Abstrict
Provided is an electronic blood pressure monitor capable of realizing
functions of blood pressure measurement in a shorter time and blood
pressure measurement with more of correctness in the same and one
construction thereof. The electronic blood pressure monitor includes:
an oscillometric measuring section capable of calculating a blood
pressure with a high precision using much of biogenic information
though a time is required since a blood pressure is calculated during
a period in which the cuff pressure is gradually changed; and an
SPD measuring section completing measurement in a short time though
a fluctuation in precision of measurement arises according to an
with less of biogenic information since individual difference a
blood pressure is calculated using only one or several pulse waves.
Since the oscillometric measuring portion performs a calibration
processing for the SPD measuring section simultaneously during measurement
thereof, calibrating operation a complicated can be practically
excluded.
Claims
What is claimed is:
1. An electronic blood pressure monitor comprising: a cuff configured
to be mounted on a predetermined portion of a subject for pressurizing
an artery of the subject; a cuff pressure controller for controlling
a cuff pressure inside the cuff; a pressure detector for detecting
the cuff pressure; a pulse wave detector for detecting a pulse wave
of the artery that is pressurized by the cuff; and a first blood
pressure measuring portion and a second blood pressure measuring
portion, the electronic blood pressure monitor selectively using
the first or second blood pressure measuring portion at a time,
wherein the first blood pressure measuring portion comprises a first
calculating unit that calculates a blood pressure of the subject
based on a set of the cuff pressures chronologically detected by
the pressure detector during a period in which the cuff pressure
is gradually changed by the cuff pressure controller and on amplitudes
of the pulse waves detected by the pulse wave detector at the timings
of the corresponding cuff pressure detection by the pressure detector,
and a calibration unit that calibrates the second blood pressure
measuring portion based on a result of the blood pressure calculation
by the first calculating unit, and the second blood pressure measuring
portion comprises a parameter measuring unit that provides a measured
value of a pulse wave parameter based on at least one of the pulse
waves detected by the pulse wave detector, the pulse wave parameter
being indicative of a waveform of the pulse wave that represents
a relative cuff pressure corresponding to a pressure difference
between the detected cuff pressure and the blood pressure of the
subject, a function memory that stores a function of the relative
cuff pressure comprising a set of sub-functions, a function selection
unit that selects one of the sub-functions that corresponds to a
level of the measured value of the pulse wave parameter, and a second
calculating unit that identifies the relative cuff pressure based
on the selected sub-function and calculates the blood pressure of
the subject by subtracting the identified relative cuff pressure
from the cuff pressure detected by the pressure detector at the
time of the pulse wave detection, wherein the calibration unit comprises
a data gathering unit that gathers, for each of the pulse waves
detected during an operation of the first blood pressure measuring
portion at the timings of the corresponding cuff pressure detection,
the corresponding relative cuff pressure and the corresponding measured
value of the pulse wave parameter, and a data updating unit that
modifies the function based on the relative cuff pressures and the
corresponding measured values of the pulse wave parameter that are
gathered by data gathering unit.
2. The electronic blood pressure monitor of claim 1, wherein during
the operation of the second blood pressure measuring portion the
parameter measuring unit provides a measured value of at least one
more pulse wave parameter, the function memory stores a plurality
of the functions for the corresponding pulse wave parameters, the
function selection units selects one of the sub-functions for each
of the pulse wave parameters, and the second calculating unit generates
a total function that provides a probability as a function of the
relative cuff pressure and determines the relative cuff pressure
for the calculation of the blood pressure as providing a maximum
probability.
3. The electronic blood pressure monitor of claim 2, wherein the
data gathering unit gathers the relative cuff pressures and the
measured values for each of the pulse wave parameters, and the data
updating unit modifies the corresponding function for each of the
pulse wave parameters.
4. The electronic blood pressure monitor of claim 1, further comprising
an input interface that allows an external data input, wherein the
first or second blood pressure measuring portion is selected by
the electronic blood pressure monitor based on the external data
input.
5. The electronic blood pressure monitor of claim 1, wherein the
data gathering unit determines the relative cuff pressures based
on the cuff pressures and a measured blood pressure as a result
of the operation of the first blood pressure measuring portion.
6. The electronic blood pressure monitor of claim 1, wherein the
second blood pressure measuring portion further comprises a pressure
setup unit that calculates a target pressure based on the cuff pressures
detected by the pressure detector while the cuff pressure is increased
by the cuff pressure controller and on the amplitudes of the pulse
waves detected by the pulse wave detector at the timings of the
cuff pressure detection during the cuff pressure increase and increases
the cuff pressure to the target pressure using the cuff pressure
controller, the target pressure being enough to assure an accurate
blood pressure measurement by the second blood pressure measurement
portion, wherein the pulse wave detected for providing the measured
value of the pulse wave parameter is detected when or after the
cuff pressure reaches the target pressure.
7. The electronic blood pressure monitor of claim 6, the target
pressure is one of or a combination of a systolic blood pressure,
a diastolic blood pressure, an average blood pressure and a cuff
pressure to provide an maximum amplitude of the pulse wave.
8. An electronic blood pressure monitor comprising: a cuff configured
to be mounted on a predetermined portion of a subject for pressurizing
an artery of the subject; a cuff pressure controller for controlling
a cuff pressure inside the cuff; a pressure detector for detecting
the cuff pressure; a pulse wave detector for detecting a pulse wave
of the artery that is pressurized by the cuff; and a first blood
pressure measuring portion comprising a first calculating unit that
calculates a blood pressure of the subject based on a set of the
cuff pressures chronologically detected by the pressure detector
during a period in which the cuff pressure is gradually changed
by the cuff pressure controller and on amplitudes of the pulse waves
detected by the pulse wave detector at the timings of the corresponding
cuff pressure detection by the pressure detector, and a second blood
pressure measuring portion comprising a parameter measuring unit
that provides a measured value of a pulse wave parameter based on
at least one of the pulse waves detected by the pulse wave detector,
the pulse wave parameter being indicative of a waveform of the pulse
wave that represents a relative cuff pressure corresponding to a
pressure difference between the detected cuff pressure and the blood
pressure of the subject, a function memory that stores a function
of the relative cuff pressure comprising a set of sub-functions,
a function selection unit that selects one of the sub-functions
that corresponds to a level of the measured value of the pulse wave
parameter, and a second calculating unit that identifies the relative
cuff pressure based on the selected sub-function and calculates
the blood pressure of the subject by subtracting the identified
relative cuff pressure from the cuff pressure detected by the pressure
detector at the time of the pulse wave detection, wherein the electronic
blood pressure monitor selectively uses the first or second blood
pressure measuring portion at a time.
9. The electronic blood pressure monitor of claim 8, wherein during
the operation of the second blood pressure measuring portion the
parameter measuring unit provides a measured value of at least one
more pulse wave parameter, the function memory stores a plurality
of the functions for the corresponding pulse wave parameters, the
function selection units selects one of the sub-functions for each
of the pulse wave parameters, and the second calculating unit generates
a total function that provides a probability as a function of the
relative cuff pressure and determines the relative cuff pressure
for the calculation of the blood pressure as providing a maximum
probability.
