 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to improvements in an apparatus for detecting
pulse wave produced from an arterial vessel of a living body.
2. Related Art Statement
The Assignee to which the present U.S. patent application is assigned,
previously filed Japanese Utility Model Application No. 62-93846 on June
18, 1987 in which they disclose a pulse wave detecting apparatus having
(a) a pulse wave sensor which is pressed against a body surface over an
arterial vessel so as to detect pulse wave produced from the artery, and
(b) pressing means for pressing the pulse wave sensor against the body
surface with an optimum pressing force, the optimum pressing force being
determined based on pulse wave signal produced by the pulse wave sensor
while the pressing force of the pressing means is varied, so that the
magnitude of the pulse wave signal is optimized.
The above pulse wave detecting apparatus operates normally so that the
pressing force of the pressing means is optimized, on the condition that
the pulse wave sensor has already been placed on the body surface of a
subject. However, if the pressing means is activated to press the pulse
wave sensor though the sensor has not been contacted with the body
surface, the pressing means is operated until pulse wave signal is
produced from the sensor. In such case, the pulse wave sensor is displaced
an excessively large operation amount or stroke by the pressing means.
This tends to cause a mechanical breakdown or failure in the apparatus.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a pulse wave
detecting apparatus characterized by having means for detecting whether or
not the housing thereof accommodating the pulse wave sensor thereof and
supporting the pressing means thereof, has been placed on a body surface
of a subject.
The above object has been achieved by the present invention, which provides
a pulse wave detecting apparatus having (a) a housing which is placed on a
body surface of a subject such that the housing is aligned with an artery
of the subject via the body surface, (b) a pulse wave sensor accommodated
in the housing, the pulse wave sensor being pressed against the body
surface for detecting pulse wave produced from the artery, and (c)
pressing means supported by the housing, the pressing means pressing the
pulse wave sensor against the body surface with an optimum pressing force,
the optimum pressing force being determined based on pulse wave signal
produced by the pulse wave sensor while the pressing force of the pressing
means is varied, the apparatus comprising (d) detecting means for
detecting whether or not the housing has been placed on the body surface
of the sujbect.
In the pulse wave detecting apparatus constructed as described above, the
detecting means detects whether or not the pulse wave sensor and pressing
means have been held in place the body surface of the subject.
Accordingly, the pressing means is protected from erroneously being
operated though the sensor and pressing means have not been contacted with
the body surface, for example when an ON/OFF switch is erroneously turned
on to activate the pressing means. Therefore, the present pulse wave
detecting apparatus is free from the problem that the pressing means is
operated by an excessively large operation amount, or the mechanical
breakdown resulting from that problem.
In a preferred embodiment of the pulse wave detecting apparatus of the
present invention, the detecting means comprises a displaceable member
slidably held by the housing such that a portion of the displaceable
member normally protrudes from a surface of the housing which surface
contacts the body surface when the housing is placed on the body surface,
and a detector switch for detecting displacement of the displaceable
member, the detector switch generating a placement signal representing
that the housing is placed on the body surface, when detecting the
displacement of the displaceable member.
In another embodiment of the apparatus of the invention, the detecting
means comprises a light emitter supported by the housing for emitting
light beam toward the body surface of the subject, and a light detector
supported by the housing for detecting the light beam reflected by the
body surface, the light detector generating a placement signal
representing that the housing is placed on the body surface, when
detecting the light beam reflected by the body surface. In this
embodiment, it is preferred that the detecting means further comprise a
first optical fiber for transmitting the light beam from the light emitter
toward the body surface, and a second optical fiber for transmitting the
light beam reflected by the body surface to the light detector.
In yet another embodiment of the apparatus of the invention, the detecting
means comprises a pair of electrodes held in a surface of the housing
which surface contacts the body surface when the housing is placed on the
body surface, and an impedance detector for detecting an impedance between
the pair of electrodes, the impedance detector generating, based on the
detected impedance, a placement signal representing that the housing is
placed on the body surface.
According to a preferred feature of the present invention, the pulse wave
detecting apparatus further comprises inhibiting means for inhibiting the
pressing means from pressing the pulse wave sensor, while the placement
signal is not generated by the detecting means.
