Pressure-pulse-wave detecting apparatus

Abstract: An apparatus for detecting pressure pulse wave, including a main body (18) having a surface (32) which is pressed against the body surface of a subject, and a plurality of through holes (34) formed therethrough and opening in the surface (32); a plate (36) secured to the surface (32) of the main body such that the plate covers the openings of the through holes, the plate (36) having flexibility and including a plurality of displaceable portions (37) each of which is aligned with the opening of a corresponding through hole (34); a plurality of optical fibers (40), one (39a) of opposite ends of each optical fiber being fitted in a corresponding through hole (34), such that an end face (41a) of the one end is opposed to a corresponding displaceable portion (37) at a predetermined distance therefrom; and a plurality of signal generating devices (42) each of which is connected to the other (39b) of the opposite ends of a corresponding optical fiber (40), each device (42) detecting the pressure pulse wave transmitted to a corresponding displaceable portion (37), based on minute displacement of the corresponding displaceable portion which is optically detected through the corresponding optical fiber, and generating an electric signal representing the detected pressure pulse wave.

Description: The present invention relates to an apparatus for detecting pressure pulse waves produced from an arterial vessel of a living body, at a plurality of positions on a body surface above the arterial vessel. Pressure pulse waves produced from an artery of a living body in synchronization with pulsation of the heart, provide information on the cardiovascular system of the subject such as the active condition of the heart, blood pressure and degree of arterial sclerosis. There is known a device which detects the pressure pulse wave produced from an artery of a subject, by using a pressure sensor which is pressed against the artery via the body surface right thereabove. However, the pressure sensor is adapted to contact at a pressing surface thereof the body surface over a whole width (or diameter) of the artery. In other words, the pressing surface of the pressure sensor is wider than the width of the artery. For this reason the detection of the pressure pulse wave may be adversely influenced by the wall of the artery, and the detected pressure pulse wave may not provide accurate information. To overcome the above-indicated problem it has been proposed to detect pressure pulse waves at a plurality of positions which are spaced apart from each other on the body surface in a direction crossing the artery, by a length smaller than the width of the artery. An example of the pressure-pulse-wave detecting device of this type is disclosed by US-A-4,423,738 and US-A-4 269 193. The device disclosed therein is capable of selecting the single one of the plurality of positions which is substantially free from the problem of the wall of the artery and at which a blood pressure approximate to an intra-arterial blood pressure is measured. In the above-indicated devices in which pressure pulse wave is detected at a plurality of positions on the body surface right above an artery, however, the number of the detecting positions was insufficiently low, in particular in the case of an artery of a comparatively small width. More specifically described, the pressure sensor employed in those devices consists of a semiconductor plate of a comparatively large thickness and a comparatively high rigidity. The semiconductor plate includes a plurality of pressure-receiving portions (i.e., pressure-detecting elements) of a comparatively small thickness which are provided by forming a plurality of recesses in one of opposite surfaces of the plate in a direction of thickness thereof by photoetching technique. Upon application of a pressure to the semiconductor plate, a strain is produced in the pressure-receiving portions. However, if each pair of adjacent recesses are formed excessively near to each other, it is not permitted to form an electrically conductive wiring pattern in an area between each pair of recesses. Further, in such a case the rigidity of the semiconductor plate as a whole is disadvantageously lowered, and the accuracy of pressure measurement is sacrificed. Thus, the pressure-receiving portions of the semiconductor plate must be spaced apart from each other by a distance greater than a required minimum length. It is therefore an object of the present invention to provide a pressure-pulse-wave detecting apparatus wherein pressure pulse wave is detected at an increased number of positions per unit distance on the body surface right above an artery. The present invention, provides a pressure-pulse-wave detecting apparatus for detecting pressure pulse waves produced from an arterial vessel of a subject, at a plurality of positions on a body surface directly above the arterial vessel, the apparatus comprising: (a) a main body having a pressing surface and which is to be pressed towards the body surface, and a plurality of through