10. The electronic blood pressure monitor of claim 8, further comprising
an input interface that allows an external data input, wherein the
first or second blood pressure measuring portion is selected by
the electronic blood pressure monitor based on the external data
input.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic blood pressure monitor,
and more particularly to an electronic blood pressure monitor using
a pressurizing section (hereinafter referred to as a "cuff")
for pressurizing a portion in one of four limbs and others of a
mammal by injecting a fluid such as air thereinto.
2. Description of the Background Art
Among methods measuring a blood pressure using a cuff, there has
been available a method in which various kinds of arterial signals
(hereinafter referred to as "pulse waves") originated
from changes in inner volume of an artery around which a pressure
is applied with the cuff are captured in the course during which
a pressure in the cuff (hereinafter referred to as a "cuff
pressure") is gradually changed to calculate and determine
a blood pressure based on the captured pulse waves. This method
is called an oscillometric method.
FIG. 14 is a diagram showing a construction of an electronic blood
pressure monitor that is applied to an example in a prior art practice
and embodiments of the present invention. The electronic blood pressure
monitor of FIG. 14 includes: a microprocessor 1 having, therein,
a CPU (an abbreviation of a central processing unit) 1A for intensively
controlling and monitoring the electronic blood pressure monitor
itself as a center and a memory 1B; a cuff 2, being placed at a
predetermined portion of a mammal in order to pressurize an artery;
a gradual pressure reduction section 3, a rapid discharging section
4, a pressurizing section 5 and a cuff pressure detecting section
6 all of which are connected to the cuff 2 by an air system; a pulse
wave detecting section 7 detecting a pulse wave originating from
a change in volume of the artery produced in the course during which
the artery is pressurized with the cuff 2; an amplifying circuit-AD
(analog-digital) converters 8 and 9; an input interface 10 and an
output interface 11. A pressure inside the cuff 2 is controlled
by the gradual pressure reduction section 3, the rapid discharging
section 4 and the pressurizing section 5.
The CPU 1A of the microprocessor 1 controls other sections. The
pressurizing section 5 has a pressure pump, by which the cuff 2
is pressurized to a predetermined cuff pressure. The gradual pressure
reduction section 3 has a valve for reducing a cuff pressure. While
the valve is closed during pressurization of the cuff 2, it works
so as to gradually reduce a cuff pressure when being opened. The
rapid discharging section 4 has a valve for reducing a cuff pressure.
While the valve is closed during pressurization of the cuff 2, it
works so as to rapidly reduce a cuff pressure when being opened.
The cuff pressure detecting section 6 has a pressure sensor to detect
a cuff pressure. The pulse wave detecting section 7 detects a pulse
wave. The amplifying circuit-AD converters 8 and 9 amplify signals
outputted from the cuff pressure detecting section 6 and the pulse
wave detecting section 7, respectively, to convert the signals to
digital values and to give the digital values to the microprocessor
1. The microprocessor 1 processes given data to calculate a blood
pressure value and to output a result of the calculation through
the output interface 11. The input interface 10 is constituted of
switches, buttons and others and installed so as to enable to be
externally operable by a user. The output interface 11 is constituted
of a display section for displaying information; a printer for printing
the information; a speech output section for outputting the information
in speech; and others.
A pulse wave is produced by a change in inner volume of an arterial
blood vessel, around which an external pressure (a cuff pressure)
is applied by pressurization of the cuff 2, due to a balance between
the cuff pressure and an pulsating inner pressure (blood pressure).
In an oscillometric method, a blood pressure value (at least one
of a systolic blood pressure, a diastolic blood pressure and an
average blood pressure) is calculated from a pattern of changes
in amplitude of pulse waves corresponding to chronological levels
of a cuff pressure that changes in the course during which the cuff
pressure increases or decreases gradually, for example, stepwise
or continuously in a range between a value in the vicinity of a
systolic blood pressure (a so-called maximum blood pressure) and
a value in the vicinity of a diastolic blood pressure (a so-called
minimum blood pressure).
In this method, though a necessity arises for raising a pressure
inside the cuff 2 to a value equal to or higher than a systolic
blood pressure at the first stage, the systolic blood pressure largely
alters according to an individual difference or various factors
of the same individual as well, so pressurization has been started
after adjusting a pressurization amount given by the pressurizing
section 5 in the cuff 5 with an change-over switch provided to the
input interface 10. Contradiction arises, however, in adjustment
of the pressurization amount performed based on in-advance estimation
of a user in an electronic blood pressure monitor with which the
user measures a blood pressure since the user uses the electronic
blood pressure monitor to measure a blood pressure unknown to the
user and such operation has actually been tough to the user.
Therefore, a method has been contrived in which a pulse wave is
detected during pressurization of the pressurizing section 5 in
the cuff 2 to estimate a systolic blood pressure with a certain
precision and to cease pressurization in the cuff 2 at an optimal
level based on the estimation. This method is called an automatic
pressure setting function and disclosed in JP patents No. 2842696,
No. 2936814, No. 2936816, No. 3008582, No. 3042051 and No. 3042052.
With the method adopted, a necessity has been removed for a manual
operation of a user to adjust a pressurization value through estimation
of a systolic blood pressure.
In an oscillometric method, however, since there is still a necessity
for gradually reducing a cuff pressure down to a comparative low
pressure equal to or lower than a diastolic blood pressure from
a high pressure higher than a systolic blood pressure, not only
has a user been placed under a restraint in a blood pressure measurement
for a long time, which is troublesome to the user, but a problem
has also arisen that an environment of usage is restricted and a
rapid change in blood pressure cannot be captured though a precision
of measurement has become high due to acquirement of information
for measuring a blood pressure over a long time, that is to say,
due to acquirement of much biogenic information. That is to say,
a time is consumed in measurement in the oscillometric method for
the reason that a cuff pressure cannot be reduced at a high speed
in order to maintain a precision.
In contrast thereto, another method has been proposed in which
a measuring time can be shortened even though the measuring method
still uses the cuff 2. For simplicity of description of the method,
the method is herein called an SPD method (Single Pulse Determination).
The SPD method is disclosed in JP patent No. 2745467, No. 2855767
and others. According to an SPD method, a cuff pressure is raised
to an arbitrary value to maintain there and a pulse wave signal
is captured by one wave or several waves, thereby enabling estimation
of a blood pressure value. A construction of an electronic blood
pressure monitor to which an SPD method is applied is almost similar
to that shown in FIG. 14 only with the exception that no necessity
arises for the gradual pressure reduction section 3.
An SPD method uses a change in a waveform of a pulse wave depending
on a value of a cuff pressure relative to a blood pressure (hereinafter
referred to as a "relative cuff pressure"). To briefly
describe a principle thereof, a cuff pressure is at first raised
to an arbitrary value to then capture at least one pulse wave and
to obtain a waveform characteristic amount of the pulse wave. The
term, a waveform characteristic amount, is one obtained by quantifying
characteristics of a waveform of a wave pulse. Then, a wave form
characteristic amount is compared with a predetermined function
defining a relationship between a relative cuff pressure and a waveform
characteristic amount of a pulse wave to estimate a relative cuff
pressure at the time when the pulse wave is captured. Finally, a
value of the estimated relative cuff pressure is subtracted from
a known cuff pressure (hereinafter referred to as an absolute cuff
pressure) detected by the cuff pressure detecting section 6 at the
time when the pulse wave was captured; thereby estimating a blood
pressure.
