Abstrict
A blood-pressure monitor apparatus including a pulse-wave sensor
including pressure sensing elements, a pressing device which presses
the pulse-wave sensor against an artery via skin tissue, a selecting
device for selecting, as an optimum element, one of the pressure
sensing elements, a determining means for changing the pressing
force of the pressing device and determining, based on the pulse
wave detected by the optimum element while the pressing force is
changed, an optimum pressing force with which the pressing device
presses the pulse wave sensor against the artery such that a portion
of a wall of the artery is flattened, a maintaining device for maintaining
the optimum pressing force of the pressing device, a determining
means for determining an estimated blood pressure according to a
predetermined relationship between blood pressure and magnitude
of pressure pulse wave, based on a magnitude of each of heartbeat-synchronous
pulses of the pulse wave detected by the optimum element in a state
in which the pulse-wave sensor is pressed against the artery with
the maintained optimum pressing force, and a display device which
displays, in a two-dimensional coordinate system, a curve representing
a change of respective amplitudes of heartbeat-synchronous pulses
of the pulse wave detected by the optimum element, with respect
to a change of the pressing force of the pressing device.
Claims
What is claimed is:
1. A blood-pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising:
a pressure-pulse-wave sensor which includes a plurality of pressure
sensing elements which are arranged in a reference direction and
each of which detects a pressure pulse wave propagated thereto from
an arterial vessel of the subject and produces a pressure-pulse-wave
signal representing the detected pressure pulse wave that includes
a plurality of heartbeat-synchronous pulses, the pressure-pulse-wave
sensor having a press surface which supports the pressure sensing
elements arranged in the reference direction and which is adapted
to be pressed against the arterial vessel via a body surface of
the subject such that the arranged pressure sensing elements intersect
the arterial vessel;
a pressing device which presses, with a pressing force, the pressure-pulse-wave
sensor against the arterial vessel via the body surface;
optimum-element selecting means for selecting, as an optimum element,
one of the pressure sensing elements that provides the detected
pressure pulse wave including a heartbeat-synchronous pulse whose
amplitude is greatest of respective amplitudes of respective heartbeat-synchronous
pulses of the detected pressure pulse waves provided by, the pressure
sensing elements;
optimum-pressing-force determining means for changing the pressing
force of the pressing device and determining, based on the pressure
pulse wave detected by the optimum element while the pressing force
is changed, an optimum pressing force with which the pressing device
presses the pressure-pulse wave sensor against the arterial vessel
via the body surface such that a portion of a wall of the arterial
vessel is substantially flattened;
optimum-pressing-force maintaining means for maintaining the optimum
pressing force of the pressing device;
estimated-blood-pressure determining means for determining an estimated
blood pressure according to a predetermined relationship between
blood pressure and magnitude of pressure pulse wave, based on a
magnitude of each of a plurality of heartbeat-synchronous pulses
of the detected pressure pulse wave represented by the pressure-pulse-wave
signal produced by the optimum element in a state in which the pressure-pulse-wave
sensor is pressed against the arterial vessel with the optimum pressing
force maintained by the optimum-pressing-force maintaining means;
and
an amplitude-change-curve displaying device which displays, in
a two-dimensional coordinate system having a first axis indicative
of pressing force and a second axis indicative of amplitude of heartbeat-synchronous
pulse of pressure pulse wave, an amplitude-change curve representing
a change of the respective amplitudes of the heartbeat-synchronous
pulses of the pressure pulse wave detected by the optimum element,
with respect to a change of the pressing force of the pressing device
caused by the optimum-pressing-force determining means.
2. An apparatus according to claim 1, further comprising an estimated-blood-pressure
displaying device which displays the estimated blood pressure determined
by the estimated-blood-pressure determining means.
3. An apparatus according to claim 1, further comprising an optimum-pressing-force
displaying device which displays, in the two-dimensional coordinate
system in which the amplitude-change curve is displayed, a symbol
representing the optimum pressing force determined by the optimum-pressing-force
determining means.
4. An apparatus according to claim 1, further comprising judging
means for judging, based on the pressure pulse wave detected by
the optimum element while the pressing force is changed by the optimum-pressing-force
determining means, whether the pressing device appropriately presses
the pressure-pulse-wave sensor against the arterial vessel via the
body surface.
5. An apparatus according to claim 1, further comprising:
a blood-pressure measuring device which includes an inflatable
cuff adapted to be wound around a body portion of the subject and
measures at least one blood pressure value of the subject based
on a pulse wave transmitted to the cuff while an air pressure in
the cuff is changed; and
a relationship determining means for determining the relationship
between blood pressure and magnitude of pressure pulse wave, based
on said at least one blood pressure value measured by the blood-pressure
measuring device and at least one magnitude of a heartbeat-synchronous
pulse of the pressure pulse wave detected by the optimum element
in the state in which the pressure-pulse-wave sensor is pressed
against the arterial vessel with the optimum pressing force maintained
by the optimum-pressing-force maintaining means.
6. A blood-pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising:
a pressure-pulse-wave sensor which includes a plurality of pressure
sensing elements which are arranged in a reference direction and
each of which detects a pressure pulse wave propagated thereto from
an arterial vessel of the subject and produces a pressure-pulse-wave
signal representing the detected pressure pulse wave that includes
a plurality of heartbeat-synchronous pulses, the pressure-pulse-wave
sensor having a press surface which supports the pressure sensing
elements arranged in the reference direction and which is adapted
to be pressed against the arterial vessel via a body surface of
the subject such that the arranged pressure sensing elements intersect
the arterial vessel;
a pressing device which presses, with a pressing force, the pressure-pulse-wave
sensor against the arterial vessel via the body surface;
optimum-element selecting means for selecting, as an optimum element,
one of the pressure sensing elements that provides the detected
pressure pulse wave including a heartbeat-synchronous pulse whose
amplitude is greatest of respective amplitudes of respective heartbeat-synchronous
pulses of the detected pressure pulse waves provided by the pressure
sensing elements;
optimum-pressing-force determining means for changing the pressing
force of the pressing device and determining, based on the pressure
pulse wave detected by the optimum element while the pressing force
is changed, an optimum pressing force with which the pressing device
presses the pressure-pulse wave sensor against the arterial vessel
via the body surface such that a portion of a wall of the arterial
vessel is substantially flattened;
optimum-pressing-force maintaining means for maintaining the optimum
pressing force of the pressing device;
estimated-blood-pressure determining means for determining an estimated
blood pressure according to a predetermined relationship between
blood pressure and magnitude of pressure pulse wave, based on a
magnitude of each of a plurality of heartbeat-synchronous pulses
of the detected pressure pulse wave represented by the pressure-pulse-wave
signal produced by the optimum element in a state in which the pressure-pulse-wave
sensor is pressed against the arterial vessel with the optimum pressing
force maintained by the optimum-pressing-force maintaining means;
and
a signal-magnitude-change-curve displaying device which displays,
in a two-dimensional coordinate system having a first axis indicative
of pressing force and a second axis indicative of magnitude of pressure-pulse-wave
signal, a signal-magnitude-change curve representing a change of
respective magnitudes of respective predetermined periodic points
of the heartbeat-synchronous pulses of the detected pressure pulse
wave represented by the pressure-pulse-wave signal produced by the
optimum element, with respect to a change of the pressing force
of the pressing device caused by the optimum-pressing-force determining
means.
7. An apparatus according to claim 6, further comprising an estimated-blood-pressure
displaying device which displays the estimated blood pressure determined
by the estimated-blood-pressure determining means.
8. An apparatus according to claim 6, further comprising an optimum-pressing-force
displaying device which displays, in the two-dimensional coordinate
system in which the signal-magnitude-change curve is displayed,
a symbol representing the optimum pressing force determined by the
optimum-pressing-force determining means.
9. An apparatus according to claim 6, further comprising judging
means for judging, based on the pressure pulse wave detected by
the optimum element while the pressing force is changed by the optimum-pressing-force
determining means, whether the pressing device appropriately presses
the pressure-pulse-wave sensor against the arterial vessel via the
body surface.
10. An apparatus according to claim 6, further comprising:
a blood-pressure measuring device which includes an inflatable
cuff adapted to be wound around a body portion of the subject and
measures at least one blood pressure value of the subject based
on a pulse wave transmitted to the cuff while an air pressure in
the cuff is changed; and
a relationship determining means for determining the relationship
between blood pressure and magnitude of pressure pulse wave, based
on said at least one blood pressure value measured by the blood-pressure
measuring device and at least one magnitude of a heartbeat-synchronous
pulse of the pressure pulse wave detected by the optimum element
in the state in which the pressure-pulse-wave sensor is pressed
against the arterial vessel with the optimum pressing force maintained
by the optimum-pressing-force maintaining means.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a continuous blood-pressure monitor
apparatus which continuously monitors blood pressure of a living
subject based on a pressure pulse wave detected by a pressure-pulse-wave
sensor, and particularly to the art of appropriately pressing the
pressure-pulse-wave sensor against an artery of the subject via
body surface of the subject.
