`
`United States Patent
`[19]
`New, Jr. et al.
`
`
`[I I) Patent Number: 4,700,708
`[45) Date of Patent: * Oct. 20,
`1987
`
`[54) CALIBRATED
`OPTICAL OXIMEfER PROBE
`
`
`[75]Inventors: New, Jr., Woodside;
`William
`James
`
`Alameda, both of Calif.
`E. Corenman,
`
`4,225,410 9/1980 Pace ................................ 204/195 R
`
`
`
`
`
`
`
`4,236,935 12/1982 Clark, III .............................. 378/48
`
`
`
`4,266,554 5/1981 Hamaguri ............................ 128/633
`
`
`
`
`4,407,272 10/1983 Yamaguchi ............................. 128/6
`
`
`
`
`4,407,290 10/1983 Wilber ................................. 128/633
`[73) Assignee:
`Hayward,
`Nellcor Incorporated,
`
`
`
`4,407,298 10/1983 Lentz et al. ......................... 128/713
`Calif.
`
`
`
`4,446,715 5/1984 Bailey ................................... 73/1 R
`
`
`
`4,494,550 I /1985 Blazek et al. ....................... 128/664
`[ *) Notice: The portion of the term of this patent
`
`
`
`
`4,621,643 11/1986 New et al. ........................... 128/633
`
`subsequent to Nov. 11, 2003 has been
`disclaimed.
`
`[21) Appl. No.: 911,978
`
`[22] Filed: Sep. 26, 1986
`
`OTHER PUBLICATIONS
`
`
`Grover, Conf. Proceed. of the 26th Annual Conf. on
`
`
`
`Engr. in Med. and Biol., Minn., Minn., Sep. 20-Oct. 4,
`1973.
`
`Schibli et al., IEEE Trans. of Biomed. Engr., vol.
`BME-25, No. I, Jan. 1978, pp. 94-96.
`
`Yee et al., IEEE Trans. Biomed. Engr., vol. BME-24,
`Feb. 5, 1986, Pat. [63) Continuation of Ser. No. 827,478,
`
`
`No. 2, Mar. 1977, pp. 195-197.
`
`
`No. 4,621,643, which is a continuation of Ser. No.
`
`
`695,402, Jan. 24, 1985, abandoned, which is a continua­
`L. Howell
`Primary Examiner-Kyle
`
`tion of Ser. No. 414,176, Sep. 2, 1982, abandoned.
`C. Hanley
`
`Assistant Examiner-John
`[51) Int. Cl.4 ................................................
`A61B 5/00
`[57]
`ABSTRACT
`[52) U.S. Cl ....................................... 356/41;
`
`128/633;
`250/252.l
`A probe apparatus for use with an optical oximeter is
`
`
`
`
`
`................ 128/633, 634, 664-666;
`[58] Field of Search
`
`
`disclosed. A pair of light emitting diodes emit light of
`
`73/1 R; 356/39-42; 280/252.1
`
`
`
`known narrow wavelengths through an appendage of a
`
`
`
`patient onto a photosensor. A resistor of coded known
`
`
`
`
`resistance is used to enable the oximeter to calculate the
`U.S. PATENT DOCUMENTS
`
`
`
`co-efficient of extinction of the wavelengths of the
`
`
`LEDs. The resistor, LEDs and photosensor are
`
`
`2,706,927 4/1955 Wood ...................................... 88/14
`
`mounted on self-attaching hook and eye tape for mount­
`
`
`3,638,640 2/1972 Shaw .................................. 128/2 R
`
`
`ing the probe onto the appendage of the patient. The
`
`
`
`
`3,704,706 12/1972 Herczfeld et al. .................. 128/2 R
`
`
`probe is detachably wired to the oximeter, rendering
`
`
`
`3,720,199 3/1973 Rishton et al. ..................... 128/1 D
`
`
`3,819,276 6/1974 Kiess et al. .......................... 356/184
`
`
`
`the probe completely disposable. The oximeter is pro­
`
`
`3,833,864 9/1974 Kiess et al. .......................... 356/184
`
`
`grammed at the factory to calculate the co-efficients of
`
`
`
`3,847,483 11/1974 Shaw et al. ........................... 356/41
`
`
`extinction of any LEDs which may be encountered in a
`
`
`
`3,880,006 4/1975 Poduje ........................... 73/362 AR
`
`
`
`
`series of disposable probes. From the co-efficients of
`
`
`
`
`
`3,9!.0,701 10/1975 Henderson et al. .................. 356/39
`
`
`
`extinction, the pulse rate and degree of arterial oxygen
`
`
`
`3,998,550 12/1976 Konishi et al. ........................ 356/39
`
`
`
`saturation is computed and displayed by the oximeter.
`
`
`
`
`4,059,991 11/1977 Dybel et al. ..................... 73/88.5 R
`
`
`
`4,086,915 5/1978 Kofsky et al. ...................... 128/2 L
`
`
`
`4,167,331 9/1979 Nielsen .................................. 356/39
`
`
`11 Claims, 6 Drawing Figures
`
`
`
`
`
`Related U.S. Application Data
`
`(56)
`
`
`
`References Cited
`
`).
`
`J
`
`51-
`
`.,,
`
`MASIMO 2007
`Apple v. Masimo
`IPR2020-01526
`
`

