 |
Claims  |
|
|
We claim:
1. A blood pressure monitoring system for continuously measuring blood
pressure of a living body, the system comprising:
pulse wave detecting means for detecting pulse waves of an arterial vessel
of said living body,
said pulse wave detecting means comprising a plurality of pressure sensors
which are adapted to be set on a body surface of said living body above
said arterial vessel, each of said pressure sensors having a dimension
smaller than a diameter of said arterial vessel as viewed in a direction
perpendicular to said arterial vessel;
pressing means for pressing said pulse wave detecting means against said
arterial vessel via said body surface and thereby at least partially
flattening said arterial vessel, at least one of said pressure sensors
detecting said pulse waves through a flattened wall of said arterial
vessel;
blood pressure measuring means for measuring an actual blood pressure of
said living body;
control means for determining a relationship between blood pressure and
magnitude of pulse waves, based on the pulse waves detected by said at
least one pressure sensor through said flattened wall of said arterial
vessel and the actual blood pressure measured by said blood pressure
measuring means, such that blood pressure is a linear function of
magnitude of said pulse waves,
said control means determining blood pressures according to the
thus-determined relationship based on magnitudes of the pulse waves
detected by said at least one pressure sensor through said flattened wall
of said arterial vessel; and
display means for displaying the blood pressures determined by said control
means.
2. A blood pressure monitoring system as recited in claim 1, wherein said
pulse wave detecting means is adapted to be located on the body surface of
said living body above a radial artery, a carotid artery, or a dorsal
pedal artery of said living body.
3. A blood pressure monitoring system as recited in claim 1, wherein said
pulse wave detecting means comprises a semiconductor strain sensor or a
piezoelectric element.
4. A blood pressure monitoring system as recited in claim 1, wherein said
pulse wave detecting means is pressed against said arterial vessel of said
living body via said body surface under a predetermined pressure by said
pressing means.
5. A blood pressure monitoring system as recited in claim 4, wherein said
pressure applied to said pulse wave detecting means is predetermined to be
a comparatively low, constant pressure not more than about 20 mmHg.
6. A blood pressure monitoring system as recited in claim 4, wherein said
pressing means comprises a band which is wound around a body portion of
said living body.
7. A blood pressure monitoring system as recited in claim 1, wherein said
pressure sensors of said pulse wave detecting means are arranged in a
direction intersecting said arterial vessel on the body surface of said
living body above said arterial vessel, each of said pressure sensors
being pressed on said body surface and generating a pulse wave signal
representative of said pulse waves produced by said arterial vessel,
the system further comprising pressure force regulating means for
regulating a pressing force of said pressing means so that a magnitude of
the pulse wave signal from the middle of a group of said plurality of
pressure sensors which group is located on a portion of said body surface
right above said arterial vessel, is lower than magnitudes of the pulse
wave signals from the opposite ends of said group.
8. A blood pressure monitoring system as recited in claim 7, wherein said
plurality of pressure sensors comprise a single semiconductor plate and a
plurality of pressure-sensitive diodes formed on said single semiconductor
plate, said semiconductor plate being pressed against said arterial vessel
via said body surface by said pressing means so as to at least partially
flatten said arterial vessel, each of said plurality of pressure-sensitive
diodes having said dimension smaller than said diameter of said arterial
vessel.
9. A blood pressure monitoring system as recited in claim 7, wherein said
pressing means comprises a main body, a presser member provided inside
said main body, an elastically deformable diaphragm which is disposed
between said presser member and said main body to air-tightly define a
pressure room and support said presser member such that said presser
member is movable relative to said main body, and a pressurized fluid
supplying means for supplying a pressurized fluid to said pressure room.
10. A blood pressure monitoring system as recited in claim 7, wherein said
pressing force regulating means determines maximum peak values of said
pulse wave signals generated by said plurality of pressure sensors and
regulates said pressing force of said pressing means so that a varying
trend of said maximum peak values in the direction intersecting said
arterial vessel has a pair of maximal points and a minimal point located
between said pair of maximal points and that the maximum peak value of
said minimal point is not more than a predetermined proportion of an
average of the maximum peak values of said maximal points.
11. A blood pressure monitoring system as recited in claim 1, wherein said
control means determines a maximum blood pressure based on a speed of
increase of the pulse wave or a rate of change of an increasing portion of
the pulse wave.
12. A blood pressure monitoring system as recited in claim 1, wherein said
control means determines said relationship by selecting, from a plurality
of pre-stored data maps representing different relationships between blood
pressure and magnitude pulse waves, one data map corresponding to a
relationship between the actual blood pressure measured by the blood
pressure measuring means and the pulse waves detected by the pulse wave
detecting means.