2. Related Art Statement
U.S. Pat. No. 5,762,610 discloses a continuous blood-pressure ("BP")
monitor apparatus which continuously monitors the BP of a living
subject. This BP monitor apparatus includes (a) a pressure-pulse-wave
("PPW") sensor which includes a plurality of pressure
sensing elements which are arranged in a reference direction and
each of which detects a PPW propagated thereto from an arterial
vessel of the subject and produces a PPW signal representing the
detected PPW that includes a plurality of heartbeat-synchronous
pulses, the PPW sensor having a press surface which supports the
pressure sensing elements arranged in the reference direction and
which is adapted to be pressed against the arterial vessel via a
body surface or skin of the subject such that the arranged pressure
sensing elements intersect the arterial vessel; (b) a pressing device
which presses, with a pressing force, the PPW sensor against the
arterial vessel via the body surface; (c) optimum-element selecting
means for selecting, as an optimum element, one of the pressure
sensing elements that provides the detected PPW including a heartbeat-synchronous
pulse whose amplitude is greatest of respective amplitudes of respective
heartbeat-synchronous pulses of the detected PPWs provided by the
pressure sensing elements; (d) optimum-pressing-force determining
means for changing the pressing force of the pressing device and
determining, based on the PPW detected by the optimum element while
the pressing force is changed, an optimum pressing force with which
the pressing device presses the PPW sensor against the arterial
vessel via the body surface such that a portion of a wall of the
arterial vessel is substantially flattened; (e) optimum-pressing
force maintaining means for maintaining the optimum pressing force
of the pressing device; and (f) estimated-BP determining means for
determining an estimated BP value according to a predetermined relationship
between BP and magnitude of PPW, based on a magnitude of each of
a plurality of heartbeat-synchronous pulses of the detected PPW
represented by the PPW signal produced by the optimum element in
a state in which the PPW sensor is pressed against the arterial
vessel with the optimum pressing force maintained by the optimum-pressing-force
maintaining means. The BP monitor apparatus monitors the BP of the
subject by successively determining the estimated BP values of the
subject.
The estimated BP values successively determined by the above BP
monitor apparatus cannot accurately reflect actual BP values of
the subject unless the PPW sensor is appropriately pressed against
the arterial vessel via the body surface such that a portion of
the wall of the artery is substantially flattened. However, the
prior BP monitor apparatus does not display the optimum pressing
force of the pressing device determined by the optimum-pressing-force
determining means, or displays the optimum pressing force alone.
Therefore, it is difficult for an operator who operates the prior
BP monitor apparatus to judge, from what is displayed thereby, whether
the optimum pressing force has been determined in an appropriate
state in which a portion of the wall of the artery is stably flattened
and accordingly the appropriate state can last for a long time,
or in an inappropriate state in which a portion of the wall of the
artery is considerably unstably flattened and accordingly the state
in which the portion of the wall of the artery is flattened cannot
last for so long a time.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
blood-pressure monitor apparatus which assures that an operator
can recognize how the apparatus presses an arterial vessel of a
living subject at the time of determination of an optimum pressing
force.
(1) According to a first feature of the present invention, there
is provided a blood-pressure monitor apparatus for monitoring a
blood pressure of a living subject, comprising a pressure-pulse-wave
sensor which includes a plurality of pressure sensing elements which
are arranged in a reference direction and each of which detects
a pressure pulse wave propagated thereto from an arterial vessel
of the subject and produces a pressure-pulse-wave signal representing
the detected pressure pulse wave that includes a plurality of heartbeat-synchronous
pulses, the pressure-pulse-wave sensor having a press surface which
supports the pressure sensing elements arranged in the reference
direction and which is adapted to be pressed against the arterial
vessel via a body surface of the subject such that the arranged
pressure sensing elements intersect the arterial vessel; a pressing
device which presses, with a pressing force, the pressure-pulse-wave
sensor against the arterial vessel via the body surface; optimum-element
selecting means for selecting, as an optimum element, one of the
pressure sensing elements that provides the detected pressure pulse
wave including a heartbeat-synchronous pulse whose amplitude is
greatest of respective amplitudes of respective heartbeat-synchronous
pulses of the detected pressure pulse waves provided by the pressure
sensing elements; optimum-pressing-force determining means for changing
the pressing force of the pressing device and determining, based
on the pressure pulse wave detected by the optimum element while
the pressing force is changed, an optimum pressing force with which
the pressing device presses the pressure-pulse wave sensor against
the arterial vessel via the body surface such that a portion of
a wall of the arterial vessel is substantially flattened; optimum-pressing-force
maintaining means for maintaining the optimum pressing force of
the pressing device; estimated-blood-pressure determining means
for determining an estimated blood pressure according to a predetermined
relationship between blood pressure and magnitude of pressure pulse
wave, based on a magnitude of each of a plurality of heartbeat-synchronous
pulses of the detected pressure pulse wave represented by the pressure-pulse-wave
signal produced by the optimum element in a state in which the pressure-pulse-wave
sensor is pressed against the arterial vessel with the optimum pressing
force maintained by the optimum-pressing-force maintaining means;
and an amplitude-change-curve displaying device which displays,
in a two-dimensional coordinate system having a first axis indicative
of pressing force and a second axis indicative of amplitude of heartbeat-synchronous
pulse of pressure pulse wave, an amplitude-change curve representing
a change of the respective amplitudes of the heartbeat-synchronous
pulses of the pressure pulse wave detected by the optimum element,
with respect to a change of the pressing force of the pressing device
caused by the optimum-pressing-force determining means.
According to this feature, the amplitude-change-curve displaying
device displays the amplitude-change curve representing the change
of the respective amplitudes of the heartbeat-synchronous pulses
of the pressure pulse wave detected by the optimum element, with
respect to the change of the pressing force of the pressing device
caused by the optimum-pressing-force determining means. Therefore,
an operator who operates the present BP monitor apparatus can recognize
how the apparatus presses the arterial vessel of the subject at
the time of determination of the optimum pressing force.
(2) According to a second feature of the present invention that
includes the first feature (1), the blood-pressure monitor apparatus
further comprises an estimated blood-pressure displaying device
which displays the estimated blood pressure determined by the estimated-blood-pressure
determining means.
(3) According to a third feature of the present invention that
includes the first or second feature (1) or (2), the blood-pressure
monitor apparatus further comprises an optimum-pressing-force displaying
device which displays, in the two-dimensional coordinate, system
in which the amplitude-change curve is displayed, a symbol representing
the optimum pressing force determined by the optimum-pressing-force
determining means. According to this feature, the operator can judge
whether the optimum pressing force has been determined at an appropriate
pressing force.
(4) According to a fourth feature of the present invention that
includes any one of the first to third features (1) to (3), the
blood-pressure monitor apparatus further comprises judging means
for judging, based on the pressure pulse wave detected by the optimum
element while the pressing force is changed by the optimum-pressing-force
determining means, whether the pressing device appropriately presses
the pressure-pulse-wave sensor against the arterial vessel via the
body surface. According to this feature, the judging means can identify
an inappropriate state in which a space is left between the PPW
sensor and the body surface because the arterial vessel is too shallow
under the body surface and accordingly the optimum pressing force
determined by the optimum-pressing-force determining means is too
small, and an inappropriate state in which the PPW sensor cannot
be pressed with a sufficiently great pressing force because the
artery is too deep under the body surface and accordingly the optimum
pressing force determined by the optimum-pressing-force determining
means is too great to be applied by the pressing device. Thus, the
present BP monitor apparatus can automatically judge whether the
state in which the PPW sensor is pressed against the artery is appropriate.
(5) According to a fifth feature of the present invention that
includes any one of the first to fourth features (1) to (4), the
blood-pressure monitor apparatus further comprises a blood-pressure
measuring device which includes an inflatable cuff adapted to be
wound around a body portion of the subject and measures at least
one blood pressure value of the subject based on a pulse wave transmitted
to the cuff while an air pressure in the cuff is changed; and a
relationship determining means for determining the relationship
between blood pressure and magnitude of pressure pulse wave, based
on the at least one blood pressure value measured by the blood-pressure
measuring device and at least one magnitude of a heartbeat-synchronous
pulse of the pressure pulse wave detected by the optimum element
in the state in which the pressure-pulse-wave sensor is pressed
against the arterial vessel with the optimum pressing force maintained
by the optimum-pressing-force maintaining means.
