US006330468B1
`(10) Patent No.:
`a2) United States Patent
`US 6,330,468 B1
`Scharf
`(45) Date of Patent:
`Dec. 11, 2001
`
`
`(54) SYSTEM USING GREEN LIGHT TO
`DETERMINE PARMETERS OF A
`CARDIOVASCULAR SYSTEM
`
`(75)
`
`Inventor:
`
`John Edward Scharf, Oldsmar, FL
`(US)
`,
`,
`(73) Assignee: University of South Florida, Tampa,
`FL (US)
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`(21) Appl. No.: 09/185,140
`(22)
`Filed:
`Nov. 3, 1998
`
`Related U.S. Application Data
`
`OTHER PUBLICATIONS
`.
`.
`oo,
`“Optimization of Portable Pulse Oximetry Through Fourier
`Analysis” by Scharf, et al., IEEE, 6/93, pp. 233-235, first
`available on Apr. 2, 1993, at
`the IEEE, 12th Southern
`Biomedical Conference at Tulane University, New Orleans,
`LA,held 4/2-4/93.
`“Pulse Oximetry Through Spectral Analysis” by Scharf, et
`al., 1993 IEEE, 6/93, pp. 227-229,first available on Apr. 2,
`1993, at the IEEE, 12th Southern Biomedical Conferenceat
`Tulane University, New Orleans, LA, held 4/2-4/93.
`“Direct Digital Capture of Pulse Oximetry Waveforms” by
`Scharf, et al., 1993 IEEE, 6/93, pp. 230-232, first available
`on Apr. 2, 1993, at IEEE, 12th Southern Biomedical Con-
`ference at Tulane University, New Orleans, LA, 4/2-4/93.
`Light-To-Frequency Converter—TSL220, Texas Instru-
`ments, Inc., D3619, 8/90, Rev. 6/91.
`Programmable Light-To-Frequency Converter—TSL230,
`Texas Instruments, Inc., SOESOO7A, 12/92, Rev. 12/93.
`CMOS—8-Bit Buffered Mulytiplying DAC—AD7524,
`Digital—To—Analog Convertes, Rev. A, pp. 2-399, 402,403.
`(63) Continuation of application No. 08/749,898,filed on Nov.
`Burr-Brown ACF2101 Advertisement and Product Data
`18, 1996, now Pat. No. 5,830,137.
`Sheet (PDS—1079, 3/91).
`Tint. Cdn? eeeeeecceseseeeecceenneseennnsneeeeeeee A61B 6/00
`(SL)
`
`
`
`
`
`
`(52) US. CD. ee ceeeceeeceeeeeeteeceeceeeeeetenereeeeteeeeeeeeneeeeees 600/476 “In Vivo Reflectance of Blood and Tissue as a Function of
`(58) Field of Search 0.0... 600/309, 310,
`Light Wavelength” by Cui, et al., IEEE, Transactions of
`600/479, 473, 475, 476, 477; 356/41; 250/214 A,
`Biomedical Engineering, vol. 37, No. 6, Jun. 1990, pp.
`214 LA, 214 LS
`632-639.
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`Primary Examiner—Brian L. Casier
`(74) Attorney, Agent, or Firm—Calfee, Halter & Griswold
`TIP
`
`3,802,776
`3,815,583
`4,109,643
`4,167,331
`4,206,554
`4,267,844
`4,357,105
`
`4/1974 Tchang .
`6/1974 Scheidt .
`8/1978 Bondetal. .
`9/1979 Nielsen.
`5/1981 Hamaguri.
`5/1981 Yamanishi.
`11/1982 Loretz .
`(List continued on next page.)
`
`FOREIGN PATENT DOCUMENTS
`63-311937
`12/1988 (IP).
`1377605
`2/1986 (SU).
`WO-9011044 * 10/1990 (WO) vce eees 600/310
`92/07505
`5/1992 (WO).