13. A blood pressure monitoring system as recited in claim 1, wherein said
control means stores said relationship, and calculates blood pressures
according to the stored relationship based on magnitudes of the pulse
waves detected after said relationship has been stored.
14. A blood pressure monitoring system as recited in claim 1, wherein said
control means updates said relationship at predetermined regular intervals
of time based on the actual blood pressures which are measured by said
blood pressure measuring means at said predetermined regulate intervals.
15. A blood pressure monitoring system as recited in claim 14, wherein the
regular interval of time is predetermined to fall within the range of
about 5 to 10 minutes.
16. A blood pressure monitoring system as recited in claim 1, wherein said
control means includes abnormal pulse wave detecting means for detecting
an abnormality of the pulse waves, said blood pressure measuring means
automatically measuring an actual blood pressure of said living body upon
the detection of said abnormality of the pulse waves, said control means
updating said relationship based on the thus-measured actual blood
pressure and the pulse waves detected after the detection of said
abnormality.
17. A blood pressure monitoring system as recited in claim 1, wherein said
blood pressure measuring means includes a cuff which is wound around a
body portion of said living body, and a pressure supplying means for
supplying a pressure to said cuff, said blood pressure measuring means
determining said actual blood pressure based on variation in magnitude of
the pulse waves of said arterial vessel which variation is detected
through said cuff as the pressure of said cuff is varied.
18. A blood pressure monitoring system as recited in claim 1, wherein said
blood pressure measuring means measures actual maximum and minimum blood
pressures of said living body, said control means determining a maximum
and a minimum magnitude of one of the pulse waves detected by said pulse
wave detecting means, and determining a first relationship between maximum
blood pressure and maximum pulse wave magnitude and a second relationship
between minimum blood pressure and minimum pulse wave magnitude, said
first and second relationships being expressed by linear functions (1) and
(2), respectively,
SYS=Kmax.multidot.Mmax (1)
DIA=Kmin.multidot.Mmin (2)
wherein
SYS is maximum blood pressure,
Kmax is a constant,
Mmax is maximum pulse wave magnitude,
DIA is minimum blood pressure,
Kmin is a constant, and
Mmin is minimum pulse wave magnitude,
said control means determining said constants Kmax, Kmin by dividing the
actual maximum and minimum blood pressures measured by said blood pressure
measuring means, by the maximum and minimum pulse wave magnitudes
determined thereby, respectively, said control means determining a maximum
and a minimum blood pressure of said living body according to said linear
functions (1), (2) based on a maximum and a minimum magnitude of each of
the pulse waves detected by said pulse wave detecting means after said
linear functions (1) and (2) have been determined. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
FIELD OF THE INVENTION
The present invention relates to a blood pressure monitoring system for
continuously monitoring blood pressures which are determined based on the
pulse waves produced by pressing a portion of a living body.
BACKGROUND OF THE INVENTION
It is a widely-employed method for measuring blood pressure of a living
body to press a portion of the living body by a cuff, etc. to detect
pressure oscillation waves (pulse waves) produced in synchronization with
heartbeats of the living body and determine values of blood pressure of
the living body based on a change in magnitude of the detected pressure
oscillation waves.
However, the above-indicated blood pressure measuring method is not
recommendable for application to such a living body, for example a patient
after a surgical operation, whose blood pressure must be continuously
monitored during a comparatively long period of time, because a portion of
the living body is successively pressed during the period, thereby giving
appreciable discomfort to the living body.
DISCLOSURE OF THE INVENTION
The present invention has been developed in the background indicated above,
and the gist thereof resides in providing a blood pressure monitoring
system of a type for continuously displaying blood pressure of a living
body on a display to monitor the blood pressure of the living body, the
system including (a) pulse wave detecting means for detecting pulse waves
of an arterial vessel of the living body; (b) blood pressure measuring
means for measuring an actual blood pressure of the living body; and (c)
control means for determining a relationship between the pulse waves
detected by the pulse wave detecting means and the actual blood pressure
measured by the blood pressure measuring means, determining blood
pressures according to the thus-determined relationship and based on the
pulse waves, and commanding the display to successively display the
thus-determined blood pressures thereon.
As shown in the view of FIG. 1 corresponding to claim, at the time the
blood pressure measuring means measures an actual blood pressure, the
control means determines a relationship between the measured actual blood
pressure and the pulse waves of an arterial vessel which are continuously
detected by the pulse wave detecting means, and a change in blood pressure
is continuously displayed on the display according to the thus-determined
relationship and based on the pulse waves.
