blood pressure
monitor shown in FIG. 1 is used commonly for all of the blood pressure
monitors as first to third embodiments of the present invention.
A time-interval detect reference point detecting portion 2 detects a time
point where an aorta pulse pressure reaches the bottom of its amplitude
variation, substantially simultaneously with generation of the
electrocardiographic R wave. The output signal of the detecting portion 2
is converted into a digital signal by an A/D converter 3 and inputted to a
CPU (central processing unit) 1. The time-interval detect reference point
detecting portion 2 may be constructed with an electrode mounted on the
chest of a subject and an electrocardiographic R wave detector connected
to the electrode.
The time-interval detect reference point detecting portion 2 may include a
photoelectric pulse wave sensor or a pulse pressure sensor for sensing a
pulse wave in the aorta, and a pulse wave detector connected to the pulse
pressure sensor.
A photoelectric pulse wave sensor 4 is attached to an ear lobe of a
subject, for example, and senses a pulse wave in the peripheral blood
vessel.
This sensor is not limited to the photoelectric pulse wave sensor but may
be a pulse pressure sensor. The output signal of the photoelectric pulse
wave sensor 4 is transmitted to a pulse wave detector 5 which detects a
pulse wave at the location to which the sensor is attached. The output
signal of the pulse wave detector 5 is converted into a digital signal by
an A/D convertor 6 and input into the CPU 1.
A key 8 is used when the parameters .alpha. and .beta. proper to a subject
are determined by the calibration.
An input member 7 is used for inputting a blood pressure value Po for
calibration or, it is used for inputting the blood pressure value Po and a
patient's height as patient information.
An instruction to output the measured data and an instruction to end the
measurement are also entered from the input member 7.
The CPU 1 executes a process program in response to the signals from the
A/D converters 3 and 6, the key 8, and the input member 7, and displays
the results of executing the process program by a display 9, and output
measured data to an external output connector 12.
The display 9 and the external output connector 12 form measuring data
output device.
The process program is stored in a memory (ROM) 10 connected to the CPU 1.
The ROM 10 stores the general equation (1) for calculating the parameter
.alpha. by using the pulse wave propagation time To, as mentioned above.
Alternatively, the ROM 10 stores the table TB1 shown in FIG. 2, which is
for obtaining the parameter .alpha. by using the pulse wave propagation
time To.
Further, the ROM 10 stores the general equation (14) for obtaining the
parameter .alpha. by using a pulse pressure Pa. In the arrangement of
claim 4, the ROM 10 stores the table TB2 shown in FIG. 3.
Data being processed is stored in a RAM 11 connected to the CPU 1.
The CPU 1 forms the pulse-wave propagation time measuring section and the
first to third computing device, forms the pulse-wave propagation time
measuring section, the pulse pressure computing device, and the first to
third computing device, or forms the pulse-wave propagation time measuring
section, and the first to fifth computing device.
The operation of the pulse-wave propagation time basis blood pressure
monitor thus constructed will be described with reference to a flowchart
shown in FIG. 4.
In a step S1, it is checked whether or not the parameters .alpha. and
.beta. proper to a subject are prepared. If these parameters are not
prepared, the key 8 is operated.
In a step S2, a blood pressure of a subject is measured by using a blood
pressure monitor with a cuff, and a blood pressure value Po for
calibration is entered from the input member 7.
The blood pressure value Po entered is stored into the RAM 11.
In a step S3, the CPU 1 receives data from the A/D converters 3 and 6 and
processes the data, and measures the pulse wave propagation time To for
calibration immediately after the blood pressure value Po is measured. The
measured pulse wave propagation time To is written into the RAM 11.
Subsequently, in a step S4, the parameter .alpha. is obtained using the
pulse wave propagation time To measured for calibration while referring to
the general equation (1) or the table TB1 shown in FIG. 1, which is stored
in the ROM 10.
In a step S5, the blood pressure value Po for calibration read out of the
RAM 11, the pulse wave propagation time To, and the parameter .alpha. are
processed by the CPU 1, the parameter .beta. is determined using the
equation (2) and written into the RAM 11. In a step S6, the measurement of
the blood pressure value P starts.
In the step S6, the data from the A/D converters 3 and 6 is processed by
the CPU 1, the pulse wave propagation time T is measured, and the result
is inputted to the RAM 11.
In a step S7, the CPU 1 executes the operation of the equation (3) by using
the pulse wave propagation time T and the parameters .alpha. and .beta.,
thereby computing the blood pressure value P.
In a step S8, the measured blood pressure value P is written into the RAM
11, and is displayed by the display 9.
When the measuring data is not output and the measurement is not yet ended,
the process from the steps S6 to S8 is repeated at preset periods, and the
blood pressure measurement is successively carried out.
In a step S9, when an instruction to output the measuring data is entered
from the input member 7, the measuring data stored in the RAM 11 is
outputted through the external output connector 12 in a step S10.
In a step S11, when an instruction of the measurement end is entered from
the input member 7, the process flow returns to the step S1.
In this case, when the blood pressure measurement is continued for the same
subject, the blood pressure monitor needs only to carry out the process
subsequent to the step S6 since the parameters .alpha. and .beta. have
been prepared.
Second Embodiment
The basic idea of a second embodiment of the present invention will be
described.
At rest, the pulse pressure as the difference between the maximum blood
pressure and the minimum blood pressure depends mainly on a volumetric
elasticity of the blood vessel. Where the volumetric elasticity of the
blood vessel is large, the pulse pressure is large, and where the
volumetric elasticity of the blood vessel is large, the parameter .alpha.
is large.
Where the volumetric elasticity of the blood vessel is small, the pulse
pressure is small, and where the volumetric elasticity of the blood vessel
is small, the parameter .alpha. is small.
Accordingly, there is a correlation between the pulse pressure and the
parameter .alpha..
The present invention is based on this knowledge.
The relationship between the pulse pressure at rest and the parameter
.alpha. at rest was measured. The measurement was carried out on a total
of 46 subjects including men of health and patients of 22 to 80 years old.
The results of the measurement are as shown in FIG. 8.
As seen from the graph of FIG. 8, the pulse pressure Pa and the parameter
.alpha. can be expressed by the following equations
pa=16.alpha.+34
.alpha.=(Pa-34)/16 (4)
The relationship between the pulse pressure Pa and the parameter .alpha.
may approximately be described by a table TB2 as shown in FIG. 3 on the
basis of the equation (4). In the table TB2, the pulse pressure Pa is
segmented every 10 mmHg.
As shown, in the table TB2, .alpha. (parameter) is -0.7 for 45 mmHg or
lower of Pa (pulse pressure); .alpha. is -1.0 for 46 to 55 mmHg of Pa;
.alpha. is -1.5 f | | |