(6) According to a sixth feature of the present invention, there
is provided a blood-pressure monitor apparatus for monitoring a
blood pressure of a living subject, comprising a pressure-pulse-wave
sensor which includes a plurality of pressure sensing elements which
are arranged in a reference direction and each of which detects
a pressure pulse wave propagated thereto from an arterial vessel
of the subject and produces a pressure-pulse-wave signal representing
the detected pressure pulse wave that includes a plurality of heartbeat-synchronous
pulses, the pressure-pulse-wave sensor having a press surface which
supports the pressure sensing elements arranged in the reference
direction and which is adapted to be pressed against the arterial
vessel via a body surface of the subject such that the arranged
pressure sensing elements intersect the arterial vessel; a pressing
device which presses, with a pressing force, the pressure-pulse-wave
sensor against the arterial vessel via the body surface; optimum-element
selecting means for selecting, as an optimum element, one of the
pressure sensing elements that provides the detected pressure pulse
wave including a heartbeat-synchronous pulse whose amplitude is
greatest of respective amplitudes of respective heartbeat-synchronous
pulses of the detected pressure pulse waves provided by the pressure
sensing elements; optimum-pressing-force determining means for changing
the pressing force of the pressing device and determining, based
on the pressure pulse wave detected by the optimum element while
the pressing force is changed, an optimum pressing force with which
the pressing device presses the pressure-pulse wave sensor against
the arterial vessel via the body surface such that a portion of
a wall of the arterial vessel is substantially flattened; optimum-pressing-force
maintaining means for maintaining the optimum pressing force of
the pressing device; estimated-blood-pressure determining means
for determining an estimated blood pressure according to a predetermined
relationship between blood pressure and magnitude of pressure pulse
wave, based on a magnitude of each of a plurality of heartbeat-synchronous
pulses of the detected pressure pulse wave represented by the pressure-
pulse-wave signal produced by the optimum element in a state in
which the pressure-pulse-wave sensor is pressed against the arterial
vessel with the optimum pressing force maintained by the optimum-pressing-force
maintaining means; and a signal-magnitude-change-curve displaying
device which displays, in a two-dimensional coordinate system having
a first axis indicative of pressing force and a second axis indicative
of magnitude of pressure-pulse-wave signal, a signal-magnitude-change
curve representing a change of respective magnitudes of respective
predetermined periodic points of the heartbeat-synchronous pulses
of the detected pressure pulse wave represented by the pressure-pulse-wave
signal produced by the optimum element, with respect to a change
of the pressing force of the pressing device caused by the optimum-pressing-force
determining means.
According to this feature, the signal-magnitude-change-curve displaying
device displays the signal-magnitude-change curve representing the
change of respective magnitudes of respective predetermined periodic
points of the heartbeat-synchronous pulses of the detected PPW represented
by the PPW signal produced by the optimum element, with respect
to the change of the pressing force of the pressing device caused
by the optimum-pressing-force determining means. Therefore, an operator
who operates the present BP monitor apparatus can recognize how
the apparatus presses the arterial vessel of the subject at the
time of determination of the optimum pressing force.
(7) According to a seventh feature of the present invention that
includes the sixth feature (6), the blood-pressure monitor apparatus
further comprises an estimated-blood-pressure displaying device
which displays the estimated blood pressure determined by the estimated-blood-pressure
determining means.
(8) According to an eighth feature of the present invention that
includes any one of the sixth or seventh feature (6) or (7), the
blood-pressure monitor apparatus further comprises an optimum-pressing-force
displaying device which displays, in the two-dimensional coordinate
system in which the signal-magnitude-change curve is displayed,
a symbol representing the optimum pressing force determined by the
optimum-pressing-force determining means. According to this feature,
the operator can judge whether the optimum pressing force has been
determined at an appropriate pressing force.
(9) According to a ninth feature of the present invention that
includes any one of the sixth to eighth features (6) to (8), the
blood-pressure monitor apparatus further comprises judging means
for judging, based on the pressure pulse wave detected by the optimum
element while the pressing force is changed by the optimum-pressing-force
determining means, whether the pressing device appropriately presses
the pressure-pulse-wave sensor against the arterial vessel via the
body surface.
(10) According to a ninth feature of the present invention that
includes any one of the sixth to ninth features (6) to (9), the
blood-pressure monitor apparatus further comprises a blood-pressure
measuring device which includes an inflatable cuff adapted to be
wound around a body portion of the subject and measures at least
one blood pressure value of the subject based on a pulse wave transmitted
to the cuff while an air pressure in the cuff is changed; and a
relationship determining means for determining the relationship
between blood pressure and magnitude of pressure pulse wave, based
on the at least one blood pressure value measured by the blood-pressure
measuring device and at least one magnitude of a heartbeat-synchronous
pulse of the pressure pulse wave detected by the optimum element
in the state in which the pressure-pulse-wave sensor is pressed
against the arterial vessel with the optimum pressing force maintained
by the optimum-pressing-force maintaining means.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and optional objects, features, and advantages of the
present invention will be better understood by reading the following
detailed description of the preferred embodiments of the invention
when considered in conjunction with the accompanying drawings, in
which:
FIG. 1 is a diagrammatic view for explaining the construction of
a continuous blood-pressure ("BP") monitor apparatus to
which the present invention is applied;
FIG. 2 is a partly cut-away, enlarged view of a pressure-pulse-wave
("PPW") detecting probe of the apparatus of FIG. 1;
FIG. 3 is a graph showing a relationship between monitor blood
pressure MBP and PPW magnitude P.sub.M that is determined by the
apparatus of FIG. 1;
FIG. 4 is a diagrammatic view for explaining essential control
functions of a control device of the apparatus of FIG. 1;
FIG. 5 is a graph for explaining the manner in which an optimum
pressing force, P.sub.HDPO, is determined by an optimum-pressing-force
determining means of the apparatus of FIG. 1;
FIG. 6 is a graph which is displayed as a screen image of a display
device of the apparatus of FIG. 1;
FIG. 7 is a graph which is displayed as a screen image of the display
device in the case where a radial artery of a patient is shallow
under body surface;
FIG. 8 is a view for explaining the manner in which a PPW sensor
of the PPW detecting probe is appropriately pressed against the
radial artery via the body surface in the case where the radial
artery is shallow under the body surface;
FIG. 9 is a graph which is displayed as a screen image of the display
device in the case where the PPW sensor is not appropriately pressed
against the radial artery;
FIG. 10 is a flow chart representing a control program according
to which the control device of the apparatus of FIG. 1 is operated
to monitor the blood pressure BP of the patient; and
FIG. 11 is a flow chart representing a control program according
to which the control device is operated, when the PPW detecting
probe is initially worn on the patient, to appropriately press the
PPW sensor of the probe against the radial artery of the patient.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, there will be described a continuous blood-pressure
("BP") monitor apparatus embodying the present invention,
by reference to the drawings. The present BP monitor apparatus is
used for monitoring the BP condition of a patient during, or after,
a surgical operation, or a living subject during an exercise test.
In FIG. 1, reference numeral 10 designates an inflatable cuff which
includes a belt-like cloth bag and a rubber bag accommodated in
the cloth bag and which is worn on a patient such that the cuff
10 is wound around an upper arm 12 of the patient. The cuff 10 is
connected to a pressure sensor 14, a deflation control valve 16,
and an air pump 18 via piping 20. The deflation control valve 16
is switchable to each of three operation states, i.e., a pressure-supply
state in which the control valve 16 allows a pressurized air to
be supplied from the air pump 18 to the cuff 10, a slow-deflation
state in which the control valve 16 allows the pressurized air to
be slowly deflated from the cuff 10, and a quick-deflation state
in which the control 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,
produces a pressure signal, SP, representing the detected air pressure,
and supplies the pressure signal SP 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 extracts, from
the pressure signal SP, a constant component representing a static
pressure of the cuff, produces a cuff-pressure signal, SK, representing
the static pressure, i.e., the cuff pressure, and supplies the cuff-pressure
signal SK to a control device 28 via an analog-to-digital ("A/D")
converter 26. The pulse-wave filter circuit 24 includes a band-pass
filter which extracts, from the pressure signal SP, an oscillatory
component representing a pulse wave transmitted to the cuff, produces
a pulse-wave signal, SM.sub.1, representing the cuff pulse wave,
and supplies the pulse-wave signal SM.sub.1 to the control device
28 via an A/D converter 30. The cuff pulse wave represented by the
pulse-wave signal SM.sub.1 is a pulse wave which is produced from
a brachial artery (not shown) of the patient in synchronism with
the heartbeat of the patient and is propagated from the brachial
artery to the inflatable cuff 10. Thus, the pulse-wave filter circuit
24 provides a cuff-pulse-wave detecting device. The cuff pulse wave
represented by the pulse-wave signal SM.sub.1 consists of successive
heartbeat-synchronous pulses which are successively produced from
the brachial artery in synchronism with successive beats of the
heart of the patient.
The control device 28 is constituted by a so-called microcomputer
including a central processing unit ("CPU") 29, a read
only memory ("ROM") 31, a random access memory ("RAM")
33, and an input-and-output ("I/O") port (not shown).