Therefore, in the present invention, it is unnecessary to successively
obtain measurements of the actual blood pressure of the living body to
monitor his or her blood pressure, and a long-time continuous monitoring
of the blood pressure may be conducted without successively pressing a
portion of the living body. Thus, the living body being monitored is
prevented from any obstruction of blood circulation and is not subjected
to appreciable discomfort.
Since the pulse wave detecting means of the present invention is adapted to
detect pulse waves of an arterial vessel, the pulse waves detected are
almost free from influence of breathing of the living body. Therefore,
accurate monitoring of blood pressure is conducted. Although it is
possible to use a cuff wound around an arm of a living body as pulse wave
detecting means to detect pressure oscillations of the cuff as pulse
waves, the pulse waves detected represent variation in volume of arteries
and veins, and the variation in volume is liable to be influenced by
breathing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view corresponding to claim of the present invention.
FIG. 2 is a diagrammatic view illustrating the arrangement of one
embodiment of the present invention.
FIG. 3 is a view showing an example of a blood pressure trend displayed on
a display of the embodiment of FIG. 2.
FIG. 4 is a view showing a pulse wave sensor of FIG. 2 when it is in
pressed contact with a portion of a living body.
FIG. 5 is a view showing a flow chart used for the operation of the
embodiment of FIG. 2.
FIG. 6 is a view showing an example of pulse waves which are continuously
detected in the embodiment of FIG. 1.
FIG. 7 is a view showing a main portion of a flow chart of another
embodiment of the present invention.
FIG. 8 is a view illustrating the location of a notch of a radius pulse
wave or a portion of the pulse wave corresponding to the diastole of the
heart.
FIG. 9 is a longitudinal cross-sectional view showing the vicinity of a
pulse wave sensor of another embodiment of the present invention.
FIG. 10 is a perspective view, partly in cross section, showing a plurality
of pressure sensors provided on the device of FIG. 9.
FIG. 11 is a view showing a flow chart used for a portion of the operation
of the device of FIG. 9.
FIG. 12 is a view of three graphs (a), (b) and (c) each showing amplitudes
of the pulse wave signals generated by the pressure sensors in a direction
perpendicular to the arterial vessel, the pressing forces employed in
cases (a), (b) and (c) being different from each other.
FIG. 13 is a view of three graphs each showing maximum peak values of the
pulse wave signals generated by the pressure sensors in the direction
perpendicular to the arterial vessel, the pressing forces used in the
three cases being different from each other.
BEST MODE FOR CARRYING OUT THE INVENTION
There will be described in detail one embodiment of the present invention
with reference to the drawings.
FIG. 2 is a view illustrating the arrangement of the present embodiment in
the form of a blood pressure monitoring system. In the figure, there is
shown a cuff 10 like a rubber bag which is wound around an upper arm, etc.
of a living body or a subject to press the arm. A pressure sensor 12, a
rapid deflating valve 14, a slow deflating valve 16, and a pressure
supplying device in the form of an electrically operated pump 18 are
connected through a tube 20 to the cuff 10. The pressure sensor 12 is
adapted to detect a pressure in the cuff 10 and supply a pressure signal
SP to both cuff pressure detect circuit 22 and pulse wave detect circuit
24. The cuff pressure detect circuit 22 includes low pass filler for
discriminating a static pressure in the cuff 10 from the pressure signal
SP, and is adapted to supply a cuff pressure signal SPc representative of
the static pressure cuff pressure) Pc, to CPU 28 via A/D converter 26. The
pulse wave detect circuit 24 includes band pass filter for discriminating
from the pressure signal SP a dynamic pressure in the cuff 10, that is, a
pressure-oscillation component (pulse waves) which is generated in
synchronization with heartbeats, and is adapted to supply a pulse wave
signal SPo representative of the pressure oscillation, to the CPU 28 via
A/D converter 30.
The CPU 28 is adapted to process input signals according to programs
pre-stored in ROM 32 while utilizing storing function of RAM 34 to
generate drive signals to the rapid deflating valve 14, slow deflating
valve 16 and electrically operated pump 18, respectively, via output
interface 36 and command a blood pressure display 38 to display values of
blood pressure. The blood pressure display 38 indicates on a Braun tube
thereof a two-dimensional table, as shown in FIG. 3, which table has a
horizontal axis 40 indicative of time and a vertical axis 42 indicative of
blood pressure (mmHg). The display 38 is adapted to timewise successively
display, on the two-dimensional table, tars 44 according to display
signals supplied from the CPU 28. The upper and lower ends A and B of each
bar 44 are indicative of a maximum and a minimum value of blood pressure.