`
`(57)
`
`ABSTRACT
`
`A reflectance pulse oximeter that determines oxygen satu-
`ration of hemoglobin using two sources of electromagnetic
`radiation in the green optical region, which provides the
`maximum reflectance pulsation spectrum. The use of green
`light allows placement of an oximetry probe at central body
`Sites (e.g., wrist, thigh, abdomen, forehead, scalp, and back).
`Preferably, the two green light sources alternately emit light
`at 560 nm and 577 nm,respectively, which gives the biggest
`difference in hemoglobin extinction coefficients between
`deoxyhemoglobin, RHb, and oxyhemoglobin, HbO,.
`
`5 Claims, 7 Drawing Sheets
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`DRIVERS
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`US6,330,468 B1
`Page 2
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`U.S. PATENT DOCUMENTS
`
`4,407,290
`4,447,150
`4,498,020
`4,586,513
`4,694,833
`4,800,495
`4,807,630
`4,807,631
`4,824,242
`4,869,254
`4,883,353
`4,911,167
`4,934,372
`4,997,769
`
`10/1983
`5/1984
`2/1985
`5/1986
`9/1987
`1/1989
`2/1989
`2/1989
`4/1989
`9/1989
`11/1989
`3/1990
`6/1990
`3/1991
`
`.
`
`Wilber.
`Heinemann .
`Gloimaet al.
`Hamaguri .
`Hamaguri .
`Smith .
`Malinouskas.
`Hershetal. .
`Frick et al.
`.
`Stone et al. .
`Hausmanetal. .
`Corenmanetal. .
`Corenmanetal. .
`Lundsgaard .
`
`5,040,539
`5,047,208
`5,078,136
`5,111,817
`5,113,861
`5,149,503
`5,167,230
`5,190,038
`5,299,570
`5,308,919
`5,365,924
`5,512,940
`5,524,617
`5,575,284
`
`8/1991
`9/1991
`1/1992
`5/1992
`5/1992
`9/1992
`12/1992
`3/1993
`4/1994
`5/1994
`11/1994
`4/1996
`6/1996
`11/1996
`
`* cited by examiner
`
`.
`Schmitt et al.
`Schweitzer et al. .
`Stone et al. .
`Clark et al.
`.
`Rother.
`Kohnoet al.
`Chance .
`Polson et al.
`Hatschek .
`Minnich .
`Erdman.
`Takasugiet al.
`Mannheimer.
`Athan et al. .
`
`.
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`.
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`2
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`

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`U.S. Patent
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`Dec. 11, 2001
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`Dec. 11, 2001
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`U.S. Patent
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`Dec. 11, 2001
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`Sheet 7 of 7
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`
`
`
`SYSTEM
`
`00
`
`COLLECT THREE
`QUARTERS OF
`DATA
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`FIG.9
`
`9
`
`

`

`US 6,330,468 B1
`
`1
`SYSTEM USING GREEN LIGHT TO
`DETERMINE PARMETERS OF A
`CARDIOVASCULAR SYSTEM
`
`Thisis a continuation of U.S. patent application Ser. No.
`08/749,898, filed Nov. 18, 1996, entitled GREEN LIGHT
`PULSE OXIMETER, now USS. Pat. No. 5,830,137.
`
`FIELD OF THE INVENTION
`
`The present invention relates generally to medical diag-
`nostic instruments and, more specifically, to a pulse oxime-
`ter using two green light sources to detect
`the oxygen
`saturation of hemoglobin in a volumeof intravascular blood.
`BACKGROUND OF THE INVENTION
`
`The degree of oxygen saturation of hemoglobin, SpO.,,in
`arterial blood is often a vital index of the condition of a
`
`patient. As blood is pulsed through the lungs by the heart
`action, a certain percentage of the deoxyhemoglobin, RHb,
`picks up oxygen so as to become oxyhemoglobin, HbO,.
`From the lungs, the blood passes through the arterial system
`until it reaches the capillaries at which point a portion of the
`HbO, gives up its oxygen to support the life processes in
`adjacent cells.
