Abstrict
A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, including a blood-pressure measuring device
which includes an inflatable cuff adapted to be wound around a body
portion of a living subject and measures a blood pressure of the
subject by changing a pressing pressure of the cuff to not lower
than a systolic blood pressure of the subject, a cuff-pressure control
device which iteratively changes, after a predetermined rest period
following the blood pressure measurement of the blood-pressure measuring
device, the pressure of the cuff to a predetermined value lower
than the systolic blood pressure of the subject, and a blood-pressure-change
identifying device for identifying a change of the blood pressure
of the subject based on (a) respective amplitudes of first heartbeat-synchronous
pulses obtained from the cuff during the blood pressure measurement
of the blood-pressure measuring device, (b) respective pressures
of the cuff when the first pulses are obtained, (c) respective amplitudes
of second heartbeat-synchronous pulses obtained from the cuff during
each of the iterative changings of the cuff pressure by the cuff-pressure
control device, and (d) respective pressures of the cuff when the
second pulses are obtained.
Claims
What is claimed is:
1. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising:
an inflatable cuff adapted to be wound around a body portion of
a living subject;
a blood-pressure measuring device in fluid communication with said
cuff which changes a pressing pressure of said cuff in a first pressure
range whose upper limit is not lower than a systolic blood pressure
of the subject and obtains a first plurality of heartbeat-synchronous
pulses from the cuff while the pressure of the cuff is changed in
said first pressure range;
a cuff-pressure control device in fluid communication with said
cuff which iteratively changes, after a predetermined rest period
following the blood pressure measurement of said blood-pressure
measuring device, the pressure of said cuff in a second pressure
range whose upper limit is a predetermined value lower than the
systolic blood pressure of the subject and obtains a second plurality
of heartbeat-synchronous pulses from the cuff while the pressure
of the cuff is changed in said second pressure range; and
blood-pressure-change identifying means for identifying a change
of the blood pressure of the subject based on (a) respective amplitudes
of said first plurality of heartbeat-synchronous pulses obtained
from said cuff during said blood pressure measurement of said blood-pressure
measuring device, (b) respective pressures of said cuff when said
first plurality of pulses are obtained, (c) respective amplitudes
of said second plurality of heartbeat-synchronous pulses obtained
from said cuff during each of the iterative changes of the cuff
pressure by said cuff-pressure control device, and (d) respective
pressures of said cuff when said second plurality of pulses are
obtained.
2. A blood pressure monitor apparatus according to claim 1, further
comprising:
a first memory which stores the respective amplitudes of said first
pulses obtained from said cuff during said blood pressure measurement
of said blood-pressure measuring device, and the respective pressures
of said cuff when said first pulses are obtained; and
a second memory which stores the respective amplitudes of said
second pulses obtained from said cuff during said each of the iterative
changes, of the cuff pressure by said cuff-pressure control device,
and the respective pressures of said cuff when said second pulses
are obtained.
3. A blood pressure monitor apparatus according to claim 1, wherein
said blood-pressure-change identifying means comprises:
cuff-pressure comparing means for comparing a first pressure of
said cuff at which one of said first plurality of pulses which has
a greatest amplitude of the first plurality of pulses obtained when
the pressures of the cuff are not higher than said predetermined
value is obtained with a second pressure of said cuff at which one
of said second plurality of pulses which has a greatest amplitude
is obtained for providing a comparison result; and
means for identifying said change of the blood pressure of the
subject when said a comparison result indicates that said second
cuff pressure is lower than said first cuff pressure.
4. A blood pressure monitor apparatus according to claim 1, wherein
said blood-pressure-change identifying means comprises:
cuff-pressure comparing means for comparing a first pressure of
said cuff at which one of said first plurality of pulses which has
a greatest amplitude of the first plurality of pulses obtained when
the pressures of the cuff are not higher than said predetermined
value is obtained with a second pressure of said cuff at which one
of said second plurality of pulses which has a greatest amplitude
is obtained; and for providing a comparison result
judging means for judging, when said comparison result indicates
that said second cuff pressure is not lower than said first cuff
pressure, whether an amplitude of said second plurality of pulses
which corresponds to a reference cuff-pressure value has changed
from an amplitude of said first plurality pulses which corresponds
to said reference cuff-pressure value, by not smaller than a predetermined
proportion of said amplitude of said first plurality of pulses;
and
means for identifying said change of the blood pressure of the
subject when said judging means makes a positive judgment.
5. A blood pressure monitor apparatus according to claim 4, wherein
said amplitude of said second plurality of pulses is a value of
an envelope or a cumulative curve of the second plurality of pulses
and said amplitude of said first plurality of pulses is a value
of an envelope or a cumulative curve of the first plurality of pulses.
6. A blood pressure monitor apparatus according to claim 1, wherein
said blood-pressure-change identifying means comprises:
rate-of-change calculating means for calculating a first rate of
change of the respective amplitudes of the first plurality of pulses
obtained when the pressures of the cuff are not higher than the
predetermined value, with respect to the corresponding pressures
of said cuff, and a second rate of change of said respective amplitudes
of said second plurality of pulses with respect to said respective
pressures of said cuff when said second plurality of pulses are
obtained; and
means for identifying said change of the blood pressure of the
subject when a difference between said first and second rates of
change is greater than a second predetermined value.
7. A blood pressure monitor apparatus according to claim 1, further
comprising:
a first pulse-rate measuring device which measures a first pulse
rate of the subject during the blood pressure measurement of said
blood-pressure measuring device; and
a second pulse-rate measuring device which measures a second pulse
rate of the subject during each of the iterative changes of the
cuff pressure by said cuff-pressure control device,
said blood-pressure-change identifying means identifying said change
of the blood pressure of the subject when said second pulse rate
has changed from said first pulse rate by not smaller than a predetermined
amount.
8. A blood pressure monitor apparatus according to claim 1, wherein
said cuff-pressure control device comprises means for iteratively
changing, after said predetermined rest period, the pressure of
said cuff in said second pressure range whose upper limit is said
predetermined value not higher than a mean blood pressure of the
subject, and wherein s aid blood-pressure-change identifying means
comprises means for identifying said change of the blood pressure
of the subject based on a first relationship between said respective
amplitudes of said first plurality of pulses and said respective
pressures of said cuff when said first plurality of pulses are obtained
and a second relationship between said respective amplitudes of
said second plurality of pulses and said respective pressures of
said cuff when said second plurality of pulses are obtained.
9. A blood pressure monitor apparatus according to claim 8, wherein
said blood-pressure-change identifying means comprises:
pulse-amplitude-window determining means for determining, in a
coordinate system defined by a first axis indicative of the cuff
pressure and a second axis indicative of the pulse amplitude, a
pulse-amplitude window which is defined by a reference line representing
said first relationship and has a first width along said second
axis;
deviation identifying means for counting, from data points plotted
in said coordinate system which points represent, as said second
relationship, said respective amplitudes of said second plurality
of pulses and said respective pressures of said cuff when said second
plurality of pulses are obtained, a first number of the data points
which fall within said pulse-amplitude window, and identifying a
deviation of said second relationship from said first relationship
based on the counted first number; and
means for identifying said change of the blood pressure of the
subject when said deviation identifying means identifies said deviation
of said second relationship from said first relationship.
10. A blood pressure monitor apparatus according to claim 9, wherein
said blood-pressure-change identifying means further comprises cuff-pressure
window determining means for determining, in said coordinate system,
a cuff-pressure window which is defined by said reference line and
has a second width along said first axis, said deviation identifying
means counting, from said data points plotted in said coordinate
system, a second number of the data points which fall within said
cuff-pressure window, and identifying a deviation of said second
relationship from said first relationship based on both said counted
first number and the counted second number, said blood-pressure-change
identifying means comprising means for identifying said change of
the blood pressure of the subject when-said deviation identifying
means identifies said deviation of said second relationship from
said first relationship based on both said first and second counted
numbers.
11. A blood pressure monitor apparatus according to claim 9, wherein
said pulse-amplitude window determining means comprises:
approximate-line determining means for determining, as said reference
line, an approximate line approximating said first relationship
within a range of the pressures of said cuff which are not higher
than said mean blood pressure of the subject; and
means for determining said pulse-amplitude window which has said
approximate line as a center line thereof and respective halves
of said first width on both sides of said approximate line.
12. A blood pressure monitor apparatus according to claim 11, wherein
said approximate-line determining means comprises means for determining,
as said approximate line, one of (a) a least-square approximate
line and (b) a regression line, based on data points plotted in
said coordinate system which points represent, as said first relationship,
said respective amplitudes of said first plurality of pulses and
said respective pressures of said cuff when said first plurality
of pulses are obtained.
13. A blood pressure monitor apparatus according to claim 10, wherein
said cuff-pressure window determining means comprises:
approximate-line determining means for determining, as said reference
line, an approximate line approximating said first relationship
within a range of the pressures of said cuff which are not higher
than said mean blood pressure of the subject; and
means for determining said cuff-pressure window which has said
approximate line as a center line thereof and respective halves
of said second width on both sides of said approximate line.
14. A blood pressure monitor apparatus according to claim 13, wherein
said approximate-line determining means comprises means for determining,
as said approximate line, one of (a) a least-square approximate
line and (b) a regression line, based on data points plotted in
said coordinate system which points represent, as said first relationship,
said respective amplitudes of said first plurality of pulses and
said respective pressures of said cuff when said first plurality
pulses are obtained.
15. A blood pressure monitor apparatus according to claim 8, wherein
said blood-pressure-change identifying means comprises:
area calculating means for calculating an area bounded by a first
line representing said first relationship and a second line representing
said second relationship, within a predetermined range of the pressures
of said cuff;
deviation identifying means for identifying a deviation of said
second relationship from said first relationship based on the calculated
area; and
means for identifying said change of the blood pressure of the
subject when said deviation identifying means identifies said deviation
of said second relationship from said first relationship.
16. A blood pressure monitor apparatus according to claim 15, wherein
said area calculating means comprises means for calculating a first
area bounded by a first portion of said first line and a first portion
of said second line which is greater than said first portion of
said first line with respect to the pulse amplitude, and a second
area bounded by a second portion of said first line and a second
portion of said second line which is smaller than said second portion
of said first line with respect to the pulse amplitude, and wherein
said blood-pressure-change identifying means comprises means for
identifying a decrease of the blood pressure of the subject when
said first area is greater than said second area.
17. A blood pressure monitor apparatus according to claim 15, wherein
said area calculating means comprises means for calculating a first
area bounded by a first portion of said first line and a first portion
of said second line which is greater than said first portion of
said first line with respect to the pulse amplitude, and a second
area bounded by a second portion of said first line and a second
portion of said second line which is smaller than said second portion
of said first line with respect to the pulse amplitude, and wherein
said blood-pressure-change identifying means comprises means for
identifying an increase of the blood pressure of the subject when
said second area is greater than said first area.
18. A blood pressure monitor apparatus according to claim 1, further
comprising a pulse-wave detector which detects, as a pressure change
produced in said cuff, an amplitude of each of said first and second
plurality of pulses.
