Sensor for tissue transmitted light

Abstract: A supporting shaft (6) stands on an external auditory canal arm (3) holding an LED (4). An attaching portion (8) holding a PD (7) is rotatably connected to one end of a holding arm (10). A column having a through hole (11b) into which the supporting shaft is slidably inserted is fixed to the other end of the holding arm. The external auditory canal arm (3) and the holding arm (10) are connected to each other by a coil spring (13).

Description: BACKGROUND OF THE INVENTION Field of the invention. The invention relates to a tissue transmitted light sensor which detects a change of the quantity of transmitted light due to absorptive substances in the blood flowing through an arterial vascular of the subject, thereby detecting the pulse wave of the blood, and particularly to a tissue transmitted light sensor which detects the pulse wave on the basis of light transmitted a tissue in the vicinity of the superficial temporal artery. Related art In order to measure the oxygen saturation of the blood of the subject or the cardiac output, the blood volume, etc. with injecting dye in the blood, the pulse photometry is used. As a probe for the pulse photometry, known is an optical sensor probe which is to be attached on an earlobe, an ear concha, a fingertip, or the like. In the probe, a light emitting unit such as an LED emits light and a light receiving unit such as a photo diode PD receives the light, thereby detecting absorptive substances in the blood flowing through an arterial vascular in the tissue in the vicinity of the attached part. The conventional optical sensor probe configured as described above has a problem in that, in the case where the probe is attached on a fingertip, the flow rate of the blood is varied when vasomotor nerves are irritated by reflex due to hyper ventilation or an injection so that a measure value becomes unstable. In the case where the probe is attached on an ear, a measure value is hardly affected by vasoconstriction due to reflex. In this case, however, there arises a problem in that the amplitude of the pulse wave is very lower than that in a fingertip and, particularly for a patient under general anesthesia or immediately after operation, the measurement cannot be stably conducted. When the cardiac output, the blood volume, etc. are to be measured by using dye, the attachment of the probe may cause a blood flow impediment. This produces a problem in that- the measurement accuracy and reproducibility are impaired. Furthermore, the clip method which is often used for attaching a probe to an earlobe has a defect that, when the subject moves, the probe easily swings and hence it is difficult to conduct the measurement stably and highly accurately, thereby easily producing a measurement error. US-A-3 810 460 according to the precharacterizing part of claim 1 discloses a tissue transmitted light sensor comprising two arms, one having an external auditory canal arm with a light emitting unit while the other arm includes a light receiving unit. The arms are adapted to be attached to a human in the vicinity of the ear. The two arms are rotatably connected one to another by means of a shaft and a spring is wound around the shaft in order to urge the portions of the arms having said light emitting unit and said light receiving unit one to another in a closing direction. EP-A-0 678 277, a document according to Article 54(3) EPC describes a tissue transmitted light sensor comprising two arms each having a bearing which are rotatably connected by means of a shaft passing through the bearings. One of the arms has an external auditory canal arm including a photo-sensing piece. The other of said arms includes a light emitting piece. A coiled spring is wound around the shaft in order to urge the ends of the arms opposite to the photo-sensing and light emitting pieces in an open direction. SUMMARY OF THE INVENTION The invention has been conducted in view of the above-mentioned circumstances. It is an object of the invention to provide a tissue transmitted light sensor, which can prevent deviation due to the difference of the space in the ear concha of the subject, from occurring, and which can be stably attached to the subject. In order to attain the object, a tissue transmitted light sensor has been provided according to the features of claim 1. In the tissue transmitted light sensor configured as described above, the external auditory canal arm and the holding arm are connected to each other via the supporting shaft so as to be slidable (movable) in an axial direction. Even when the space in the ear concha of the subject is different in size among individuals, therefore, the angle of the holding arm with respect to the external auditory canal arm is kept substantially constant so that the attaching portion held by the holding arm is prevented from slipping off, thereby enabling the sensor to be stably attached. According to the present invention, the superficial temporal artery is prevented from being pressed by a cartilage in the vicinity of the external auditory canal so that a change of the quantity of transmitted light due to absorptive substances in the blood flowing through the artery can be stably detected without impeding the blood flow. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram illustrating the attached state of an embodiment of the tissue transmitted light sensor of the invention. Fig. 2 is an exploded perspective view showing the configuration of the main portion of the tissue transmitted light sensor of Fig. 1. Figs. 3 (a) and (b) show section views illustrating the structure for connecting an external auditory canal arm with a holding arm shown in Fig. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIEMTNS Hereinafter, an embodiment of the tissue transmitted light sensor of the invention will be described with reference to the accompanying drawings. Figs. 1 to 3 show the configuration of the embodiment of the invention. In Figs. 1 and 2, an LED 4 which serves as the light emitting unit is disposed on the upper face of an external auditory canal arm 3 which is to be inserted into an external auditory canal 2 via a cavum conchae 1. The upper face of the external auditory canal arm 3 is formed as a curved face of a shape which conforms to that of the inner face of the external auditory canal 2, and provided with non-slip processing such as a suede form. A sponge member 5 which elastically abuts against the inner face of the external auditory canal 2 is disposed on the lower face of the external auditory canal arm 3. A supporting shaft 6 stands in a substantially perpendicular direction at one end of the external auditory canal arm 3 which outward protrudes from the cavum conchae 1. A PD 7 which serves as the light receiving unit is disposed on an attaching portion 8 so as to oppose the LED 4. The attaching portion 8 is rotatably held by one end of a holding arm 10 via a shaft 9. A flange 10a which protrudes in three directions as shown in Figs. 2 and 3 is integrally formed at the other end of the holding arm 10. A prismatic or circular column 11 downward protrudes from the center portion of the area of the holding arm 10 where the flange 10a is formed. A part of the column 11 is connected to the holding arm 10 via a connecting part lla. A projection (stopper) 12 is integrally formed at a lower end of the outer face of the column 11. A through hole 11b is formed so as to pass through the center of the column 11 in the axial direction. The shape of the through hole 11b is similar to the section shape of the supporting shaft 6. On the other hand, a coil spring 13 is wound around the supporting shaft 6 which stands at the one end of the external auditory canal arm 3. The ends of the coil spring are engaged with the external auditory canal arm 3 and the column 11, respectively. A cover 14 is integrally formed on the external auditory canal arm 3 so as to surround the supporting shaft 6 and the coil spring 13. The column 11 can be fitted into the cover 14 so as to be slidable (movable) in the axial direction. A guide groove 14a into which the projection 12 formed on the column 11 is fitted is formed in the cover 14 so as to elongate in the axial direction. When the supporting shaft 6 is passed through the through hole 11b of the column 11, the projection 12 is engaged with the guide groove 14a so that the column 11 is prevented from being rotated with respect to the cover 14. A flange 15 is screwed to the upper end of the supporting shaft 6. In the tissue transmitted light sensor configured as described above, when the flanges 10a and 15 are nipped by fingers and pressed in the directions of arrows A and B as shown in Fig. 3(a), the external auditory canal arm 3 and the holding arm 10 are separated from each other. Under this state, the external auditory canal arm 3 is inserted into the external auditory canal 2. When the external auditory canal arm 3 and the holding arm 10 are thereafter released, as shown in Fig. 3(b), the urging force of the coil spring 13 causes the external auditory canal arm 3 and the holding arm 10 to be attracted to each other so as to be close together. As a result, as shown in Fig. 1, the attaching portion 8 is closely attached to the surface of the temporal, thereby completing the attaching operation. When the LED 4 emits light, the PD 7 can detect light which transmits the vicinity of the superficial temporal artery. In the embodiment, the external auditory canal arm 3 and the holding arm 10 are connected via the supporting shaft 6 to each other so as to be slidable (movable) in the axial direction. Even when the space in the ear concha of the subject is different in size among individuals, therefore, the angle of the holding arm 10 with respect to the external auditory canal arm 3 is kept substantially constant so that the attaching portion 8 held by the holding arm 10 is prevented from slipping off, thereby enabling the sensor to be stably attached. In the above, the embodiment in which the supporting shaft 6 has a circular column-like shape has been described. Alternatively, the supporting shaft 6 may have a prismatic or elliptical column-like shape and the through hole 11b may have a shape conforming to that of the supporting shaft. In the alternative, the holding arm 10 can be prevented from being rotated with respect to the external auditory canal arm 3, and hence the projection 12 formed on the column 11, and the guide groove 14a formed in the cover 14 are not necessary. As described above, according to the tissue transmitted light sensor of the invention, since the external auditory canal arm and the holding arm are connected to each other via the supporting shaft so as to be movable in an axial direction, the angle formed by the external auditory canal arm and the holding arm is kept substantially constant so that the attaching portion is prevented from slipping off, thereby enabling the sensor to be stably attached.