`By medical definition, the oxygen saturation level is the
`percentage of HbO, divided by the total hemoglobin;
`therefore, SpO,=HbO.,/(RHb+HbO,). The saturation value
`is a very important physiological value. A healthy, conscious
`person will have an oxygen saturation of approximately 96
`to 98%. A person can lose consciousnessor suffer permanent
`brain damage if that person’s oxygen saturation value falls
`to very low levels for extended periods of time. Because of
`the importance of the oxygen saturation value, “Pulse oxim-
`etry has been recommendedasa standard of care for every
`general anesthetic.” Kevin K. Tremper & Steven J. Barker,
`Pulse Oximetry, Anesthesiology, January 1989, at 98.
`An oximeter determines the saturation value by analyzing
`the change in color of the blood. When radiant energy
`interacts with a liquid, certain wavelengths may be selec-
`tively absorbed by particles which are dissolved therein. For
`a given path length that the light traverses throughthe liquid,
`Beer’s law (the Beer-Lambert or Bouguer-Beer relation)
`indicates that
`the relative reduction in radiation power
`(P/Po) at a given wavelength is an inverse logarithmic
`function of the concentration of the solute in the liquid that
`absorbs that wavelength.
`the
`For a solution of oxygenated human hemoglobin,
`extinction coefficient maximumis at a wavelength of about
`577 nm (green) O. W. Van Assendelft, Spectrophotometry of
`Haemoglobin Derivatives, Charles C. Thomas, Publisher,
`1970, Royal Vangorcum LTD., Publisher, Assen, The Neth-
`erlands.
`Instruments that measure this wavelength are
`capable of delivering clinically useful information as to
`oxyhemoglobinlevels. In addition, the reflectance pulsation
`spectrum showsa peak at 577 nm as well. Weijia Cui, Lee
`L. Ostrander, Bok Y. Lee, “In Vivo Reflectance of Blood and
`Tissue as a Function of Light Wavelength”, IEEE Trans.
`Biom. Eng. 37:6:1990, 632-639.
`In general, methods for noninvasively measuring oxygen
`saturation in arterial blood utilize the relative difference
`
`between the electromagnetic radiation absorption coefficient
`of deoxyhemoglobin, RHb, and that of oxyhemoglobin,
`HboO,,.The electromagnetic radiation absorption coefficients
`ot RHb and HbO, are characteristically tied to the wave-
`length of the electromagnetic radiation traveling through
`them.
`
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`In practice of the transmittance pulse oximetry technique,
`the oxygen saturation of hemoglobin in intravascular blood
`is determined by (1) alternatively illuminating a volume of
`intravascular blood with electromagnetic radiation of two or
`more selected wavelengths, e.g., a red (600-700 nm) wave-
`length and an infrared (800-940 nm) wavelength, (2) detect-
`ing the time-varying clectromagnetic radiation intensity
`transmitted through by the intravascular blood for each of
`the wavelengths, and (3) calculating oxygen saturation val-
`ues for the patient’s blood by applying the Lambert-Beer’s
`transmittance law to the transmitted electromagnetic radia-
`tion intensities at the selected wavelengths.
`Whereas apparatus is available for making accurate mea-
`surements on a sample of blood in a cuvette, it is not always
`possible or desirable to withdraw blood from a patient, and
`it obviously impracticable to do so when continuous moni-
`toring is required, such as while the patient is in surgery.
`Therefore, much effort has been expanded in devising an
`instrument for making the measurement by noninvasive
`means.
`
`A critical limitation in prior art noninvasive pulse oxime-
`ters is the few number of acceptable sites where a pulse
`oximeter probe may be placed. Transmittance probes must
`be placed in an area of the body thin enough to pass the
`red/infrared frequencies of light from one side of the body
`part to the other, e.g., ear lobe, finger nail bed, and toe nail
`bed. Although red/infrared reflectance oximetry probes are
`knownto those skilled in the art, they do not function well
`because red and infrared wavelengths transmit through the
`tissue rather than reflect back to the sensor. Therefore,
`red/infrared reflectance sensor probesare not typically used
`for many potentially important clinical applications includ-
`ing: use at central body sites (e.g., thigh, abdomen, and
`back), enhancing poor signals during hypoperfusion,
`decreasing motion artifact, etc.
