Organism information measuring apparatus and pulse-wave measuring apparatus

Abstract: An organism information measuring apparatus and an arm wear type pulse-wave measuring apparatus having a sensor unit having a size that does not obstruct the exercise of a user, such as jogging, so that information about an organism, such as the pulse rate, is measured. The arm wear type pulse-wave measuring apparatus has a wrist band (12) for securing the body (10) of the apparatus to the arm of the user; and a sensor unit (30) that is put on the root of a finger by a sensor securing band (40). If the finger is irradiated with light by an LED (31) in the foregoing state, light reaches the blood vessel and light is reflected. Reflected light is received by a phototransistor (32) in such a manner that the quantity of received light corresponds to change in the quantity of blood occurring due to pulse waves of the blood. The LED is an LED capable of emitting blue light and has a light emission wavelength peak of 450 nm. The phototransistor has a light receiving wavelength region in a range from 300 nm to 700 nm.

Description: The present invention relates to an organism information measuring apparatus, such as a pulse-wave measuring apparatus. The apparatus may display information about the pulse wave, such as the pulse rate. More particularly, but not exclusively, the present invention relates to an apparatus that irradiates an organism such as a blood vessel with light and detects light reflected by the organism to measure information about the organism, such as the pulse waves. The present invention also relates to a pulse-wave measuring apparatus which is worn on the user's arm, and which is capable of measuring information about the organism during an exercise, such as jogging, running or cycling. Devices for detecting information (such as pulse waves) from an organism (such as a blood vessel) include electronic apparatus of a type that optically detects changes in the quantity of blood to display information about an organism in accordance with results of the detection. In an optical pulse-wave measuring apparatus (an organism information measuring apparatus) of the foregoing type, a light emitting device, such as an LED (Light Emitting Diode), irradiates the fingertip or the like with light, and light reflected by the organism (the blood vessel) is received by a light receiving device, such as a phototransistor, so that changes in the quantity of blood passing through the blood vessel occurring due to the pulse waves of the blood are detected as changes in the quantity of the received light. In response to a pulse wave signal obtained by the detection, changes in the pulse rate or the pulse waves are displayed. As the light to be emitted for radiation from the light emitting device, infrared rays have been employed. If external light (sunlight or the like) is incident upon the light receiving device this causes the quantity of received light to change. Therefore, the conventional pulse-wave measuring apparatus employs a light shielding cover to cover the area, such as on the fingertip, where light detection occurs so that the influence of the external light is prevented or reduced. However, use of the apparatus in a place, such as outdoors, where it is irradiated with external light results in a portion of the external light passing through the finger and reaching the light receiving device. Thus, the conventional pulse-wave measuring apparatus has a problem in that the change in the illuminance of external light causes pulse waves to be detected erroneously even when the area where light is detected is covered. Therefore, the conventional pulse-wave measuring apparatus encounters a limitation in that it can be used only in a place that is not irradiated with external light or a place in which the constant illuminance of external light can be attained. To overcome the foregoing limitation, a larger-scale light shielding structure must be provided to prevent influence of external light which passes through the finger. Therefore, the size of the pulse-wave measuring apparatus cannot be reduced, and the conventional pulse-wave measuring apparatus cannot be used as an apparatus that is able to measure information about pulse waves during exercise, such as jogging, running or cycling. DE 2805202A describes a pulse monitor of the above type which may be in the form of a wristwatch. The monitor utilises a light emitting diode which emits light having a wavelength in the range of 600 to 650 nm. To overcome the foregoing problem, a pulse-wave sensor has been disclosed in Japanese Utility-Model Laid-Open No. 57-74009 which, in addition to the device for detecting pulse waves, comprises an external-light detection device for detecting external light and which compensates for the influence of external light in accordance with results of the detection of external light obtained by the external-light detection device. However, provision of the external-light detection device and a compensation circuit for the pulse waves sensor prevents size and cost reductions. As described above, any of the conventional countermeasures against external light has been unsatisfactory in view of practical use. Furthermore, there has been a requirement for a pulse-wave measuring apparatus of the foregoing type which is worn on the arm and that is capable of measuring the pulse rate of the wearer and the like during jogging, running, cycling or a marathon race. To provide a pulse-wave measuring apparatus of this type, a small sensor unit is required which can be put on the root of the finger (i.e. the part of the finger closest to the palm of the hand). This is because, if a small sensor is put on the root of the finger, the wearer is able to lightly clench the fist. GB 2052050A describes a pulse wave monitor in the form of a watch provided with a remote sensing feature which is arranged for mounting on the finger of a user. The remote sensor is coupled to the watch by a cable and information regarding the user's pulse is displayed on the face of the watch. In view of the foregoing, the inventors of the present invention have performed a variety of investigations into the reasons why pulse waves are erroneously detected due to changes in the illuminance of external light. As a result, it is concluded that infrared rays for use in the detection system of the conventional pulse-wave measuring apparatus have an excessively large transmittance with respect to the organism that causes external light to easily reach the light receiving device through the organism even if a light shielding cover is provided. Thus, if the foregoing problem can be overcome, a practical countermeasure against external light can be provided. Accordingly, an object of the present invention is to realize an organism information measuring apparatus having an optical system, which is not easily affected by external light, to omit a large-scale light shielding structure and to overcome the limitations of conditions for use. According to a first aspect of the present invention there is provided an organism information measuring apparatus comprising: a light emitting means for irradiating a portion of an organism of a person with light; a detection means having a light receiving means for receiving light emitted by the light emitting means and reflected by the portion of the organism; characterised in that said light receiving means is arranged to detect only light having a wavelength of substantially 700 nm or less, such that the measuring apparatus can be arranged to provide information about the organism on the basis of light transmitted from the light emitting means and reflected by the portion of the organism but not to provide information arising from external