`

`US» Patent Oct. 20,1987
`
`Sheetl of4
`
`4,700,708
`
`
`
`

`

`US“ Patent Oct. 20,1987
`
`Sheet 2 of 4
`
`JOE‘Sa”:
`
`2925...“.32
`
`
`
`‘:wmbayw
`
`$63M:
`
`
`
`29253&2
`
`

`

`MS.» Patent Oct. 20,1987
`
`Sheet3 of4
`
`4,700,708
`
`
`
`

`

`US“ Patent Oct. 20,1987
`
`Sheet 4 of4
`
`4,700,708
`
`
`
`

`

`ll
`
`[4,700,708
`
`CALIBRATED OPTICAL OXIMETER PROBE
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation of copending
`United States patent application Ser. No. 827,478, filed
`Feb. 5, 1986, now US. Pat. No. 4,621,643, which is a
`continuation of United States patent application Ser.
`No. 695,402, filed Jan. 24, 1985, now abandoned, which
`was a continuation of United States patent application
`Ser. No. 414,176, filed Sept. 2, 1982, now abandoned.
`FIELD OF THE INVENTION
`
`This invention relates to solid state monitors for pho-
`toelectric determination of arterial oxygen saturation
`and of pulse rate in a human or animal patient, more
`particularly to a disposable probe calibrated through a
`remote sensing apparatus including a transducer herein
`called an information encoding component.
`
`BACKGROUND OF THE INVENTION
`
`A serious problem exists in operating rooms. Specifi—
`cally, the chemical determination of oxygen level in
`blood consumes at least 3 to 5 minutes. A patient de—
`prived of blood oxygen for such a duration typically
`incurs irreversible brain damage if not death.
`US. Pat. No. 2,706,927 to Wood disclosed the com-
`
`5
`
`10
`
`15
`
`20
`
`25
`
`35
`
`45
`
`putation of oxygen saturation from measurements of 30
`light absorption of body tissue at two wavelengths. A
`series of devices and procedures have been founded
`using this technology.
`A required peripheral device of such photoelectric
`oximeters is a photoelectric probe. Typically, such a
`probe is clamped to an appendage of a patient’s body,
`such as an ear or a finger. Such probes require at least
`one light source for directing light into the appendage
`and at least one sensor for receiving light diffused out of
`the appendage. One method of obtaining light of the 40
`desired frequency had been to use a light source of
`indeterminate wavelength range in combination with a
`monochromatic filter of known output. Such devices
`are inefficient, and result in unwanted power demands
`and heat generation.
`U.S. Pat. No. 3,704,706 to Herczfeld et a1. disclosed
`the use of a solid state red laser in an optical probe with
`a solid state photodetector. Although lasers are useful
`for emitting monochromatic light of known wave-
`length, thereby eliminating need for a filter, they re-.5o
`main expensive and unwieldy.
`US. Pat. No. 3,847,483 to Shaw et a1. disclosed the
`use of light emitting diodes to provide the necessary
`monochromatic light. The probe of Shaw required ex»
`pensive fiber optic cables.
`‘
`A problem with all prior art devices is that they are
`too expensive to be readily disposable. The need for a
`truly disposable probe is great, given the many surgical
`applications in which sterility must be assured. The
`prior art optical probes, being more or less permanent
`portions of their respective oximeters, were subjected
`to a one time determination of the wavelength of the
`light sources therein and the oximeter was then pro-
`grammed or adjusted to process light of the known
`wavelength.
`A problem in developing disposable probes, there-
`fore, has been the necessity to avoid having to repro-
`gram or adjust the oximeter for each new probe or
`
`55
`
`60
`
`65
`
`2
`alternately to maintain probes within narrow limits of
`wavelength variation, a clearly impractical task.
`Re-calibration, perhaps necessitating return of the
`oximeters to the factory, can become necessary even for
`prior art devices when, for example, a probe is broken.
`Alternatively, a supply of light sources having consis-
`tently identical wavelengths is required. In particular,
`light emitting diodes are known to vary in wavelengths
`from unit-to—unit.
`
`Other optical probes are shown in patents to Shaw,
`US. Pat. No. 3,683,640, Neilsen, U.S. Pat. No.
`4,167,331, and Konishi, US. Pat. No. 3,998,550.
`
`SUMMARY OF THE INVENTION
`The present invention provides an optical oximeter
`probe which includes at least one narrow bandwidth
`light emitting diode and at least one photoelectric sen-
`sor. An information encoding component such as a
`resistor of known resistance is selected to correspond to
`the measured wavelength of the LED and is provided
`with each probe. The elements are mounted on a flexi-
`ble fastening medium. The wires from the electrical
`elements terminate at a connector for detachably con-
`necting the probe to the related oximeter. Coding in
`other manners, such as the wiring of a multiconductor
`plug in a digital value or binary array or into a dispos-
`able memory containing the color information is dis-
`closed.
`The primary object of this invention is to provide
`apparatus for directing light onto a portion of a human
`body for the detection of oxygenated blood flow which
`is inexpensive, replaceable, easily applied and which
`overcomes the disadvantages and limitations of the
`prior art.
`It is a further object of this invention to provide an
`optical probe whose wavelength emission characteris-
`tics are readily ascertainable by the attendant oximeter.
`Another object of this invention is to enable factory
`calibration of LEDs for use in such probes. Typically,
`LEDs are purchased in batches of one general wave-
`length, but whose exact wavelength characteristics are
`unknown and vary from piece to piece.
`It is a further object of this invention to eliminate the
`necessity for oximeters to be calibrated for new probes,
`other than the initial factory calibration.
`Yet another object of this invention is to provide
`fleitible attachment means for the probe which will
`allow rapid attachment to human or animal appendages
`of varying sizes yet maintain the photoelectric sensor in
`direct optical isolation from the LEDs.
`Yet another object of this invention is to disclose
`wiring of a multiconductor plug in a binary array to
`transmit probe calibration.
`DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a part perspective, part schematic diagram
`of the optical probe of the preferred embodiment of the
`present invention.
`FIG. 2 is an end view of a patient’s finger showing
`placement of the probe of the present invention.
`'
`FIG. 3 is a side elevation of an embodiment of a
`photoelectric sensor of the probe.
`FIG. 4 is a simplified schematic circuit diagram illus-
`trating the method in which an oximeter microproces-
`sor decodes the wavelength values of the probe through
`use of a coded resistor.
`
`

