Abstrict
A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for successively obtaining blood pressure-relating
information which decreases or increases with a decrease or an increase
of the blood pressure of the subject, or blood pressure-relating
information which increases or decreases with a decrease or an increase
of the blood pressure of the subject; decrease or increase determining
means for determining a decrease or an increase of the blood pressure-relating
information successively obtained by the obtaining means; and abnormality
judging means for judging that the blood pressure of the subject
is abnormal when the decrease or increase of the blood pressure-relating
information is greater than a predetermined reference value (.gamma..sub.1,
.gamma..sub.2), or abnormality judging means for judging that the
blood pressure of the subject is abnormal when the blood pressure-relating
information is greater than a predetermined reference value (TH.sub.H)
or smaller than a predetermined reference value (TH.sub.L).
Claims
What is claimed is:
1. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for obtaining, successively in synchronization with
a heartbeat of the subject, blood pressure-relating information
which decreases with a decrease of the blood pressure of the subject
and which comprises at least one of an estimated blood pressure
(EBP), a normalized pulse-wave area (S.sub.F), and a pulse-wave
propagating velocity (V.sub.M); decrease determining means for determining
a decrease of the blood pressure-relating information obtained by
said obtaining means successively in synchronization with the heartbeat
of the subject; abnormality judging means for judging that the blood
pressure of the subject is abnormal when said decrease of the blood
pressure-relating information is greater than a predetermined reference
value (.gamma..sub.1); and a reference value determining means for
determining said reference value (.gamma..sub.1) based on the blood
pressure-relating information successively obtained by said obtaining
means, by utilizing a predetermined relationship between said reference
value and said blood pressure-relating information, said relationship
being predetermined such that a smaller reference value corresponds
to blood pressure-relating information corresponding to a lower
blood pressure.
2. A blood pressure monitor apparatus according to claim 1, wherein
said decrease is selected from the group consisting of an amount
of decrease of the blood pressure-relating information and a rate
of decrease of the blood pressure-relating information.
3. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for obtaining, successively in synchronization with
a heartbeat of the subject, blood pressure-relating information
which increases with an increase of the blood pressure of the subject
and which comprises at least one of an estimated blood pressure
(EBP), a normalized pulse-wave area (S.sub.F), and a pulse-waving
propagating velocity (V.sub.M); increase determining means for determining
an increase of the blood pressure-relating information obtained
by said obtaining means successively in synchronization with the
heartbeat of the subject; abnormality judging means for judging
that the blood pressure of the subject is abnormal when said increase
of the blood pressure-relating information is greater than a predetermined
reference value (.gamma..sub.2); and reference value determining
means for determining said reference value (.gamma..sub.2) based
on the blood pressure-relating information successively obtained
by said obtaining means, by utilizing a predetermined relationship
between said reference value and said blood pressure-relating information,
said relationship being predetermined such that a smaller reference
value corresponds to blood pressure-relating information corresponding
to a higher blood pressure.
4. A blood pressure monitor apparatus according to claim 3, wherein
said increase is selected from the group consisting of an amount
of increase of the blood pressure-relating information and a rate
of increase of the blood pressure-relating information.
5. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for obtaining, successively in synchronization with
a heartbeat of the subject, blood pressure-relating information
which decreases with an increase of the blood pressure of the subject
and which comprises a pulse-wave propagation time (DT); decrease
determining means for determining a decrease of the blood pressure-relating
information obtained by said obtaining means successively in synchronization
with the heartbeat of the subject; abnormality judging means for
judging that the blood pressure of the subject is abnormal when
said decrease of the blood pressure-relating information is greater
than a predetermined reference value (.gamma..sub.2); and reference
value determining means for determining said reference value (.gamma..sub.2)
based on the blood pressure-relating information successively obtained
by said obtaining means, by utilizing a predetermined relationship
between said reference value and said blood pressure-relating information,
said relationship being predetermined such that a smaller reference
value corresponds to blood pressure-relating information corresponding
to a higher blood pressure.
6. A blood pressure monitor apparatus according to claim 5, wherein
said decrease is selected from the group consisting of an amount
of decrease of the blood pressure-relating information and a rate
of decrease of the blood pressure-relating information.
7. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for obtaining, successively in synchronization with
a heartbeat of the subject, blood pressure-relating information
which increases with a decrease of the blood pressure of the subject
and which comprises a pulse-wave propagation time (DT); increase
determining means for determining an increase of the blood pressure-relating
information obtained by said obtaining means successively in synchronization
with the heartbeat of the subject; abnormality judging means for
judging that the blood pressure of the subject is abnormal when
said increase of the blood pressure-relating information is greater
than a predetermined reference value (.gamma..sub.1); and reference
value determining means for determining said reference value (.gamma..sub.1)
based on the blood pressure-relating information successively obtained
by said obtaining means, by utilizing a predetermined relationship
between said reference value and said blood pressure-relating information,
said relationship being predetermined such that a smaller reference
value corresponds to blood pressure-relating information corresponding
to a lower blood pressure.
8. A blood pressure monitor apparatus according to claim 7, wherein
said increase is selected from the group consisting of an amount
of increase of the blood pressure-relating information and a rate
of increase of the blood pressure-relating information.
9. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for successively obtaining blood pressure-relating
information which decreases with a decrease of the blood pressure
of the subject; abnormality judging means for judging that the blood
pressure of the subject is abnormal when the blood pressure-relating
information successively obtained by said obtaining means is smaller
than a predetermined reference value (TH.sub.L); decrease determining
means for determining a decrease of the blood pressure-relating
information successively obtained by said obtaining means; and reference
value determining means for determining said reference value (TH.sub.L)
based on said decrease of the blood pressure-relating information
successively obtained by said obtaining means, by utilizing a predetermined
relationship between reference value and decrease of blood pressure-relating
information, said relationship being predetermined such that a greater
reference value (TH.sub.L) corresponds to a greater decrease of
blood pressure-relating information.
10. A blood pressure monitor apparatus according to claim 9, wherein
said decrease is selected from the group consisting of an amount
of decrease of the blood pressure-relating information and a rate
of decrease of the blood pressure-relating information.
11. A blood pressure monitor apparatus according to claim 9, wherein
said blood pressure-relating information is selected from the group
consisting of an estimated blood pressure, a pulse-wave propagation
velocity and a normalized pulse-wave area.
12. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for successively obtaining blood pressure-relating
information which increases with an increase of the blood pressure
of the subject; abnormality judging means for judging that the blood
pressure of the subject is abnormal when the blood pressure-relating
information successively obtained by said obtaining means is greater
than a predetermined reference value (TH.sub.H); increase determining
means for determining an increase of the blood pressure-relating
information successively obtained by said obtaining means; and reference
value determining means for determining said reference value (TH.sub.H)
based on said increase of the blood pressure-relating information
successively obtained by said obtaining means, by utilizing a predetermined
relationship between reference value and increase of blood pressure-relating
information, said relationship being predetermined such that a smaller
reference value (TH.sub.H) corresponds to a greater increase of
blood pressure-relating information.
13. A blood pressure monitor apparatus according to claim 12, wherein
said increase is selected from the group consisting of an amount
of increase of the blood pressure-relating information and a rate
of increase of the blood pressure-relating information.
14. A blood pressure monitor apparatus according to claim 12, wherein
said blood pressure-relating information is selected from the group
consisting of an estimated blood pressure, a pulse-wave propagation
velocity and a normalized pulse-wave area.
15. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for successively obtaining blood pressure-relating
information which decreases with an increase of the blood pressure
of the subject; abnormality judging means for judging that the blood
pressure of the subject is abnormal when the blood pressure-relating
information successively obtained by said obtaining means is smaller
than a predetermined reference value (TH.sub.L); decrease determining
means for determining a decrease of the blood pressure-relating
information successively obtained by said obtaining means; and reference
value determining means for determining said reference value (TH.sub.L)
based on said decrease of the blood pressure-relating information
successively obtained by said obtaining means, by utilizing a predetermined
relationship between reference value and decrease of blood pressure-relating
information, said relationship being predetermined such that a greater
reference value (TH.sub.L) corresponds to a greater decrease of
blood pressure-relating information.
16. A blood pressure monitor apparatus according to claim 15, wherein
said decrease is selected from the group consisting of an amount
of decrease of the blood pressure-relating information and a rate
of decrease of the blood pressure-relating information.
17. A blood pressure monitor apparatus according to claim 15 wherein
said blood pressure-relating information comprises a pulse-wave
propagation time.
18. A blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for successively obtaining blood pressure-relating
information which increases with a decrease of the blood pressure
of the subject; abnormality judging means for judging that the blood
pressure of the subject is abnormal when the blood pressure-relating
information successively obtained by said obtaining means is greater
than a predetermined reference value (TH.sub.H); increase determining
means for determining an increase of the blood pressure-relating
information successively obtained by said obtaining means; and reference
value determining means for successively determining said reference
value (TH.sub.H) based on said increase of the blood pressure-relating
information successively obtained by said obtaining means, by utilizing
a predetermined relationship between reference value and increase
of blood pressure-relating information, said relationship being
predetermined such that a smaller reference value (TH.sub.H) corresponds
to a greater increase of blood pressure-relating information.
19. A blood pressure monitor apparatus according to claim 18, wherein
said increase is selected from the group consisting of an amount
of increase of the blood pressure-relating information and a rate
of increase of the blood pressure-relating information.
20. A blood pressure monitor apparatus according to claim 18, wherein
the blood pressure-relating information comprises a pulse-wave propagation
time.
Description The present application is based on Japanese Patent Application
No. 10-337696 filed Nov. 27, 1998, the contents of which are incorporated
hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a blood pressure monitor apparatus
which monitors a blood pressure of a living subject based on blood
pressure-relating information which changes with a change of the
blood pressure of the subject.
2. Discussion of the Related Art
There has been proposed a blood pressure monitor apparatus which
successively obtains blood pressure-relating information of a living
subject (patient) and judges abnormality of the blood pressure when
the blood pressure-relating information is greater than a predetermined
upper reference value or smaller than a predetermined lower reference
value. The blood pressure-relating information includes a blood
pressure which is measured by using a catheter or a cuff, pulse-wave
propagation velocity-relating information such as a pulse-wave propagation
velocity at which a pulse wave propagates through an artery or a
pulse-wave propagation time during which a pulse wave propagates
between predetermined two portions of an artery, heart rate-relating
information such as a heart rate or a pulse period which changes
due to conditions of a central organ (heart) of the subject, peripheral
blood volume-relating information such as a peripheral pulse-wave
area which indicates a peripheral blood volume and which changes
due to conditions of a peripheral organ (blood vessels) of the subject,
and blood oxygen saturation. The above-indicated conventional blood
pressure monitor apparatus which monitors the blood pressure-relating
information automatically determines abnormality of the blood pressure
of the subject based on the obtained blood pressure-relating information,
so that the abnormal condition of the patient can be quickly dealt
with.
The conventional blood pressure monitor apparatus determines abnormality
of the blood pressure of the patient when the detected or obtained
blood pressure-relating information is greater than a predetermined
upper reference value or smaller than a predetermined lower reference
value. Accordingly, the conventional blood pressure monitor apparatus
equally determines abnormality of the blood pressure due to an abrupt
change thereof in a considerably short period of time and due to
a gradual change thereof in a relatively long period of time. In
general, the abnormal condition of the patient detected when the
blood pressure-relating information has abruptly changed should
be dealt with as quickly as possible, as compared with that detected
when the blood pressure-relating information has gradually changed.
The conventional apparatus described above, however, cannot assure
that a suitable medical treatment is given without delay on the
patient whose blood pressure-relating information has abruptly changed.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
blood pressure monitor apparatus which is capable of quickly detecting
abnormality of the blood pressure of a patient when the blood pressure
has changed abruptly.
The above object may be attained according to a first aspect of
the present invention, which provides a blood pressure monitor apparatus
for monitoring a blood pressure of a living subject, comprising:
blood pressure-relating information obtaining means for successively
obtaining blood pressure-relating information which decreases with
a decrease of the blood pressure of the subject; decrease determining
means for determining a decrease of the blood pressure-relating
information successively obtained by the obtaining means; and abnormality
judging means for judging that the blood pressure of the subject
is abnormal when the decrease of the blood pressure-relating information
is greater than a predetermined reference value (.gamma..sub.1).
The above object may also be attained according to a second aspect
of the present invention, which provides a blood pressure monitor
apparatus for monitoring a blood pressure of a living subject, comprising:
blood pressure-relating information obtaining means for successively
obtaining blood pressure-relating information which increases with
a increase of the blood pressure of the subject; increase determining
means for determining an increase of the blood pressure-relating
information successively obtained by the obtaining means; and abnormality
judging means for judging that the blood pressure of the subject
is abnormal when the increase of the blood pressure-relating information
is greater than a predetermined reference value (.gamma..sub.2).
The above object may also be attained according to a third aspect
of the present invention, which provides a blood pressure monitor
apparatus for monitoring a blood pressure of a living subject, comprising:
blood pressure-relating information obtaining means for successively
obtaining blood pressure-relating information which decreases with
an increase of the blood pressure of the subject; decrease determining
means for determining a decrease of the blood pressure-relating
information successively obtained by the obtaining means; and abnormality
judging means for judging that the blood pressure of the subject
is abnormal when the decrease of the blood pressure-relating information
is greater than a predetermined reference value (.gamma..sub.2).
The above object may also be attained according to a fourth aspect
of the present invention, which provides a blood pressure monitor
apparatus for monitoring a blood pressure of a living subject, comprising:
blood pressure-relating information obtaining means for successively
obtaining blood pressure-relating information which increases with
a decrease of the blood pressure of the subject; increase determining
means for determining an increase of the blood pressure-relating
information successively obtained by the obtaining means; and abnormality
judging means for judging that the blood pressure of the subject
is abnormal when the increase of the blood pressure-relating information
is greater than a predetermined reference value (.gamma..sub.1).
In the blood pressure monitor apparatuses constructed as described
above, the decrease or increase determining means determines a decrease
or an increase of the blood pressure-relating information successively
obtained by the blood pressure-relating information obtaining means,
and the abnormality judging means judges that the blood pressure
of the living subject (patient) is abnormal when the decrease or
increase of the blood pressure-relating information is greater than
the predetermined reference value. In other words, when the blood
pressure-relating information has abruptly decreased or increased,
the abnormality judging means judges that the blood pressure of
the patient is abnormal even if the blood pressure-relating information
may be normal or permissible. Accordingly, the abnormality of the
blood pressure of the patient can be detected without delay when
the blood pressure has abruptly decreased or increased.
In a preferred form of the above first or fourth aspect of the
present invention, the blood pressure monitor apparatus further
comprises reference value determining means for determining the
reference value (.gamma..sub.1) based on the blood pressure-relating
information successively obtained by the obtaining means, by utilizing
a predetermined relationship between reference value and blood pressure-relating
information, the relationship being predetermined such that a smaller
reference value corresponds to blood pressure-relating information
corresponding to a lower blood pressure.
