Abstrict
A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, wherein the blood pressure is judged to be
abnormal when a first change value as a change of each of a plurality
of blood pressure values iteratively obtained from the subject,
from a standard blood pressure obtained from the subject, does not
fall in a first reference range (TH1), wherein the improvement comprises:
the first reference range being determined based on the standard
blood pressure of the subject, according to a relationship between
first reference range and standard blood pressure wherein a plurality
of different first reference ranges correspond to a plurality of
different standard blood pressures, respectively.
Claims
What is claimed is:
1. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: a first-change-value calculating
device for calculating a first change value as a change of each
of a plurality of blood pressure values iteratively obtained from
the subject, from a standard blood pressure obtained from the subject;
a relationship obtaining device for obtaining a relationship between
first reference range and standard blood pressure wherein a plurality
of different first reference ranges correspond to a plurality of
different standard blood pressures, respectively; a first-reference-range
determining device for determining a first reference range based
on the standard blood pressure obtained from the subject and according
to the relationship between first reference range and standard blood
pressure obtained by the relationship obtaining device; and an abnormality
judging device for judging that the blood pressure of the subject
is abnormal when the first change value calculated by the first-change-value
calculating device does not fall in the first reference range determined
by the first-reference-range determining device.
2. A blood pressure monitor apparatus according to claim 1, wherein
the relationship between first reference range and standard blood
pressure is determined by an operator of the blood pressure monitor
apparatus.
3. A blood pressure monitor apparatus according to claim 2, wherein
the relationship between first reference range and standard blood
pressure is recorded on a recording medium which is attachable to,
and detachable from, the apparatus.
4. A blood pressure monitor apparatus according to claim 1, wherein
the first reference range is defined by an upper first threshold
which is used to judge whether an increase of the blood pressure
of the subject is abnormal, the relationship between first reference
range and standard blood pressure being determined such that a smaller
upper first threshold corresponds to a higher standard blood pressure.
5. A blood pressure monitor apparatus according to claim 1, wherein
the first reference range is defined by a lower first threshold
which is used to judge whether a decrease of the blood pressure
of the subject is abnormal, the relationship between first reference
range and standard blood pressure being determined such that a greater
lower first threshold corresponds to a lower standard blood pressure.
6. A blood pressure monitor apparatus according to claim 1, further
comprising: a second-change-value calculating device for calculating
a second change value as a change of said each of said blood pressure
values from a blood pressure value obtained a predetermined time
period before said each of said blood pressure values; and a second-reference
range determining device for determining a second reference range;
wherein the abnormality judging device judges that the blood pressure
of the subject is abnormal when the second change value calculated
by the second-change-value calculating device does not fall in the
second reference range is determined by the second-reference-range
determining device.
7. A blood pressure monitor apparatus according to claim 6, further
comprising: a third-reference-range determining device for determining
a third reference range; wherein the abnormality judging device
judges that the blood pressure of the subject is abnormal when said
each of said blood pressure values does not fall in the third reference
range determined by the third-reference-range determining device.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a blood pressure monitor apparatus
which monitors blood pressure values iteratively obtained from a
living subject.
2. Related Art Statement
A blood pressure monitor apparatus is used, for instance, for continuously
monitoring the blood pressure of a patient or a living subject during
an operation. One example of the blood pressure monitor apparatus
is adapted to judge the abnormality of blood pressure of the subject
when the blood pressure is higher than a predetermined upper threshold
or lower than a predetermined lower threshold. Another example of
the blood pressure monitor apparatus is adapted to determine, as
a standard blood pressure of the subject, a blood pressure measured
at a certain time point, and judge the abnormality of the blood
pressure of the subject when an amount or a rate of change of the
blood pressure of the subject from the standard blood pressure does
not fall in a prescribed reference range. For instance, JP-A-11-318837
or its corresponding U.S. Pat. No. 6,027,455 discloses a technique
to judge the abnormality of blood pressure of the subject, wherein
1) an estimated blood pressure is iteratively determined based on
pulse-wave-propagation-velocity-related information which is related
to a velocity at which a pulse wave propagates in the subject, and
the abnormality of blood pressure of the subject is judged when
the iteratively determined estimated blood pressure does not fall
in a prescribed alert range, and 2) a blood pressure obtained at
a prescribed period by using a cuff is determined as a standard
blood pressure, and the abnormality of blood pressure of the subject
is judged when a rate of change of the iteratively determined estimated
blood pressure from the standard blood pressure does not fall in
a prescribed reference range.
Where the abnormality of blood pressure of the subject is judged
when the blood pressure is higher than the prescribed upper threshold
or lower than the prescribed lower threshold, the abnormality of
blood pressure is not found so long as the changed (increased or
decreased) blood pressure falls within a normal or permissible range
defined by the upper and lower thresholds, even if the change (increase
or decrease) of the blood pressure may be large. In this case, an
abrupt or rapid change of the physical condition of the patient
may not be quickly detected. Where the abnormality of blood pressure
is judged when the amount or rate of change of the blood pressure
of the patient from the standard blood pressure does not fall in
the prescribed reference range, the blood pressure of the subject
may be judged to be abnormal even if the blood pressure may fall
in the normal or permissible range. In this arrangement, however,
the blood pressure of the patient may be judged to be abnormal even
if the change of the blood pressure from the standard blood pressure
may be toward a normal value. For instance, where the standard blood
pressure is as low as the lower threshold of the normal range, it
is not necessary to judge the abnormality of blood pressure even
in the event of a great increase of the blood pressure. On the other
hand, where the standard blood pressure is as high as the upper
threshold of the normal range, it is not necessary to judge the
abnormality of blood pressure even in the event of a great decrease
of the blood pressure. However, the conventional blood pressure
monitor apparatus described above judges that the blood pressure
is abnormal when the amount or rate of change of the blood pressure
from the standard blood pressure does not fall in the prescribed
reference range, irrespective of the magnitude of the standard blood
pressure. Thus, the conventional blood pressure monitor apparatus
may judge the abnormality of blood pressure even in the above-described
cases where a great increase or decrease of the blood pressure is
not abnormal.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
blood pressure monitor apparatus capable of judging an abnormality
of a blood pressure of a living subject with high accuracy.
The above-indicated object of the present invention has been achieved
by the present invention. According to the present invention, there
is provided a blood pressure monitor apparatus for monitoring a
blood pressure of a living subject, wherein the blood pressure is
judged to be abnormal when a first change value, which is determined
as a change of each of a plurality of blood pressure values iteratively
obtained from a standard blood pressure obtained from the subject,
does not fall in a first reference range, wherein the improvement
comprises: the first reference range being determined based on the
standard blood pressure of the subject, according to a relationship
between first reference range and standard blood pressure wherein
a plurality of different first reference ranges correspond to a
plurality of different standard blood pressures, respectively.