`

`4,700,708
`
`3
`FIG. 5 is a schematic of the probe of this invention
`calibrated by a multiconductor plug and wired in a
`binary array; and
`FIG. 6 is a circuit schematic of an oximeter utilizing
`the calibrated probe of this invention.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`Referring to FIG. 6, the pulse oximeter of this inven-
`tion is illustrated.
`Conventional microprocessor 116 has a bus 117 ex-
`tending therefrom. Bus 117 has connected thereto con-
`ventional ROM 118 and RAM 119. An LED display
`120 is schematically illustrated having a select latch 121
`and a digit designation latch 122.
`Having set forth the more or less conventional por-
`tions of the microprocessor, attention will now be di-
`rected to the analog portions of the circuitry.
`Finger 14 of a patient is illustrated with probe 101
`having schematic detection circuitry. First light emit-
`ting diode 132 in the red range and a second light emit-
`ting diode 130 in the infrared range are sequentially
`pulsed to emit light in their respective frequencies by
`amplifiers 131, 133. Typically, LED 132 is in the 660
`nanometer range with LED 130 being in the 940 nano—
`meter range.
`It is necessary that maximum light from the active
`light emitting diode go through the flesh in finger 14.
`Therefore, a light impervious barrier 136 is placed be-
`tween photosensor 138 and the paths to the light emit-
`ting diodes 130 and 132 which are not through finger
`14. Barrier 136, terminating in contact with the flesh of
`finger 14, make the path between the respective light
`emitting diodes 130, 132 and the light receiving diode
`138 occur only through the flesh of finger 14.
`Signal received from each respective light emitting
`diode first passes through a pre—amplifier 140. This sig-
`nal is thereafter amplified in parallel at amplifiers 141,
`142. As amplified, the signal is passed in parallel from
`each amplifier through respective phase detectors 143,
`144. Passage through respective low pass filters 145, 146
`thereafter occurs. Amplification at offset amplifiers 147,
`148 then takes place. The pulsatile component is passed
`to multiplexer 150.
`to a comparator 152.
`Multiplexer 150 has output
`Comparator 152 is ramped in half steps by a 12 bit digi—
`tal to analog converter (hereinafter DAC) 154. DAC
`154 places a comparison signal divided in one part from
`4096 parts with the comparator outputting to bus 117.
`The reader will recognize that not all human fingers
`and appendages are the same. Specifically, the differ-
`ence between the races, skin pigment, weight, age, ma-
`turity and other factors all can lead to different signals
`being sensed at photosensor 138, even though the fre-
`quency and intensity of the light signal output at each of 55
`the diodes 130, 132 is the same.
`Accordingly, microprocessor 116 is programmed to
`receive a signal from photosensor 138 within an opti-
`mum range. Utilizing a second operating phase of DAC
`154, and communicating a signal to a sample hold 157,
`the individual LED’s 130, 132 are given voltage outputs
`160, 161. These voltage outputs 160, 161 are adjusted so
`that in each case photosensor 138 looks at a signal well
`withing the range of the DAC.
`Clock 170 controls the sequential output of light from
`the light emitting diodes 130, 132 to a duty cycle of at
`least 1
`in 4. This is schematically illustrated by signals
`(1)1 through (1)4. Reception of signal at detector 143
`
`40
`
`45
`
`50
`
`60
`
`65
`
`4
`occurs during time periods (1)1 and (1)2 and reception of