light incident on the person and having a wavelength of substantially 700nm or more which is able to propagate through skin tissue of the person to the light receiving means. Preferably, the light emitting means has a light emitting wavelength region at least in a range from substantially 300 nm to substantially 700 nm. Advantageously the apparatus is characterised by an organism information display portion for displaying information about the organism on the basis of light detected by the receiving means, the light having a wavelength of substantially 700 nm or less. Another object of the present invention is to provide a pulse-wave measuring apparatus for wearing on the arm having a sensor unit of a small size for mounting on a finger that does not obstruct a user from performing exercises, and such as jogging, and which is capable of measuring information such as the pulse rate. Accordingly, the apparatus is characterised in that the measuring apparatus is arranged to be worn on an arm of a person and comprises; a sensor unit including the light emitting means and the light receiving means, securing means for securing said sensor unit in such a manner that a light receiving surface of said light receiving means and a light emitting surface of said light emitting means face the surface of a finger of the person; a body portion having a display portion for displaying information about pulse waves of the person obtained in accordance with results of receipt of light performed by said light receiving means; a wrist band for securing said body portion on the arm of the person; a signal transmission portion which extends from said sensor unit to said body portion and through which a signal representative of the light received by said light receiving means is input to said body portion; wherein said information about pulse waves is displayed on the basis of light detected by the receiving means, the light having a wavelength of substantially 700 nm or less; and said sensor unit has a size such that said sensor unit may be mounted on the root of the finger of the person. The sensor unit may be used in a state where the sensor unit is put on the region from the root of the finger to the joint of the finger so that a user is able to lightly clench the fist if the sensor unit is put on the finger. It is preferable that an InGaN type (Indium-Gallium-Nitrogen type) blue LED be employed as the light emitting portion, and a GaAsP type (Gallium-Arsenic-phosphorus type) phototransistor be employed as the light receiving portion. According to a further aspect of the present invention there is provided a method of measuring the pulse rate of a person, including irradiating a portion of an organism of the person with light from a light emitting means and detecting the light by a detection means having a light receiving means, characterised in that only light having a wavelength of 700nm or less is detected such that the pulse rate can be measured on the basis of the light from the light emitting means and not on the basis of external light incident on the person and having a wavelength of substantially 700nm or more which is able to propagate through skin tissue of the person to the light receiving means. Preferably, irradiation is performed on a blood vessel in the root of the finger or thumb of a person. Therefore, erroneous detection of pulse waves due to external light can be prevented so far as external light is not directly made incident upon the detection portion. Thus, a large-scale light shielding structure is not required. As a result, even if a small sensor unit, that can be put on a portion from the root to the knuckle of the thumb, the middle finger, the ring finger or the little finger. is used, external light can satisfactorily be shielded. If the foregoing small sensor unit is used, it does not cover the finger when it is put on the root of the finger whereby allowing a user to lightly clench the fist. Thus, no problem arises during exercise, such as jogging, running or cycling. Hemoglobin in the blood has a light absorption factor with respect to light having a wavelength region in a range from 300 nm to 700 nm which is considerably larger than the light absorption factor with respect to infrared rays. When an organism is irradiated with light having the wavelength region in the range from 300 nm to 700 nm to be adaptable to the light absorption characteristics of hemoglobin, the intensity of light reflected by the organism (the blood vessel) is considerably changed to follow the change in the quantity of the blood. Therefore, the S/N ratio of the pulse wave signal can be raised. As a result of measurement of the distribution of body temperature from the palm to the fingertip, the temperature of the fingertip is considerably lowered when the ambient temperature is low. On the other hand, the temperature of the root of the finger cannot relatively be lowered. That is, the bloodstream at the root of the finger is not reduced excessively even in a cold day. Therefore, putting of the sensor unit at the root of the finger enables information about an organism such as the pulse rate, to be accurately measured if a user performs exercise outdoors, such as running. The method according to an embodiment of the present invention is an excellent measuring method that cannot be obtained by a so-called finger acuminate pulse wave measuring method that is a conventional method for measuring the bloodstream at the fingertip. In one embodiment a pulse rate measuring apparatus is provided including light emitting means for irradiating a blood vessel with light, and a light detecting means for detecting the light after it has irradiated the blood vessel. The light detecting means is sensitive to light having a wavelength of substantially 700 nm or less. The light emitting and light detecting means are mounted on one side of a sensor securing band. When the apparatus is in use the securing band is positioned on the user's body such that the light emitting and detecting means are located in a space between the sensor securing band and the skin of the user. The sensor securing band acts as a shield to external light and prevents it from directly irradiating the light detecting means. Light having a wavelength shorter than 700 nm cannot easily penetrate and/or is easily absorbed by the skin. Therefore, external light does not irradiate the light detecting means because: (i) light having a wavelength shorter than 700 nm which irradiates the skin around the sensor securing band does not penetrate the skin or is absorbed easily by the skin before it reaches the light detecting means, and (ii) light having a wavelength longer than 700 nm is outside the range of sensitivity of the light detecting means. Thus, the sensor securing band may be relatively small and cover an area of the skin substantially equal to the size of the light emitting and detecting means. For a better understanding of the invention, embodiments will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 is an explanatory view showing a state where a pulse-wave measuring apparatus for wearing on the arm (an organism information detecting apparatus) according to an embodiment of the present invention is used; Fig. 2 (a) is a plan view of an optical unit of a sensor unit (a detection unit) for use in the pulse-wave measuring apparatus shown in Fig. 1; Fig. 2 (b) is an explanatory view showing a state where a sensor securing band of the sensor unit (the detection unit) for use in the pulse-wave measuring apparatus is deployed; Fig. 2 (c) is an explanatory view showing the structure of another sensor unit (a detection unit); Fig. 3 is an explanatory view showing a state of the sensor unit of the pulse-wave measuring apparatus shown in Fig. 1 put