holes formed therethrough and opening in the pressing surface; (b) a plate member secured at the pressing surface of the main body such that the plate member covers the openings of the plurality of through holes, the plate being flexible so that a plurality of displaceable portions of the plate are aligned with the openings of corresponding through holes; (c) a plurality of optical fibers, one end of each fiber being fitted in a corresponding one of the plurality of through holes of the main body, such that its end face is opposed to a corresponding one of the plurality of displaceable portions of the plate member and is spaced at a predetermined distance therefrom; and (d) a plurality of signal generating devices each of which is connected to the other end of a corresponding optical fiber, each signal generating device detecting the pressure pulse wave transmitted to a corresponding one of the plurality of displaceable portions of the plate member, by means of displacement of the corresponding displaceable portion being optically detected through the corresponding optical fiber, and generating an electric signal representing the detected pressure pulse wave. In the pressure-pulse-wave detecting apparatus of the invention constructed as described above, the plate member with flexibility is secured to the pressing surface of the main body at which open the plurality of through holes. The plurality of optical fibers are connected to the main body such that each of the optical fibers is fitted at one end in a corresponding one of the through holes with its end face opposed to the plate member secured to the main body. With the plate member pressed against the body surface directly above an arterial vessel of a subject, the displaceable portions of the plate member which are aligned with the corresponding through holes, minutely displace upon application of the pressure pulse wave thereto. The signal generating devices optically measure the minute displacements of the displaceable portions of the plate member, through the optical fibers, and detect the pressure pulse wave based on the measured minute displacements of the plate member. Thus, the main body used in the present apparatus does not require electrically conductive wiring patterns to be formed between the measuring points, specifically the through holes of the main body, in contrast to the known apparatus. Further, the thickness of the main body is not limited to a certain value, and may be of a comparatively large thickness. Also, the main body may consist of a member having a comparatively high rigidity. Thus, the main body does not suffer from the problem of reduced rigidity, though the plurality of through holes are formed therethrough. Therefore, each pair of adjacent through holes can be formed so as to be spaced apart from each other by a very small distance. Consequently the present apparatus is capable of detecting pressure pulse wave at a sufficiently large number of positions per unit distance on the body surface directly above the artery, namely, by utilizing a sufficiently high density of measuring points. According to a preferred feature of the present invention, the apparatus further comprises pressing means for pressing the plate member secured at the pressing surface of the main body, against the body surface, the pressing means comprising a cylindrical housing with a bottom wall, for accommodating the main body; a flexible diaphragm disposed between the housing and the main body, for securing the main body to the housing, the diaphragm cooperating with the housing to define a fluid-tight pressure chamber; a band for setting the housing on the body surface; and a pressure source for supplying the pressure chamber with pressurized fluid so as to press the main body towards the body surface. Preferably the main body has rigidity. Preferably the main body has grooves formed in the pressing surface thereof, the grooves being covered by the plate member secured to the pressing surface, the plurality of through holes communicating with the exterior via the grooves. Preferably also the plurality of through holes are formed through the main body such that the through holes are arranged in a row at regular intervals . In this case, it is recommended that each of the regular intervals be about 0.2 mm. Also, in this case, it is preferred that, with the main body pressed against the body surface, 3 to 5 through holes out of the plurality of through holes are located directly above the arterial vessel. In a prefered embodiment of the apparatus of the invention, each of the signal generating devices comprises a laser source for emitting laser beams having a single wavelength; a first convex lens for forming the laser beams into parallel beams; a non-polar beam splitter for dividing the parallel beams into a first and a second beam, such that the beam splitter transmits the first beam and reflects the second beam; a second convex lens for permitting the first beam to be incident on an end face of the other of the opposite ends of a corresponding one of the plurality of optical