`
`SUMMARYOF THE INVENTION
`
`According to the present invention, a reflectance oximeter
`is provided using two green light sources to detect the
`oxygen saturation of hemoglobin in a volume of intravas-
`cular blood. Preferably the two light sources emit green light
`centered at 560 nm and 577 nm,respectively, which gives
`the biggest difference in absorption between
`deoxyhemoglobin, RHb, and oxyhemoglobin, Hbo,. The
`green reflectance oximeter is a significant
`improvement
`compared to the red/infrared state of the art because the
`reflectance pulsation spectrum peaks at 577 nm.Practically,
`several combinations of two green light sources can be used.
`Ideally, these light sources comprise very narrow band(e.g.,
`1.0 nm wide) sources such as laser diodes at the desired
`frequencies. However, the benefits of the present invention
`can be realized using other green light sources, such as
`narrow band(e.g., 10 nm wide) light emitting diodes (LEDs)
`at two green frequencies (e.g., 562 nm and 574 nm) with
`optional ultra-narrowband (e.g., 0.5—4.0 nm wide) filters at
`two green frequencies (¢.g., 560 nm and 577 nm).
`In one embodimentof the present invention, two filtered
`green LEDsalternatively illuminate an intravascular blood
`sample with two green wavelengths of electromagnetic
`radiauion. The electromagnetic radiation interacts with the
`blood and a residual optical signalis reflected by the blood.
`Preferably a photodiode in a light-to-frequency converter
`(LFC) detects the oximetry optical signals from the intra-
`vascular blood sample illuminated by the two LEDs. The
`LEC produces a periodic electrical signal in the form of a
`pulse train having a frequency proportional to the light
`
`10
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`

`

`US 6,330,468 B1
`
`3
`iotensity. The data becomes an input to a high-speed digital
`counter, either discrete or internal to a processor(e.g., digital
`signal processor, microprocessor, or microcontroller), which
`converts the pulsatile signal into a digital word suitable to be
`analyzed by the processor. In the alternative, a separate
`silicon photodiode, a current-to-voltage converter (a tran-
`simpedance amplificr), a preamplificr, a filter, a sample and
`hold, and an analog-to-digital (A/D) converter can be used
`to capture the oximetry signal.
`Once inside the processor, the time-domain data is con-
`verted into the frequency domain by, for example, perform-
`ing the well-known Fast Fourier Transform (FFT). The
`frequency domain data is then processed to determine the
`oxygen saturation value using any of a number of methods
`knownto those skilled in the art.
`
`It is therefore an advantage of the present invention to
`provide a green-light
`reflectance-type pulse oximeter
`capable of measuring oxygen saturation at central body
`surfaces.
`
`10
`
`15
`
`is a further object of this invention to provide a
`It
`reflectance-type pulse oximeter using only green wave-
`lengths of light to measure oxygen saturation.
`These and other advantages of the present invention shall
`become more apparent from a detailed description of the 5
`invention.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`In the accompanying drawings, which are incorporated in
`and constitute a part of this specification, embodiments of
`the invention are illustrated, which, together with a general
`description of the invention given above, and the detailed
`description given belowserve to example the principles of
`this invention.
`
`FIG. 1 is a block diagram of a pulse oximeter of the
`present invention;
`FIG. 2 is a block diagram of an alternative circuit of a
`pulse oximeter of the present invention;
`FIG. 3 is a bottom plan view of an oximeter probe
`according to the present invention;
`FIG. 4 is a sectional view taken substantially along the
`plane designated by the line 4—4of FIG. 3;
`FIG. 5 is a bottom plan view of a face 88 of the oximeter
`probe of FIGS. 3 and 4;
`FIG. 6 is an exploded view of the oximeter probe of FIGS.