According to an SPD method, in such a way, changes in pulse waves
(changes in amplitude) are not captured while a cuff pressure is
altered over a wide range as done in an oscillometric method but
a blood pressure is estimated from the absolute value of a waveform
characteristic amount of one pulse wave, thereby, enabling calculation
of a blood pressure value from one pulse wave according to the principle.
Therefore, since a necessity arises only for a very short time length
during which a user is placed under restraint in measurement of
a blood pressure, advantages are attained that detection of even
a rapid change in blood pressure can be achieved, measurement can
be done at anytime and anywhere without selecting an environment
of usage and the measurement is comfortable without a pain accompanied
therewith. An SPD method, however, is very much reduced in measuring
time, but contrary to this, a case has arisen where a precision
is insufficient for a particular user since a blood pressure is
determined from less of biogenic information and an individual difference
is present in a relationship between a relative cuff pressure and
a waveform characteristic amount.
In this way, since blood pressure measurements of an oscillometric
method and an SPD method have respective characteristics conflicting
with each other, a desire has been arisen that a user selectively
uses one of the measuring methods according to a situation such
as a time, a place or the like. That is to say, there has been a
desire of selective use of the methods according to a situation
that a user at work measures a blood pressure in a short time period
with a blood pressure measurement of a SPD method but the user at
home measures a blood pressure in an enough time that is allowed
to spend with a good precision using an oscillometric method. However,
since there have not been available an electronic blood pressure
monitor having both functions of blood pressure measurement of an
oscillometric method and an SPD method, a user has had to purchase
electronic blood pressure monitors of an oscillometric method and
an SPD method, which negates an economy.
Furthermore, though an SPD method is very much reduced in measuring
time, a case has been encountered where a precision is not sufficient
for a need of a particular user, so a necessity has been arisen
for adjusting a relationship between a relative cuff pressure and
a waveform characteristic amount with information showing characteristics
of a pulse wave different according to an individual to calibrate
a result of measurement in an application requiring a high precision.
The information used for calibration of a result of measurement
is hereinafter referred to as calibration information. In other
words, both of electronic blood pressure monitors of a SPD method
and a prior art electronic blood pressure monitor are both operated,
separately purchasing an electronic blood pressure monitor in the
prior art (for example, an electronic blood pressure monitor according
to an oscillometric method) for use in calibration to obtain calibration
information when a precision is required, and a value of the prior
art electronic blood pressure monitor, that is to say, calibration
information, has to be inputted to an electronic blood pressure
monitor of an SPD method, having lead to requirement of a complicated
operation.
Though an SPD method can calculate a blood pressure in a procedure
in which the cuff 2 is pressurized to an arbitrary value to capture
at least one pulse wave under the pressure from the principle thereof,
a pulse wave transmitted from a mammal is very weak in a case where
a pressurization value is raised to a value excessively larger than
a blood pressure, which increases a noise component in a relatively
large value, that is to say, deteriorates an S/N ratio, to disable
a waveform characteristic amount of a pulse wave to be correctly
calculated, having also resulted in a problem to produce a large
error.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide
an electronic blood pressure monitor capable of performing measurement
of a blood pressure in a shorter time and with more of correctness.
It is another object of the present invention to provide an electronic
blood pressure monitor capable of realizing functions of blood pressure
measurement in a shorter time and blood pressure measurement with
more of correctness in the same and one construction thereof.
An electronic blood pressure monitor according to an aspect of
the present invention includes a cuff configured to be mounted on
a predetermined portion of a subject for pressurizing an artery
of the subject, a cuff pressure controller for controlling a cuff
pressure inside the cuff, a pressure detector for detecting the
cuff pressure, a pulse wave detector for detecting a pulse wave
of the artery that is pressurized by the cuff, and a first blood
pressure measuring portion and a second blood measuring portion
being selectively used by the electronic blood pressure monitor
at a time.
The first blood pressure measuring portion includes a first blood
pressure calculation unit and a calibration unit for calibrating
the second blood pressure measuring portion. The first blood pressure
calculating unit calculates and outputs a blood pressure of the
subject based on a set of cuff pressures chronologically detected
by the pressure detector during a period in which the cuff pressure
is gradually changed by the cuff pressure controller and on amplitudes
of the pulse waves detected by the pulse wave detector at the timings
of the corresponding cuff pressure detection by the pressure detector.
The second blood pressure measuring portion includes a parameter
measuring unit, a function memory, a function selection unit and
a second blood pressure calculating unit.
The parameter measuring unit provides a measured value of pulse
wave parameter based on at least one of the pulse waves detected
by the pulse wave detector, the pulse wave parameter being indicative
of a waveform of the pulse wave that represents a relative cuff
pressure corresponding to a pressure difference between the detected
cuff pressure and the blood pressure of the subject.
The function memory stores a function of the relative cuff pressure
including a set of sub-functions.
A function selection unit selects one of the sub-functions that
corresponds to a level of the measured value of the pulse wave parameter.
A second calculating unit identifies the relative cuff pressure
based on the selected sub-function and calculates the blood pressure
of the subject subtracting the identified relative cuff pressure
from the cuff pressure detected by the pressure detector at the
time of the pulse wave detection.
The calibration unit includes a data gathering unit that gathers,
for each of the pulse waves detected during an operation of the
first blood pressure measuring portion at the timings of the corresponding
cuff pressure detection, the corresponding relative cuff pressure
and the corresponding measured value of the pulse wave parameter,
and a data updating unit that modifies the function based on the
relative cuff pressures and the corresponding measured values of
the pulse wave parameter that are gathered by the data gathering
unit.
Therefore, since the first blood pressure measuring portion further
includes the calibration unit that calibrates the second blood pressure
measuring portion, improvement can be realized on a precision of
blood pressure measurement using the second blood pressure measuring
portion that can measure a blood pressure in a shorter time while
practically enabling exclusion of a complicated calibrating operation.
To practically enable exclusion of the calibrating operation means
to complete calibration by the calibration unit during measurement
of a blood pressure performed by a user in advance with the first
blood pressure measuring portion, to be detailed. In other words,
the data gathering unit gathers calibration information necessary
for calibration of the second blood pressure measuring portion,
that is to say, a blood pressure value calculated by the first blood
pressure measuring portion at the time of blood pressure measurement,
and pulse wave parameters (a characteristic amount) from one wave
or several waves over a wide relative pressure range with the blood
pressure value as a reference, and the data updating unit modifies
values of functions corresponding to the pulse wave parameters in
the function memory using the gathered relative cuff pressures and
the corresponding values of the pulse wave parameters with respect
to the pulse wave parameters; therefore, the user simply performs
blood pressure measurement with the first blood pressure measuring
portion without requiring any specific operation in addition.
