Abstrict
A blood pressure monitor system, including a pulse wave detecting
device detecting a pulse wave produced from an artery of a living
subject, a blood pressure measuring device including a pressing
device, for measuring a blood pressure of the subject by pressing
a body portion of the subject with the pressing device, a relationship
determining device determining a relationship between blood pressure
and pulse wave magnitude, based on a pulse wave magnitude detected
by the pulse wave detecting device and a blood pressure value measured
by the blood pressure measuring device, a blood pressure monitor
device continuously determining, according to the relationship,
blood pressure values of the subject based on magnitudes of the
pulse wave detected by the pulse wave detecting device, the relationship
determining device updating the relationship at intervals of time,
based on blood pressure values measured by the blood pressure measuring
device, a blood pressure variation determining device determining
a variation of the blood pressure of the subject, based on at least
two of the magnitudes of the pulse wave detected by the pulse wave
detecting device, and an update-interval changing device changing
the interval of updating based on the blood pressure variation determined
by the blood pressure variation determining device.
Claims
What is claimed is:
1. A blood pressure monitor system, comprising:
pulse wave detecting means for detecting a series of pulses of
a pressure pulse wave produced from a single artery of a living
subject in synchronism with heartbeat of said subject, said detecting
means including a plurality of pressure sensing elements which are
adapted to contact a body surface of said subject directly above
said artery, said artery extending in a blood flow direction and
said sensing elements extending in a direction crossing said blood
flow direction;
pressing means for pressing said pulse wave detecting means against
said artery through said body surface to partially flatten a wall
of said artery, so that at least one of said pressure sensing elements
detects said pulse wave through the flattened wall of said artery;
blood pressure measuring means including an inflatable cuff, for
measuring a blood pressure of said subject by pressing a body portion
of said subject with said cuff;
relationship determining means for determining a relationship between
blood pressure and pulse wave magnitude, based on a pulse wave magnitude
detected by said at least one pressure sensing element of said pulse
wave detecting means through said flattened wall of said artery
and a blood pressure value measured by said blood pressure measuring
means, said relationship determining means determining a linear
function equation defining said relationship, said linear function
equation being expressed as P=a.multidot.M+b wherein P is blood
pressure, M is pulse wave magnitude, and a, b are constants;
blood pressure monitor means for continuously determining, according
to said relationship, blood pressure values of said subject based
on magnitudes of the pulse wave detected by said at least one pressure
sensing element of said pulse wave detecting means through said
flattened wall of said artery;
said relationship determining means updating said relationship
at intervals of time, based on blood pressure values measured by
said blood pressure measuring means;
blood pressure variation determining means for determining a variation
of the blood pressure of said subject, based on at least two of
said magnitudes of the pulse wave detected by said at least one
pressure sensing element of said pulse wave detecting means; and
update-interval changing means for changing said interval of updating
based on the blood pressure variation determined by said blood pressure
variation determining means.
2. The blood pressure monitor system as set forth in claim 1, wherein
said blood pressure variation determining means determines, as said
variation of the blood pressure of said subject, an absolute value
of a difference between a maximum magnitude of each of said pulses
of the pulse wave detected by said pulse wave detecting means and
a maximum magnitude of a prior one of said pulses detected a predetermined
time before said each pulse.
3. The blood pressure monitor system as set forth in claim 2, wherein
said update-interval changing means changes said interval of updating,
by commanding said blood pressure measuring means and said relationship
determining means to update said relationship, when said variation
of the blood pressure is greater than a predetermined reference
value.
4. The blood pressure monitor system as set forth in claim 1, wherein
said blood pressure variation determining means determines, as a
first variation of the blood pressure of said subject, an absolute
value of a difference between a maximum magnitude of each of said
pulses of the pulse wave detected by said pulse wave detecting means
and a maximum magnitude of a first prior one of said pulses detected
a first predetermined time before said each pulse, and determines,
as a second variation of the blood pressure, an absolute value of
a difference between said maximum magnitude of said each pulse and
a maximum magnitude of a second prior one of said pulses detected
a second predetermined time before said each pulse, said second
predetermined time being shorter than said first predetermined time,
said update-interval changing means changing said interval of updating,
by commanding said blood pressure measuring means and said relationship
determining means to update said relationship, when said first and
second variations of the blood pressure are greater than a first
and a second predetermined reference value, respectively.
5. The blood pressure monitor system as set forth in claim 1, wherein
said blood pressure variation determining means calculates an amplitude
of each of said pulses of the pulse wave detected by said pulse
wave detecting means, by subtracting a minimum magnitude of said
each pulse from a maximum magnitude of said each pulse, and determines
as said variation of the blood pressure of said subject an absolute
value of a difference between said amplitude of said each pulse
and an amplitude of a prior one of said pulses detected a predetermined
time before said each pulse.
6. The blood pressure monitor system as set forth in claim 5, wherein
said update-interval changing means changes said interval of updating,
by commanding said blood pressure measuring means and said relationship
determining means to update said relationship, when said variation
of the blood pressure is greater than a reference value.
7. The blood pressure monitor system as set forth in claim 6, wherein
said update-interval changing means determines said reference value
based on said amplitude of said prior one pulse.
8. The blood pressure monitor system as set forth in claim 1, wherein
said blood pressure variation determining means determines, as a
first variation of the blood pressure of said subject, an absolute
value of a difference between an amplitude of each of said pulses
of the pulse wave detected by said pulse wave detecting means and
an amplitude of a first prior one of said pulses detected a first
predetermined time before said each pulse, and determines, as a
second variation of the blood pressure, an absolute value of a difference
between said amplitude of said each pulse and an amplitude of a
second prior one of said pulses detected a second predetermined
time before said each pulse, said second predetermined time being
shorter than said first predetermined time,
said update-interval changing means determining a first reference
value based on said amplitude of said first prior one pulse, and
a second reference value based on said amplitude of said second
prior one pulse,
said update-interval changing means changing said interval of updating,
by commanding said blood pressure measuring means and said relationship
determining means to update said relationship, when said first and
second variations of the blood pressure are greater than said first
and second reference values, respectively.
9. The blood pressure monitor system as set forth in claim 1, wherein
said blood pressure variation determining means determines (a) as
a first variation of the blood pressure of said subject an absolute
value of a difference between a maximum magnitude of each of said
pulses of the pulse wave detected by said pulse wave detecting means
and a maximum magnitude of a first prior one of said pulses detected
a first predetermined time before said each pulse, determines (b)
as a second variation of the blood pressure an absolute value of
a difference between said maximum magnitude of said each pulse and
a maximum magnitude of a second prior one of said pulses detected
a second predetermined time before said each pulse, said second
predetermined time being shorter than said first predetermined time,
determines (c) as a third variation of the blood pressure an absolute
value of a difference between an amplitude of said each pulse and
an amplitude of said first prior one pulse, and determines (d) as
a fourth variation of the blood pressure an absolute value of a
difference between said amplitude of said each pulse and an amplitude
of said second prior one pulse,
said update-interval changing means changing said interval of updating,
by commanding said blood pressure measuring means and said relationship
determining means to update said relationship, when said first,
second, third, and fourth variations of the blood pressure are greater
than a first and a second predetermined reference value and a third
and a fourth reference value, respectively,
said update-interval changing means determining said third reference
value based on said amplitude of said first prior one pulse, and
said fourth reference value based n said amplitude of said second
prior one pulse.