According to the above preferred form of the first or fourth aspect
of the invention, the reference value determining means determines
the reference value (.gamma..sub.1) which is used in judging the
abnormality of the blood pressure of the patient by the abnormality
judging means, such that a smaller reference value corresponds to
blood pressure-relating information corresponding to a lower blood
pressure. According to this arrangement, when the blood pressure
of the patient is relatively low, the abnormality judging means
judges that the blood pressure of the patient is abnormal even if
the decrease or increase of the blood pressure-relating information
may be relatively small, so that the abnormality of the blood pressure
of the patient can be quickly detected without delay when the blood
pressure has abruptly decreased. When the blood pressure of the
patient is not so low, the abnormality judging means judges that
the blood pressure of the patient is abnormal only when the decrease
or increase of the blood pressure-relating information is relatively
large, so that the judgment of the abnormality of the blood pressure
is prevented when the blood pressure of the patient is not so low.
In the case where the abnormality of the blood pressure is determined
on the basis of only the decrease or increase of the blood pressure-relating
information, the reference value must be set at a small value in
an attempt to be able to find an abnormal blood pressure even if
the blood pressure may gradually decrease. In this case, however,
the blood pressure may unnecessarily be judged to be abnormal when
the blood pressure is not so low.
In a preferred form of the above second or third aspect of the
invention, the blood pressure monitor apparatus further comprises:
reference value determining means for determining the reference
value (.gamma..sub.2) based on the blood pressure-relating information
successively obtained by the obtaining means, by utilizing a predetermined
relationship between reference value and blood pressure-relating
information, the relationship being predetermined such that a smaller
reference value corresponds to blood pressure-relating information
corresponding to a higher blood pressure.
According to the above preferred form of the above second or third
aspect of the present invention, the reference value determining
means determines the reference value (.gamma..sub.2) which is used
in judging abnormality of the blood pressure of the patient by the
abnormality judging means, such that a smaller reference value corresponds
to the blood pressure-relating information corresponding to a higher
blood pressure. According to this arrangement, when the blood pressure
of the patient is relatively high, the abnormality judging means
judges that the blood pressure of the patient is abnormal even when
the increase or decrease of the blood pressure-relating information
may be relatively small, so that the abnormality of the blood pressure
of the patient can be quickly detected without delay when the blood
pressure has abruptly increased. In contrast, when the blood pressure
of the patient is not so high, the abnormality judging means judges
that the blood pressure of the patient is abnormal only when the
increase or decrease of the blood pressure-relating information
is relatively large, so that the determination of the abnormality
of the blood pressure is prevented when the blood pressure of the
patient is not so high. In the case where the abnormality of the
blood pressure is determined on the basis of only the increase or
decrease of the blood pressure-relating information, the reference
value must be set at a small value in an attempt to be able to find
an abnormal blood pressure of the patient even when the blood pressure
may gradually increase. In this case, however, the blood pressure
may unnecessarily be determined to be abnormal when the blood pressure
is not so high.
In a preferred form of the above first or third aspect of the invention,
the decrease is selected from the group consisting of an amount
of decrease of the blood pressure-relating information and a rate
of decrease of the blood pressure-relating information.
In a preferred form of the above second or fourth aspect of the
invention, the increase is selected from the group consisting of
an amount of increase of the blood pressure-relating information
and a rate of increase of the blood pressure-relating information.
In a preferred form of the above first or second aspect of the
invention, the blood pressure-relating information is selected from
the group consisting of an estimated bloodpressure (EBP), a normalizedpulse-wave
area (S.sub.F), and a pulse-wave propagating velocity (V.sub.M).
In a preferred form of the above third or fourth aspect of the
invention, the blood pressure-relating information comprises a pulse-wave
propagation time (DT).
The above-indicated object of the present invention may also be
attained according to a fifth aspect of the invention, which provides
a blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for successively obtaining blood pressure-relating
information which decreases with a decrease of the blood pressure
of the subject; abnormality judging means for judging that the blood
pressure of the subject is abnormal when the blood pressure-relating
information successively obtained by the obtaining means is smaller
than a predetermined reference value (TH.sub.L); decrease determining
means for determining a decrease of the blood pressure-relating
information successively obtained by the obtaining means; and reference
value determining means for determining the reference value (TH.sub.L)
based on the decrease of the blood pressure-relating information
successively obtained by the obtaining means, by utilizing a predetermined
relationship between reference value and decrease of blood pressure-relating
information, the relationship being predetermined such that a greater
reference value (TH.sub.L) corresponds to a greater decrease of
blood pressure-relating information.
In the blood pressure monitor apparatus constructed as described
above, the reference value determining means determines the reference
value TH.sub.L which is used in judging abnormality of the blood
pressure of the subject by the abnormality judging means, based
on the decrease of the blood pressure-relating information successively
obtained by the obtaining means, by utilizing a predetermined relationship
between reference value and decrease of the blood pressure-relating
information, the relationship being predetermined such that a greater
reference value (TH.sub.L) corresponds to a greater decrease of
the blood pressure-relating information. Further, the abnormality
judging means judges that the blood pressure of the subject has
abnormally decreased when the blood pressure-relating information
obtained by the obtaining means is smaller than the reference value
(TH.sub.L). According to this arrangement wherein a greater reference
value corresponds to a greater decrease of the blood pressure-relating
information, the abnormality judging means judges abnormal decrease
of the blood pressure of the subject without delay when the blood
pressure has abruptly decreased. In addition, since a smaller reference
value corresponds to a smaller decrease of the blood pressure-relating
information, the present arrangement prevents determination of abnormal
decrease of the blood pressure when the blood pressure of the subject
is not so low and the blood pressure has gradually decreases.
In a preferred form of the above fifth or sixth aspect of the invention,
the blood pressure-relating information is selected from the group
consisting of an estimated blood pressure (EBP), a pulse-wave propagation
velocity (V.sub.M) and a normalized pulse-wave area (S.sub.F).
The above-indicated object of the present invention may also be
attained according to a sixth aspect of the invention, which provides
a blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for successively obtaining blood pressure-relating
information which increases with an increase of the blood pressure
of the subject; abnormality judging means for judging that the blood
pressure of the subject is abnormal when the blood pressure-relating
information successively obtained by the obtaining means is greater
than a predetermined reference value (TH.sub.H); increase determining
means (60) for determining an increase of the blood pressure-relating
information successively obtained by the obtaining means; and reference
value determining means for determining the reference value (TH.sub.H)
based on the increase of the blood pressure-relating information
successively obtained by the obtaining means, by utilizing a predetermined
relationship between reference value and increase of blood pressure-relating
information, the relationship being predetermined such that a smaller
reference value (TH.sub.H) corresponds to a greater increase of
blood pressure-relating information.
In the blood pressure monitor apparatus constructed as described
above, the reference value determining means determines the reference
value TH.sub.H which is used in judging abnormality of the blood
pressure of the subject by the abnormality judging means, based
on the increase of the blood pressure-relating information successively
obtained by the obtaining means, by utilizing a predetermined relationship
between reference value and increase of the blood pressure-relating
information, the relationship being predetermined such that a smaller
reference value (TH.sub.H) corresponds to a greater increase of
the blood pressure-relating information. Further, the abnormality
judging means judges that the blood pressure of the subject has
abnormally increased when the blood pressure-relating information
obtained by the obtaining means is greater than the reference value.
According to this arrangement wherein a smaller reference value
corresponds to a greater increase of the blood pressure-relating
information, the abnormality judging means judges abnormal increase
of the blood pressure of the subject without delay when the blood
pressure has abruptly increased. In addition, since a greater reference
value corresponds to a smaller increase of the blood pressure-relating
information, the present arrangement prevents determination of abnormal
increase of the blood pressure when the blood pressure of the subject
is not so high and the blood pressure gradually increases.