Furthermore, an electronic blood pressure monitor includes: the
first blood pressure measuring portion capable of calculating a
blood pressure at a high precision using much of biogenic information
though a time is required since a blood pressure is calculated during
a period in which the cuff pressure is gradually changed; and a
second blood pressure measuring portion completing measurement in
a short time though a fluctuation in precision of measurement arises
according to an individual difference with less of biogenic information
since a blood pressure is calculated using at least one pulse wave.
Therefore, since blood measuring functions with respective different
workings and characteristics are integrated in the same electronic
blood pressure monitor, no necessity arises for separately purchasing
blood pressure monitors with blood pressure measuring functions
with respective different workings and characteristics, which is
convenient and economical to a user.
Since the same electronic blood pressure monitor integrally has
the two kinds of blood pressure measuring functions, different in
operation and feature from each other in construction, a manufacturing
cost of the equipment can be greatly reduced without a necessity
for separate manufacture of two electronic blood pressure monitors.
Furthermore, if both functions are built in, for example, a microprocessor
or the like in design and the measuring functions are selectively
changed over therebetween by setting on a small scale, products
with respective different functions working on different principles
can also be manufactured in a single manufacture line.
According to another aspect of the present invention, an electronic
blood pressure monitor is of a construction including: a cuff configured
to be mounted on a predetermined portion of a subject for pressurizing
an artery of the subject; a cuff pressure controller for controlling
a cuff pressure inside the cuff; a pressure detector for detecting
the cuff pressure; a pulse wave detector for detecting a pulse wave
of the artery that is pressurized by the cuff and further includes
a first blood pressure measuring portion and a second blood measuring
portion being selectively used by the electronic blood pressure
monitor at a time.
The first blood pressure measuring portion includes: a first blood
pressure calculating unit. The first blood pressure calculating
unit calculates and outputs a blood pressure of the subject based
on a set of cuff pressures chronologically detected by the pressure
detector during a period in which the cuff pressure is gradually
changed by the cuff pressure controller and on amplitudes of the
pulse waves detected by the pulse wave detector at the timings of
the corresponding cuff pressure detection by the pressure detector.
The second blood pressure measuring portion includes: a parameter
measuring unit; a function memory; and a function selection unit;
and a second blood pressure calculating unit.
The parameter measuring unit provides a measured value of pulse
wave parameter based on at least one of the pulse waves detected
by the pulse wave detector, the pulse wave parameter being indicative
of a waveform of the pulse wave that represents a relative cuff
pressure corresponding to a pressure difference between the detected
cuff pressure and the blood pressure of the subject.
The function memory stores a function of the relative cuff pressure
including a set of sub-functions.
A function selection unit selects one of the sub-functions that
corresponds to a level of the measured value of the pulse wave parameter.
A second calculating unit identifies the relative cuff pressure
based on the selected sub-function and calculates the blood pressure
of the subject subtracting the identified relative cuff pressure
from the cuff pressure detected by the pressure detector at the
time of the pulse wave detection.
In such a way, an electronic blood pressure monitor includes: the
first blood pressure measuring portion capable of calculating a
blood pressure at a high precision using much of biogenic information
though a time is required since a blood pressure is calculated during
a period in which the cuff pressure is gradually changed; and a
second blood pressure measuring portion completing measurement in
a short time though a fluctuation in precision of measurement arises
according to an individual difference with less of biogenic information
since a blood pressure is calculated using at least one pulse wave.
Therefore, since blood pressure measuring functions with respective
different workings and characteristics are integrated in the same
electronic blood pressure monitor, no necessity arises for separately
purchasing blood pressure monitors with blood pressure measuring
functions with respective different workings and characteristics,
which is convenient and economical to a user.
Since the same electronic blood pressure monitor integrally has
the two kinds of blood pressure measuring functions, different in
operation and feature from each other in construction, a manufacturing
cost of the equipment can be greatly reduced without a necessity
for separate manufacture of two electronic blood pressure monitors.
Furthermore, if both functions are built in, for example, a microprocessor
or the like in design and the measuring functions are selectively
changed over therebetween by setting on a small scale, products
with respective different functions working on different principles
can also be manufactured in a single manufacture line.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing a function construction for electronic
blood pressure measurement relating to respective embodiments;
FIG. 2 is a flowchart showing an overall operation in an electronic
blood pressure monitor relating to a first embodiment;
FIG. 3 is a flowchart showing an overall operation in blood pressure
measurement according to an oscillometric method relating to the
first embodiment;
FIGS. 4A to 4D are graphs showing pulse wave parameters;
FIGS. 5A to 5D are graphs showing values of pulse wave parameters
plotted using the abscissas on which a scale for a relative cuff
pressure is calibrated;
FIG. 6 is diagram illustrating a probability density function calculated
from a probability density distribution;
FIGS. 7A to 7E are graphs showing extracted probability density
functions and an integrated probability density function;
FIG. 8 is a flowchart for blood pressure measurement with an SPD
method;
FIGS. 9A and 9B are representations showing tables filled out with
4 kinds of pulse wave parameters and values of an absolute cuff
pressure for each of pulse waves;
FIG. 10 is a graph showing ranks formed in a plane of a coordinate
system using a scale for a relative cuff pressure calibrated on
the abscissa and a scale for a parameter level calibrated on the
ordinate;
FIG. 11 is a graph showing a curve formed by parameter data of
an individual plotted on the coordinate system with ranks;
FIG. 12 is a graph showing parameter data of an individual filled
in regularly patterned ranks;
FIG. 13 is a flowchart for an overall operation in an SPD method
added with a pressure setting optimization function; and
FIG. 14 is a diagram showing an equipment construction of an electronic
blood pressure monitor that is applied to an example in a prior
art practice and embodiments of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Description will be given of embodiments of the present invention
below with reference to the accompanying drawings. Note that while
a pulse wave is detected based on the pulse waves (cuff pressure
pulse waves) super imposing a cuff pressure signal, detection of
a pulse wave has also been realized based on an optical or electrical
principle other than a cuff pulse pressure pulse but no specific
limitation is imposed thereto.
(First Embodiment)
In the first embodiment, a processing is performed that improves
a precision of measurement in an SPD method based on information
detected according to an oscillometric method. Description will
be given of this processing in the order of a equipment construction
of an electronic blood pressure monitor, an overall operation therein,
operations in blood pressure measurement according to an oscillometric
method, the principle of blood pressure measurement according to
an SPD method, operations in blood pressure measurement of an SPD
method according to this embodiment and the principle of calibration
for an individual difference in an SPD method applied to this embodiment.
(Equipment Construction)
No description is given of an equipment construction of each of
electronic blood pressure monitors relating to the embodiments since
the equipment construction is similar to that shown in FIG. 14.
In FIG. 1, there is shown a function construction for electronic
blood pressure measurement relating to the embodiments.
Referring to FIG. 1, an electronic blood pressure monitor includes:
an oscillometric measuring section 20 measuring a blood pressure
according to an oscillometric method performing a processing while
referring to information stored in a memory 1B; and an SPD blood
pressure measuring section 30 measuring a blood pressure according
to a SPD method performing a processing while referring to information
stored in the memory 1B. Included in information stored in the memory
1B are: plural probability density functions FG; and a table TB
for storing, therein, a determined systolic blood pressure SYS and
a determined diastolic blood pressure DIA, and calibration information.