fibers, the first beam being transmitted by the corresponding optical fiber, reflected by a corresponding one of the displaceable portions of the plate member, again transmitted by the corresponding optical fiber, and reflected by the non-polar beam splitter, the first beam being varied in phase due to any displacement of the corresponding displaceable portion; a reflector mirror for reflecting the second beam, the second beam reflected by the reflector mirror being transmitted by the non-polar beam splitter; a photosensor for detecting a mixture consisting of the first beam reflected by the beam splitter and the second beam transmitted through the beam splitter; and a detector circuit for reading a variation in phase of the mixture light at regular intervals of time, and generating an electric signal based on the periodically obtained readings. In another embodiment of the invention, the apparatus further comprises a control device for processing the electric signals supplied from the plurality of signal generating devices, selecting one of the electric signals which is free from influences of the wall of the arterial vessel, and monitoring blood pressure of the subject based on the selected electric signal. In yet another embodiment of the invention, the apparatus further comprises a control device for receiving the electric signals from the plurality of signal generating devices while varying the pressing force with which the main body is pressed against the body surface, and determining a degree of arterial sclerosis of the arterial vessel based on the received electric signals. 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, given by way of example and in which: Fig. 1 is an illustrative view of a general arrangement of the pressure-pulse-wave detecting apparatus of the present invention; Fig. 2 is an illustrative view of a detector head and a signal generating device of the apparatus of Fig. 1; Fig. 3 is a view of a pressing surface of a main body accommodated in the detector head of the apparatus of Fig. 1; and Fig. 4 is a view of a graph showing a cycle of pressure pulse wave represented by an electric signal generated by the signal generating device of Fig. 2. Referring to Fig. 1 there is illustrated a general arrangement of a pressure-pulse-wave detecting apparatus of the present invention. In the figure, reference numeral 12 designates a detector head which is detachably fixed on a surface of a wrist 10 of a subject with the help of a wrist band 14. The detector head 12 includes a cylindrical housing 16 having a bottom wall, a main body 18 accommodated in the housing 16, and a flexible diaphragm 22 disposed between the housing 16 and the main body 18 for securing the main body 18 to the housing 16. The flexible diaphragm 22 cooperates with the housing 16 to define a fluid-tight pressure chamber 20. When pressurized gas is supplied from an electric pump 24 to the pressure chamber 20 via a pressure-regulating valve 26, the main body 18 is pressed via the body surface against a radial artery 30 running adjacent to a radius 28. Thus, the housing 16, diaphragm 22, band 14, pump 24 and other members cooperate with each other to serve as pressing means for pressing the main body 18 against the radial artery 30. The main body 18 consists of a member having a comparatively high rigidity, such as a metallic or ceramic member, and has a thickness of 2 to 20 mm. As shown in Figs. 2 and 3, the main body 18 has a plurality of through holes 34 formed therethrough to open in a pressing surface 32 of the main body 18 and to be in a row along a predetermined straight line. A presser plate 36 is bonded to the pressing surface 32 of the main body 18 such that the presser plate 36 covers the through holes 34 opening in the pressing surface 32. The presser plate 36 is constituted by, for example, a glossy plated metal sheet of a comparatively small thickness, or a stainless-steel sheet of a comparatively small thickness, so that the presser plate 36 has a certain degree of flexibility. As most clearly shown in Fig. 3, the pressing surface 32 of the main body 18 has grooves 38 formed therein which are covered by the presser plate 36 secured to the pressing surface 32. The through holes 34 communicate with the atmosphere or ambient air via the grooves 38 covered by the presser plate 36, so as to prevent a pressure difference between the through holes 34 and the atmosphere. The plurality of through holes 34 are formed at regular intervals of distance. The distance intervals of the through holes 34 correspond to intervals of distance between the detecting positions at which pressure pulse wave produced from the radial artery 30 is detected. The distance intervals of the through holes 34 are predetermined to be sufficiently smaller than a width or diameter of the radial artery 30, for example about 0.2 mm, so that 3 to 5 through holes 34, and accordingly the same number of detecting positions, are located on the body surface right above the radial artery 30. As shown in Fig. 2, a plurality of optical fibers 40a, 40b, 40c, ... are connected to the main