The above-indicated object of the present invention may also be
attained according to a seventh aspect of the invention, which provides
a blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for successively obtaining blood pressure-relating
information which decreases with an increase of the blood pressure
of the subject; abnormality judging means for judging that the blood
pressure of the subject is abnormal when the blood pressure-relating
information successively obtained by the obtaining means is smaller
than a predetermined reference value (TH.sub.L); decrease determining
means for determining a decrease of the blood pressure-relating
information successively obtained by the obtaining means; and reference
value determining means for determining the reference value (TH.sub.L)
based on the decrease of the blood pressure-relating information
successively obtained by the obtaining means, by utilizing a predetermined
relationship between reference value and decrease of blood pressure-relating
information, the relationship being predetermined such that a greater
reference value (TH.sub.L) corresponds to a greater decrease of
blood pressure-relating information.
The above-indicated object of the present invention may also be
attained according to an eighth aspect of the invention, which provides
a blood pressure monitor apparatus for monitoring a blood pressure
of a living subject, comprising: blood pressure-relating information
obtaining means for successively obtaining blood pressure-relating
information which increases with a decrease of the blood pressure
of the subject; abnormality judging means for judging that the blood
pressure of the subject is abnormal when the blood pressure-relating
information successively obtained by the obtaining means is greater
than a predetermined reference value (TH.sub.H); increase determining
means for determining an increase of the blood pressure-relating
information successively obtained by the obtaining means; and reference
value determining means for determining the reference value (TH.sub.H)
based on the increase of the blood pressure-relating information
successively obtained by the obtaining means, by utilizing a predetermined
relationship between reference value and increase of blood pressure-relating
information, the relationship being predetermined such that a smaller
reference value (TH.sub.H) corresponds to a greater increase of
blood pressure-relating information.
In a preferred form of the above fifth or seventh aspect of the
present invention, the decrease is selected from the group consisting
of an amount of decrease of the blood pressure-relating information
and a rate of decrease of the blood pressure-relating information.
In a preferred form of the above sixth or eighth aspect of the
present invention, the increase is selected from the group consisting
of an amount of increase of the blood pressure-relating information
and a rate of increase of the blood pressure-relating information.
In a preferred form of the above fifth or sixth aspect of the present
invention, the blood pressure-relating information is selected from
the group consisting of an estimated blood pressure (EBP), a pulse-wave
propagation velocity (V.sub.M) and a normalized pulse-wave area
(S.sub.F).
In a preferred form of the above seventh or eighth aspect of the
present invention, the blood pressure-relating information comprises
a pulse-wave propagation time (DT).
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 of a blood pressure monitor apparatus
constructed according to one embodiment of the present invention;
FIG. 2 is a block diagram for illustrating essential functions
of an electronic control device of the apparatus of FIG. 1;
FIG. 3 is a graph explaining a photoelectric pulse wave detected
by a photoelectric pulse-wave sensor of the apparatus of FIG. 1;
FIG. 4 is a graph showing a relationship between normalized pulse-wave
area and estimated blood pressure, which relationship is used in
the apparatus of FIG. 1;
FIG. 5 is a flow chart representing a control routine for determining
the relationship between the normalized pulse-wave area and the
estimated blood pressure, which control routine is executed by the
electronic control device of the apparatus of FIG. 1;
FIG. 6 is a flow chart representing a control routine for monitoring
a blood pressure of the subject executed by the electronic control
device of the apparatus of FIG. 1;
FIGS. 7(a)-(c) are graphs showing relationships between the estimated
blood pressure and the first and/or second reference value;
FIG. 8 is a diagrammatic view of a blood pressure monitor apparatus
constructed according to another embodiment of the present invention;
FIG. 9 is a flow chart representing a control routine for monitoring
the blood pressure of the subject executed by the electronic control
device of the apparatus of FIG. 8; and
FIG. 10 is a graph showing relationships between the decrease of
the blood pressure-relating information and the lower reference
value (TH.sub.L), and between the increase of the blood pressure-relating
information and the upper reference value (TH.sub.H), which relationships
are used in the apparatus of FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is shown a blood pressure (BP)
monitor apparatus 8 constructed according to a first embodiment
of the present invention. The BP monitor apparatus 8 of FIG. 1 includes
an inflatable cuff 10 which has an elongate fabric bag and a rubber
bag accommodated in the elongate fabric bag and which is to be wound
around an upper arm 12 of a patient, for instance. A pressure sensor
14, a selector valve 16, and an air pump 18 are connected to the
cuff 10 via a conduit piping 20.
The pressure sensor 14 detects an air pressure in the cuff 10 and
supplies a pressure signal SP representative of the detected pressure
to a static-pressure filter circuit 22 and a pulse-wave filter circuit
24. The static-pressure filter circuit 22 includes a low-pass filter
and transmits a static component of the signal SP as a cuff-pressure
signal SK representative of a static cuff pressure Pc to an electronic
control device 28 via a first analog-to-digital (A/D) converter
26.
The pulse-wave filter circuit 24 has a band-pass filter and transmits
an oscillating component of the pressure signal SP as a pulse-wave
signal SM.sub.1 to the electronic control device 28 via a second
analog-to-digital (A/D) converter 29. The pulse-wave signal SM.sub.1
represents a pulse wave, i.e., an oscillatory pressure wave which
is produced from a brachial artery (not shown) of the patient in
synchronism with the heartbeat of the patient and is transmitted
to the cuff 10.
The electronic control device 28 is constituted by a so-called
microcomputer which includes a central processing unit (CPU) 30,
a read only memory (ROM) 32, a random access memory (RAM) 34, and
an input and output (I/O) port not shown. The CPU 30 performs signal
processing operations according to control programs stored in the
ROM 32 by utilizing a temporary data storage function of the RAM
34, generates drive signals through the I/O port for controlling
the selector valve 16 and the air pump 18, and outputs a display
signal to a display device 36 through the I/O port.
The BP monitor apparatus 8 further includes a photoelectric pulse-wave
sensor 40 which functions as a volume pulse-wave detecting device
for detecting a volume pulse-wave (plethysmograph) of peripheral
blood vessels of the subject. The photoelectric pulse-wave sensor
40 includes a housing 42 for accommodating a body portion (e.g.,
an end portion of a finger) of the living subject therein. The housing
42 is provided with a light-emitting element 44 and a light-receiving
element 46 which are opposed to each other on predetermined locations
of the inner surface of the housing 42. The light-emitting element
44 emits, toward the skin of the body portion accommodated in the
housing 42, a red or infrared light having a wavelength which can
be reflected by hemoglobin present in blood of the body portion,
preferably the light having a wavelength of about 800 nm at which
the light is not influenced by blood oxygen saturation. The light-receiving
element 46 receives and detects the light transmitted through the
body portion. The thus constructed photoelectric pulse-wave sensor
40 generates a photoelectric pulse-wave signal SM.sub.2 representative
of the blood volume in the blood capillaries (capillary vessels)
of the body portion. The generated signal SM.sub.2 is supplied to
the electronic control device 28 through a third analog-to-digital
(A/D) converter 48.
FIG. 2 illustrates essential functions of the electronic control
device 28 of the BP monitor apparatus 8 of the present embodiment.
The BP monitor apparatus 8 includes blood pressure (BP) measuring
means 50, cuff pressure regulating means 52, normalized pulse-wave
area calculating means 54, relationship determining means 56 for
determining a relationship between blood pressure and normalized
pulse-wave area, estimated blood pressure determining means (blood
pressure-relating information obtaining means) 58, change (i.e.,
decrease or increase) determining means 60, abnormality judging
means 62, and reference value determining means 64.
The BP measuring means 50 measures a systolic blood pressure BP.sub.sys,
a mean blood pressure BP.sub.MEAN, and a diastolic blood pressure
BP.sub.DIA of the subject according to a known oscillometric method.