The CPU 29 processes signals according to control programs pre-stored
in the ROM 31, by utilizing a temporary-storage function of the
RAM 33, and outputs, via the I/O port, drive signals to respective
drive circuits (not shown) of the deflation control valve 16 and
the air pump 18. Thus, the control device controls the control valve
16 and the air pump 18. When the present BP monitor apparatus carries
out a BP measuring operation using the cuff 10, the control device
28 first increases the air pressure of the cuff 10 up to a predetermined
target value (e.g., 180 mmHg) which is estimated to be sufficiently
higher than a systolic BP value of the patient, and then decreases
the Cuff pressure from the target value at a predetermined low rate,
e.g., 3 mmHg/sec. Based on the change of respective amplitudes of
successive heartbeat-synchronous pulses of the pulse-wave signal
SM.sub.1 obtained during the slow deflation of the cuff pressure,
the control device 28 determines a systolic and a diastolic BP value
(i.e., standard BP values) of the patient according to known oscillometric
method or Korotkoff-sound method, and commands the display 32 to
display the thus determined BP values.
The present BP monitor apparatus further includes a pressure-pulse-wave
detecting probe 34 which includes a container-like sensor housing
36; a drive device 39 which includes an electric motor (not shown);
a feed screw 41 which is threadedly engaged with the sensor housing
36 and is driven or rotated by the electric motor to move the sensor
housing 36 in a widthwise direction of a radial artery 56 of a wrist
of the patient; and a casing 37 which accommodates the sensor housing
36, the drive device 39, and the feed screw 41. A band 40 which
is connected to the casing 37 is wound around a wrist 42 of one
arm (e.g., left arm) of the patient that is opposite to the other
arm (e.g., right arm) around which the cuff 10 is wound, in the
state in which an open end of the sensor housing 36 is opposed to
a body surface 38 of the patient.
As shown in FIG. 1, the sensor housing 36 accommodates a pressure-pulse-wave
("PPW") sensor 46, and supports the PPW sensor 46 via
a rubber diaphragm 44 such that the PPW sensor 46 is movable relative
to the sensor housing 36 and is projectable out of the open end
of the housing 36. The housing 36 and the diaphragm 44 cooperate
with each other to define a first pressure chamber 48 to which a
pressurized air is supplied from an air pump 50 via a pressure control
valve 52. Thus, the PPW sensor 46 is pressed on the body surface
38 with a pressing force corresponding to the air pressure in the
first pressure chamber 48. In the present embodiment, the pressing
force applied to the PPW sensor 46 is expressed in terms of the
air pressure (mmHg) of the first pressure chamber 48.
The sensor housing 36 and the diaphragm 44 cooperate with each
other to provide a pressing device 54 which presses the PPW sensor
46 against the radial artery 56 via the body surface 38; and the
feed screw 41 and the electric motor (not shown) cooperate with
each other to provide a pressing-position changing device, i.e.,
a widthwise-direction moving device 58 which moves the PPW sensor
46 in the widthwise direction of the radial artery 56 and thereby
changes the position where the sensor 46 is pressed against the
artery 56.
The PPW sensor 46 includes a protruding portion 60 which protrudes
away from the diaphragm 44 toward the open end of the sensor housing
36. The protruding portion 60 has an end surface which provides
a press surface 62 in which a number of semiconductor pressure-sensing
elements (not shown) are provided in an array, at a predetermined
interval of distance equal to about 0.2 mm, in the widthwise direction
of the radial artery 56, i.e., a direction parallel to the feed
screw 41 along which which the PPW sensor 46 is moved. When the
press surface 62 is pressed against the radial artery 56 via the
body surface 38 of the wrist 42, each of the pressure-sensing elements
detects an oscillatory pressure wave which is produced from the
radial artery 56 and is propagated to the press surface 62, that
is, a pressure pulse wave ("PPW"), produces a PPW signal,
SM.sub.2, representing the detected PPW, and supplies the PPW signal
SM.sub.2 to the control device 28 via an A/D converter 64.
The PPW sensor 46 includes an annular portion which surrounds the
central protruding portion 60, faces the body surface 38, and supports
an annular rubber bellows 66 fixed thereto. The rubber bellows 66
is expansible and contractable in a direction in which the PPW sensor
46 is moved toward and away from the body surface 38. The rubber
bellows 66 defines a second pressure chamber 68 therein. An annular
plate 70 is fixed to one end of the bellows 66 that is opposite
to the other end thereof fixed to the annular portion of the PPW
sensor 46. The second pressure chamber 68 is supplied with a pressurized
air from the air pump 50 via a pressure control valve 72 and a rubber
pipe 74. Thus, when the first pressure chamber 48 is supplied with
the pressurized air and the protruding portion 60 of the sensor
46 is pressed on the body surface 38, a press surface 76 of the
annular plate 70 is pressed, together with the press surface 62
of the protrusion 60, on the body surface 38 of the wrist 42. An
amount of projection of the press surface 62 of the protrusion 60
from the press surface 76 of the annular plate 70 can be adjusted
by adjusting the air pressure of the second pressure chamber 68.
Restrictor rings (not shown) are provided on the inner and outer
wall surfaces of the rubber bellows 66, to prevent the bellows 66
from being irregularly deformed in radial directions thereof.
The CPU 29 of the control device 28 processes signals according
to the control programs pre-stored in the ROM 31 by using the temporary-storage
function of the RAM 33, and outputs, via the I/O port, drive signals
to respective drive circuits (not shown) of the air pump 50 and
the two pressure control valves 52, 72. Thus, the control device
28 controls the respective air pressures of the first and second
pressure chambers 48, 68. When the present BP monitor apparatus
is operated in a BP monitoring operation, the control device 28
determines, based on the PPW represented by the PPW signal SM.sub.2
supplied from the PPW sensor 46 while the pressure of the first
chamber 48 is slowly changed, the most appropriate or optimum pressing
force, P.sub.HDPO, that is applied to the PPW sensor 46 to substantially
flatten a portion of the wall of the radial artery 56, and commands
the pressure control valve 52 to maintain the thus determined optimum
pressing force P.sub.HDPO.
In addition, the control device 28 determines a maximum magnitude,
P.sub.Mmax, and a minimum magnitude, P.sub.Mmin, of a heartbeat-synchronous
pulse of the PPW signal SM.sub.2 which is detected, in the state
in which the pressure of the first chamber 48 is maintained at the
optimum pressing force P.sub.HDPO, by one pressure-sensing element
(hereinafter, referred to as the "active element") of
the array of pressure-sensing elements of the PPW sensor 46 that
is positioned right above the radial artery 56 and produces the
PPW signal SM.sub.2 representing the PPW including a heartbeat-synchronous
pulse whose amplitude is the greatest of the respective amplitudes
of the respective heartbeat-synchronous pulses of the PPWs represented
by the PPW signals SM.sub.2 produced by the pressure-sensing elements
of the PPW sensor 46. Based on the systolic BP value, BP.sub.SYS,
and the diastolic BP value, BP.sub.DIA, measured using the cuff
10, and the determined maximum and minimum magnitudes P.sub.Mmax,
P.sub.Mmin of the PPW signal SM.sub.2, the control device 28 determines
a BP-PPW relationship between blood pressure BP and PPW magnitude
P.sub.M. According to the thus determined BP-PPW relationship, the
control device 28 successively determines (i.e., estimates) a systolic
and a diastolic monitor (i.e., estimated) BP value, MBP.sub.SYS,
MBP.sub.DIA, of the patient based on a maximum and a minimum magnitude
P.sub.Mmax, P.sub.Mmin of each of successive heartbeat-synchronous
pulses of the PPW signal SM.sub.2 detected by the active element
of the PPW sensor 46. The control device 28 commands the display
32 to successively display, in digits, the systolic and diastolic
monitor BP values MBP.sub.SYS, MBP.sub.DIA determined for the each
pulse of the PPW signal SM.sub.2, and continuously display a waveform
representing the monitor BP values MBP continuously obtained by
calibrating the PPW signal SM.sub.2 according to the BP-PPW relationship.
FIG. 3 shows an example of the BP-PPW relationship that is expressed
by the following equation:
where
A is a constant indicating a slope, and
B is a constant indicating an intercept.
FIG. 4 shows essential control functions of the control device
28 of the continuous BP monitor apparatus constructed as described
above. When a BP measurement is carried out, the pressure sensor
14 detects the pressing pressure of the cuff 10 that is changed
by a cuff-pressure control means 78. A BP measuring means 80 measures
a systolic BP value BP.sub.SYS, a mean BP value BP.sub.MEAN, and
a diastolic BP value BP.sub.DIA (i.e., standard BP values), according
to oscillometric method or Korotkoff-sound method. In the oscillometric
method, the BP measuring means 80 determines the standard BP values
based on the change of respective amplitudes of successive heartbeat-synchronous
pulses of the pulse-wave signal SM.sub.1 obtained by the pressure
sensor 14 (or the pulse-wave filter circuit 24) while the pressing
pressure of the cuff 10 is slowly changed at a predetermined rate
of from 2 to 3 mmHg/sec. In the Korotkoff-sound method, the BP measuring
means 80 determines the standard BP values based on the first and
last detections of Korotkoff sounds by a microphone (not shown)
while the cuff pressure is slowly changed at the predetermined rate.