10. The blood pressure monitor system as set forth in claim 1,
wherein said blood pressure variation determining means selects,
rom the pulses of the pulse wave detected by said pulse wave detecting
means during a first predetermined time duration after said relationship
is updated by said relationship determining means, a pulse having
a greatest maximum magnitude, MAX, of maximum magnitudes of said
pulses and a pulse having a smallest minimum magnitude, MIN, of
minimum magnitudes of said pulses, calculates an average, MID, of
said magnitudes MAX, MIN, calculates an average, AV, of the maximum
and minimum magnitudes of said pulses except said magnitudes MAX,
MIN, determines as a deviation, D, an absolute value of a difference
between said averages MID, AV, and successively calculates an average,
AV', of maximum and minimum magnitudes of the pulses of the pulses
wave detected during every second predetermined time duration after
said deviation D is determined,
said blood pressure variation determining means determining, as
said variation of the blood pressure of said subject, an absolute
value of a difference between time-wise adjacent two of said average
AV and the averages AV'.
11. The blood pressure monitor system as set forth in claim 10,
wherein said update-interval changing means changes said interval
of updating, by commanding said blood pressure measuring means and
said relationship determining means to update said relationship,
when said variation of the blood pressure is greater than said deviation
D.
12. The blood pressure monitor system as set forth in claim 1,
wherein said blood pressure variation determining means selects,
from the pulses of the pulse wave detected by said pulse wave detecting
means during a predetermined time duration after said relationship
is updated by said relationship determining means, pulse having
a greatest maximum magnitude of maximum magnitudes of said pulses
and a pulse having a smallest maximum magnitude of said maximum
magnitudes, and determines, as said variation of the blood pressure
of said subject, an absolute value of a difference between said
greatest and smallest maximum magnitudes.
13. The blood pressure monitor system as set forth in claim 12,
wherein said update-interval changing means determines a first weighted
value, a, corresponding to said variation of the blood pressure,
and a second weighted value, b, corresponding to a value of a physiological
indicator indicative of a physical condition of said subject different
from the maximum magnitude of the pulses of the pulse wave, and
changes said interval of updating based on said weighted values
a, b.
14. The blood pressure monitor system as set forth in claim 13,
wherein said update-interval changing means changes said interval
of updating to a value obtained by dividing a reference value by
a sum of said weighted values a, b.
15. The blood pressure monitor system as set forth in claim 1,
wherein said blood pressure variation determining means determines
said variation of the blood pressure of said subject, by utilizing
at least one physiological indicator selected from maximum magnitude,
minimum magnitude, average magnitude, and amplitude of the pulses
of the pulse wave.
16. The blood pressure monitor system as set forth in claim 1,
further comprising display means for displaying a waveform of said
pulse wave detected by said pulse wave detecting means, said blood
pressure value measured by said blood pressure measuring means,
and said blood pressure values determined by said blood pressure
monitor means.
17. A blood pressure monitor method, comprising the steps of:
pressing a pulse wave sensor including a plurality of pressure
sensing elements, against a single artery of a living subject through
a body surface of said subject, such that said pulse wave sensor
partially flattens a wall of said artery and that said pressure
sensing elements contact said body surface of said subject directly
above said artery, said artery extending in a blood flow direction
and said sensing elements extending in a direction crossing said
blood flow direction,
detecting, using at least one of said pressure sensing elements
of said pulse wave sensor, a series of pulses of a pressure pulse
wave produced from the flattened wall of said artery of said living
subject in synchronism with a heartbeat of said subject,
measuring, using an inflatable cuff, a blood pressure of said subject
by pressing a body portion of said subject with said cuff,
determining a relationship between blood pressure and pulse wave
magnitude, based on a pulse wave magnitude detected by said at least
one pressure sensing element through said flattened wall of said
artery and a blood pressure value measured using said cuff, such
that said relationship is defined by a linear function equation
which is expressed as P=a.multidot.M+b wherein P is blood pressure,
M is pulse wave magnitude, and a, b are constants,
continuously determining, according to said relationship, blood
pressure values of said subject based on magnitudes of the pulse
wave detected by said at least one pressure sensing element through
said flattened wall of said artery,
updating said relationship at intervals of time, based on blood
pressure values measured using said cuff,
determining a variation of the blood pressure of said subject,
based on at least two of said magnitudes of the pulse wave detected
by said at least one pressure sensing element, and
changing said interval of updating based on the determined blood
pressure variation.
18. A blood pressure monitor system, comprising:
pulse wave detecting means for detecting a series of pulses of
a pressure pulse wave produced from a single artery of a living
subject in synchronism with heartbeat of said subject, said detecting
means including a plurality of pressure sensing elements which are
adapted to contact a body surface of said subject directly above
said artery, said artery extending in a blood flow direction and
said sensing elements extending in a direction crossing said blood
flow direction;
pressing means for pressing said pulse wave detecting means against
said artery through said body surface to partially flatten a wall
of said artery, so that at least one of said pressure sensing elements
detects said pulse wave through the flattened wall of said artery;
blood pressure measuring means including an inflatable cuff, for
measuring a blood pressure of said subject by pressing a body portion
of said subject with said cuff;
relationship determining means for determining a relationship between
blood pressure and pulse wave magnitude, based on a pulse wave magnitude
detected by said at least one pressure sensing element of said pulse
wave detecting means through said flattened wall of said artery
and a blood pressure value measured by said blood pressure measuring
means;
blood pressure monitor means for continuously determining, according
to said relationship, blood pressure values of said subject based
on magnitudes of the pulse wave detected by said at least one pressure
sensing element of said pulse wave detecting means through said
flattened wall of said artery;
said relationship determining means updating said relationship
at intervals of time, based on blood pressure values measured by
said blood pressure measuring means;
blood pressure variation determining means for determining a variation
of the blood pressure of said subject, based on at least two of
said magnitudes of the pulse wave detected by said at least one
pressure sensing element of said pulse wave detecting means,
said blood pressure variation determining means selecting, from
the pulses of the pulse wave detected by said pulse wave detecting
means during a first predetermined time duration after said relationship
is updated by said relationship determining means, a pulse having
a greatest maximum magnitude, MAX, of maximum magnitudes of said
pulses and a pulse having a smallest minimum magnitude, MIN, of
minimum magnitudes of said pulses, calculating an average, MID,
of said greatest maximum and smallest minimum magnitudes MAX, MIN,
calculating an average, AV, of the maximum and minimum magnitudes
of said pulses except said magnitudes MAX, MIN, determining as a
deviation, D, an absolute value of a difference between said averages
MID, AV, and successively calculating an average, AV', of maximum
and minimum magnitudes of the pulses of the pulse wave detected
during every second predetermined time duration after said deviation
D is determined, said blood pressure variation determining means
determining, as said variation of the blood pressure of said subject,
an absolute value of a difference between time-wise adjacent two
of said average AV and the averages AV'; and
update-interval changing means for changing said interval of updating
based on the blood pressure variation determined by said blood pressure
variation determining means.
19. The blood pressure monitor system as set forth in claim 18,
wherein said update-interval changing means changes said interval
of updating, by commanding said blood pressure measuring means and
said relationship determining means to update said relationship,
when said variation of the blood pressure is greater than said deviation
D.