Described in detail, after the pressure in the cuff 10 wound around
on the upper arm of the subject is first increased up to a predetermined
target value P.sub.CM (e.g., about 180 mmHg) by the cuff pressure
regulating means 52, the pressure in the cuff 10 is slowly lowered
at a rate of about 3 mmHg/sec. The blood pressure values BP.sub.sys,
BP.sub.MEAN, and BP.sub.DIA are determined on the basis of the change
of respective amplitudes of successive pulses of the pulse-wave
signal SM.sub.1 obtained while the cuff pressure is slowly lowered.
The determined blood pressure values BP.sub.sys, BP.sub.MEAN, and
BP.sub.DIA are indicated on the display 36.
The normalized pulse-wave area calculating means 54 calculates
an area S.sub.F which is defined by a waveform of each of successive
pulses of the photoelectric pulse-wave signal SM.sub.2 and is normalized
based on a period W and an amplitude L of each pulse of the photoelectric
pulse-wave signal SM.sub.2. As shown in the graph of FIG. 3, the
waveform of each pulse of the photoelectric pulse-wave signal SM.sub.2
is defined by a series of data points indicative of respective instantaneous
magnitudes of the photoelectric pulse-wave signal SM.sub.2 which
are Input to the control device 28 at a predetermined interval such
as several milliseconds to several tens of milliseconds. A pulse-wave
area S is obtained by integrating, in the period W of the pulse
of the photoelectric pulse-wave signal SM.sub.2, the respective
magnitudes of the pulse of the signal SM.sub.2, and then the normalized
pulse-wave area S.sub.F is calculated according to the following
expression: S.sub.F =S/(W.times.L). The normalized pulse-wave area
S.sub.F is a dimensionless value indicative of a ratio of the pulse-wave
area S to an area defined by the period W and the amplitude L of
the each pulse of the photoelectric pulse wave. A symbol %MAP may
be used in place of the symbol S.sub.F.
The relationship determining means 56 determines a relationship
between the blood pressure BP (one of the systolic, mean and diastolic
blood pressure BP.sub.sys, BP.sub.MEAN, and BP.sub.DIA) measured
by the BP measuring means 50 and the normalized pulse-wave area
S.sub.F calculated by the normalized pulse-wave area calculating
means 54, when the blood pressure BP is measured by the BP measuring
means 50. This relationship (hereinafter referred to as "BP-S.sub.F
relationship") is indicated in the graph of FIG. 4 by way of
example, and is represented by an equation: EBP=.alpha..multidot.S.sub.F
+.beta., for instance, where .alpha. is a constant indicative of
a gradient, .beta. is a constant indicative of an intercept, and
EBP is an estimated blood pressure value. In the case where the
BP-S.sub.F relationship represented by the equation EBP=f (S.sub.F)
is determined based on one set of blood pressure BP and normalized
pulse-wave area S.sub.F, one of the constants .alpha. and .beta.
is a statistically obtained value which is selected depending upon
the sexuality and age of the subject. When the BP-S.sub.F relationship
represented by the equation EBP=f (S.sub.F) is determined based
on at least two sets of blood pressure BP and normalized pulse-wave
area S.sub.F, the constants .alpha. and .beta. in the equation are
determined for each individual subject. The determined constants
.alpha. and .beta. may be corrected each time a blood pressure is
measured by the BP measuring means 50.
The estimated blood pressure determining means 58 functioning as
the blood pressure-relating information obtaining means successively
determines an estimated blood pressure EBP of the subject, based
on each of the normalized pulse-wave area values S.sub.F successively
calculated by the normalized pulse-wave area calculating means 54,
according to the equation EBP=f (S.sub.F) determined by the BP-S.sub.F
relationship determining means 56. The successively determined estimated
blood pressure values EBP are indicated in a trend graph on the
display device 36. When the systolic blood pressure value BP.sub.sys
is used to determine the BP-S.sub.F relationship represented by
the equation EBP=f(S.sub.F), the estimated blood pressure value
EBP determined by the determining means 58 indicates the systolic
blood pressure of the subject. When the mean blood pressure value
BP.sub.MEAN is used to determine the relationship (EBP=f (S.sub.F)),
the value EBP indicates the mean blood pressure, while the value
EBP indicates the diastolic blood pressure when the diastolic blood
pressure value BP.sub.DIA is used to determine the relationship.
The change (i.e., decrease or increase) determining means 60 determines
a change value .DELTA.EBP of the estimated blood pressure EBP. The
change value .DELTA.EBP represents an absolute value of a change
of the estimated blood pressure EBP. For instance, the change value
.DELTA.EBP is an absolute value of a rate of change or an amount
of change of the currently determined estimated blood pressure value
EBP from a moving blood-pressure average EBP.sub.AV obtained for
a predetermined number of pulses (e.g., about 20 to 30 pulses) or
within a predetermined time period ranging from 30 seconds to several
minutes. Alternatively, the change value .DELTA.EBP may be an absolute
value of a rate of change or an amount of change of the currently
determined estimated blood pressure value EBP from the estimated
blood pressure value EBP obtained in the prior blood pressure measurement
of the BP measuring means 50. Further, the change value .DELTA.EBP
may be an absolute value of a rate of change or an amount of change
of the currently determined estimated blood pressure value EBP from
the estimated blood pressure value obtained a predetermined time
period (e.g., 10 minutes) before the current estimated blood pressure
value EBP has been obtained, or from the estimated blood pressure
value obtained for a prior pulse which has preceded the currently
detected pulse by a predetermined number. The change value .DELTA.EBP
is represented as .vertline.EBP.sub.AV -EBP.vertline. or .vertline.
(EBP.sub.AV -EBP)/EBP.sub.AV.vertline..
The abnormality judging means 62 judges that the blood pressure
of the subject is abnormal when the change value .DELTA.EBP determined
by the determining means 60 is greater than a predetermined reference
value .gamma., in other words, if the determined change value .gamma.EBP
is greater than at least one of a first reference value .gamma..sub.1
and a second reference value .gamma..sub.2 which are determined
by the reference value determining means 64 including first reference
value determining means 66 and second reference value determining
means 68. Described more specifically, the first reference value
determining means 66 successively determines a first reference value
.gamma..sub.1 used in judging abnormality of the blood pressure
by the abnormality judging means 62, based on an estimated blood
pressure EBP successively determined by the determining means 58,
by utilizing a predetermined relationship between first reference
value .gamma..sub.1 and estimated blood pressure EBP, which relationship
is predetermined such that a smaller first reference value .gamma..sub.1
corresponds to a smaller estimated blood pressure EBP. The second
reference value determining means 68 successively determines a second
reference value .gamma..sub.2 used in judging abnormality of the
blood pressure of the subject by the abnormality judging means 62,
based on an estimated blood pressure EBP successively determined
by the determining means 58, by utilizing a predetermined relationship
between second reference value .gamma..sub.2 and estimated blood
pressure EBP, which relationship is predetermined such that a smaller
second reference value .gamma..sub.2 corresponds to a greater estimated
blood pressure EBP.
There will be described the operation of the electronic control
device 28 referring to the flow chart of FIG. 5.
A control routine of FIG. 5 for determining a BP-S.sub.F relationship
(a relationship between blood pressure and normalized pulse-wave
area) is initiated with Step SA1 in which counters and registers
(not shown) are reset. Step SA 1 is followed by Step SA2 corresponding
to the cuff pressure regulating means 52 to quickly increase the
cuff pressure for effecting a blood pressure measurement, by placing
the selector valve 16 to its inflation position and actuating the
air pump 18.
Step SA 2 is followed by Step SA3 corresponding to the normalized
pulse-wave area calculating means 54. In this Step SA3, a pulse-wave
area S, a period W, and an amplitude L of each pulse of the photoelectric
pulse wave are obtained based on the photoelectric pulse-wave signal
SM.sub.2 (shown in the graph of FIG. 3) detected by the photoelectric
pulse-wave sensor 40. On the basis of the obtained pulse-wave area
S, period W, amplitude L of each pulse of the photoelectric pulse
wave, a normalized pulse-wave area S.sub.F is calculated according
to the expression S.sub.F =S/(W.times.L).