An optimum-pressing-position determining means 82 determines an
optimum pressing position where the PPW sensor 46 is most appropriately
pressed against the radial artery 56 by the pressing device 54,
when a predetermined pressing-position-determining condition is
satisfied. The predetermined pressing-position-determining condition
is, for example, when the PPW detecting probe 34 is initially worn
on the patient, or when the above-explained active element of the
PPW sensor 46 is identified as one of a predetermined number of
elements present in each of opposite end portions of the array of
pressure-sensing elements provided in the press surface 62. More
specifically described, the optimum-pressing-position determining
means 82 controls the pressing device 54 to press the PPW sensor
46 against the radial artery 56 with a first predetermined pressing
force, P.sub.1, which is sufficiently smaller than an optimum pressing
force P.sub.HDPO, described later, and judges whether the active
element of the PPW sensor 46 is one of a predetermined number of
elements present in a central portion of the array of pressure-sensing
elements provided in the press surface 62. If a negative judgement
is made, that is, if the active element of the PPW sensor 46 is
not present in the central portion of the array of pressure-sensing
elements, the means 82 controls the pressing device 54 to move once
the PPW sensor 46 away from the body surface 38, subsequently controls
the widthwise-direction moving device 58 to move the pressing device
54 and the PPW sensor 46 by a predetermined distance, and then controls
the pressing device 54 again as described above and judges again
as described above. On the other hand, if a positive judgment is
made, that is, if the active element of the PPW sensor 46 is present
in the central portion of the array of pressure-sensing elements,
the means 82 judges that the PPW sensor 46 is positioned at the
optimum pressing position, selects the active element of the PPW
sensor 46 as an optimum pressure-sensing element of the same 46,
and stores, in the RAM 33, data indicative of a sequential number
which is given to the optimum element and represents the position
of the optimum element in the array of pressure-sensing elements.
Thus, the optimum-pressing-position determining means 82 also functions
as an optimum-pressure-sensing-element selecting means.
An optimum-pressing-force determining means 84 controls the pressing
device 54 positioned at the optimum pressing position by the means
82, to continuously increase the pressing force P applied thereby
to the PPW sensor 46, and determines an optimum pressing force P.sub.HDPO
based on the PPW represented by the PPW signal SM.sub.2 which is
produced by the optimum pressure-sensing element of the PPW sensor
46 while the pressing force P is increased. An initial pressing
force, i.e., a minimum pressing force from which the pressing force
P of the pressing device 54 is increased by the means 84, is experimentally
determined, in advance, as a value which is sufficiently lower than
the optimum pressing force P.sub.HDPO to be determined, even if
different optimum pressing forces P.sub.HDPO may be determined for
different individual patients. A terminal pressing force, i.e.,
a maximum pressing force at which the increasing of the pressing
force P is ended, may be experimentally determined, in advance,
as a value which is sufficiently higher than the optimum pressing
force P.sub.HDPO to be determined, like the initial pressing force.
Alternatively, the increasing of the pressing force P may be ended
at a time when an amplitude-change curve, C.sub.A, and/or a signal-magnitude-change
curve, C.sub.S, described later, are/is obtained during the increasing
of the pressing force P and the optimum pressing force P.sub.HDPO
is determined based on the amplitude-change curve C.sub.A and/or
the signal-magnitude-change curve C.sub.S.
FIG. 5 shows an example of the PPW signal SM.sub.2 which is produced
by the optimum pressure-sensing element of the PPW sensor 46 while
the pressing force P of the pressing device 54 is continuously increased.
As the pressing force P increases, the magnitude of the PPW signal
SM.sub.2 increases while oscillating or pulsating. In the graph
of FIG. 5, the signal-magnitude-change curve C.sub.S, indicated
at broken line, is obtained by connecting respective magnitudes
of respective predetermined periodic points (e.g., respective magnitudes,
S.sub.Mmin, of respective minimum points) of successive heartbeat-synchronous
pulses of the PPW signal SM.sub.2. The signal-magnitude-change curve
C.sub.S includes a substantially flat portion where the magnitude
of the signal SM.sub.2 does not substantially change as the pressing
force P increases. As the pressing force P increases in a low pressing-force
range in which the wall of the radial artery 56 is not flattened
yet, the magnitude of the signal SM.sub.2 gradually increases because
of increased reaction of the wall of the artery 56. However, as
the pressing force further increases, a portion of the wall of the
artery 56 supported by the radius bone located under the same 56
is flattened so that the reaction of the arterial wall does not
increase and the magnitude of the signal SM.sub.2 is kept constant.
Therefore, the curve C.sub.S exhibits a flat portion in which the
magnitude of the signal SM.sub.2 does not change as the pressing
force P increases and the intraarterial blood pressure is directly
transmitted to the PPW sensor 46 via the flattened wall of the artery
56. As the pressing force still further increases, the reaction
of the wall of the artery 56 increases again whereas the artery
56 still more flattens and the pulsation of the signal SM.sub.2
decreases.
FIG. 5 also s hows an example of the amplitude-change curve C.sub.A
as an envelope of respective amplitudes of the successive heartbeat-synchronous
pulses of the PPW signal SM.sub.2 that is produced by the optimum
pressure-sensing element of the PPW sensor 46 while the pressing
force P of the pressing device 54 is continuously increased. That
is, the curve CA represents an alternating-current component of
the signal SM.sub.2. As the pressing force P increases in a low
pressing-force range, the curve C.sub.A increases; and as the pressing
force P further increases in a high pressing-force range, the curve
C.sub.A decreases because the radial artery 56 flattens and the
pulsation of the signal SM.sub.2 decreases.
The means 84 determines, as the optimum pressing force P.sub.HDPO,
a value which falls in a first reference range whose center is equal
to the maximum value of the curve C.sub.A and/or in a second reference
range whose center is equal to the center of the flat portion of
the curve C.sub.S.
An optimum-pressing-force maintaining means 86 controls the pressure
control valve 52 and thereby maintains the air pressure of the first
pressure chamber 48 at the optimum pressing force P.sub.HDPO determined
by the means 84.
A relationship determining means 88 determines a BP-P.sub.M relationship
between blood pressure BP and PPW magnitude P.sub.M, as shown in
FIG. 3, based on the BP values BP measured by the BP measuring means
80 and the magnitudes P.sub.M of the PPW signal SM.sub.2 produced
by the optimum pressure-sensing element of the PPW sensor 46 pressed
with the optimum pressing force P.sub.HDPO. The optimum pressure-sensing
element is positioned right above the radial artery 56.
An estimated-BP determining means 90 successively determines an
estimated BP value MBP according to the BP-P.sub.M relationship
determined by the means 88, based on a magnitude of each of successive
heartbeat-synchronous pulses of the PPW represented by the PPW signal
SM.sub.2 produced by the optimum pressure-sensing element of the
PPW sensor 46 pressed with the optimum pressing force P.sub.HDPO.
An amplitude-change-curve displaying means 92 controls the display
device 32 to display, in a two-dimensional coordinate system having
a first axis indicative of pressing force P and a second axis indicative
of amplitude of heartbeat-synchronous pulse of PPW, the amplitude-change
curve C.sub.A representing the change of the respective amplitudes
of the heartbeat-synchronous pulses of the PPW signal SM.sub.2 detected
by the optimum pressure-sensing element, with respect to the change
of the pressing force of the pressing device 54 caused by the optimum-pressing-force
determining means 84. That is, the display device 32 displays the
amplitude-change curve C.sub.A which is obtained when the optimum-pressing-force
determining means 84 determines the optimum pressing force P.sub.HDPO.
A signal-magnitude-change-curve displaying means 94 controls the
display device 32 to display, in a two-dimensional coordinate system
having a first axis indicative of pressing force P and a second
axis indicative of magnitude of PPW signal SM.sub.2, the signal-magnitude-change
curve C.sub.S representing the change of respective magnitudes of
respective predetermined periodic points of the heartbeat-synchronous
pulses of the detected PPW represented by the PPW signal SM.sub.2
produced by the optimum pressure-sensing element, with respect to
the change of the pressing force P of the pressing device 54 caused
by the optimum-pressing-force determining means 84. That is, the
display device 32 displays the signal-magnitude-change curve C.sub.S
which is obtained when the optimum-pressing-force determining means
84 determines the optimum pressing force P.sub.HDPO.
An optimum-pressing-force displaying means 96 controls the display
device 32 to display, in the two-dimensional coordinate system in
which the amplitude-change curve C.sub.A is displayed, and/or in
the two-dimensional coordinate system in which the signal-magnitude-change
curve C.sub.S is displayed, a straight line 97 as a symbol representing
the optimum pressing force P.sub.HDPO determined by the optimum-pressing-force
determining means 84.