20. A blood pressure monitor system, comprising;
pulse wave detecting means for detecting a series of pulses of
a pressure pulse wave produced from a single artery of a living
subject in synchronism with heartbeat of said subject, said detecting
means including a plurality of pressure sensing elements which are
adapted to contact a body surface of said subject directly above
said artery, said artery extending in a blood flow direction and
said sensing elements extending in a direction crossing said blood
flow direction;
pressing means for pressing said pulse wave detecting means against
said artery through said body surface to partially flatten a wall
of said artery, so that at least one of said pressure sensing elements
detects said pulse wave through the flattened wall of said artery;
blood pressure measuring means including an inflatable cuff, for
measuring a blood pressure of said subject by pressing a body portion
of said subject with said cuff;
relationship determining means for determining a relationship between
blood pressure and pulse wave magnitude, based on a pulse wave magnitude
detected by said at least one pressure sensing element of said pulse
wave detecting means through said flattened wall of said artery
and a blood pressure value measured by said blood pressure measuring
means;
blood pressure monitor means for continuously determining, according
to said relationship, blood pressure values of said subject based
on magnitudes of the pulse wave detected by said at least one pressure
sensing element of said pulse wave detecting means through said
flattened wall of said artery;
said relationship determining means updating said relationship
at intervals of time, based on blood pressure values measured by
said blood pressure measuring means;
blood pressure variation determining means for determining a variation
of the blood pressure of said subject, based on at least two of
said magnitudes of the pulse wave detected by said at least one
pressure sensing element of said pulse wave detecting means,
said blood pressure variation determining means selecting, from
the pulses of the pulse wave detected by said pulse wave detecting
means during a predetermined time duration after said relationship
is updated by said relationship determining means, a pulse having
a greatest maximum magnitude out of maximum magnitudes of said pulses
and a pulse having a smallest maximum magnitude out of said maximum
magnitudes of said pulses, and determining, as said variation of
the blood pressure of said subject, an absolute value of a difference
between said greatest and smallest maximum magnitudes; and
update-interval changing means for changing said interval of updating
based on the blood pressure variation determined by said blood pressure
variation determining means.
21. The blood pressure monitor system as set forth in claim 20,
wherein said update-interval changing means determines a first weighted
value, a, corresponding to said variation of the blood pressure,
and a second weighted value, b, corresponding to a value of a physiological
indicator indicative of a physical condition of said subject different
from the maximum magnitude of the pulses of the pulse wave, and
changes said interval of updating based on said weighted values
a, b.
22. The blood pressure monitor system as set forth in claim 21,
wherein said update-interval changing means changes said interval
of updating to a value obtained by dividing a reference value by
a sum of said weighted values a, b.
Description BACKGROUND OF THE INVENTION
Field of the Invention
The present invention generally relates to a blood pressure monitor
system and in particular to such a monitor system which continuously
determines blood pressure values of a living subject, according
to a predetermined relationship between blood pressure and pulse
wave magnitude, based on detected magnitudes of a pulse wave.
Related Art Statement
There is known a blood pressure monitor apparatus of the type which
includes (a) a pulse wave detecting device detecting a pulse wave
produced from an artery of a living subject, (b) a blood pressure
measuring device measuring a blood pressure of the subject by pressing
the subject's body portion with a pressing device, (c) a relationship
determining means determining a relationship between blood pressure
and pulse wave magnitude, based on a pulse wave magnitude detected
by the pulse wave detecting device and a blood pressure value measured
by the blood pressure measuring device, and (d) a blood pressure
monitor means continuously determining, according to the determined
relationship, blood pressure values of the subject based on magnitudes
of the pulse wave detected by the pulse wave detecting device, and
in which apparatus the relationship determining means updates the
relationship at predetermined regular intervals of time, based on
blood pressure values measured by the blood pressure measuring device.
An example of the monitor system is disclosed in a Japanese Patent
Application filed by the Assignee of the present application, which
was laid open under Publication No. 1(1989)161707. The monitor system
is used for, for example, monitoring the blood pressure of a patient
after, or during, a surgical operation.
For sufficiently accurately monitoring the blood pressure of the
patient based on the pulse wave detected by the pulse wave detecting
device, it is desirable to update as frequently as possible the
relationship between blood pressure and pulse wave magnitude (hereinafter,
referred to as the "BP-PW relationship"). However, for
updating of the BP-PW relationship, the blood pressure measuring
device is required to measure an actual or standard blood pressure
of the patient, which in turn involves the pressing of his or her
body portion (e.g., upper arm) with the pressing device (e.g., inflatable
cuff). If the BP-PW relationship is updated so frequently, however,
the patient feels discomfort each time due to the pressing of the
upper arm. Thus, the requirement that the blood pressure monitoring
be effected with accuracy is not compatible with the requirement
that patient's discomfort be reduced. In the conventional blood
pressure monitor apparatus, the interval of updating of the BP-PW
relationship is selected, as a compromise between the above two
requirements, at a time duration (e.g., 5 to 10 minutes) which is
not too long and not too short. However, if the patient's blood
pressure varies largely in a very short time, the BP-PW relationship
tends to be inappropriate or inaccurate, thereby lowering the accuracy
of the blood pressure monitor based on the pulse wave detected by
the pulse wave detecting device.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
blood pressure monitoring system which continuously determines blood
pressure values of a living subject, according to a relationship
between blood pressure and pulse wave magnitude, based on actually
detected magnitudes of a pulse wave, and updates the relationship
at intervals of time based on blood pressure values actually measured
using a pressing device, which system reduces patient's discomfort
due to the unnecessarily frequent pressing with the pressing device
when the patient's blood pressure does not vary so largely and provides
accurate blood pressure monitoring when the blood pressure varies
largely.
The above object has been achieved by the present invention, which
provides a blood pressure monitoring system, comprising (a) pulse
wave detecting means for detecting a pulse wave produced from an
artery of a living subject, (b) blood pressure measuring means including
a pressing device, for measuring a blood pressure of the subject
by pressing a body portion of the subject with the pressing device,
(c) relationship determining means for determining a relationship
between blood pressure and pulse wave magnitude, based on a pulse
wave magnitude detected by the pulse wave detecting means and a
blood pressure value measured by the blood pressure measuring means,
(d) blood pressure monitoring means for continuously determining
according to the relationship, blood pressure values of the subject
based on magnitudes of the pulse wave detected by the pulse wave
detecting means, the relationship determining means updating the
relationship at intervals of time, based on blood pressure values
measured by the blood pressure measuring means, (e) blood pressure
variation determining means for determining a variation of the blood
pressure of the subject, based on at least two of the magnitudes
of the pulse wave detected by the pulse wave detecting means, and
update-interval changing means for changing the interval of updating
based on the blood pressure variation determined by the blood pressure
variation determining means.
In the blood pressure monitoring system constructed as described
above, the relationship determining means determines a relationship
between blood pressure and pulse wave magnitude, based on a pulse
wave magnitude detected by the pulse wave detecting means and a
blood pressure value measured by the blood pressure measuring means,
and the blood pressure monitoring means continuously determines
or estimates, according to the relationship, blood pressure values
of the subject based on respective magnitudes of the pulse wave
detected by the pulse wave detecting means. The relationship determining
means updates the relationship at intervals of time, based on standard
blood pressure values actually measured by the blood pressure measuring
means. The present monitor system further includes blood pressure
variation determining means for determining a variation of the blood
pressure of the subject, based on at least two of the above-indicated
respective magnitudes of the pulse wave, and update-interval changing
means for changing the interval of updating based on the blood pressure
variation determined by the blood pressure variation determining
means. For example, when the variation of the blood pressure is
sufficiently small and therefore the detected pulse wave is stable,
the present system lengthens the interval of updating and consequently
the interval of the blood pressure measurement using the pressing
device. Thus, the present system advantageously reduces patient's
discomfort due to otherwise more frequent pressing of his or her
body portion with the pressing device. Meanwhile, when the blood
pressure variation is excessively large, the present system shortens
the interval of updating, for determining an appropriate relationship
to provide accurate blood pressure monitoring based on the pulse
wave detected by the pulse wave detecting means.
