Abstrict
A blood-pressure monitor, including a blood-pressure measuring
device including a cuff, an information obtaining device which iteratively
obtains, from a living subject, physical information which changes
with change of blood pressure of the subject, a measurement starting
device for starting a measurement of the blood-pressure measuring
device, when a subsequent piece of information obtained by the obtaining
device after the measuring device has measured a last blood pressure
of the subject in a last measurement thereof has been deviated by
not less than a predetermined amount from an initial piece of information
obtained by the obtaining device when the measuring device measured
the last blood pressure of the subject, a display device which displays
a graph representing the pieces of information obtained by the obtaining
device, and a control device which controls the display device to
display the graph representing the initial piece of information
and each one of subsequent pieces of information iteratively obtained
by the obtaining device after the measuring device has measured
the last blood pressure of the subject, so that the initial piece
of information and the each one subsequent piece of information
can be compared with each other.
Claims
What is claimed is:
1. A blood-pressure monitor apparatus, comprising:
a blood-pressure measuring device which includes an inflatable
cuff adapted to apply a pressing pressure to a portion of a living
subject and which measures a blood pressure of the subject by changing
the pressure of the cuff applied to said portion of the subject;
a blood-pressure-relating-information obtaining device which iteratively
obtains, from the living subject, blood-pressure-relating information
which changes with change of the blood pressure of the subject;
a blood-pressure-measurement starting means for starting a blood-pressure
measurement of the blood-pressure measuring device, when a subsequent
piece of blood-pressure-relating information obtained by the blood-pressure-relating-information
obtaining device after the blood-pressure measuring device has measured
a last blood pressure of the living subject in a last blood pressure
measurement thereof has deviated by not less than a predetermined
amount from an initial piece of blood-pressure-relating information
obtained by the obtaining device when the blood-pressure measuring
device measured the last blood pressure of the subject;
a display device which displays a graph representing the pieces
of blood-pressure-relating information obtained by the blood-pressure-relating-information
obtaining device; and
a control device which comprises a determining means for determining
a proportion of an amount of change, from said initial piece of
blood-pressure-relating information, of each one of subsequent pieces
of blood-pressure-relating information iteratively obtained by the
obtaining device after the blood-pressure measuring device has measured
the last blood pressure of the subject; and a control means for
controlling the display device to display the graph representing
the initial piece of blood-pressure-relating information and the
determined proportion of the amount of change of said each one of
subsequent pieces of blood-pressure-relating information, so that
the initial piece of blood-pressure-relating information and the
determined proportion of the amount of change of said each one subsequent
piece of blood-pressure-relating information can be compared with
each other on the display device.
2. An apparatus according to claim 1, wherein the blood-pressure-relating
information obtaining device comprises a first obtaining means for
iteratively obtaining, from the living subject, a first sort of
blood-pressure-relating information which changes with change of
the blood pressure of the subject; a second obtaining means for
iteratively obtaining, from the living subject, a second sort of
blood-pressure-relating information which changes with change of
the blood pressure of the subject; and a third obtaining means for
iteratively obtaining, from the living subject, a third sort of
blood-pressure-relating information which changes with change of
the blood pressure of the subject.
3. An apparatus according to claim 2, wherein the determining means
determines a proportion of an amount of change of each one of subsequent
pieces of each of the first, second, and third sorts of blood-pressure-relating
information iteratively obtained by the first, second, and third
obtaining means after the blood-pressure measuring device has measured
the last blood pressure of the subject, from an initial piece of
a corresponding one of the first, second, and third sorts of blood-pressure-relating
information obtained by the first, second, and third obtaining means
when the blood-pressure measuring device has measured the last blood
pressure, and the control means controls the display device to display
the graph representing the respective initial pieces of the first,
second, and third sorts of blood-pressure-relating information and
the respective determined proportions of respective amounts of change
of the respective subsequent pieces of the first, second, and third
sorts of blood-pressure-relating information, so that each of the
respective initial pieces of the first, second, and third sorts
of blood-pressure-relating information and a corresponding one of
the respective determined proportions of respective amounts of change
of the respective subsequent pieces of the first, second, and third
blood-pressure-relating information can be compared with each other
on the display device.
4. An apparatus according to claim 3, wherein the display device
comprises means for displaying the graph in a radar chart which
is defined by three axes which intersect one another at a common
origin and which represent respective proportions of respective
amounts of change of respective subsequent pieces of the first,
second, and third sorts of blood-pressure-relating information,
the graph comprising a reference triangle having three apexes representing
the respective initial pieces of the first, second, and third sorts
of blood-pressure-relating information; and a change-proportion
triangle having three apexes representing the respective determined
proportions of respective amounts of change of the respective subsequent
pieces of the first, second, and third sorts of blood-pressure-relating
information.
5. An apparatus according to claim 1, wherein the blood-pressure-relating
information obtaining device comprises means for obtaining, as the
blood-pressure-relating information, at least one of a pulse period
and a pulse area from the subject.
6. A blood-pressure monitor apparatus, comprising:
a blood-pressure measuring device which includes an inflatable
cuff adapted to apply a pressing pressure to a portion of a living
subject and which measures a blood pressure of the subject by changing
the pressure of the cuff applied to said portion of the subject;
a blood-pressure-relating-information obtaining device which iteratively
obtains, from the living subject, blood-pressure-relating information
which changes with change of the blood pressure of the subject;
a blood-pressure-measurement starting means for starting a blood-pressure
measurement of the blood-pressure measuring device, when a subsequent
piece of blood-pressure-relating information obtained by the blood-pressure-relating-information
obtaining device after the blood-pressure measuring device has measured
a last blood pressure of the living subject in a last blood pressure
measurement thereof has deviated by not less than a predetermined
amount from an initial piece of blood-pressure-relating information
obtained by the obtaining device when the blood-pressure measuring
device measured the last blood pressure of the subject;
a display device which displays a graph representing the pieces
of blood-pressure-relating information obtained by the blood-pressure-relating-information
obtaining device; and
a control device which comprises a determining means for determining
a proportion of an amount of change, from said initial piece of
blood-pressure-relating information of a most deviated one of subsequent
pieces of blood-pressure-relating information iteratively obtained
by the obtaining device after the blood-pressure measuring device
has measured the last blood pressure of the subject; and a control
means for controlling the display device to display the graph representing
the initial piece of blood-pressure-relating information and the
determined proportion of the amount of change of said most deviated
one of subsequent pieces of blood-pressure-relating information,
so that the initial piece of blood-pressure-relating information
and the determined proportion of amount of the change of said most
deviated subsequent piece of blood-pressure-relating information
can be compared with each other on the display device, said most
deviated subsequent piece of blood-pressure-relating information
being more deviated from the initial piece of blood-pressure-relating
information, than any other subsequent piece of blood-pressure-relating
information.
7. An apparatus according to claim 6, wherein the determining means
determines a proportion of an amount of change, from said initial
piece of blood-pressure-relating information, of each one of subsequent
pieces of blood-pressure-relating information iteratively obtained
by the obtaining device after the blood-pressure measuring device
has measured the last blood pressure of the subject, and wherein
the display device comprises a display means for displaying, in
a two-dimensional coordinate system which is defined by a first
axis representing time and a second axis representing proportion
of amount of change of each one of subsequent pieces of blood-pressure-relating
information, the graph comprising a symbol representing the determined
proportion of the amount of change of said each one of subsequent
piece of blood-pressure-relating information.
8. An apparatus according to claim 7, wherein the display means
displays, in the two-dimensional coordinate system, the graph comprising
a reference line which represents the last blood pressure of the
subject and which extends parallel to the first axis and intersects
the second axis at a reference point, 0%, representing the initial
piece of blood-pressure-relating information.
9. An apparatus according to claim 7, wherein the blood-pressure
measuring device comprises means for measuring a blood pressure
of the subject at a predetermined blood-pressure-measurement period,
and wherein the display means displays the graph in the two-dimensional
coordinate system having the first axis having a length corresponding
to the predetermined blood-pressure-measurement period.
10. An apparatus according to claim 7, wherein the display means
displays the graph in the two-dimensional coordinate system having
the second axis having a length corresponding to said predetermined
amount, so that the blood-pressure-measurement starting means starts
a blood-pressure measurement of the blood-pressure measuring device,
when the determined proportion of the amount of change of one of
the subsequent pieces of blood-pressure-relating information is
deviated by not less than the predetermined amount from the initial
piece of blood-pressure-relating information and does not fall in
the two-dimensional coordinate system.
Description BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a blood-pressure monitor apparatus
which monitors the chance of blood pressure of a living subject,
based on blood-pressure-relating information which changes in relation
with the change of blood pressure of the subject.
2. Related Art Statement
As a pulse-wave-propagation-velocity ("PWPV") relating
information which relates to a velocity at which a pulse wave propagates
through an artery of a living subject, there is known a propagation
time, DT, in which the pulse wave propagates between two different
portions of the artery, or the propagation velocity, V.sub.M, (m/s)
itself. It is known that the PWPV-relating information has, within
a certain range, a substantially proportional relationship with
the blood pressure, BP, (mmHg) of the living subject. Hence, there
has been proposed a blood-pressure ("BP") monitor apparatus
which determines, in advance, unknown coefficients, .alpha. and
.beta., of a linear expression, EBP=.alpha.(DT)+.beta. (.alpha.
is a negative constant), or EBP=.alpha.(V.sub.C)+.beta. (.alpha.
is a positive constant), based on subject's BP value, BP, and a
piece of PWPV-relating information (DT or V.sub.M) both of which
are measured in advance, and then determines, according to the thus
determined linear expression, an estimated BP value, EBP, of the
subject based on each one of pieces of PWPV-relating information
iteratively obtained after the last BP measurement using a cuff.
