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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to 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 application is assigned, previously filed
Japanese patent application No. 62-109594 on May 2, 1987 and Japanese
Utility Model Application No. 62-178067 on Nov. 20, 1987 in each of which
they disclosed a device having a sensor for detecting pulse wave produced
from an artery of a subject, the sensor being movable along a cross line
crossing the artery so as to be positioned in place relative to the
artery, and pressed against a body surface over the artery so as to detect
the pulse wave. Each of the devices also has a pair of air-tight chambers
formed of bellows or rubber bags, on both sides of the pulse wave sensor,
and the pulse wave sensor is moved along the cross line as a result that
pressure level in each of the pair of chambers are varied.
The above-indicated pulse wave detecting devices, however, suffer from a
problem that, even after the pulse wave sensor has been positioned in
place, the sensor may be moved due to changed pressure difference between
the pressure levels of the pair of air-tight chambers resulting from, for
example, failure of electric power applied to the device or leakage of air
from one of the chambers.
The above Japanese patent application No. 62-109594 further teaches that
the pulse wave sensor may be moved by means of a feeding screw rotated by
a drive motor. This arrangement assures that the sensor is retained in
place. However, if the drive motor is located spaced apart from the body
surface of the subject via the pulse wave sensor disposed therebetween, an
overall height of the pulse wave detecting device would be
disadvantageously increased. Japanese patent application No. 62-109594 was
laid-open under Publication No. 63-275320 on Nov. 14. 1988.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a pulse wave
detecting apparatus which is capable of securely retaining the pulse wave
sensor in place and has a comparatively small height.
The above object has been achieved by the present invention, which provides
a pulse wave detecting apparatus comprising, (a) a pulse wave sensor for
detecting pulse wave produced from an arterial vessel of a subject, the
pulse wave sensor being movable along a cross line crossing the arterial
vessel so as to be positioned in place relative to the arterial vessel,
and pressed against a body surface of the subject so as to detect the
pulse wave produced from the arterial vessel; (b) a frame member for being
set on the body surface of the subject; (c) guide means supported by the
frame member, for guiding the pulse wave sensor within a predetermined
length along the cross line; (d) a feeding screw supported by the frame
member such that the feeding screw is rotatable about a longitudinal axis
thereof extending parallel to the cross line, the feeding screw being
threadedly engaged with the pulse wave sensor; (e) a drive motor supported
by the frame member such that the drive motor is disposed adjacent to the
body surface when the frame member is set on the body surface of the
subject; and (f) a transmission device provided between the drive motor
and the feeding screw, for transmitting rotating force of the drive motor
to the feeding screw, so as to move the pulse wave sensor along the cross
line.
In the pulse wave detecting apparatus constructed as described above, the
pulse wave sensor is moved along a cross line crossing an arterial vessel,
while being guided by the guide means supported by the frame member, as a
result that the feeding screw threadedly engaged with the sensor is
rotated by the drive motor via the transmission device. Once the pulse
wave sensor is accurately positioned relative to the arterial vessel, the
sensor is advantageously prevented, due to the thread engagement with the
feeding screw, from being moved in an axial direction of the feeding
screw. Thus, the pulse wave sensor is securely retained in place.
Furthermore, in the present apparatus, the drive motor is supported by the
frame member such that the motor is located adjacent to the body surface
of the subject when the frame member is set on the body surface, and the
power transmission device is provided between the drive motor and the
feeding screw. Thus, the pulse wave sensor, drive motor and transmission
device are supported by the frame member such that all of them are located
along the body surface of the subject when the frame member is set on the
surface. The present apparatus does not suffer from the problem of the
increased height thereof due to the employment of the feeding screw, drive
motor and transmission device.
In a preferred embodiment of the present invention, the apparatus further
comprises detecting means for detecting that the pulse wave sensor has
been moved along the cross line to a middle point of the predetermined
length. In this case, the pulse wave sensor is movable over a sufficient
length in opposite directions from the middle point, and accordingly the
sensor is reliably positioned in place relative to the target arterial
vessel.
In a preferred form of the above embodiment of the invention, the detecting
means comprises a reflection plate mounted on the pulse wave sensor, and a
photocoupler supported by the frame member, for emitting a light beam
toward the reflection plate and detecting the light beam reflected by the
reflection plate, the photocoupler generating electric signal if an
intensity of the received light beam exceeds a reference value, the signal
representing that the pulse wave sensor has been moved to the middle point
of the predetermined length.