In the present blood pressure monitor apparatus, the first reference
range is determined based on the standard blood pressure obtained
from the living subject, according to the relationship wherein a
plurality of different first reference ranges correspond to a plurality
of different standard blood pressures. Accordingly, the first reference
range changes with the standard blood pressure, so that the abnormality
of blood pressure can be judged with high accuracy.
In the case where an anesthesiologist judges the abnormality of
blood pressure of a patient during an operation, his or her criteria
for Judgment of abnormal blood pressure may differ from those of
other anesthesiologists. Further, the judgment of abnormal blood
pressure made by the anesthesiologist may vary depending upon various
factors such as the kind of the operation, or the physical power
and age of the patient. In view of this, the above-indicated relationship
between first reference range and standard blood pressure is preferably
determined by an operator of the blood pressure monitor apparatus.
According to this arrangement, the relationship between first reference
range and standard blood pressure is determined by the operator
of the apparatus depending upon the circumstances. Accordingly,
the relationship can be determined for each specific operation,
for instance, in view of a medical judgment of a doctor in charge,
the kind of the operation, and the physical power and age of each
specific patient who undergoes the operation. Therefore, the present
arrangement assures that the first reference range is appropriately
determined according to the thus determined relationship, and that
the abnormality of blood pressure of the patient is accurately judged.
According to another preferred feature of the invention, the relationship
between first reference range and standard blood pressure is recorded
on a recording medium which is attachable to, and detachable from,
the apparatus. According to this arrangement, the recording medium
on which the above-described relationship is recorded can be installed
on another blood pressure monitor apparatus, whereby the same blood
pressure monitoring operation can be carried out in that apparatus.
Further, if the relationship is recorded on a plurality of recording
media, the plurality of recording media can be installed on respective
blood pressure monitor apparatuses, whereby the same blood pressure
monitoring operation can be carried out in the plurality of monitor
apparatuses.
The above-described relationship between first reference range
and standard blood pressure may be determined in advance. The first
reference range is defined by at least one of an upper first threshold
which is used to judge whether an increase of the blood pressure
is abnormal, and a lower first threshold which is used to judge
whether a decrease of the blood pressure is abnormal.
Where the first reference range is defined by the upper first threshold
and the relationship between upper first threshold and standard
blood pressure is determined, the relationship is preferably determined
such that a smaller upper first threshold corresponds to a higher
standard blood pressure. According to this arrangement wherein the
upper first threshold decreases with the increase in the standard
blood pressure obtained from the subject, the apparatus judges that
the blood pressure of the subject is abnormal even if an increase
of the blood pressure may be small where the standard blood pressure
is high. On the other hand, the apparatus does not judge that the
blood pressure is abnormal even if an increase of the blood pressure
may be large where the standard blood pressure is low. Therefore,
the present arrangement assures an accurate judgment of abnormal
blood pressure.
Where the first reference range is defined by the lower first threshold
and the relationship between lower first threshold and the standard
blood pressure is determined, the relationship is preferably determined
such that a greater lower first threshold corresponds to a lower
standard blood pressure obtained from the subject, in other words,
a smaller absolute value of lower first threshold corresponds to
a lower standard blood pressure. According to this arrangement wherein
the lower first threshold increases with the decrease of the standard
blood pressure, in other words, the absolute value of the lower
first threshold decreases with the decrease of the standard blood
pressure, the apparatus judges that the blood pressure of the subject
is abnormal even if a decrease of the blood pressure may be small
where the standard blood pressure is low, while the apparatus does
not judge that the blood pressure is abnormal even if a decrease
of the blood pressure may be large where the standard blood pressure
is high. Therefore, the present arrangement assures an accurate
judgment of abnormal blood pressure.
In still another preferred feature of the invention, the blood
pressure of the subject is judged to be abnormal when a second change
value as a change of the above-indicated each of the blood pressure
values from a blood pressure value obtained a predetermined time
period before the each of the blood pressure values does not fall
in a second reference range. According to this arrangement, the
blood pressure of the subject is judged to be abnormal based on
not only the change of the each of the iteratively obtained blood
pressure values from the standard blood pressure, but also the change
of the each of the iteratively obtained blood pressure values from
the blood pressure value obtained the predetermined time period
before the each of the iteratively obtained blood pressure values.
Thus, the blood pressure monitor apparatus according to the present
feature is capable of accurately judging the abnormality of blood
pressure of the subject.
In yet another preferred feature of the invention, the blood pressure
of the subject is judged to be abnormal when the each of the blood
pressure values does not fall in a third reference range. According
to this arrangement, the blood pressure of the subject can be judged
to be abnormal based on the each of the iteratively obtained blood
pressure values itself, irrespective of the change of blood pressure
of the subject. Accordingly, the blood pressure monitor apparatus
according to the present feature is capable of accurately judging
the abnormality of blood pressure of the subject.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and optional objects, features, and advantages of the
present invention will be better understood by reading the following
detailed description of preferred embodiments of the invention when
considered in conjunction with the accompanying drawings, in which:
FIG. 1 is a diagrammatic view for explaining a construction of
a blood pressure monitor apparatus to which the present invention
is applied;
FIG. 2 is a block diagram for explaining essential control functions
of a CPU (central processing unit) of a control device of the apparatus
of FIG. 1;
FIG. 3 is a view for explaining a relationship between first reference
range and standard blood pressure, which relationship is recorded
on a recording medium shown in FIG. 1;
FIG. 4 is a flow chart for explaining more concretely a portion
of the control functions of the CPU, shown in the diagrammatic view
of FIG. 2, the flow chart representing an initializing routine for
obtaining the relationship between first reference range and standard
blood pressure, and other control parameters;
FIG. 5 is a flow chart for explaining more concretely another portion
of the control functions of the CPU, shown in the diagrammatic view
of FIG. 2, the flow chart representing an EBP-PWV relationship determining
routine for determining an EBP-PWV relationship between estimated
blood pressure and pulse-wave propagation velocity;
FIG. 6 is a flow chart for explaining more concretely still another
portion of the control functions of the CPU, shown in the diagrammatic
view of FIG. 2, the flow chart representing a blood pressure monitoring
routine; and
FIG. 7 is a view for explaining another relationship between first
reference range and standard blood pressure.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Hereinafter, there will be described one embodiment of the present
invention, by reference to the drawings. FIG. 1 is a diagrammatic
view for explaining the construction of a blood pressure (BP) monitor
apparatus 10 to which the present invention is applied. The BP monitor
apparatus 10 is used, for instance, to monitor a blood pressure
of a patient who is undergoing an operation.