Thus, the BP monitor apparatus can monitor the blood pressure of
the subject. If one of the estimated BP values EBP iteratively determined
after the last BP measurement has largely deviated from the estimated
BP value at the time of the last BP measurement, the BP monitor
apparatus starts a BP measurement using the cuff.
Meanwhile, it is known that the blood pressure of a living subject
is regulated by the cardiac output (1/min), and the peripheral vascular
resistance, of the subject. More specifically described, as the
cardiac output increases, the blood pressure increases; and as the
cardiac output decreases, the blood pressure decreases. As the peripheral
vascular resistance increases, that is, the peripheral blood vessels
contract, the blood pressure increases; and as the peripheral vascular
resistance decreases, that is, the peripheral blood vessels expand,
the blood pressure decreases. The cardiac output is obtained as
the product of stroke volume (i.e., volume of blood Output from
the heart per stroke or beat) and heart rate. Therefore, heart-rate-relating
information which relates to heart rate, such as heart (pulse) rate
itself, or pulse period, changes with the change of the blood pressure.
In addition, as the peripheral vascular resistance increases, i.e.,
the peripheral blood vessels contract, the area enveloped by the
waveform of each of heartbeat-synchronous pulses of a peripheral
pulse wave detected from subject's peripheral portion, decreases.
Thus, the area of each pulse of the peripheral pulse wave is influenced
by the change of the peripheral vascular resistance. That is, the
area of each pulse of the peripheral pulse wave changes with the
change of the blood pressure. These phenomena are utilized by another
BP monitor apparatus which starts a BP measurement using a cuff
if one of pieces of pulse-rate-relating information iteratively
obtained, or one of pulse areas iteratively obtained, after the
last BP measurement using the cuff has deviated by not less than
a predetermined amount from the piece of pulse-rate-relating information,
or the pulse area, at the time of the last BP measurement. An example
of this BP monitor apparatus is disclosed in Japanese Patent Publication
No. 10-43147 and the corresponding U.S. Pat. No. 5,752,920.
However, the conventional BP monitor apparatuses do not display
any piece of BP-relating information, or display only the current
one of pieces of BP-relating information iteratively obtained after
the last BP measurement using the cuff. Therefore, a person such
as the subject as a patient or a medical staff who attends the patient
cannot judge, from the screen image displayed by each conventional
monitor apparatus, that the patient's current condition is not at
a critical level which needs a BP measurement using the cuff, but
is near to that level, or that the patient's current condition has
not changed so much from his or her condition at the time of the
last BP measurement. In addition, regarding the conventional BP
monitor apparatus which displays only the current one of pieces
of BP-relating information iteratively obtained after the last BP
measurement, it may be difficult for a person to select an appropriate
threshold value, relative to the piece of BP-relating information
at the time of the last BP measurement, that is used in judging
whether the current piece of BP-relating information is abnormal,
that is, whether a BP measurement using the cuff is needed.
In addition, the relationship between subject's blood pressure
and PWPV-relating information changes because it is influenced by
the condition of subject's central body portion, such as the condition
of cardiac muscle, and the condition of subject's peripheral body
portion, such as the hardness of peripheral blood vessels or the
resistance to blood flows. Therefore, in the BP monitor apparatus
disclosed in the above-indicated Japanese Patent Publication No.
10-43147 (and the U.S. Pat. No. 5,752,920), the heart-rate-relating
information is used as the central-side information, the area of
each pulse of the peripheral pulse wave is used as the peripheral-side
information and, if the current PWPV-relating information (or the
current estimated BP value determined based on the current PWPV-relating
information) has changed by not less than a predetermined amount
from the PWPV-relating information (or the estimated BP value) at
the time of the last BP measurement and simultaneously if the heart-rate-relating
information and/or the area of each pulse of the peripheral pulse
wave has changed by not less than a predetermined amount from the
heart-rate-relating information and/or the area of one pulse of
the peripheral pulse wave at the time of the last BP measurement,
a BP measurement using the cuff is started.
However, in the above conventional BP monitor apparatus which uses
plural sorts of BP-relating information in judging whether a BP
measurement should be started, no pieces of BP-relating information
of each sort are displayed, or only the current one of pieces of
BP-relating information of each sort, iteratively obtained after
the last BP measurement, or a time-wise change of the pieces of
BP-relating information of each sort is displayed. Therefore, it
is more difficult for a person to judge, from the screen image displayed
by the BP monitor apparatus, that the patient's current condition
is not at a critical level which needs a BP measurement using the
cuff, but is near to that level, or that the patient's current condition
has not changed so much from his or her condition at the time of
the last BP measurement, than to judge, based on a single sort of
BP-relating information, whether a BP measurement should be started.
In addition, even when the BP monitor apparatus may start a BP measurement
using the cuff, the display device of the apparatus informs only
that the abnormality of BP-relating information has occurred, and
does not inform which sort of BP-relating information has become
abnormal. For example, in the case of the BP monitor apparatus which
starts a BP measurement using the cuff if the current PWPV-relating
information has changed by not less than a predetermined amount
from the PWPV-relating information at the time of the last BP measurement
and simultaneously if the heart-rate-relating information and/or
the area of each pulse of the peripheral pulse wave has changed
by not less than a predetermined amount from the heart-rate-relating
information and/or the area of one pulse of the peripheral pulse
wave at the time of the last BP measurement, a person cannot judge
whether the PWPV-relating information and the heart-rate-relating
information have largely changed, whether the PWPV-relating information
and the area of each pulse of the peripheral pulse wave have largely
changed, or whether all of the PWPV-relating information, the heart-rate-relating
information, and the area of each pulse of the peripheral pulse
wave have largely changed.
Moreover, in the above conventional BP monitor apparatus, since
plural sorts of BP-relating information are employed in judging
whether a BP measurement should be started, a person has a high
degree of freedom in selecting respective threshold values which
are used in judging whether a BP measurement should be started.
Thus, it is more difficult for a person to select, for each of the
plural sorts of BP-relating information, an appropriate threshold
value, relative to the piece of BP-relating information of the each
sort at the time of the last BP measurement, that is used in judging
whether a BP measurement using the cuff should be started, than
to select, for a single sort of BP-relating information, an appropriate
threshold value to be used in judging whether a BP measurement should
be started.
SUMMARY OF INVENTION
It is therefore an object of the present invention to provide a
blood-pressure monitor apparatus which monitors the change of blood
pressure of a living subject, based on the blood-pressure-relating
information which changes in relation with the change of blood pressure
of the subject, and which enables a person to recognize to what
degree the current piece of blood-pressure-relating information
has deviated from the piece of blood-pressure-relating information
at the time of the last blood pressure measurement.
The above object may be achieved according to a first feature of
the present invention, which provides a blood-pressure monitor apparatus,
comprising a blood-pressure measuring device which includes an inflatable
cuff adapted to apply a pressing pressure to a portion of a living
subject and which measures a blood pressure of the subject by changing
the pressure of the cuff applied to the portion of the subject;
a blood-pressure-elating-information obtaining device which iteratively
obtains, from the living subject, blood-pressure-relating information
which changes with change of the blood pressure of the subject;
a blood-pressure-measurement starting means for starting a blood-pressure
measurement of the blood-pressure measuring device, when a subsequent
piece of blood-pressure-relating information obtained by the blood-pressure-relating-information
obtaining device after the blood-pressure measuring device has measured
a last blood pressure of the living subject in a last blood pressure
measurement thereof has deviated by not less than a predetermined
amount from an initial piece of blood-pressure-relating information
obtained by the obtaining device when the blood-pressure measuring
device measured the last blood pressure of the subject; a display
device which displays a graph representing the pieces of blood-pressure-relating
information obtained by the blood-pressure-relating-information
obtaining device; and a control device which controls the display
device to display the graph representing the initial piece of blood-pressure-relating
information and each one of subsequent pieces of blood-pressure-relating
information iteratively obtained by the obtaining device after the
blood-pressure measuring device has measured the last blood pressure
of the subject, so that the initial piece of blood-pressure-relating
information and the each one subsequent piece of blood-pressure-relating
information can be compared with each other on the display device.
The present BP monitor apparatus displays, on the display device,
the graph representing the initial piece of blood-pressure-relating
information at the time when the blood-pressure measuring device
measured the last blood pressure of the subject, and each one of
subsequent pieces of blood-pressure-relating information iteratively
obtained by the obtaining device after the blood-pressure measuring
device has measured the last blood pressure of the subject, so that
the initial piece of blood-pressure-relating information and the
each one subsequent piece of blood-pressure-relating information
can be compared with each other on the display device. Thus, a person
such as the living subject (e.g. a patient) or a medical staff can
recognize, from the graph, to what degree each subsequent piece
of blood-pressure-relating information has deviated from the initial
piece of blood-pressure-relating information at the time of the
last blood pressure measurement.