19. A blood pressure monitor apparatus according to claim 18, further
comprising a cuff-pressure detector which detects the pressing pressure
of said cuff when said each of said first and second plurality of
pulses is detected by said pulse-wave detector.
20. A blood pressure monitor apparatus according to claim 1, further
comprising an output device which informs a user of occurrence of
an abnormal blood-pressure change when said blood-pressure-change
identifying means identifies said change of the blood pressure of
the subject.
21. A blood pressure monitor apparatus according to claim 1, further
comprising a blood-pressure re-measuring device which substantially
immediately measures a new blood pressure of the subject when said
blood-pressure-change identifying means identifies said change of
the blood pressure of the subject.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a blood-pressure monitor apparatus
which monitors the blood pressure of a living subject.
2. Related Art Statement
The blood pressure of a living subject such as a patient may continuously
be monitored by using an automatic blood-pressure (BP) measuring
device including an inflatable cuff adapted to be wound around a
body portion (e.g., upper arm) of the subject. In this case, the
BP measuring device periodically carries out BP measuring operations
at a regular interval of time. However, if this interval is shortened
to improve the reliability of the BP monitoring, then the frequency
of pressing of the cuff against the subject's body portion increases,
thereby causing the subject to feel even serious discomfort.
In contrast, a different BP monitoring method is disclosed in Japanese
Patent Applications laid open for inspection under Publication Nos.
61-103432 and 60-241422. In this method, an inflatable cuff is wound
around a body portion of a living subject and is inflated to apply
an appropriate pressing pressure to the body portion, and a pulse-wave
sensor continuously detects heartbeat-synchronous pulses produced
as pressure oscillations in the cuff. The disclosed BP monitor device
continuously estimates the BP values of the subject based on the
respective amplitudes of the continuous pulses.
However, in the above-described BP monitor device, the pressing
pressure of the cuff cannot be decreased to sufficiently low levels
to be able to reduce the physical and/or psychological load to the
subject, because the changing of the pulse amplitudes at such low
levels does not accurately correspond to the changing of the subject's
blood pressure. A curve indicated at solid line in FIG. 35 represents
the envelope of the pulse amplitudes which are obtained from the
cuff as the cuff pressure Pc is changed. If the blood pressure of
the subject decreases from a normal level represented by the solid-line
curve, the solid-line curve is changed into a curve indicated at
one-dot chain line in the same graph. In the case where the pulse
amplitudes are detected at a low cuff pressure, P.sub.K, the amount
of changing of the pulse amplitudes is significantly smaller than
that of the subject's blood pressure, thereby lowering the accuracy
of monitoring of the prior BP monitor device.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
blood-pressure monitor apparatus which monitors the blood pressure
of a living subject with high accuracy and without causing the subject
to feel discomfort.
The above object has been achieved by the present invention, which
provides a blood pressure monitor apparatus for monitoring a blood
pressure of a living subject, comprising a blood-pressure measuring
device which includes an inflatable cuff adapted to be wound around
a body portion of a living subject and measures a blood pressure
of the subject by changing a pressing pressure of the cuff to not
lower than a systolic blood pressure of the subject, a cuff-pressure
control device which iteratively changes, after a predetermined
rest period following the blood pressure measurement of the blood-pressure
measuring device, the pressure of the cuff to a predetermined value
lower than the systolic blood pressure of the subject, and blood-pressure-change
identifying means for identifying a change of the blood pressure
of the subject based on (a) respective amplitudes of first heartbeat-synchronous
pulses obtained from the cuff during the blood pressure measurement
of the blood-pressure measuring device, (b) respective pressures
of the cuff when the first pulses are obtained, (c) respective amplitudes
of second heartbeat-synchronous pulses obtained from the cuff during
each of the iterative changings of the cuff pressure by the cuff-pressure
control device, and (d) respective pressures of the cuff when the
second pulses are obtained.
The blood-pressure monitor apparatus constructed as described above
monitors the blood pressure of the subject with high accuracy, because
the apparatus utilizes both the pulse amplitudes and corresponding
cuff pressures obtained in the BP measurement of the BP measuring
device and the pulse amplitudes and corresponding cuff pressures
obtained during each cuff-pressure changing of the cuff-pressure
control device. In addition, since the present monitor apparatus
monitors the subject's blood pressure by iteratively changing the
cuff pressure within a low pressure range between the atmospheric
pressure and the predetermined pressure value lower than the subject's
systolic blood pressure, the monitor apparatus does not cause the
subject to feel serious discomfort.
In a preferred embodiment of the .present invention, the blood
pressure monitor apparatus further comprises a first memory which
stores the respective amplitudes of the first pulses obtained from
the cuff during the blood pressure measurement of the blood-pressure
measuring device, and the respective pressures of the cuff when
the first pulses are obtained, and a second memory which stores
the respective amplitudes of the second pulses obtained from the
cuff during the each of the iterative changings of the cuff pressure
by the cuff-pressure control device, and the respective pressures
of the cuff when the second pulses are obtained.
In another embodiment of the present invention, the blood-pressure-change
identifying means comprises cuff-pressure comparing means for comparing
a first pressure of the cuff at which one of the first pulses which
has a greatest amplitude of the first pulses obtained when the pressures
of the cuff are not higher than the predetermined value is obtained,
with a second pressure of the cuff at which one of the second pulses
which has a greatest amplitude is obtained, and means for identifying
the change of the blood pressure of the subject, when the cuff-pressure
comparing means provides a first comparison result that the second
cuff pressure is lower than the first cuff pressure.
In another embodiment of the present invention, the blood-pressure-change
identifying means comprises cuff-pressure comparing means for comparing
a first pressure of the cuff at which one of the first pulses which
has a greatest amplitude of the first pulses obtained when the pressures
of the cuff are not higher than the predetermined value is obtained,
with a second pressure of the cuff at which one of the second pulses
which has a greatest amplitude is obtained, judging means for judging,
when the cuff-pressure comparing means provides a second comparison
result that the second cuff pressure is not lower than the first
cuff pressure, whether an amplitude of the second pulses which corresponds
to a reference cuff-pressure value has changed from an amplitude
of the first pulses which corresponds to the reference cuff-pressure
value, by not smaller than a predetermined proportion of the amplitude
of the first pulses, and means for identifying the change of the
blood pressure of the subject when the judging means makes a positive
judgment. In this embodiment, the judging means may comprise means
for judging whether the amplitude of the second pulses obtained
as a value of an envelope or a cumulative curve of the second pulses
which value corresponds to the reference cuff-pressure value has
changed from the amplitude of the first pulses obtained as a value
of an envelope or a cumulative curve of the first pulses which value
corresponds to the reference cuff-pressure value.
In another embodiment of the present invention, the blood-pressure-change
identifying means comprises rate-of-change calculating means for
calculating a first rate of change of the respective amplitudes
of the first pulses obtained when the pressures of the cuff are
not higher than the predetermined value, with respect to the corresponding
pressures of the cuff, and a second rate of change of the respective
amplitudes of the second pulses with respect to the respective pressures
of the cuff when the second pulses are obtained, and means for identifying
the change of the blood pressure of the subject when a difference
between the first and second rates of change is greater than a predetermined
value.
In another embodiment of the present invention, the blood pressure
monitor apparatus further comprises a first pulse-rate measuring
device which measures a first pulse rate of the subject during the
blood pressure measurement of the blood-pressure measuring device,
and a second pulse-rate measuring device which measures a second
pulse rate of the subject during the each of the iterative changings
of the cuff pressure by the cuff-pressure control device, the blood-pressure-change
identifying means identifying the change of the blood pressure of
the subject when the second pulse rate has changed from the first
pulse rate by not smaller than a predetermined amount.
In another embodiment of the present invention, the cuff-pressure
control device comprises means for iteratively changing, after the
predetermined rest period, the pressure of the cuff to the predetermined
value not higher than a mean blood pressure of the subject, and
the blood-pressure-change identifying means comprises means for
identifying the change of the blood pressure of the subject based
on a first relationship between the respective amplitudes of the
first pulses and the respective pressures of the cuff when the first
pulses are obtained and a second relationship between the respective
amplitudes of the second pulses and the respective pressures of
the cuff when the second pulses are obtained. The present monitor
apparatus monitors the blood pressure of the subject with .higher
accuracy, because the apparatus identifies a change of the subject's
blood pressure based on both the first relationship between the
pulse amplitudes and corresponding cuff pressures obtained in the
BP measurement of the BP measuring device and the second relationship
between the pulse amplitudes and corresponding cuff pressures obtained
during each cuff-pressure changing of the cuff-pressure control
device. In addition, since the monitor apparatus monitors the subject's
blood pressure by iteratively changing the cuff pressure within
a low pressure range between the atmospheric pressure and the predetermined
pressure value lower than the subject's mean blood pressure, the
apparatus more effectively prevents the subject from feeling discomfort.
In another embodiment of the present invention, the blood-pressure-change
identifying means comprises pulse-amplitude-window determining means
for determining, in a coordinate system defined by a first axis
indicative of the cuff pressure and a second axis indicative of
the pulse amplitude, a pulse-amplitude window which is defined by
a reference line representing the first relationship and has a first
width along the second axis, deviation identifying means for counting,
from data points plotted in the coordinate system which points represent,
as the second relationship, the respective amplitudes of the second
pulses and the respective pressures of the cuff when the second
pulses are obtained, a first number of the data points which fall
within the pulse-amplitude window, and identifying a deviation of
the second relationship from the first relationship based on the
counted first number, and means for identifying the change of the
blood pressure of the subject when the deviation identifying means
identifies the deviation of the second relationship from the first
relationship. In this embodiment, a change of the subject's blood
pressure is identified based on a deviation of the pulse amplitudes
of the second relationship from those of the first relationship.
According to a preferred feature of the present invention, the
blood-pressure-change identifying means further comprises cuff-pressure
window determining means for determining, in the coordinate system,
a cuff-pressure window which is defined by the reference line and
has a second width along the first axis, the deviation identifying
means counting, from the data points plotted in the coordinate system,
a second number of the data points which fall within the cuff-pressure
window, and identifying a deviation of the second relationship from
the first relationship based on both the counted first number and
the counted second number, the blood-pressure-change identifying
means comprising means for identifying the change of the blood pressure
of the subject when the deviation identifying means identifies the
deviation of the second relationship from the first relationship
based on both the first and second counted numbers. In this case,
a change of the subject's blood pressure is identified based on
both a deviation of the pulse amplitudes of the second relationship
from those of the first relationship and a deviation of the pressures
of the second relationship from those of the first relationship.
According to another feature of the present invention, the the
pulse-amplitude window determining means comprises approximate-line
determining means for determining, as the reference line, an approximate
line approximating the first relationship within a range of the
pressures of the cuff which are not higher than the mean blood pressure
of the subject, and means for determining the pulse-amplitude window
which has the approximate line as a center line thereof and respective
halves of the first width on both sides of the approximate line.