According to another feature of the present invention, the pulse wave
detecting apparatus further comprises permitting means for permitting the
pulse wave sensor to be subjected to zero adjustment, while the placement
signal is not generated by the detecting means. In this case, the zero
adjustment of the pulse wave sensor is performed only on the condition
that the sensor and pressing means are not placed on the body surface of
the subject. Thus, the zero adjustment of the pulse wave sensor is free
from influence from the subject. This assures accurate zero adjustment of
the pulse wave sensor.
According to yet another feature of the present invention, the pulse wave
detecting apparatus further comprises permitting means for permitting
generation of an aberrant signal representing that the pulse wave signal
from the pulse wave sensor is aberrant, while the placement signal is
generated by the detecting means. When the magnitude of the pulse wave
signal has fallen below a predetermined value, for example, an aberrant
signal is generated for example to activate an alarm device so as to
inform the medical staff of the aberration of the subject. In this
apparatus, however, no aberrant signal is generated while the housing
(pulse wave sensor and pressing means) is not placed on the body surface,
namely, so long as the housing is located apart from the subject.
Therefore, the apparatus is free from a problem that alarming sound is
erroneously produced as a result of confusion between the aberrant signal
representing the aberrant pulse wave and slight oscillation (pressure
variation) detected by the pulse wave sensor spaced apart from the subject
.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and optional objects, features and advantages of the present
invention will be better understood by reading the following detailed
description of the presently preferred embodiments of the invention, when
considered in conjunction with the accompanying drawings, in which:
FIG. 1 is an illustrative view showing a general construction of a pulse
wave detecting apparatus of the present invention;
FIG. 2 is an enlarged cross-sectional view of a switch device of the
apparatus of FIG. 1;
FIG. 3 is a flow chart showing the operation of the apparatus of FIG. 1;
FIGS. 4 and 5 are flow charts partially showing the operation of other
embodiments of the pulse wave detecting apparatus of the invention; and
FIGS. 6 through 8 are enlarged cross-sectional views of modified switch
devices employed in the pulse wave detecting apparatus of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, there is shown a pulse wave detecting apparatus
embodying the present invention. In the figure, reference numeral 10
designates a body surface of a subject, for example, the surface of an
upper arm. An arterial vessel 12 extends along the body surface 10. Right
above the artery 12 a pulse wave detecting probe 16 is fixed with a band
14 fastened around the upper arm.
The pulse wave detecting probe 16 includes a rectangular box-like housing
18, a pulse wave sensor 20 accommodated in the housing 18, a generally
annular rubber diaphragm 22 and a switch device 24. The housing 18 is open
at a bottom end thereof as viewed in FIG. 1 and is formed of comparatively
rigid material. The pulse wave sensor 20 consists of a pressure-sensitive
semiconductor element, for example. The diaphragm 22 is disposed between
the housing 18 and the pulse wave sensor 20 such that the diaphragm 22
secures the sensor 20 to the housing 18, and such that the diaphram 22
cooperates with the housing 18 and sensor 20 to define a fluid-tight space
19 in the housing 18. The fluid-tight space 19 communicates with an
electrically operated pump 28 via a pipe 26 and a pressure-regulating
valve 30 which is operated under control of a microcomputer 42 (described
below in detail). The space 19 is supplied with a pressurized fluid from
the pump 28 whose pressure is regulated by the valve 30. More specifically
described, as the pressurized fluid is supplied from the pump 28 to the
fluid-tight space 19, pressure level in the space 19 is progressively
increased and the diaphragm 22 is inflated or swollen toward the body
surface 10. Consequently, the pulse wave sensor 20 is pressed against the
body surface 10. The sensor 20 detects pulse wave of the artery 12,
namely, oscillatory pressure wave of the artery 12 which is produced by
expansion and contraction of the artery 12 synchronized with heart beat of
the subject, and generates pulse wave signal SM representing the detected
pulse wave, to the microcomputer 42. In the present embodiment, the
diaphragm 22 serves as the pressing means of the pulse wave detecting
apparatus.