The above object may be achieved according to a second feature
of the present invention, which provides a blood-pressure monitor
apparatus, comprising a blood-pressure measuring device which includes
an inflatable cuff adapted to apply a pressing pressure to a portion
of a living subject and which measures a blood pressure of the subject
by changing the pressure of the cuff applied to the portion of the
subject; a blood-pressure-relating-information obtaining device
which iteratively obtains, from the living subject, blood-pressure-relating
information which changes with change of the blood pressure of the
subject; a blood-pressure-measurement starting means for starting
a blood-pressure measurement of the blood-pressure measuring device,
when a subsequent piece of blood-pressure-relating information obtained
by the blood-pressure-relating-information obtaining device after
the blood-pressure measuring device has measured a last blood pressure
of the living subject in a last blood pressure measurement thereof
has deviated by not less than a predetermined amount from an initial
piece of blood-pressure-relating information obtained by the obtaining
device when the blood-pressure measuring device measured the last
blood pressure of the subject; a display device which displays a
graph representing the pieces of blood-pressure-relating information
obtained by the blood-pressure-relating-information obtaining device;
and a control device which controls the display device to display
the graph representing the initial piece of blood-pressure-relating
information and a most deviated one of subsequent pieces of blood-pressure-relating
information iteratively obtained by the obtaining device after the
blood-pressure measuring device has measured the last blood pressure
of the subject, so that the initial piece of blood-pressure-relating
information and the most deviated subsequent piece of blood-pressure-relating
information can be compared with each other on the display device,
the most deviated subsequent piece of blood-pressure-relating information
being most deviated from the initial piece of blood-pressure-relating
information, than any other subsequent piece of blood-pressure-relating
information.
The present BP monitor apparatus displays, on the display device,
the graph representing the initial piece of blood-pressure-relating
information at the time when the blood-pressure measuring device
measured the last blood pressure of the subject, and the most deviated
one of the subsequent pieces of blood-pressure-relating information
iteratively obtained by the obtaining device after the blood-pressure
measuring device has measured the last blood pressure of the subject,
so that the initial piece of blood-pressure-relating information
and the most deviated subsequent piece of blood-pressure-relating
information can be compared with each other on the display device.
Thus, a person can recognize, from the graph, to what degree the
most deviated subsequent piece of blood-pressure-relating information
has deviated from the initial piece of blood-pressure-relating information
at the time of the last blood pressure measurement.
BRIEF DESCRIPTION OF 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 of a circuit arrangement of a blood-pressure
(BP) monitor apparatus embodying the present invention,
FIG. 2 is a diagrammatic view for explaining important control
functions of an electronic control device 28 of the BP monitor apparatus;
FIG. 3 is a view for explaining a manner in which the control device
28 determines a time difference, DT.sub.RP ;
FIG. 4 is a view for explaining a manner in which the control device
28 determines a normalized pulse area, VR;
FIG. 5 is a view for explaining reference BP-relating information
and actual BP-relating information which are displayed on a display
device 32 and are compared with each other by the control device
28 to judge whether a BP measurement using a cuff 10 is to be started;
FIG. 6 is a flow chart representing a BP monitor routine which
is carried out by the control device 28 to control the BP monitor
apparatus;
FIG. 7 is a flow chart representing a BP-measurement-start judging
routine which is carried out at Step SA12 of FIG. 6 by the control
device 28;
FIG. 8 is a view showing respective proportions of respective amounts
of change of an estimated BP value, EBP, a pulse period, RR, and
a pulse area, VR, that are displayed, in place of a radar chart
98 (FIG. 5), in a BP-relating-information display area 96 of a display
screen 94 of a display device 32 which is employed in another BP
monitor apparatus as a second embodiment of the present invention;
FIG. 9 is a view showing respective proportions of respective amounts
of change of an estimated BP value EBP, a pulse period RR, and a
pulse area VR that are displayed, in place of the radar chart 98
(FIG. 5), in a BP-relating-information display area 96 of a display
screen 94 of a display device 32 which is employed in another BP
monitor apparatus as a third embodiment of the present invention;
FIG. 10 is a view showing a proportion of an amount of change of
a pulse area VR that is displayed, in place of the radar chart 98
(FIG. 5), in a BP-relating-information display area 96 of a display
screen 94 of a display device 32 which is employed in another BP
monitor apparatus as a fourth embodiment of the present invention;
FIG. 11 is a view showing a proportion of an amount of change of
an estimated BP value EBP that is displayed, in place of the radar
chart 98 (FIG. 5), in a BP-relating-information display area 96
of a display screen 94 of a display device 32 which is employed
in another BP monitor apparatus as a fifth embodiment of the present
invention;
FIGS. 12A, 12B, and 12C are views showing respective proportions
of respective amounts of change of estimated BP values EBP each
of which is displayed, in place of the radar chart 98 (FIG. 5),
in a BP-relating-information display area 96 of a display screen
94 of a display device 32 which is employed in another BP monitor
apparatus as a sixth embodiment of the present invention;
FIG. 13 is a view showing a proportion of an amount of change of
an estimated BP values EBP that is displayed, in place of the radar
chart 98 (FIG. 5), in a BP-relating-information display area 96
of a display screen 94 of a display device 32 which is employed
in another BP monitor apparatus as a seventh embodiment of the present
invention; and
FIG. 14 is a view showing the greatest one of respective proportions
of respective amounts of change of estimated BP values EBP that
is displayed, in place of a two-dimensional coordinate system defined
by two axes 108, 110 (FIG. 5), in a maximum-change display area
106 of a display screen 94 of a display device 32 which is employed
in another BP monitor apparatus as an eighth embodiment of the present
invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Hereinafter, there will be described a blood-pressure ("BP")
monitor apparatus 8 embodying the present invention, by reference
to FIGS. 1 to 7.
In FIG. 1, the BP monitor apparatus 8 includes a cuff 10 which
includes a rubber bag and a belt-like cloth bag in which the rubber
bag is accommodated. The cuff 10 is wound around, e.g., an upper
arm 12 of a patient as a living subject. The monitor apparatus 8
additionally includes a pressure sensor 14, a switch valve 16, and
an air pump 18 which are connected to the cuff 10 via piping 20.
The switch valve 16 is selectively placed in three states, that
is, a pressure-supply state in which the valve 16 allows pressurized
air to be supplied from the air pump 18 to the cuff 10, a slow-deflation
state in which the valve 16 allows the pressurized air to be slowly
deflated from the cuff 10, and a quick-deflation state in which
the valve 16 allows the pressurized air to be quickly deflated from
the cuff 10.
The pressure sensor 14 detects an air pressure in the cuff 10,
and supplies a pressure signal, SP, representing the detected pressure,
to a static-pressure filter circuit 22 and a pulse-wave filter circuit
24. The static-pressure filter circuit 22 includes a low-pass filter
which selects, from the pressure signal SP, a cuff-pressure signal,
SK, representing a static pressure contained in the pressure represented
by the pressure signal SP. The cuff-pressure signal SK is supplied
to an electronic control device 28 via an analog-to-digital converter
("A/D") converter 26. The pulse-wave filter circuit 24
includes a band-pass filter which selects, from the pressure signal
SP, a pulse-wave signal, SM.sub.1, representing oscillatory components
contained in the pressure represented by the pressure signal SP,
that is, a cuff pulse wave produced in the cuff 10. The pulse-wave
signal SM.sub.1, is supplied to the control device 28 via an A/D
converter 30. The cuff pulse wave represented by the pulse-wave
signal SM1 is an oscillatory pressure wave that is produced from
a brachial artery (not shown) of the patient in synchronism with
the heartbeat of the patient and is transmitted to the cuff 10 worn
on the upper arm 12 of the patient.
The control device 28 is provided by a microcomputer including
a central processing unit ("CPU") 29, a read only memory
("ROM") 31, a random access memory ("RAM") 33,
and an I/O port (not shown). The CPU 29 processes, according to
control programs pre-stored in the ROM 31, input signals while utilizing
a temporary-storage function of the RAM 33, and outputs, via the
I/O port, drive signals to the switch valve 16 and the air pump
18 to control the same 16, 18.
An electrocardiograph ("ECG") device 34 includes a plurality
of electrodes 36 which are put on predetermined locations on the
patient, and continuously detects, through the electrodes 36, an
electrocardiogram ("ECG") waveform representing action
potential of the cardiac muscle of the patient. The ECG device 34
supplies an ECG signal, SM.sub.2, representing the ECG waveform,
to the control device 28. The ECG waveform represented by the ECG
signal SM.sub.2 includes a Q-wave or an R-wave representing a time
when the heart of the patient starts outputting blood toward the
aorta. Thus, the ECG device 34 functions as a central or first pulse-wave
detecting device.
A photoelectric-pulse-wave detecting probe 38 is for use in blood-oxygen-saturation
measurements. The probe 38 detects, in the form of a photoelectric
pulse wave, a pulse wave transmitted to a peripheral artery including
capillaries. Thus, the probe 38 functions as a peripheral or second
pulse-wave detecting device. For example, the probe 38 is held in
close contact with a body surface (i.e., skin) 40 of a portion (e.g.,
finger) of the patient, with the help of a fastening band (not shown).
The probe 38 includes a housing 42, a plurality of first light-emitting
elements 44a, a plurality of second light-emitting elements 44b,
a light-receiving element 46, a transparent resin 48, and an annular
light-shield member 50. The housing 42 has a container-like cylindrical
shape with a circular bottom wall and a circular opening. The first
and second light-emitting elements 44a, 44b are supported by a radially
outer portion of the circular bottom wall of the housing 42, such
that the first and second elements 44a, 44b are alternate with each
other in the circumferential direction of the circular bottom wall.
