as) United States
`a2) Patent Application Publication 0) Pub. No.: US 2002/0188210 Al
`
` Aizawa (43) Pub. Date: Dec. 12, 2002
`
`
`US 20020188210A1
`
`(54) PULSE WAVE SENSOR AND PULSE RATE
`DETECTOR
`
`Publication Classification
`
`(76)
`
`Inventor: Nobuyuki Aizawa, Gunma (JP)
`
`Tint. C7 eeeeeeccceccceeeeeeseeenneeeeceesnnesecenneeeee A61B 5/02
`(SV)
`(52) US. C1 ceeeccccssseeeeesseesnnnneeesseesnnnnees 600/503; 600/502
`
`Correspondence Address:
`KANESAKA & TAKEUCHI
`1423 Powhatan Street
`Alexandria, VA 22314 (US)
`(21) Appl. No.:
`10/152,818
`
`(22)
`
`Filed:
`
`May23, 2002
`
`(30)
`
`Foreign Application Priority Data
`
`Jun. 11, 2001
`
`(TP) sssssssssssesscnssnsensesne 2001-175909
`
`(57)
`
`ABSTRACT
`
`Apulse wave sensor for detecting a pulse wave by detecting
`light output from a light emitting diode and reflected from
`the artery of a wrist of a subject, the sensor comprising four
`photodetectors disposed around the light emitting diode
`symmetrically on a circle concentric to the light emitting
`diode, and a pulse rate detector comprising the pulse wave
`sensor and means of computing the pulse rate of a subject
`based on the output of the pulse wave sensor.
`
`APPLE 1006
`
` 1
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`APPLE 1006
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`1
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`

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`Patent Application Publication Dec. 12,2002 Sheet 1 of 3
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`US 2002/0188210 Al
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`FIG.
`
`1 (a)
`
`1
`
`
`FIG.
`
`1 (b)
`
`2
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`

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`Patent Application Publication Dec. 12,2002 Sheet 2 of 3
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`US 2002/0188210 Al
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`2 F
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`IG. 3
`
`FIG.
`
`
`
`3
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`

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`Patent Application Publication Dec. 12,2002 Sheet 3 of 3
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`US 2002/0188210 Al
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`FIG. 4 (a)
`
`FIG. 4 (b)
`
`
`
`4
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`

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`US 2002/0188210 Al
`
`Dec. 12, 2002
`
`PULSE WAVE SENSOR AND PULSE RATE
`DETECTOR
`
`BACKGROUND OF THE INVENTION
`
`[0001]
`
`1. Field of the Invention
`
`invention relates to a pulse wave
`[0002] The present
`sensor for detecting the pulse wave of a subject from light
`reflected from a red corpuscle in the artery of a wrist of the
`subject by irradiating the artery of the wrist with light having
`a wavelength of an infrared range and to a pulse rate detector
`for detecting the pulse rate of the subject from the above
`pulse wave data.
`
`[0003]
`
`2. Description of the Prior Art
`
`Inrecent years, along with shift to the aging society
`[0004]
`and westernized eating habits, an increase in the numberof
`diseases caused bylife habits, such as hyperpiesia, diabetes
`mellitus, heart diseases and cerebrovascular diseases of the
`brain is becoming a big social problem. As means of
`preventing these diseasesor treating the diseases, a personal
`exercise cure such as walking is widely adopted. In this
`exercise cure, a pedometer or kinetic calorimeter is carried
`to know the quantity of motion. There has recently been
`proposed a method of estimating a burden on the heart of a
`person who takes exercise by real-time measuring his/her
`heart rate at the time of exercise.
`
`[0009] Accordingto a first aspect of the present invention,
`there is provided a pulse wave sensor for detecting a pulse
`wave by detecting light output from a light emitting diode
`and reflected from the artery of a wrist of a subject, the
`sensor comprising at least
`three photodetectors disposed
`aroundthe light emitting diode and not linearly. Even when
`the attachment position of the sensoris dislocated, a pulse
`wave can be detected accurately.
`
`[0010] According to a second aspect of the present inven-
`tion, there is provided a pulse sensor, wherein a near infrared
`LED which is a general-purpose product is used as the light
`emitting diode. This makes it possible to produce an inex-
`pensive sensor.
`
`[0011] According to a third aspect of the present inven-
`tion, there is provided a pulse sensor, wherein the photode-
`tectors are disposed at an equal distance from the light
`emitting diode.