on the root of the finger and the operation of the same; Fig. 4 is a plan view showing the structure of the detection unit (the optical unit) of the pulse-wave measuring apparatus shown in Fig. 1; Fig. 5 is a cross sectional view taken along line A-A' of Fig. 4; Fig. 6 is a cross sectional view taken along line B-B' of Fig. 4; Fig. 7 is a cross sectional view taken along line C-C' of Fig. 4; Fig. 8 is an explanatory graph showing the light emission spectrum of an InGaN type blue LED for use in the pulse-wave measuring apparatus shown in Fig. 1; Fig. 9 is an explanatory graph showing the light receiving characteristics of the InGaP type phototransistor for use in the pulse-wave measuring apparatus shown in Fig. 1; Fig. 10 is an explanatory graph showing the light receiving characteristics of a phototransistor unit having an optical filter for use in the pulse-wave measuring apparatus shown in Fig. 1; Fig. 11 is a block diagram showing the structure of a data processing circuit of the pulse-wave measuring apparatus shown in Fig. 1; Fig. 12 (a) is a graph showing the relationship between the wavelength of light and light transmittance of the skin; Fig. 12 (b) is an explanatory graph showing the relationship between the wavelength of light and the light absorption factors of various hemoglobin; Fig. 13 is an explanatory graph showing the light receiving characteristics of a silicon type phototransistor for use in a conventional pulse-wave measuring apparatus; Figs. 14(a) to (e) show respective experimental conditions in which the amount of the finger which is shielded from light is changed to evaluate the degree of introduction of external light into the arm wear type pulse-wave measuring apparatus according to the present invention; Figs. 15(a) to (c) show the results of analysis of the frequency of results of detection of pulse waves of the pulse-wave measuring apparatus according to the present invention to evaluate influence of external light upon the arm wear type pulse-wave measuring apparatus according to the present invention; Figs. 16(a) to (c) show the results of analysis of the frequency of results of detection of pulse waves of a pulse-wave measuring apparatus according to a comparative example to evaluate influence of external light upon the arm wear type pulse-wave measuring apparatus according to the present invention; Fig. 17 is an explanatory graph showing light emission spectrum of a GaP type LED for use in the pulse-wave measuring apparatus shown in Fig. 1; and Fig. 18 is an explanatory graph showing light receiving characteristics of a GaAsP type phototransistor for use in the pulse-wave measuring apparatus shown in Fig. 1. Overall Structure Fig. 1 is an explanatory view showing a state where pulse-wave measuring apparatus for wearing on the user's arm (hereinafter referred to as "an arm-wear type" pulse wave measuring apparatus) according to a first embodiment is being used. Fig. 2 (a) is a plan view of an optical unit of a sensor unit (a detection unit) employed in the foregoing arm wear type pulse-wave measuring apparatus. Fig. 2 (b) is an explanatory view showing a state where a sensor securing band for the sensor unit employed in the arm wear type pulse-wave measuring apparatus is deployed. Fig. 2 (c) is an explanatory view showing the structure of another sensor unit. Fig. 3 is an explanatory view showing a state of the sensor unit put on the root of the finger and as well as showing the operation of the sensor unit. Referring to Fig. 1, the arm wear type pulse-wave measuring apparatus 1 (an organism information measuring apparatus) according to this embodiment comprises an apparatus body 10 (a body of the pulse-wave measuring apparatus 1) having the structure of a wristwatch; a cable 20 (a signal transmission portion) connected to the apparatus body 10; and a sensor unit 30 disposed at the leading end of the cable 20. The apparatus body 10 is made detachable with respect to the arm by means of a wrist band 12. The sensor unit 30 has a sensor securing band 40 that is about 15 mm in width. The sensor securing band 40 enables the sensor unit 30 to be put on the root of the finger. Since the cable 20 extending from the sensor to unit 30 is provided with a connector portion 70 with which switching can be performed between a state where the cable 20 is connected to the apparatus body 10 and a state where the same is removed from the apparatus body 10, removal of the sensor unit 30 and the cable 20 from the apparatus body 10 enables the arm wear type pulse-wave measuring apparatus 1 to be used as a normal wristwatch. Structure of Apparatus Body The apparatus body 10 comprises a watch case 11 including a time measuring function portion. The watch case 11 has, on the upper surface thereof, a liquid crystal display unit 13 (a display portion) for displaying, in addition to the present time and date, information about pulse waves (information about the organism) in accordance with results of detection obtained by the sensor unit 30. The watch case 11 includes a data processing circuit 50 for processing, for example, a detection signal to display changes in the pulse rate or and the like in accordance with the results of the detection obtained by the sensor unit 30. The data processing circuit 50 and the liquid crystal display unit 13 form an organism information display portion 60. Note that the watch case 11 has, on the outer surface thereof, button switches 111, 112, 113, 114 and 115 for adjusting time and switching the display mode. Electric power is supplied to the arm wear type pulse-wave measuring apparatus 1 from a battery (not shown) included in the watch case 11. The cable 20 is used to supply electric power from the battery to the sensor unit 30 and to input the results of the detection obtained by the sensor unit 30 to the data processing circuit 50. Structure of Sensor Unit The sensor unit 30 comprises the sensor securing band 40 and an optical unit 300. The sensor securing band 40 is made of a resin molded member having a thickness which permits flexibility so that the sensor securing band 40 is curled up in its natural state. In order to mount the sensor on the finger, the sensor securing band 40 is uncurled, followed by being wound around the root of the finger. When the sensor has been mounted on the finger it remains in place due to the shape restoring force of the securing band 40. The sensor securing band 40 has a thick portion at substantially the central portion thereof, the thick portion having a hole 41 that is capable of accommodating the optical unit 300. As shown in Fig. 2 (a), the optical unit 300 is, with resin, molded into a rectangular shape having a pair of projection portions 311 and 312 on the two sides thereof. The cable 20 is extended from the inside portion of the optical unit 300. On the other hand, as shown in Fig. 2 (b), the hole 41 of the sensor securing band 40 has the shape and size which permit accommodation of the optical unit 300 therein. The hole 41 has concavities 411 and 412 for receiving the projections 311 and 312 when the optical unit 300 is placed in the hole 41 so that undesirable separation is prevented. The sensor securing band 40 has four narrow portions 410 for easily putting the sensor securing band 40 on the finger. In view of the sensor unit 30 being required to enable the fist to be clenched lightly in a state where the same is put on the root of the finger, the width of the sensor securing band 40 may be about 20 mm to 25 mm. As shown in Fig. 2 (c), a structure may be employed in which only a portion of the sensor securing band 40, to which the optical unit 300 is attached, is widened. As the sensor securing member, that is typified by the sensor securing band 40, it may be in the form of a ring-like shape that is