According to a preferred feature of the present invention, the
blood pressure variation determining means determines (a) as a first
variation of the blood pressure of the subject an absolute value
of a difference between a maximum magnitude of each of pulses of
the pulse wave detected by the pulse wave detecting means and a
maximum magnitude of another of the pulses detected a first predetermined
time before the each pulse, determines (b) as a second variation
of the blood pressure an absolute value of a difference between
the maximum magnitude of the each pulse and a maximum magnitude
of yet another of the pulses detected a second predetermined time
before the each pulse, the second predetermined time duration being
shorter than the first predetermined time duration, determines (c)
as a third variation of the blood pressure an absolute value of
a difference between an amplitude of the each pulse and an amplitude
of the another pulse, and determines (d) as a fourth variation of
the blood pressure an absolute value of a difference between the
amplitude of the each pulse and an amplitude of the yet another
pulse, the update-interval changing means changing the interval
of updating, by commanding the blood pressure measuring means and
the relationship determining means to update the relationship, when
the first, second, third, and fourth variations of the blood pressure
are greater than a first and a second predetermined reference value
and a third and a fourth reference value, respectively, the update-interval
changing means determining the third reference value based on the
amplitude of the another pulse, and the fourth reference value based
on the amplitude of the yet another pulse.
According to another feature of the present invention, the blood
pressure variation determining means selects, from pulses of the
pulse wave detected by the pulse wave detecting means during a first
predetermined time duration after the relationship is updated by
the relationship determining means, a pulse having a greatest maximum
magnitude, MAX, of maximum magnitudes of the pulses and a pulse
having a smallest minimum magnitude, MIN, of minimum magnitudes
of the pulses, calculates an average, MID, of the magnitudes MAX,
MIN, calculates an average, AV, of the maximum and minimum magnitudes
of the pulses except the magnitudes MAX, MIN, determines as a deviation,
D, an absolute value of a difference between the averages MID, AV,
and successively calculates an average, AV', of maximum and minimum
magnitudes of pulses of the pulse wave detected during every second
predetermined time duration after the deviation D is determined,
the blood pressure variation determining means determining, as the
variation of the blood pressure of the subject, an absolute value
of a difference between time-wise adjacent two out of the average
AV and the averages AV'. In this case, the update-interval changing
means may change the interval of updating, by commanding the blood
pressure measuring means and the relationship determining means
to update the relationship, when the variation of the blood pressure
is greater than the deviation D.
According to yet another feature of the present invention, the
blood pressure variation determining means selects, from pulses
of the pulse wave detected by the pulse wave detecting means during
a predetermined time duration after the relationship is updated
by the relationship determining means, a pulse having a greatest
maximum magnitude of maximum magnitudes of the pulses and a pulse
having a smallest maximum magnitude of the maximum magnitudes, and
determines, as the variation of the blood pressure of the subject,
an absolute value of a difference between the greatest and smallest
maximum magnitudes. In this case, the update-interval changing means
may determine a first weighted value, a, corresponding to the variation
of the blood pressure, and a second weighted value, b, corresponding
to a value of a physiological indicator indicative of a physical
condition of the subject different from the maximum magnitude of
the pulses of the pulse wave, and changes the interval of updating
based on the weighted values a, b. The update-interval changing
means may change the interval of updating to a value obtained by
dividing a reference value by a sum of the weighted values a, b.
According to a further feature of the present invention, the blood
pressure variation determining means determines the variation of
the blood pressure of the subject, by utilizing at least one physiological
indicator selected from maximum magnitude, minimum magnitude, average
magnitude, and amplitude of the pulses of the pulse wave detected
by the pulse wave detecting means.
According to another feature of the present invention, the monitor
system further comprises display means for displaying a waveform
of the pulse wave detected by the pulse wave detecting means, the
blood pressure value measured by the blood pressure measuring means,
and the blood pressure values determined by the blood pressure monitoring
means.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and optional objects, features and advantages of the
present invention will be better understood by reading the following
detailed description of the presently preferred embodiments of the
invention when considered in conjunction with the accompanying drawings,
in which:
FIG. 1 is a diagrammatic view of a blood pressure monitor system
embodying the present invention;
FIG. 2 is a flow chart representing a cuff-using blood pressure
measure routine carried out by the blood pressure monitor system
of FIG. 1;
FIG. 3 is a flow chart representing the blood pressure monitoring
routine carried out, in parallel with the routine of FIG. 2, by
the blood pressure monitor system of FIG. 1;
FIG. 4 is a flow chart representing a blood pressure variation
determination routine as a part of the blood pressure monitor routine
of FIG. 3;
FIG. 5 is a flow chart representing another blood pressure variation
determination routine which may be used i the blood pressure monitor
system of FIG. 1;
FIG. 6 is a flow chart representing another cuff-using blood pressure
measurement routine which may be used in the blood pressure monitor
system of FIG. 1; and
FIG. 7 is a flow chart representing a cuff-using BP (blood pressure)
measurement interval change routine as a part of the cuff-using
blood pressure measurement routine of FIG. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is shown a blood pressure monitoring
system embodying the present invention. The present monitor system
is used for, for example, monitoring the physical condition of a
patient during, or after, a surgical operation. In the figure, reference
numeral 10 designates a bag-like, inflatable cuff formed of rubber.
The cuff 10 is worn on the patient by being wound around, for example,
an upper arm 12 of the patient. A pressure sensor 14, a selector
valve 16, and a first air pump 18 are connected to the cuff 10 via
piping 20.
The selector valve 16 is selectively placed in an INFLATION position,
a SLOW-DEFLATION position, and a QUICK-DEFLATION position. In the
INFLATION position, the selector valve 16 permits pressurized air
to be supplied from the first air pump 18 to the cuff 10; in the
SLOW-DEFLATION position, the valve 16 permits the pressurized air
to slowly be discharged from the cuff 10 to atmosphere; and in the
QUICK-DEFLATION position, the valve 16 permits the pressurized air
to quickly be discharged from the cuff 10 to atmosphere.
The pressure sensor 14 detects the air pressure in the cuff 10,
and supplies an electric signal, SP, representative of the detected
pressure, to a static-pressure filter circuit 22 and a pulse-wave
filter circuit 24. The static-pressure filter circuit 22 includes
a low-pass filter and transmits, as a cuff-pressure signal SK, a
static ("DC") component of the signal SP. The cuff pressure
signal SK is representative of a static pressure, P, of the cuff
10 (hereinafter, referred to simply as the "cuff pressure P").
The cuff pressure signal SK is supplied to a control device 28 via
a first analog to digital (A/D) converter 26.
Meanwhile, the pulse-wave filter circuit 24 includes a band-pass
filter and transmits, as a pulse-wave signal SM.sub.1, an oscillating
("AC") component of the signal SP. The pulse wave signal
SM.sub.1 is supplied to the control device 28 via a second analog
to digital (A/D) converter 30. The pulse wave signal SM.sub.1 is
representative of a pulse wave, i.e., oscillatory pressure wave
produced from a brachial artery of the patient in synchronism with
heartbeat of the patient and transmitted to the cuff 10 via the
tissue positioned between the artery and the cuff 10. In the present
embodiment, the cuff 10 serves as a pressing device for pressing
the patient's upper arm 12 as a body portion of a living subject.