A pulse wave sensor 46 is connected to the CPU 28 via a cable 48 and A/D
converter 50. As shown in FIG. 4, the pulse wave sensor 46 is attached to
a band 52 having a pair of zippers (not shown) at the opposite ends of the
band 52. The pulse wave sensor 46 is located above a radius of the living
body in the vicinity of a wrist where pulse waves are easily gathered, and
is locally pressed against an arterial vessel above the radius under a
comparatively low constant pressure not more than about 20 mmHg, for
example, by winding the band 52 around the wrist of the living body and
zipping the pair of zippers of the band 52. The pulse wave sensor 46 is
adapted to detect pulse waves of the arterial vessel above the radius and
supply a pulse wave signal SP.sub.T indicative of the pulse waves, to the
CPU 28 via A/D converter 50. As the pulse wave sensor 46, is used a
semiconductor strain sensor or a piezoelectric element capable of
converting a pulsation of an arterial vessel to an electric signal. An
ON/OFF switch 54 is adapted to supply an ON/OFF signal to the CPU 28 upon
depression thereof, and the system is turned on or off each time the
ON/OFF switch 54 is operated by depression. A clock signal generator 56 is
adapted to supply to the CPU 28 pulse signals CK having a predetermined
frequency.
There will be described the operation of the present embodiment with
reference to the flow chart of FIG. 5.
Upon operation of a power switch (not shown), step S1 is executed to check
whether or not the ON/OFF switch 54 has been depressed, that is, whether
or not ON/OFF signal is present at the CPU 28. After the ON/OFF switch 54
has been operated by depression with the cuff 10 wound around the upper
arm, etc. of the living body, step S1 is followed by step S2 to clear
counting T of timer to zero so that the timer thereafter re-starts
counting the pulse signals CK supplied from the clock signal generator 56.
Step S2 is followed by step S3 to close the rapid and slow deflating
valves 14 and 16 and actuate the electrically operated pump 18.
Consequently, the cuff pressure Pc is raised. Step S3 is followed by step
S4 to check whether or not the cuff pressure Pc has reached a
predetermined maximum pressure P1. The maximum pressure Pl is
predetermined to be above an estimated maximum blood pressure of the
living body, for example about 180 mmHg. Where the cuff pressure Pc has
reached the maximum pressure Pl, step S4 is followed by step S5.
Step S5 is provided to stop the electrically operated pump 18 and open the
slow deflating valve 16 to slowly discharge air from the cuff 10 and
thereby gradually lower the cuff pressure Pc. In this process, is executed
a blood pressure measuring routine of step S6, which corresponds to blood
pressure measuring means of the present embodiment. That is, a maximum
blood pressure H (mmHg) and a minimum blood pressure L (mmHg) are
determined based on the cuff pressure Pc and a variation in magnitude of
the pulse waves, that is, pressure oscillations of the cuff 10 represented
by the pulse wave signal SPo, and the thus-determined values H and L are
stored in the RAM 34.
Upon completion of step S6, step S7 is implemented to open the rapid
deflating valve 14 to rapidly discharge air from the cuff 10. Step S7 is
followed by steps S8 and the following, in which, as shown in FIG. 6,
successive pulse waves MK1, MK2, . . . are detected and stored, and a
maximum blood pressure SYS and a minimum blood pressure DIA are
successively determined based on magnitudes of the thus-stored pulse
waves.
More specifically, step S8 is provided to check whether or not one pulse
wave has been detected, based on a pulse wave signal SP.sub.T supplied
from the pulse wave sensor 46. In the case where the first pulse wave MK1
has been detected, the first pulse wave MK1 detected is stored. Step S8 is
followed by step S9 to determine a maximum value M.sub.1 (mmHg) and a
minimum value m.sub.1 (mmHg) of the pulse wave MK1 based on the stored
pulse wave. Step S9 is followed by step S10 to check whether or not have
been determined a pair of constants Kmax and Kmin which are employed in
the following equations (1) and (2) for determining a maximum and a
minimum value SYS and DIA of blood pressure based on a maximum value Mmax
(mmHg) and a minimum value Mmin (mmHg) of each pulse wave, respectively:
SYS=Kmax.multidot.Mmax (1)
DIA=Kmin.multidot.Mmin (2)
In the case where the constants Kmax and Kmin have been determined, step 10
is followed by step S11. However, since the first pulse wave MKI has been
just detected and stored now and accordingly the constants Kmax and Kmin
have not been determined yet, step S10 is followed by step S12.