put on the finger, as well as in the form of the band type shape that is wound around the finger. An example of the sensor securing member has a hollow and cylindrical shape made of fibre, such as rubber, rendering it resiliently deformable so that it can clamp itself on the finger. The foregoing member has a structure, in which the sensor unit 30 is enclosed in the ring-like shape, in place of the band-like structure according to this embodiment. Therefore, the foregoing sensor securing member is put on the finger in such a manner that it is received by the leading end of the finger, followed by being moved to the root of the finger, instead of being wound around the finger. As the method of securing the sensor unit 30, either of the foregoing sensor securing members may be employed. The hole 41 according to this embodiment so formed in the sensor securing band 40 as to accommodate the sensor unit 30 may be omitted from the structure. That is, the sensor securing member and the sensor unit 30 have independent shapes in the foregoing case. In the foregoing case, the sensor unit 30 is held by the hand when the sensor securing band 40 is wound around the finger. By employing the foregoing method, the shape of the sensor securing band 40 and that of the sensor unit 30 can be simplified so that advantages are obtained in that the manufacturing process can be performed easily and that the cost can be reduced. Structure of Optical Unit In this embodiment, as shown in Fig. 3, an LED 31 irradiates the finger with light, and light reflected by the organism (the blood vessel) is received by a phototransistor 32 so as to detect pulse waves from the blood vessel. Referring to Fig. 3, the optical unit 300 has the outer shape formed by a sensor frame 301 serving as the case body, a reverse cover 302 and a glass plate 304, and a circuit board 305 (Figs. 4 and 5) opposing the glass plate 304. Referring to Figs. 4 to 7, the structure of the optical unit 300 will now be described in detail. Fig. 4 is a plan view of the optical unit 300, Fig. 5 is a cross sectional view taken along line A-A' of Fig. 4, Fig. 6 is a cross sectional view taken along line B-B' of Fig. 4, and Fig. 7 is a cross sectional view taken along line C-C' of Fig. 4. As shown in the foregoing figures, the reverse cover 302 is mounted on the sensor frame 301 serving as the case body of the optical unit 300 so that the internal portion serves as a space for accommodating elements. The reverse cover 302 is secured to the sensor frame 301 with three reverse-cover securing screws 303. The reverse-cover securing screws 303 secure the sensor securing band 40 to the lower surface of the reverse cover 302, while the sensor securing band 40 extends from the optical unit 300 into the two side directions. The cable 20 is extended from the inside portion of the sensor frame 301 in a direction perpendicular to the sensor securing band 40. The glass plate 304 serves as an optical filter and has a light transmissive window on the upper surface of the sensor frame 301. The circuit board 305 is so secured in the sensor frame 301 as to oppose the glass plate 304. Electronic parts, such as an LED 31, a phototransistor 32 (a sensor unit having a filter), a transistor 309, resistors and capacitors (not shown), are mounted on the circuit board 305. The light emitting surface and the light receiving surface of the corresponding LED 31 and the phototransistor 32 are caused to face the glass plate 304. Note that the circuit board 305 is secured to the sensor frame 301 in such a manner that circuit-board securing threads 307 are fastened by two pins 306 inserted from the upper surface of the sensor frame 301. Also an earth plate 308 is secured by the pins 306. This embodiment is characterized in that a blue LED made of InGaN (Indium-Gallium-Nitrogen type) material is employed to serve as the LED 31. The emission spectrum of the LED 31 has the emission peak at 450 nm as shown in Fig. 8, while the emission wavelength region of the same ranges from 350 nm to 600 nm. A GaAsP (Gallium-Arsenic-phosphorus type) phototransistor is employed as the phototransistor 32 because it is suitable for use with the LED 31 having the foregoing light emission characteristics. The light receiving wavelength region of the phototransistor 32 is, as shown in Fig. 9, such that the main sensitive region is in a range from 300 nm to 600 nm and also a sensitive region exists in a region lower than 300 nm. As the phototransistor 32, a sensor unit of a type having an optical filter attached to the device may be employed. An example of the light receiving wavelength region of the sensor unit of this type is, as shown in Fig. 10, the main sensitive region being in a range from 400 nm to 550 nm. Since the LED 31 and the phototransistor 32 consume a relatively small amount of electric power, a long operation time can be realized even if one small-size battery is used, for example, to operate the arm wear type pulse-wave measuring apparatus 1 having the time measuring function and the pulse wave measuring function. Structure of Data Processing Circuit Referring to Fig. 11, the structure of the data processing circuit 50 disposed in the watch case 11 will now be described. Fig. 11 is a block diagram showing the structure of the data processing circuit 50. In the data processing circuit 50, a pulse-wave signal conversion portion 51 converts a signal supplied from the sensor unit 30 through the cable 20 into a digital signal to transmit the digital signal to a pulse-wave storage portion 52. The pulse-wave storage portion 52 is a RAM for storing pulse wave data converted into the digital signal. A pulse-wave signal calculating portion 53 reads the signal stored in the pulse-wave storage portion 52 to analyze the frequency of the signal so as to transmit results of the analysis to a pulse-wave component extraction portion 54. The pulse-wave component extraction portion 54 extracts the pulse wave component from the signal supplied from the pulse-wave signal calculating portion 53 to transmit the extracted component to a pulse-rate calculating portion 55. The pulse-rate calculating portion 55 calculates the pulse rate in accordance with the frequency component of the supplied pulse waves to transmit results of the calculation to the liquid crystal display unit 13. The operation of the thus-constituted arm wear type pulse-wave measuring apparatus 1 will now be described briefly with reference to Figs. 1, 3 and 11. Referring to Fig. 1, when the arm wear type pulse-wave measuring apparatus 1 is used as a normal wristwatch, the apparatus body 10 is put on the arm by means of the wrist band 12 in a state where the cable 20 and the sensor unit 30 are removed from the connector portion 70 of the apparatus body 10. In a case where the arm wear type pulse-wave measuring apparatus 1 is used to measure information about pulse waves, such as the pulse rate, during exercise, such as jogging or running, the cable 20 is connected to the connector portion 70 of the apparatus body 10, and then the apparatus body 10 is put on the arm by means of the wrist band 12. After the sensor unit 30 (the glass plate 304 of the optical unit 300) has been brought into close contact with the finger by the sensor securing band 40, exercise, such as jogging or running, is performed. In the foregoing state, when the LED 31 emits light to the finger as schematically shown in Fig. 3, light reaches the blood vessel, and a portion of light is absorbed by the hemoglobin in the blood. Another portion of light is reflected by the hemoglobin. Light reflected by the finger (the blood vessel) is received by the phototransistor 32; thus the change in the quantity of received light corresponds to change in the quantity of blood occurring due to pulse