The control device 28 consists of a microcomputer which includes
a central processing unit (CPU), a read only memory (ROM), a random
access memory (RAM), and an input and output (I/O) port. The CPU
processes supplied signals according to control programs stored
in the ROM by utilizing a temporary-storage function of the RAM,
and supplies drive signals to the selector valve 16 and the first
air pump 18 through the I/O port and respective drive circuits (not
shown) so as to regulate the cuff pressure P. In addition, the CPU
of the control device 28 operates for determining a blood pressure
(e.g., systolic and diastolic pressures) of the patient, based on
variation of the amplitudes of pulses of the pulse wave signal SM.sub.1
obtained while the cuff pressure P is slowly decreased. The control
device 28 commands a display 32 including a cathode ray tube (CRT),
to indicate the measured blood pressure values on the CRT. The control
device 28 repeats this blood pressure measurement using the cuff
10, at predetermined intervals of time. In the present embodiment,
the cuff 10, pressure sensor 14, selector valve 16, first air pump
18, static-pressure filter circuit 22, pulse-wave filter circuit
24, first and second A/D converters 26, 30, and control device 28
cooperate with each other to serve as blood pressure measuring means
for measuring an actual or standard blood pressure of a subject
by pressing a body portion of the subject with the cuff 10 as a
pressing device.
As shown in FIG. 1, the present monitor system further includes
a pulse wave detector probe 34. The probe 34 includes a container-like
housing 36 which is detachably set on a body surface 38 of a wrist
42 of the patient with a pair of bands 40, 40 fastened around the
wrist 42, such that the open end of the housing 36 contacts the
body surface 38 of the wrist 42. In the present embodiment, the
probe 34 is worn on one of two superior limbs of the patient different
from the other superior limb on which the cuff 10 is worn.
A pulse wave sensor 46 is supported by the housing 36 via an elastic
diaphragm 44, such that the pulse wave sensor 46 is displaceable
relative to the housing 36, when the diaphragm 44 is inflated, so
as to be advanceable out of the open end of the housing 36. The
housing 36, diaphragm 44 and pulse wave sensor 46 cooperate with
each other to define a pressure chamber 48, to which pressurized
air is supplied from a second air pump 50 via a pressure-regulator
valve 52. Thus, the pulse wave sensor 46 is pressed against the
body surface 38 with a pressing force corresponding to the air pressure
in the pressure chamber 48.
The pulse wave sensor 46 includes a plurality of semiconductor
pressure-sensing elements (not shown) which are provided in one
of opposite surfaces of a semiconductor substrate, such as a monocrystalline
silicon, which one surface serves as a press surface 54 of the sensor
46. The pressure-sensing elements are arranged in an array at small
intervals of distance in the press surface 54. The pulse wave sensor
46 is pressed on the body surface 38 of the wrist 42 such that the
array of pressure-sensing elements cross over, or intersect, a radial
artery 56 of the patient. Thus, each of the pressure-sensing elements
of the pulse wave sensor 46 detects a pulse wave produced from the
radial artery 56 in synchronism with heartbeat of the patient and
transmitted to the body surface 38 or pressure surface 54, and generates
a pulse-wave signal, SM.sub.2, representative of the detected pulse
wave. The pulse wave signals SM.sub.2 from the pressure-sensing
elements of the pulse wave sensor 46 are supplied to the control
device 28 via a third analog to digital (A/D) converter 58. In the
present embodiment, the radial artery 56 serves as an artery from
which the pulse wave is detected, and the pulse wave detector probe
34, second air pump 50 and pressure-regulator valve 52 cooperate
with each other to serve as pulse wave detecting means for detecting
the pulse wave produced from the radial artery 56.
The control device 28 operates according to the control programs
stored in the ROM, for supplying drive signals to the second air
pump 50 and the pressure-regulator valve 52 via respective drive
circuits (not shown), so as to regulate the air pressure in the
pressure chamber 48. While slowly increasing the pressure in the
chamber 48, the control device 28 collects the pulse wave signals
SM.sub.2 supplied from the individual pressure-sensing elements
of the pulse wave sensor 46. Based on the thus collected pulse wave
signals SM.sub.2, the control device 28 determines an optimum air
pressure (i.e., optimum pressing force) to be applied to the pulse
wave sensor 46, by identifying an air pressure value in the chamber
48 at the time when the radial artery 56 is partially flattened
under the pressing force of the pulse wave sensor 46. Since the
manner of determination of the optimum pressing force is well known
in the art, no more description is provided.
Based on the collected pulse wave signals SM.sub.2, the control
device 28 additionally selects an optimum pressure-sensing element
located directly above the center of the radial artery 56, by identifying
one of the pressure-sensing elements of the pulse wave sensor 46
which element provides a pulse wave signal SM.sub.2 having the greatest
amplitude of the amplitudes of all the pressure-sensing elements.
Thus, the control device 28 controls the pressure regulator valve
52 so as to maintain the pressure chamber 48 at the determined optimum
air pressure, and collects the pulse wave signal SM.sub.2 from the
optimum pressure-sensing element with the chamber 48 being maintained
at the optimum air pressure. The control device 28 commands the
display 32 to display a waveform of the pulse wave signal SM.sub.2
from the optimum element. It is considered that, since the optimum
element is located directly above the center of an artery 56, the
pulse wave signal SM.sub.2 from the optimum element is free of the
influence due to the elastic, tensile force produced in the wall
of the artery 56 and therefore accurately represents blood pressure
variation inside the artery 56. That is, the waveform of the pulse
wave signal SM.sub.2 from the optimum pressure-sensing element accurately
indicates variation in the blood pressure of the patient.
In addition, each time actual systolic and diastolic blood pressures
are measured using the cuff 10, the control device 28 operates according
to the control programs stored in the ROM, for determining a relationship
between blood pressure and pulse wave magnitude ("BP-PW relationship),
based on the measured systolic and diastolic blood pressure values
and a maximum and a minimum magnitude (i.e., upper and lower peak
magnitudes) of one pulse of the pulse wave signal SM.sub.2 from
the pulse wave sensor 46 (specifically, optimum pressure-sensing
element). According to the thus determined BP-PW relationship, the
control device 28 successively determines a systolic and a diastolic
blood pressure of the patient, based on a maximum and a minimum
magnitude of each of respective pulses of the pulse wave signal
SM.sub.2 after the BP-WP relationship has been determined, and commands
the display 32 to indicate the determined blood pressure values
one after another.
Furthermore, the control device 28 evaluates variation of the blood
pressure of the patient, based on the maximum magnitudes and amplitudes
of respective pulses of the pulse wave signal SM.sub.2 after the
BP-PW relationship has been determined. In the case where the maximum
magnitudes and amplitudes of the pulse wave signal SM.sub.2 satisfy
predetermined conditions, the control device 28 evaluates the blood
pressure variation as being large, and immediately effects a blood
pressure measurement using the cuff 10 and updates the BP-PW relationship.
On the other hand, in the case where the maximum magnitudes and
amplitudes of the pulse wave signal SM.sub.2 do not satisfy the
predetermined conditions, the control device 28 deems the blood
pressure variation as being small, and therefore permits the cuff-using
blood pressure measurement and the BP-PW relationship updating to
occur at the predetermined, considerably long interval. In the present
embodiment, the control device 28 serves as (a) relationship determining
means for determining a BP-PW relationship, and updates the relationship
at intervals of time; (b) blood pressure monitoring means for continuously
determining, according to the relationship, blood pressure values
of the subject based on magnitudes of the pulse wave detected by
the pulse wave detecting means; (d) blood pressure variation evaluating
or determining means for determining a variation of the blood pressure
of the subject; and (e) update-interval changing means for changing
the interval of updating based on the blood pressure variation determined
by the blood pressure variation evaluating or determining means.