In this case, the approximate-line determining means may comprise
means for determining, as the approximate line, at least one of
(a) a least-square approximate line and (b) a regression line, based
on data points plotted in the coordinate system which points represent,
as the first relationship, the respective amplitudes of the first
pulses and the respective pressures of the cuff when the first pulses
are obtained.
According to another feature of the present invention, the cuff-pressure
window determining means comprises approximate-line determining
means for determining, as the reference line, an approximate line
approximating the first relationship within a range of the pressures
of the cuff which are not higher than the mean blood pressure of
the subject, and means for determining the cuff-pressure window
which has the approximate line as a center line thereof and respective
halves of the second width on both sides of the approximate line.
In this case, the approximate-line determining means comprises means
for determining, as the approximate line, at least one of (a) a
least-square approximate line and (b) a regression line, based on
data points plotted in the coordinate system which points represent,
as the first relationship, the respective amplitudes of the first
pulses and the respective pressures of the cuff when the first pulses
are obtained.
In another embodiment of the present invention, the blood-pressure-change
identifying means comprises area calculating means for calculating
an area bounded by a first line representing the first relationship
and a second line representing the second relationship, within a
predetermined range of the pressures of the cuff, deviation identifying
means for identifying a deviation of the second relationship from
the first relationship based on the calculated area, and means for
identifying the change of the blood pressure of the subject when
the deviation identifying means identifies the deviation of the
second relationship from the first relationship. In this embodiment,
a change of the subject's blood pressure is identified based on
a deviation of the pulse amplitudes of the second relationship from
those of the first relationship.
According to a preferred feature of the present invention, the
area calculating means comprises means for calculating a first area
bounded by a first portion of the first line and a first portion
of the second line which is greater than the first portion of the
first line with respect to the pulse amplitude, and a second area
bounded by a second portion of the first line and a second portion
of the second line which is smaller than the second portion of the
first line with respect to the pulse amplitude, and wherein the
blood-pressure-change identifying means comprises means for identifying
a decrease of the blood pressure of the subject when the first area
is greater than the second area. In this embodiment, a change of
the subject's blood pressure, more particularly, a decrease of the
same is identified.
According to another feature of the present invention, the area
calculating means comprises means for calculating a first area bounded
by a first portion of the first line and a first portion of the
second line which is greater than the first portion of the first
line with respect to the pulse amplitude, and a second area bounded
by a second portion of the first line and a second portion of the
second line which is smaller than the second portion of the first
line with respect to the pulse amplitude, and wherein the blood-pressure-change
identifying means comprises means for identifying an increase of
the blood pressure of the subject when the second area is greater
than the first area. In this embodiment, a change of the subject's
blood pressure, more particularly, an increase of the same is identified.
According to another feature of the present invention, the blood
pressure monitor apparatus further comprising a blood-pressure re-measuring
device which immediately measures a new blood pressure of the subject
when the blood-pressure-change identifying means identifies the
change of the blood pressure of the subject.
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 preferred embodiments of the invention
when considered in conjunction with the accompanying drawings, in
which:
FIG. 1 is a diagrammatic view for illustrating an electrical construction
of a blood-pressure monitor apparatus embodying the present invention;
FIG. 2 is a diagrammatic view for illustrating various functions
of a control device of the apparatus of FIG. 1;
FIG. 3 is a time chart showing the time-wise change of cuff pressure
Pc controlled by the control device of FIG. 1;
FIG. 4 is a flow chart representing a control program according
to which the control device of FIG. 1 functions as illustrated in
FIG. 2;
FIG. 5 is a flow chart representing an abnormal blood-pressure
change identifying routine carried out at Step S9 of FIG. 4;
FIG. 6 is a graph showing a series of pulse amplitudes obtained
in a BP-measuring period shown in FIG. 3 and stored in a first memory
shown in FIG. 2;
FIG. 7 is a graph showing a series of pulse amplitudes obtained
in a BP-monitoring period shown in FIG. 3 and stored in a second
memory shown in FIG. 2, in comparison with a series of pulse amplitudes
obtained in a BP-measuring period, wherein a cuff pressure, Pm.sub.mmax,
at which the greatest amplitude, Am.sub.mmax, of the pulse amplitudes,
Am.sub.m, obtained in the BP-monitoring period in which the cuff
pressure Pc is increased to a predetermined value, P.sub.CH, is
lower than a cuff pressure, Pm.sub.smax, at which the greatest amplitude,
Am.sub.smax, of the pulse amplitudes, Am.sub.s, obtained in the
BP-measuring period when the cuff pressures Pc are lower than the
predetermined pressure P.sub.CH is obtained;
FIG. 8 is a graph showing a series of pulse amplitudes obtained
in a BP-monitoring period in comparison with a series of pulse amplitudes
obtained in a BP-measuring period, wherein the pulse amplitudes,
Am.sub.m, obtained in the BP-monitoring period in which the cuff
pressure Pc is increased to a predetermined value, P.sub.CH, are
comparable with the pulse amplitudes, Am.sub.s, obtained in the
BP-measuring period when the cuff pressures Pc are lower than the
predetermined pressure P.sub.CH ;
FIG. 9 is a graph showing a series of pulse amplitudes obtained
in a BP-monitoring period in comparison with a series of pulse amplitudes
obtained in a BP-measuring period, wherein a pulse amplitude, M.sub.m,
obtained in the BP-monitoring period in which the cuff pressure
Pc is increased to a predetermined value, P.sub.CH, is lower than
a pulse amplitude, M.sub.s, obtained in the BP-measuring period
when the cuff pressures Pc are lower than the predetermined pressure
P.sub.CH, by a predetermined proportion of the pulse amplitude Ms;
FIG. 10 is a graph showing a series of pulse amplitudes obtained
in a BP-monitoring period in comparison with a series of pulse amplitudes
obtained in a BP-measuring period, wherein a pulse amplitude, M.sub.m,
obtained in the BP-monitoring period in which the cuff pressure
Pc is increased to a predetermined value, P.sub.CH, is higher than
a pulse amplitude, M.sub.s, obtained in the BP-measuring period
when the cuff pressures Pc are lower than the predetermined pressure
P.sub.CH ;
FIG. 11 is a graph showing a series of pulse amplitudes obtained
in a BP-monitoring period in comparison with a series of pulse amplitudes
Obtained in a BP-measuring period, wherein a rate of change, K.sub.m,
of the pulse amplitudes, Am.sub.m, obtained in the BP-monitoring
period in which the cuff pressure Pc is increased to a predetermined
value, P.sub.CH, is smaller than a rate of change, K.sub.s, of the
pulse amplitudes, Am.sub.s, obtained in the BP-measuring period
when the cuff pressures Pc are lower than the predetermined pressure
P.sub.CH ;
FIG. 12 is a graph showing a series of pulse amplitudes obtained
in a BP-monitoring period in comparison with a series of pulse amplitudes
obtained in a BP-measuring period, wherein a rate of change, K.sub.m,
of the pulse amplitudes, Am.sub.m, obtained in the BP-monitoring
period in which the cuff pressure Pc is increased to a predetermined
value, P.sub.CH, is greater than a rate of change, K.sub.s, of the
pulse amplitudes, Am.sub.s, obtained in the BP-measuring period
when the cuff pressures Pc are lower than the predetermined pressure
P.sub.CH ;
FIG. 13 is a graph showing a series of pulse amplitudes obtained
in a BP-monitoring period in comparison with a series of pulse amplitudes
obtained in a BP-measuring period, wherein a pulse rate, PR.sub.m,
determined from the pulse amplitudes, Am.sub.m, obtained in the
BP-monitoring period in which the cuff pressure Pc is increased
to a predetermined value, P.sub.CH, is higher than a pulse rate,
PR.sub.s, determined from the pulse amplitudes, Am.sub.s, obtained
in the BP-measuring period when the cuff pressures Pc are lower
than the predetermined pressure P.sub.CH ;
FIG. 14 is a graph, corresponding to the graph of FIG. 7, wherein
in a BP-monitoring period the cuff pressure Pc is increased to a
predetermined value P.sub.CH slightly higher than a mean blood pressure,
P.sub.MEAN, of a living subject;
FIG. 15 is a graph, corresponding to the graph of FIG. 8, wherein
in a BP-monitoring period the cuff pressure Pc is increased to a
predetermined value P.sub.CH slightly higher than a mean blood pressure
P.sub.MEAN of a living subject;
FIG. 16 is a graph, corresponding to the graph of FIG. 9, wherein
in a BP-monitoring period the cuff pressure Pc is increased to a
predetermined value P.sub.CH slightly higher than a mean blood pressure
P.sub.MEAN of a living subject;
FIG. 17 is a graph, corresponding to the graph of FIG. 10, wherein
a BP-monitoring period the cuff pressure Pc is increased to a predetermined
value P.sub.CH slightly higher than a mean blood pressure P.sub.MEAN
of a living subject;
FIG. 18 is a graph, corresponding to the graph of FIG. 11, wherein
in a BP-monitoring period the cuff pressure Pc is increased to a
predetermined value P.sub.CH slightly higher than a mean blood pressure
P.sub.MEAN of a living subject;
FIG. 19 is a graph, corresponding to the graph of FIG. 12, wherein
in a BP-monitoring period the cuff pressure Pc is increased to a
predetermined value P.sub.CH slightly higher than a mean blood pressure
P.sub.MEAN of a living subject;
FIG. 20 is a graph, corresponding to the graph of FIG. 13, wherein
in a BP-monitoring period the cuff pressure Pc is increased to a
predetermined value P.sub.CH slightly higher than a mean blood pressure
P.sub.MEAN of a living subject;
FIG. 21 is a graph, corresponding to the graph of FIG. 7, wherein
in a BP-monitoring period the cuff pressure Pc is increased to a
predetermined value P.sub.CH lower than a systolic blood pressure,
P.sub.SYS, of a living subject by a predetermined value;
FIG. 22 is a graph, corresponding to the graph of FIG. 13, wherein
in a BP-monitoring period the cuff pressure Pc is increased to a
predetermined value P.sub.CH lower than a systolic blood pressure
P.sub.SYS of a living subject by a predetermined value;
FIG. 23 is a diagrammatic view corresponding to FIG. 2, for illustrating
various functions of a control device of another blood-pressure
monitor apparatus as a second embodiment of the invention;
FIG. 24 is a graph showing a series of pulse amplitudes, Ams.sub.n,
obtained in a BP-measuring period shown in FIG. 29 and stored in
a first memory shown in FIG. 23, in relation with cuff pressures,
Pms.sub.n, when the pulse amplitudes Ams.sub.n are obtained;
FIG. 25 is a graph showing a series of pulse amplitudes, Amm.sub.m,
obtained in a BP-monitoring period shown in FIG. 29 and stored in
a second memory shown in FIG. 23, in relation with cuff pressures,
Pmm.sub.m, when the pulse amplitudes Amm.sub.m are obtained;
FIG. 26 is a graph for illustrating an approximate line, L.sub.s
, representing a relationship between the pulse amplitudes and cuff
pressures collected in a BP-measuring period; a pulse-amplitude
window, W.sub.A ; and a cuff-pressure window, W.sub.P all of which
are determined by the apparatus of FIG. 23;
FIG. 27 is a flow chart corresponding to FIG. 4, which represents
a control program according to which the control device of the second
BP apparatus functions as illustrated in FIG. 23;
FIG. 28 is a flow chart representing an abnormal blood-pressure
change identifying routine carried out at Step T9 of FIG. 27;
FIG. 29 is a time chart showing the time-wise change of cuff pressure
Pc controlled by the control device of the apparatus of FIG. 23;
FIG. 30 is a diagrammatic view corresponding to FIG. 23, for illustrating
various functions of a control device of yet another blood-pressure
monitor apparatus as a third embodiment of the invention;
FIG. 31 is a flow chart corresponding to FIG. 28, which represents
a control program according to which the control device of the third
BP apparatus functions as illustrated in FIG. 30;
FIG. 32 is a graph showing a first curve (indicated at solid line)
representing a first relationship between the pulse amplitudes and
cuff pressures detected in a BP-measuring period, in comparison
with a second curve (indicated at broken line) representing a second
relationship between the pulse amplitudes and cuff pressures detected
in a BP-monitoring period following the BP-measuring period, wherein
the subject's blood pressure does not change;
FIG. 33 a graph showing a first curve (indicated at solid line)
representing a first relationship between the pulse amplitudes and
cuff pressures detected in a BP-measuring period, in comparison
with a second curve (indicated at broken line) representing a second
relationship between the pulse amplitudes and cuff pressures detected
in a BP-monitoring period, wherein the subject's blood pressure
increases;
FIG. 34 is a graph showing a first curve (indicated at solid line)
representing a first relationship between the pulse amplitudes and
cuff pressures detected in a BP-measuring period, in comparison
with a second curve (indicated at broken line) representing a second
relationship between the pulse amplitudes and cuff pressures detected
in a BP-monitoring period, wherein the subject's blood pressure
decreases; and
FIG. 35 is a view for illustrating a conventional manner in which
the blood pressure of a living subject is monitored based on the
pulse amplitudes obtained from an inflatable cuff wound around a
body portion of the subject.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is shown a blood pressure monitor
apparatus embodying the present invention (hereinafter, referred
to as the "BP monitor").