Since the determined systolic blood pressure SYS and the determined
diastolic blood pressure DIA are used for a calibration processing
in a SPD method, the pressures may be called calibration information.
The oscillometric measuring section 20 includes: a blood pressure
calculating section 21 for measuring a blood pressure to calculate
and a calibration section 22 for calibrating a precision of measurement
in an SPD method. The calibration section 22 has therein an data
gathering section 23 gathering calibration information; and an updating
section 24 updating information referred to in the SPD method based
on the gathered calibration information.
The SPD measuring section 30 includes: a parameter measuring section
31 providing parameters showing characteristics of a wave form of
a measured pulse wave; a function selection section 32 selectively
extracting corresponding functions based on measured values of the
parameters provided; and a blood pressure calculating section 33
calculating a blood pressure using the selected functions; and a
pressure set up section 34. The pressure set up section 34 determines
a pressurization level of the cuff 2 in advance to actual measurement
of a pulse wave by the parameter measuring section 31 so as to enable
a pulse wave to be detected at an optimal cuff pressure to operate
so as to pressurize the cuff 2 to the level.
Description will be given of details of the sections later.
(Overall Operation)
FIG. 2 is a flowchart showing an overall operation in an electronic
blood pressure monitor relating to this embodiment. Herein, a systolic
blood pressure and a diastolic blood pressure, both estimated, are
called a systolic blood pressure SP and a diastolic blood pressure
DP. The finally determined systolic blood pressure and diastolic
blood pressure are called a systolic blood pressure SYS and diastolic
blood pressure DIA, respectively. A user can select one of measurement
modes of an oscillometric method and an SPD method by a switch operation
in the input interface 10.
Referring to FIG. 2, the CPU 1A at first determines which of measurement
modes is selected, an oscillometric method or an SPD method based
on the switch operation in the input interface 10 by the user or
the like (ST1). When the oscillometric method is selected, a blood
pressure measurement processing according to the oscillometric method
is performed by the oscillometric measuring section 20 (ST2), while
when the SPD method is selected, a blood pressure measurement processing
according to the SPD method is performed by the SPD measuring section
30 (ST3) to end the measurement operations after performing them
in both of the cases. Description will be given of the two blood
pressure measurement processings later.
Though not shown in FIG. 2, a calibration processing is performed
by the calibration section 22 during the blood pressure measurement
processing in the oscillometric method based on calibration information
of an individual for improving a precision of measurement in the
SPD method. In other words, the data gathering section 23 sequentially
stores a waveform characteristic amount of each pulse wave and a
cuff pressure as calibration information showing up during the measurement
operation of a blood pressure in the oscillometric method into the
table TB of the memory 1B and the updating section 24 performs a
calibration processing based on calibration information of stored
contents.
The calibration processing used herein means in particular to process
characteristics, that is a waveform characteristic amount, of a
waveform of a pulse wave of a user as an individual obtained by
an oscillometric method so as to be able to be reflected in an algorithm
for measurement of a blood pressure according to an SPD method.
Therefore, when the calibration processing is performed, a precision
of measurement is improved even in a SPD method since measurement
according to characteristics of a pulse wave of an individual is
enabled.
Herein, since characteristics of a pulse wave are altered by various
kinds of factors, for example, by variations in physiologic conditions
and others accompanied with a seasonal fluctuation, progress in
illness or recovery therefrom, or variation of physiological conditions
due to administration of medicine, even for a user as a particular
individual, it is desirable to use the latest calibration information
at all times in calibration processing. Therefore, it is desirable
that a calibration processing is repeatedly performed based on new
calibration information each time when a predetermined time elapses.
In this embodiment, therefore, for example, the CPU 1A, when a
predetermined time elapses from execution of the last calibration
processing, the oscillometric measuring section 20 is forcibly activated
to perform measurement of a blood pressure in an oscillometric method
and a calibration processing even in a case where a user selects
a measurement mode according to an SPD method. Moreover, while no
calibration information on a user as an individual is reflected
in an algorithm of an SPD method immediately after purchase of an
electronic blood pressure monitor by the user, in such a case as
well, the CPU 1A recognizes whether or not the equipment is used
for the first time and when a first time use is recognized, the
oscillometric measuring section 20 is unconditionally activated,
followed by measurement of a blood pressure according to an oscillometric
method and a calibration processing.
Description will be given of measurement of a blood pressure according
to an oscillometric method, a calibration processing included therein,
and measurement of a blood pressure according to an SPD method in
the order below.
(Operations in Measurement of a Blood Pressure According to Oscillometric
Method)
FIG. 3 is a flowchart showing an overall operation in blood pressure
measurement according to an oscillometric method relating to this
embodiment. A processing of FIG. 3 corresponds to the processing
in ST2 of FIG. 2.
When an operation in measurement is activated by a switch operation
or the like through the input interface 10 of a user, pressurization
in the cuff 2 is started by the pressurizing section 5 (ST101).
The pulse wave detecting section 7 recognizes each pulse wave during
the pressurization (ST102) and when amplitude data of a pulse wave
is calculated, the values are sequentially stored into the memory
1B (ST103). Furthermore, data of a cuff pressure corresponding to
the recognized pulse wave is detected by the cuff pressure detecting
section 6 to be related to amplitude data of the pulse wave and
stored into the memory 1B (ST104).
Such detection and storage operation are repeated till a state
is reached where contents of storage in the memory 1B can estimate
a systolic blood pressure SP to be estimated. A systolic blood pressure
SP is estimated based on cuff pressures and amplitude data of pulse
waves stored and accumulated by this repetition (ST105). In a state
where a systolic blood pressure SP cannot be still estimated (No
in ST106), the process returns to ST102 and the processing between
ST102 to ST105 is repeated till a state is reached where the systolic
blood pressure SP can be estimated (Yes in ST106).
When it is determined that estimation of the systolic blood pressure
SP has been completed (yes in ST106), it is further determined whether
or not a current cuff pressure has reached a pressurization target
value set based on a value of the systolic blood pressure SP (ST107)
and when it is determined that a current cuff pressure has reached
(Yes in ST107), pressurization in the cuff 2 performed by the pressurizing
section 5 is stopped (ST108).
The above operations are those performed by the above automatic
pressure setting function. Note that a systolic blood pressure SP
estimated here is an estimated value obtained in the course during
which pressurization progresses at high speed for performing pressure
setting which is different from another estimated value finally
determined as a measured value and displayed through the output
interface 11.
After the stoppage of pressurization, a cuff pressure is gradually
reduced by the gradual pressure reduction section 3 for the purpose
to measure a blood pressure (ST109). A systolic blood pressure SYS
and a diastolic blood pressure DIA are sequentially calculated and
determined by a similar processing to that during pressurization
using amplitudes of pulse waves and cuff pressures chronologically
detected during reduction in pressure. The systolic blood pressure
SYS and the diastolic blood pressure DIA are stored into the memory
1B. At this time, an average blood pressure may be determined (ST110
to ST114).