The control flow then goes to Step SA4 to judge whether or not
the cuff pressure P.sub.C is increased up to or higher than a predetermined
target value P.sub.CM (e.g., 180 mmHg). If a negative decision is
made in Step SA4, the control flow goes back to Step SA2 so as to
continue the increasing of the cuff pressure P.sub.C. If the cuff
pressure P.sub.C is equal to or higher than the target value P.sub.CM,
an affirmative decision is made in Step SA4 and the control flow
goes to Step SA5 corresponding to the blood pressure measuring means
50 to perform a blood pressure measuring algorithm. Described in
detail, the air pump 18 is turned off and the selector valve 16
is switched from the inflation position to its slow-deflation position
where the selector valve16 permits the pressurized air to be slowly
discharged from the cuff 10, so that the pressure in the cuff 10
is slowly decreased at a predetermined rate of 3 mmHg/sec. A systolic
blood pressure BP.sub.sys, a mean blood pressure BP.sub.MEAN, and
a diastolic blood pressure are determined based on the variation
of amplitudes of successive pulses of the pulse wave represented
by the pulse-wave signal SM.sub.1 obtained during the slow decreasing
of the cuff pressure, according to a well-known oscillometric blood
pressure determining algorithm. Further, the pulse rate is determined
based on an interval between successive adjacent two pulses of the
pulse wave. The thus determined blood pressure values BP.sub.sys,
BP.sub.MEAN, BP.sub.DIA, and the pulse rate are indicated on the
display device 36, and the selector valve 16 is switched from the
slow-deflation position to its rapid-deflation position, whereby
the pressure in the cuff 10 is rapidly lowered.
Step SA5 is followed by Step SA6 corresponding to the BP-S.sub.F
relationship determining means 56. In this Step SA 6, the control
device 28 determines a relationship between the normalized pulse-wave
area S.sub.F obtained in Step SA3 corresponding to the normalized
pulse-wave calculating means 54 and the blood pressure value BP.sub.sys,
BP.sub.MEAN, BP.sub.DIA obtained in Step SA5 corresponding to the
blood pressure measuring means 50 using the cuff 10. The relationship
(represented by the expression: EBP=.alpha..multidot.S.sub.F +.beta.)
is determined based on one set of data consisting of one of the
blood pressure values BP.sub.sys, BP.sub.MEAN, BP.sub.DIA obtained
in Step SA5 and the normalized pulse-wave area S.sub.F obtained
in Step SA3, and another set of data obtained in Steps SA5, SA3
in the prior control cycle according to the control routine of FIG.
5.
After the BP-S.sub.F relationship is determined as described above,
the electronic control device 28 executes a blood pressure monitor
routine as indicated by a flow chat of FIG. 6. The control routine
of FIG. 6 is initiated with Step SB1 to judge whether or not the
photoelectric pulse wave has been detected. As long as a negative
judgment is made in Step SB1, this step is repeatedly implemented.
If an affirmative judgment is made in Step SB1, the control flow
goes to Step SB2 corresponding to the normalized pulse-wave area
calculating means 54 to calculate a normalized pulse-wave area S.sub.F
of a pulse of the photoelectric pulse wave read in Step SB1, in
the same manner as carried out in Step SA3 of the control routine
of FIG. 5.
Step SB2 is followed by Step SB3 corresponding to the estimated
blood pressure determining means 58. In this Step SB3, an estimated
blood pressure EBP is determined based on the normalized pulse-wave
area S.sub.F calculated in Step SB2, according to the BP-S.sub.F
relationship (EBP=.alpha..multidot.S.sub.F +.beta.) determined in
Step SA6 of the control routine of FIG. 5. The determined estimated
blood pressure EBP is output to the display device 36 so as to indicate
a trend graph of the estimated blood pressure values determined
for the respective pulses of the pulse wave.
The control flow then goes to Steps SB4 and SB5 cooperating with
each other to constitute the reference value determining means 64.
In Step SB4 corresponding to the first reference value determining
means 66, a first reference value .gamma..sub.1 is determined based
on the estimated blood pressure EBP determined in Step SB3, by utilizing
a predetermined relationship between first reference value .gamma..sub.1
and estimated blood pressure EBP, as shown in the graph of FIG.
7 (a). Described in detail, the first reference value .gamma..sub.1
is predetermined such that the first reference value .gamma..sub.1
linearly decreases as the estimated blood pressure value EBP obtained
in Step SB3 decreases from a first empirical value EBP.sub.1, and
such that the first reference value .gamma..sub.1 is kept at a constant
value (e.g., 40%) when the estimated blood pressure EBP is higher
than the first empirical value EBP.sub.1.
In the following Step SB5 corresponding to the second reference
value determining means 68, a second reference value Y.sub.2 is
determined based on the estimated blood pressure EBP determined
in Step SB3, by utilizing a .gamma..sub.2 predetermined relationship
between second reference value .gamma..sub.2 and estimated blood
pressure EBP, as shown in the graph of FIG. 7 (b). Described in
detail, the second reference value .gamma..sub.2 is predetermined
such that the second reference value .gamma..sub.2 linearly decreases
as the estimated blood pressure EBP obtained in Step SB3 increases
form a second empirical value EBP.sub.2, and such that the second
reference value .gamma..sub.2 is kept at a constant value (e.g.,
40%) when the estimated blood pressure EBP is lower than the second
empirical value EBP.sub.2.
The control flow then goes to Step SB6 corresponding to the change
determining means 60 to determine, as a change value .DELTA.EBP,
a rate of change of the estimated blood pressure EBP determined
in Step SB3 with respect to the estimated blood pressure EBP obtained
in the prior blood pressure measurement using the cuff 10, in other
words, the estimated blood pressure EBP determined immediately after
the blood pressure value BP was measured in the prior blood pressure
measuring operation using the cuff 10.
Step SB6 is followed by Step SB7 corresponding to the abnormality
judging means 62 to judge whether or not the change value .DELTA.EBP
determined in Step SB6 is greater than at least one of the first
reference value .gamma..sub.1 determined in Step SB4 and the second
reference value .gamma..sub.2 determined in Step SB5. Described
more specifically referring to the graph of FIG. 7(c) in which the
graphs of FIGS. 7(a) and 7(b) are superimposed on each other, it
is judged in Step SB7 whether or not the change value .DELTA.EBP
determined in Step SB6 is greater than the first reference value
.gamma..sub.1 when the estimated blood pressure EBP determined in
Step SB3 is lower than the first empirical value EBP.sub.1, whether
or not the change value .DELTA.EBP determined in Step SB6 is greater
than the first reference value .gamma..sub.1, namely, the second
reference value .gamma..sub.2, when the estimated blood pressure
EBP determined in Step SB3 is higher than the first empirical value
EBP.sub.1 and lower than the second empirical value EBP.sub.2, and
whether or not the change value .DELTA.EBP calculated in Step SB6
is greater than the second reference value .gamma..sub.2 when the
estimated blood pressure EBP is higher than the second empirical
value EBP.sub.2.
If a negative judgment is made in Step SB7, the control flow goes
to Step SB8 to judge whether or not a predetermined period (e.g.,
15 to 20 minutes), that is, a calibration period, has passed after
the control routine of FIG. 5 for determining the BP-S.sub.F relationship
was performed. If a negative judgment is made in Step SB8, the control
flow goes back to Step SB1 and the following steps so as to repeat
the blood pressure monitor routine, that is, successively determine
the estimated blood pressure EBP for each of the pulses, and timewise
indicate the trend graph of the determined estimated blood pressure
values EBP on the display device 36.