In FIG. 1, reference numeral 10 designates an inflatable cuff 10
adapted to be wound around, e.g., an upper arm of a living subject,
such as a patient, so as to press the arm. The cuff 10 includes
an inflatable bag 10a formed of an elastic sheet such as a rubber
sheet or a vinyl sheet. The inflatable bag 10a is accommodated in
an arm belt 10b formed of a non-stretchable sheet. The bag 10a of
the Cuff 10 is connected to a pressure sensor 12, an air pump 14,
and a pressure control valve 16 via air piping 18. The pressure
control valve 16 controls the pressing pressure (i.e., air pressure)
of the cuff 10 applied to the upper arm of the subject. The control
valve 16 provides part of a cuff-pressure control device 56 which
will be described later.
The pressure sensor 12 includes a semiconductor pressure-sensing
element, detects the air pressure in the cuff 10, and supplies a
pressure signal, SP, representative of the detected cuff pressure,
to a low-pass filter 20 and a band-pass filter 22. The low-pass
filter 20 permits only a direct-current component of the pressure
signal SP to pass therethrough, thereby supplying a cuff-pressure
signal, SK, representative of a cuff pressure (i.e., static pressure),
Pc, to an analog-to-digital (A/D) converter 24. The low-pass filter
provides part of a cuff-pressure detecting device 50 which will
be described later.
The band-pass filter 22 permits only a 1 to 10 Hz frequency-band
component of the pressure signal SP, thereby supplying, to the A/D
converter 24, a pulse-wave signal, SM1, representative of a pulse
wave containing heartbeat-synchronous pulses that are pressure oscillations
or changes produced in the cuff 10 because of pulsation of the arterial
vessels running in the subject's arm. The band-pass filter 22 has
a narrow frequency-band characteristic to extract, from the pressure
signal SP, pulse amplitudes, i.e., pressure oscillations produced
in the cuff 10 in synchronism with subject's heartbeats while the
cuff pressure is slowly changed (e.g., decreased) at, e.g., 2 to
3 mmHg/sec. Thus, the extracted pulse-wave signal SM1 is free from
noise such as motion-related artifact noise. The A/D converter 24
includes a multiplexer for concurrently dealing with the two input
signals, SK and SM1, by time sharing. The band-pass filter 22 provides
part of a pulse-wave detecting device 52 which will be described
later.
The present BP monitor has a control device 26 which is provided
by a microcomputer including a central processing unit (CPU) 28,
a random access memory (RAM) 30, a read only memory (ROM) 32, a
first output interface 34, and a second output interface 36. The
CPU 28 processes the signals received from the A/D converter 24,
by utilizing a temporary-storage function of the RAM 30, according
to a control program pre-stored in the ROM 32. In addition, the
CPU 28 drives and controls the air pump 14 and the pressure control
valve 16 via the first interface 34, and drives and controls an
output device 38 via the second interface 36. The output device
38 includes a display panel for displaying an image which consists
of a multiplicity of picture elements and represents numerals and/or
waveforms, and a printer for recording the image with an ink on
a recording sheet.
A mode-selection switch 40 is operable for switching the BP monitor
between a single-measurement mode and a continuous-monitor mode.
The mode switch 40 supplies, to the CPU 40, a mode signal representing
a selected mode. A start/stop switch 42 is provided to alternately
supply, to the CPU 28, an ON signal to start the BP monitor and
an OFF signal to stop the same, each time the switch 42 is operated.
FIG. 2 illustrates various functions of the control device 26 of
the BP monitor. The BP monitor includes an oscillometric blood-pressure
(BP) measuring device 54 which determines two cuff pressures at
which the rate of change of the pulse amplitudes obtained during
the changing of the cuff pressure becomes maximal, as a systolic
(P.sub.SYS) and a diastolic (P.sub.DIA) blood pressure of the subject,
and determines a cuff pressure at which the greatest pulse amplitude
is obtained, as a mean (P.sub.MEAN) blood pressure of the subject.
The BP measuring device 54 carries out a BP measurement not only
when the start/stop switch 42 is operated to start the BP monitor
with the mode switch 40 being placed in the monitor mode, but also
when a blood-pressure-change identifying means 70 identifies that
the blood pressure of the subject has abnormally changed, as described
later. Thus, the BP measuring device 54 also functions as a BP re-measuring
device 72.
As shown in FIG. 3, in a BP-measuring period of the BP measuring
device 54, the cuff-pressure control device 56 quickly increases
the pressing pressure Pc of the cuff 10 to a target pressure, P.sub.CM,
which is pre-determined to be higher than a systolic blood pressure
of the subject, and subsequently slowly decreases the cuff pressure
Pc at 2 to 3 mmHg/sec. In a non-measurement period in which the
BP measuring device 54 does not work, the cuff-pressure control
device 56 iteratively increases and decreases the cuff pressure
Pc to and from a predetermined pressure value, P.sub.CH, which is
pre-determined to be not higher than a diastolic blood pressure
of the subject, while inserting a predetermined rest period between
successive two BP-monitoring periods.
A first memory 58 stores the respective amplitudes of heartbeat-synchronous
pulses, Am.sub.s (s=1, 2, 3, . . . , j), produced as pressure oscillations
in the cuff 10 while the cuff pressure Pc is slowly changed by the
BP measuring device 54 in a BP-measuring period. The first memory
58 also stores the cuff pressures, Pm.sub.s (s=1, 2, 3, . . . ,
j), detected by the cuff-pressure detecting device 50 when the corresponding
pulse amplitudes Am.sub.s are detected by the pulse-wave detecting
device 52. A second memory 60 stores the respective amplitudes of
heartbeat-synchronous pulses, Am.sub.m (m=1, 2, 3, . . . , k), detected
by the pulse-wave detecting device 52 while the cuff pressure Pc
is slowly changed by the cuff-pressure control device 56 in each
BP-monitoring period subsequent to a BP-measuring period, and also
stores the cuff pressures, Pm.sub.m (m=1, 2, 3, . . . , k), detected
by the cuff-pressure detecting device 50 when the corresponding
pulse amplitudes Am.sub.m are detected.
A cuff-pressure comparing means 62 compares a cuff pressure, Pm.sub.smax,
at which a pulse having the greatest or maximum amplitude, Am.sub.smax,
out of the pulses obtained and stored in the first memory 58 when
the cuff pressures Pc are not higher than the predetermined value
P.sub.CH is obtained, with a cuff pressure at which a pulse having
the greatest or maximum amplitude, Am.sub.mmax, out of all the pulses
stored in the second memory 60 is obtained. A rate-of-change calculating
means 64 calculates a rate of change, K.sub.s, of the respective
pulse amplitudes Am.sub.s detected and stored in the first memory
58 when the cuff pressure Pc is not higher than the predetermined
value P.sub.CH, with respect to the corresponding cuff pressures
Pm.sub.s stored in the same memory 58, and a rate of change, K.sub.m,
of the respective pulse amplitudes Am.sub.m stored in the second
memory 60 with respect to the corresponding cuff pressures Pm.sub.m
stored in the same memory 60. The rate of change K.sub.s is defined
as the slope of an approximate line, such as a least-square approximate
line or a regression line, which is determined based on the data
points plotted in a two-dimensional coordinate system having an
axis of abscissa indicative of the cuff pressure Pc and an axis
of ordinate indicative of the pulse amplitude. Those data points
or the approximate line represents a relationship between the pulse
amplitudes Am.sub.s and cuff pressures Pm.sub.s detected and stored
in the first memory 58 when the cuff pressure Pc is not higher than
the predetermined value P.sub.CH. Similarly, the rate of change
K.sub.m is defined as the slope of an approximate line which is
determined based on the data points plotted in the same coordinate
system, and those data points or the approximate line represents
a relationship between the pulse amplitudes Am.sub.m and cuff pressures
Pm.sub.m stored in the second memory 60.
A first pulse-rate determining means 66 determines and stores a
pulse rate, PR.sub.s, of the subject based on the pulses obtained
in a BP-measuring period, and a second pulse-rate determining means
68 determines and stores a pulse rate, PR.sub.m, of the subject
based on the pulses obtained in each of BP-monitoring periods following
a BP-measuring period.