body 18 such that one end 39a of opposite ends 39a, 39b of each optical fiber 40 is fitted in a corresponding one of the plurality of through holes 34, and that an end face 41a of the one end 39a is opposed to or faces the presser plate 36 at a predetermined distance therefrom. The other end 39b of each optical fiber 40 is connected to a signal generating device 42. Accordingly, the instant apparatus includes a plurality of signal generating devices 42 whose number corresponds to that of the through holes 34. All of the devices 42 have the same configuration and operate in the same way. There will be described in detail the signal generating device 42 connected to the optical fiber 40a. The signal generating device 42 includes a laser source 44 which emits laser beams having a single wavelength; a first convex lens 46 which forms the laser beams emitted by the laser source 44, into parallel beams; and a non-polar beam splitter 48 which divides the parallel beams into a first and a second beam such that the beam splitter 48 transmits the first beam and reflects the second beam. The signal generating device 42 further includes a reflector mirror 49 which reflects the second beam reflected by the beam splitter 48; and a second convex lens 50 which permits the first beam transmitted through the beam splitter 48 to be incident on an end face 41b of the other end 39b of the optical fiber 40a. The second beam reflected by the reflector mirror 49 is incident on the beam splitter 48. The first beam is transmitted by the optical fiber 40a which acts as a rod lens, reflected by the presser plate 36, again transmitted by the optical fiber 40a, and is incident on the beam splitter 48. The signal generating device 42 also includes a photosensor 52 which receives a mixture light consisting of the second beam transmitted through the beam splitter 48 and the first beam reflected by the beam splitter 48, and generates an electric signal representing the detected mixture light; and a detector circuit which generates a pressure-pulse-wave electric signal SMa (hereinafter, referred to as PPW signal SMa) based on the electric signal supplied from the photosensor 52. More specifically described, PPW signal SMa generated by the detector circuit 54 of the signal generating device 42 connected to the optical fiber 40a, represents the pressure pulse wave transmitted to a displaceable portion 37a of the presser plate 36 which portion is aligned with the opening of the corresponding through hole 34 and is opposed to the end face 41a of the one end 39a of the optical fiber 40a. As described above, the mixture light detected by the photosensor 52, consists of the first beam reflected by the presser plate 36 and the second beam reflected by the reflector mirror 49. Upon application of pressure pulse wave from the radial artery 30 to the displaceable portion 37a of the presser plate 36, the displaceable portion 37a minutely displaces due to its flexibility, resulting in changing the optical path of the first beam and thereby varying the phase of the first beam. The optical path of the second beam is not changed, and the second beam is used as a reference light having a reference phase. The detector circuit 54 reads a shift of the phase of the first beam with respect to the reference phase of the second beam, which shift corresponds to a minute displacement of the presser plate 36, at regular minute intervals of time, and generates PPW signal SMa based on the periodically read shifts. Thus, PPW signal SMa represents the pressure pulse wave continuously acting on the displaceable portion 37a of the presser plate 36 in synchronization with pulsation of the heart of the subject. In the graph of Fig. 4 there is shown a cycle of the pressure pulse wave represented by PPW signal SMa, which corresponds to one pulsation of the heart. The instant pressure-pulse-wave detecting apparatus further has a control device 56 which receives PPW signals SMa, SMb, SMc, ... from the respective signal generating devices 42 connected to the respective optical fibers 40a, 40b, 40c, .... Each of PPW signals SMa, SMb, SMc, ... represents the pressure pulse wave transmitted to a corresponding one of the displaceable portions 37a, 37b, 37c, ... of the presser plate 36, namely, the pressure pulse wave detected at a corresponding one of the plurality of positions on the body surface right above the radial artery 30. The control device 56 processes the received PPW signals SMa, SMb, SMc, ... according to software programs pre-stored therein, so as to select the single one of PPW signals, or the single one of the detecting positions, which is free from influences of the wall of the radial artery 30, as is taught by the previously indicated U.S. Patent 4,423,738. The control device 56 monitors blood pressure of the subject based on the selected one PPW signal SM. Alternatively, the control device 56 may be adapted to receive PPW signals SM from the signal generating devices 42 while varying the pressing force with which the main body 18 is pressed against the radial artery 30, by controlling the