Hereinafter, there will be described the operation of the present
blood pressure monitoring system by reference to the flow charts
f FIGS. 2 to 4.
Upon application of electric power to the present monitor system,
the CPU of the control device 28 initializes the present system
by, for example, clearing the contents of a flag, F, (described
later). Subsequently, the CPU operates for effecting, in a parallel
fashion, both the cuff-using blood pressure measuring routine of
FIG. 2 and the blood pressure monitoring routine of FIG. 3.
The following explanation begins with the cuff-using blood pressure
measuring routine of FIG. 2. In Step SA1 of this routine, the CPU
judges whether or not a START switch (not shown) has been turned
ON. If the judgement in Step SA1 is negative (NO), the control of
the CPU waits for the START switch to be operated. If the judgement
in Step SA1 is affirmative (YES), the control proceeds with Step
SA2 in which the CPU judges whether or not a predetermined interval
of time (e.g., twenty minutes) has elapsed. When a clock, register
counts down to zero, the judgement in Step SA2 becomes affirmative.
The present system is adapted such that the contents of the clock
register is zero for the first or initial measurement cycle immediately
after the START switch has been operated. In the first cycle, therefore,
the judgement in SA2 is affirmative, and the control of the CPU
goes to Step SA4. In Step SA4, the CPU places the selector valve
16 in the INFLATION position and actuates the first air pump 18,
so as to increase the air pressure P in the cuff 10 up to a predetermined
target value, Pm, (e.g., 180 mmHg) sufficiently higher than an estimated
systolic (maximum) blood pressure of the patient. and then maintains
the cuff pressure P at the target pressure Pm. Step SA4 is followed
by Step SA5 to place the selector valve 16 in the SLOW-DEFLATION
position, thereby causing the cuff pressure P to slowly be decreased.
Step SA5 is followed by Step SA6 to judge whether or not one pulse
of the pulse wave signal SM.sub.1 corresponding to one heartbeat
of the patient has been supplied from the pulse-wave filter circuit
24. If the judgement in Step SA6 is negative, the CPU repeats Step
SA6 until an affirmative judgement is made. If the judgement in
Step SA6 becomes affirmative, the control of the CPU goes to Step
SA7, i.e., blood pressure determination routine. In this step or
routine, a systolic and a diastolic blood pressure are determined
based on variation of the amplitudes of individual pulses of the
pulse wave signal SM.sub.1 obtained during the slow decreasing of
the cuff pressure P. This is the well-known "oscillometric"
blood pressure measuring method. In this step, a known algorithm
is used for carrying out this method. Subsequently, the control
of the CPU goes to Step SA8 to judge whether or not the blood pressure
determination in Step SA7 has been completed. If the judgement in
Step SA8 is negative, Steps SA6 and SA7 are repeated.
If the judgement in Step SA8 becomes affirmative after the blood
pressure determination in Step SA7 has terminated, the control of
the CPU goes to Step SA9 to reset the flag F to zero (F=0). Step
SA9 is followed by Step SA10 to place the selector valve 16 in the
QUICK-DEFLATION position, thereby deflating the cuff 10 and causing
the cuff pressure P to quickly be decreased. Step SA10 is followed
by Step SA11 in which the blood pressure values determined in Step
SA7 are indicated on the display 32. Then, the control of the CPU
goes back to Step SA1.
In the next or second measurement cycle, a negative judgement is
made in Step SA2. Therefore, the control of the CPU proceeds with
Step SA3 to judge whether or not the flag F is in the state of F=1.
The flag F may be set to F=1 as a result of execution of the blood
pressure monitoring routine of FIG. 3 (described later). The flag
F is indicative of whether variation of the blood pressure of the
patient is large or small; the state F=1 of the flag F indicates
that the blood pressure variation is large. If the judgement in
Step SA3 is negative, Steps SA2 and SA3 are repeated until an affirmative
judgement is made in Step SA3. If the judgement in Step SA3 is affirmative,
that is, if the blood pressure variation is large, the control of
the CPU goes to Step SA4 and the following steps are performed to
effect an actual or standard blood pressure measurement using the
cuff 10, without any longer waiting for elapsing of the predetermined
interval in Step SA2. Thus, the predetermined interval of standard
blood pressure measurement is shortened when the blood pressure
variation of the patient is identified as being large.
Meanwhile, in the blood pressure monitoring routine of FIG. 3,
first, in Step SB1, it is judged whether or not the aforementioned
START switch has been turned ON. If the judgement in Step SB1 is
negative, the control of the CPU repeats this step. If the judgement
in this step becomes affirmative, the control goes to Step SB2.
In this step, as described previously, the CPU determines the optimum
air pressure (optimum pressing force) to be applied to the pulse
wave sensor 46, based on the pulse wave signals SM2 supplied from
the pressure-sensing elements of the pulse wave sensor 46 during
the slow decreasing of the air pressure in the pressure chamber
48, and maintains the pressure in the chamber 48 at the determined
optimum pressure. In addition, the CPU selects, from the pressure-sensing
elements of the pulse wave sensor 46, the optimum pressure-sensing
element which supplies a pulse wave signal SM2 having the greatest
amplitude.
Step SB2 is followed by Step SB3 to determine a BP-PW relationship,
based on the systolic and diastolic blood pressure values measured
using the cuff 10, and a maximum and a minimum magnitude of a pulse
of the pulse wave signal SM.sub.2 from the optimum pressure-sensing
element. In each of the second and following cycles, a new BP-PW
relationship is determined to replace the old one determined in
the preceding cycle in this step. The manner of determination of
the BP-PW relationship, is described in detail in U.S. Pat. No.
5,139,026 assigned to the Assignee of the present application, the
disclosure of which is incorporated herein by reference.
Step SB3 is followed by Step SB4 to judge whether or not a pulse
of the pulse wave signal SM.sub.2 corresponding to a heartbeat of
the patient has been supplied from the optimum pressure-sensing
element after the BP-PW relationship has been determined or updated
in Step SB3. If the judgement in Step SB4 is negative, the CPU repeats
this step. If an affirmative judgement is made in Step SB4, the
control of the CPU proceeds with Step SB5 to determine the maximum
and minimum magnitude of the pulse obtained in Step SB3, and store
sets of data indicative of the determined pulse magnitudes in the
RAM. In addition, a set of data indicative of the determined maximum
magnitude is stored in a first ring buffer consisting of 150 storage
areas each of which is capable of storing a set of pulse magnitude
data. The first ring buffer is provided in the RAM of the control
device 28.
Subsequently, the control of the CPU goes to Step SB6 to determine
or estimate, according to the BP-PW relationship determined or updated
in Step SB3, a systolic and a diastolic blood pressure of the patient,
based on the maximum and minimum magnitudes of the pulse obtained
in Step SB4. Step SB6 is followed by Step SB7 to indicate the determined
blood pressure values and the waveform of the obtained pulse wave,
on the display 32.
Step SB7 is followed by Step SB8 to judge whether or not a blood
pressure measurement using the cuff 10 is being progressed in the
routine of FIG. 2. If the judgement in Step SB8 is negative, the
control of the CPU goes to Step SB9, i.e., blood pressure variation
determination routine of FIG. 4, in which variation of the blood
pressure of the patient is evaluated or determined based on the
pulse wave signal SM.sub.2 from the optimum pressure-sensing element
of the pulse wave sensor 46. Step SB9 is followed by Step SB11.