The BP-change identifying means 70 identifies a change of the blood
pressure of the subject, (a) when the cuff-pressure comparing means
62 provides a comparison result that the cuff pressure Pm.sub.mmax
is lower than the cuff pressure Pm.sub.smax, (b) when the cuff-pressure
comparing means 62 provides a comparison result that the cuff pressure
Pm.sub.mmax is not lower than the cuff pressure Pm.sub.smax, and
simultaneously when a pulse amplitude, M.sub.s, which is obtained
and stored in the first memory 58 when the cuff pressure Pc takes
a reference value has changed from a pulse amplitude, M.sub.m, which
is obtained and stored in the second memory 60 when the cuff pressure
Pc takes the reference value, by not smaller than a predetermined
proportion of the pulse amplitude M.sub.s, (c) when the difference
between the two rates of change K.sub.s, K.sub.m is greater than
a predetermined value, or (d) when the pulse rate PR.sub.m has changed
from the pulse rate PR.sub.s by not smaller than a predetermined
amount. The pulse amplitude M.sub.s may be obtained as the value
of an envelope or a cumulative curve of the pulse amplitudes Am.sub.s
stored in the first memory 58, which value corresponds to the reference
value of the cuff pressure Pc, and the pulse amplitude M.sub.m may
be obtained as the value of an envelope or a cumulative curve of
the pulse amplitudes Am.sub.m stored in the second memory 60, which
value corresponds to the reference value of the cuff pressure Pc.
The BP-change identifying means 70 obtains, from the above-described
various identification or judgment results, change evaluation values,
D.sub.1, D.sub.2, U.sub.1, U.sub.2, H, and a non-change evaluation
value, I, which will be described later, and carries out an overall
BP-change evaluation, based on those evaluation values, according
to the following expression (1):
where k.sub.1, k.sub.2, k.sub.3, k.sub.4, k.sub.5, and k.sub.6
are predetermined constants.
When the overall evaluation value S does not fall within a reference
range, the BP-change identifying means 70 identifies or judges that
the blood pressure of the subject has changed abnormally, and the
BP re-measuring device 72 immediately starts a BP measuring period
to carry out a BP measurement on the subject. Thus, the output device
38 displays and/or records the subject's BP values measured immediately
after the abnormal BP change.
Next, there will be described the operation of the control device
26 of the BP monitor by reference to the flow chart of FIG. 4 which
represents the control program pre-stored in the ROM 32, and the
flow chart of FIG. 5 which describes Step S9 of FIG. 4, i.e., abnormal
BP-change identifying routine.
At steps not shown in FIG. 4, the CPU 28 of the control device
26 judges whether the start/stop switch 42 has been operated to
start the present BP monitor, and judges whether the mode-selection
switch 40 has been operated to select the continuous-monitor mode.
If positive judgments are made at the two steps, the control of
the CPU 28 carries out Step S1, i.e., BP measuring routine that
provides part of the BP measuring device 54. At Step S1 corresponding
to the initial BP-measuring period shown in FIG. 3, the pressing
pressure Pc of the cuff 10 is quickly increased up to a target value,
P.sub.CM, which is pre-determined to be higher than a systolic blood
pressure of the subject and subsequently is slowly decreased at
2 to 3 mmHg/sec. A cuff pressure at which pulse amplitudes being
detected largely increase during the slow decreasing of the cuff
pressure Pc, is determined as a systolic blood pressure P.sub.SYS
of the subject; a cuff pressure at which the pulse amplitudes largely
decrease is determined as a diastolic blood pressure P.sub.DIA of
the subject; and a cuff pressure at which the greatest pulse amplitude
is detected is determined as a mean blood pressure P.sub.MEAN of
the subject. After the blood pressure measurement is completed,
the cuff pressure Pc is quickly decreased.
Subsequently, at Step S2, the respective amplitudes Am.sub.s (s=1,
2, 3, . . . , j) of the heartbeat-synchronous pulses produced as
pressure oscillations in the cuff 10 during the slow changing of
the cuff pressure Pc in the above BP-measuring period, and the cuff
pressures Pm.sub.s (s=1, 2, 3, . . . , j) at which the pulse amplitudes
Am.sub.s are respectively detected, are stored in an appropriate
memory area of the RAM 30. In addition, a pulse rate PR.sub.s of
the subject is calculated based on the difference of two times when
two successive pulses are respectively detected, and is stored in
another appropriate memory area of the RAM 30. FIG. 6 shows an example
of a series of pulse amplitudes Am.sub.s stored at Step S2. Thus,
the appropriate memory areas of the RAM 30 used at Step S2 provide
the first memory 58 and part of the first pulse-rate determining
means 66, respectively.
Step S2 is followed by Step S3 to judge. whether a time or contents,
CT, measured or counted by a time-signal counter provided in the
microcomputer 26, has exceeded a predetermined time interval, T.sub.1M.
The counter CT starts to count the number of time-signals produced
after a blood pressure measurement ends at Step S1. The interval
T.sub.1M is also the interval between each pair of successive BP-monitoring
periods following the initial BP-measuring period. At the beginning,
negative judgments are made at Step S3, so that the control of the
CPU 28 goes to Step S4 to add "one" to the contents CT
of the counter and then goes back to Step S3. Thus, Steps S3 and
S4 are repeated.
Meanwhile, if a positive judgment is made at Step S3, the control
goes to Step S5 to start a first BP-monitoring period shown in FIG.
3, i.e., quickly increase the cuff pressure Pc up to a target value
P.sub.CH which is pre-determined to be not higher than the measured
diastolic blood pressure P.sub.DIA of the subject. At Step S6, the
CPU 28 judges whether the cuff pressure Pc has been increased to
the target value P.sub.CH. If a positive judgment is made at Step
S6, the control goes to Step S7 to slowly decrease the cuff pressure
Pc at 2 to 3 mmHg/sec as shown in FIG. 3.
At the following Step S8, the respective amplitudes Am.sub.m (m=1,
2, 3, . . . , k) of the heartbeat-synchronous pulses detected during
the slow changing of the cuff pressure Pc in the above BP-monitoring
period, and the cuff pressures Pm.sub.m (m=1, 2, 3, . . . , k) at
which the pulse amplitudes Am.sub.m are respectively detected, are
stored in an appropriate memory area of the RAM 30. In addition,
a pulse rate PR.sub.m of the subject is calculated based on the
difference of two times when two successive pulses are respectively
detected, and is stored in another appropriate memory area of the
RAM 30. Thus, the appropriate memory areas of the RAM 30 used at
Step S8 provide the second memory 60 and part of the second pulse-rate
determining means 68, respectively.
Step S8 is followed by Step S9, i.e., abnormal BP change identification
routine corresponding to part of the BP-change identifying means
70. At Step S9, the CPU 28 judges whether the blood pressure of
the subject has been changed abnormally. The abnormal BP-change
identification routine of Step S9 will be described in detail by
reference to the flow chart of FIG. 5.
First, at Step SM1 corresponding to part of the cuff-pressure comparing
means 62, the CPU 28 compares a cuff pressure Pm.sub.smax detected
at the time of detection of a pulse having the greatest amplitude
Am.sub.smax out of the pulses which are detected when the cuff pressures
Pc are not higher than the predetermined value P.sub.CH and stored
in the first memory 58, with a cuff pressure Pm.sub.mmax detected
at the time of detection of a pulse having the greatest amplitude
Am.sub.mmax out of all the pulses stored in the second memory 60,
and judges whether the cuff pressure Pm.sub.mmax is lower than the
cuff pressure Pm.sub.smax. If a positive judgment is made at Step
SM1, the control goes to Step SM2 to judge that the blood pressure
of the subject has decreased, i.e., identify a decrease of the subject's
blood pressure. The CPU 28 determines and stores a change evaluation
value D.sub.1 indicative of a degree of BP decreasing, according
to the following function: D.sub.1 =Pm.sub.smax -Pm.sub.mmax, or
other appropriate functions of (Pm.sub.smax -Pm.sub.mmax). FIG.
7 shows the case where a positive judgment is obtained at Step SM1.
On the other hand, if a negative judgment is made at Step SM1,
the control goes to Step SM3 corresponding to part of specific pulse-amplitude
calculating means. At Step SM3, the CPU 28 calculates a specific
pulse amplitude M.sub.s of the pulses obtained when the cuff pressures
Pc are not higher than the predetermined value P.sub.CH and stored
in the first memory 58, which amplitude corresponds to a reference
cuff pressure value, and a specific pulse amplitude M.sub.m of the
pulses stored in the second memory 60, which amplitude corresponds
to the reference cuff pressure value. The specific pulse amplitude
M.sub.s may be obtained as the value of an envelope or a cumulative
curve of the pulse amplitudes Am.sub.s stored in the first memory
58, which value corresponds to the reference cuff pressure value,
and the specific pulse amplitude M.sub.m may be obtained as the
value of an envelope or a cumulative curve of the pulse amplitudes
Am.sub.m stored in the second memory 60, which value corresponds
to the reference cuff pressure value.
Step SM3 is followed by Step SM4 corresponding to part of pulse-amplitude
comparing means. At Step SM4, the CPU 28 compares the specific pulse
amplitudes M.sub.s, M.sub.m. In the case where the pulse amplitude
M.sub.m falls within, e.g., the range of .+-.20% of the pulse amplitude
M.sub.s, the control of the CPU 28 goes to Step SM5 and judges that
the subject's blood pressure has not changed, i.e., identifies the
unchanged blood pressure. The CPU 28 determines and stores a non-change
evaluation value I indicative of a degree of unchanging of blood
pressure, according to the following function: I=1.vertline.M.sub.s
-M.sub.m .vertline., or other appropriate functions of 1/.vertline.M.sub.s
-M.sub.m .vertline.. FIG. 8 shows the case where the pulse amplitude
M.sub.m for the BP-monitoring period has not changed from the pulse
amplitude M.sub.s for the BP-measuring period.
At Step SM4, in the case where the pulse amplitude M.sub.m does
not fall within, e.g., the range of .+-.50% of the pulse amplitude
M.sub.s, the control goes to Step SM6 and judges that the subject's
blood pressure has increased, i.e., identifies an increase of the
blood pressure. The CPU 28 determines and stores a change evaluation
value U.sub.1 indicative of a degree of BP increasing, according
to the following function: I=.vertline.M.sub.s -M.sub.m .vertline.,
or other appropriate functions of .vertline.M.sub.s -M.sub.m .vertline..
FIGS. 9 and 10 show the case where the pulse amplitude M.sub.m has
decreased from the pulse amplitude M.sub.s and the case where the
pulse amplitude M.sub.m has increased from the pulse amplitude M.sub.s,
respectively.
In the other cases than described above, the control directly goes
to Step SM7 corresponding to part of the rate-of-change calculating
means 64. At Step SM7, the CPU 28 calculates a rate of change K.sub.s
of the respective pulse amplitudes Am.sub.s detected and stored
in the first memory 58 when the cuff pressures Pc are not higher
than the predetermined value P.sub.CH, with respect to the corresponding
cuff pressures Pm.sub.s stored in the same memory 58, and a rate
of change K.sub.m of the respective pulse amplitudes Am.sub.m stored
in the second memory 60 with respect to the corresponding cuff pressures
Pm.sub.m stored in the same memory 60. The rate of change K.sub.s
may be determined as, e.g., the slope of a regression line determined
based on data points plotted in a two-dimensional coordinate system
having an axis of abscissa indicative of the cuff pressure Pc and
an axis of ordinate indicative of the pulse amplitude as shown in
FIG. 11 or 12.