As shown in FIG. 1, the present BP monitor apparatus 10 includes
a cuff 12 which has a belt-like cloth bag and a rubber bag accommodated
in the cloth bag and which is adapted to be wound around an upper
arm 14 of a patient as a living subject, a pressure sensor 16 and
a pressure control valve 18. The pressure sensor 16 and the pressure
control valve 18 are connected to the cuff 12 via a piping 20. An
air pump 24 is connected to the pressure control valve 18 via a
piping 22. The pressure control valve 18 adjusts a pressure of a
pressurized air supplied from the air pump 24, and supplies the
pressure-adjusted air to the cuff 12, or discharges the pressurized
air from the cuff 12, so as to control an air pressure in the cuff
12.
The pressure sensor 16 detects the air pressure in the cuff 12,
and supplies a pressure signal SP representing the detected air
pressure, to a static-pressure filter circuit 26 and a pulse-wave
filter circuit 28. The static-pressure filter circuit 26 has a low-pass
filter and extracts, from the pressure signal SP, a cuff-pressure
signal SC representing a static-pressure component contained in
the signal SP, i.e., a pressing pressure of the cuff 12 (hereinafter
referred to as "cuff pressure PC"). The cuff-pressure
signal SC is supplied to an electronic control device 32 which will
be described, via an analog-to-digital (AID) converter 30. The pulse-wave
filter circuit 28 includes a band-pass filter which transmits a
frequency component of the pressure signal SP that has frequencies
in a range of about 1 to 30 Hz, and extracts, from the pressure
signal SP, a cuff-pulse-wave signal SM1. The cuff-pulse-wave signal
SM1 is supplied to the control device 32 via an A/D converter 34.
The cuff-pulse-wave signal SM1 represents an upper-arm pulse wave
which is transmitted from the upper arm 14 to the cuff 12.
The BP monitor apparatus 10 further includes: a photoelectric-pulse-wave
detecting sensor 36; a reading and recording device 48 to and from
which a recording medium 46 is attached and detached; a heart-sound
microphone 50; a heart-sound-signal amplifier 52; an input device
54; the electronic control device 32; and a display device 62.
The photoelectric-pulse-wave detecting sensor 36 functions as a
volumetric pulse-wave detecting device which detects a volumetric
pulse wave (plethysmograph) from peripheral blood vessels of the
subject, and may have a construction similar to that of one which
is used to detect pulse. The photoelectric-pulse-wave detecting
sensor 36 is worn on a body portion of the subject, i.e., an end
portion of a finger of an arm of the subject around which the cuff
12 is not wound. The sensor 36 includes: a housing 38 which can
accommodate a body portion of the subject; a light-emitting element
40 as a light source which emits, toward a skin of the subject,
a red or infrared light in such a wavelength band that can be reflected
by hemoglobin, preferably a light having a wavelength of about 800
nm that is not influenced by blood oxygen saturation; and a light-receiving
element 42 which is opposed to the light-emitting element 40 and
detects the light transmitted through the body portion. The sensor
36 outputs a photoelectric pulse-wave signal SM2 representing respective
instantaneous volumes of the blood present in the capillaries of
the body portion, and supplies the signal SM2 to the control device
32 via an A/D converter 44.
On the recording medium 46 such as a memory card, a photomagnetic
disc, a compact disc, a flexible disc, etc., there is recorded a
relationship between first reference range TH1 and standard blood
pressure BP.sub.ST that is used to determine a first reference range
TH1 for judging an abnormality of a first change value indicative
of a change of each of a plurality of blood pressure values iteratively
obtained from the subject, from a standard blood pressure BP.sub.ST
obtained from the subject. This relationship will be described in
greater detail, later. The recording medium 46 is attachable to,
and detachable from, the reading and recording device 48 which has
functions of: reading information from the recording medium 46 and
outputting the information read from the recording medium 46 to
the control device 32; and recording, on the recording medium 46,
the relationship obtained on the basis of data inputted through
the input device 54.
The heart-sound microphone 50 is fixed, with an adhesive tape,
not shown, to a prescribed location on a chest of a living subject.
The microphone 50 accommodates a piezoelectric element, not shown,
which converts heart sounds produced from the heart of the subject,
into an electric signal, i.e., a heart-sound signal SH. The heart-sound-signal
amplifier 52 includes four sorts of filters, not shown, which cooperate
with one another to attenuate a low-pitch component having a great
energy and thereby amplifies and filters a high-pitch component
of the heart-sound signal SH. The heart-sound signal SH outputted
from the amplifier 52 is supplied to the electronic control device
32 via an A/D converter, not shown.
The input device 54 includes a plurality of keys through which
a plurality of sorts of information are inputted. The plurality
of sorts of information include a stature T of the subject; the
above-described relationship between first reference range and standard
blood pressure; a time period used for calculating a second change
value (which will be described in greater detail) indicative of
a change of each of the iteratively obtained blood pressure values
during the time period; a second reference range TH2 used for judging
whether or not the second change value is abnormal; and a third
reference range TH3 used for judging whether or not each of the
blood pressure values iteratively obtained from the subject is abnormal.
The input device 54 outputs, to the control device 32, signals respectively
representing the plurality of sorts of information inputted through
the keys.
The electronic control device 32 is essentially provided by a so-called
microcomputer including a CPU (central processing unit) 56, a ROM
(read only memory) 58, a RAM (random access memory) 60, an input-and-output
(I/O) port, not shown, etc, and the CPU 56 processes signals according
to control programs pre-stored in the ROM 58, while utilizing a
temporary-storage function of the RAM 60. The control device 32
outputs, from the I/O port, drive signals to the air pump 24 and
the pressure control valve 18 so as to control the respective operations
thereof and thereby control the cuff pressure PC. In addition, the
CPU 56 iteratively determines a blood pressure BP and an estimated
blood pressure EBP according to the control functions shown in FIG.
2, and controls the display device 62 to iteratively display the
determined blood pressure BP and estimated blood pressure EBP. Further,
the CPU 56 carries out a blood pressure monitoring operation based
on the determined blood pressure BP and estimated blood pressure
EBP.
FIG. 2 is a block diagram for explaining essential control functions
of the CPU 56 of the present BP monitor apparatus 10.