The elements 44a, 44b are provided by, e.g., light-emitting diodes
("LEDs"). Hereinafter, the first and second light-emitting
elements 44a, 44b will be referred to as the light-emitting elements
44, in the case where it is not necessary to distinguish the first
and second elements 44a, 44b from each other. The light-receiving
element 46 is supported by a central portion of the circular bottom
wall of the housing 42, and is provided by, e.g., a photodiode or
a phototransistor. The transparent resin 48 completely fills an
inner space of the housing 42 to cover the light-emitting elements
44 and the light-receiving element 46. The annular light-shield
member 50 is provided, in the housing 42, between the light-emitting
elements 44 and the light-receiving element 46, and prevents the
light emitted from the light-emitting elements 44 and reflected
from the body surface 40, from being incident to the light-receiving
element 46. Thus, the light-shield member 50 assures that the light
emitted from the light-emitting elements 44 and reflected from the
tissue (e.g., capillaries) under the body surface 40 are incident
to the light-receiving element 46.
The first light-emitting elements 44a emit a red light having,
e.g., a 660 nm wavelength, and the second light-emitting elements
44b emit an infrared light having, e.g., an 800 nm wavelength. The
first and second light-emitting elements 44a, 44b alternately emit
the red light and the infrared light, each for a predetermined time
duration, at a predetermined frequency. The respective lights emitted
from the light-emitting elements 44 and reflected from the capillaries
of the tissue under the body surface 40 are received by the common
light-receiving element 46. The first and second light-emitting
elements 44a, 44b may emit respective lights whose wavelengths are
different from the above-indicated wavelengths, so long as oxygenated
hemoglobin and reduced hemoglobin exhibit largely different absorption
constants with respect to the red light emitted by the first elements
44a, and exhibit a substantially same absorption constant with respect
to the infrared light emitted by the second elements 44b, i.e.,
both reflect the infrared light.
The light-receiving element 46 outputs, to a low-pass filter 52,
a photoelectric-pulse-wave signal, SM.sub.3, representing the amount
of light received thereby. An amplifier may be provided, as needed,
between the element 46 and the low-pass filter 52. The low-pass
filter 52 removes, from the photoelectric-pulse-wave signal SM.sub.3,
noise having higher frequencies than that of the pulse wave, and
supplies the filtered signal SM.sub.3 to a demultiplexer 54. The
photoelectric pulse wave represented by the photoelectric-pulse-wave
signal SM.sub.3 is a volumetric pulse wave that is produced in synchronism
with the heartbeat of the patient.
The demultiplexer 54 is switched, in response to switch signals
supplied from the control device 28, in synchronism with the alternate
light emissions of the first and second light-emitting elements
44a, 44b, so that the demultiplexer 54 supplies an electric signal,
SM.sub.R, representing the red light, to the I/O port of the control
device 28 via a sample-hold circuit 56 and an A/D converter 58,
and supplies an electric signal, SM.sub.IR, representing the infrared
light, to the I/O port of the control device 28 via a sample-hold
circuit 60 and an A/D converter 62. The sample-hold circuits 56,
60 hold or keep the electric signals SM.sub.R, SM.sub.IR input thereto,
until the A/D converters 58, 62 finish the conversions of the prior
electric signals SM.sub.R, SM.sub.IR.
The CPU 29 of the control device 28 carries out, according to the
control programs pre-stored in the ROM 31, a measuring operation
while utilizing the temporary-storage function of the RAM 33. More
specifically described, the control device 28 outputs a control
signal to a drive circuit 64 to cause the first and second light-emitting
elements 44a, 44b to alternately emit the red and infrared lights
at the predetermined frequency, each for the predetermined time
duration, and outputs a switch signal to the demultiplexer 54 in
synchronism with the alternate light emissions of the first and
second elements 44a, 44b. Thus, the electric signal SM.sub.R is
supplied to the sample-hold circuit 56, and the electric signal
SM.sub.IR is supplied to the sample-hold circuit 60. The CPU 29
calculates a blood oxygen saturation of the patient based on respective
magnitudes of the electric signals SM.sub.R, SM.sub.IR according
to a mathematical expression which is pre-stored in the ROM 31.
Since this process is well known in the art, no description is provided
here.
The BP monitor apparatus 8 additionally includes a display device
32 which is provided by a cathode ray tube ("CRT") or
a liquid crystal display ("LCD") and which is connected
to the I/O port of the control device 28.
FIG. 2 shows various control functions of the electronic control
device 28 of the BP monitor apparatus 8. In FIG. 2, a cuff-pressure
control means 72 quickly increases the pressing pressure of the
cuff 10 wound around the upper arm 12 of the patient, up to a predetermined
target pressure value, PCM, (e.g., 180 mmHg) and then slowly decreases
the pressure of the cuff 10 at a low rate of 3 mmHg/sec. During
the slow cuff deflation period, a BP determining means 70 continuously
obtains the pulse-wave signal SM.sub.1, and determines a systolic
BP value, BP.sub.SYS, a mean BP value, BP.sub.MEAN, and a diastolic
BP value, BP.sub.DIA, based on the change of respective amplitudes
of heartbeat-synchronous pulses of the signal SM1, according to
a well-known oscillometric BP determining method.
A pulse-wave-propagation-velocity ("PWPV") relating information
obtaining means 74 as a sort of BP-relating-information obtaining
means includes a time-difference calculating means for successively
calculating, as illustrated in FIG. 3, a time difference (i.e.,
pulse-wave propagation time), DT.sub.RP, between a predetermined
periodic point (e.g., R-wave) on each of successive heartbeat-synchronous
pulses of the ECG waveform detected by the ECG device 34, and a
predetermined periodic point (e.g., rising point or lower-peak point)
on a corresponding one of successive heartbeat-synchronous pulses
of the photoelectric pulse wave detected by the probe 38. The PWPV-relating-information
obtaining means 74 successively calculates, based on the time difference
DT.sub.RP successively calculated by the time-difference calculating
means, a pulse-wave propagation velocity, V.sub.m, (m/sec) at which
the pulse wave propagates through the artery of the patient, according
to the following expression (1) that is pre-stored in the ROM 31:
In the above expression (1), L (m) is the distance from the left
ventricle of the heart of the patient, via the aorta, to the location
where the probe 38 is worn on the patient; and T.sub.PEP (sec) is
the pre-ejection period from the R-wave of the ECG waveform to the
lower-peak point of the aortic pulse wave. L and T.sub.PEP are constants
which are experimentally obtained in advance. However, the PWPV-relating-information
obtaining means 74 may be modified to calculate a pulse-wave propagation
velocity V.sub.M for every second, third, . . . , heartbeat-synchronous
pulse of each of the ECG waveform detected by the ECG device 34
and the photoelectric pulse wave detected by the probe 38.
A relationship determining means 76 determines coefficients, .alpha.
and .beta., of the following expression (2) or (3) as a relationship
between BP and PWPV-relating information, based on a systolic BP
value BP.sub.SYS determined by the BP determining means 70 and a
pulse-wave propagation time DT.sub.RP, or a pulse-wave propagation
velocity V.sub.M, measured during the current BP measurement in
which the systolic BP value BP.sub.SYS is determined (e.g., an average
of a plurality of pulse-wave propagation times DT.sub.RP, or an
average of a plurality of pulse-wave propagation velocities V.sub.M,
measured during the current BP measurement):
where .alpha. is a negative constant and .beta. is a positive constant.
where .alpha. is a positive constant and .beta. is a positive constant.
However, the coefficients .alpha., .beta. of the expression (2)
or (3) may be determined based on a mean BP value BP.sub.MEAN, or
a diastolic BP value BP.sub.DIA, determined by the BP determining
means 70. That is, in the case where systolic BP values BP.sub.SYS
of the patient are determined as estimated (monitored) BP values,
EBP, the coefficients .alpha., .beta. of the expression (2) or (3)
are determined based on the systolic BP value BP.sub.SYS determined
by the BP determining means 70; in the case where mean BP values
BP.sub.SYS of the patient are determined as estimated BP values
EBP, the coefficients .alpha., .beta. are determined based on the
mean BP value BP.sub.MEAN determined by the BP determining means
70; and in the case where diastolic BP values BP.sub.SYS of the
patient are determined as estimated BP values EBP, the coefficients
.alpha., .beta. are determined based on the diastolic BP value BP.sub.DIA
determined by the BP determining means 70.
An estimated-BP-value determining means 78 successively determines,
according to the relationship between BP and PWPV-relating information
that is represented by the second or third expression (2) or (3),
an estimated BP value EBP based on the actual pulse-wave propagation
time DT.sub.RP or the actual pulse-wave propagation velocity V.sub.M
successively obtained by the PWPV-relating-information obtaining
means 74.
A pulse-period determining means 82 as another sort of BP-relating-information
obtaining means successively determines a pulse period, RR, by measuring
a time interval between respective predetermined periodic points
on successive heartbeat-synchronous pulses of the ECG waveform detected
by the ECG device 34 (e.g., a time interval between the respective
R-waves of successive pulses of the ECG waveform).