Step SM7 is followed by Step SM8 to compare the rates of change
K.sub.s, K.sub.m with each other. In the case where the rate of
change K.sub.m is smaller by more than a predetermined positive
value, .alpha., than the rate of change K.sub.s, the control goes
to Step SM9 and judges that the subject's blood pressure has increased,
i.e., identifies a BP increase. The CPU 28 determines and stores
a change evaluation value U.sub.2 indicative of a degree of BP increasing,
according to the following function: U.sub.2 =K.sub.s -K.sub.m,
or other appropriate functions of (K.sub.s -K.sub.m). FIG. 11 shows
the case where the pulse amplitude K.sub.m has decreased from the
pulse amplitude K.sub.s. On the other hand, in the case where the
rate of change K.sub.m is greater by more than the predetermined
value .alpha. than the rate of change K.sub.s, the control goes
to Step SM10 and judges that the subject's blood pressure has decreased,
i.e., identifies a BP decrease. The CPU 28 determines and stores
a change evaluation value D.sub.2 indicative of a degree of BP decreasing,
according to the following function: D.sub.2 =K.sub.m -K.sub.s,
or other appropriate functions of (K.sub.m -K.sub.s). FIG. 12 shows
the case where the pulse amplitude K.sub.m has increased from the
pulse amplitude K.sub.s.
In the other cases than described above, the control directly goes
to Step SM11 to compare the pulse rate PR.sub.s of the subject determined
based on the pulses obtained in a BP-measuring period, with the
pulse rate PR.sub.m of the subject determined based on the pulses
obtained in a BP-monitoring period after the BP-measuring period,
and judge whether a ratio of the pulse rate PR.sub.m to the pulse
rate PR.sub.s, PR.sub.m /PR.sub.s, is greater than a predetermined
value, K, greater than one. If a negative judgment is made at Step
SM11, the control of the CPU 28 skips Step SM12 and directly goes
to Step SM13. On the other hand, if a positive judgment is made,
the control goes to Step SM12 and judges that the subject's blood
pressure has changed, i.e., identifies a BP change. The CPU 28 determines
and stores a change evaluation value H indicative of a degree of
BP changing, according to the following function: H=PR.sub.m /PR.sub.s,
or other appropriate functions of PR.sub.m /PR.sub.s. FIG. 13 shows
the case where the pulse rate PR.sub.m has changed from the pulse
rate PR.sub.s.
At Step SM13, the CPU 28 makes an overall evaluation on the change
of the subject's blood pressure, based on the change evaluation
values D.sub.1, D.sub.2, non-change evaluation value I, change evaluation
values U.sub.1, U.sub.2, and change evaluation value H, i.e., obtains
an overall evaluation value S according to the previously-described
expression (1). If the overall evaluation value S does not fall
within a reference range, the CPU 28 judges that the subject's blood
pressure has abnormally increased or decreased.
If at Step SM13 the CPU 28 does not identify an abnormal BP change,
a negative judgment is made at Step S9 of FIG. 4, so that the control
goes to Step S10 to clear or reset the contents CT of the timer
and then repeats Step S3 and the following steps. On the other hand,
if a positive judgment is made at Step S9, the control goes to Step
S11 to operate the output device 38 to inform the user of the identification
of the abnormal BP change, and operates the BP re-measuring device
72 to immediately start a BP measuring period and carry out a BP
measurement on the subject like at Step S1. Thus, the output device
38 displays and/or records the subject's BP values measured immediately
after the identification of the abnormal BP change. Thus, Step S11
corresponds to part of the BP re-measuring device 72.
As is apparent from the foregoing description, in the present embodiment,
the pulse amplitudes Am.sub.s (s=1 to j) are detected as the pressure
oscillations produced in the cuff 10 during the slowing decreasing
of the cuff pressure Pc, in a BP measurement carried out at Step
S1 corresponding to part of the BP measuring device 54, and the
pulse amplitudes Am.sub.s and the cuff pressures pm.sub.s (s=1 to
j) detected at the respective times of detection of the pulse amplitudes
Am.sub.s are stored in the first memory 58. In addition, the pulse
amplitudes Am.sub.m (m=1 to k) are detected during the slowing decreasing
of the cuff pressure Pc from the predetermined value P.sub.CH, in
each of BP monitoring periods following a BP measurement of the
BP-measuring device 54, and the pulse amplitudes Am.sub.m and the
cuff pressures Pm.sub.m (m=1 to k) detected at the respective times
of detection of the pulse amplitudes Am.sub.m are stored in the
second memory 60. At Step S9 corresponding to part of the BP-change
identifying means 70, a change of the blood pressure of the subject
is identified based on the pulse amplitudes Am.sub.s and cuff pressures
Pm.sub.s stored in the first memory 58 and the pulse amplitudes
Am.sub.m and cuff pressures Pm.sub.m stored in the second memory
60.
The present BP monitor can monitor the blood pressure of the subject
with high accuracy, because the apparatus identifies a change of
the subject's blood pressure based on both the pulse amplitudes
Am.sub.s and cuff pressures pm.sub.s obtained in a BP-measuring
period and the pulse amplitudes Am.sub.m and cuff pressures pm.sub.m
obtained in a BP-monitoring period. In addition, since the BP monitor
monitors the subject's blood pressure by iteratively changing the
cuff pressure Pc within a low pressure range between the atmospheric
pressure and the pre-determined pressure value P.sub.CH lower than
the subject's diastolic blood pressure P.sub.DIA, the apparatus
does not cause the subject to feel serious discomfort.
In the present embodiment, the BP monitor makes an overall evaluation
on the change of the subject's blood pressure, based on the change
evaluation values D.sub.1, D.sub.2, non-change evaluation value
I, change evaluation values U.sub.1, U.sub.2, and change evaluation
value H, according to the previously-described expression (1). Thus,
the BP monitor can monitor the subject's blood pressure with high
reliability.
If an abnormal BP change is identified by the BP-change identifying
means 70, the BP re-measuring device 72 immediately carries out
a BP measurement using the cuff 10, and outputs the BP values obtained
at the time of identification of the abnormal BP change. Thus, a
medical worker such as a doctor or a nurse can quickly give appropriate
treatments on the subject.
In the present embodiment, the cuff-pressure control device 56
increases, in each BP-monitoring period, the cuff pressure Pc up
to a target value P.sub.CH which is predetermined to be not higher
than the subject's diastolic blood pressure P.sub.DIA. However,
the cuff-pressure control device 56 may be modified to increase,
in each BP-monitoring period, the cuff pressure Pc up to a different
target value P.sub.CH which is predetermined to be slightly higher
than the subject's mean blood pressure P.sub.MEAN. FIGS. 14 to 20
correspond to FIGS. 7 to 13, respectively, and show the cases where
the cuff pressure Pc is increased to a predetermined target value
P.sub.CH slightly higher than the mean blood pressure P.sub.MEAN.
Moreover, the cuff-pressure control device 56 may be modified to
increase, in each BP-monitoring period, the cuff pressure Pc up
to a different target value P.sub.CH which is predetermined to be
higher than the mean blood pressure P.sub.MEAN and lower by a predetermined
value than the systolic blood pressure P.sub.SYS. FIGS. 21 and 22
correspond to FIGS. 7 and 13, respectively, and show the cases where
the cuff pressure Pc is increased to a predetermined target value
P.sub.CH higher than the mean blood pressure P.sub.MEAN and lower
than the systolic blood pressure P.sub.SYS.
Next, there will be described a second embodiment of the present
invention. The second embodiment also relates to a BP monitor and
has the same hardware construction as that of the first embodiment
shown in FIG. 1. However, the second BP monitor is operated according
to the control program represented by the flow charts of FIGS. 27
and 28 in place of the program represented by the flow charts of
FIGS. 4 and 5 for the first embodiment.
FIG. 23 shows various functions of a control device 26 of the second
BP monitor. The second BP monitor includes an inflatable cuff 10,
a cuff-pressure detecting device 50, a pulse-wave detecting device
52, an oscillometric BP measuring device 54, and a BP re-measuring
device 72 all of which are the same as the counterparts of the first
BP monitor shown in FIG. 2.
The second BP monitor includes a cuff-pressure control device 156
which quickly increases, in a BP-measuring period of the BP measuring
device 54 shown in FIG. 29, a pressing pressure Pc of the cuff 10
to a target pressure P.sub.CM which is pre-determined to be higher
than a systolic blood pressure of the subject, and subsequently
slowly decreases the cuff pressure Pc at 2 to 3 mmHg/sec. In a non-measurement
period in which the BP measuring device 54 does not work, the cuff-pressure
control device 156 iteratively increases and decreases the cuff
pressure Pc to and from a target pressure value, P.sub.CH, which
is predetermined to be not higher than a mean blood pressure P.sub.MEAN
of the subject, while inserting a predetermined rest period between
successive two BP-monitoring periods. During the slow decreasing
of the cuff pressure Pc in each BP-monitoring period, the second
BP monitor collects pulse amplitudes and cuff pressures.
A first memory 158 stores the respective amplitudes of heartbeat-synchronous
pulses, Ams.sub.n (n=1, 2, 3, . . . , j), produced as pressure oscillations
in the cuff 10 while the cuff pressure Pc is slowly changed by the
BP measuring device 54 in a BP-measuring period. The first memory
158 also stores the cuff pressures, Pms.sub.n (n=1, 2, 3, . . .
, j), detected by the cuff-pressure detecting device 50 when the
corresponding pulse amplitudes Ams.sub.n are detected by the pulse-wave
detecting device 52. FIG. 24 shows a series of pulse amplitudes
Ams.sub.n which are obtained as the cuff pressures pms.sub.n are
changed. A second memory 160 stores the respective amplitudes of
heartbeat-synchronous pulses, Amm.sub.m (m=1, 2, 3, . . . , k),
detected by the pulse-wave detecting device 52 while the cuff pressure
Pc is slowly changed by the cuff-pressure control device 156 in
each BP-monitoring period subsequent to a BP-measuring period, and
also stores the cuff pressures, Pmm.sub.m (m=1, 2, 3, . . . , k),
detected by the cuff-pressure detecting device 50 when the corresponding
pulse amplitudes Amm.sub.m are detected. FIG. 25 shows a series
of pulse amplitudes Amm.sub.m which are obtained as the cuff pressures
Pmm.sub.m are changed. The first memory 158 stores the pulse amplitudes
Ams.sub.n in relation with the corresponding cuff pressures Pms.sub.n,
and the second memory 160 stores the pulse amplitudes Amm.sub.m
in relation with the corresponding cuff pressures Pmm.sub.m. Thus,
it can be said that the first memory 158 stores a first relationship
between the cuff pressures pms.sub.n and the pulse amplitudes Ams.sub.n
and that the second memory 160 stores a second relationship between
the cuff pressures Pmm.sub.m and the pulse amplitudes Amm.sub.m.