`signal occurs at detector 144 during time periods (1)3 and
`(1)4.
`It can be immediately realized that during respective
`time periods (1)1, (1)3 active signal from the light emitting
`diodes 130, 132 is being received. During the time peri-
`ods (1)2 and (1)4, no signal and only noise is being re-
`ceived. As will hereinafter become apparent, by ampli-
`fying the negative signal before passage through the
`low pass filter. noise can be subtracted out utilizing the
`illustrated l in 4 duty cycle.
`Applicants herewith incorporate by reference their
`United States application entitled “Pulse Oximeter,”
`US. patent application Ser. No. 414,174, filed Sept. 12,
`1982, abandoned in favor of US. patent application Ser.
`No. 417,311, filed Sept. 13,1982, now abandoned. FIG.
`6 is a copy of the FIG. 2 from that application.
`The Summary of Invention in the incorporated appli-
`cation is:
`
`SUMMARY OF INVENTION
`
`A pulse oximeter is disclosed of the type wherein
`light of two different wavelengths is passed through
`any human or animal body pulsatile tissue bed, such as
`a finger, an ear, the nasal septum or the scalp, so as to be .
`modulated by the pulsatile component of arterial blood
`therein, and thereby allowing indication of oxygen satu—
`ration, blood perfusion and heart rate. The level of
`incident light is continually adjusted for optimal detec-
`tion of the pulsatile component, while permitting ac—
`commodation to variable attenuations due to skin color,
`flesh thickness and other invariants. At significant slope
`reversal of the pulsatile component to negative (indicat-
`ing a wave maximum), wave form analysis of blood
`flow occurs. A quotient of the pulsatile component of
`light transmission over the constant component of light
`transmission is measured for each of two wavelengths
`by direct digital tracking. The respective quotients are
`thereafter converted to a ratio, which ratio may be
`thereafter fitted to a curve of independently derived of
`oxygen saturation for the purpose of calbration. The
`saturation versus ratio calibration curve may be charac—
`terized by various mathematical techniques including
`polynomial expansion whereby the coefficients of the
`polynomial specify the curve. An output of pulse rate,
`pulsatile flow and oxygen saturation is given. An inci-
`dent light source duty cycle is chosen to be at least I in
`4 so that noise, inevitably present in the signal, may be
`substantially eliminated and filtered.
`A representative claim is:
`A pulse oximeter for determining arterial oxygen
`saturation and arterial pulse amplitude in a patient, said
`oximeter comprising: first and second light emitting
`sources for emitting sequential light pulses in the red
`and infrared into the flesh of a human; a sensor sensitive
`to each of said light sources having an indirect light
`path through the flesh of said human from said first and
`second light sources; said sensor sequentially outputting
`signals to an amplifier from each of said light sources;
`means for digitally tracking the light absorption; means
`for dividing the change of light transmission due to the
`pulsatile component of blood flow with respect to the
`total light transmission to determine a quotient of light
`absorption for each optical wavelength; means for mak-
`ing a ratio related directly to the respective quotients of
`light transmission at each said frequency and means for
`fitting the ratios of light transmission to experimentally
`
`
`
`

