United States Patent
`
`1191“
`
`‘ Smart et al.
`
`1111
`
`3,769,974
`
`[45]
`
`‘ Nov. 6, 1973
`
`[54]. BLOOD PULSE MEASURING EMPLOYING
`REFLECTED RED LIGHT
`
`Primary Examiner—William E. Kamm
`Attorney—Phillip L. DeArment et al.
`
`.
`
`[75]
`
`Inventors: Richard C. Smart, Denver;
`Kenneth D. Swonger, Littleton,
`both of C010.
`
`[73] Assignee: Martin Marietta Corporation,
`New York, NY.
`
`[22]
`
`Filed:
`
`June 29, 1971
`
`[2]] Appl. N0.: 157,944
`
`[52] US. Cl. ............................................ 128/205 P
`[51]
`Int. Cl............................................... A6lb 5/02
`[58] Field of Search ................... 128/205 E, 2.05 P,
`128/205 R, 2.05 T, 2 C
`
`[56]
`
`I References Cited
`UNITED STATES PATENTS
`
`3,040,737
`3,628,525
`3,167,658
`3,228,391
`3,139,086
`
`6/1962 Kompelien et'al....'..._...... 128/205 E
`12/1971
`Polanyi et al .........
`.. 128/205 P
`
`1/1965
`Richter ......
`128/205 P
`Fitter et al.
`1/1966
`128/205 T
`
`Botsch eta .................... 128/205 P
`6/1964
`
`[57]
`
`,
`
`ABSTRACT
`
`An improved pulse transducer for providing an output
`signal which varies as a function of.the pulse rate of a
`living body includes a plurality of light emitting diodes
`from which red light of a wavelength of from 6,000 to
`9,000 angstroms is emitted. This red light is transmitted
`through the skin of a portion of the body to the blood
`in an artery. The wavelength of this light is such that it
`is not transmitted through the blood but is reflected to
`a sensor with an intensity which varies as a function of
`.variations in pulse wave pressure in the artery. The
`light emitting diodes are relatively cool
`to minimize
`changes in the characteristics of the blood vessels dur-
`ing examination. In addition, the use of red light tends
`to maximize the amount of light reflected back to the
`sensor from the red blood and to minimize the amount
`of light reflected by the white skin to'thereby minimize
`the signal—to-noise ratio in the output signal from the
`sensor.
`
`2 Claims, ’3 Drawing Figures
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`|PR2018—01093
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`Apple Inc. Ex. 1008 Page 1
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`IPR2018-01093
`Apple Inc. Ex. 1008 Page 1
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`

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`|PR2018—01093
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`Apple Inc. Ex. 1008 Page 2
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`IPR2018-01093
`Apple Inc. Ex. 1008 Page 2
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`

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`1
`BLOOD PULSE MEASURING EMPLOYING
`REFLECTED RED LIGHT
`This invention relates generally to the measurement
`of pulse in a living body, and particularly relates to a
`new and improved pulse transducer and method for
`measuring pulse.
`Pulse transducers of the photoelectric type com-
`monly include a bulb which provides a source of white
`light which is directed toward a portion of the body
`through which blood is flowing. This white light is re- 10
`flected from the body to a sensor. The intensity of the
`light reflected to the sensor will vary with variations in
`the pulse (arterial pulse pressure wave). Since the bulb
`is placed close to the skin, heat from the bulb may
`cause dilation of the blood vessels and alteration of the 15
`vascular bed of the portion of the body being exam-
`ined. In addition, a considerable portion of the white
`light is reflected from the skin, instead of the blood,
`thereby tending to provide a relatively large signal-to-
`noise ratio.
`.
`In a known photoelectric pulse transducer, an at-
`tempt was made to reduce the effect of heat from a
`white light source or bulb by providing a metal block
`around the light source to act as a heat sink. In addi-
`tion, in an effort to eliminate exterior and skin reflected 25
`light, red filters have been provided in association with
`the photosensors. One example of such a pulse trans-
`ducer is disclosed in U.S. Pat. No. 3,103,214. Although
`these known photoelectric type pulse transducers have
`been used with varying degrees of success, they are not 30
`entirely satisfactory due to a relatively high rate of
`power consumption and heat generation by the light
`source and the relatively large signal-to-noise ratio
`which is produced by using white light.