Referring next to FIG. 2, there is illustrated the switch device 24. The
switch device 24 includes a casing 32, a displaceable member 34, an
actuator 36 and an ON/OFF switch 38. The casing 32 is fixed to an upper
surface of the housing 18. The displaceable member 34 extends through a
side wall of the housing 18 such that the displaceable member 34 is
slidable vertically as viewed in FIG. 1. The displaceable member 34 has a
flanged head 34a. The actuator 36 is fixed to an upper surface of the
flanged head 34a of the displaceable member 34. The ON/OFF switch 43 is
secured immovable to an inner wall surface of the casing 32 by fastening
members (not shown), and has a pair of terminals 38a, 38b one of which 38a
is in contact with the actuator 36. As shown in FIG. 2, while the pulse
wave detecting probe 16 (housing 18) is not placed on the body surface 10,
namely, is spaced apart from the subject, the displaceable member 34 is
placed at a non-displacement position thereof in which the flanged head
34a thereof is in contact with the upper surface of the housing 18 and is
fitted in an opening 40 formed through a bottom wall of the casing 32 and
a free end 34b of a leg portion of the displaceable member 34 protrudes
from a bottom surface 18a of the housing 18 which surface contacts the
body surface 10 when the probe 14 is placed on the body surface 10. The
actuator 36 includes a box-like member 41 which is fixed to the upper
surface of the displaceable member 34 (flanged head 34a) and is open at an
bottom end thereof, a contact member 43 which is accommodated in the
box-like member 41 and partially protrudes outward through an upper wall
of the box-like member 41, and a spring 45 disposed between the contact
member 43 and the head 43a of the displaceable member 43.
If the pulse wave detecting probe 16 is fastened around the upper arm of
the subject and the housing 18 is held in place on the body surface 10,
the free end 34b of the leg portion of the displaceable member 34
protruding from the bottom surface of the housing 18, is pressed and
displaced inward as a result of contact with the body surface 10, and the
above-indicated one terminal 38a contacting the actuator 36 is closed by
the displacement of the displacement member 34. Thus, the switch 38
generates from the other terminal 38b a displacement signal SA
representing that the probe 16 is placed on the body surface 10, to the
microcomupter 42. In the present invention, the switch device 24 serves as
the placement-condition detecting means for detecting whether or not the
probe 16 (housing 18) has been placed on the body surface 10 of the
subject. The spring 45 serves to accommodate an excessive displacement or
stroke of the displaceable member 34, thereby contributing to protect the
switch 38 from mechanical damage.
The microcomputer 42 includes a CPU (central processing unit), a RAM
(random access memory), a ROM (read only memory) and an I/O interface (all
not shown), and the CPU processes the input signals according to programs
stored in the ROM by utilizing the temporary-storage function of the RAM,
and controls the pressure-regulating valve 30 to regulate the pressure
level of the pressurized fluid in the fluid-tight space 19 in the housing
18. More specifically described, upon operation of a START button (not
shown), the microcomputer 42 activates the valve 30 to allow the
pressurized fluid to be supplied from the electric pump 28 to the
fluid-tight space 19. Subsequently the microcomputer 42 calculates the
magnitude of the pulse wave signal SM, for example the amplitude or
electric power of the signal SM, and thereby determines whether or not the
magnitude of the signal SM has been saturated. If the signal SM has been
saturated, the microcomputer 42 commands the pressure-regulating valve 30
to maintain the current pressure level in the space 19. This process is
performed by feed back control.
The CPU of the microcomputer 42 determines blood pressure of the subject
based on the pulse wave signal SM, and commands a blood pressure display
44 to indicate the thus-determined blood pressure and concurrently
commands a waveform display 36 to indicate the waveform of the pulse wave
represented by the signal SM. Since an upper peak value of the pulse wave
corresponds to a maximum blood pressure and a lower peak value of the
pulse wave corresponds to a minimum blood pressure, actual blood pressure
indicated by the blood pressure display 44 is determined according to a
pre-determined relationship between the pulse wave and the blood pressure
and based on the actual upper and lower peak values of the pulse wave
represented by the signal SM. Further, the waveform of the pulse wave
indicated by the waveform display 36 represents variation in arterial
pulse pressure, which provides clinically or medically important
information. One of the blood pressure display 44 and the waveform display
46 may be omitted.