On the other hand, if an affirmative judgment is made in Step SB7,
the control flow goes to Step SB9 to indicate abnormality of the
blood pressure on the display device 36, and implement the control
routine of FIG. 5 for updating the BP-S.sub.F relationship, in order
to perform a reliable blood pressure measurement by using the cuff
10, and determine a new BP-S.sub.F relationship (EBP=.alpha..multidot.S.sub.F
+.beta.).
In the present embodiment explained above, the change determining
means 60 (Step SB6) determines the change value .DELTA.EBP of the
estimated blood pressure EBP successively determined by the estimated
blood pressure determining means 58 (Step SB3). The abnormality
judging means 62 (Step SB7) judges that the blood pressure of the
subject is abnormal when the change value .DELTA.EBP determined
by the change determining means 60 (Step SB6) is greater than at
least one of the first and second reference values .gamma..sub.1
and .gamma..sub.2. In other words, the abnormality judging means
62 judges the abnormality of the blood pressure of the subject when
the estimated blood pressure EBP has abruptly changed even if the
estimated blood pressure EBP is a relatively normal value. According
to this arrangement, the abnormality of the blood pressure of the
subject can be quickly detected without delay when the blood pressure
has abruptly changed.
In the present embodiment, the first reference value determining
means 66 (SB4) determines the first reference value .gamma..sub.1
used by the abnormality judging means 62 (Step SB7) for judging
the abnormality of the blood pressure, such that a smaller first
reference value .gamma..sub.1 corresponds to a smaller estimated
blood pressure value EBP determined by the estimated blood pressure
determining means 58 (SB3) In the present arrangement, when the
blood pressure of the subject is relatively low, the abnormality
of the blood pressure is detected even when the change value .DELTA.EBP
is relative small. On the other hand, when the blood pressure of
the subject is not so low, the abnormality of the blood pressure
is detected only when the change value .DELTA.EBP is relatively
large. Accordingly, the present arrangement permits the determination
of abnormal blood pressure without delay when the blood pressure
has abruptly changed, and eliminates the determination of abnormal
blood pressure when the blood pressure of the subject is not so
low.
In the present embodiment, the second reference value determining
means 68 (SB5) determines the second reference value .gamma..sub.2
used by the abnormality judging means 62 (Step SB7) for judging
the abnormality of the blood pressure, such that a smaller second
reference value .gamma..sub.2 corresponds to a greater estimated
blood pressure EBP determined by the estimated blood pressure determined
means 58 (SB3). In the present arrangement, when the blood pressure
of the subject is relatively high, the abnormality of the blood
pressure is detected even when the change value .DELTA.EBP is relative
small. On the other hand, when the blood pressure of the subject
is not so high, the abnormality of the blood pressure is detected
only when the change value .DELTA.EBP is relatively large. Accordingly,
the present arrangement permits the determination of abnormal blood
pressure without delay when the blood pressure has abruptly changed,
and eliminates the determination of abnormal blood pressure when
the blood pressure of the subject is not so high.
Referring next to FIG. 8, there will be described a second embodiment
of the present invention. In this second embodiment, the same reference
numerals as used in the previous first embodiment are used to identify
the corresponding components and the detailed explanation thereof
is dispensed with.
FIG. 8 is a block diagram for explaining essential functions of
an electronic control device 28 of a BP monitor apparatus as the
second embodiment. The BP monitor apparatus of this second embodiment
has the same hardware construction and control circuit as those
of the BP monitor apparatus according to the first embodiment shown
in FIG. 1, except that abnormality judging means 70 in the second
embodiment is different from that in the first embodiment as described
below.
In FIG. 8, the abnormality judging means 70 judges that the blood
pressure of the subject is abnormal when the estimated blood pressure
EBP successively determined by the estimated blood pressure determining
means 58 is smaller than a predetermined lower reference value TH.sub.L
or greater than a predetermined upper reference value TH.sub.H.
Described more specifically, a lower reference value determining
means 72 successively determines a lower reference value TH.sub.L
used by the abnormality judging means 70 for judging abnormality
of the blood pressure of the subject, based on a change value .DELTA.EBP
of the estimated blood pressure, i.e., an absolute value of a change
of the estimated blood pressure EBP, determined by the change (i.e.,
decrease or increase) determining means 60, by utilizing a predetermined
relationship between lower reference value TH.sub.L and change value
.DELTA.EBP, which relationship is predetermined such that a greater
lower reference value TH.sub.L corresponds to a greater change value
.DELTA.EBP. On the other hand, an upper reference value determining
means 74 successively determines an upper reference value TH.sub.H
used by the abnormality judging means 70 for judging abnormality
of the blood pressure of the subject, based on a change value .DELTA.EBP
of the estimated blood pressure, i.e., an absolute value of a change
of the estimated blood pressure EBP, determined by the change determining
means 60, by utilizing a predetermined relationship between upper
reference value TH.sub.H and change value .DELTA.EBP, which relationship
is predetermined such that a smaller upper reference value TH.sub.H
corresponds to a greater change value .DELTA.EBP.
The electronic control device 28 of the BP monitor apparatus in
the second embodiment executes a blood pressure monitor routine
as shown in a flow chart of FIG. 9. In Steps SC1 through Steps SC3,
the same operation as executed in Steps SB1 through SB3 of FIG.
6 is implemented so as to determine an estimated blood pressure
EBP for each pulse and to output the determined estimated blood
pressure EBP to the display device 36. The control flow then goes
to Step SC4 corresponding to the change determining means 60 to
determine a change value .DELTA.EBP in a manner similar to that
in Step SB6 of FIG. 6, namely, a rate of change of the estimated
blood pressure EBP determined in Step SC3 with respect to the estimated
blood pressure EBP obtained in the prior blood pressure measurement
by using the cuff 10.
Step SC 4 is followed by Step SC5 corresponding to the lower reference
value determining means 72 to determine a lower reference value
TH.sub.L based on the change value .DELTA.EBP determined in Step
SC4, by utilizing the predetermined relationship between lower reference
value TH.sub.L and change value .DELTA.EBP, as indicated in the
graph of FIG. 10. The relationship shown in the graph of FIG. 10
is empirically determined such that the lower reference value TH.sub.L
increases in steps with the increase of the change value .DELTA.EBP.
While the lower reference value TH.sub.L changes in four steps in
the present embodiment, the value TH.sub.L may change in a different
number of steps.
Step SC5 is followed by Step SC6 corresponding to the upper reference
value determining means 74 to determine an upper reference value
TH.sub.H based on the change value .DELTA.EBP determined in Step
SC4, by utilizing the predetermined relationship between upper reference
value TH.sub.H and change value .DELTA.EBP, as also indicated in
the graph of FIG. 10. The relationship shown in the graph of FIG.
10 is empirically determined such that the upper reference value
TH.sub.H decreases in steps with the increase of the change value
.DELTA.EBP. The upper reference value TH.sub.H may also change in
a different number of steps.
The control flow then goes to Step SC7 corresponding to the abnormality
judging means 70 to judge whether or not the estimated blood pressure
EBP determined in Step SC3 is smaller than the lower reference value
TH.sub.L or greater than the upper reference value TH.sub.H.
If a negative judgment is made in Step SC7, the control flow goes
to Step SC8 to implement the same operation as in Step SB 8 of FIG.
6, namely, to judge whether or not a predetermined calibration period
has passed. If a negative judgment is made in Step SC8, the control
flow goes back to Step SC1 and the following steps to repeatedly
implement the blood pressure monitor routine. If an affirmative
judgment is made in Step SC8, the control routine (FIG. 5) for determining
the BP-S.sub.F relationship is executed to determine a new BP-S.sub.F
relationship. When an affirmative judgment is made in Step SC7,
the control flow goes to Step SC9 to control the display device
36 to indicate the abnormality of the blood pressure of the subject.