A pulse-area calculating means 84 as yet another sort of BP-relating-information
obtaining means successively calculates a normalized pulse area,
VR, by dividing a pulse area, S, defined by each heartbeat-synchronous
pulse of the photoelectric pulse wave detected by the probe 38,
by the product of a period, W, and an amplitude, L, of that each
pulse. However, the pulse-area calculating means 84 may be modified
to calculate a normalized pulse area VR for every second, third,
. . . , heartbeat-synchronous pulse of the photoelectric pulse wave
detected by the probe 38. As illustrated in FIG. 4, the photoelectric
pulse wave consists of a series of data points which are input to
the control device 28 at a predetermined sampling period of, e.g.,
several milliseconds or several tens of milliseconds and each of
which represents a magnitude of the photoelectric pulse wave. The
pulse area S is calculated by integrating (summing) the respective
magnitudes of the data points in the pulse period W. Thus, the normalized
pulse area VR is calculated according to the expression: VR=S(W.times.L).
The normalized pulse area VR is a dimensionless value indicating
the ratio of the pulse area S to the rectangular area defined by
the pulse period W and the pulse amplitude L, and is also used with
a symbol, % MAP.
A BP-measurement starting means 86 causes the BP determining means
70 and the cuff-pressure control means 72 to start a BP measurement,
if the estimated BP value EBP determined by the estimated-BP-value
determining means 78 has largely changed from the BP value measured
in the last BP measurement and simultaneously if at least one of
the pulse period RR and the pulse area VR has largely changed from
a corresponding one of the pulse period RR and the pulse area VR
measured in the last BP measurement. That is, the BP-measurement
starting means 86 includes an EBP-change judging means 87 for judging
whether the estimated BP value EBP has largely changed by judging
whether the estimated BP value EBP successively determined by the
means 78 has changed from the actual BP value measured using the
cuff 10 in the last BP measurement, by more than a predetermined
value, or more than a predetermined proportion of the last, actual
BP value; an RR-change judging means 88 for judging whether the
pulse period RR has largely changed by judging whether the pulse
period RR successively determined by the pulse-period determining
means 82 has changed from the pulse period RR (e.g., the average
pulse period RR) measured during the last BP measurement, by more
than a predetermined value, or more than a predetermined proportion
of the pulse period RR measured during the last BP measurement;
and an VR-change judging means 89 for judging whether the pulse
area VR has largely changed by judging whether the pulse area VR
successively determined by the pulse-area determining means 84 has
changed from the pulse area VR (e.g., the average pulse period RR)
measured during the last BP measurement, by more than a predetermined
value, or more than a predetermined proportion of the pulse area
VR measured during the last BP measurement. If the EBP-change judging
means 87 judges that the estimated BP value EBP has largely changed
and simultaneously if the RR-change judging means 88 judges that
the pulse period RR has largely changed or the VR-change judging
means 89 judges that the pulse area VR has largely changed, the
BP-measurement starting means 86 starts a BP measurement of the
cuff-pressure control means 72 and the BP determining means 70.
Since the estimated BP value EBP is determined based on the pulse-wave
propagation time DT.sub.RP or the pulse-wave propagation velocity
V.sub.M, according to the second or third expression (2) or (3),
the EBP-change judging means 87 indirectly judges whether the PWPV-relating
information has largely changed.
An abnormality displaying means 90 displays, when the BP-measurement
starting means 86 starts a BP measurement of the cuff-pressure control
means 72 and the BP determining means 70, at least one character
and/or at least one symbol representing the BP-relating information
(i.e., the estimated BP value EBP, the pulse period RR, and/or the
pulse area VR) whose large change has been judged by the starting
means 86 (i.e., the EBP-change judging means 87, the RR-change judging
means 88, and/or the VR-change judging means 89), on the display
device 32.
A change-proportion determining means 91 determines, after each
BP measurement, an amount of change of each estimated BP value EBP
successively determined by the EBP determining means 78 after the
each BP measurement, from the actual BP value measured in the last
BP measurement, and determines a proportion of the amount of change
with respect to the actual BP value; determines an amount of change
of each pulse period RR successively determined by the RR determining
means 82 after the each BP measurement, from the pulse period RR
measured in the last BP measurement, and determines a proportion
of the amount of change with respect to the latter pulse period
RR; and determines an amount of change of each pulse area VR successively
determined by the VR determining means 84 after the each BP measurement,
from the pulse area VR measured in the last BP measurement, and
determines a proportion of the amount of change with respect to
the latter pulse area VR.
A BP-relating-information displaying means 92 displays, on the
display device 32, respective graphic representations of the actual
BP value, the pulse period RR, and the pulse area VR, measured in
the last BP measurement, and respective graphic representations
of each estimated BP value, each pulse period RR, and each pulse
area VR, successively determined by the EBP determining means 78,
the RR determining means 82, and the VR determining means 84 after
the each BP measurement, so that the patient or a medical staff
such as a doctor or a nurse can compare the actual BP value measured
in the last BP measurement with the each estimated BP value successively
determined by the EBP determining means 78, can compare the pulse
period RR measured in the last BP measurement with the each pulse
period RR successively determined by the RR determining means 82,
and can compare the pulse area VR measured in the last BP measurement
with the each pulse area VR successively determined by the VR determining
means 84.
FIG. 5 shows a display screen 94 of the display device 32 that
displays the above-indicated graphic representations. The display
screen 94 includes a BP-relating-information display area 96 in
which the BP-relating-information displaying means 92 displays a
radar chart 98 defined by three axes which intersect one another
at the origin and which represent estimated BP value EBP, pulse
period RR, and pulse area VR, respectively. The radar chart 98 shows
a reference triangle 102 whose apexes represent the actual BP value,
the pulse period RR, and the pulse area VR, measured in the last
BP measurement, respectively; and a change-proportion triangle 100
whose apexes represent the respective proportions (%) of respective
amounts of change of each estimated BP value, each pulse period
RR, and each pulse area VR, successively determined by the EBP determining
means 78, the RR determining means 82, and the VR determining means
84 after the last BP measurement. The respective proportions (%)
of the respective amounts of change of each estimated BP value,
each pulse period RR, and each pulse area VR are ones which have
been determined by the change-proportion determining means 91. Thus,
the patient or the medical staff can compare, on the display screen
94, can compare the actual BP value measured in the last BP measurement
with each estimated BP value successively determined by the EBP
determining means 78, can compare the pulse period RR measured in
the last BP measurement with each pulse period RR successively determined
by the RR determining means 82, and can compare the pulse area VR
measured in the last BP measurement with each pulse area VR successively
determined by the VR determining means 84.
An estimated-BP-value-change displaying means 104 displays, in
a maximum-change display area 106 of the display screen 94, a two-dimensional
coordinate system having a time axis 108 representing time and a
change-proportion axis 110 representing proportion (%) of amount
of change of each estimated BP value from the BP value measured
in the last BP measurement. The coordinate system shows a time-wise
change of the respective proportions of the respective amounts of
change of the estimated BP values EBP that are successively determined
by the change-proportion determining means 91. The coordinate system
includes a reference line 112 which represents the BP value measured
in the last BP measurement and which intersects the change-proportion
axis 110 at reference point (0%), and extends parallel to the time
axis 108. The time axis 108 has a length corresponding to a predetermined
BP-measurement period at which BP measurements are periodically
carried out by the present BP monitor apparatus 8. Therefore, the
patient or the medical staff can compare, on the display screen
94, the BP value measured in the last BP measurement with the most
deviated one of the estimated BP values EBP determined by the EBP
determining means 78 after the last BP measurement. The absolute
value of the difference between the BP value measured in the last
BP measurement and the most deviated estimated BP value EBP is not
smaller than that of the difference between the BP value measured
in the last BP measurement and any other estimated BP value EBP
determined after the last BP measurement. Thus, the EBP-change displaying
means 104 functions as a maximum-change displaying means. Based
on this comparison, the patient or the medical staff can easily
determine, and input, a reference value which is to be used by the
BP-measurement starting means 86 in judging whether or not to start
a BP measurement.
As shown in FIG. 5, the display screen 94 includes, in addition
to the BP-relating-information display area 96 and the maximum-change
display area 106, an ECG display area 114 in which the ECG waveform
is displayed; a heart-rate display area 116 in which a heart rate,
HR, (bpm: beats per minute) of the patient is displayed; a BP display
area 118 in which the predetermined BP measurement period or interval,
the time which has passed after the last BP measurement, and the
BP values measured using the cuff 10 in the last BP measurement
are displayed; and a respiration-rate display area 120 in which
a respiration rate (i.e., respirations per minute) of the patient
is displayed.
Hereinafter, there will be described the operation of the control
device 28 of the BP monitor apparatus 8 constructed as described
above, by reference to the flow charts of FIGS. 6 and 7 that represent
the control programs pre-stored in the ROM 31.
First, at Step SA1 of FIG. 6, flags, counters, and registers (not
shown) of the control device 28 are initialized. Step SA1 is followed
by Step SA2 corresponding to the PWPV-relating-information obtaining
means 74, the pulse-period determining means 82, and the pulse-area
determining means 84. At Step SA2, the control device 28 or the
CPU 29 thereof determines, immediately before the cuff pressure
is increased by the cuff-pressure control means 72, a propagation
time DT.sub.RP by measuring a time difference between an R wave
of a pulse of the ECG waveform detected by the ECG device 34 and
a rising point of a corresponding pulse of the photoelectric pulse
wave detected by the probe 38, determines a pulse period RR by measuring
a time difference of the R wave of the current pulse of the ECG
waveform from that of the preceding pulse of the same, and determines
a normalized pulse area VR based on the current pulse of the photoelectric
pulse wave.