`The present invention provides a pulse transducer of 35
`the photoelectric type which includes light emitting di-
`odes which remain relatively cool while providing red
`light. The wavelength of thisred light is such that it is
`transmitted through the skin' to the blood and is then
`reflected back to a sensor. When the blood pressure in
`an artery changes in response to a heart beat, the artery
`enlarges providing a relatively large reflecting surface
`'and the intensity of the light reflected to the sensor is
`changed by a corresponding amount. Therefore, the
`output-signal from the sensor is an analog of pulse wave
`pressure. Due to the light emitting diodes, the heat sink
`of the prior art is unnecessary and yet the heat prob-
`lems are eliminated. Moreover, due to the red light
`source, a relatively low signal-to-noise ratio is obtained.
`Accordingly, the principal object of the present in-
`vention is to provide a new and improved method for
`measuring pulse in a living body by directing red light
`onto a portion of the body through which blood is flow-
`ing and sensing the intensity of the reflected red light,
`and wherein the temperature of the portion of~the body
`against which the light is directed is unaffected during
`pulse measurement.
`Another object of this invention is to provide a new
`and improved method which includes a red light source
`for providing light of a wavelength which is reflected
`from the blood rather than the skin of a body with an
`. intensity which varies with variations in pulse wave
`pressure.
`,
`These and other objects and features of the invention 65
`will become more apparent upon a consideration of the
`following description taken in connection with the ac-
`companying drawings wherein:
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`FIG. 1 is a schematic illustration of a pulse trans-
`ducer constructed in accordance with the present in-
`vention and shown in association with an artery in a
`portion of a body being examined;
`FIG. 2 is a plan view, taken generally along line 2—2
`of FIG. 1, illustrating the relationship between a plural-
`ity of light emitting diodes and a phototransistor sensor
`in the pulse transducer; and
`FIG. 3 is a schematic illustration of electrical cir-
`cuitry for the pulse transducer of FIG. 1.
`A pulse transducer 10 constructed in accordance
`with the present invention is shown in FIG. 1 in associa-
`tion with a portion 12 of a living body. The transducer
`10 produces an analog signal which is representative of
`arterial pulse pressure. This signal can be used to deter-
`mine, among other things, heart rate, pulse wave veloc-
`ity, total peripheral resistance, and cardiovascular de-
`conditioning. Although the pulse transducer 10 is dis-
`closed herein in association with a human being,
`it
`should be understood that the pulse transducer could
`be utilized to examine an animal.
`
`The pulse transducer 10 is of the photoelectric type
`and includes a plurality of light sources 16 which emit
`light rays 20. The light rays 20 are reflected from blood
`22 flowing in an artery 24 to a phototransistor sensor
`28 in the manner illustrated schematically in FIG. 1.
`Since the size of the artery 24 increases with increasing
`pulse pressure, the intensity of the light reflected from
`the artery to the sensor 28 varies with variations in the
`pulse wave pressure in the artery.
`Variations in the light received by the sensor 28 re-
`sult in the provision of an output signal, on a lead 30,
`which is an electrical analog of the arterial blood pres—
`sure wave. After the electrical signal has been strength-
`ened by an amplifier 32,'it is connected to a chart-re-
`corder 36. Of course, other types of display devices
`could be utilized rather than the chart recorder 36. The
`recorder 36 produces a curve 38 which is a printed ana-
`log of the arterial pulse pressure wave. On analysis, the
`curve 38 can be used to determine heart rate, pulse ve-
`locity, total peripheral resistance, cardiovascular de-
`conditioning, and many other things.
`In accordance with the present invention, the light
`sources 16 are light emitting diodes. The diodes 16
`emit only red light having a wavelength of between
`6,000 and 9,000 angstroms. In one specific embodi-
`ment of the invention, the diodes l6 emitted light hav-
`ing a wavelength of approximately 7,000 angstroms.
`- Since the light rays 20 from the diodes 16 are red,
`they are not reflected by the white skin 42 of an indi-
`vidual being examined. The red light rays 20 pass
`through the skin 42 and are reflected by the red blood
`22 in the artery 24. Since the light which is received by
`the sensor 28 is reflected from the blood 22, the signal-
`to-noise ratio on the output lead 30 is relatively low. If
`the diode 16 emitted white light, a substantial portion
`of this light would be reflected by the skin 42 instead
`of the blood 22 and would result in a relatively high sig—
`nal-to-noise ratio.
`
`The diodes 16 provide a relatively cool source of
`light. Therefore, the diodes 16 do not increase the tem-
`perature of the adjacent tissue with a resulting alter-
`ation in the characteristics of the blood vessel 24. If a
`filament type bulb was utilized for the light source 16,
`a substantial amount of heat would be generated by the
`bulb. With a known pulse transducer of the photoelec-
`tric type having a bulb which provides a white light
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`|PR2018—01093
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`3
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`3,769,974
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`In view of the foregoing description, it can be seen
`that the pulse transducer 10 includes a plurality of red
`light emitting diodes 16. The red light from the diodes
`16 is transmitted through the skin 42 to the blood 22.