Described in detail, if it is judged in Step SC7 that the estimated
blood pressure EBP is smaller than the lower reference value TH.sub.L,
characters or symbols indicative of the abnormal decrease of the
blood pressure of the subject are indicated on the display device
36. On the other hand, if it is judged in Step SC7 that the estimated
blood pressure EBP is greater than the upper reference value TH.sub.H,
characters or symbols indicative of the abnormal increase of the
blood pressure of the subject are indicated on the display device
36. After Step SC9 is implemented, the BP-S.sub.F relationship determining
routine of FIG. 5 is implemented again for performing a reliable
blood pressure measuring operation using the cuff 10 and for determining
a new BP-S.sub.F relationship (EBP=.alpha..multidot.S.sub.F +.beta.).
In the present embodiment described above, the lower reference
value determining means 72 (SC5) determines the lower reference
value TH.sub.L used in judging abnormal blood pressure by the abnormality
determining means 70 (SC7), based on the change value .DELTA.EBP
successively determined by the change determining means 60 (SC4),
by utilizing the relationship predetermined such that a greater
lower reference value TH.sub.L corresponds to a greater change value
.DELTA.EBP. The abnormality judging means 70 (SC7) judges that the
blood pressure of the subject has abnormally decreased when the
estimated blood pressure EBP successively determined by the estimated
blood pressure determining means 58 (SC3) is smaller than the lower
reference value TH.sub.L determined by the lower reference value
determining means 72 (SC5). According to this arrangement wherein
a greater lower reference value TH.sub.L corresponds to a greater
change value .DELTA.EBP of the estimated blood pressure, the abnormality
judging means judges abnormality of the blood pressure of the subject
without delay when the blood pressure has abruptly decreased. In
addition, since a smaller lower reference value TH.sub.L corresponds
to a smaller change value .DELTA.EBP of the estimated blood pressure,
the present arrangement prevents determination of abnormality of
the blood pressure when the blood pressure of the subject is not
so low and the blood pressure gradually decreases.
In the present embodiment described above, the upper reference
value determining means 74 (SC6) determines the upper reference
value TH.sub.H used in judging abnormal blood pressure by the abnormality
determining means 70 (SC7), based on the change value .DELTA.EBP
successively determined by the change determining means 60 (SC4),
by utilizing the relationship predetermined such that a smaller
upper reference value TH.sub.H corresponds to a greater change value
.DELTA.EBP. The abnormality judging means 70 (SC7) judges that the
blood pressure of the subject has abnormally increased when the
estimated blood pressure EBP successively determined by the estimated
blood pressure determining means 58 (SC3) is greater than the upper
reference value TH.sub.H determined by the upper reference value
determining means 74 (SC6). According to this arrangement wherein
a smaller upper reference value TH.sub.H corresponds to a greater
change value .DELTA.EBP, the abnormality judging means judges abnormality
of the blood pressure of the subject without delay when the blood
pressure has abruptly increased. In addition, since a greater upper
reference value TH.sub.H corresponds to a smaller change value .DELTA.EBP
of the estimated blood pressure, the present arrangement prevents
determination of abnormality of the blood pressure when the blood
pressure of the subject is not so high and the blood pressure gradually
increases.
While the present invention has been described in its presently
preferred embodiments, it is to be understood that the invention
may be otherwise modified.
In the illustrated embodiments, the estimated pressure EBP determined
based on the normalized pulse-wave area S.sub.F is used as the blood
pressure-relating information. Other parameters may be employed
as the blood pressure-relating information such as the normalized
pulse-wave area S.sub.F and a pulse-wave propagation time DT during
which a pulse wave propagates between predetermined two portions
of an artery of a living subject.
If the previously described pulse-wave propagation velocity V.sub.M
or the normalized pulse-wave area S.sub.F which decreases with a
decrease of the blood pressure and which increases with an increase
of the blood pressure is employed as the blood pressure-relating
information, for instance, the first and second reference values
.gamma..sub.1 and .gamma..sub.2 used in determining the abnormal
blood pressure in the first embodiment, and the lower and upper
reference values TH.sub.L and TH.sub.H used in determining the abnormal
blood pressure in the second embodiment are determined as follows:
Namely, in the first embodiment, the first reference value determining
means 66 determines the first reference value .gamma..sub.1 such
that a smaller first reference value .gamma..sub.1 corresponds to
a smaller blood pressure-relating information V.sub.M or S.sub.F,
while the second reference value determining means 68 determines
the second reference value .gamma..sub.2 such that a smaller second
reference value .gamma..sub.2 corresponds to a greater blood pressure-relating
information V.sub.M or S.sub.F. In the second embodiment, the lower
reference determining means 72 determines the lower reference value
TH.sub.L such that a greater lower reference value TH.sub.L corresponds
to a greater change value of the blood pressure-relating information
V.sub.M or S.sub.F, while the upper reference determining means
74 determines the upper reference value TH.sub.H such that a smaller
upper reference value TH.sub.H corresponds to a greater change value
of the blood pressure-relating information V.sub.M or S.sub.F.
On the contrary, if the pulse-wave propagation time DT which increases
with a decrease of the blood pressure and which decreases with an
increase of the blood pressure is employed as the blood pressure-relating
information, for instance, the first and second reference values
.gamma..sub.1 and .gamma..sub.2 used in determining the abnormal
blood pressure in the first embodiment, and the lower and upper
reference values TH.sub.L and TH.sub.H used in determining the abnormal
blood pressure in the second embodiment are determined as follows:
Namely, in the first embodiment, the first reference value determining
means 66 determines the first reference value .gamma..sub.1 such
that a smaller first reference value .gamma..sub.1, corresponds
to a greater blood pressure-relating information DT, while the second
reference value determining means 68 determines the second reference
value .gamma..sub.2 such that a smaller second reference value .gamma..sub.2
corresponds to a smaller blood pressure-relating information DT.
In the second embodiment, the lower reference determining means
72 determines the lower reference value TH.sub.L such that a greater
lower reference value TH.sub.L corresponds to a greater change value
of the blood pressure-relating information DT, while the upper reference
determining means 74 determines the upper reference value TH.sub.H
such that a smaller upper reference value TH.sub.H corresponds to
a greater change value of the blood pressure-relating information
DT.
The BP monitor apparatus in each of the illustrated first and second
embodiments controls the display device 36 to indicate abnormality
of the blood pressure of the subject, and to effect the blood pressure
measurement by the blood pressure measuring means 50 (SA5) when
the abnormality judging means 62 (SB7) or 70 (SC7) judges abnormality
of the blood pressure. However, the BP monitor apparatus may be
modified to effect only one of the indication of abnormality of
the blood pressure on the display device 36 and the blood pressure
measurement by the blood pressure measuring means 50 (SA5).
While both of the first and second reference values .gamma..sub.1
and .gamma..sub.2 are used in judging the abnormality of the blood
pressure by the abnormality judging means 62 (SB7) in the illustrated
first embodiment, only one of the first and second reference values
.gamma..sub.1 and .gamma..sub.2 may be employed.
In the illustrated second embodiment, the abnormal decrease or
abnormal increase of the blood pressure of the subject is judged
by the abnormality judging means 70 (SC7) using the lower and upper
reference values TH.sub.L and TH.sub.H. However, only one of the
lower and upper reference values TH.sub.L and TH.sub.H may be used.
Although the first and second reference values .gamma..sub.1 and
.gamma..sub.2 in the illustrated first embodiment and the lower
and upper reference values TH.sub.L and TH.sub.H in the illustrated
second embodiment are determined for each of the pulses, these values
may be determined for every predetermined number of pulses not less
than two.
It is to be understood that the present invention may be embodied
with other changes, modifications, and improvements that may occur
to those skilled in the art without departing from the scope of
the invention defined in the attached claims. |