A cuff-pressure changing means or device 70 operates, based on
the cuff-pressure signal SC supplied from the static-pressure filter
circuit 26, the pressure control valve 18 and the air pump 24 so
as to quickly increase the cuff pressure PC to a prescribed target
pressure PC.sub.M (e.g., 180 mmHg) that would be higher than a systolic
blood pressure BP.sub.SYS of the subject and, subsequently, slowly
decrease the cuff pressure at a rate of, e.g., 2 or 3 mmHg/sec.
After a blood-pressure determining means or device 72, described
below, determines a blood pressure BP of the subject, the cuff-pressure
changing means 70 releases the cuff pressure PC to an atmospheric
pressure.
After a prescribed calibration period T.sub.C set at about 20 to
30 minutes has passed or when the blood pressure of the subject
is judged to be abnormal by an abnormality judging means or device
98 described below, the blood pressure determining means 72 determines,
according to a well-known oscillometric algorithm, a systolic blood
pressure value BP.sub.SYS, a mean blood pressure value BP.sub.MEAN,
and a diastolic blood pressure value BP.sub.DIA of the upper arm
14, based on the cuff pressure PC represented by the cuff-pressure
signal SC and the upper-arm pulse wave represented by the cuff pulse-wave
signal SM1, which signals SC and SM1 are continuously supplied from
the static-pressure filter circuit 26 and the pulse-wave filter
circuit, 28, respectively, during the slow decreasing of the cuff
pressure PC under the control of the cuff-pressure changing means
70. The thus determined blood pressure values BP.sub.SYS, BP.sub.MEAN,
BP.sub.DIA are displayed by the display device 62.
A pulse-wave-propagation-velocity determining means or device 74
which functions as a pulse-wave-propagation-velocity-related information
obtaining means obtains a time difference between a time of detection
of a prescribed periodic portion (e.g., a start point of a heart
sound I) of each heart-sound waveform iteratively detected by the
heart-sound microphone 50, and a time of detection of a prescribed
periodic portion of a corresponding photoelectric pulse wave iteratively
detected by the photoelectric-pulse-wave detecting sensor 36. This
time difference is a pulse-wave-propagation time DT (second) which
is needed for the pulse wave to propagate from the heart to a position
where the sensor 36 is worn on the subject.
Further, the pulse-wave-propagation-velocity determining means
74 substitutes the subject's stature T supplied from the input device
54, with the following Expression (1) which represents a relationship
between propagation distance L and stature T and which is pre-stored
in the ROM 58, thereby obtaining a propagation distance L from the
heart of the subject to the position where the sensor 36 is worn.
The pulse-wave-propagation-velocity determining means 74 additionally
substitutes the propagation distance L and the propagation time
DT obtained as described above, with the following Expression (2),
thereby obtaining a pulse-wave propagation velocity PWV (cm/sec):
(a and b are experimentally determined constants)
An EBP (estimated blood pressure)-PWV (pulse-wave propagation velocity)
relationship determining means or device 76 determines two coefficients
.alpha. and .beta. in the following Expression (3) for calculating
an estimated blood pressure value EBP, based on any one of the systolic
blood pressure value BP.sub.SYS, mean blood pressure value BP.sub.MEAN,
and diastolic blood pressure value BP.sub.DIA determined by the
blood pressure determining means 72, and the pulse-wave propagation
velocity PWV determined by the pulse-wave-propagation-velocity determining
means 74 during, immediately before, or immediately after, the blood
pressure measurement period. Expression (3) represents a relationship
between estimated blood pressure EBP and pulse-wave propagation
velocity PWV. The EBP-PWV relationship is determined based on one
set of data consisting of the systolic blood pressure BP.sub.SYS
and the pulse-wave propagation velocity PWV obtained immediately
after the blood pressure measurement period, and another set of
data consisting of the systolic blood pressure BP.sub.SYS and the
pulse-wave propagation velocity PUV determined in the prior blood
pressure measurement period.
Where the systolic blood pressure BP.sub.SYS is used to determine
Expression (3) representing the above-indicated EBP-PWV relationship
between estimated blood pressure and pulse-wave propagation velocity,
the estimated blood pressure EBP obtained from Expression (3) is
an estimated systolic blood pressure EBP.sub.SYS. Where the mean
blood pressure BP.sub.MEAN is used to determine Expression (3),
the estimated blood pressure EBP obtained from Expression (3) is
an estimated mean blood pressure EBP.sub.MEAN. Where the diastolic
blood pressure BP.sub.DIA is used to determine Expression (3), the
estimated blood pressure EBP obtained from Expression (3) is an
estimated diastolic blood pressure EBP.sub.DIA. In short, the EBP-PWV
relationship between estimated blood pressure and pulse-wave propagation
velocity is determined depending upon which one of the systolic,
mean, and diastolic blood pressure values is selected as an estimated
(monitor) blood pressure EBP.
An estimated blood pressure determining means or device 78 substitutes
the pulse-wave propagation velocity PWV iteratively determined by
the pulse-wave-propagation-velocity determining means 74, with Expression
(3) determined by the EBP-PWV relationship determining means 76,
and thereby iteratively determines an estimated blood pressure value
EBP as a non-invasively obtained blood pressure value of the subject.
The thus determined estimated blood pressure EBP is iteratively
displayed by the display device 62. While the estimated blood pressure
EBP is preferably determined at a relatively short period corresponding
to one pulse or several pulses, the estimated blood pressure EBP
may be determined at any suitable period which is shorter than the
above-described calibration period T.sub.C.
A first-change-value calculating means or device 80 determines,
as a standard blood pressure BP.sub.ST, one of the systolic blood
pressure BP.sub.SYS, mean blood pressure BP.sub.MEAN, and diastolic
blood pressure BP.sub.DIA determined by the BP determining means
72, which one is employed by the EBP-PWV relationship determining
means 76 for determining the EBP-PWV relationship between estimated
blood pressure and pulse-wave propagation velocity, and iteratively
calculates a first change value as a change of each of the estimated
blood pressure values EBP iteratively determined by the EBP determining
means 78 from the standard blood pressure BP.sub.ST. The first change
value is a rate of change, or an amount of change, of each of the
estimated blood pressure values EBP from the standard blood pressure
BP.sub.ST.