`

`4,700,708
`
`5
`determined saturations at said ratio to enable the optical
`determination of saturation.
`Referring to FIG. 1, a part-schematic, part-perspec-
`tive view of the optical probe 1 is shown. A suitable
`length of adjustable, self-fastening tape 50 is provided,
`such as that sold under the trademark VELCRO, ob-
`tainable from American Velcro, Inc. Incorporated into
`tape 50 at suitably spaced intervals are the electrical
`components of probe 1. Photoelectric sensor 30 is at-
`tached to the outside of tape 50 and protrudes slightly
`from the underside of tape 50. Sensor 30 has ground
`wire G and lead wire 31. Light emitting diode 10, typi—
`cally emitting frequencies in the infrared range of the
`spectrum, is mounted to and pierces tape 50 in a similar
`manner to sensor 30 and at a distance from sensor 30
`selected upon the basis of the typical appendage size
`expected to be encountered. LED 10 is connected to
`ground wire G and has input lead wire 11. Placed in
`proximity to LED 10 is a second LED 20, typically
`having wavelength emission characteristics in the red
`range of the spectrum. LED 20 attaches to ground wire
`G and has input lead wire 21.
`Resistor 40 is shown mounted to tape 50 between
`sensor 30 and LED 10. However, the physical location
`of resistor 40 is not important and it may be mounted to
`probe 1 at any other convenient location. Resistor 40
`has input lead wire 41 and is connected to ground wire
`G.
`Wires G, 11, 21, 31, 41 lead to connector 52 so that
`probe 11 may be readily disconnected from the oxime-
`ter 60 (schematically illustrated in FIG. 4).
`The probe 1 illustrated in FIG. 1 is designed for use in
`connection with an oximeter 60 designed to operate in
`conjunction with two LEDs 10, 20 sequentially trans-
`mitting light to a single sensor 30. However, the mecha-
`nism of the instant invention works equally well for
`oximeters requiring only a single LED and single or
`. multiple photo sensors. Oximeters requiring more than
`two LEDs may be equally well accommodated by the
`probe of the present invention.
`FIG. 2 is an end elevation of typical finger 51 of a
`human patient. Finger 51 is encircled by probe 1 at its
`tip by overlapping the ends of self-connecting tape 50.
`Light emitted from LEDs 10, 20 enter the flesh of finger
`51 and are subjected to diffusion and scattering. Sensor
`30 picks up only light which has been diffused through
`the flesh of finger 51.
`FIG. 3 is a detailed side elevation of sensor 30, show-
`ing the manner in which it is assured that no light emit-
`ted by LEDs 10, 20 is received by sensor 30 without
`first passing through finger 51. Sensor element 32 is
`recessed somewhat within metal cylinder wall 33 of the
`sensor housing. Since tape 50 presses sensor 30 directly
`against the skin of finger 51, it is readily seen that no
`light passes to sensor element 32 other than through the
`flesh of finger 51.
`Probe 1 is constructed in the following manner:
`LED’s 10, 20 are selected from batches of LEDs with
`generally known wavelength characteristics. The exact
`wavelength characteristics of the specific LED’s 10, 20
`chosen are determined at
`this time through readily
`available metering means. Resistor 40 or a similar impe-
`dance reference is then selected to have an impedance
`or specifically a resistance whose amount is exactly
`specified by a table made available to the factory techni-
`cian for this purpose, of all possible wavelength combi-