`3 and 4;
`FIG. 7 is an enlarged partially exploded view showing the
`housing and housing spacer of the oximeter probe of FIGS.
`3 and 4;
`FIG. 8 is a schemato-block diagram showing the interface
`between the processor, the LED drivers, and the light-to-
`frequency converter of the pulse oximeter of present inven-
`tion.
`
`FIG. 9 is a flow chart showing the major process steps
`taken by the processor in calculating the saturation value.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`While the present invention will be described more fully
`hereinafter with reference to the accompanying drawings, in
`which a preferred embodiment of the present invention is
`shown,it is to be understood at the outset of the description
`which follows that persons of skill in the appropriate arts
`may modify the invention here described while still achiev-
`ing the favorable results of this invention. Accordingly, the
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`description which follows is to be understood as being a
`broad, teaching disclosure directed to personsof skill in the
`appropriate arts, and notas limiting upon the present inven-
`tion.
`
`two green light
`invention,
`According to the present
`sources alternatively illuminate a patient’s skin 2 and an
`associated intravascular blood sample 4 with two different
`green wavelengths of electromagnetic radiation. The elec-
`tromagnetic radiation interacts with the blood 4 and a
`residual optical signalis reflected by the blood 4 to the LFC.
`A processor analyzes this optical signal, determines the
`oxygen saturation from the signal, and displays a number
`corresponding to the determined saturation value.
`Referring now more particularly to the accompanying
`drawings, FIG. 1 showsa pulse oximeter 10 accordingto the
`present invention. ‘he oximeter 10 of the present invention
`comprises two emitters of green light 12, 14 that illuminate
`a volumeof intravascular blood 4, The green light sources
`12, 14 are shown schematically as including light emitting
`diodes (IEDs) 13, 15 in FIG. 1; however, other greenlight
`sources can be uscd, suchas laser diodes,filtered white light
`sources, filtered broad-band LEDs,etc. Suitable LEDs 13,
`15 include part. nos. TLGA-183P (peak wavelength 574 nm)
`and TLPGA-183P (peak wavelength 562 nm) from Toshiba
`Ltd.
`through various sources, such as Marktech
`International, 5 Hemlock Street, Latham, N.Y., 12110, (518)
`786-6591. The wavelengths of light that can be used range
`from about 500 nm to about 600 nm.
`
`Depending onthe particular green light sources chosen,
`green optical filters 16, 18 might be needed. For example,if
`the Toshiba Ltd. part nos. TLGA183P and TLPGA-183P are
`used as green LEDs 13, 15 then narrow-band optical filters
`16, 18 need to be used. Suitable optical filters include
`custom-made molded acrylic aspheric lens/filters having
`peak wavelengths of 560 nm and 580 nm, respectively, and
`which have bandwidths of less than 5 nm, which are
`available from Innovations In Optics, Inc., address 38
`Montvale Avenue, Suite 215, Storeham, Mass. 02180, (716)
`279-0806. Also, depending on the particular green light
`sources used, more than one emitter of green light might be
`needed. For example,
`if green LEDs TLGA183P and
`TLPGA-183Pare used, then one to four LEDsof each green
`frequency are needed.
`Whichever particular green light sources are used, the
`greenlight 20 emitted fromthe first emitter of green light 12
`must have a peak wavelength that is different than the peak
`wavelength of the green light 22 emitted by the second
`emitter of green light 14. Also, the wavelength bands of the
`green light emitted by the green light sources 12, 14 must be
`narrow enoughthat usably different signals are generated by
`the interaction between the light 20, 22 and the volume of
`intravascular blood 4, For example, either of two sets of
`wavelengths is equally functional: 542 and 560 nm or 560
`and 577 nm. 560 and 577 nm are preferred duc to current
`commercial availability.