waves of the blood. That is, if the quantity of blood is large, the reflected light is weakened. If the quantity of blood is small, the reflected light is strengthened. Therefore, observation of the change in the intensity of the reflected light performed by the phototransistor 32 enables the pulse waves or the like to be detected. To perform the foregoing detection, the data processing circuit 50 shown in Fig. 11 converts the signal supplied from the phototransistor 32 (the sensor unit 30) into a digital signal to analyze the frequency of the digital signal to calculate the pulse rate. The pulse rate obtained due to the calculation is displayed on the liquid crystal display unit 13. That is, the arm wear type pulse-wave measuring apparatus 1 serves as a pulsimeter. Referring back to Fig. 3, a portion of light emitted by the LED 31 is allowed to pass through the finger to reach the blood vessel 500 as indicated by an arrow C. Thus, reflected light from the hemoglobin in the blood reaches the phototransistor 32, as indicated by an arrow D. The quantity of light received through the foregoing route is the quantity of light reflected by the organism. A portion of light emitted by the LED 31 is reflected by the surface of the finger as indicated by an arrow E to reach the phototransistor 32. The quantity of light received through the foregoing route is the quantity of light reflected by the skin. A portion of light emitted by the LED 31 and that reflected by the blood vessel are absorbed or dispersed in the finger, as indicated by arrows F and G, so that the portions of the light do not reach the phototransistor 32. To detect the pulse waves, results of detection performed in the wavelength region from 350 nm to 600 nm is, in this embodiment, used in place of infrared rays as have been employed in the conventional structure to display information about an organism. That is, the sensor unit 30 comprises the LED 31, the light emission wavelength region of which is in the range from 350 nm to 600 nm; and the phototransistor 32, the main light receiving wavelength region of which is in the range from 300 nm to 600 nm. In accordance with results of detection in the wavelength region from 350 nm to 600 nm, in which the foregoing two regions overlap, information about the organism is displayed. By using the foregoing sensor unit 30, light included in external light, the wavelength region of which is shorter than 700 nm, does not reach the phototransistor 32 (the light receiving portion) through the finger serving as a phototransistor, as described later. On the other hand, light, the wavelength of which is shorter than 300 nm, is substantially absorbed by the surface of the skin. Therefore, the results of the detection are not affected by external light. Thus, in accordance with the results of the detection in the wavelength region from 300 nm to 700 nm obtained due to only light from the light emitting portion, information about an organism can be measured. In view of obtaining information about pulse waves without influence of external light, the LED 31 may be an LED having the light emission wavelength region of 300 nm to 700 nm and the phototransistor 32 may be a phototransistor having the light receiving wavelength region of 700 nm or shorter. Effect of the Embodiment As described above, the arm wear type pulse-wave measuring apparatus 1 according to this embodiment comprises the LED 31 having the light emission wavelength region of 350 nm to 600 nm, and the phototransistor 32 having the main sensitive region of the light receiving wavelength region of 300 nm to 600 nm. When the phototransistor 32 is a unit formed by combining the device and the filter, the light receiving wavelength region is in a range from 400 nm to 550 nm. Therefore, if the pulse waves are measured in the simple light shielding state shown in Fig. 1, light included in external light that has the wavelength region of 700 nm or shorter does not reach the phototransistor 32 (the light receiving portion) through the finger serving as the photoconductor. Only light having a wavelength region that does not affect the detection passes through the finger serving as the photoconductor. Therefore, in this embodiment, if the exposed portion of the finger is irradiated with external light, results of detection of pulse waves are not affected by external light. As a result, the sensor unit 30 having the detection portion that is light-shielded by the narrow sensor securing band 40 can be employed. Thus, the small sensor unit 30 according to this embodiment enables the user to lightly clench the fist with the same put on the root of the finger thereof so that no problem arises during exercise, such as jogging, running or cycling. Since the cable 20 can be shortened if the sensor unit 30 is put on the root of the finger, the cable 20 is not obstructive during exercise, such as jogging. Therefore, the arm wear type pulse-wave measuring apparatus 1 according to this embodiment is suitable to measure the pulse rate during exercise, such as jogging. With regard to the distribution of temperature from the palm to the fingertip, the temperature of the fingertip is lowered considerably when the ambient temperature is low, whereas the temperature of the root of the finger is lowered much less, or not at all. That is, the bloodstream is not lowered considerably at the root of the finger. Thus, if the sensor unit is put on the root of the finger, the information about an organism, such as the pulse rate, can accurately be measured if the user performs exercise outdoors, such as running, in a cold day. Since the information about pulse waves is obtained by using light having the wavelength region from about 300 nm to about 700 nm, the S/N ratio of the pulse wave signal in accordance with the change in the quantity of the blood is high. The reason for this will be described later. First, the reason why the influence of external light can be eliminated satisfactorily will now be described with reference to Fig. 12 (a). Fig. 12 (a) shows the relationship between the wavelength of light and light transmittance of the skin. Polygonal line a indicates transmission characteristic with respect to light having a wavelength of 200 nm, polygonal line b indicates transmission characteristic with respect to light having a wavelength of 300 nm, polygonal line c indicates transmission characteristic with respect to light having a wavelength of 500 nm, polygonal line d indicates transmission characteristic with respect to light having a wavelength of 700 nm and polygonal line e indicates transmission characteristic with respect to light having a wavelength of 1 µm. As can be understood from Fig. 12 (a), light included in external light that has a wavelength of 700 nm or shorter does not easily penetrate the finger. Therefore, if the portion of the finger that is not covered with the sensor securing band 40 is irradiated with external light, external light does not reach the phototransistor 32 through the finger as indicated by dashed line X shown in Fig. 3. Thus, if light having the wavelength of 700 nm or shorter is used as detection light, influence of external light can be prevented by covering only the minimum area of the finger in place of covering the finger over a large area. As a result, the arm wear type pulse-wave measuring apparatus 1 according to this embodiment can be used outdoors. Since a major portion of light in a wavelength region lower than 300 nm is absorbed in the surface of the skin, the substantial light receiving wavelength region is 300 nm to 700 nm even if the light receiving wavelength region is made to be 700 nm or shorter. In contrast, if an LED having a light emission peak in a region adjacent to 880 nm, which is in the infrared region, and