Claims: A tissue transmitted light sensor comprising: an external auditory canal arm (3) which holds one of a light emitting unit (4) and a light receiving unit; an attaching portion (8) holding the other one of said light emitting unit and said light receiving unit (7), said attaching portion (8) being adapted to be attached on an outer face of a temporal in the vicinity of the ear; a supporting shaft (6); a holding arm (10) rotatably holding at one end said attaching portion (8) and having a column (11) at the other end, a through hole (11b) being formed in said column (11), said supporting shaft (6) being inserted into said through hole (11 b) so as to be slidable in an axial direction; and a spring (13) wound around said supporting shaft (6) and connecting said external auditory canal arm (3) with said holding arm (10), being characterized by the supporting shaft (6) standing in a perpendicular direction to the holding arm (10) at the end of said external auditory canal arm (3) protruding outwards and said external auditory canal arm (3) being formed at the upper face as a curved face of a shape which conforms to that of the inner face of the external auditory canal to be inserted into an external auditory canal (2) of an ear of a subject. A tissue transmitted light sensor as claimed in claim 1, wherein an angle defined by said external auditory canal arm (3) and said holding arm (10) is kept substantially constant.

Inventors: AOYAGI TAKUO, FUSE MASAYOSHI, AOYAGI, TAKUO, FUSE, MASAYOSHI, Aoyagi, Takuo, c/o Nihon Kohden Corporation, Fuse, Masayoshi, c/o Nihon Kohden Corporation
Applicants: NIHON KOHDEN CORP, NIHON KOHDEN CORPORATION
Application year: 1996
Main classification: A61B5
IPC codes: A61B5