Step S12 is provided to determine according the following equations (3) and
(4) constants Kmax and Kmin based on the maximum and minimum blood
pressure H and L stored in the RAM 34 at step S6 and the maximum and
minimum values M.sub.1 and m.sub.1 of the first pulse wave MK1 determined
at step S9:
Kmax=H/M.sub.1 (3)
Kmin=L/m.sub.1 (4)
Thus, a relationship between the radius pulse waves and the upper-arm blood
pressure H and L is determined.
Step 12 is followed by step S13 to supply a display signal representative
of the maximum and minimum blood pressure H and L to the blood pressure
display 38, which upon receipt of the display signal displays on the Braun
tube thereof the first bar 44 indicative of the blood pressure H and L.
Subsequently, step S14 is implemented to check whether or not the ON/OFF
switch 54 has been operated again. In the case where the switch 54 has
been operated, the operation of the system is ended. However, since a
sufficient trend of the blood pressure has not been obtained yet, normally
the ON/OFF switch 54 has not been re-operated. Accordingly, step S14 is
followed by step S15 to check whether or not the counting T of the timer
has reached a predetermined value To. The value To corresponds to the time
of a predetermined regular interval at which the correspondence
relationship determined at step S12 is updated for correction, and is
predetermined to be within the range of about 5 to 10 minutes.
Accordingly, where the counting T has reached the value To, step S15 is
followed by steps S2 and the following. However, since the first pulse
wave MK1 has been just detected now after the operation of the instant
system is started, the counting T has not reached the value To yet.
Therefore, step S15 is followed by steps S8 and the following.
Where the second pulse wave MK2 following the first pulse wave MK1 in
detected at step S8, step S8 is followed by step S9 to determine a maximum
value M.sub.2 (mmHg) and a minimum value m.sub.2 (mmHg) of the second
pulse wave MK2. Since the constants Kmax and Kmin have been determined at
step S12, as previously described, the checking at step S10 following step
S9 is formed to be affirmative. Accordingly, step S10 is followed by step
Sll to determine according to the above-indicated equations (1) and (2) a
maximum and a minimum blood pressure SYS and DIA corresponding to the
maximum and minimum values M.sub.2 and m.sub.2 of the second pulse wave
MK2. The thus-determined blood pressure SYS and DIA are estimated to be
equal to actual blood pressure of the living body at the time of detection
of the second pulse wave MK2. Step 13 is provided to display the
thus-estimated blood pressure SYS and DIA on the Braun tube of the display
38. Therefore, steps Sll, S12 and S13 correspond to control means of the
present embodiment.
Thereafter, the implementation of steps S8 through S15 is repeated until
the checking at step S14 or step S15 is found to be affirmative. Each time
a pulse wave is detected, that is, each time the arterial vessel is
pulsated, a maximum and a minimum value of blood pressure is successively
determined according to the correspondence-relationship equations (1) and
(2) and based on the maximum and minimum values on the detected pulse
wave, and successively displayed on the display 38.
When the counting T of the timer has reached the value To and accordingly
the checking at step S15 is found to be affirmative, steps S2 and the
following are implemented to obtain another measurement of maximum and
minimum values H and L of the actual blood pressure at step S6, and
determine maximum and minimum values of a leading pulse wave at step S8.
Based on the another measurement of the actual blood pressure and the
maximum and minimum values of the leading pulse wave, another pair of
constants Kmax and Kmin for the correspondence-relationship equations (1)
and (2) are determined. According to the newly-determined
correspondence-relationship equations (1) and (2), the blood pressure is
continuously determined based on maximum and minimum values of each of the
pulse waves detected following the leading pulse wave, and the
thus-determined values of the blood pressure are successively displayed.
In the present embodiment, while the maximum and minimum values of the
actual blood pressure are periodically measured, the pulse waves are
detected above the radius by pressing the pulse wave sensor 46 against the
radial artery under a comparatively low pressure not more than about 20
mmHg. The correspondence relationship between the maximum and minimum
values of the pulse waves and the maximum and minimum values of the actual
blood pressure is periodically updated. The blood pressure is continuously
determined according to the periodically-updated correspondence
relationship and based on magnitudes of the pulse waves detected by the
pulse wave sensor 46, and the thus-determined blood pressure is
continuously displayed. Accordingly, in the present embodiment, for
continuously monitoring the blood pressure, the living body has only to
undergo pressing of a portion of the body which is conducted at regular
intervals of about 5 to 10 minutes, for example, to periodically measure
the actual blood pressure of the living body, as opposed to the
conventional system which is adapted to always press a portion of a living
body to continuously monitor the blood pressure of the living body.