a silicon type phototransistor are used as have been employed in the conventional structure, the light receiving wavelength region is 350 nm to 1200 nm, as shown in Fig. 13. Therefore, since the conventional optical system (the detection unit) detects pulse waves in accordance with results of detection by means of light included in external light that has a wavelength of 1 µm that easily reaches the light receiving portion through the finger serving as the photoconductor as indicated by arrow Y shown in Fig. 3, that is, light indicated by polygonal line e of Fig. 12 (a), erroneous detection easily takes place due to change in external light. The reason why the pulse-wave measuring apparatus 1 according to this embodiment causes high S/N ratio of the pulse wave signal to be obtained will now be described with reference to Fig. 12 (b). Fig. 12 (b) is a graph of explanatory showing the relationship between wavelengths of light and light absorption characteristics of a variety of hemoglobin. Fig. 12 (b) shows, with curve Hb, the light absorption characteristics of hemoglobin that has not been bonded with oxygen and light absorption characteristics of hemoglobin that has been bonded with oxygen with curve HbO 2 . As indicated by the foregoing curves, hemoglobin in the blood has a large light absorption factor with respect to light having a wavelength of 300 nm to 700 nm, the light absorption factor being several times to about 100 times the light absorption factor with respect to light having the wavelength of 880 nm which is the conventional detection light. Therefore, if light having a wavelength region (300 nm to 700 nm) having a large light absorption factor is used as detection light to be adaptable to the light absorption factor of hemoglobin as is employed in this embodiment, the detection values change in accordance with the change in the quantity of blood, with excellent sensitivity attained. Therefore, a high detection ratio (the S/N ratio) of the pulse waves in accordance with change in the quantity of blood can be obtained. Quantity of Introduction of External Light Depending Upon the Light Shielding Condition To evaluate the arm wear type pulse-wave measuring apparatus 1 according to this embodiment, only the quantity of introduction of external light was measured in such a manner that the light shielding range with respect to the finger was changed from condition 1 to condition 5 as shown in Figs. 14 (a) to 14 (e) so as to be subjected to a comparison with that realized in the conventional pulse-wave measuring apparatus (comparative examples). As the pulse-wave measuring apparatus 1 according to this embodiment, sample 1 comprising the phototransistor 32 having the light receiving sensitivity of 400 nm to 600 nm and sample 2 comprising the phototransistor 32 having the light receiving sensitivity of 300 nm to 700 nm were evaluated. As the comparative examples, samples 3, 4 and 5 were evaluated that had the light receiving sensitivities which exceeds the range of 300 nm to 700 nm. Note that condition 1 was a state where the root of the finger was covered with the light shielding cover having a width of 10 mm as shown in Fig. 14 (a), condition 2 was a state where the root of the finger was covered with the light shielding cover having a width of 20 mm as shown in Fig. 14 (b), condition 3 was a state where the root of the finger was covered with the light shielding cover having a width of 40 mm as shown in Fig. 14 (c), condition 4 was a state where the root of the finger was covered with the light shielding cover having a width of 70 mm as shown in Fig. 14 (d), and condition 5 is a state where the overall body of the forefinger, the root of the thumb, the root of the middle finger and portions adjacent to the roots of all fingers were covered with a light shielding cover. Results of measurement of the quantity of introduction of external light under the foregoing conditions were shown in Table 1. The quantities of introduced external light were represented by output currents (unit: µA) from the phototransistor. Samples Structure of Sensors According to Examples Structure of Sensors According to Comparative Examples Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Light Receiving Wavelength Region 400nm to 600nm 300nm to 700nm 300nm to 1000nm 300nm to 750nm 300nm to 800nm Light Shielding Conditions Condition 1 0.006 0.008 55.3 18.3 30.4 Condition 2 0.005 0.007 46.4 12.2 25.2 Condition 3 0 0.001 30.2 7.8 17.3 Condition 4 0 0 5.1 2.2 4.4 Condition 5 0 0 0.008 0.002 0.004 As shown in Table 1, the pulse-wave measuring apparatus 1 according to this embodiment (samples 1 and 2) receives light in the wavelength region from 300 nm to 700 nm so that influence of external light can be ignored under any of the foregoing conditions. The reason for this is that light included in external light that has the wavelength region of 700 nm or shorter does not reach the phototransistor 32 (the light receiving portion) through the finger serving as the photoconductor. Therefore, the pulse-wave measuring apparatus 1 according to this embodiment requires the finger to be covered with the sensor unit 30 or the sensor securing band 40 (the light shielding cover) only by a width of 10 mm. On the other hand, the pulse-wave measuring apparatus according to the comparative examples (samples 3, 4 and 5) are able to ignore the influence of external light only in the state (condition 5) where the finger is covered widely such that the overall body of the forefinger, the root of the thumb, the root of the middle finger and portions adjacent to the roots of all fingers were covered with a light shielding cover. Thus, a large-scale light shielding structure is required. Influence of External Light Upon the Environment The pulse-wave measuring apparatus 1 according to this embodiment comprising the LED 31 (the blue light source) having the light emission wavelength peak of 450 nm; and the GaAsP type phototransistor 32 having the light receiving wavelength region of 300 nm to 600 nm; and the pulse-wave measuring apparatus (the comparative example) comprising the LED having the light emission wavelength peak of 880 nm and the phototransistor having the light receiving wavelength region of 350 nm to 1200 nm were used to compare and investigate the degree of influence of external light. Results were shown in Figs. 15 and 16. Data shown in Figs. 15 and 16 were results of analysis of the frequency to be used as the results of the detection of pulse waves. Among a multiplicity of peaks, peaks each given an arrow correspond to the frequency of the pulse waves. Fig. 15 (a) shows results of measurement of pulse waves when a user having the arm wear type pulse-wave measuring apparatus according to this embodiment runs in a dark room. Fig. 15 (b) shows results of measurement of pulse waves when the user having the arm wear type pulse-wave measuring apparatus according to this embodiment runs in a direction toward sunlight. Fig. 15 (c) shows results of measurement of pulse waves when the user having the arm wear type pulse-wave measuring apparatus according to this embodiment runs in a multiplicity of directions such that the relative direction of sunlight varied. In any of the conditions shown in the foregoing figures, the peaks of the pulse waves, each of which is indicated by an arrow, is clear as compared with other peaks. Thus, it can be understood that the arm wear type pulse-wave measuring apparatus 1 according to this embodiment cannot easily be affected by external light. Fig. 16 (a) shows results of measurement of pulse waves when the user having the conventional arm wear type pulse-wave measuring apparatus 510 run in a dark room. Fig. 16 (b) shows results of measurement of pulse waves when the user having the