In another embodiment of the apparatus of the invention, the pulse wave
sensor comprises a movable member including a threaded portion with which
the feeding screw is threadedly engaged, a diaphragm supported by the
movable member such that the diaphragm defines a fluid-tight space in the
movable member, a presser member supported by the diaphragm such that the
presser member is movable relative to the movable member in a direction
substantially perpendicular to the body surface of the subject as pressure
in the fluid-tight space is varied, and a pressure detector secured to the
presser member, for detecting the pulse wave produced from the arterial
vessel of the subject and generating electric signal representing the
detected pulse wave, the pressure detector being pressed against the body
surface when the presser member is moved toward the body surface.
In a further embodiment of the apparatus of the invention, the guide means
comprises a pair of parallel guide rails supported by the frame member.
In yet another embodiment of the apparatus of the invention, the
transmission device comprises a reduction-gear train consisting of a
plurality of gears.
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 embodiment of the invention, when
considered in conjunction with the accompanying drawings in which:
FIG. 1 is a cross-sectional view of a pulse wave detecting apparatus of the
present invention set on a wrist of a subject;
FIG. 2 is a plan view of the apparatus of FIG. 1, with a part thereof
removed;
FIG. 3 is a cross sectional view taken along line III--III of FIG. 1,
partly showing the apparatus of FIG. 1; and
FIG. 4 is a reduced perspective view of the apparatus of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A pulse wave detecting apparatus embodying the present invention is
illustrated in FIGS. 1-4. In the figures, reference numeral 10 designates
a housing having a single opening which is opposed to a body surface 12 of
a wrist 16 of a subject when the housing 10 is set on the wrist 16. The
housing 10 is detacheably set on the body surface 12 with the help of a
band 14. In the present embodiment, the housing 10 serves as the frame
member.
As clearly shown in the perspective view of FIG. 4, the housing 10 has a
pair of generally crescent-shaped longitudinal side walls 18, 20, and an
outwardly protruded or swollen ceiling 21. The protruded portion extends
longitudinally of the housing 10, and widely occupies a central portion of
the ceiling 21. The housing 10 further has a first and a second plate-like
support portion 22, 24 at longitudinally intermediate locations thereof.
The first and second support portions 22, 24 extend parallel to each
other, and each are connected at opposite ends thereof to the pair of
longitudinal side walls 18, 20. A feeding screw 30 is supported at
opposite ends thereof by the first support portion 22 and a left-hand
sidewall 26 (FIG. 1) opposed to the first support portion 22, such that
the screw 30 is rotatable about a longitudinal axis thereof. The feeding
screw 30 extends longitudinally of the housing 10 at a middle location
between the pair of longitudinal side walls 18, 20 near the ceiling 21.
When the housing 10 is set on the body surface 12, the longitudinal axis
of the feeding screw 30 crosses over a radial artery 28. A pulse wave
sensor 32 is threadedly engaged with the feeding screw 30. In the present
embodiment, the radial artery 28 corresponds to the arterial vessel from
which the present apparatus pulse wave sensor 32 detects pulse wave.
The pulse wave sensor 32 includes a rectangular casing 36, a diaphragm 38
and a presser member 40. The casing 36 has a threaded portion 34
protruding from a central portion of an upper surface thereof (FIG. 1).
The pulse sensor 32 is threadedly engaged with the feeding screw 30 at the
threaded portion 34. The diaphragm 38 is supported by the casing 36 such
that the diaphragm 38 defines an air-tight space 42 in the casing 36. The
presser member 40 is supported by the diaphragm 38 such that the presser
member 40 is movable relative to the casing 36 in a direction
perpendicular to the body surface 12. Thus, the presser member 40 is
advanced out of the casing 36 and retracted into the casing 36. The
air-tight space 42 is supplied with pressurized fluid such as pressurized
air from a fluid supplying device (not shown). Upon expansion of the
diaphragm 38 due to the pressurized fluid supplied to the air-tight space
42, the presser member 40 is moved relative to the casing 36, and pressed
against the body surface 12 with a pressing force corresponding to
pressure level in the space 42. A pressure detector such as a
pressure-sensitive diode (not shown) is secured to a pressing surface 44
of the presser member 40. The pressure detector detects pulse wave, that
is, pressure oscillation transmitted thereto from the radial artery 28 via
the body surface 12, and generates pulse wave signal representing the
detected pulse wave to a control device (not shown).
As clearly shown in FIG. 3, the rectangular casing 36 has a pair of guide
grooves 46, 46 in opposite side walls extending parallel to the axis of
the feeding screw 30. Meanwhile, the longitudinal side walls 18, 20 have
at inner surfaces thereof a pair of guide rails 48, 48 between the first
support portion 22 and the opposed side wall 26. The pulse wave sensor 32
(casing 36) is movable within a predetermined permitted length in a
direction substantially perpendicular to the radial artery 28, such that
the casing 36 is slid or guided on the pair of guide rails 48, 48 with the
guide grooves 46, 46 thereof fitted on the rails 48, 48. In the present
embodiment, the guide rails 48, 48 serve as the guide means for guiding
the pulse wave sensor along the cross line crossing the arterial vessel.