`
`[0012] According to a fourth aspect of the present inven-
`tion, there is provided a pulse sensor, wherein cavities are
`formed in a contact face between a holder for holding the
`light emitting diode and the photodetectors and the wrist, the
`light emitting face of the light emitting diode and the light
`receiving faces of the photodetectors are disposed at respec-
`tive predetermined distances from the contact face, and the
`sectional forms of the cavities are tapered such that their
`widths increase toward the contact face. Since this makesit
`
`[0005] For the measurement of the above heart rate, an
`optical pulse wave sensor for detecting the pulse wave of a
`subject from reflected lightor transmitted light by irradiating
`[0013] Accordingtoafifth aspect of the present invention,
`the site of a blood vessel with light having an infrared or near
`there is provided a pulse sensor, wherein a transparent
`infrared range is widely used. Stated more specifically, a
`plate-like memberis provided on a portion includingat least
`pulse wave sensor which comprises a pair of an LED (light
`the light emitting face and the light receiving faces of the
`emitting diode) and a phototransistor (photodetector) is
`contact face. This makes it possible to improve adhesion
`attached to a finger or ear to measure the heart rate by
`between the sensor and the wrist and thereby further
`calculating the cycle (frequency) of pulse waves from the
`improve the detection efficiency of pulse waves.
`waveform ofreflected light or transmitted light detected by
`the above photodetector.
`
`possible to expand the light emitting area and the light
`receiving area, a pulse wave can be easily detected even
`when the attachment position of the sensor is dislocated.
`
`[0006] However, although the conventional pulse wave
`sensor to be attached to the finger or ear is small in size, a
`signal from the sensor is weak becauseit detects the motion
`of a red corpuscle in the capillary and is easily affected by
`noise caused by the shaking of the body of the subject. Also,
`as some pressure is applied to the measurementsite at the
`time of detection, the subject cannot carry the detector for a
`long time when walking or the like.
`
`[0007] Meanwhile, since a strong signal is obtained when
`the motion of a red corpuscle in the artery is detected, a
`detector to be attached to a wrist or arm is conceivable. As
`understood when the pulse of the wrist is actually taken, it
`is difficult to attach the sensor to a predetermined position.
`Whenthe attachmentposition is dislocated, no output can be
`obtained, thereby makingit difficult to implement the detec-
`tor.
`
`SUMMARYOF THE INVENTION
`
`It is an object of the present invention which has
`[0008]
`been made in view of the above problem to provide a pulse
`wave sensor which is easily attached and is capable of
`detecting a pulse wave accurately and a pulse rate detector
`comprising this pulse wave sensor.
`
`[0014] According to a sixth aspect of the present inven-
`tion, there is provided a pulse rate detector comprising the
`pulse wave sensor of claim 1 and means of computing the
`pulse rate of a subject based on the output of the pulse wave
`sensor.
`
`[0015] According to a seventh aspect of the present inven-
`tion, there is provided a pulse rate detector which comprises
`a transmitter for transmitting the measured pulserate data to
`a display for displaying the pulse rate data and a device for
`computing the amount of motion load from the pulse rate.
`
`[0016] The above and other objects, advantages and fea-
`tures of the present invention will become apparent from the
`following description when taken in conjunction with the
`accompanying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0017] FIGS. 1 are schematic diagrams of a pulse rate
`detector according to an embodiment of the present inven-
`tion;
`
`[0018] FIG. 2 is a diagram showing that the pulse rate
`detector is attached.
`
`[0019] FIG. 3 is a schematic diagram of a pulse wave
`which is the output of a photodetector;
`5
`
`5
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`

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`US 2002/0188210 Al
`
`Dec. 12, 2002
`
`FIGS. 4 are diagrams showing other arrangements
`[0020]
`of a light emitting diode and photodetectors according to the
`present invention; and
`
`[0021] FIG. 5 is a diagram showing a pulse rate detector
`according to another embodimentof the present invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`[0022] Preferred embodiments of the present invention
`will be described hereinbelow with reference to the accom-
`
`panying drawings.
`
`[0023] FIGS. 1(a@) and 1(6) are schematic diagrams of a
`pulse rate detector according to an embodiment of the
`present invention. FIG. 1(a) is a plan view and FIG.1(6)is
`a sectional view of the pulse rate detector whenit is attached.