A second-change-value calculating means or device 82 calculates
a second change value as a change of the each of the estimated blood
pressures values EBP determined by the EBP determining means 78
from an estimated blood pressure value EBP determined a predetermined
time period before the each of the estimated blood pressure values
EBP. The above-described predetermined time period used for determining
the second change value (hereinafter referred to as "second-change-value-related
time period") may be inputted through the input device 54,
or may be a prescribed constant value. It is preferable that the
second-change-value-related time period be sufficiently shorter
than the above-described calibration period T.sub.C. For instance,
the second-change-value-related time period is preferably not longer
than ten minutes, more preferably not longer than five minutes.
The second-change-value-related time period which is a short time
period described above is effective to accurately detect an abrupt
change of the blood pressure of the subject.
A relationship obtaining means or device 84 obtains, as a relationship
between first reference range and standard blood pressure to be
used in a current blood pressure monitoring operation, a relationship
between first reference range and standard blood pressure which
has been read from the recording medium 46 by the reading and recording
device 48 or which has been inputted through the input device 54.
The graph of FIG. 3 shows one example of the relationship between
first reference range TH1 and standard blood pressure BP.sub.ST
recorded on the recording medium 46. The relationship shown in the
graph of FIG. 3 includes an upper-first-threshold relationship 86
for determining an upper first threshold TH1.sub.U, and a lower-first-threshold
relationship 88 for determining a lower first threshold TH1.sub.L.
The two relationships 86, 88 are represented by respective straight
lines in the graph of FIG. 3. The upper first threshold TH1.sub.U
is used to judge whether an increase of the blood pressure of the
subject is abnormal. The upper-first-threshold relationship 86 is
determined such that the upper first threshold TH1.sub.U linearly
decreases with the increase of the standard blood pressure BP.sub.ST.
The lower first threshold TH1.sub.L is used to judge whether a decrease
of the blood pressure of the subject is abnormal. The lower-first-threshold
relationship 88 is determined such that the lower first threshold
TH1.sub.L linearly increases, in other words, the absolute value
of the lower first threshold TH1.sub.L linearly decreases, with
the decrease of the standard blood pressure BP.sub.ST. In the relationship
shown in the graph of FIG. 3, the straight line representing the
upper-first-threshold relationship 86 and the straight line representing
the lower-first-threshold relationship 88 are parallel to each other.
The upper-first-threshold relationship 86 and the lower-first-threshold
relationship 88 are determined such that the upper first threshold
TH1.sub.U and the lower first threshold TH1.sub.L continuously change
with the change of the standard blood pressure BP.sub.ST. However,
those relationships 86, 88 may be determined such that the upper
first threshold TH1.sub.U and the lower first threshold TH1.sub.L
change in steps with the change of the standard blood pressure BP.sub.ST.
In this case, the upper-first-threshold relationship 86 is defined
by at least two upper first thresholds TH1.sub.U and the lower-first-threshold
relationship 88 is defined by at least two lower first thresholds
TH1.sub.L, so as to correspond to at least two different standard
blood pressures BP.sub.ST.
A relationship recording means or device 90 records, on the recording
medium 46 installed on the reading and recording device 48, the
relationship between first reference range and standard blood pressure
when the relationship is inputted through the input device 54.
A first-reference-range determining means or device 92 determines,
according to the relationship between the first reference range
and standard blood pressure obtained by the relationship obtaining
means 84, a first reference range TH1 which corresponds to the standard
blood pressure BP.sub.ST, namely, one of the three blood pressure
values BP.sub.SYS, BP.sub.MEAN, BP.sub.DIA, each determined by the
BP determining means 72, which one is used by the EBP-PWV relationship
determining means 76 to determine the EBP-PWV relationship between
estimated blood pressure and pulse-wave propagation velocity. The
thus determined first reference range TH1 is used to monitor the
blood pressure of the subject.
A second-reference-range determining means or device 94 and a third-reference-range
determining means or device 96 determine a second reference range
TH2 and a third reference range TH3, respectively, based on the
input signals supplied from the input device 54.
An abnormality judging means or device 98 judges that the blood
pressure of the subject is abnormal, when the estimated blood pressure
EBP iteratively determined by the EBP determining means 78 does
not fall in the third reference range TH3 determined by the third-reference-range
determining means 96, when the first change value iteratively calculated
by the first-change-value calculating means 80 does not fall in
the first reference range TH1 determined by the first-reference-range
determining means 92, or when the second change value iteratively
calculated by the second-change-value calculating means 82 does
not fall in the second reference range TH2 determined by the second-reference-range
determining means 94. When the blood pressure of the subject is
judged to be abnormal by the abnormality Judging means 98, the control
device 32 operates the display device 64 to display characters or
symbols indicating the abnormality of the blood pressure, and operates
the blood-pressure determining means 72 to start a reliable blood
pressure measurement using the cuff 12.
FIGS. 4 through 6 are flow charts for explaining the control functions
of the CPU 56, illustrated in the block diagram of FIG. 2. The flow
chart of FIG. 4 shows an initializing routine for obtaining the
relationship between first reference range and standard blood pressure,
described above. The flow chart of FIG. 5 shows an EBP-PWV relationship
determining routine for determining the EBP-PWV relationship described
above and determining the upper first threshold TH1.sub.U and the
lower first threshold TH1.sub.L. The flow chart of FIG. 6 shows
a blood pressure monitoring routine for monitoring the blood pressure
of the subject based on the estimated blood pressure EBP determined
for each pulse.
There will be first explained the initializing routine of FIG.
4. The CPU 56 carries out Step SA1 (hereinafter, "Step"
is omitted, if appropriate) corresponding to the relationship obtaining
means 84. At SA1, the CPU 56 reads in the relationship between first
reference range and standard blood pressure from the recording medium
46 installed on the reading and recording device 48, and determines
the relationship which has been read from the recording medium 46
as a relationship between first reference range and standard blood
pressure to be used in the current blood pressure monitoring operation.
Where the relationship is inputted through the input device 54,
the CPU 56 determines the inputted relationship as the relationship
to be used in the current blood pressure monitoring operation. Here,
it is assumed that the CPU 56 obtains the relationship shown in
the graph of FIG. 3.
SA1 is followed by SA2 to judge whether or not a signal indicative
of the stature T of the subject has been supplied from the input
device 54. If a negative judgment is made at SA2, the control of
the CPU 56 goes to SA4 and the following steps. If a positive or
affirmative judgment is made at SA2, SA3 is implemented to substitute
the stature T with Expression (1), and calculate a propagation distance
L from the heart of the subject to the position where the photoelectric-pulse-wave
detecting sensor 36 is worn.