The CPU of the microcomputer 42 continues to measure the blood pressure by
utilizing the pulse wave signal SM, while the microcomputer 42 receives
the placement signal SA from the switch device 24. However, while the
microcomputer 42 does not receive the signal SA, namely, while the pulse
wave detecting probe 16 is not placed on the body surface 10, the
microcomputer 42 inhibits the pressure-regulating valve 30 from supplying
the fluid-tight space 19 in the housing 18 with the pressurized fluid from
the electric pump 28.
There will be described the operation of the pulse wave detecting apparatus
constructed as illustrated above, in conjuction with the flow chart of
FIG. 3.
Upon operation of the START button (not shown), initially the CPU of the
microcomputer 42 executes step S1 at which it is judged whether or not the
placement signal SA is generated by the switch device 24, namely, whether
or not the pulse wave detecting probe 16 has been placed on the body
surface 10. If the judgement at step S1 is negative, namely, if it is
judged that the probe 16 has not been placed on the body surface 10, the
CPU control again executes step S1. On the other hand, if the judgement at
step S1 is affirmative, namely, if it is judged that the probe 16 has been
placed on the body surface 10, step S1 is followed by step S2 at which the
CPU reads in the pulse wave signal SM supplied from the pulse wave sensor
20. At the following step S3, it is judged whether or not the difference
between the amplitude of the currently read-in pulse wave signal SM and
that of the preceding pulse wave signal SM.sup.-1, namely (SM-SM.sup.-1),
is smaller than a predetermined very small value .alpha.. Step S3 is
provided for determining whether or not the magnitude of the pulse wave
signal has been saturated, based on the fact that, once the pulse wave
signal is saturated, the difference between the amplitudes of the
successive two signals SM.sup.-1 and SM does not exceed the very small
value .alpha.. At the beginning of the operation the magnitude of the
pulse wave signal has not been saturated yet. Accordingly, the judgement
at step S3 is found to be negative. Thus, step S3 is followed by steps S4
through S6. At step S4 the CPU adds a comparatively small value .DELTA.P
to a fluid pressure P.sup.-1 in the fluid-tight space 19 which has been
stored in the RAM of the microcomputer 42 for the current pulse wave
detecting cycle, so as to determine a target fluid pressure P to be used
for detecting the following pulse wave signal. At the following step S5
the CPU controls the pressure-regulating valve 30 to increase the fluid
pressure in the fluid-tight space 19 from the stored value P.sup.-1 to the
target value P, and at step S6 the CPU stores the new value P in the RAM
in place of the previous value P.sup.-1 for the following pulse wave
detecting cycle. As shown in the flow chart of FIG. 3, the new value P is
stored as P.sup.-1 in the RAM. As steps S1 through S6 are repeated, the
fluid pressure P in the space 19 is increased little by little, namely, by
.DELTA.P for each cycle. In this process, if the judgement at step S3 is
turned to be affirmative, namely, if the magnitude of the pulse wave
signal SM is saturated, step S3 is followed by steps S7 and S8. At step S7
the CPU determines the pressure P.sup.-1 used in the current cycle, as a
target pressure P to be used for the following pulse wave detecting cycle,
without adding the small value .alpha. to the pressure P.sup.-1. Step S7
is followed by step S8 at which the waveform of the pusle wave represented
by the signal SM read in at step S2, is displayed on the waveform display
46 and concurrently the maximum and minimum blood pressure is determined
based on the pulse wave signal SM and displayed on the blood pressure
display 44. At the following step S5 the CPU controls the
pressure-regulating valve 30 to maintain the fluid pressure P in the
fluid-tight space 19 in the housing 18 and at step S6 the CPU stores the
value P as P.sup.-1 in the RAM.
As is apparent from the foregoing, in the present embodiment, at step S1 it
is judged whether or not the pulse wave detecting probe 16 has been placed
on the body surface 10, and if the judgement at step S1 is negative, the
pulse wave sensor 20 is by no means pressed against the body surface 10 by
the diaphragm 22, namely, the diaphragm 22 is not inflated by the
pressurized fluid from the electric pump 28. Accordingly, even if the
START button is erroneously operated though the probe 16 (sensor 20) has
not been held in place on the body surface 10, the pressurized fluid is
not supplied to the fluid-tight space 19 in the housing 18. Thus, the
instant apparatus has overcome the problem that the pulse wave sensor 20
is displaced beyond its permissible operation amount or stroke though the
sensor 20 has not been placed on the body surface 10, and the problem of
the mechanical breakdown or failure of the apparatus due to the excessive
displacement of the sensor 20.