`nations which may be expected to be encountered from
`the available supplies of LEDs. The following table is
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`an example of how a single resistor 40 might be selected
`for any hypothetical combination of LED’s 10, 20 in a
`case where each has only two possible wavelengths:
`TABLE A
`LED 10
`940 nM
`950 nM
`940 nM
`950 nM
`
`Resistor 40
`150 ohms
`160 ohms
`l7O ohms
`l80 ohms
`
`LED 20
`660 nM
`660 nM
`670 nM
`670 nM
`
`A typical probe will have an infrared LED 10 of
`wavelength 940 nanometers and a red LED 20 of wave-
`length 660 nanometers. According to the above table, a
`probe having such wavelength characteristics will be
`supplied at the factory with a resistor 40 of one, and
`only one, resistance value, in this case shown to be 150
`ohms.
`The value in having such a unique known resistance
`incorporated into probe 1 is shown by reference to FIG.
`4. Oximeter 60 contains a microprocessor 61, and a read
`only memory 62 and random access memory 63. Table
`A (the same table used for calibrating probe 1 at the
`factory) no matter how extensive, may be easily pro-
`grammed into ROM 62 at the time oximeter 60 is fabri-
`cated. Current 1 from current source 69 is passed
`through resistor 40. The resulting voltage (per Ohm’s
`law) is passed through multiplexor 66 through compara-
`tor 65, to microprocessor 61.
`Microprocessor 61 may be programmed to calculate
`the resistance of resistor 40 and thereafter to look up the
`wavelengths of LED’s 10, 20 from Table A in ROM 62.
`Microprocessor 61 is also programmed to itself recali-
`brate the optical comparison circuitry of oximeter 60
`once the wavelengths of LEDs 10, 20 are known. By
`this means,
`it
`is not required to recalibrate by hand
`oximeter 60 for each new probe 1 nor, alternatively, to
`require that LEDs 10, 20 be of precisely standardized
`wavelengths.
`'
`The specific function and design of the circuitry sche-
`matically illustrated in FIG. 4 is seen as obvious when
`taken in combination with the general description of its
`function. The functions of microprocessors and read
`only memories are well known and understood and it is
`well within the capability of a person with ordinary skill
`in the art to design and program microprocessor 61 to
`calculate the resistance' of resistor 40 and thereby obtain
`the wavelengths of LEDs 10, 20 from a simple lookup
`table in a ROM 62.
`Probe 1 may be used with any number of prior art
`oximeters, the method of operation of which is well
`understood and beyond the scope of the teaching of the
`present invention. Basically, for each heart beat, fresh
`arterial blood is pumped into the capillaries of finger 51,
`thereby causing a periodic increase and decrease in light
`intensity observed by sensor 30. The oxygen saturation
`of hemoglobin in the pulsatile blood may be determined
`by the oximeter 60. For any known wavelength, there is
`a known extinction coefficient B. Given B and measur—
`ing the intensity of diffused light received by sensor 30
`the oxygen saturation can be computed and displayed.
`In fact, the coefficients B of the various wavelengths of
`table A can be substituted for the wavelengths directly
`when the table is programmed into ROM 62, thereby
`eliminating a computational step.
`Microprocessor 61, through LED control circuitry
`67, operates LEDs 10, 20. Light from LEDs 10, 20
`results in current in sensor 30 which passes through
`
`