Subsequently, the CPU carries out SA4 to judge whether or not the
second-change-value-related time period has been inputted through
the input device 54. If a negative judgment is made at SA4, the
control of the CPU 56 goes to SAG and the following steps. If an
affirmative judgment is made at SA4, the control of the CPU 56 goes
to SA5 to determine the value inputted through the input device
54 as the second-change-value-related time period. Herein it is
assumed that the second-change-value-related time period is set
at four minutes.
Subsequently, the CPU 56 carries out SA6 to judge whether or not
a second reference range TH2 has been inputted through the input
device 54. If a negative judgment is made at SA6, the control of
the CPU 56 goes to SA8 and the following steps. If an affirmative
judgment is made at SA6, the CPU 56 carries out SA7 corresponding
to the second-reference-range determining means 94. At SA7, the
CPU 56 determines the second reference range TH2 which has been
inputted through the input device 54 as a second reference range
TH2 to be used in the current blood pressure monitoring operation.
Here, it is assumed that the second reference range TH2 is defined
by a second reference value TH2 equal to 40 mmHg.
SA7 is followed by SA8 to judge whether or not a third reference
range TH3 has been inputted through the input device 54. If a negative
judgment is made at SA8, the CPU 56 carries out SA10. If an affirmative
judgment is made at SA8, the control of the CPU 56 goes to SA9 corresponding
to the third-reference-range determining means 96. At SA9, the CPU
56 determines the third reference range TH3 which has been inputted
through the input device 54, as a third reference range TH3 to be
used in the current blood pressure monitoring operation. Here, it
is assumed that the third reference range TH3 is defined by an upper
third threshold TH3.sub.U set at 180 mmHg, and a lower third threshold
TH3.sub.L set at 80 mmHg.
SA9 is followed by SA10 to judge whether or not all of the propagation
distance L, second-change-value-related time period, second reference
range TH2, and third reference range TH3 have been determined. If
a negative judgment is made at SA9, the CPU 56 repeats SA2 and the
following steps. If an affirmative judgment is made at SA10, the
CPU 56 carries out the EBP-PWV relationship determining routine
shown in FIG. 5.
The control of the CPU 56 begins with SB1 of the EBP-PWV relationship
determining routine of FIG. 5, where the CPU 56 reads in respective
one-heartbeat lengths of the heart-sound signal SH supplied from
the heart-sound microphone 50 and the photoelectric-pulse-wave signal
SM2 supplied from the sensor 36.
Subsequently, the CPU 56 carries out SB2 corresponding to the pulse-wave-propagation-velocity
determining means 74. At SB2, the CPU 56 determines a start point
of a heart sound I in the heart-sound waveform represented by the
heart-sound signal SH read in at SB1 and a rising point of the photoelectric
pulse-wave represented by the photoelectric-pulse-wave signal SM2
read in at SB1, and obtains, as a pulse-wave-propagation time DT,
a time difference between a time of detection of the start point
of the heart-sound I and a time of detection of the rising point
of the photoelectric pulse wave. Then, the CPU 56 substitutes the
thus obtained pulse-wave-propagation time DT and the propagation
distance L calculated at SA3 of the control routine of FIG. 4, with
Expression (2), thereby determining a pulse-wave propagation velocity
PWV.
SB2 is followed by SB3 where the CPU 56 drives the air pump 24
and operates the pressure control valve 18, so as to start quickly
increasing the cuff pressure PC. Subsequently, at SB4, the CPU 56
judges whether the cuff pressure PC is equal to or higher than a
prescribed target pressure value PC.sub.M (i.e., 180 mmHg). If a
negative judgment is made at SB4, the CPU 56 repeats this step and
continues increasing the cuff pressure PC. In the meantime, if an
affirmative judgment is made at SB4, the control flow goes to SB5
to stop the air pump 24 and operate the pressure control valve 18
so as to slowly decrease the cuff pressure PC at a rate of about
3 mmHg/sec.
SB5 is followed by SB6 corresponding to the BP pressure determining
means 72. At SB6, a systolic blood pressure value BP.sub.SYS, a
mean blood pressure value BP.sub.MEAN, and a diastolic blood pressure
value BP.sub.DIA are determined according to a well known oscillometric
BP determining algorithm, based on the variation of respective amplitudes
of successive heartbeat-synchronous pulses of the upper-arm pulse
wave (cuff pulse wave) represented by the cuff-pulse-wave signal
SM1 continuously obtained while the cuff pressure PC is slowly decreased.
The determined blood pressure values BP.sub.SYS, BP.sub.MEAN, and
BP.sub.DIA are displayed by the display device 62.
After the blood pressure values have been determined at SB6, SB7
is implemented to switch the pressure control valve 18 to its quick-deflation
position, so that the cuff pressure PC is quickly lowered to an
atmospheric pressure. In the control routine of FIG. 5, SB3 through
SB5, and SB7 correspond to the cuff-pressure changing means 70.
Subsequently, the CPU 56 carries out SB8 corresponding to the EBP-PWV
relationship determining means 76. At SB8, the constants .alpha.
and .beta. in Expression (3) are determined based on one set of
data consisting of the pulse-wave propagation velocity PWV obtained
at SB2 and the systolic blood pressure BP.sub.SYS obtained at SB6,
and another set of data obtained at SB2 and SB6 in the prior control
cycle according to the EBP-PWV relationship determining routine
of FIG. 5. Where the EBP-PWV relationship determining routine is
executed for the first time, a standard pulse-wave propagation velocity
PWV and a standard systolic blood pressure BP.sub.SYS which are
pre-stored in the ROM 58 are used as the above-indicated another
set of data.
Subsequently, the CPU 56 carries out SB9 corresponding to the first-reference-range
determining means 92. At SB9, the CPU 56 determines, as a standard
blood pressure BP.sub.ST, the systolic blood pressure BP.sub.SYS
determined at SB6. The CPU 56 further determines, according to the
relationship (shown in the graph of FIG. 3) obtained at SA1 of the
control routine of FIG. 4, the upper first threshold TH1.sub.U and
the lower first threshold TH1.sub.L corresponding to the systolic
blood pressure BP.sub.SYS, i.e., the standard blood pressure BP.sub.ST,
as an upper first threshold TH1.sub.U and a lower first threshold
TH1.sub.L to be used in the blood pressure monitoring routine of
FIG. 6. The upper first threshold TH1.sub.U and the lower first
threshold TH1.sub.L which are determined according to the relationship
shown in the graph of FIG. 3 change such that, with the increase
of the systolic blood pressure BP.sub.SYS obtained at SB6, the upper
first threshold TH1.sub.U decreases and the lower first threshold
TH1.sub.L decreases, namely, the absolute value of the lower first
threshold TH1.sub.L increases. In other words, the upper first threshold
TH1.sub.U and the lower first threshold TH1.sub.L change such that,
with the decrease of the systolic blood pressure BP.sub.SYS, the
upper first threshold TH1.sub.U increases and the lower first threshold
TH1.sub.L increases, namely, the absolute value of the lower first
threshold TH1.sub.L decreases.