FIG. 6 shows a screen image which is displayed on the display device
32 and which includes a two-dimensional coordinate system in which
the amplitude-change curve C.sub.A is displayed by the means 92,
and the signal-magnitude-change curve C.sub.S is displayed by the
means 94, along a common axis indicative of pressing force P of
the pressing device 54. In addition, in the coordinate system, the
straight line 97 representative of the optimum pressing force P.sub.HDPO
is displayed by the means 96 such that the straight line 97 is perpendicular
to the common pressing-force axis. Since the amplitude-change curve
C.sub.A or the signal-magnitude-change curve C.sub.S is displayed
on the display device 32, an operator who operates the present BP
monitor apparatus can recognize how the PPW sensor 46 is pressed
against the radial artery 56 via the body surface 38 at the time
of determination of the optimum pressing force P.sub.HDPO. FIG.
6 shows that the amplitude-change curve C.sub.A has a maximum amplitude
value, substantially monotonously increases from an initial amplitude
value corresponding to the initial pressing force, to the maximum
amplitude value, and substantially monotonously decreases from the
maximum amplitude value, and that the straight line 97 representative
of the optimum pressing force P.sub.HDPO is displayed around the
maximum amplitude value. In this case, the operator can judge that
the PPW sensor 46 is appropriately pressed against the radial artery
56. In addition, FIG. 6 shows that the signal-magnitude-change curve
C.sub.S includes a substantially flat portion and that the straight
line 97 representative of the optimum pressing force P.sub.HDPO
is displayed around the center of the flat portion. In this case,
too, the operator can judge that the state in which the PPW sensor
46 is pressed against the radial artery 56 is appropriate.
The amplitude-change curve C.sub.A shown in FIG. 6 is a normalized
curve which is obtained by normalizing the pressing-force axis with
a pressing-force range (i.e., a pressing-force change width) over
which the pressing force of the pressing device 54 has been changed
by the optimum-pressing-force determining means 84 to determine
the optimum pressing force P.sub.HDPO, and normalizing the amplitude
axis with the maximum amplitude value of the PPW signal SM.sub.2
that has been obtained by the means 84 to determine the optimum
pressing force P.sub.HDPO. Similarly, the signal-magnitude-change
curve C.sub.S shown in FIG. 6 is a normalized curve which is obtained
by normalizing the pressing-force axis with the pressing-force range
and normalizing the signal-magnitude axis with a maximum signal
magnitude of the PPW signal SM.sub.2 that has been obtained by the
means 84 to determine the optimum pressing force P.sub.HDPO. Therefore,
even if the PPW signal SM.sub.2 provides different maximum values
or different amplitude values for different individual subjects,
or the means 84 controls the pressing device 54 to change the pressing
force P in different pressing-force ranges having different maximum
pressing-force values for different individual subjects, each of
the curves C.sub.A, C.sub.S is always displayed in a predetermined
size, so that the operator can easily recognize how the PPW sensor
46 is pressed against the radial artery 56 at the time of determination
of the optimum pressing force P.sub.HDPO.
FIG. 7 shows an example of a screen image which is displayed on
the display device 32 and which includes an amplitude-change curve
C.sub.A only. FIG. 7 shows that the curve C.sub.A has a considerably
great amplitude value at the initial or minimum pressing force of
the pressing-force range, and has a maximum amplitude value at a
considerably small pressing force. This amplitude-change curve C.sub.A
is obtained in the case where the radial artery 56 is located at
a considerably shallow position under the body surface 38 because,
e.g., the patient is thin. In this case, if the press surface 62
of the protruding portion 60 of the PPW sensor 46, shown in FIGS.
1 and 2, is projecting by a considerably great amount out of the
press surface 76 of the annular plate 70, an optimum pressing force
P.sub.HDPO may be determined in a considerably unstable state in
which a space may be adversely created between the body surface
38 and the press surface 76 of the annular plate 70. Therefore,
the operator can judge that it will be difficult to maintain, for
a long time, the appropriate state in which the PPW sensor 46 is
pressed against the radial artery 56.
When from the amplitude-change curve C.sub.A displayed on the display
device 32 the operator judges, as explained above, that the state
in which the PPW sensor 46 is pressed against the radial artery
56 is not appropriate, the operator can operate an operation panel
(not shown) of the present BP monitor apparatus to operate the pressure
control valve 72 to supply pressurized air from the air pump 50
to the second pressure chamber 68, so that the press surface 76
of the annular plate 70 is projected to a position substantially
equal to the position of the press surface 62 of the protruding
portion 60, as shown FIG. 8. Thus, the space present between the
body surface 38 and the press surface 76 of the annular plate 70
is eliminated, and accordingly the appropriate state in which the
PPW sensor 46 is pressed against the wall of the radial artery 56
can be maintained for a long time even in the case where the artery
56 is considerably shallow under the body surface 38.
FIG. 9 shows an example of a screen image which is displayed on
the display device 32 and which includes a signal-magnitude-change
curve C.sub.S only. FIG. 9 shows that as the pressing force P increases,
the curve C.sub.S monotonously increases without having a flat or
substantially flat portion. In this case, the operator can judge
that the state in which the PPW sensor 46 is pressed against the
radial artery 56 is not appropriate. This signal-magnitude-change
curve C.sub.S is obtained in the case where the subject has a considerably
thick skin tissue and the radial artery 56 is considerably deep
under the body surface 38, but the press surface 62 of the protruding
portion 60 is not projected by so great an amount out of the press
surface 76 of the annular plate 70. That is, when the press surface
62 being not projected so much from the press surface 76 is used
to press the radial artery 56 considerably deep under the body surface
38, the pressing device 54 must apply a great pressing force to
the PPW sensor 46 to substantially flatten a portion of the wall
of the artery 56. However, if the pressing device 54 cannot apply
such a great pressing force, the curve C.sub.S shown in FIG. 9 is
obtained.
When from the signal-magnitude-change curve C.sub.S displayed on
the display device 32 the operator judges, as explained above, that
the state in which the PPW sensor 46 is pressed against the artery
56 is not appropriate the operator can operate the operation panel
(not shown) to operate the pressure control valve 72 to deflate
the pressurized air from the second pressure chamber 68, so that
the press surface 76 of the annular plate 70 is retracted from the
press surface 62 of the protruding portion 60, as shown in FIG.
1. Thus, the press surface 62 of the protruding portion 60 is projected
from the the press surface 76 of the annular plate 70. In this way,
with a considerably small pressing force within the pressing-force
range of the pressing device 54, the PPW can be appropriately pressed
against the radial artery 56 which is considerably deep under the
body surface 38, so that a portion of the wall of the artery 56
is substantially flattened.
A pressing-state judging means 98 judges, based on the PPW represented
by the PPW signal SM.sub.2 obtained while the pressing force P of
the pressing device 54 is changed by the means 84, whether the state
in which the PPW sensor 46 is pressed against the radial artery
56 is appropriate. More specifically described, based on the amplitude-change
curve C.sub.A and the signal-magnitude-change curve C.sub.S obtained
by the means 84, the judging means 98 makes a judgment. For example,
the judging means 98 judges whether the amplitude-change curve C.sub.A
has an amplitude value smaller than a predetermined proportion (e.g.,
75%) of its maximum amplitude value, within a pressing-force range
smaller than a pressing force corresponding to the maximum amplitude
value. A negative judgment means that the radial artery pressed
by the PPW sensor 46 is considerably shallow under the body surface
38. If the negative judgment is obtained and simultaneously the
judging means 98 judges that the press surface 62 of the protruding
portion 60 is projected by more than a predetermined distance from
the press surface 76 of the annular plate 70, the judging means
98 judges that the state in which the PPW sensor 46 is pressed against
the artery 56 is not stable.
In addition, the pressing-state judging means 98 judges, based
on the signal-magnitude-change curve C.sub.S, whether the curve
C.sub.S has a flat or substantially flat portion, i.e., a portion
in which the signal magnitude does not change as the pressing force
P increases. For example, if the curve C.sub.S obtained by the means
84 is one as shown in FIG. 9, the judging means 98 makes a negative
judgment. That is, if the artery 56 pressed by the PPW sensor 46
is considerably deep under the body surface 38 and simultaneously
the press surface 62 of the protruding portion 60 is not projected
from the press surface 76 of the annular plate 70, as shown in FIG.
8, the judging means 98 judges that the state in which the sensor
46 is pressed is not appropriate.
A projection-amount adjusting means 100 adjusts an amount of projection
of the press surface 62 of them protruding portion 60 from the press
surface 76 of the annular plate 70, by supplying drive signals to
the air pump 50 and the pressure control valve 72 and thereby adjusting
the pressure of the second pressure chamber 68, in the case where
the judging means 98 judges that the state in which the PPW sensor
46 is pressed against the radial artery 56 is not appropriate, or
in the case where the operator judges from the amplitude-change
curve C.sub.A and/or the signal-magnitude-change curve C.sub.S displayed
on the display device 32, that the state in which the sensor 46
is pressed is not appropriate, and operates the operation panel
(not shown) to eliminate the inappropriate state.