In a processing of ST113, various kinds of pulse parameters (a
pulse wave characteristic amount) of a user is calculated by the
data gathering section 23 and stored into the table TB of the memory
1B. Description will be given of details of the processing of ST113
later.
Thereafter, when it is determined that the systolic blood pressure
SYS and the diastolic pressure DIA have been determined (Yes in
ST115), the cuff pressure is completely removed by the rapid discharging
section 4 and the systolic blood pressure SYS and the diastolic
blood pressure DIA, which are results of measurement, are outputted
as data through the output interface 11 (ST116 and ST117). Thereafter,
a calibration processing is performed by the updating section 24
(ST118). In other words, in a SPD method, calculation is performed
of a function (hereinafter referred to as a corrective function)
applied for calibrating a precision of measurement for each individual
and values of probability density functions FG in the memory 1B
is updated using the corrective function. Thereafter, the operation
in measurement of a blood pressure according to an oscillometric
method ends. Description will be given of details of the processing
of ST118 later.
(Principle of Measurement of Blood Pressure According to SPD Method)
Herein, a value showing by how much a current cuff pressure is
higher or lower than a blood pressure (one of a systolic blood pressure
SYS, a diastolic blood pressure DIA and an average blood pressure)
is called a relative cuff pressure RPc.
FIGS. 4A to 4D are graphs showing pulse wave parameters. FIGS.
5A to 5D are graphs showing values of pulse wave parameters plotted
using the abscissas on which a scale for a relative cuff pressure
RPc is calibrated. FIG. 6 is a diagram illustrating a probability
density function calculated from a probability density distribution.
A waveform of a pulse wave alters depending on a level of a relative
cuff pressure RPc.
A principle of measurement of a SPD method is based on a relationship
between a relative cuff pressure RPc and a change in waveform of
a pulse wave (hereinafter referred to as a "relationship between
a pressure and a waveform"). A pulse wave is captured by raising
a cuff pressure to an arbitrary value and a waveform characteristic
amount is compared with a relationship between a pressure and a
waveform shown by a set of probability density functions FG stored
in advance in the memory 1B to estimate a relative cuff pressure
RPc at a time when a pulse wave is captured. Since a cuff pressure
at a time when a pulse wave is captured (hereinafter referred to
as an "absolute cuff pressure" Pc) can be easily known
from the cuff pressure detecting section 6, a blood pressure can
be estimated as a remainder obtained by subtracting a value of a
relative cuff pressure RPc from an absolute cuff pressure Pc.
While waveform characteristics of a pulse wave can be thought in
various ways, for example, 4 kinds of pulse wave parameters are
calculated in order to quantify the waveform characteristics: such
as a pulse wave amplitude AMP, a pulse wave integrated level RAV,
a relative waveform width WID and a degree of curving CON as shown
in FIGS. 4A to 4D. There has only to be available at least one or
one kind of pulse wave parameter showing a waveform characteristic
of a pulse wave, no specific limitation is placed to the above 4
kinds of characteristics. Since a procedure in which the pulse wave
parameters are calculated is disclosed in JP patent No. 2745467
(U.S. Pat. No. 5,156,158 corresponding to the JP), description is
here omitted of the calculating procedure and of the various kinds
of variables in the figures. Values of the 4 kinds of pulse wave
parameters were gathered from a great number of individuals in test
in advance to plot them in a plane of a two-dimensional coordinate
system with a relative cuff pressure RPc assigned to the abscissa;
thereby obtaining distribution statuses as shown in FIGS. 5A to
5D.
It can be seen from the figures that a distribution region of values
of a pulse wave parameter alters depending on a relative cuff pressure
RPc. This shows that a pulse wave is actually measured to compare
measured values of the pulse wave parameters with distributed values
in the figures; thereby enabling estimation of a relative cuff pressure
RPc to be in a limited range with some accuracy. In other words,
distribution statuses as shown in FIGS. 5A to 5D can be each considered
to be a probability density distribution of a relative cuff pressure
RPc depending on a level of a pulse parameter (a value read using
a scale on the ordinate). It is further understood from comparison
between FIGS. 5A to 5D that a distribution region depending on a
relative cuff pressure RPc is different according to a kind of a
pulse parameter. This means that though a relative cuff pressure
RPc cannot be specified within a sufficiently narrow range only
with respect to a single individual pulse parameter, a combination
of plural kinds of pule wave parameters having respective different
distributions can specify a relative cuff pressure RPc within a
narrower range.
Each of distribution information on the pulse wave parameters of
FIGS. 5A to 5D is to be compared with measured values of the parameters
of a pulse wave in a case where a blood pressure is measured in
an SPD method and stored in a memory 1B or a memory, installed separately,
and not shown, in advance. Though a distribution information of
each of the pulse wave parameters maybe stored in the memory 1B
in the format accompanied with an expression, a way of storage in
the memory 1B can considered to save a memory capacity that a plane
between a relative cuff pressure RPc (on the abscissa) and a level
of a pulse wave parameter (on the ordinate) is two-dimensionally
divided into ranks at a sufficiently small spacing in both directions
and the distribution information of each of the pulse wave parameters
is stored in the memory 1B in the format of a data table with the
number of points included in each of the ranks as a value of a probability
density function. Note that FIG. 6 is a data table constructed using
data of FIG. 5B. Each of the data tables of the respective pulse
wave parameters can be considered to be a set of plural probability
density functions of parameter levels in a range. Herein, a set
of functions are provided for each kind of pulse wave parameters
and stored in the memory 1B as a set of probability density functions
FG.
Then, description will be given of a processing when a blood pressure
is actually measured by the SPD measuring section 30.
The cuff 2 is at first pressurized to an arbitrary pressure through
the pressurizing section 5. A pressure value (an absolute cuff pressure
Pc) in the case can be detected with ease by the cuff pressure detecting
section 6. Then, at least one pulse wave is captured by the pulse
wave detecting section 7 under the absolute cuff pressure Pc and
values of kinds of pulse wave parameters of the captured pulse wave
are calculated in the parameter measuring section 31. The values
of the pulse wave parameters calculated with respect to the captured
pulse wave are each called a measured value of a parameter. Then,
the function selection section 32 selectively extracts a probability
density function of a parameter level coinciding with the measured
values of a parameter among a set of corresponding probability density
functions FG for each of the kinds of pulse wave parameters. A probability
density function extracted in such a way is called a sub-probability
density function.
When in this embodiment, sub-probability density functions are
extracted with respect to the respective above 4 kinds of pulse
wave parameters (a pulse wave amplitude AMP, a pulse wave integrated
level RAV, a relative waveform width WID and a degree of curving
CON), for example, as shown in FIGS. 7A to 7D, 4 sub-probability
density functions Pamp, Prav, Pwid and Pcon are selectively extracted
from respective sets of probability density functions FG. In other
words, a probability density of a relative cuff pressure RPc based
on distributions of values of the respective pulse wave parameters
and measured values of the parameters is shown with 4 sub-probability
density functions Pamp, Prav, Pwid and Pcon.