Subsequently, the CPU 56 carries out the blood pressure monitoring
routine shown in FIG. 6. The CPU 56 carries out SC1 and SC2 which
are the same as SB1 and SB2 of the control routine of FIG. 5, thereby
determining a pulse-wave propagation velocity PVW. Described more
specifically, at SC1, the CPU 56 reads in respective one-heartbeat
lengths of the heart-sound signal SH and the photoelectric-pulse-wave
signal SM2. At SC2 corresponding to the pulse-wave-propagation-velocity
determining means 74, the CPU 56 determines the pulse-wave propagation
velocity PWV based on the signals read in at SC1.
SC2 is followed by SC3 corresponding to the estimated blood pressure
(EBP) determining means 78. At SC3, the CPU 56 substitutes the pulse-wave
propagation velocity PWV obtained at SC2, with Expression (3) indicative
of the EBP-PWV relationship determined at SB8 of the control routine
of FIG. 5, and determines an estimated blood pressure EBP. The thus
determined estimated blood pressure EBP is displayed by the display
device 62.
Subsequently, the control of the CPU 56 goes to SC4 to judge whether
the estimated blood pressure EBP determined at SC3 falls within
the third reference range TH3 determined at SA9 in the control routine
of FIG. 4. Described in detail, the CPU 56 judges at SC4 whether
the estimated blood pressure EBP determined at SC3 is greater than
the upper third threshold TH3.sub.U determined at SA9 (i.e., 180
mmHg in this embodiment) or smaller than the lower third threshold
TH3.sub.L determined at SA9 (i.e., 80 mmHg in this embodiment).
If an affirmative judgment is made at SC4, there is a high possibility
that the blood pressure of the subject is abnormal. In this case,
the CPU 56 carries out SC5 to operate the display device 62 to indicate
the abnormality of blood pressure, and carries out again the EBP-PWV
relationship determining routine of FIG. 5 so as to quickly obtain
a reliable blood pressure BP using the cuff 12.
In the meantime, if a negative judgment is made at SC4, the control
of the CPU goes to SC6 corresponding to the first-change-value-calculating
means 80. At SC6, the CPU 56 determines, as a first change value,
a first EBP difference .DELTA.EBP1 which is obtained by subtracting
the systolic blood pressure BP.sub.SYS determined at SB6 of the
control routing of FIG. 5, from the estimated blood pressure EBP
determined at SC3, namely according to the following Expression
(4):
SC6 is followed by SC 7 to judge whether the first EBP difference
.DELTA.EBP1 calculated at SC6 falls within the first reference range
TH1 determined at SB9 of the control routine of FIG. 5. Described
more specifically, at SC7, the CPU 56 judges whether the first EBP
difference .DELTA.EBP1 is greater than the upper first threshold
TH1.sub.U determined at SB9 or smaller than the lower first threshold
TH1.sub.L determined at SB9. At this step, the CPU 56 judges whether
or not a change of the current blood pressure from the blood pressure
obtained by using the cuff 12 is abnormal. If an affirmative judgment
is made at SC7, there is a high possibility that the blood pressure
of the subject is abnormal. In this case, the CPU 56 caries out
again the EBP-PWV relationship determining routine of FIG. 5 after
execution of SC5 to indicate the blood pressure abnormality on the
display device 62.
Subsequently, the control of the CPU 56 goes to SC8 corresponding
to the second-change-value calculating means 82. At SC8, the CPU
56 determines, as a second change value, a second EBP difference
.DELTA.EBP2 which is obtained by subtracting, from the estimated
blood pressure EBP obtained at SC3, an estimated blood pressure
which had been obtained at SC3 a predetermined time period before.
The predetermined time period corresponds to the second-change-value-related
time period determined at SA4 of the control routine of FIG. 4,
i.e., four minutes in the present embodiment.
Subsequently, the CPU 56 carries out SC9 to judge whether an absolute
value of the second EBP difference .DELTA.EBP2 determined at SC8
is greater than the second reference value TH2 (i.e., 40 mmHg in
this embodiment) determined at SA7 of the control routine of FIG.
4. Namely, the CPU 56 judges whether a change of the blood pressure
of the subject within a short period of time is large enough to
indicate the abnormality of blood pressure. If an affirmative judgment
is made at SC9, there is a high possibility that the blood pressure
of the subject is abnormal. In this case, the CPU 56 carries out
again the EBP-PVUV relationship determining routine of FIG. 5 after
execution of SC5 to indicate the blood pressure abnormality on the
display device 62. In the control routine of FIG. 6, SC4, SC5, SC7,
and SC9 correspond to the abnormality judging means 98.
SC9 is followed by SC10 to judge whether a time period which has
elapsed after the cuff-using BP measurement according to the control
routine of FIG. 5 is longer than the calibration period T.sub.C
pre-set at about 20 to 30 minutes. If a negative judgment is made
at SC10, the CPU 56 repeats SC1 and the following steps. If an affirmative
judgment is made at SC10, the CPU 56 carries out again the control
routine of FIG. 5 to again determine another EBP-PWV relationship
and another first reference range TH1.
In the embodiment employing the flow charts described above, a
systolic blood pressure BP.sub.SYS actually obtained by using the
cuff 12 is determined as a standard blood pressure BP.sub.ST, and
different first reference ranges TH1 are determined based on different
standard blood pressures BP.sub.ST. Accordingly, the first reference
range TH1 can be appropriately determined, and the abnormality of
blood pressure of the subject can be reliably judged.
Described more specifically, in the embodiment employing the above-described
flow charts, the upper first threshold TH1.sub.U is determined such
that the threshold TH1.sub.U decreases with the increase of the
systolic blood pressure BP.sub.SYS actually obtained from the subject
by using the cuff 12. Accordingly, the present arrangement determines
the abnormality of blood pressure of the subject even if an increase
of the blood pressure is relatively small where the systolic blood
pressure BP.sub.SYS is relatively high. That is, the present arrangement
prevents determination of the abnormality of blood pressure if an
increase of the blood pressure is relatively large where the systolic
blood pressure BP.sub.SYS is not so high. Further, the lower first
threshold TH1.sub.L is determined such that the threshold TH1.sub.L
increases, namely, the absolute value of the threshold TH1.sub.L
decreases, with the decrease of the systolic blood pressure BP.sub.SYS
actually obtained from the subject by using the cuff 12. Accordingly,
the present arrangement determines the abnormality of blood pressure
even if a decrease of the blood pressure is relatively small where
the systolic blood pressure BP.sub.SYS is relatively low. That is,
the present arrangement prevents determination of the abnormality
of blood pressure if a decrease of the blood pressure is relatively
large where the systolic blood pressure BP.sub.SYS is not so low.