Step S2 is followed by Steps SA3 and SA4 corresponding to the cuff-pressure
control means 72. At Step SA3, the switch valve 16 is switched to
the pressure-supply state and the air pump 18 is operated, so that
the air pressure in the cuff 10 is quickly increased for a blood-pressure
measurement. At Step SA4, it is judged whether the cuff pressure
P.sub.C has reached the predetermined target value P.sub.CM (e.g.,
180 mmHg). If a negative judgment is made at Step SA4, Steps SA3
and SA4 are repeated to continue increasing the cuff pressure P.sub.C.
Meanwhile, if a positive judgment is made at Step SA4, Step SA4
is followed by Step SA5 corresponding to the BP determining means
70. At Step SA5, a BP determining algorithm is carried out. More
specifically described, the air pump 18 is stopped and the switch
valve 16 is switched to the slow-deflation state, so that the cuff
pressure PC is slowly decreased at the predetermined low rate (e.g.,
3 mmHg/sec). Based on the change of respective amplitudes of successive
pulses of the pulse-wave signal SM.sub.1 detected during this slow
deflation of the cuff 10, the control device 28 determines a systolic
BP value BP.sub.SYS, a mean BP value BP.sub.MEAN, and a diastolic
BP value BP.sub.DIA of the patient, according to a well-known oscillometric
BP determining algorithm. In addition, the control device 28 determines
a pulse rate based on a time difference between two successive pulses
of the pulse-wave signal SM1. The control device 28 commands the
display device 32 to display the thus measured BP values and pulse
rate, and causes the switch valve 16 to be switched to the quick-deflation
state so that the cuff pressure P.sub.C is quickly decreased to
the atmospheric level.
Step SA5 is followed by Step SA6 corresponding to the relationship
determining means 76. At Step SA6, the control device 28 determines
a relationship between estimated blood pressure EBP and propagation
time DT.sub.RP. More specifically described, the control device
28 determines a relationship between estimated systolic, mean, or
diastolic blood pressure EBP.sub.SYS, EBP.sub.MEAN, or EBP.sub.DIA
and propagation time DT.sub.RP, i.e., the above-indicated expression
(2), based on one of the systolic, mean, or diastolic BP value BP.sub.SYS,
BP.sub.MEAN, or BP.sub.DIA determined at Step SA5 and the propagation
time DTRP determined at SA2. This relationship is used to determine,
based on the propagation time DT.sub.RP determined at Step SA2,
an estimated BP value EBP at the time when the last BP measurement
using the cuff 10 was carried Out. This estimated BP value EBP is
equal to the actual BP value measured in the last BP measurement
using the cuff 10.
Step SA6 is followed by Step SA7 to judge whether the control device
28 has received an R wave of a pulse of the ECG waveform and a rising
point of a corresponding pulse of the photoelectric pulse wave.
If a negative judgment is made at Step SA7, the control device 28
repeats Step SA7. Meanwhile, if a positive judgment is made at Step
SA7, Step SA7 is followed by Step SA8 corresponding to the PWPV-relating-information
obtaining means 74, the pulse-period determining means 82, the pulse-area
determining means 84, and the EBP determining means 78. Like at
Step SA2, the control device 28 determines a propagation time DT.sub.RP
by measuring a time difference between the R wave of the current
pulse of the ECG waveform and the rising point of the corresponding
pulse of the photoelectric pulse wave, determines a pulse period
RR by measuring a time difference of the R wave of the current pulse
of the ECG waveform from that of the preceding pulse of the same,
and determines a normalized pulse area VR based on the current pulse
of the photoelectric pulse wave. In addition, the control device
28 determines an estimated BP value EBP based on the thus determined
propagation time DT.sub.RP according to the relationship determined
at Step S6.
Step SA8 is followed by Step SA9 corresponding to the change-proportion
determining means 91. At Step SA9, the control device 28 calculates
respective amounts of change of the estimated BP value EBP, the
pulse period RR, and the pulse area VR determined at Steps SA8,
from the estimated BP value EBP, the pulse period RR, and the pulse
area VR determined at Steps SA2 and SA6, respectively, and calculates
respective proportions (%) of the thus calculated respective amounts
of change of the estimated BP value EBP, the pulse period RR, and
the pulse area VR determined at Steps SA8, with respect to the estimated
BP value EBP, the pulse period RR, and the pulse area VR determined
at Steps SA2 and SA6, respectively.
Step SA9 is followed by Step SA10 corresponding to the BP-relating-information
displaying means 92. As indicated in the BP-relating-information
display area 96 of the display device 32, shown in FIG. 5, the control
device 28 displays, in the radar chart 98, the reference triangle
102 whose apexes represent the estimated BP value EBP, the pulse
period RR, and the pulse area VR, at the time when the last BP measurement
was carried out, respectively, and the change-proportion triangle
100 whose apexes represent the respective proportions (%) of respective
amounts of change of the estimated BP value, the pulse period RR,
and the pulse area VR, determined at Step SA9, respectively. When
the patient's condition can be considered as being normal, that
is, if the respective amounts of change of the estimated BP value,
the pulse period RR, and the pulse area VR, determined at Step SA8,
have not been deviated so much from the estimated BP value EBP,
the pulse period RR, and the pulse area VR, at the time when the
last BP measurement was carried out, that is, if the change-proportion
triangle 100 has not been deviated so much from the reference triangle
102, the control device 28 commands the display device 32 to display
the change-proportion triangle 100 with a color (e.g., green) indicating
the normal condition. On the other hand, if the amount of deviation
of the change-proportion triangle 100 from the reference triangle
102 is increased and eventually does not fall within a predetermined
reference range, the display device 32 displays the change-proportion
triangle 100 with a different color, e.g., first yellow and then
red.
Step SA10 is followed by Step SA11 corresponding to the EBP-change
displaying means 104. At Step SA11, the control device 28 updates,
based on the proportion of the amount of change of the estimated
BP value EBP that was determined at Step SA9, a graph representing,
on the two-dimensional coordinate system in the maximum-change display
area 106 of the display screen 94, the time-wise change of respective
proportions of respective amounts of change of the estimated BP
values EBP that are successively determined by the change-proportion
determining means 91. Depending upon the respective deviations of
the change proportions (%) as the data points of the graph, from
the origin (0%) of the change-proportion axis 110, the data points
(indicated at symbols "-" in FIG. 5) are displayed with
different colors, so that the patient or the medical staff can easily
recognize those deviations. For example, if a change proportion
as a data point of the graph falls within the first range of from
-10% to +10%, the data point is displayed with green; if a change
proportion as a data point falls within the second range of from
-20% to -10% or from +10% to +20%, the data point is displayed with
yellow; and if a change proportion as a data point does not fall
within the first or second range, the data point is displayed with
red.
Step SA11 is followed by Step SA12 corresponding to the BP-measurement
starting means 86. At Step SA12, the control device 28 carries out
the BP-measurement-start judging routine represented by the flow
chart of FIG. 7, and if the control device 28 judges that the estimated
BP value EBP determined at Step SA8 has largely changed from the
EBP value at the time of the last BP measurement and simultaneously
if at least one of the pulse period RR and the pulse area VR determined
at Step SA8 has largely changed from a corresponding one of the
pulse period RR and the pulse area VR measured in the last BP measurement,
the control device 28 causes the cuff-pressure control means 72
and the BP determining means 70 to start a BP measurement.
First, at Step SB1 of the flow chart of FIG. 7, corresponding to
the RR-change judging means 88, the control device 28 judges whether
the respective proportions of respective amounts of change of not
less than a predetermined number (e.g., 20) of successive pulse
periods RR each determined at Step SA9 in not less than the same
number of successive control cycles according to the routine of
FIG. 7 do not fall within the range of from -5% to +5%. If not,
the control device 28 judges that the pulse periods RR have largely
or significantly changed. If the pulse periods RR have not largely
changed, the control goes to Step SB3 and the following steps. On
the other hand, if the pulse periods RR have largely changed, the
control goes to Step SB2 to set an RR flag to an "ON"
state indicating that the pulse periods RR have largely changed.
Step SB2 is followed by SB3 to judge whether the waveform of the
pulse of the photoelectric pulse wave, detected at Step SA7, is
normal. This step is provided for removing one or more pulses each
having an abnormal waveform, such as a pulse whose waveform has
a base line inclined by more than a reference angle, or a pulse
whose waveform is discontinued by the calibration of the relationship
at Step SA6. If a negative judgment is made at Step SB3, the control
goes to Step SB8 and the following steps. On the other hand, if
a positive judgment is made, the control goes to Step SB4 corresponding
to the VR-change judging means 89.
At Step SB4, the control device 28 judges whether the respective
proportions of respective amounts of change of not less than a predetermined
number (e.g., 20) of successive normalized pulse areas VR each determined
at Step SA9 in not less than the same number of successive control
cycles according to the routine of FIG. 7 do not fall within the
range of from -3% to -3% If not, the control device 28 judges that
the pulse areas VR have largely or significantly changed. If the
pulse areas VR have not largely changed, the control goes to Step
SB6 and the following steps. On the other hand, if the pulse areas
VR have largely changed, the control goes to Step SB5 to set a VR
flag to an "ON" state indicating that the pulse areas
VR have largely changed.