pressuring-regulating valve 26, so as to determine a degree of arterial sclerosis of the radial artery 30 based on the received PPW signals SM, as taught by the previously indicated Japanese Patent Application No. 63-87720. In either case, the control device 56 commands a display (not shown) to display the measured blood pressure or degree of sclerosis of the subject. It follows from the foregoing that in the instant apparatus it is not required to provide the plurality of through holes 34 with electrically conductive wiring patterns, in contrast to the conventional apparatus in which electrically conductive wiring patterns are provided between individual pressure-sensitive elements. Further, the main body 18 is free from limitation regarding thickness thereof. Also, as previously described, the main body 18 consists of a comparatively rigid member. Therefore, the rigidity of the main body 18 is not significantly reduced, even with the through holes 34 formed therethrough. Consequently, the through holes 34 are formed very near to each other. That is, the instant apparatus is capable of measuring the pressure pulse wave at a sufficiently large number of detecting positions per unit distance on the body surface right above the radial artery 30, namely by utilizing a sufficiently high density of detecting points. The instant apparatus has no electric circuit in any parts thereof which directly contact the body surface of the subject, thereby ensuring use thereof with a higher safety. While the presently preferred embodiment of the invention has been described with particularities for illustrative purpose only, it is understood that the present invention is not limited to the details of the illustrated embodiment but may be otherwise embodied. For example, in place of the single presser plate 36 used in the illustrated embodiment, it is possible to use a plurality of separate displaceable or deformable members which are fitted in the openings of the correponding through holes 34. While in the illustrated embodiment the main body 18 is moved with the diaphragm 22 expanded toward the wrist surface or radial artery 30, it is possible to further employ a device for moving the main body 18 in a direction crossing the radial artery 30, or a device for angularly positioning the main body 18 about an axis extending parallel to the radial artery 30. Although in the illustrated embodiment each of the optical fibers 40a, 40b, 40c, ... consists of a single fiber, it is possible to use a bundle of fibers in place of the single fiber. While in the illustrated embodiment pressure pulse wave is detected based on variation in the phase of the mixture light received by the photosensor 52, it is possible to detect the pressure pulse wave based on variation in amount or intensity of the light reflected by the presser plate 36. In this case it is preferred that at least one central optical fiber from which light is emitted toward the presser plate 36, and a bundle of outer optical fibers surrounding the at least one central fiber, for receiving the light reflected by the presser plate 36, be associated with each detecting position on the body surface right above the radial artery 30. The light transmitted by the bundle of outer optical fibers is received by a photosensor, which generates a PPW signal based on the received light. It is required that the light emitted toward the presser plate 36 is of a constant intensity or energy. As long as this requirement is satisfied, various conventional light sources such as an LED (light emitting diode) and a lamp may be used. Alternatively, pressure pulse wave may be detected by utilizing Doppler shift in the frequency of the light reflected by the presser plate 36, which displaces due to the pressure pulse wave transmitted thereto. The Doppler shift is measured by a well-known photo-heterodyne system. In this case it is preferred to use a light source which emits a pair of different laser beams having a pair of different polarization planes orthogonal to each other and a a pair of different frequencies, and a splitter for dividing the mixture laser beams into a first and a second beam. The first beam is reflected by the presser plate 36, and accordingly the optical path of the first beam is changed due to a minute displacement of the displaceable portion 37 of the presser plate 36. The optical path of the second beam is not changed. A first mixture light consisting of the mixture laser beams which have been just emitted by the laser source, is used as a reference light, and a reference beat signal is produced based on the reference light. Meanwhile, a second mixture light consisting of the first beam reflected by the presser plate 36 and the second beam whose optical path is not changed, is used as a measurement light having a shift of beat frequency corresponding to the pressure pulse wave transmitted to the presser plate 36, and a measurement beat signal is produced based on the measurement light. The pressure pulse wave is detected based on the frequency shift of the measurement beat signal from the reference beat signal.