FIGS. 10 and 11 show two flow charts representing two control programs
according to which the control device 28 is operated. FIG. 10 shows
a main routine, and FIG. 11 shows a pressing-state display-and-judge
routine according to which the control device 28 is operated, when
the PPW detecting probe 34 is initially worn on a patient, to control
the display device 32 to display a state in the PPW sensor 46 is
pressed against a radial artery 56 via a body surface 38, and judges
whether the state in which the PPW sensor 46 is pressed is appropriate.
First, at Step SA1 of FIG. 10, the control device 28 judges whether
a predetermined calibration period (e.g., from ten and several minutes
to several tens of minutes) has elapsed after the BP-P.sub.M relationship
had been updated at Step SA7 in the prior control cycle according
to the main routine. Usually, a negative judgment is made at Step
SA1, and the control of the control device 28 goes to Step SA2 to
judge whether a predetermined pressing-position updating condition
(hereinafter, referred to as the "APS starting condition")
has been satisfied. For example, the control device 28 judges whether
the active element of the PPW sensor 46 that detects the greatest
amplitude of all the pressure-sensing elements of the sensor 46
is present in one of opposite end portions of the array of the pressure-sensing
elements provided in the press surface 62 of the sensor 46.
If the current pressing position where the PPW sensor 46 is pressed
against the radial artery 56 is within a normal range, a negative
judgment is made at Step SA2, and the control goes to Step SA3 to
judge whether a predetermined BP-P.sub.M -relationship updating
condition or a predetermined optimum-pressing-force-determination
starting condition (hereinafter, referred to as the "HDP starting
condition") has been satisfied. For example, the control device
28 judges whether a physical motion of the patient that changes
the condition under which the PPW sensor 46 is pressed, so greatly
as to change the current BP-P.sub.M relationship, or whether the
monitor BP values MBP have changed by more than a predetermined
amount from the standard BP value BP measured in the prior BP measurement
using the cuff 10.
If a negative judgment is made at Step SA3, the control of the
control device 28 goes to Step SA8 to judge, based on the PPW signal
SM.sub.2 supplied from the optimum (active) element of the PPW sensor
46 pressed with the optimum pressing force P.sub.HDPO, whether one
heartbeat-synchronous pulse of the PPW has been detected by the
PPW sensor 46. If a negative judgment is made at Step SA8, Steps
SA1, SA2, SA3, and SA8 are repeated. Meanwhile, if a positive judgment
is made, the control goes to Step SA9 corresponding to the estimated-BP
determining means 90. At Step SA9, the control device 28 determines,
based on the detected one pulse of the PPW, a maximum magnitude
P.sub.Mmax and a minimum magnitude P.sub.Mmin of the one pulse,
determines an estimated systolic BP value MBP.sub.SYS and an estimated
diastolic BP value MBP.sub.DIA according to the current BP-P.sub.M
relationship based on the determined maximum magnitude P.sub.Mmax
and minimum magnitude P.sub.Mmin of the one pulse, respectively,
and controls the display device 32 to display, in digits, the estimated
or monitor systolic and diastolic BP values MBP.sub.SYS, MBP.sub.DIA
determined for the one pulse. In addition, the control device 32
calibrates the continuous waveform of the one pulse of the PPW represented
by the PPW signal SM.sub.2, according to the current BP-P.sub.M
relationship, and controls the display device 32 to display the
thus calibrated continuous waveform representing the estimated BP
values of the patient.
If a positive judgment is made at Step SA1 while Steps SA1 to SA3,
SA8, and SA9 are repeated, the control of the control device 28
goes to Step SA6 to carry out a BP measurement using the cuff 10,
and then to Step SA7 to update the current BP-P.sub.M relationship,
and then to Steps SA8, SA9. More specifically described, at Step
SA6 corresponding to the BP measuring means 80, the control device
28 switches the deflation control valve 16 to its pressure-supply
state and actuates the air pump 18 to increase the pressure of the
cuff 10 up to a predetermined target value (e.g., 180 mmHg) higher
than an estimated systolic BP value of the patient, and subsequently
stops the pump 18 and switches the control valve 16 to its slow-deflation
state to decrease the pressure of the cuff 10 at a predetermined
low rate of, e.g., 3 mmHg/sec. Based on change of respective amplitudes
of successive heartbeat-synchronous pulses of the pulse wave represented
by the pulse-wave signal SM.sub.1 obtained during the slow deflation
of the cuff 10, the control device 28 determines a systolic, a mean,
and a diastolic BP values BP.sub.SYS, BP.sub.MEAN, BP.sub.DIA (i.e.,
standard BP values), according to a well-known oscillometric BP-determine
algorithm. In addition, based on an interval between two successive
heartbeat-synchronous pulses of the pulse wave, the control device
28 determines a pulse rate (i.e., heart rate) of the patient. The
control device 28 controls the display device 32 to display, in
digits, the thus measurerd BP values and pulse rate, and switches
the deflation control valve 16 to its quick-deflation state to quickly
deflate the cuff 10.
Step SA6 is followed by Step SA7 corresponding to the relationship
determining means 88. At Step SA7, the control device 28 determines
a new BP-P.sub.M relationship based on magnitudes of the PPW detected
by the optimum element of the PPW sensor (i.e., magnitudes of the
PPW signal SM.sub.2) and the BP values BP.sub.SYS, BP.sub.DIA measured
using the cuff 10 at Step SA6, and updates the current BP-P.sub.M
relationship with the thus determined new BP-P.sub.M relationship.
More specifically described, the control device 28 reads in one
heartbeat-synchronous pulse of the PPW detected by the optimum element
of the PPW sensor 46, determines, based on the read-in one pulse
of the PPW, a maximum magnitude P.sub.Mmax and a minimum magnitude
P.sub.Mmin Of the one pulse, and determines a new relationship between
blood pressure BP and PPW magnitude, as shown in FIG. 3, based on
the thus determined maximum and minimum magnitudes P.sub.Mmax, P.sub.Mmin
of the one pulse, and the systolic and diastolic BP values BP.sub.SYS,
BP.sub.DIA measured using the cuff 10 at Step SA6.
If the APS starting condition is satisfied, for example, if the
pressing position where the PPW sensor 46 is pressed against the
radial artery 56 is moved out of position, a positive judgment is
made at Step SA2, and the control goes to Step SA4, i.e., an APS
control routine corresponding to the optimum-pressing-position determining
means 82. According to the APS control routine, the control device
28 controls the pressing device 54 to press the PPW sensor 46 with
a predetermined pressing force which is sufficiently smaller than
the optimum pressing force P.sub.HDPO, determines, based on the
respective PPW signals SM.sub.2 supplied from the pressure-sensing
elements of the PPW sensor 46, an active element that detects the
greatest amplitude of all the elements of the PPW sensor 46, and
determines an optimum pressing position where the active element
of the PPW sensor 46 is determined as one located around the center
of the array of elements of the sensor 46. After the PPW sensor
46 is thus positioned at the optimum pressing position and the active
element of the sensor 46 is selected as an optimum element of the
same 46, the control goes to Step SA5, i.e., a HDP control routine.
According to the HDP control routine, the control device 28 controls
the pressing device 54 to continuously increase the pressing force
P applied to the PPW sensor 46, determines, as a new optimum pressing
force P.sub.HDpO, a pressing force of the pressing device 54 at
which respective amplitudes of successive heartbeat-synchronous
pulses of the PPW detected by the optimum element of the PPW sensor
46, positioned right above the radial artery 56, take a maximum
value during the increasing of the pressing force P, and updates
the current optimum pressing force P.sub.HDPO with the thus determined
new optimum pressing force P.sub.HDPO. The control device 28 maintains
the pressing force P of the pressing device 54 at the updated optimum
pressing force P.sub.HDPO. Thus, Step SA5 corresponds to the optimum-pressing-force
determining means 84 and the optimum-pressing-force maintaining
means 86. Then, in the state in which the PPW sensor 46 is pressed
with the optimum pressing force P.sub.HDpO, the control device 28
carries out Step SA6 and the following steps.
If a negative judgment is made at Step SA2, that is, if it is judged
that the PPW sensor 46 is pressed at an appropriate position and
the BP of the patient can be continuously monitored by the present
apparatus, but if a positive judgment is made at Step SA3, the control
device 28 carries out the HDP control routine of Step SA5, and then
the following steps.
Next, by reference to FIG. 11, there will be described the pressing-state
display-and-judge routine according to which the control device
28 is operated, when the PPW detecting probe 34 is initially worn
on the patient, and before the control device 28 is operated according
to the main routine of FIG. 10. According to the display-and-judge
routine, the control device 28 controls the display device 32 to
display a state in the PPW sensor 46 is pressed against the radial
artery 56 via the body surface 38, and judges whether the state
in which the PPW sensor 46 is pressed is appropriate.