Step SB5 is followed by Step SB6 corresponding to the EBP-change
judging means 87. At Step SB6, the control device 28 judges whether
the respective proportions of respective amounts of change of not
less than a predetermined number (e.g., 20) of successive estimated
BP values EBP each determined at Step SA9 in not less than the same
number of successive control cycles according to the routine of
FIG. 7 do not fall within the range of from -30% to -30%. If not,
the control device 28 judges that the estimated BP values EBP have
largely or significantly changed. If the estimated BP values EBP
have not largely changed, the control goes to Step SB8 and the following
steps. On the other hand, if the estimated BP values EBP have largely
changed, the control goes to Step SB7 to set an EBP flag to an "ON"
state indicating that the estimated BP values EBP have largely changed.
Step SB7 is followed by Step SB8 to judge whether the EBP flag
and the RR flag are both in the "ON" state, or whether
the EBP flag and the VR flag are both in the "ON" state.
If a negative judgment is made at Step SB8, the control goes to
Step SA13 of FIG. 6. At Step SA13, the control device 28 judges
whether, after the last BP measurement using the cuff 10 at Step
SA5, time has passed by a predetermined measurement (i.e., calibration)
period (e.g., 15 or 20 minutes). If a negative judgment is made
at Step SA13, the control device 28 carries out Step SA7 and the
following steps to repeat the BP monitor routine, i.e., successively
determine an estimated BP value EBP, a pulse period RR, and a pulse
area VR based on each of successive heartbeat-synchronous pulses
of each of the ECG waveform and the photoelectric pulse wave, and
display the thus determined values EBP, RR, VR in the radar chart
98 in the BP-relating-formation display area 96 of the display screen
94. From the radar chart 98, the patient or the medical staff can
judge, in the case where a negative judgment is made at Step SB8
and accordingly a BP measurement is not started, whether the condition
of the patient is actually near abnormality which needs a BP measurement,
or near normality which does not need it.
On the other hand, if a positive judgment is made at Step SA13,
the control device 28 carries out Step SA2 and the following steps,
i.e., the calibration routine, to update the relationship at Step
SA6. In addition, if a positive judgment is made at Step SB8, the
control goes to Step SA14 of FIG. 6 corresponding to the abnormality
displaying means 90. At Step SA14, the control device 28 commands
the display device 32 to display characters or symbols representing
one or more sorts of BP-relating-information corresponding to one
or more of the RR flag, the VR flag, and the EBP flag that is or
are in the "ON" state. For example, in the case where
the estimated BP values EBP and the pulse periods RR have largely
or significantly changed, the display device 32 displays the characters
indicating that the estimated BP values EBP and the pulse periods
RR have largely changed. Step SA14 is followed by Step SA2 and the
following steps to update the relationship at Step SA6. Thus, a
BP measurement using the cuff 10 is started. Since the radar chart
96 continues to indicate the estimated BP value EBP, the pulse period
RR, and the pulse area VR at the time when the positive judgment
is made at Step SA12, the patient or the medical staff can judge
which one of the three sorts of BP-relating-formation EBP, RR, VR
has largely changed.
As is apparent from the foregoing description, the present BP monitor
8 displays, in the radar chart 98 in the BP-relating-formation display
area 96 in the display screen 94, both the reference triangle 102
whose apexes represent the estimated BP value EBP, the pulse period
RR, and the pulse area VR at the time of the last BP measurement
using the cuff 10, and the change-proportion triangle 100 whose
apexes represent the respective proportions of respective amounts
of change of the estimated BP value EBP, the pulse period RR, and
the pulse area VR that are determined at Step SA9, in each of successive
control cycles according to the routine of FIG. 6, after the last
BP measurement. Therefore, the patient or the medical staff can
recognize to what degree each of the estimated BP value, the pulse
period RR, and the pulse area VR, determined at Step SA9 in each
of successive control cycles, has changed from a corresponding one
of the three values EBP, RR, VR at the time of the last BP measurement.
In addition, the two-dimensional coordinate system in the maximum-change
display area 106 of the display screen 94 shows both the reference
line 112 which represents the estimated BP value EBP at the time
of the last BP measurement using the cuff 10, and the time-wise
change of the respective proportions of respective amounts of change
of the estimated BP values EBP that are determined at Step SA9,
in each of successive control cycles according to the routine of
FIG. 6, after the last BP measurement. In addition, the time axis
108 represents the time interval (i.e., the predetermined BP-measurement
period) between the last BP measurement and the next BP measurement.
Therefore, the patient or the medical staff can recognize, on the
display screen 94, to what degree the most deviated one of all the
estimated BP values EBP obtained after the last BP measurement has
changed from the estimated BP value at the time of the last BP measurement.
While the present invention has been described in its preferred
embodiment, it is to be understood that the present invention may
otherwise be embodied.
For example, in the illustrated embodiment, the radar chart 98
displayed in the BP-relating-information display area 96 shows the
reference triangle 102 whose apexes represent the estimated BP value,
the pulse period RR and the pulse area VR at the time of the last
BP measurement, and the change-proportion triangle 100 whose apexes
represent the estimated BP value, the pulse period RR and the pulse
area VR that are determined at Step SA9 in each of successive control
cycles according to the routine of FIG. 6 after the last BP measurement.
However, the radar chart 98 displayed in the BP-relating-information
display area 96 may be replaced with three bar graphs shown in FIG.
8, or a time-wise changing graph shown in FIG. 9.
In FIG. 8, three inverted triangles ".gradient." indicate
the respective proportions of respective amounts of change of the
estimated BP value, the pulse period RR and the pulse area VR that
are determined at Step SA9 in each of successive control cycles
according to the routine of FIG. 6 after the last BP measurement.
Respective origins (0%) of the three bar graphs represent the estimated
BP value, the pulse period RR and the pulse area VR at the time
of the last BP measurement using the cuff 10. Therefore, the three
inverted triangles ".gradient." correspond to the change-proportion
triangle 100 shown in FIG. 5, and the respective origins (0%) of
the three bar graphs correspond to the reference triangle 102 shown
in FIG. 5. However, in the embodiment shown in FIG. 8, the three
inverted triangles ".gradient." indicate respective absolute
values of the respective proportions of respective amounts of change
of the estimated BP value, the pulse period RR and the pulse area
VR. Depending upon the respective deviations of the absolute values
of the change proportions (%) from the corresponding origins (0%),
the bar graphs are displayed, in steps, with different colors, so
that the patient or the medical staff can easily recognize those
steps of the deviations.
FIG. 9 shows a graph representing, along a common time axis, a
time-wise change 122 of the respective proportions of respective
amounts of change of the estimated BP values EBP successively determined
after the last BP measurement using the cuff 10; a time-wise chance
124 of the respective proportions of respective amounts of change
of the pulse periods RR successively determined after the last BP
measurement; and a time-wise change 126 of the respective proportions
of respective amounts of change of the pulse areas VR successively
determined after the last BP measurement. The graph includes, at
the left-hand end thereof, an EBP reference mark 128, an RR reference
mark 130, and a VR reference mark 132 which indicate the estimated
BP value EBP, the pulse period RR, and the pulse area VR at the
time of the last BP measurement, respectively, so as so that the
EBP reference mark 128, the RR reference mark 130, and the VR reference
mark 13 can be compared with the current estimated BP value EBP,
the current pulse period RR, and the current pulse area VR, respectively,
which are determined after the last BP measurement. Thus, the three
marks 128, 130, 132 correspond to the reference triangle 102 shown
in FIG. 5. The graph shown in FIG. 9 includes, at the right-hand
end thereof, a blank area 134 which is provided for the patient
or the medical staff to be able to recognize that the three sorts
of BP-relating information are being successively obtained and estimate,
based on the time-wise changes 124, 126, 128, respective future
changes of those sorts of BP-relating information. In addition,
one of the three sorts of BP-relating information (e.g., the estimated
BP values EBP) is selected, in advance, as being the most important
for the monitoring of the blood pressure of the patient, and the
time-wise change of the most important sort of information (e.g.,
the time-wise change 122) is displayed in thicker lines or symbols
than the respective time-wise changes of the other sorts of information
(e.g., the time-wise changes 124, 126), as shown in FIG. 9, so that
the most important sort of information can be more easily observed
than the other sorts of information.
In the illustrated embodiment, the three sorts of BP-relating information,
that is, the estimated BP value, the pulse period RR, and the pulse
area VR are employed. However, since each of the three sorts of
BP-relating information reflects the change of blood pressure of
a living subject, it is possible to use only one or two of the three
sorts of information. Each of FIG. 10 and FIG. 11 shows a graph
which represents a single sort of BP-relating information and which
may be displayed in place of the radar chart 98 (FIG. 5) in the
BP-relating-information display area 96. FIG. 10 shows a circle
graph corresponding to the bar graph shown in FIG. 8, and representing
the proportion (%) of amount of change (absolute value) of each
of the pulse areas VR successively determined after the last BP
measurement. The origin (0%) of the circle graph represents the
pulse area VR at the time of the last BP measurement and corresponds
to the reference triangle 102 shown in FIG. 5. Like the bar graph
shown in FIG. 8, the circle graph is displayed, in steps, with different
colors, depending upon the respective amounts of deviation of the
successively determined pulse areas VR from the pulse area VR at
the time of the last BP measurement. FIG. 11 shows an arrow 136
which represents the proportion (%) of amount of change (absolute
value) of each of the estimated BP values EBP successively determined
after the last BP measurement. The origin (0%) of the circle represents
the estimated BP value EBP at the time of the last BP measurement
and corresponds to the reference triangle 102 shown in FIG. 5. A
background 138 of the arrow 136 is displayed with a first color,
when each of the successively determined estimated BP values EBP
is smaller than the estimated BP value EBP at the time of the last
BP measurement (that is, when the amount of change of the each value
EBP is negative); and the background 138 is displayed with a second
color different from the first color, when the each of the successively
determined estimated BP values EBP is greater than the estimated
BP value EBP at the time of the last BP measurement (that is, when
the amount of change of the each value EBP is positive). Thus, a
person can more easily recognize the change of the estimated BP
values EBP.