Thus, the present arrangement assures an accurate determination
of the abnormal blood pressure.
In the BP monitor apparatus 10 constructed as described above,
the relationship between first reference range and standard blood
pressure can be inputted through the input device 54, so that the
relationship is determined depending upon the circumstances. For
instance, the relationship is determined for each specific operation
in view of a medical judgment of the doctor in charge, the sort
of the operation, and the physical power and age of each individual
patient who undergoes the operation. If the first reference range
TH1 is determined based on the relationship inputted through the
input device 54, a first reference range TH1 can be appropriately
determined, so that the abnormality of blood pressure can be determined
with high accuracy.
In the BP monitor apparatus constructed as described above, if
the relationship between first reference range and standard blood
pressure is inputted through the input device 54, the relationship
is recorded by the relationship recording means 90 on the recording
medium 46 which is attachable to, and detachable from, the apparatus
10. Accordingly, the recording medium 46 on which the relationship
has been recorded can be attached to another BP monitor apparatus,
whereby the same blood pressure monitoring operation can be effected.
Further, if the relationship is recorded on a plurality of recording
media 46, the plurality of recording media 46 on which the common
relationship is recorded are attached to a plurality of apparatuses,
so that the same blood pressure monitoring operation can be effected
in each of the plurality of apparatuses.
In the embodiment employing the above-described flow charts, the
abnormality of blood pressure is determined when the absolute value
of the second EBP difference .DELTA.EBP2 is greater than the second
reference value TH2 pre-set at 40 mmHg. The second EBP difference
.DELTA.EBP2 is indicative of an amount of change, during four minutes,
of each estimated blood pressure value EBP determined for each pulse.
Accordingly, the abnormality of blood pressure is determined based
on not only the change of each of iteratively determined estimated
blood pressure values EBP from the standard blood pressure BP.sub.ST
(the systolic blood pressure BP.sub.SYS), but also the change of
each of the iteratively determined estimated blood pressure values
EBP from the estimated blood pressure obtained the predetermined
time period before the each estimated blood pressure. Therefore,
the abnormality of blood pressure can be determined with high accuracy.
In the embodiment employing the above-described flow charts, the
abnormality of blood pressure of the subject is determined when
each of the estimated blood pressures EBP determined for respective
pulses does not fall within the third reference range TH3 defined
by the upper third threshold TH3.sub.U and the lower third threshold
TH3.sub.L, in other words, when each of the estimated blood pressures
EBP is greater than the upper third threshold TH3.sub.U pre-set
at 180 mmHg, or smaller than the lower third threshold TH3.sub.L
pre-set at 80 mmHg. Therefore, the abnormality of blood pressure
can be determined based on each estimated blood pressure value itself
determined for each pulse, irrespective of the change of the each
estimated blood pressure. Thus, an accurate determination of the
abnormality of blood pressure is assured.
While the present invention has been described in detail in its
presently preferred embodiment, by reference to the drawings, the
invention may otherwise be embodied.
For instance, in place of the relationship between first reference
range and standard blood pressure, shown in the graph of FIG. 3,
a different relationship between first reference range and standard
blood pressure, shown in FIG. 7 may be employed. In the relationship
of FIG. 7, upper and lower first thresholds TH1.sub.U, TH1.sub.L
smoothly change, as indicated by respective curved lines, with the
decrease or increase of standard blood pressure BP.sub.ST.
In the BP monitor apparatus 10 constructed as described above,
the blood pressure BP obtained from the subject by using the cuff
12 is used as the standard blood pressure BP.sub.ST for determining
the first change value. The estimated blood pressure EBP determined
at any suitable time point may be used as the standard blood pressure
BP.sub.ST. Further, the standard blood pressure BP.sub.ST may be
inputted through the input device 54.
The illustrated BP monitor apparatus 10 is adapted to iteratively
obtain the pulse-wave propagation velocity PWV, determine the estimated
blood pressure EBP based on the obtained pulse-wave propagation
velocity PWV, and monitor the blood pressure of the subject based
on the estimated blood pressure EBP. In place of the estimated blood
pressure values EBP, blood pressure values iteratively obtained
through a tonometric sensor may be employed. The tonometric sensor
detects a pressure pulse wave produced from a suitable artery, such
as a radial artery, on which the sensor is pressed via the skin,
and blood pressure values are iteratively obtained based on the
detected pressure pulse wave. Alternatively, the estimated blood
pressure values EBP may be replaced with blood pressure values iteratively
obtained in an invasive method using a catheter which is inserted
into an artery of the subject.
In the BP monitor apparatus 10 constructed as described above,
the second reference range TH2 and the third reference range TH3
are inputted through the input device 54. However, these ranges
TH2, TH3 may be prescribed ranges that are pre-stored in the ROM
58.
In the BP monitor apparatus 10 constructed as described above,
the relationship between first reference range and standard blood
pressure is read from the recording medium 46 or inputted through
the input device 54. However, the relationship may be pre-stored
in the ROM 58.
The illustrated BP monitor apparatus 10 is adapted to monitor the
blood pressure of the subject based on the systolic blood pressure
BP.sub.SYS. Alternatively, the BP monitor apparatus may be arranged
to monitor the blood pressure of the subject based on the diastolic
blood pressure BP.sub.DIA or the mean blood pressure BP.sub.MEAN.
Alternatively, at least two of the BP.sub.SYS, BP.sub.MEAN, and
BP.sub.DIA may be employed to monitor the blood pressure.
The illustrated BP monitor apparatus 10 is adapted to measure the
blood pressure BP from the subject by using the cuff 12, determine
the pulse-wave propagation velocity PVW, and determine the estimated
blood pressure EBP based on the pulse-wave propagation velocity
PWV. However, the BP monitor apparatus need not be arranged to measure
the blood pressure BP or determine the estimated blood pressure
EBP, since the principle of the present invention is applicable
to a central monitor device adapted to monitor the blood pressure
of the subject based on blood pressure BP and estimated blood pressure
EBP which are obtained by using respective separate devices.
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 spirit and
scope of the invention. |