First, at Step SB1 of FIG. 11, corresponding to the optimum-pressing-position
determining means 82, the control device 28 carries out the same
APS control routine as that employed at Step SA4 of FIG. 10. In
short, the control device 28 determines, based on the respective
PPW signals SM.sub.2 supplied from the pressure-sensing elements
of the PPW sensor 46, an optimum pressing position where the active
element of the sensor 46 that detects the greatest amplitude of
all the elements of the sensor 46 is one located in the vicinity
of the center of the array of elements provided in the press surface
62 of the sensor 46.
Step SB1 is followed by Step SB2 corresponding to the optimum-pressing-force
determining means 84. At this step, the control device 28 controls
the pressing device 54 to continuously increase the pressing force
P applied to the PPW sensor 46, and obtains an amplitude-change
curve C.sub.A and a signal-magnitude-change curve C.sub.S from the
PPW signal SM.sub.2 supplied from the optimum element of the PPW
sensor 46 during the continuous increasing of the pressing force.
In addition, the control device 28 determines, as an optimum pressing
force P.sub.HDPO, a pressing force corresponding to the center of
an overlapping portion of (a) a first predetermined pressing-force
range whose center corresponds to the maximum amplitude value of
the amplitude-change curve C.sub.A and (b) a second predetermined
pressing-force range whose center corresponds to the center of the
flat portion of the signal-magnitude-change curve C.sub.S.
Step SB2 is followed by Step SB3 to normalize the amplitude-change
curve C.sub.A and the signal-magnitude-change curve C.sub.S obtained
when the optimum pressing force P.sub.HDPO is determined at Step
SB2, and control the display device 32 to display the normalized
curves C.sub.A, C.sub.S in the two-dimensional coordinate system
having the common pressing-force axis and the PPW-amplitude axis
or the PPW-signal-magnitude axis, and additionally display the straight
line 97 indicative of the optimum pressing force P.sub.HDPO on the
common pressing-force axis. Thus, Step SB3 corresponds to the amplitude-change-curve
displaying means 92, the signal-magnitude-change-curve displaying
means 94, and the optimum-pressing-force displaying means 96. FIG.
6 shows an example of the screen image displayed on the display
device 32 at Step SB3 when the state in which the PPW sensor 46
is pressed against the radial artery 56 is appropriate.
Step SB3 is followed by Step SB4 corresponding to the pressing-state
judging means 98. At Step SB4, the control device 28 judges, in
the state in which the press surface 62 of the protruding portion
60 is projected from the press surface 76 of the annular plate 70
by more than a predetermined amount, as shown in FIG. 1, whether
the amplitude-change curve C.sub.A obtained at Step SB2 has an amplitude
value smaller than 75% of its maximum amplitude value, in a pressing-force
range whose upper limit is equal to a pressing force corresponding
to the maximum amplitude value, or whether the signal-magnitude-change
curve C.sub.S obtained at Step SB2 has a flat or substantially flat
portion. If at least one of those two judgments is negative, the
control device 28 judges that the state in which the PPW sensor
46 is pressed against the radial artery 56 is not appropriate.
If a negative judgment is made at Step SB4, the control goes to
Step SB6 corresponding to the projection-amount adjusting means
100. At this step, the control device 28 supplies drive signals
to the air pump 50 and the pressure control valve 72 to adjust the
pressure in the second pressure chamber 68 and thereby adjust the
amount of projection of the press surface 62 of the protruding portion
60 from the press surface 76 of the annular plate 70, so that the
PPW sensor 46 is appropriately pressed against the radial artery
56. Then, the control device 28 repeats Step SB1 and the following
steps.
On the other hand, if a positive judgment is made at Step SB4,
the control goes to Step SB5 to judge whether the operator who has
judged that the state in which the sensor 46 is pressed is not appropriate
has operated the operation panel (not shown) to adjust the amount
of projection of the press surface 62 of the protruding portion
60 from the press surface 76 of the annular plate 70. Even though
a negative judgment may not be made at Step SB4, the operator may
judge, based on the curves C.sub.A, C.sub.S displayed on the display
device 32 at Step SB3, that the state in which the sensor 46 is
pressed is not appropriate. In this case, the operator can adjust
the amount of projection of the press surface 62 of the protruding
portion 60 from the press surface 76 of the annular plate 70, by
operating the operation panel.
If a positive judgment is made at Step SB5, the control proceeds
with Step SB6 to adjust the amount of projection of the press surface
62 according to the operation of the operation panel, and then goes
back to Step SB1. However, if a negative judgment is made at Step
SB5, the control device 28 quits the display-and-judge routine of
FIG. 11 and enters the main routine of FIG. 10.
It emerges from the foregoing description that in the illustrated
embodiment the amplitude-change-curve displaying means 92 (Step
SB3) displays the amplitude-change curve C.sub.A which represents
the change of the respective amplitudes of the successive heartbeat-synchronous
pulses of the PPW detected by the optimum element of the PPW sensor
46, with respect to the change of the pressing force P of the pressing
device 54 caused by the optimum-pressing-force determining means
84 (Step SB2). Therefore, the operator who operates the present
BP monitor apparatus can recognize how the PPW sensor 46 is pressed
against the radial artery 56 at the time of determination of the
optimum pressing force P.sub.HDPO.
In the illustrated embodiment, the signal-magnitude-change-curve
displaying means 94 (Step SB3) displays, on the display device 32,
the signal-magnitude-change curve C.sub.S which represents the change
of the respective magnitudes of the respective periodic minimum
points of successive heartbeat-synchronous pulses of the PPW detected
by the optimum element of the PPW sensor 46, with respect to the
change of the pressing force P of the pressing device 54 caused
by the optimum-pressing-force determining means 84 (Step SB2). Therefore,
the operator-who operates the present BP monitor apparatus can judge
whether the state in which the PPW sensor 46 is pressed against
the radial artery 56 at the time of determination of the optimum
pressing force P.sub.HDpO is appropriate.
In the illustrated embodiment, the optimum-pressing-force displaying
means 96 (Step SB3) displays, in the two-dimensional coordinate
system in which the amplitude-change curve C.sub.A or the signal-magnitude-change
curve C.sub.S, the straight line 97 indicative of the optimum pressing
force P.sub.HDPO. Thus, the operator can judge whether the optimum
pressing force P.sub.HDPO has been determined at an appropriate
pressing force.
In the illustrated embodiment, the pressing-state judging means
98 (Step SB4) can identify the inappropriate state in which a space
is left between the annular plate 70 of the PPW sensor 46 and the
body surface 38 because the radial artery 56 is too shallow under
the body surface 38 and accordingly the optimum pressing force P.sub.HDPO
determined by the means 84 (Step SB2) is too small, and the inappropriate
state in which the PPW sensor 46 cannot be pressed with a sufficiently
great pressing force because the radial artery 56 is too deep under
the body surface 38 and accordingly the optimum pressing force P.sub.HDPO
determined by the means 84 (Step SB2) is too great to be applied
by the pressing device 54. Thus, the control device 28 can automatically
judge whether the state in which the PPW sensor 46 is pressed against
the radial artery 56 is appropriate.
While the present invention has been described in its preferred
embodiments, the present invention may be otherwise embodied.
For example, in the illustrated embodiment, the pressing-state
judging means 98 (Step SB4) automatically judges whether the state
in which the PPW sensor 46 is pressed against the radial artery
56 is appropriate. However, it is possible to omit the judging means
98.
In the illustrated embodiment, the PPW sensor 46 is appropriately
pressed against the radial artery 56, by the adjustment of the amount
of projection of the press surface 62 of the protruding portion
60 from the press surface 76 of the annular plate 70, irrespective
of whether the artery 56 may be considerably shallow or considerably
deep under the body surface 38. However, it is possible to employ
and use a PPW detecting probe 34 which has a single sort of PPW
sensor 46 which has an amount of projection of its press surface
62 that just corresponds to the depth of the radial artery 56 under
the body surface 38, or to select and use one of a plurality of
sorts of PPW sensors 46 that has an amount of projection of its
press surface 62 that just corresponds to the depth of the radial
artery 56 under the body surface 38 and detachably attach the selected
PPW sensor 46 to a PPW detecting probe 34.
In the illustrated embodiment, the optimum-pressing-force displaying
means 96 displays the straight line 97 indicative of the optimum
pressing force P.sub.HDpO. However, it is possible to use any other
symbol than the straight line 97 so long as the symbol can indicate
the optimum pressing force P.sub.HDPO and can be displayed with
the amplitude-change curve C.sub.A or the signal-magnitude-change
curve C.sub.S.
In the illustrated embodiment, the PPW is detected from the radial
artery 56. However, a PPW may be detected from any other artery
than the radial artery 56, such as a dorsal pedal artery.
It is to be understood that the present invention may be embodied
with other changes, improvements, and modifications that may occur
to one skilled in the art without departing from the scope and spirit
of the invention defined in the appended claims. |