`In these figures, reference numeral 2 denotes a pulse wave
`sensor which comprises an LED 21 (to be referred to as
`“light emitting diode” hereinafter) for emitting light having
`a wavelength of a near infrared range, four phototransistors
`22 (to be referred to as “photodetectors” hereinafter) dis-
`posed around the light emitting diode 21 symmetrically on
`a circle concentric to the light emitting diode 21, a holder 23
`for storing the above light emitting diode 21 and the pho-
`todetectors 22, and a drive detection circuit 24 for detecting
`a pulse wave by amplifying the outputs of the photodetectors
`22,3 is an arithmetic circuit for computing a pulse rate from
`the detected pulse wave data, 4 a transmitter for transmitting
`the above pulse rate data to an unshowndisplay, 5 an outer
`casing for storing the above pulse wave sensor 2,
`the
`arithmetic circuit 3 and the transmitter 4, 6 an acrylic
`transparent plate mounted to the detection face 23a of the
`holder 23 to be described hereinafter, and 7 an attachment
`belt attached to the above outer casing.
`
`[0024] The above light emitting diode 21 and the above
`photodetectors 22 are stored in cavities 23b and 23c formed
`in the detection face 23a whichis a contact side between the
`
`holder 23 and a wrist 10, respectively, at positions where the
`light emitting face 21s of the light emitting diode 21 and the
`light receiving faces 22s of the photodetectors 22 are set
`back from the above detection face 23a. In this embodiment,
`to expandthe light emitting area of the light emitting diode
`21 andthe light receiving areas of the photodetectors 22, the
`sectional formsof the above cavities 23b and 23¢are tapered
`such that their widths increase toward the contact face.
`
`[0025] Adescription is subsequently given of the method
`of measuring a pulse rate.
`
`[0026] As shown in FIG. 2, a subject carries the above
`pulse rate detector 1 on the innerside of his/her wrist 10 with
`a belt in such a mannerthat the light emitting face 21s of the
`light emitting diode 21 faces down(onthe wrist 10 side). As
`shownin FIG.1(b), the abovebelt 7 is fastened such that the
`acrylic transparent plate 6 becomesclose to the artery 11 of
`the wrist 10. Thereby, adhesion between the wrist 10 and the
`pulse rate detector 1 is improved. When the pulse rate
`detector 1 is attached to the wrist 10 with the belt 7, pulse
`wave data can be detected at the same pressure as that for
`attaching a wrist watch with a belt. Therefore, the wrist 10
`is not pressed hard, thereby makingit possible to carry it for
`a long time.
`
`[0027] Near infrared radiation output toward the wrist 10
`from the light emitting diode 21 is reflected by a red
`
`corpuscle running through the artery 11 of the wrist 10 and
`this reflected light is detected by the plurality of photode-
`tectors 22 so as to detect a pulse wave (see FIG. 1(5)). Since
`four photodetectors 22 are disposed around the light emit-
`ting diode 21 on a circle concentric to the light emitting
`diode 21 in this embodiment, even when the attachment
`position of the pulse rate detector 1 is dislocated, one of the
`photodetectors 22 is located near the artery 11,
`thereby
`making it possible to detect a pulse wave accurately. If the
`plurality of photodetectors 22 are disposedlinearly, all of the
`photodetectors 22 may be far from the artery 11. Therefore,
`it is desired that the photodetectors 22 should not be dis-
`posed linearly.
`[0028] FIG. 3 schematically shows the waveform of a
`pulse wave which is the output of the above photodetector
`22. The detected pulse wave data is amplified by the drive
`detection circuit 24 and the amplified pulse wave data is
`transmitted to the arithmetic circuit 3. The arithmetic circuit
`3 has a threshold value and computes the numberof outputs
`above the threshold value per unit time so as to calculate a
`pulse rate and the transmitter4 transmits the pulse rate to a
`display for displaying the above pulse rate data and a device
`for computing the amount of motion load. Since the output
`of the above photodetector 22 is generally low, after the
`output is amplified, the amplified output is converted into a
`digital signal for the computation of a pulse rate in this
`embodiment.
`
`[0029] According to this embodiment, the pulse wave of
`the wrist 10 of the subject is detected by the pulse wave
`sensor 2 which comprises the light emitting diode 21 for
`emitting light having a wavelength of a near infrared range
`and four photodetectors 22 disposed around the light emit-
`ting diode 21 symmetrically on a circle concentric to the
`light emitting diode 21, and a pulse rate is computed from
`the pulse wave data by the arithmetic circuit 3. Therefore,
`even when the attachmentposition of the pulse rate detector
`1 is dislocated, a pulse wave can be detected accurately.