Sub-probability density functions of the pulse wave parameters,
as shown in FIGS. 7A to 7D, do not coincide with each other. A necessity
arises for integrating information of the sub-probability density
functions to obtain one estimated value of a relative cuff pressure
RPc in order to obtain a blood pressure. Therefore, the blood pressure
calculating section 33 performs an operation such as multiplication
or addition on values of different sub-probability density functions
corresponding to the same level of a relative cuff pressure RPc
therebetween. A result obtained in this way is one probability density
function according to a relative cuff pressure RPc as shown in FIG.
7E. This is called a total probability density function P.
Since the total probability density function P integrates information
of all the pulse parameters to show a relative cuff pressure RPc
that can be produced at each level, a value of a relative cuff pressure
RPc corresponding to the maximum value of the total probability
density function P can be the most probable value, that is to say,
an estimated value. The blood pressure calculating section 33 attains
an estimated value of a blood pressure by subtracting the estimated
value of a relative cuff pressure RPc from a value of an absolute
cuff pressure Pc when a pulse wave is captured.
According to a SPD method, as described above, since a blood pressure
can be estimated only by capturing one pulse wave in the principle,
it has a feature that a time required for measurement can be greatly
shortened compared with an oscillometric method.
An equipment construction of an electronic blood pressure monitor
based on the principle of measurement of an SPD method may be altogether
in common with that shown in FIG. 14. However, in a case where a
cuff pressure is preferably constant during capturing of a pulse
wave, a discharging valve of the gradual pressure reduction section
3 may also be completely shut off.
(Operations in Measurement of a Blood Pressure According to SPD
Method According to This Embodiment)
Description will be given of measurement of a blood pressure relating
to this embodiment of a SPD method based on the principle of measurement
as described above following a flowchart for measurement of a blood
pressure according to an SPD method of FIG. 8. The flowchart of
FIG. 8 corresponds to the processing of ST3 of FIG. 2.
When a user at first performs a switch operation of the input interface
10 to activate an operation in measurement of a blood pressure with
the SPD measuring section 33, the pressurizing section 5 operates
to start pressurization inside the cuff 2 (ST201), and when it is
determined that a cuff pressure detected by the cuff pressure detecting
section 6 has reached a predetermined pressurization target value
(yes in ST202), the pressurization by the pressurizing section 5
is stopped (ST203).
At least one pule wave is detected by the pulse wave detecting
section 7 (ST204) and calculations are performed to obtain values
of 4 kinds of pulse wave parameters as described above, that is
to say, measured values of parameters with respect of the at least
one pulse (ST205). Then, an absolute cuff pressure Pc, which is
a cuff pressure at a time when the pulse wave is detected is detected
by the cuff pressure detecting section 6, a value of the absolute
cuff pressure Pc is stored into the memory 1B (ST206) and the cuff
pressure is rapidly reduced by the rapid discharging section 4 to
be eventually removed (ST207).
Then, the function selection section 32 determines which of parameters
ranks of a corresponding set of probability density functions FG
stored in advance in the memory 1B a level of each of the obtained
measured values of the 4 kinds of parameters corresponds to and
selectively extracts corresponding probability density functions.
That is to say, sub-probability density functions are extracted
for the 4 kinds of respective measured parameters (ST208).
Then, the blood pressure calculating section 33 performs operations
on the values of the sub-probability density functions selectively
extracted with respect to the measured value of the respective parameters
at a level of the corresponding relative cuff pressure RPc (ST209).
This corresponds to the processing in which the sub-probability
density functions Pamp, Prav, Pwid and Pcon shown in FIGS. 7A to
7D are subjected to operations (addition or multiplication) to attain
a total probability density function P (see FIG. 7E).
Then, determination is performed on a value of the relative cuff
pressure RPc imparting the maximum value to the total probability
density function P (ST210). Finally, an estimated value of the relative
cuff pressure RPc is subtracted from a value of the absolute cuff
pressure Pc to output a result of the operation as an estimated
value of blood pressure (at least one of a systolic blood pressure,
a diastolic blood pressure and an average blood pressure) (ST211).
Note that while, in the above description, a systolic blood pressure
and a diastolic blood pressure are collectively called a blood pressure,
a systolic blood pressure and a diastolic blood pressure are in
common in all of the process for calculation. In a case where each
of systolic and diastolic pressures is calculated, kinds and the
number of measured parameters and probability density functions
may be different according to a kind of pressure since kinds of
pulse wave parameters to be obtained with a high precision are not
always the same.
Then, description will be given of processing for combining a blood
pressure measuring function of an SPD method with that of an oscillometric
method in effective use and operations in measurement with an electronic
blood pressure monitor based on this embodiment.
Description will be given at first of a calibration processing
for improvement on a precision of measurement with an SPD method
(see S113 and S118 of FIG. 3). An SPD method uses a relationship
between each of plural kinds of pulse wave parameters and a relative
cuff pressure RPc obtained from a great number of individuals in
test to estimate a blood pressure. There is, however, an individual
difference in a relationship between a pressure and a waveform.
Therefore, a necessity arises for causing a relationship between
a pressure and a waveform for a particular individual to be reflected
in a process for calculation of a blood pressure in order to improve
a precision of measurement in an SPD method.
(Calibration Processing for Individual in SPD Method)
A processing for capturing calibration information for each individual
in ST113 of FIG. 3 is repeated in each detection of a pulse wave
till a blood pressure (a systolic blood pressure SYS and a diastolic
blood pressure DIA) is determined. Therefore, the data gathering
section 23 provides, for each pulse wave, measured values of the
4 kinds of parameters through calculation, detects an absolute cuff
pressure Pc corresponding to the pulse wave and stores, for each
pulse wave, the provided measured values and the detected value,
being related with each other, onto the table TB of the memory 1B.
FIGS. 9A and 9B are representations showing tables TB filled out
with values of 4 kinds of pulse wave parameters and corresponding
values of an absolute cuff pressure Pc for each of pulse waves.
In the table TB of FIG. 9A, there are registered measured values
P1 (i) to P4 (i) of the 4 kinds of parameters through calculation
related with a value Pc (i) of detected absolute cuff pressures
Pc, also registered there, for the ith pulse wave, where i=1,2 3,
. . . , N.
Then, it is considered to cause data of pulse wave parameters,
which is calibration information for the table TB, to be reflected
in probability density functions as shown in FIG. 6. Pulse wave
parameters of an individual as are cannot be related to probability
density functions. This is because probability density functions
are defined as functions of a relative cuff pressure RPc; therefore,
a value of a probability density function given in each regular
rank at a particular pair of a relative cuff pressure RPc and a
parameter level, whereas data of pulse wave parameters of an individual
registered in the table TB of FIG. 9A assumes the format of irregular
discrete data corresponding to each absolute cuff pressure Pc.
Therefore, in this embodiment, when calibration information for
an individual is acquired in the table TB, a calibration processing
in a SPD method of FIG. 3 is performed (ST118). To be concrete,
the data gathering section 23 causes data of pulse wave parameters
of an individual to be related with a relative cuff pressure RPc.