Therefore, a living body whose blood pressure is being monitored by the
instant system is free from any obstruction on blood circulation even
during a long-time continuous monitoring, and feels little discomfort.
Moreover, the present embodiment provides information of medical
significance, that is, a maximum and a minimum blood pressure
corresponding to each pulsation of an arterial vessel of the living body.
Furthermore, in the present embodiment, since the pulse waves are detected
by the pulse wave sensor 46 from the arterial vessel located above the
radius, the detected pulse waves are almost free from influence of
breathing of the living body, contributing to assuring accurate monitoring
of the blood pressure. In this connection, it is noted that it is possible
to use as the pulse wave detecting means a cuff wound around an upper arm
of a living body and detect pressure oscillations of the cuff as pulse
waves. In this case, however, the pulse waves detected are under influence
of variation in volume of arteries and veins, which variation in volume is
at to be influenced by breathing of the living body. Also, it is to be
understood that the present embodiment may be adapted to continuously
determine one of the maximum and minimum blood pressure, average blood
pressure defined as the average value of the maximum and minimum blood
pressure, or other sorts of blood pressure.
There will be described another embodiment of the present invention. It is
noted that, in the following embodiments, the same parts thereof as those
of the above described embodiment are designated by the same reference
numerals, and descriptions about such parts are skipped.
As shown in FIG. 7, it is possible to add step S16, as abnormal pulse wave
detecting means, for updating the relationship in the case where it is
judged from the radius pulse waves that the blood pressure determined
based on the pulse waves has been deflected from the upper arm blood
pressure measured at step S6, for example in the case of a motion of the
portion of the living body at which the pulse waves are detected or in the
case of a change in resistance to peripheral blood flow. When the
condition of the pressed pressure sensor 12 is changed due to a motion of
the detection portion of the living body, or when the resistance to the
peripheral blood flow is changed due to contraction or expansion of
peripheral blood vessels, the values of blood pressure determined based on
the radius pulse waves are deflected from the upper-arm blood pressure.
Step S16 is provided, for example between steps S9 and S10 of FIG. 5, for
detecting an abnormality of the radius pulse waves. In the case of
occurrence of a motion of the detection portion of the living body, step
S16 is implemented to check whether or not the amplitudes of the radius
pulse waves, or the peak values of the same as measured from a reference
line (e.g., zero volt line) has been varied more than 50% during unit time
(e.g., 5 sec). If the checking at step S16 is found to be affirmative, it
means the occurrence of an abnormality of the radius pulse waves.
Alternatively, step S16 may be adapted to check whether or not a pulse
wave has appeared more than 30% before or after a normal cycle for the
radius pulse waves. On the other hand, as shown in FIG. 8, for detecting a
change in the resistance tc the peripheral blood flow, step S16 is adapted
to check whether or not a value indicative of the position of a stepped
portion (notch) in the radius pulse wave e.g., length A between the upper
peak and the notch / length B between the lower peak and the notch) is
varied more than 30% during unit time. The affirmative checking means the
occurrence of an abnormality of the pulse waves. Alternatively, step S16
may be adapted to provide an abnormality checking upon detection of a
great variation in rate of change (slope) of a portion of the pulse wave
corresponding to the diastole of the heart (a down slope C following the
notch). In a further alternative, an abnormality of the radial pulse wave
is detected by checking whether or not the difference between the values
of blood pressure determined based on the leading radius pulse wave, which
at step S12 has been utilized together with the upper-arm blood pressure H
and L to determine a relationship between the radius pulse waves and the
upper-arm blood pressure H and L, and the values of blood pressure based
on one of the pulse waves following the leading pulse wave, exceeds 40
mmHg, for example.
In another embodiment of the present invention, a pulse wave sensor 58 as
shown in FIG. 9 is used as the pulse wave detecting means in place of the
pulse wave sensor 46 employed in the above described embodiments. In the
figure, reference numeral 60 designates a hollow main body which has an
opening 62 at its lower end. The main body 60 is removably attached to the
living body with the help of a band 66, witt the opening 62 opposed to a
body surface of the body above a radius of the living body. The main body
60 consists of an annular side-wall member 70 and a lid member 74 fixed to
an upper end of the side wall member 70 with an outer peripheral portion
of a diaphragm 72 interposed between the members 70 and 74. An inner
peripheral portion of the diaphragm 72 is fixed to a presser member 76.