conventional arm wear type pulse-wave measuring apparatus run in a direction toward the sunlight. Fig. 16 (c) shows results of measurement of pulse waves when the user having conventional the arm wear type pulse-wave measuring apparatus runs in a multiplicity of directions such that the relative direction of sunlight varied. As shown in the figures above, the conventional pulse-wave measuring apparatus is able to measure the pulse waves only in the dark room, and the measurement cannot be performed under conditions where external light exists. Relative Sensitivity of Pulse Wave Signal The arm wear type pulse-wave measuring apparatus 1 according to this embodiment and the conventional pulse-wave measuring apparatus (the comparative example) were used to compare and investigate the pulse wave signal level (µA), the overall level of reflected light (µA) and the ratio of the pulse wave signal included in reflected light, results being shown in Table 2. As the pulse-wave measuring apparatus 1 according to this embodiment, sample 6 comprising the LED 31 (that emits blue light) having the light emission wavelength region of 420 nm to 480 nm; and sample 7 comprising the LED 31 (that emits green light) having the light emission wavelength region of 540 nm to 570 nm were evaluated. Sample 7 comprised the GaP type LED 31 that emits green light. The GaP type LED 31 had the light emission spectrum as shown in Fig. 17 such that the main light emission region was in a range from 540 nm to 570 nm and the overall light emission region was in a range from 520 nm to 600 nm. Sample 7 comprising the foregoing GaP type LED 31 comprised the GaP type phototransistor 32 to be adaptable to the light emission characteristics of the LED 31. The GaP type phototransistor 32 had the light receiving sensitivity such that the sensitive region existed in a range from 200 nm to near 700 nm, as shown in Fig. 18. As comparative examples, samples 8, 9 and 10 each having the light emission wavelength region that was out of the range from 300 nm to 700 nm were evaluated. Table 2 showed results of the evaluation. Samples Structure of Sensors According to Examples Structure of Sensors According to Comparative Examples Sample 6 Sample 7 Sample 8 Sample 9 Sample 10 Light Emission Wavelength Region 420nm to 480nm 540nm to 570nm 800nm to 850nm 850nm to 900nm 900nm to 970nm Level of Pulse Wave Signal (µA) 0.12 0.10 0.04 0.07 0.06 Level of Reflected light (µA) 6.32 7.42 29.4 36.2 31.1 Ratio of Pulse Wave Signal in Reflected Light 0.019 0.013 0.0014 0.0019 0.0019 As shown in Table 2, the arm wear type pulse-wave measuring apparatus 1 (samples 6 and 7) according to this embodiment uses light having the light emission wavelength region of 300 nm to 700 nm to be adaptable to the wavelength region in which the light absorption factor of hemoglobin in the blood is large. Therefore, high ratios of pulse wave signals included in reflected light of 0.019 and 0.013 are attained; that is, excellent sensitivity can be obtained. As contrasted with this, the pulse-wave measuring apparatuses according to the comparative examples (samples 8, 9 and 10) has low ratios of the pulse wave signals included in reflected light of less than 0.002; that is, the sensitivity is unsatisfactory. Namely, the sensitivity of the arm wear type pulse-wave measuring apparatus 1 according to this embodiment provides a significant improvement over the prior art such that the S/N ratio of the pulse wave signal can be raised to about 10 times that of the conventional structure. Influence of Skin Colour Results of investigation that the advantage of the significant sensitivity of the arm wear type pulse-wave measuring apparatus 1 according to this embodiment is not affected by the skin colour are shown in Table 3. The evaluation was performed by using the arm wear type pulse-wave measuring apparatus 1 (sample 11) comprising the LED (the blue light source) having the light emission wavelength peak of 450 nm that could not easily be reflected by the surface of the skin; and the conventional pulse-wave measuring apparatus (comparative example and sample 12) comprising the LED having the light emission wavelength peak of 880 nm that could easily be reflected by the surface of the skin. The pulse waves of the "yellow-skinned" races, "white" races and the "black" races were measured to calculate the quantity of reflection of light from the skins, the quantity of reflection of light from the organisms (the quantity of light from the blood vessels) and pulse wave components. Skin Type "Yellow" "White" "Black" Example Comparative Example Example Comparative Example Example Comparative Example Sample Sample 11 Sample 12 Sample 11 Sample 12 Sample 11 Sample 12 Wavelength of LED (nm) 450 880 450 880 450 880 Quantity of Irradiation with Light from LED (µA) 100 100 100 100 100 100 Quantity of Reflection from Skin (1) (µA) 14.0 35.0 28.0 35.0 9.3 21.0 Quantity of Reflection from Organism (2) (µA) 15.9 24.5 19.6 24.5 8.4 29.4 Pulse Component (µA) 0.31 0.01 0.39 0.01 0.17 0.02 Total Quantity of Received Light (1+2)(µA) 29.9 59.5 47.6 59.5 17.7 50.4 As a result, as shown in Table 3, a fact was confirmed that the ratio of the pulse wave components with respect to the overall quantity of received light was high, that is, the measuring sensitivity with respect to information about the organism was excellent where the subjects had yellow, white or black skin types. Other Embodiments The sensor unit according to the present invention can be put on another finger (the thumb, the middle finger, the ring finger or the little finger) as well as on the forefinger. If the sensor unit is put on any finger, the user is able to lightly clench the fist with the sensor unit put on the finger. Therefore, the user is able to select the finger on which the sensor unit is put as desired. As the means for transmitting the result of receipt of light (the signal) from the light receiving portion of the sensor unit to the body of the pulse-wave measuring apparatus, a wireless method may be employed in place of the wired method typified by the cable 20 according to the foregoing embodiment. That is, a transmission circuit is included in the sensor unit or the sensor securing band or the like, on which the sensor unit is mounted; and a receiving circuit is included in the body of the apparatus. In the case of the arm wear type pulse-wave measuring apparatus according to the present invention, the distance from the transmitting portion (the root of the finger) to the receiving portion (arm) is very short so that only a very weak output of electric waves is required. Therefore, a very small transmission circuit/receiving circuit can be formed. A portion or the overall body of the sensor securing band may be used as an antenna of the transmission circuit. Information about an organism other than the pulse waves is exemplified as follows. Since the light absorption characteristics of hemoglobin in the blood is, as shown in Fig. 12 (b), different between hemoglobin that has not been bonded with oxygen and hemoglobin that has been bonded with hemoglobin, use of light having the wavelength from 300 nm to 700 nm, for example, about 470 nm, as detection light enables the quantity of each hemoglobin and the total quantity of hemoglobin to be measured as information about an organism in accordance with the intensity of the detection light. Furthermore, the difference in the light absorption characteristics between the skin and water can be used to measure water contained in the skin as information about an organism. As described above, the arm wear type pulse-wave measuring apparatus (the organism information measuring apparatus) according to the present invention is characterized in that the fingertip or the like is irradiated