Referring back to FIG. 1, a drive motor 50 is supported by the second
support portion 24 such that the drive motor 50 is located near the body
surface 12 and spaced apart a predetermined distance from the pulse wave
sensor 32 along the body surface 12. A reduction-gear train 54 consisting
of a plurality of gears is provided between the first and second support
portion 22, 24. Specifically, the gear train 54 operatively connects
between an output shaft 52 of the drive motor 50 and a right-hand end of
the feeding screw 30 (FIGS. 1 and 2). Thus, rotating force of the drive
motor 50 is transmitted to the feeding screw 30 via the reduction gear
train 54. In the present embodiment, the reduction gear train 54 serves as
the transmission device.
A first and a second elongate reflection plates 56, 58 are fixed to the
upper surface of the casing 36 (FIG. 1) on both sides of the threaded
portion 34, each in a parallel relationship with the feeding screw 30.
Meanwhile, a first and a second photocouplers 60, 62 are secured to the
inner surface of the ceiling 21 of the housing 10, such that the first and
second photocouplers 60, 62 are aligned with the first and second
reflection plates 56, 58, respectively, as viewed longitudinally of the
housing 10, and located at a longitudinally middle location between the
first support portion 22 and the opposed side wall 26 (or a middle
location of the length of the guide rails 48, 48). In FIG. 2, the second
photocoupler 62 is not illustrated. Each of the photocouplers 60, 62 emit
a light beam toward the upper surface of the pulse wave sensor 32 (casing
36), and detecting the reflected light beam therefrom. If an intensity of
the detected light beam is higher than a reference value, each
photocoupler 60, 62 generates detection signal representing detection of
the intense light beam, to the previously-indicated control device.
The first reflection plate 56 includes a reflection portion 64, and a
non-reflection portion 66 bounded by the reflection portion 64 at a
longitudinally middle position of the plate 56. The second reflection
plate 58 includes a pair of small non-reflection portions 68, 70 at
opposite ends thereof and a large reflection portion 72 between the
non-reflection portions 68, 70. Upon reception of the light beams
reflected by the reflection portions 64, 72 of the first and second
reflection plates 56, 58, the respective first and second photocouplers
60, 62 generate the above-described reflection signal to the control
device. Thanks to the first reflection plate 56 and the first photocoupler
60 it is possible to judge to which side the pulse wave sensor 32 is
currently deviated from a middle point of the predetermined permitted
length within which the sensor 32 is permitted to be moved relative to the
housing 10, because the line separating the reflection and non-reflection
portions 64, 66 from each other corresponds to the middle point of the
permitted length. Meanwhile, it is possible to regulate an amount of
movement of the pulse wave sensor 32 in each of the opposite directions,
by utilizing the first and second reflection plates 56, 58 and the first
and second photocouplers 60, 62.
There will be described the operation of the pulse wave detecting apparatus
constructed as described above, for detecting the pulse wave produced from
the radial artery 28.
Upon application of electric power to the control device (not shown) to
which the housing 10 is connected via electric wiring or the like, the
pulse wave sensor 32 is accurately positioned at the middle point of the
above-described predetermined permitted length. If the first photocoupler
60 generates detection signal to the control device in the case where the
reflection portion 64 of the first reflection plate 56 is located on a
thumb side of the body surface 12 (or wrist 16) and accordingly the
non-reflection portion 66 of the same 56 is located on a little-finger
side, it is judged that the pulse wave sensor 32 is deviated to the thumb
side. Consequently, the sensor 32 is moved to the little-finger side as a
result that the feeding screw 30 is rotated by the drive motor 50
activated. If the first photocoupler 60 ceases generating detection
signal, the drive motor 50 is stopped and the sensor 32 is positioned at
the target middle point of the permitted length and retained thereat. In
the present embodiment, the first reflection plate 56 and the first
photocoupler 60 serve as the detecting means for detecting that the pulse
wave sensor has been moved to the middle point of the permitted length.
With the pulse wave sensor 32 retained at the middle point of the permitted
length, the housing 10 is set on the body surface 12 such that the presser
member 40 is positioned generally above the radial artery 28. Upon
operation of an activation switch provided on the control device, the
air-tight space 42 is supplied with pressurized air from the supplying
device and the pressure detector secured to the pressing surface 44 of the
presser member 40 is pressed against the body surface 12. The pressure
level in the air-tight space 42 is controlled so that the amplitude of
pulse wave signal supplied from the pressure detector is increased to a
maximum. The pulse wave sensor 32 is moved, as needed, by the feeding
screw 30, so as to be accurately positioned relative to the radial artery
28, namely, right above the artery 28. It is recommended that it be judged
whether or not the pulse wave sensor 32 is retained in place right above
the radial artery 28 at regular intervals of time or each time a
predetermined number of pulses of the pulse wave have been detected, and
that, if the judgement is negative, the sensor 32 is automatically
re-positioned right above the artery 28 as described above. Even in the
case where the pulse wave sensor 32 (housing 10) is moved relative to the
radial artery 28 during the detection of the pulse wave due to, for
example, physical motion of the subject, the present apparatus is capable
of accurately detecting pulse wave.