The diaphragm 72 is formed of an elastically deformable material such as
rubber, and the presser member 76 is supported by the diaphragm 72 within
the main body 60 such that the presser member 76 is movable relative to
the main body 60. A pressure room 78 is defined by the main body 60 and
the presser member 76. The pressure room 78 is supplied with a pressurized
fluid such as a pressurized air, from a pressurized fluid supplying device
80 via a pressure regulating valve 82, whereby the presser member 76 is
brought into pressed contact with the body surface of the living body.
The presser member 76 consists of an annular side-wall member 86, a 1-d
member 88 fixed to an upper end of the side wall member 86 with the inner
peripheral portion of the diaphragm 72 fixed between the members 86, 88,
and a presser plate 90 provided in the vicinity of a lower end of the side
will member 86. As shown in FIG. 10, the presser plate 90 consists of a
semiconductor chip (semiconductor plate) 92 formed of monocrystalline
silicon, etc., and a multiplicity of pressure sensitive diodes 94 formed
on an upper surface of the chip 92. The diodes 94 are provided with
individual terminals 98. A common terminal 96 and each of the terminals 98
cooperate with each other to provide an electrical signal indicative of a
variation in pressure of an interface between the corresponding diode 94
and the chip 92. The multiplicity of pressure sensitive diodes 94 are
formed on the chip 92 such that, with the main body 60 held on the living
body, the diodes 94 are located at regular intervals of distance in a
direction substantially perpendicular to a direction of extension of a
radial artery 100 whose pulse waves are detected. The width of each diode
94 as viewed in the direction substantially perpendicular to the artery
100 and the above-indicated regular interval of distance are determined
such that at least three (seven in the present embodiment) of the diodes
94 are located right above the radial artery 100 and within a length
substantially equal to a diameter of the artery 100. The diodes 94 may be
formed with an appropriate shape and with an appropriate dimension in a
direction parallel to the artery 100.
The presser plate 92 has in a lower surface 102 thereof a multiplicity of
recesses at portions corresponding to the multiplicity of diodes 94
provided in the upper surface, each recess being filled with a rubber
filler 104. The rubber fillers 104 are provided on the chip 92 such that
the fillers 104 do not apply a load to the pressure sensitive diodes 94
and become flush with the lower surface 102. With the pressure sensor 58
held on the body surface of the living body, a portion of the body surface
right above, and in the vicinity of, the radial artery 100 is pressed flat
under the lower surface 102 of the presser plate 90, and pressure
oscillations or pulse waves produced by the artery 100 are transmitted to
the diodes 94 through the rubber fillers 104. The portions of the chip 92,
at which the recesses to be filled with the fillers 104 are formed, are
formed with a remarkably small thickness such as about 15 .mu.m. Where
pressure oscillations are transmitted to the rubber fillers 104, the
interfaces of the diodes 94 are subjected to a change in pressure, and
consequently each diode 94 generates a pulse wave signal SP.sub.T, that is
an electrical signal indicative of the pressure variation.
The presser plate 90 is fixed to a lower open end of a box-like support
member 106 formed of an electrically insulating material and disposed
inside the side wall member 86, whereby electrical leakage from the
semiconductor chip 92 is prevented. The support member 106 and the presser
member 90 cooperate with each other to define a room 108. The room 108 is
maintained in communication with atmospheric air through a rubber tube
110, whereby the pressure in the room 108 is not varied due to a body
temperature of the living body, etc. Thus, the pulse wave signals SP.sub.T
generated by the diodes 94 are free from influence of such a pressure
variation.
The pulse wave signals SP.sub.T generated by the pressure sensitive diodes
94 are supplied to a control device 112 via amplifier, band pass filter
for selectively passing a frequency component of the pulse waves, and so
on (all not shown). The control device 112 is constituted by microcomputer
including the A/D converter 50, CPU 28, RAM 34, ROM 32, clock signal
generator 56, output interface 36, etc. of the previously described
embodiments. As in those embodiments, the control device 112 is adapted to
detect pulse waves of the radial artery 100 based on the input pulse wave
signals SP.sub.T and command the blood pressure display 38 to display
values of blood pressure determined based on the detected pulse waves. The
control device 112 also generates a drive signal SD to the pressure
regulating valve 82 to regulate the pressure of the pressurized fluid
supplied to the pressure room 78.
There will be described the operation of the present embodiment constructed
as described above.
With the main body 60 held in the vicinity of a wrist of the living body
with the help of the band 66, and with the presser plate 90 of the presser
member 76 covering right above the radial artery 100, steps S1 to S7 of
the flow chart of FIG. 5 are implemented to measure a maximum and a
minimum value of the actual blood pressure of the living body by the cuff
10. Subsequently, the pulse wave detect routine as shown in FIG. 11 is
executed in place of steps S8 and S9 of FIG. 5.