with light by the light emitting portion, such as the LED; reflected light from the blood or the like is detected by the light receiving portion, such as the transistor; information about an organism is measured in accordance with results of detection in the wavelength region from 300 nm to 700 nm obtained by the foregoing detection means. When the detection in the foregoing wavelength region is performed, determination of the wavelength region of the light emitting portion to be at least in the range from 300 nm to 700 nm and the light receiving wavelength region to be 700 nm or shorter causes light included in external light that has the wavelength region of 700 nm or shorter not to reach the light receiving portion through the finger serving as the photoconductor. On the other hand, light in the wavelength region shorter than 300 nm is substantially completely absorbed by the surface of the skin. Therefore, the results of the detection is not affected by external light, and information about an organism can be measured in accordance with the result of detection in the wavelength region from 300 nm to 700 nm according to only light from the light emitting portion. Thus, if external light is not directly made incident on the detection portion, erroneous detection of pulse waves occurring due to external light can be prevented. Thus, a large-scale light shielding structure is not required. Therefore, the size of the sensor unit can be reduced to the size that enables the sensor unit to be put on the root of the finger. The foregoing small sensor unit enables the user to lightly clench the fist with the sensor unit put on, whereby no problem arises to perform exercise, such as jogging, running or cycling. As a result, the foregoing sensor unit is suitable when the pulse rate or the like is measured during exercise, such as jogging. Since the bloodstream is not relatively reduced in the root of the finger, the sensor unit put on the root of the finger enables the pulse rate or the like to be measured accurately even if a user performs exercise on a cold day. Hemoglobin in the blood has a light absorption factor with respect to light having the wavelength region in a range from 300 nm to 700 nm that is considerably larger than the light absorption factor with respect to infrared rays. When light, the wavelength region of which is in the range from 300 nm to 700 nm, is applied toward an organism to be adaptable to the light absorption characteristic of hemoglobin, the intensity of light reflected by the organism (the blood vessel) is considerably changed to follow the change in the quantity of blood. As a result, the S/N ratio of the pulse wave signal can be raised so that an effect is obtained with the arm wear type pulse-wave measuring apparatus according to the present invention in that excellent sensitivity can be attained in measuring the pulse waves. By employing the InGaN (Indium-Gallium-Nitrogen) type blue LED as the light emitting portion and by employing the GaAsP (Gallium-Arsenic-phosphorus) type phototransistor as the light receiving portion, excellent measuring sensitivity can be attained and the electric current consumption can be reduced so that, advantageously, measurement for a long time period is possible. Thus, the structure of the present invention is suitable to form a portable pulse-wave measuring apparatus (organism information measuring apparatus) of an arm wear type, the power source of which is limited. Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form can be changed in the details of construction and the combination and arrangement of parts may be resorted to without departing from the scope of the invention as hereinafter claimed.

Claims: An organism information measuring apparatus comprising: a light emitting means (31) for irradiating a portion of an organism of a person with light; a detection means having a light receiving means (32) for receiving light emitted by the light emitting means and reflected by the portion of the organism; characterised in that said light receiving means (32) is arranged to detect only light having a wavelength of substantially 700 nm or less, such that the measuring apparatus can be arranged to provide information about the organism on the basis of light transmitted from the light emitting means (31) and reflected by the portion of the organism but not to provide information arising from external light incident on the person and having a wavelength of substantially 700nm or more which is able to propagate through skin tissue of the person to the light receiving means (32). Measuring apparatus according to claim 1, wherein said light emitting means (31) has a light emitting wavelength region at least in a range from substantially 300 nm to substantially 700 nm. Measuring apparatus according to claim 1 or 2 characterised by an organism information display portion for displaying information about the organism on the basis of light detected by the receiving means (32). Measuring apparatus according to any one of claims 1 to 3 characterised in that the measuring apparatus is arranged to be worn on an arm of a person and comprises; a sensor unit (30) including the light emitting means (31) and the light receiving means (32), securing means (40) for securing said sensor unit (30) in such a manner that a light receiving surface of said light receiving means (32) and a light emitting surface of said light emitting means (31) face the surface of a finger of the person; a body portion (10) having a display portion (13) for displaying information about pulse waves of the person obtained in accordance with results of receipt of light performed by said light receiving means (32); a wrist band (12) for securing said body portion (10) on the arm of the person; a signal transmission portion (20) which extends from said sensor unit (30) to said body portion (10) and through which a signal representative of the light received by said light receiving means (32) is input to said body portion (10); wherein said information about pulse waves is displayed on the basis of light detected by the receiving means (32), the light having a wavelength from about 300 nm to substantially 700 nm; and said sensor unit (30) has a size such that said sensor unit may be mounted on the root of the finger of the person. Measuring apparatus according to any one of the preceding claims, wherein a Light Emitting Diode is employed as said light emitting means (31), said Light Emitting Diode having a main light emitting wavelength region in a range from 350 nm to 600 nm. Measuring apparatus according to claim 5, wherein an Indium-Gallium-Nitrogen type blue Light Emitting Diode is employed as said light emitting means (31). Measuring apparatus according to any one of the preceding claims, wherein a Gallium-Arsenic-phosphorus type phototransistor is employed as said light receiving means (32). A method of measuring the pulse rate of a person, including irradiating a portion of an organism of the person with light from a light emitting means (31) and detecting the light by a detection means having a light receiving means (32), characterised in that only light having a wavelength of 700nm or less is detected such that the pulse rate can be measured on the basis of the light from the light emitting means and not on the basis of external light incident on the person and having a wavelength of substantially 700nm or more which is able to propagate through skin tissue of the person to the light receiving means.

Inventors: HONDA KATSUYUKI, KAWATA MASAYUKI, KONDO YUTAKA, HONDA, KATSUYUKI, KAWATA, MASAYUKI, KONDO, YUTAKA
Applicants: SEIKO EPSON CORP, SEIKO INSTR INC, SEIKO EPSON CORPORATION, SEIKO INSTRUMENTS INC.
Application year: 1995
Main classification: A61B5
IPC codes: A61B5