On the other hand, if an affirmative judgement is made in Step SB8,
the control goes to Step SB10 to clear the contents of both the
aforementioned first ring buffer and a second ring buffer (described
later). Step SB10 is followed by Step SB11.
In Step SB11, it is judged whether or not the START switch has
been turned OFF. If the judgement in Step SB11 is affirmative, the
control of the CPU goes back to Step SB1, and waits for another
operation of the START switch. On the other hand, if the judgement
in Step SB11 is negative, the control goes to Step SB12 to judge
whether or not another blood pressure measurement using the cuff
10 has been effected and completed according to the algorithm of
FIG. 2. So long as the judgement in Step SB12 continues to be negative,
Steps SB4 to SB12 are repeated so that, each time a pulse of the
pulse wave signal SM.sub.2 is supplied in Step SB4, a systolic and
a diastolic blood pressure are determined based on a maximum and
a minimum magnitude of the pulse by using the BP-PW relationship,
and the determined blood pressure values are displayed together
with the waveform of the pulse wave. Concurrently, the variation
of the blood pressure of the patient is evaluated in Step SB9.
On the other hand, if the judgement in Step SB12 is affirmative,
the control goes back to Step SB3 to update the BP-PW relationship
by replacing the old one with a new one determined based on the
systolic and diastolic blood pressures measured using the cuff 10
and a maximum and a minimum magnitude of a pulse of the pulse wave
signal SM.sub.2 supplied just before, or after, the blood pressure
measurement using the cuff 10 is completed. Thus, the BP-PW relationship
is updated each time the cuff-using blood pressure measuring routine
of FIG. 2 is effected to measure actual or standard systolic and
diastolic blood pressure values. According to the periodically updated
BP-PW relationship, the blood pressure of the patient is monitored
by utilizing the pulse wave signal SM.sub.2 supplied from the pulse
wave sensor 46 (optimum pressure-sensing element).
In Step SB9, i.e., in the blood pressure variation determination
routine of FIG. 4, first, in Step SC1, an amplitude, A.sub.0, of
the pulse of the signal SM.sub.2 obtained in Step SB4 in the current
cycle is calculated by subtracting from the maximum magnitude, M.sub.max0,
of the pulse the minimum magnitude, M.sub.min0, of the pulse both
of which are determined in Step SB5. A set of data indicative of
the calculated amplitude A.sub.0 is stored in a second ring buffer
consisting of 150 storage areas each of which is capable of storing
a set of pulse amplitude data.
Step SC1 is followed by Step SC2 to judge whether or not the first
and second ring buffers hold a set of data indicative of a pulse
maximum magnitude, M.sub.max20, and a set of data indicative of
a pulse amplitude, A.sub.20, respectively, both of which relate
to a pulse supplied twenty seconds before the current pulse is supplied.
If the judgement in Step SC2 is affirmative, the control of the
CPU goes to Step SC3 to judge whether or not the absolute value
of the difference between the amplitudes A.sub.20 and A.sub.0 falls
within a quarter (25%) of the amplitude A.sub.20.
If the judgement in Step SC3 is negative, the control proceeds
with Step SC4 to judge whether or not the absolute value of the
difference between the maximum magnitudes M.sub.max20 and M.sub.max0
falls within 8 mmHg in terms of pressure (i.e., blood pressure).
If the judgement in Step SC4 is negative, the control goes to Step
SC5 to judge whether or not the absolute value of the difference
between the amplitude A.sub.10 of the pulse obtained ten seconds
before and the amplitude A.sub.0 of the current pulse falls within
a quarter (25%) of the amplitude A.sub.10. If the judgement in Step
SC5 is negative, the control goes to Step SC6 to judge whether or
not the absolute value of the difference between the maximum magnitude
M.sub.max10 of the pulse obtained ten seconds before and the maximum
magnitude M.sub.max0 of the current pulse falls within 6 mmHg.
If the judgement in Step SC6 is negative, the control goes to Step
SC7 to judge whether or not the absolute value of the difference
between the amplitude A.sub.3 of the pulse obtained three seconds
before and the amplitude A.sub.0 of the current pulse falls within
a half (50%) of the amplitude A.sub.3. If the judgement in Step
SC7 is negative, the control goes to Step SC8 to judge whether or
not the absolute value of the difference between the maximum magnitude
M.sub.max3 of the pulse obtained three seconds before and the maximum
magnitude M.sub.max0 of the current pulse falls within 4 mmHg.
If the judgement in Step SC8 is negative, that is, if the judgement
in Step SC2 is affirmative and, at the same time, if all the judgements
in Steps SC3 to SC8 are negative, the control of the CPU goes to
Step SC9 to set the flag F to F=1 indicating that the variation
of the blood pressure of the patient is excessively large. Thus,
the control exits this routine and goes to Step SB11 of FIG. 3.
On the other hand, if the judgement in Step SC2 is negative, or
if any of the judgements in Steps SC3 to SC8 is affirmative, the
control maintains the flag F at F=0 indicating that the blood pressure
variation of the patient is sufficiently small. Similarly, the control
exits this routine and goes to Step SB11.
In the case where the flag F is set to F=1 as a result of execution
of the routine of FIG. 4, the judgement in Step SA3 of FIG. 2 turns
affirmative, so that a blood pressure measurement using the cuff
10 is immediately initiated without any longer waiting for elapsing
of the predetermined interval of time. Based on the thus measured
actual or standard blood pressure values, the BP-PW relationship
is updated in Step SB3. On the other hand, so long as the flag F
continues to be at the state of F=0, the cuff-using blood pressure
measurement and the BP-PW relationship updating are carried out
at the predetermined interval.
In the present embodiment, the monitor system evaluates variation
of the blood pressure of a living subject, based on the maximum
magnitudes and amplitudes of respective pulses of the pulse wave
signal SM.sub.2 supplied from the pulse wave sensor 46 (or optimum
pressure-sensing element), while the control device 28 monitors
the blood pressure of the subject by using the currently effective
BP-PW relationship. If the evaluation of the blood pressure variation
shows that the variation is excessively large, the monitor system
immediately carries out a blood pressure measurement using the cuff
10 and updates the BP-PW relationship based on the measured blood
pressure, so that the monitor system continues to monitor the blood
pressure of the subject by using the updated, accurate BP-PW relationship.
Thus, even in the case where the blood pressure variation of the
subject may be excessively large, the present monitoring system
can continue to provide accurate blood pressure reading by utilizing
the pulse wave signal SM.sub.2 supplied from the pulse wave sensor
46.
In addition, while the blood pressure variation is sufficiently
small or stable, the monitoring system carries out the cuff-using
blood pressure measurement and the BP-PW relationship updating,
at the predetermined, considerably long intervals. Thus, the present
monitoring system advantageously reduces the patient's discomfort
by lowering the frequency of pressing of patient's upper arm 12
with the inflatable cuff 10.
Hereinafter, there will be described other embodiments in accordance
with the present invention.
FIG. 5 shows another blood pressure variation determination routine
which may be used in Step SB9 of FIG. 3 in place of the routine
of FIG. 4. For effecting the routine of FIG. 5, pulses of the pulse
wave signal SM.sub.2 are, in advance, collected and stored for ten
seconds after the BP-PW relationship has been determined or updated,
and the greatest maximum magnitude, MAX, and the smallest minimum
magnitude, MIN, are selected from the collected pulses. In addition,
are calculated an average, MID, of the magnitudes MAX and MIN, and
an average, AV, of all the maximum and minimum magnitudes of the
collected pulses except the magnitudes MAX, MIN. Then, the absolute
value of the difference between the averages MID and AV is obtained
as a deviation, D. The deviation D is indicative of a physiological
blood pressure variation due to respiration of the patient.