There will be described below other embodiments of the pulse wave detecting
apparatus of the present invention.
In one embodiment, the pulse wave detecting apparatus is operated according
to the flow chart of FIG. 4 which includes the same steps as those of the
flow chart of FIG. 3 except for step S1, and a sub-routine consisting of
steps SS1 and SS2 in place of step S1 of FIG. 3. The sub-routine is
executed in an initialization process of the apparatus. More specifically
described, at step SS1 it is judged whether or not a placement signal SA
is present, namely, whether or not the probe 16 has been placed on the
body surface 10, similar to step S1 of the embodiment of FIG. 3. If the
judgement at step SS1 is affirmative, the same operations as indicated at
steps S2 and the following of FIG. 3 are executed. On the other hand, if
the judgement at step SS1 is negative, step SS1 is followed by step SS2 at
which a zero-adjustment routine is performed. The zero-adjustment routine
is provided for adjusting a zero point of the pulse wave sensor 20 (for
example, pressure-sensitive semiconductor element). The zero adjustment is
conducted by eliminating any drift of the zero point of the sensor 20. In
other words, the sensor 20 is re-calibrated. Thus, the detection accuracy
of the sensor 20 is maintained high. The zero adjustment of the sensor 20
is required to be performed while the sensor 20 is not pressed against the
body surface 10, namely, while the sensor 20 is detecting atmospheric
pressure. Step SS2 is followed by the same steps as steps S2-S8 of the
embodiment of FIG. 3. The zero-adjustment routine of step SS2 is performed
only in the case where the judgement at step SS1 is negative, namely,
while the pulse wave detecting probe 16 is not placed on the body surface
10. Thus, the zero adjustment (re-calibration) of the pulse wave sensor 20
is performed in a reliable manner.
In another embodiment of FIG. 5, the pulse wave detecting apparatus has a
construction similar to that of the embodiment of FIG. 1, but is different
therefrom in that an alarm device (not shown) is coupled to a CPU of a
microcomputer 42 of the instant apparatus. When the CPU detects that the
pulse wave signal SM is aberrant, and generates an aberrant signal, the
alarm device is activated to produce alarming sound so as to inform the
medical staff of the aberration of the subject. The instant apparatus is
operated according to a flow chart consisting of a main routine which
includes the same steps as those of the flow chart of FIG. 3 except for
step S1, and a sub-routine which is inserted between appropriate
successive steps and includes steps ST1, ST2 and ST3. At step ST1 it is
judged whether or not a placement signal SA is present, namely, whether or
not a pulse wave detecting probe 16 is placed on a body surface of a
subject. If the judgement at step ST1 is negative, the control of the CPU
returns to the main routine. On the other hand, if the judgement at step
ST1 is affirmative, step ST1 is followed by step ST2 at which it is judged
whether or not the amplitude of the pulse wave signal SM is smaller than a
pre-determined value .beta.. The value .beta. is pre-determined to be
considerably small as compared with a normal amplitude of the pulse wave
signal SM. Accordingly, if the amplitude of the pulse wave signal SM
supplied from the sensor 20 is smaller than the value .beta., it is judged
that the signal SM is aberrant (or abnormal), namely, that the pulse wave
of the subject is aberrant. If the judgement at step ST2 is thus found to
be affirmative, the CPU generates an aberrant signal to the alarm device
(not shown). At the following step ST3, the alarm device responds to the
aberrant signal to produce alarming sound.
In the embodiment of FIG. 5, the CPU permits generation of the aberrant
signal representing that the pulse wave signal SM is aberrant, only while
the pulse wave detecting probe 16 is placed on the body surface 10 of the
subject. Thus, the instant pulse wave detecting apparatus is free from the
problem that alarming sound is erroneously produced though the probe 16 is
not held in place on the body suface 10 as a result of confusion between
aberrant pulse wave and slight oscillation (pressure variation) detected
by the sensor 20 spaced apart from the body surface 10.