A pulse-amplitude window determining means 162 determines a Pulse-amplitude
window, W.sub.A, based on the first relationship between the cuff
pressures Pms.sub.n and pulse amplitudes Ams.sub.n stored in the
first memory 158. The pulse-amplitude window determining means 162
includes an approximate-line determining means 164 for determining
an approximate line, L.sub.S, which approximates a portion of the
first relationship stored in the first memory 158 which portion
falls within a predetermined cuff-pressure range not higher than
the subject's mean blood pressure P.sub.MEAN (e.g., range between
the subject's diastolic blood pressure P.sub.DIA and the target
pressure value P.sub.CH), that is, approximates an envelope of the
data points which represent the cuff pressures Pms.sub.n falling
within the above cuff-pressure range and the corresponding pulse
amplitudes Ams.sub.n. The approximate-line determining means 164
determines, as the approximate line L.sub.S, a least-square approximate
line or a regression line based on the above data points. The approximate
line L.sub.S is employed as a center line of the pulse-amplitude
window W.sub.A. The pulse-amplitude window determining means 162
further includes a pulse-amplitude window-width calculating means
166 for calculating a width, H.sub.A, of the pulse-amplitude window
W.sub.A along the axis of ordinate indicative of the pulse amplitude.
The window W.sub.A has respective halves of the width H.sub.A on
both sides of the approximate line L.sub.S as the center line thereof,
as shown in FIG. 26.
A cuff-pressure window determining means 168 determines a cuff-pressure
window, W.sub.P, based on the first relationship between the cuff
pressures Pms.sub.n and pulse amplitudes Ams.sub.n stored in the
first memory 158. The cuff-pressure window determining means 168
includes the above-described approximate-line determining means
164 for determining the approximate line L.sub.S, which is employed
as a center line of the cuff-pressure window W.sub.P. The cuff-pressure
window determining means 168 further includes a cuff-pressure window-width
calculating means 170 for calculating a width, Hp, of the cuff-pressure
window W.sub.P along the axis of abscissa indicative of the cuff
pressure Pc. The window W.sub.P has respective halves of the width
Hp on both sides of the approximate line L.sub.S as the center line
thereof, as shown in FIG. 26. In FIG. 26, symbols "o"
(white circles) represents the data points corresponding to the
first relationship between the cuff pressures Pms.sub.n and pulse
amplitudes Ams.sub.n stored in the first memory 158.
A BP-change identifying means 172 identifies a change of the subject's
blood pressure based on the first relationship (FIG. 24) between
the cuff pressures Pms.sub.n and pulse amplitudes Ams.sub.n stored
in the first memory 158 and the second relationship (FIG. 25) between
the cuff pressures Pmm.sub.m and pulse amplitudes Amm.sub.m stored
in the second memory 160. More specifically described, the BP-change
identifying means 172 includes the first and second memories 158,
160, the pulse-amplitude and cuff-pressure window determining means
162, 168, and a deviation identifying means 174. The deviation identifying
means 174 identifies a deviation of the second relationship from
the first relationship based on the data points falling within the
pulse-amplitude window W.sub.A out of the data points representing
the pulse amplitudes Amm.sub.m (m=1 to k) and cuff pressures Pmm.sub.m
(m=1 to k) stored in the second memory 160, and the data points
falling within the cuff-pressure window W.sub.P out of the same
data points. When the deviation identifying means 174 identifies
a deviation between the first and second relationships, i.e., when
the BP-change identifying means 172 identifies a change of the subject's
blood pressure, the BP re-measuring device 72 immediately starts
a BP measuring period to carry out a BP measurement on the subject.
Thus, the output device 38 displays and/or records the subject's
BP values measured upon identification of the BP change.
Next, there will be described the operation of the control device
26 of the second BP monitor by reference to the flow chart of FIG.
27 which represents the control program pre-stored in a ROM 32,
and the flow chart of FIG. 28 which describes Step T9 of FIG. 27,
i.e., abnormal BP-change identifying routine.
At steps not shown in FIG. 27, a CPU 28 of the control device 26
judges whether a start/stop switch 42 has been operated to start
the second BP monitor, and judges whether a mode-selection switch
40 has been operated to select a continuous-monitor mode. If positive
judgments are made in the two steps, the control of the CPU 28 carries
out Step T1, i.e., BP measuring routine that provides part of the
BP measuring device 54. At Step T1 corresponding to the initial
BP-measuring period shown in FIG. 29, the pressing pressure Pc of
the cuff 10 is quickly increased up to a target value P.sub.CM which
is pre-determined to be higher than a systolic blood pressure of
the subject and subsequently is slowly decreased at 2 to 3 mmHg/sec.
A cuff pressure at which pulse amplitudes (FIG. 24) being detected
largely increase during the slow decreasing of the cuff pressure
Pc, is determined as a systolic blood pressure P.sub.SYS of the
subject; a cuff pressure at which the pulse amplitudes largely decrease
is determined as a diastolic blood pressure P.sub.DIA of the subject;
and a cuff pressure at which the greatest pulse amplitude is detected
is determined as a mean blood pressure P.sub.MEAN of the subject.
After the blood pressure measurement is completed, the cuff pressure
Pc is quickly decreased.
Subsequently, at Step T2, the respective amplitudes Ams.sub.n (n=1,
2, 3, . . . , j) of the heartbeat-synchronous pulses produced as
pressure oscillations in the cuff 10 during the slow changing of
the cuff pressure Pc in the above BP-measuring period, and the cuff
pressures Pms.sub.n (n=1, 2, 3, . . . , j) at which the pulse amplitudes
Ams.sub.n are respectively detected, are stored in an appropriate
memory area of a RAM 30. FIG. 24 shows an example of a series of
pulse amplitudes Ams.sub.n stored at Step T2. Thus, the appropriate
memory area of the RAM 30 used at Step T2 corresponds to the first
memory 158.
Step T2 is followed by Step T3 to judge whether a time or contents,
CT, measured or counted by a time-signal counter provided in the
microcomputer 26, has exceeded a predetermined time interval, T.sub.1M.
The counter CT starts to count the number of time-signals produced
after a BP measurement ends at Step T1. The interval T.sub.1M is
also the interval between each pair of successive BP-monitoring
periods following the initial BP-measuring period. At the beginning,
negative judgments are made at Step T3, so that the control of the
CPU 28 goes to Step T4 to add "one" to the contents CT
of the counter and then goes back to Step T3. Thus, Steps T3 and
T4 are repeated.
Meanwhile, if a positive judgment is made at Step T3, the control
goes to Step T5 to start a first BP-monitoring period shown in FIG.
29, i.e., quickly increase the cuff pressure Pc up to a target value
P.sub.CH which is pre-determined to be not higher than the measured
mean blood pressure P.sub.DIA of the subject. At Step ST, the CPU
28 judges whether the cuff pressure Pc has been increased up to
the target value P.sub.CH. If a positive judgment is made at Step
T6, the control goes to Step T7 to slowly decrease the cuff pressure
Pc at 2 to 3 mmHg/sec as shown in FIG. 29.
At the following Step T8, the respective amplitudes Amm.sub.m (m=1,
2, 3, . . . , k) of the heartbeat-synchronous pulses detected during
the slow changing of the cuff pressure Pc in the above BP-monitoring
period, and the cuff pressures Pmm.sub.m (m=1, 2, 3, . . . , k)
at which the pulse amplitudes Amm.sub.m are respectively detected,
are stored in an appropriate memory area of the RAM 30. Thus, the
appropriate memory area of the RAM 30 used at Step T8 corresponds
to the second memory 160.
Step T8 is followed by Step T9, i.e., abnormal BP change identification
routine corresponding to part of the BP-change identifying means
170. At Step T9, the CPU 28 judges whether the blood pressure of
the subject has been changed abnormally. The abnormal BP-change
identification routine of Step T9 will be described in detail by
reference to the flow chart of FIG. 28.
First, at Step T9-1 corresponding to part of the approximate-line
determining means 164, the CPU 28 determines an approximate line
L.sub.S which approximates a portion of the first relationship stored
in an appropriate memory area (i.e., first memory 158) of the RAM
30 which portion falls within a predetermined cuff-pressure range
not higher than the subject's mean blood pressure P.sub.MEAN, that
is, range between the subject's diastolic blood pressure P.sub.DIA
and the target pressure value P.sub.CH. The approximate line L.sub.S
approximates an envelope of the data points which represent the
cuff pressures Pms.sub.n falling within the above cuff-pressure
range and the corresponding pulse amplitudes Ams.sub.n. The CPU
28 determines, as the approximate line L.sub.S, a least-square approximate
line or a regression line based on the above data points. The approximate
line L.sub.S is employed as a center line of a pulse-amplitude window
W.sub.A.
At the following Step T9-2 corresponding to part of the pulse-amplitude
window-width calculating means 166, the CPU 28 calculates a width
H.sub.A of the pulse-amplitude window W.sub.A along the axis of
ordinate indicative of the pulse amplitude, in such a manner that
the upper and lower limits of the width or range H.sub.A are equal
to .+-.30% of the approximate line L.sub.S, respectively. The window
W.sub.A has respective halves of the width H.sub.A on the upper
and lower sides of the approximate line L.sub.S as the center line
thereof as shown in FIG. 26. At the following Step T9-3 corresponding
to part of the cuff-pressure window-width calculating means 168,
the CPU 28 calculates a width, Hp, of a cuff-pressure window W.sub.P
along the axis of abscissa indicative of the cuff pressure Pc, in
such a manner that the upper (right-hand) and lower (left-hand)
limits of the width or range Hp are equal to .+-.30% of the approximate
line L.sub.S, respectively. The window W.sub.P has respective halves
of the width Hp on the left-hand and right-hand sides of the approximate
line L.sub.S as the center line thereof as shown in FIG. 26. Broken
lines representing the upper and lower limits of the width H.sub.A,
i.e., pulse-amplitude window W.sub.A, are not parallel to the approximate
line L.sub.S, and similarly one-dot chain lines representing the
upper and lower limits of the width Hp, i.e., cuff-pressure window
W.sub.P, are not parallel to the approximate line L.sub.S.
Step T9-3 is followed by Step T9-4 to judge whether a proportion
of the data points falling within the pulse-amplitude window W.sub.A
out of the data points (indicated at symbols ".quadrature."
(white quadrangles) in FIG. 26) representing the pulse amplitudes
Amm.sub.m (m=1 to k) and cuff pressures Pmm.sub.m (m=1 to k) stored
in the appropriate memory area (i.e., second memory 160) of the
RAM 30, is not lower than a first reference value, A. At the following
Step T9-5, the CPU 28 judges whether a proportion of the data points
falling within the cuff-pressure window W.sub.P out of the same
data points is not lower than a second reference value, B. The reference
values A, B are employed to identify a change of the subject's blood
pressure and each value may be predetermined at 50%. In the present
embodiment, Steps T9-4 and T9-5 correspond to part of the deviation
identifying means 174.
If a positive judgment is made at either one of Steps T9-4 and
T9-5, the control of the CPU 28 goes to Step T9-6 to judge or identify
that the subject's blood pressure remains unchanged. On the other
hand, if a negative judgment is made at each of Steps T9-4 and T9-5,
the control goes to Step T9-7 to judge that the subject's blood
pressure has changed abnormally.