In other words, values of relative cuff pressures RPc(1), RPc(2),
. . . , RPc(N) are obtained by subtracting a value of a systolic
blood pressure SYS, a diastolic blood pressure DIA or an average
blood pressure, which are stored in the memory 1B after being determined
in ST114 of FIG. 3, from values of absolute cuff pressure Pc(1),
Pc(2), . . . , Pc(N) in the table TB of FIG. 9A. For example, in
a case of the subtraction with a value of systolic blood pressure
SYS, the values of relative cuff pressures RPc(1), RPc(2), . . .
, RPc (N) are obtained in such a manner that RPc(1)=Pc(1)-SYS, RPc(2)=Pc(2)-SYS,
. . . , RPc(N)=Pc(N)-SYS.
As a result, a calculated value RPc(i) of a relative cuff pressure
RPc is additionally registered in the table TB, which is transformed
into that of FIG. 9B.
The updating section 24 causes irregular discrete data of pulse
wave parameters of an individual to be reflected in probability
density functions. Description will be given of this processing.
FIG. 10 shows a state of a graph in which levels of a value RPc(i)
of a relative cuff pressure RPc and each of pulse wave parameters
P1(i) to P4(i) are divided into the same ranks in lattice as in
the set of probability density functions registered in the memory
1B in advance. When data of a kind of pulse wave parameter Pj(i)
(j=1, 2, 3 and 4) of an individual of FIG. 9B described above is
plotted using the coordinate system with divided ranks arranged
in lattice, a curve obtained by the plotting passes through part
of the lattice cells as shown in FIG. 11. In other words, it can
be said that this user has a low probability to provide a relationship
between a pressure and a waveform in regions other than the part
of the lattice cells.
Then, a corrective function is obtained that is used for correcting
a set of probability density functions FG so as to be closer to
the relationship between a pressure and a waveform of this individual.
To be concrete, as shown in FIG. 12, a function is at first provided
that has initial values of, for example, 1 or the like in all the
ranks arranged in lattice. Then, values of the function only in
the ranks through which the curve of FIG. 11 passes are altered
to values larger than the initial ones, for example 3 to obtain
the corrective function. At the final stage, values of each of the
set of probability density functions FG corresponding to ranks are
multiplied by respective values (1 or 3) of the ranks of the corrective
function. As a result of the multiplication, in the set of probability
density functions FG, a probability density function assume relatively
larger values in a region in which the relationship between a pressure
and a waveform for the individual is produced; thereby enabling
increase in precision of an estimated value since data of an individual
is reflected in the course of estimation of a blood pressure with
an SPD method.
Note that while multiplication is herein used in an operation using
the corrective function and a probability density function, no specific
limitation is placed to multiplication, but for example, addition
may be used as the operation instead.
Furthermore, while the 4 kinds of parameters are required as measured
values thereof, at least one kind of parameter will be sufficient.
(Second Embodiment)
Calculation of a blood pressure is enabled at an arbitrary level
of a cuff pressure in the principle according to an SPD method,
whereas if a level of a cuff pressure level is excessively apart
from an actual blood pressure level, an amplitude of a pule wave
becomes small to reduce an S/N ratio and thereby a probability density
function does not give a correct estimated value of blood pressure
to deteriorate a precision of calculation of a blood pressure. Therefore,
in the second embodiment, an automatic pressure setting function
of the pressure set up section 34 is applied to the blood pressure
measuring function according to an SPD method of the first embodiment
to optimize a pressurization value in the SPD method and to, as
a result, obtain a higher precision of measurement.
(Optimization of Pressure Setting in SPD Method)
In FIG. 13, there is shown a flowchart for an overall operation
in blood pressure measurement with an SPD method in the second embodiment.
When a user performs a switch operation of the input interface 10
and an operation in blood pressure measurement is activated by the
SPD blood pressure measuring section 30, pressurization is started
in the cuff 2 by the pressurizing section 5 (ST301). Then, detection
of a pulse wave is started by the pule wave detecting section 7
to give a detected pulse wave data to the microprocessor 1; therefore,
the CPU 1A sequentially calculates amplitude data of a given pulse
wave to store the data into the memory 1B (ST302 and ST303). At
this time, since a corresponding absolute cuff pressure Pc is simultaneously
detected by the cuff pressure detecting section 6 and given to the
microprocessor 1, data of the absolute cuff pressure Pc is similarly
related with amplitude data of the pusle wave to be sequentially
stored into the memory 1B (ST304).
Then, pressurization is performed up to a target cuff pressure
value in order to perform blood pressure measurement with an SPD
method and the target cuff pressure value is calculated based on
contents of the memory 1B (ST305).
As to a procedure for the calculation, various ways can be applied
according to what value a target cuff pressure value is set to.
For example, if one of a systolic blood pressure SYS and a diastolic
blood pressure DIA is thought more than the other and desired to
be calculated with more of a precision, an estimation processing
of a blood pressure similar to an oscillometric method has only
to be performed using data of an amplitude of a pulse wave and a
cuff pressure Pc calculated and stored in ST303 and ST304 to obtain
an estimated value of one of a systolic blood pressure and a diastolic
blood pressure and to adopt the estimated value as a target cuff
pressure value. Furthermore, it is also allowed to obtain an estimated
value of an average blood pressure value and to adopt the estimated
value as a target cuff pressure value. If a characteristic amount
of a waveform of pulse wave is desired to be calculated with a good
precision, it is recommended that a cuff pressure Pc value that
has the maximum amplitude of a pule wave is detected to adopt the
cuff pressure Pc value as a target cuff pressure value. Moreover,
a value may be adopted that is calculated from a combination of
at least two of estimated values of a systolic blood pressure, a
diastolic blood pressure and an average blood pressure, and a cuff
pressure Pc value at which a pulse wave takes the maximum amplitude
value.
In any way, when a target cuff pressure value is calculated in
ST305, it is determined in ST306 whether or not the calculation
is over and a processing from ST302 to ST305 is repeated as long
as it is not determined that the calculation is over. If it is determined
that the calculation is over (Yes in ST306), pressurization in the
cuff 2 of the pressurizing section 5 is stopped. (ST307) and if
a target cuff pressure value is lower than a current cuff pressure
Pc, the cuff pressure Pc is reduced by the rapid pressure reduction
section 4 till the cuff pressure is rendered to be a target cuff
pressure value (ST308).
Then, a result of a blood pressure measurement is obtained (ST309)
by performing an SPD blood pressure measuring processing to which
a calibration processing according to the first embodiment (ST204
to ST211) is applied. Thereafter, a cuff pressure is completely
removed by the rapid discharging section 4 (ST310) to output the
result of the measurement through the output interface 11 and to
thereby terminate the operation.
In the second embodiment, since automatic pressure setting function
is applied to a blood pressure measuring function according to an
SPD method of the first embodiment to optimize a pressurization
value of the SPD method, a higher precision of measurement can be
obtained.
It should be understood that the embodiments disclosed herein are
presented by way of illustration but not by way of limitation at
all respects. It is intended that the scope of the present invention
is not shown by the above description of the specification but by
the scope of the claims, and includes all modifications or alterations
thereof within the scope of the claims and ones equivalent thereto. |