Like FIGS. 10 and 11, FIGS. 12A, 12B, and 12C shows a graph which
represents a single sort of BP-relating information and which may
be displayed in place of the radar chart 98 (FIG. 5) in the BP-relating-information
display area 96. The graph includes an arrow 140 which represents
the proportion (%) of amount of change of each of the estimated
BP values EBP successively determined after the last BP measurement.
The graph shown in FIGS. 12A to 12C differs from the graph shown
in FIG. 11, in that the origin (0%) of the former graph that represents
the estimated BP value EBP at the time of the last BP measurement
and corresponds to the reference triangle 102 shown in FIG. 5, is
set at the right-hand one of two points where a horizontal line
passing through the center of a circle 142 intersects the circle
142 and in that the former graph can indicate both a positive and
a negative proportion (%) corresponding to both a positive and a
negative amount of change of each estimated BP value EBP. FIG. 12A
shows the arrow 140 indicating a horizontal and rightward direction
and thereby indicating that the current estimated BP value EBP has
not deviated from the estimated BP value EBP at the time of the
last BP measurement; FIG. 12B shows the arrow 140 indicating that
the current estimated BP value EBP has increased slightly (e.g.
increased by 10%) from the estimated BP value EBP at the time of
the last BP measurement; and FIG. 12C shows the arrow 140 indicating
that the current estimated BP value EBP has decreased largely (e.g.
decreased by 30%) from the estimated BP value EBP at the time of
the last BP measurement. In the graph shown in FIGS. 12A to 12C,
too, the arrow 140 or a background 144 thereof is displayed, in
steps, with respective different colors, depending upon the respective
amounts of deviation of the successively determined estimated BP
values EBP from the estimated BP value EBP at the time of the last
BP measurement. In FIGS. 12A to 12C, the indication of values, 0
(%), +30, and -30, may be eliminated because the inclination of
the arrow 140 indicates the proportion of amount of change of each
of the successively determined estimated BP values EBP, so that
the inclination of the arrow 140 can be compared with the horizontal
line indicating the estimated BP value EBP at the time of the last
BP measurement.
FIG. 13 also shows a graph which represents a single sort of BP-relating
information and which may be displayed in place of the radar chart
98 (FIG. 5) in the BP-relating-information display area 96. The
graph includes an arrow 146 which represents the proportion (%)
of amount of change of each of the estimated BP values EBP successively
determined after the last BP measurement. Like the graph shown in
FIGS. 12A to 12C, a head portion of the arrow 146 included in the
graph shown in FIG. 13 can indicate both a positive and a negative
proportion (%) corresponding to both a positive and a negative amount
of change of each estimated BP value EBP. More specifically described,
the arrow 146 whose head portion points a horizontal and rightward
direction, indicates that the current estimated BP value EBP has
not deviated from the estimated BP value EBP at the time of the
last BP measurement; the arrow 146 whose head portion is inclined
upward, indicates that the current estimated BP value EBP has increased
from the estimated BP value EBP at the time of the last BP measurement;
and the arrow 146 whose head portion is inclined downward, as shown
in FIG. 13, indicates that the current estimated BP value EBP has
decreased from the estimated BP value EBP at the time of the last
BP measurement. In addition, a base portion 148 from which the head
portion 146 extends indicates how the estimated BP value EBP at
the time of the last BP measurement has deviated or changed from
the estimated BP value EBP at the time of the second last BP measurement,
i.e., the measurement preceding the last measurement. Since the
base portion 148 shown in FIG. 13 is horizontal, it indicates that
the value EBP at the time of the last measurement has not changed
from the value EBP at the time of the second last measurement. In
the graph shown in FIG. 13, too, the arrow 146 or a background 150
thereof is displayed, in steps, with respective different colors,
depending upon the respective amounts of deviation of the successively
determined values EBP from the value EBP at the time of the last
measurement.
In the illustrated embodiment, the maximum-change display area
106 of the display screen 94 shows a time-wise change of the respective
proportions (%) of respective amounts of change of the estimated
BP values EBP successively determined after the last BP measurement
using the cuff 10 and before the next BP measurement. Thus, the
patient or the medical staff can recognize, on the display area
106, one of the successively determined values EBP that is most
deviated from the value EBP at the time of the last measurement.
However, it is possible to display the most deviated one estimated
BP value EBP only. In this case, when a value EBP newly determined
is more deviated than the current most deviated one value EBP, the
newly determined value EBP is adopted as the new most deviated value
EBP to replace the current most deviated value EBP being displayed
and thereby update the same. An example of this case is shown in
FIG. 14, which shows a bar graph representing the proportion (%)
of amount of change of the most deviated one estimated BP value
EBP obtained after the last BP measurement using the cuff 10, A
line indicating the origin (0%) of the bar graph represents the
value EBP at the time of the last BP measurement. Likewise, the
bar graph shown in FIG. 14 is displayed, in steps, with respective
different colors, depending upon the respective amounts of deviation
of the successively determined values EBP from the value EBP at
the time of the last measurement.
In the illustrated embodiment, the maximum-change display area
106 of the display screen 94 shows the most deviated one of the
estimated BP values EBP as a sort of BP-relating information. However,
it is possible to display, in the display area 106, the most deviated
value of a different sort of BP-relating information, such as pulse-rate-relating
information (e.g., pulse period RR, pulse rate HR, etc.) or pulse
area VR. Otherwise, it is possible to display, in the area 106,
the respective most deviated values of plural sorts of BP-relating
information. In the last case, the patient or the medical staff
can visually compare the respective most deviated values of plural
sorts of BP-relating information, with the respective values of
those sorts of information at the time of the last measurement.
Therefore, the person can easily judge whether each of the respective
threshold values used, for those sorts of information, in judging
whether a BP measurement should be started, is appropriate or not.
In the illustrated embodiment, the radar chart 98 shown in the
BP-relating-information display area 96 includes the reference triangle
102 representing the respective values of the plural sorts of BP-relating
information (i.e., the estimated BP value EBP, the pulse period
RR, and the pulse area VR) at the time of the last BP measurement,
and the change-proportion triangle 100 representing the respective
proportions of respective amounts of change of the respective current
values of those sorts of information, successively determined by
the change-proportion determining means 91, so that the reference
triangle 102 and the change-proportion triangle 100 can be compared
with each other. However, it is possible to display a graph including
the respective values of the plural sorts of BP-relating information
at the time of the last BP measurement, and the respective current
values of those sorts of information, successively determined by
the change-proportion determining means 91, after the last BP measurement.
Likewise, it is possible to display, in the maximum-change display
area 106, a graph including the value or values of one or more sorts
of BP-relating information at the time of the last BP measurement,
and the most deviated value or values of that or those sorts of
information determined after the last measurement.
In the illustrated embodiment, the estimated BP value is employed
as a sort of BP-relating information. However, since the value EBP
corresponds, one by one, to the pulse-wave propagation time DT.sub.RP
or the pulse-wave propagation velocity V.sub.M, as indicated by
the mathematical expressions (2), (3), the propagation time DT.sub.RP
or the propagation velocity V.sub.M may be used in place of the
value or information EBP.
In the illustrated embodiment, the pulse period RR is employed
as a sort of BP-relating information. However, since the pulse period
RR (sec) corresponds, one by one, to the pulse rate HR (beats/min)
according to the following expression: HR=60/RR, the heart rate
HR may be employed, in place of the pulse period RR, by the RR determining
means 82, the RR-change judging means 88, the change-proportion
determining means 91, and the BP-relating-information displaying
means 92.
The BP monitor apparatus 8 shown in FIG. 1 utilizes the probe 38
as part of the pulse oximeter, and measures a blood oxygen saturation,
SpO2, as a sort of physical information other than the BP-relating
information. This physical information may be included in the radar
chart 98 shown in FIG. 5, or in the graph shown in FIG. 8 or in
each of FIGS. 10 to 14. If the current piece of physical information
does not fall within a predetermined reference range, the abnormality
displaying means 90 (Step SA14) may command the display device 32
to display characters and/or symbols indicating that the physical
information has become abnormal.
In the illustrated embodiment, the abnormality displaying means
90 commands the display device 32 to display characters and/or symbols
indicating which one of the above-indicated three sorts of BP-relating
information has largely deviated. However, it is possible to employ
a speaker (not shown) which produces sound or voice for the same
purpose. For example, in the case where the BP monitor apparatus
8 judges that the estimated BP value EBP and the pulse period RR
have largely deviated, the speaker outputs a message that respective
large deviations of estimated BP value and pulse rate have been
detected.
While the present invention has been described in its preferred
embodiments, the present invention is not limited to the features
described in SUMMARY OF INVENTION and the features described in
PREFERRED EMBODIMENTS OF INVENTION and may be embodied with other
changes, improvements, and modifications that may occur to a person
skilled in the art without departing from the scope and spirit of
the invention defined in the appended claims. |