If at Step T9-6 the CPU 28 does not identify an abnormal BP change,
a negative judgment is made at Step T9 of FIG. 27, so that the control
goes to Step T10 to clear or reset the contents CT Of the timer
and then repeats Step T3 and the following steps. On the other hand,
if a positive judgment is made at Step T9, the control goes to Step
T11 to operate an output device 38 to inform the user of the identification
of the abnormal BP change, and operates the BP re-measuring device
72 to immediately start a BP measuring period and carry out a BP
measurement on the subject like at Step T1. This BP-measuring period
is shown at the right-hand end of FIG. 29. Thus, the output device
38 displays and/or records the subject's BP values measured immediately
after the identification of the abnormal BP change. Thus, Step T11
corresponds to part of the BP re-measuring device 72.
As is apparent from the foregoing description, in the second embodiment,
the pulse amplitudes Ams.sub.n are detected as the pressure oscillations
produced in the cuff 10 during the slowing decreasing of the cuff
pressure Pc, in a BP measurement carried out at Step T1 corresponding
to part of the BP measuring device 54, and the pulse amplitudes
Ams.sub.n and the cuff pressures Pms.sub.n detected at the respective
times of detection of the pulse amplitudes Ams.sub.n are stored
in the first memory 158. In addition, the pulse amplitudes Amm.sub.m
are detected during the slowing decreasing of the cuff pressure
Pc from the predetermined value P.sub.CH not higher than the mean
blood pressure P.sub.MEAN of the subject, in each of BP monitoring
periods following a BP measurement of the BP-measuring device 54,
and the pulse amplitudes Amm.sub.m and the cuff pressures Pmm.sub.m
detected at the respective times of detection of the pulse amplitudes
Amm.sub.m are stored in the second memory 160.
At Steps T9-1 and T9-2 corresponding to part of the pulse-amplitude
window determining means 162, the pulse-amplitude window W.sub.A
is determined based on the first relationship between the cuff pressures
Pms.sub.n and pulse amplitudes Ams.sub.n stored in the first memory
158. At Steps T9-1 and T9-3 corresponding to part of the cuff-pressure
window determining means 168, the cuff-pressure window W.sub.P is
determined based on the first relationship between the cuff pressures
Pms.sub.n and pulse amplitudes Ams.sub.n stored in the first memory
158. At Steps T9-4 and T9-5 corresponding to part of the deviation
identifying means 174, whether the subject's blood pressure has
changed or not is judged based on the data points falling within
the pulse-amplitude window W.sub.A or cuff-pressure window W.sub.P
out of all the data points representing the cuff pressures Pmm.sub.m
and pulse amplitudes Amm.sub.m stored in the second memory 160.
The second BP monitor can monitor the blood pressure of the subject
with high accuracy, because the apparatus identifies a change of
the subject's blood pressure based on both the pulse amplitudes
Ams.sub.n and cuff pressures Pms.sub.n obtained in a BP-measuring
period and the pulse amplitudes Amm.sub.m and cuff pressures Pmm.sub.m
obtained in a BP-monitoring period. In addition, since the BP monitor
monitors the subject's blood pressure by iteratively changing the
cuff pressure Pc within a low pressure range between the atmospheric
pressure and the pre-determined pressure value P.sub.CH lower than
the subject's mean blood pressure P.sub.MEAN, the apparatus does
not cause the subject to feel discomfort.
In the second embodiment, at Steps T9-4 and T9-5 corresponding
to part of the deviation identifying means 174, the BP monitor identifies
a change of the subject's blood pressure, when a proportion of the
data points falling within the pulse-amplitude window W.sub.A is
lower than the reference value A, and simultaneously when a proportion
of the data points falling within the cuff-pressure window W.sub.P
is lower than the reference value B. Thus, the present BP monitor
can monitor the subject's blood pressure with higher reliability.
Moreover, in the second embodiment, the pulse-amplitude window
determining means 162 or the cuff-pressure window determining means
168 includes an approximate-line determining means 164 for determining
an approximate line L.sub.S which approximates a portion of the
first relationship stored in the first memory 158 which portion
falls within a predetermined cuff-pressure range lower than the
pressure value P.sub.CH pre-determined to be not higher than the
subject's mean blood pressure P.sub.MEAN. The approximate-line determining
means 164 determines, as the approximate line L.sub.S, a least-square
approximate line or a regression line based on the data points which
represent the cuff pressures Pms.sub.n falling within the above
cuff-pressure range and the corresponding pulse amplitudes Ams.sub.n.
The approximate line L.sub.S is employed as a center line of the
pulse-amplitude window W.sub.A or cuff-pressure window W.sub.P.
Thus, the windows W.sub.A, W.sub.P are determined with accuracy.
If an abnormal BP change is identified by the BP-change identifying
means 172, the BP re-measuring device 72 immediately carries out
a BP measurement using the cuff 10, and outputs the BP values obtained
at the time of identification of the abnormal BP change. Thus, a
medical worker such as a doctor or a nurse can quickly give appropriate
treatments on a patient.
Next, there will be described a third embodiment of the present
invention. The third embodiment also relates to a BP monitor and
has the same hardware construction as that of the first embodiment
shown in FIG. 1. However, the third BP monitor is operated according
to a control program represented by the flow chart of FIG. 27 employed
in the second embodiment, and the flow chart of FIG. 31, in place
of the program represented by the flow charts of FIGS. 4 and 5 for
the first embodiment.
FIG. 30 shows various functions of a control device 26 of the third
BP monitor. The third BP monitor includes an inflatable cuff 10,
a cuff-pressure detecting device 50, a pulse-wave detecting device
52, an oscillometric BP measuring device 54, and a BP re-measuring
device 72 all of which are the same as the counterparts of the first
BP monitor shown in FIG. 2, and additionally includes a cuff-pressure
control device 156 which is the same as the counterpart of the second
BP monitor shown in FIG. 23.
A BP-change identifying means 280 identifies a change of subject's
blood pressure based on a first relationship (FIG. 24) between cuff
pressures Pms.sub.n and pulse amplitudes Ams.sub.n which are obtained
in a BP-measuring period of the BP-measuring device 54 and are stored
in a first memory 258 and based on a second relationship (FIG. 25)
between cuff pressures Pmm.sub.m and pulse amplitudes Amm.sub.m
which are obtained in a BP-monitoring period of the cuff-pressure
control device 156 and are stored in a second memory 260. More specifically
described, the BP-changing identifying means 280 includes the first
and second memories 258, 260, an area calculating means 282, a deviation
identifying means 284, a BP-increase identifying means 286, and
a BP-decrease identifying means 288.
The area calculating means 282 calculates an area, S (=SA+SB),
which is bounded by a first line representing the first relationship
between the cuff pressures Pms.sub.n and pulse amplitudes Ams.sub.n
stored in the first memory 258, and a second line representing the
second relationship between the cuff pressures Pmm.sub.m and pulse
amplitudes Amm.sub.m stored in the second memory 260, within a range,
R, of the cuff pressure Pc which is predetermined to be not higher
than subject's mean blood pressure P.sub.MEAN (e.g., range between
subject's diastolic blood pressure P.sub.DIA and the target pressure
value P.sub.CH, or range between subject's diastolic and mean blood
pressures P.sub.DIA and P.sub.MEAN). The first line is a portion
of an envelope of the pulse amplitudes Ams.sub.n which portion falls
within the cuff-pressure range R, and the second line is a portion
of an envelope of the pulse amplitudes Ams.sub.n which portion falls
within the cuff-pressure range R. More specifically, the area calculating
means 282 calculates a first area, S.sub.A, which is bounded by
a first portion of the first line and a first portion of the second
line which is greater than the first portion of the first line with
respect to the pulse amplitude, and a second area, S.sub.B, which
is bounded by a second portion of the first line and a second portion
of the second line which is smaller than the second portion of the
first line with respect to the pulse amplitude. In FIGS. 32, 33,
and 34, the first line is indicated at solid line and the second
line is indicated at broken line.
The deviation identifying means 284 identifies a deviation of the
second relationship from the first relationship, based on the area
S and the first and second areas S.sub.A, S.sub.B each calculated
by the area calculating means 282. The BP-change identifying means
280 identifies a change of the subject's blood pressure when the
deviation identifying means 284 identifies the deviation of the
second relationship from the first relationship. More specifically,
the blood-pressure-increase identifying means 286 identifies an
increase of the subject's blood pressure when the area S is not
smaller than a reference value, S.sub.O, and simultaneously when
the first area S.sub.A is smaller than the second area S.sub.B,
and the blood-pressure-decrease identifying means 288 identifies
a decrease of the subject's blood pressure when the area S is not
smaller than the reference value S.sub.O and simultaneously when
the first area S.sub.A is not smaller than the second area S.sub.B.
FIG. 31 shows an abnormal BP change identifying routine which is
carried out at Step T9 of the flow chart of FIG. 27 by a control
device 26 of the third BP monitor. At Step T9-11, a CPU 28 of the
control device 26 calculates the first and second areas S.sub.A,
S.sub.B based on the data stored in the first and second memories
258, 260. At Step T9-12, the CPU 28 adds the first and second areas
S.sub.A, S.sub.B to each other, thereby providing the area S (=S.sub.A+S.sub.B)
which is bounded by the first line representing the first relationship
between the cuff pressures Pms.sub.n and pulse amplitudes Ams.sub.n
stored in the first memory 258 and the second line representing
the second relationship between the cuff pressures Pmm.sub.m and
pulse amplitudes Amm.sub.m stored in the second memory 260, within
the cuff-pressure range R pre-determined to be not higher than the
subject's mean blood pressure P.sub.MEAN. In the present embodiment,
Steps T9-11 and T9-12 correspond to part of the area calculating
means 282.
At Step T9-13 corresponding to part of the deviation identifying
means 284, the CPU 28 judges whether the area S is not smaller than
the reference value S.sub.O which is pre-determined based on experimental
results to identify an abnormal change of human beings' blood pressure.
If a negative judgment is made at Step T9-13, the control of the
CPU 28 goes to Step T9-14 and judges that the subject's blood pressure
has not changed. FIG. 32 shows the case where the deviation of the
second line indicated at broken line from the first line indicated
at solid line is small in a normal range.
On the other hand, if a positive judgment is made at Step T9-13,
the control of the CPU 28 goes to Step T9-15 to judge whether the
first area S.sub.A is not smaller than the second area S.sub.B.
If a negative judgment is made at Step T9-15, the control goes to
Step T9-16 corresponding to part of the BP-increase identifying
means 286 and judges that the subject's blood pressure has increased
abnormally. FIG. 33 shows the case where the second line is largely
deviated from the first line and the second area S.sub.B is greater
than the first area S.sub.A. On the other hand, if a positive judgment
is made at Step T9-15, the control goes to Step T9-17 corresponding
to part of the BP-decrease identifying means 288 and judges that
the subject's blood pressure has decreased abnormally. FIG. 34 shows |