`[0030] Since the acrylic transparent plate 6 is provided on
`the detection face 23a of the holder 23, adhesion between
`the pulse rate detector 1 and the wrist 10 can be improved,
`thereby further improving the detection efficiency of a pulse
`wave.
`
`In this embodiment, the pulse rate detector 1 is
`[0031]
`attached with the same pressure as that for attaching a
`timepiece to the wrist with a belt. Therefore, the subject can
`carry the pulse rate detector 1 for a long time without
`pressing his/her wrist excessively.
`four photodetectors
`[0032]
`In the above embodiment,
`which are disposed symmetrically are used to detect the
`pulse wave of the wrist 10. The arrangement of the light
`emitting diode 21 and the photodetectors 22 is not limited to
`this. For example, to further improve detection efficiency, as
`shown in FIG. 4(a), the number of the photodetectors 22
`may be increased. Alternatively, to reduce the size of the
`pulse rate detector 1, as shown in FIG.4(b), the number of
`photodetectors may be reduced. In either case, it is desired
`that the photodetectors 22 should be disposed around the
`light emitting diode 21 on a circle concentric to the light
`emitting diode 21 to detect a pulse wave accurately even
`whenthe attachment position of the pulse rate detector 1 is
`dislocated.
`
`In the above embodiment, a plurality of photode-
`[0033]
`tectors 22 are provided for one light emitting diode 21. The
`6
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`6
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`

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`US 2002/0188210 Al
`
`Dec. 12, 2002
`
`same effect can be obtained when the number of photode-
`tectors 22 is 1 and a plurality of light emitting diodes 21 are
`disposed around the photodetector 22. In this case, the size
`and power consumption of the pulse wave sensor 2 become
`larger than this embodiment.
`
`In the above embodiment, the acrylic transparent
`[0034]
`plate 6 is provided on the detection face 23a of the holder 23
`to improve adhesion to the wrist 10. Even when the detec-
`tion face 23a is projected from the outer casing 5 as shown
`in FIG. 5, adhesion can be improved.
`
`In the above embodiment, the pulse rate data is
`[0035]
`transmitted to the display or the device for computing the
`amount of motion load. When notonly a pulse rate but also
`pulse wave data (waveform itself) are transmitted, the pulse
`rate detector 1 of the present invention can be coupled to
`devices making use of bio signals.
`
`[0036] As described above, according to the present
`invention, since a pulse wavesensoris constituted such that
`light output from a light emitting diode and reflected from
`the artery of the wrist of a subject is detected byat least three
`photodetectors disposed around the light emitting diode and
`not linearly to detect a pulse wave, even whenthe attach-
`mentposition of the sensoris dislocated, the pulse wave can
`be detected accurately. Using this sensor, a pulse rate
`detector whichis easily attached and hasa stable output can
`be constructed.
`
`Whatis claimedis:
`1. A pulse wave sensor for detecting a pulse wave by
`detecting light output
`from a light emitting diode and
`reflected from the artery of a wrist of a subject, the sensor
`comprising at least three photodetectors disposed around the
`light emitting diode.
`2. The pulse wave sensor of claim 1, wherein a near
`infrared LED is used as the light emitting diode.
`3. The pulse wave sensor of claim 1, wherein the photo-
`detectors are disposed at an equal distance from the light
`emitting diode.
`4. The pulse sensor of claim 1, wherein cavities are
`formed in a contact face between a holder for holding the
`light emitting diode and the photodetectors and the wrist, the
`light emitting face of the light emitting diode and the light
`receiving faces of the photodetectors are disposed at respec-
`tive predetermined distances from the contact face, and the
`sectional forms of the cavities are tapered such that their
`widths increase toward the contact face.
`
`5. The pulse wave sensor of claim 1, wherein a transparent
`plate-like memberis provided on a portion includingat least
`the light emitting face and the light receiving faces of the
`contact face.
`
`6. A pulse rate detector comprising the pulse wave sensor
`of claim 1 and means of computingthe pulse rate of a subject
`based on the output of the pulse wave sensor.
`7. The pulse rate detector of claim 6 which comprises a
`transmitter for transmitting the measured pulse rate data.
`*
`*
`*
`*
`*
`
`7
`
`