While the present invention has been described with detailed
particularities of the presently preferred embodiments, it is to be
understood that the invention may be embodied with various modifications.
While in the illustrated embodiment of FIG. 1 the switch device 24 is
constructed to utilize mechanical displacement of the displacement member
34 for detecting that the pulse wave detecting probe 16 is placed on the
body surface 10, it is possible to employ a switch device 48 of an optical
type as shown in FIG. 6, in place of the mechanical switch device 24. The
optical switch device 48 includes a light emitter 50 and a light detector
52 both of which are secured to the upper surface of the housing 18, and a
pair of first and second optical fibers 54, 56 which are connected to the
light emitter 50 and the light detector 52, respectively, and extend
through a side wall of the housing 18. A recess 58 having a V-shaped
profile in cross section is formed in a bottom surface 18a of the side
wall of the housing 18 which surface contacts the body surface 10 when the
probe 16 is placed on the body surface 10. The first optical fiber 54
connected at one end thereof to the light emitter 50, is exposed at the
other end thereof in a tapered surface of the recess 58. Similarly, the
second optical fiber 56 connected at one end thereof to the light detector
52, is exposed at the other end thereof in the tapered surface of the
recess 58. When the probe 16 is placed on the body surface 10 and the
light emitter 50 is activated to emit light beam, the first optical fiber
54 transmits the light beam from the light emitter 50, and emits the light
beam at the recess 58 toward the body surface 10. The second optical fiber
56 transmits the light beam reflected by the body surface 10, to the light
detector 52. Upon detection of the light beam, the light detector 52
generates a placement signal SA representing that the probe 16 is placed
on the body surface 10, to the microcomputer 42 (CPU). Thus, the CPU of
the microcomputer 42 detects that the probe 16 is placed on the body
surface 10.
Furthermore, it is possible to use a switch device 60 as shown in FIG. 7 in
place of the switch device 24 of FIG. 2 or the switch device 48 of FIG. 6.
The switch device 60 includes a light emitter 64 and a light detector 66
both of which are embedded in a side wall of the housing 18 and exposed in
a recess 62 formed in a bottom surface 18a of the side wall of the housing
18 which surface contacts the body surface 10 when the probe 16 is placed
on the body surface 10. The recess 62 has a tapered surface, and a
V-shaped profile in cross section, like the recess 58 of FIG. 6. The light
emitter 64 is coupled to a light source (not shown), and emits light beam
from the tapered surface of the recess 62 toward the body surface 10. The
light detector 64 detects the light beam reflected by the body surface 10.
When the pulse wave detecting probe 16 is placed on the body surface 10,
the light beam emitted from the light emitter 64 is reflected by the body
surface 10 and detected by the light detector 66. Upon detection of the
light beam reflected by the body surface 10, the light detector 66
generates a placement signal SA to the microcomputer 42, similar to the
light detector 52 of the switch device 48 of FIG. 6.
Referring to FIG. 8, there is shown another switch device 68 which is used
in place of the switch devices 24, 48, 60 of FIGS. 2, 6, 7. The switch
device 68 is adapted to detect that the pulse wave detecting probe 16 is
placed on the body surface 10, by utilizing impedance of the body surface
or skin 10. The switch device 68 includes a pair of electrodes 70, 70
embedded in a pair of cavities 69, 69 formed in a pair of opposed side
walls of the housing 18. More specifically described, the pair of cavities
69, 69 are formed in a bottom surface 18a of the housing 18 which surface
contacts the body surface 10 when the probe 16 is placed on the body
surface 10. A small current is applied between the pair of electrodes 70,
70. With the probe 16 placed on the body surface 10, the pair of
electrodes 70, 70 contact the body surface 10. When the pair of electrodes
70, 70 contact the body surface 10, an impedance of the body surface 10
between the electrodes 70, 70 is detected by an impedance detector 76
through a pair of wirings 72 and an amplifier 74. Upon detection of the
impedance of the body surface 10, the impedance detector 76 of the switch
device 68 generates a placement signal SA to the microcomputer 42.
It is to be understood that the present invention may be embodied with
other changes, improvements and modifications which may occur to those
skilled in the art without departing from the scope and spirit of the
invention defined in the appended claims.
* * * * *
|
|
 |
|
 |
Description |
|