To begin with, step ST1 is implemented to generate a drive signal SD for
supplying the pressure room 78 with a pressurized fluid with a
predetermined constant pressure. Consequently, the presser member 76 is
moved relative to the main body 60 toward the body surface of the living
body, and eventually the lower surface 102 of the presser plate 90 is
brought into pressed contact with the body surface. With the lower surface
102 being in pressed contact with the body surface, pressure oscillations
or pulse waves produced by the artery 100 are transmitted to the pressure
sensitive diodes 94, which generate pulse wave signals SP.sub.T indicative
of the pressure oscillations. The constant pressure, under which the
presser plate 76 is pressed on the body surface, is determined at such a
degree that the pressure oscillations of the pulse waves can be detected
by the diodes 94.
Step ST1 is followed by step ST2 to determine an amplitude A of each of the
pulse wave signals SP.sub.T generated by the multiplicity of pressure
sensitive diodes 94 arranged in the direction substantially normal to the
direction of extension of the artery 100. Subsequently, step ST3 is
implemented to determine a maximum amplitude maxA of the thus-determined
amplitudes A. Step ST3 is followed by step ST4 to calculate a reference
value As by multiplying the maximum amplitude maxA by a predetermined
coefficient k1 (1>k1>0), and step ST5 to select pulse wave signals
SP.sub.T(A) whose amplitudes A are greater than the reference value As.
Step ST5 is followed by step ST6 to determine a maximum peak value P of
each of the thus-selected pulse wave signals SP.sub.T(A). The maximum peak
value P, a magnitude of signal, corresponds to a value of blood pressure
within the artery 100 at the period of the systole of the heart of the
living body. Step ST6 is followed by step ST7 to check whether or not a
varying trend of the maximum peak values P of the pulse wave signals
SP.sub.T(A) in the direction intersecting the artery 100 has a pair of
maximal points.
Steps ST2 through ST5, above indicated, are provided for selecting the
pulse wave signals generated by the pressure sensitive diodes 94
positioned in the vicinity of a portion of the body surface right above
the artery 100. More specifically, as shown in FIG. 12, the amplitudes A
of the pulse wave signals SP.sub.T generated by the diodes 94 located
right above the artery 100 are greater than those of the signals generated
by the other diodes 94, as viewed in the direction normal to the artery
100. In the case where the presser member 76 is pressed on the body
surface such that the artery 10f becomes generally depressed under the
pressure exerted by the presser member 76, nine pulse wave signals
SP.sub.T from the nine diodes 94 located in the vicinity of the portion of
the body surface right above the artery 100, are selected as the signals
SP.sub.T(A), as shown by the graph (c) in FIG. 12. The coefficient k1
employed for calculation of the reference value As is pre-determined so
that the pulse wave signals SP.sub.T generated by the pressure sensitive
diodes 94 in the vicinity of the portion of the body surface right above
the artery 100 can be selected as the signals SP.sub.T(A).
The graph (c) of FIG. 13 illustrates a varying trend of the maximum peak
values P of the selected pulse wave signals SP.sub.T(A) in the direction
intersecting artery 100. Likely, the graph has a minimal point at a
position corresponding to a generally middle point of the portion of the
body surface right above the artery 100 and a pair of maximal points at
the opposite ends of the portion of the body surface right above the
artery 100. In such a case, the checking at step ST7 is found to be
affirmative. The reason of this is that, since with the artery 100
assuming a generally depressed shape a portion of the wall of the artery
100 corresponding to around the middle point of the portion of the body
surface right above the artery 100 is in parallel relationship with the
presser plate 90, pressure oscillations or pulse waves transmitted
perpendicularly to the parallel portion of the artery wall are almost free
from influence of tension of the wall, on the other hand the diodes 94
positioned in the vicinity of the opposite ends of the portion of the body
surface right above the artery 100 detect a relatively high pressure since
pressure oscillations transmitted to curved portions of the artery wall
located on both sides of the parallel portion thereof and corresponding to
the above-indicated opposite ends, are influenced by the tension of the
artery wall.
However, at present, when the pressure of the pressurized air supplied to
the pressure room 78 is relatively low, the pressing force under which the
presser member 76 is pressed on the body surface of the living body is
small, and accordingly the artery 100 does not assume the depressed shape.
The graph (a) of FIG. 12 shows this condition, that is, a varying trend of
the amplitudes A of the pulse wave signals SP.sub.T, which has a maximal
point | | |