Specifically, in Step SD1, it is judged whether or not every ten
seconds (ten, twenty, thirty, seconds) have elapsed after the deviation
D is determined. If the judgement in Step SD1 is negative, the control
of the CPU exits this routine and goes to Step SB 11 of FIG. 3.
Meanwhile, if an affirmative judgement is made in Step SD1, the
control goes to Step SD2 to calculate, like the average AV, an average,
AV', of all the maximum and minimum magnitudes of the pulses obtained
in the ten seconds except the greatest pulse maximum magnitude and
the smallest pulse minimum magnitude. Step SD2 is followed by Step
SD3 to calculate the absolute value, .DELTA.AV, of the difference
between the time-wise adjacent two averages, that is, the average
AV' of the current ten-second period and the average AV' of the
preceding ten-second period (only for the first or initial cycle,
the latter is the average AV). Subsequently, the control goes to
Step SD4 to judge whether or not the difference .DELTA.AV is greater
than the deviation D. If the judgement in Step SD4 is affirmative,
the CPU sets the flag F to F= 1 in Step SD5. If otherwise, the CPU
sets the flag F to F=0 in Step SD6. Step SD6 may be omitted. In
this case, the difference .DELTA.AV is used as a variation of the
blood pressure of the patient.
FIG. 6 shows another cuff-using blood pressure measuring routine
which may be used in place of the routine of FIG. 2. In the routine
of FIG. 6, the cuff-using blood pressure measurement interval, i.e.,
BP-PW relationship updating interval is changed based on the blood
pressure variation and other physiological indicators of the patient,
each time a cuff-using blood pressure measurement is completed.
The routine of FIG. 6 is different from the routine of FIG. 2 only
with respect to Steps SE2 and SE10 to SE12, which will be described
below.
In Step SE2, the CPU waits for elapsed of a time duration, .alpha..
In Step SE10, it is judged whether or not the START switch has been
turned OFF. If the judgement in Step SE10 is affirmative, the control
goes back to Step SE1 and waits. Meanwhile, if otherwise, the control
goes to Step SE11, i.e., cuff-using BP (blood pressure) measurement
interval determination routine of FIG. 7. In the routine of FIG.
7, first, in Step SF1, the CPU determines the absolute value, WID,
of the difference between the greatest and smallest ones of the
maximum magnitudes of the respective pulses of the signal SM.sub.2
obtained during ten seconds after the BP-PW relationship is determined
or updated in Step SB3 of FIG. 3. In addition, a pulse rate, R,
(number of pulses per minute) of the patient is calculated based
on the number of the pulses actually obtained during the ten seconds.
Step SF1 is followed by Step SF2 in which the CPU selects, from
TABLE I, weighted values, a, b and c, which respectively correspond
to the systolic blood pressure, SYS, obtained in Step SE6 in the
current cycle, the aforementioned difference WID, and the pulse
rate R. Step SF2 is followed by Step SF3 to calculate a time duration
.alpha. by the following formula: .alpha.=180/(a+b+c). Thus, the
CPU exits this routine and goes to Step SE12 of FIG. 6. In Step
SE12, the CPU replaces the old time duration by the new one .alpha.
determined in Step SF 3 of FIG. 7. Then, the control of the CPU
goes back to Step SE2.
TABLE I ______________________________________ PHYSIOLOGICAL WEIGHTED
INDICATORS RANKS VALUES ______________________________________ DIFFERENCE
WID WID .gtoreq. 20 60 (mmHg) 20 > WID .gtoreq. 15 40 15 >
WID .gtoreq. 10 27 10 > WID .gtoreq. 5 10 5 > WID 1 BLOOD
PRESSURE SYS .gtoreq. 160 60 SYS (mmHg) 160 > SYS .gtoreq. 140
38 140 > SYS .gtoreq. 100 1 100 > SYS 60 PULSE RATE R R .gtoreq.
110 60 110 > R .gtoreq. 70 1 70 > R 60 ______________________________________
The weighted values shown in Table I are determined so that the
time duration .alpha. is shortened in concordance with the increased
blood pressure variation (represented by the difference WID), and
lengthened in concordance with the decreased blood pressure variation.
In the present embodiment, Step SF1 of FIG. 7 and a portion of the
control device 28 for effecting this step serve as blood pressure
variation determining means, and Steps SF2 and SF3 and a portion
of the control device 28 for effecting these steps serve as update-interval
changing means for changing the time duration or update interval
.alpha.. In this embodiment, Steps SB8 to SB10 are omitted from
the routine of FIG. 3.
While the present invention has been described in its preferred
embodiments, it is to be understood that the invention may otherwise
be embodied.
For example, the blood pressure monitor system of FIG. 1 may be
adapted to produce an alarm, or light a lamp, indicating that the
variation of blood pressure of a subject is excessively large, when
the system detects it.
While in the embodiment of FIGS. 1 to 4 the monitoring system evaluates
the variation of blood pressure of a subject based on the maximum
magnitudes and amplitudes of the pulse wave signal SM.sub.2, the
blood pressure variation may be evaluated based on the combination
of the maximum and minimum magnitudes of the signal SM.sub.2, as
shown in the embodiment of FIG. 5, or the maximum magnitudes of
the signal SM.sub.2 as shown in the embodiment of FIG. 7. Otherwise,
it is possible to evaluate the blood pressure variation by utilizing
the maximum magnitude, minimum magnitude, average magnitude, or
amplitude of the pulses of the signal SM.sub.2, either in any appropriate
combination thereof, or alone.
Although in the illustrated embodiments it is assumed that the
cuff 10 and the pulse wave sensor 46 are worn on the different superior
limbs of a subject, it is possible to set the two elements 10, 46
on the same and one superior limb. In this particular case, Step
SB8 is effected . after Step SB3 and before Step SB4 in the blood
pressure monitoring routine of FIG. 3.
While in the illustrated embodiments the cuff 10 is set on the
upper arm 12 of the patient and the pulse wave detector probe 34
is set on the wrist 42 of the patient, it is possible that the cuff
10 be set on a thigh of the patient and the probe 34 be set on an
ankle of the patient.
Although in the illustrated embodiments the pulse wave signal SM.sub.2
from the pulse wave sensor 34 is used for monitoring the blood pressure
of the patient, it is possible to use for the same purpose the pulse
wave signal SM.sub.1 supplied from the pulse wave filter circuit
24, by pressing the upper arm 12 with the cuff 12 at a considerably
small pressure during each intermediate duration between time-wise
adjacent blood pressure measurements using the cuff 10. In this
case, the pulse wave detector probe 34 and its associated elements
50, 52, 58 are omitted.
While in the illustrated embodiments the cuff-using blood pressure
measurement is effected by the "oscillometric" method
using the pressure sensor 14, it is possible to carry out that measurement
by the well-known "Korotkoff-sound" method in which a
microphone is used for detecting appearance and disappearance of
Korotkoff sounds from an artery when the cuff pressure P is decreased
or increased.
It is to be understood that the present invention may be embodied
with other changes, improvements and modifications that may occur
to those skilled in the art without departing from the scope and
spirit of the invention defined in the appended claims. |