Claims: A pressure-pulse-wave detecting apparatus for detecting pressure pulse waves produced from an arterial vessel of a subject, at a plurality of positions on a body surface directly above said arterial vessel, the apparatus comprising: a main body (18) having a pressing surface (32) and which is to be pressed towards said body surface, and a plurality of through holes (34) formed therethrough and opening in said pressing surface; a plate member (36) secured at said pressing surface of said main body such that said plate member covers the openings of said plurality of through holes, said plate being flexible so that a plurality of displaceable portions (37) of the plate are aligned with the openings of corresponding through holes; a plurality of optical fibers (40), one (39a) end of each fiber being fitted in a corresponding one of said plurality of through holes of said main body, such that end face (41a) is opposed to a corresponding one of said plurality of displaceable portions of said plate member and is spaced at a predetermined distance therefrom; and a plurality of signal generating devices (42) each of which is connected to the other (39b) end of a corresponding optical fiber, each signal generating device detecting the pressure pulse wave transmitted to a corresponding one of said plurality of displaceable portions of said plate member, by means of displacement of said corresponding displaceable portion being optically detected through said corresponding optical fiber, and generating an electric signal representing the detected pressure pulse wave. The apparatus as set forth in claim 1, further comprising pressing means for pressing said plate member (36) secured at said pressing surface (32) of said main body (18), against said body surface, said pressing means comprising a cylindrical housing (16) with a bottom wall, for accommodating said main body, a flexible diaphragm (22) disposed between said housing and said main body, for securing said main body to said housing, said diaphragm cooperating with said housing to define a fluid-tight pressure chamber (20), a band (14) for setting said housing on said body surface, and a pressure source (24) for supplying said pressure chamber with pressurized fluid so as to press said main body towards said body surface. The apparatus as set forth in claim 1 or claim 2, wherein said main body (18) has rigidity. The apparatus as set forth in any one of claims 1-3, wherein said main body (18) has grooves (38) formed in said pressing surface (32) thereof, said grooves being covered by said plate member (36) secured to said pressing surface, said plurality of through holes (34) communicating with the exterior via said grooves. The apparatus as set forth in any one of claims 1-4, wherein said plurality of through holes (34) are formed through said main body (18) such that the through holes are arranged in a row at regular intervals. The apparatus as set forth in claim 5, wherein each of said regular intervals is about 0.2 mm. The apparatus as set forth in any preceding claim, wherein said through holes are so located in said main body that, with said main body (18) pressed against said body surface, from 3 to 5 through holes (34) are located right above said arterial vessel. The apparatus as set forth in any one of claims 1-7, wherein each of said signal generating devices (42) comprises a laser source (44) for emitting laser beams having a single wavelength, a first convex lens (46) for forming said laser beams into parallel beams, a non-polar beam splitter (48) for dividing said parallel beams into a first and a second beam, such that said beam splitter transmits said first beam and reflects said second beam, a second convex lens (50) for permitting said first beam to be incident on an end face (41b) of the other (39b) of the opposite ends of a corresponding one of said plurality of optical fibers (40), said first beam being transmitted by said corresponding optical fiber, reflected by a corresponding one of said displaceable portions (37) of said plate member (36), again transmitted by said corresponding optical fiber, and reflected by said non-polar beam splitter, said first beam being varied in phase due to any displacement of said corresponding displaceable portion, a reflector mirror (49) for reflecting said second beam, said second beam reflected by said reflector mirror being transmitted by said non-polar beam splitter, a photosensor (52) for detecting a mixture consisting of the first beam reflected by said beam splitter and the second beam transmitted through said beam splitter, and a detector circuit (54) for reading a variation in phase of said mixture light at regular intervals of time, and generating an electric signal based on the periodically obtained readings. The apparatus as set forth in any one of claims 1-8, further comprising a control device (56) for processing the electric signals supplied from said plurality of signal generating devices (42), selecting one of said electric signals which is free from influences of the wall of said arterial vessel, and monitoring blood pressure of said subject based on the selected electric singal. The apparatus as set forth in any one of claims 1-9, further comprising a control device (56) for receiving the electric signals from said plurality of signal generating devices (42) while varying the pressing force with which said main body (18) is pressed against said body surface, and determining a degree of arterial sclerosis of said arterial vessel based on the received electric signals.

Inventors: HARADA CHIKAO, KUROSAWA KIMIMASA, NIWA MINORU, SAKAI HIROSHI, HARADA, CHIKAO, KUROSAWA, KIMIMASA, NIWA, MINORU, SAKAI, HIROSHI
Applicants: COLIN CORP, COLIN CORPORATION
Application year: 1989
Main classification: A61B5
IPC codes: A61B5