`

`7
`amplification and filtration circuitry 68 to multiplexor
`66. Comparator 65 and a digital to analog converter 70
`are operative as an analog to digital converter means to
`present a digital signal
`to the microprocessor 61,
`thereby allowing microprocessor 61 to determine oxy-
`gen saturation and/or pulse rate. Results are shown on
`display 64.
`Referring to FIG. 5, an alternate way of coding a
`probe of this invention is illustrated. Specifically, an
`eight pin connector 52 similar to the connector 52 of
`FIG. 4 illustrated having respective lead lines 201, 202,
`203 respectively communicating to light emitting diode
`130, light emitting diode 132 and photodetector 138.
`Conductor 204 is illustrated providing the ground con-
`nection.
`It will be noted that the eight pin connector 52 of
`FIG. 5 has four empty channels. These channels can be
`provided to communicate the coded value of the probe.
`For example, assuming that
`the connectors when
`provided with a common potential provide a true bi—
`nary value and when independent of any potential (i.e.,
`a high impedance or open circuit) provide a false binary
`value. Thus, the four conductors of plug 57., as illus-
`trated in FIG. 5, would communicate the binary value
`1100. Thus, communication of the resistance value of
`the connected probe would be possible by coding the
`connector to a value of 1 part in 16.
`Those skilled in the art will appreciate that other
`binary connections could as well be made. For example,
`by expanding the number of connectors on the probe
`relatively large expansions can occur.
`Those skilled in the art will realize that in determin-
`ing the variable transmission of light in human flesh the
`frequency at which the flesh is integrated by a substan-
`tially monochromatic light source is critical. If the fre-
`quency varies the results of the instrument can be inac-
`curate with such variation. Simply stated, at different
`points in the spectral frequency, oxygenated hemoglo-
`bin and reduced hemoglobin transmit varying amounts
`of light.
`Commercially produced light emitting diodes do
`have variation in their spectral frequency from diode to
`diode. Therefore if such commercially produced diodes
`are going to be used as replaceable probes in an instru=
`ment it has been found that provision must be made for
`a probe by probe calibration of the instrument. Thus,
`effectively disposable probes can be readily used even
`though they are affecting integration at differing fre-
`quencies from probe to probe.
`Some comment can be made directed specifically at
`calibrating the disposable probe of the instrument
`herein. As a practical matter, the blood of a human is
`interrogated through the skin by light transmission uti-
`lizing red and infrared. The rate of change of constants
`in the infrared is relatively flat. Therefore a variance in
`the frequency of the infrared diode has little effect.
`Not so in the red range. It has been found that the
`attenuation of light in oxygenated and unoxygenated
`hemoglobin has a rapidly changing slope in the red
`range. This being the case, it is of primary concern to
`calibrate in the particular instrument illustrated in the
`red range.
`Those skilled in the art will realize that there are
`many ways in which change of instrument calibration
`can occur. Specifically, separate look—up tables can be
`generated for various grouped relationships. Alter—
`nately, and perhaps more productively,
`incremental
`alternation to the constants of curvature between the
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4,700,708
`
`5
`
`10
`
`15
`
`8
`saturation level S and the ratio of quotients R of light
`transmission can be determined.
`Although the foregoing invention is described in
`some detail by way of illustration and example for pur-
`pose of clarity of understanding, it is understood that
`certain changes and modifications may be practiced and
`equivalents employed within the spirit of the invention
`as limited only by the scope of the appended claims. For
`example, two resistors may be used in place of one, each
`resistor coded to the wavelength of a separate LED.
`Other components could be used in place of resistors,
`e.g., capacitors or the like. Therefore, the above de—
`scription and illustrations should not be construed as
`limiting the scope of the invention which is defined by
`the appended claims.
`What is claimed is:
`1. An oximeter probe system for use with an oxime—
`ter, said system comprising:
`a first light emitting means emitting light having a
`20'
`first known wavelength value;
`means for sensing the light emitted by said first light
`emitting means;
`means for detachably wiring the probe to the oxime-
`ter and for providing communication of electrical
`signals between the probe and the oximeter; and
`encoding means for providing signals to the oximeter
`which are indicative of the known wavelength
`value of said first light emitting means.
`2. The system of claim 1, further comprising a second
`light emitting means emitting light having a second
`known wavelength value;
`wherein said light sensing means also senses light
`emitted by said second light emitting means; and
`wherein said encoding means further provides elec-
`trical signals to the oximeter
`indicative of the
`known wavelength value of the light emitted by
`the second light emitting means.
`3. The system of claim 1, wherein said encoding
`means comprises an electrical impedance element, the
`value of which is preselected to correlate with said
`known wavelength value.
`4. The system of claim 3 wherein said electrical impe-
`dance element is a resistor.
`5. The system of claim 4 wherein said signals which
`are indicative of said known wavelength value are volt-
`age signals produced by passing a current through said
`resistor.
`6. The system of claim 1 wherein said means for de-
`tachably wiring the probe to the oximeter has associ-
`ated therewith a plurality of connector pins, and
`wherein the presence or absence of electrical connec-
`tions between certain of said connector pins comprises
`part of said encoding means.
`7. An oximeter probe system comprising:
`a first light emitting means emitting light having a
`first known wavelength value;
`means for sensing the light emitted by said first light
`emitting means;
`means for detachably wiring the probe to the oxime-
`ter and for providing communication of electrical
`signals between the probe and the oximeter;
`encoding means for providing signals to the oximeter
`which are indicative of the known wavelength
`value of said first light emitting means, said encod—
`ing means comprising an electrical impedance ele—
`ment, the value of which is preselected to correlate
`with said known wavelength value; and
`
`4O
`
`