`The wavelength of this red light is between 6,000 and
`9,000 angstroms so that it is not transmitted through
`the red blood but is reflected back to the phototransis-
`tor sensor 28. When the blood pressure in the artery 24
`changes, in response to a heart beat, the amount of re-
`flected light reaching the phototransistor 28 changes
`and the output signal on the lead 30 is varied. As a re~
`sult, the output signal is an accurate electrical analog
`of the arterial pulse pressure wave. The red light from
`the diodes 16 is reflected by the red blood with a rela-
`tively small signal-to-noise ratio so that the output sig-
`nal on the lead 30 accurately represents the arterial
`blood pressure wave. An accurate reading by the trans-
`ducer 10 is promoted by the fact that the diodes 16
`emit very little heat so that there is little or no dilation
`of the blood vessels and alteration of the vascular bed
`under examination.
`
`Having described a specific preferred embodiment of
`the invention, the following is claimed:
`1. A method of sensing variations in pulsatile blood
`in a living body without substantially heating the pulsa-
`tile blood or tissue of the living body, said method com-
`prising the steps of providing a plurality of light sources
`capable of emitting red light of a wavelength between
`6,000 and 9,000 angstroms at substantially ambient
`temperature, positioning the light sources adjacent to
`the outer surface of the skin of the living body, trans-
`mitting red light of a wavelength between 6,000 and
`9,000 angstroms from the light sources through the
`skin of the living body toward a portion of the living
`body in which pulsatile blood is flowing without heating
`the living body, reflecting red light from the pulsatile
`blood of the living body, sensing the intensity of the
`light reflected from the pulsatile blood of the living
`body, and providing an output signal
`in accordance
`with the intensity of the sensed light.
`2. A method as set forth in claim 1 wherein said step
`of providing a plurality of light sources includes the
`step of providing a plurality of light emitting diodes and
`said step of transmitting red light includes the step of
`energizing the light emitting diodes.
`*
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`1k
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`source, a rise in skin temperature to approximately
`100° F. occurred. With one specific embodiment of the
`present invention in which light emitting diodes 16
`were utilized as a source of red light, the rise in skin
`temperature was less than 2° F. Of course, the relatively
`large amount of heat provided by the filament type
`bulb of the known pulse transducer resulted in a dila-
`tion of the blood vessels and alteration of the vascular
`bed which was being examined.
`The transducer 10 includes a housing 50 in which the
`diodes 16 are disposed in a circular array about the
`center of the phototransistor 28 (see FIG. 2). The
`housing 50 includes an opaque outer or upper wall 54
`formed of epoxy. An annular lower wall 56 is also
`formed of opaque epoxy with a surface 57 which en-
`gages the skin 42 on the portion of the body being ex-
`amined. An annular inner wall 58 is formed of opaque
`epoxy and blocks the direct transmission of light from
`the diodes 16 to the phototransistor sensor 28. The
`concentric walls 56 and 58 of the housing 50 prevent
`stray light from being transmitted to the sensor 28.
`The diodes 16 and phototransistor sensor 28 are ad-
`vantageously sealed or encapsulated in the housing 50
`to enable the transducer 10 to be utilized in many dif-
`ferent types of environments, such as environments
`where there is a relatively high humidity or explosive
`atmosphere. Accordingly, the space between the inner
`and outer walls 56 and 58 of the transducer 10 is filled
`with a transparent epoxy to form an annular window 64
`which completely seals the diodes 16 from the sur-
`rounding environment. In addition, a circular window
`66 formed of transparent epoxy is disposed in the cen-
`ter of the housing and seals the phototransistor sensor
`28 from the surrounding environment.
`The diodes 16 are mounted in the housing 50 on a
`substrate 70 by thick-film semiconductor fabrication
`techniques. The diodes 16 are connected in parallel
`with each other (see FIG. 3) and are connected to a
`common voltage source 72. A current limiting resistor
`74 is advantageously provided in series with the diodes
`16. The phototransistor 28 is of the N—P—N type and is
`mounted on the substrate 70. As was previously ex-
`plained, when the intensity of the light striking the pho-
`totransistor 28 is varied, the output signal on a lead 30
`varies. A loading resistor 78 is connected in series with
`the phototransistor 28.
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`|PR2018-O1093
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