As is apparent from the foregoing description, in the present pulse wave
detecting apparatus, the pulse wave sensor 32 is threadedly engaged with
the feeding screw 30 through the threaded portion 34 thereof, and the
feeding screw 30 is rotated by the drive motor 50 via the reduction-gear
train 54. Once the pulse wave sensor 32 is positioned at the middle point
of the predetermined permitted length, or once the sensor 32 is positioned
right above the radial artery 28, the sensor 32 is advantageously
prevented, due to the thread engagement with the feeding screw 30 from
being moved along the axis of the feeding screw 30. Thus, the pulse wave
sensor 32 is securely retained relative to the radial artery 28. Also, the
pulse wave sensor 32 positioned at the middle point of the predetermined
permitted length is prevented from being moved therefrom, for example when
the housing 10 is set on the wrist 16.
Furthermore, in the present apparatus, the drive motor 50 is accommodated
in the housing 10 such that the motor 50 is spaced apart a predetermined
distance from the pulse wave sensor 32 along the body surface 12, and the
reduction gear train 54 is provided between one end of the feeding screw
30 and the drive motor 50. Thus, the pulse wave sensor 32, drive motor 50
and reduction-gear train 54 are located adjacent to the body surface 12
when the housing 10 is set on the wrist 16. Consequently, the employment
of the drive motor 50, feeding screw 30 and reduction-gear train 54, does
not lead to increasing the dimension of height of the overall apparatus
(overall housing 10).
Moreover, in the present apparatus, thanks to the first photocoupler 60 and
the first reflection plate 56, the pulse wave sensor 32 is accurately
positioned at the middle point of the predetermined permitted length
within which the sensor 32 is permitted to be moved. Thus, the sensor 32
is movable over a sufficient length in each of the opposite directions,
namely, to both the thumb and little-finger sides of the wrist 16. This
arrangement contributes to reliably positioning the sensor 32 relative to
the radial artery 28.
While in the illustrated embodiment an axis of the output shaft 52 of the
drive motor 50 extends parallel to the axis of the feeding screw 30, it is
possible to dispose the drive motor such that the axis of the output shaft
of the drive motor is angled with respect to the axis of the feeding screw
30, so that the drive motor is positioned more suitably along a curvature
of the body surface 12 when the apparatus (housing 10) is set on the wrist
16. In this case, the plurality of gears of the reduction-gear train 54,
which transmits the rotating force of the drive motor to the feeding screw
30, may be replaced with a transmission device of a type including a
flexible joint. Alternatively, the drive motor may be disposed such that
the axis of the output shaft of the drive motor is normal to the axis of
the feeding screw 30, and that the rotating force of the drive motor is
transmitted to the feeding screw 30 via a transmission device of a type
including a worm and a pinion.
While in the illustrated embodiment the pair of guide rails 48, 48 serving
as the guide means are supported by the longitudinal side walls 18, 20 of
the housing 10 and the pair of guide grooves 46, 46 in which the guide
rails 48, 48 are slidably fitted are formed in the corresponding side
walls of the casing 36 of the pulse wave sensor 32, it is possible to form
a pair of guide grooves serving as the guide means, in the side walls 18,
20 of the housing 10, and provide a pair of guide rails on the
corresponding sides walls of the casing 36 of the sensor 32.
Alternatively, it is possible to use, as the guide means, the side walls
18, 20 of the housing 10, without providing the walls 18, 20 with any
exclusive elements such as guide rails or guide grooves. In this case, the
sensor 32 is slid directly on the side walls 18, 20.
Although in the illustrated embodiment the housing serving as the frame
member has the single opening, it is possible to employ as the frame
member a housing having one or more through-holes formed therethrough.
It is to be understood that the illustrated apparatus provides various
advantages even in the case where none of the photocouplers 60, 62 or the
reflection plates 56, 58 are employed.
While the illustrated apparatus is adapted to detect pulse wave produced
from a radial artery, it is possible to apply the principle of the present
invention to an apparatus adapted to detect pulse wave produced from other
arteries such as a dorsal pedal artery.
While the present invention has been described in its presently preferred
embodiment with detailed particularities, it is to be understood that the
invention may be embodied with various changes, improvements and
modifications that may occur to those skilled in the art without departing
from the spirit and scope of the invention defined in the appended claims.
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