`

`4,700,708
`
`9
`decoding means responsive to said encoded signals
`for selecting appropriate calibration coefficients
`for use in calculating oxygen saturation based upon
`the known wavelength of said first light emitting
`means.
`
`8. The system of claim 7 wherein said electrical impe-
`dance element is a resistor.
`9. The system of claim 8 wherein said signals which
`are indicative of said known wavelength value are volt-
`age signals produced by passing a current through said
`resistor.
`10. An oximeter probe system comprising:
`a first light emitting means emitting light having a
`first known wavelength value;
`means for sensing the light emitted by said first light
`emitting means;
`means for detachably wiring the probe to the oxime-
`ter and for providing communication of electrical
`signals between the probe and the oximeter, said
`means for detachably wiring the probe to the oxim-
`eter having associated therewith a plurality of con-
`nector pins;
`encoding means for providing signals to the oximeter
`which are indicative of the known wavelength
`value of said first light emitting means, the pres—
`ence or absence of electrical connections between
`
`10
`certain of said connector pins comprising part of
`said encoding means; and
`decoding means responsive to said encoded signals
`for selecting appropriate calibration coefficients
`for use in calculating oxygen saturation based upon
`the known wavelength of said first light emitting
`means.
`
`11. An oximeter probe system comprising:
`a first light emitting means emitting light having a
`first known wavelength value;
`means for sensing the light emitted by said first light
`emitting means;
`'
`means for detachably wiring the probe to the oxime-
`ter and for providing communication of electrical
`signals between the probe and the oximeter;
`encoding means for providing signals to the oximeter
`which are indicative of the known wavelength
`value of said first light emitting means; and
`decoding means responsive to said encoded signals
`for