`Whichever peak wavelengths and wavelength bands are
`used, what is importantis that electromagnetic radiation 20
`from the first source 12 must have an absorption coefficient
`with respect to oxyhemoglobin that is substantially different
`(i.c., measurably different) than the absorption coefficient
`with respect to oxyhemoglobin of electromagnetic radiation
`22 emitted by the second source 14. Likewise, if some other
`substance other than oxygen (e.g., carbon monoxide
`(HbCO)) is to be detected, what is important is that elec-
`tromagnetic radiation 20 from the first source 12 must have
`an absorption coefficient with respect to the substance to be
`
`11
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`11
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`

`

`US 6,330,468 B1
`
`5
`(i-e., measurably
`is substantially different
`detected that
`different) than the absorption coefficient with respect to the
`substance to be detected of electromagnetic radiation 22
`emitted by the second source 14. If levels of oxygen and
`carbon monoxide saturation are to be detected, a third green
`wavelength is added to determine RHb, HbO,, and HbCO
`components. These three components are then used to
`determine levels of oxygen and carbon monoxidesaturation.
`Saturation of HbCO and other blood components is deter-
`mined in a mannerlike HbO.,as disclosed herein.In short,
`the two green light sources alternatively illuminate the blood
`and the resulting signals are placed in the frequency domain
`and used to determine a ratio (R) value. From the R value,
`the saturation value is determined using a look-up table.
`The green light 20, 22 alternately illuminating the volume
`of intravascular blood 4 results in an optical signal 24 with
`a time-varying intensity reflected back from the intravascu-
`lar blood 4 for each of the wavelengths. The resulting signal
`24 comprises the data needed to determine the saturation of
`oxygen in the hemoglobin. The signal 24 is detected by an
`optical detector 26 such as a photodiode 26 of a light-to-
`frequency converter (LFC) 28, which is interfaced to a
`processor 30 via an LFC signal line 32. The LFC signalis
`input into a counter 34, which is in circuit communication
`with the processor 30.
`The LFC 28 produces a periodic electrical signal in the
`form of a pulse train having a frequency corresponding to
`the intensity of the broadband optical signal received by the
`LEC 28. One suitable LFC 52 is the 'I'SL235, manufactured
`and sold by Texas Instruments, P.O. Box 655303, Dallas,
`Tex. 75265. Other LFCs in Texas Instruments’ TSL2XX
`
`series may also be used. Using an LFC eliminates the need
`for a separate silicon photodiode, a current-to-voltage con-
`verter (a transimpedance amplifier), a preamplifier, filter
`stage, a sample and hold, and an analog-to-digital (A/D)
`converter to capture the oximetry signal. As shownin FIG.
`2, and described below in the text accompanying FIG. 2,
`these components can be used in the alternative.
`Referring back to FIG. 1,
`the counter 34 may be an
`external counter or a counter internal to the processor 30, as
`shownin FIG. 1. If the counter 34is an external counter, any
`high speed counter capable of being interfaced to a proces-
`sor may be used. One suitable counter is the 4020 CMOS
`counter, which is manufactured by numerous manufacturers,
`e.g., Texas Instruments, P.O. Box 655303, Dallas, Tex.
`75265, as is well knownin the art.
`The processor 30 may be any processor that can process
`oximetry data in real time and interface and control the
`various devices shown in FIG. 1. One suitable processor is
`a PIC17C43 8-bit CMOS EPROMmicrocontroller, which is
`available from Microchip Technology Inc., address 2355
`West Chandler Blvd., Chandler, Ariz. 85224-6199, (602)
`786-7668. Another suitable processor is the TMS 320C32
`digital signal processor, also manufactured by Texas Instru-
`ments. Another suitable processor is a Zilog 893XX. These
`processors have internal counters 34. Many other CISC and
`RISC microprocessors, microcontrollers, and digital signal
`processors can be used. Some might require random access
`memory (RAM), read-only memory (ROM), andassociated
`control circuitry, such as decoders and multi-phase clocks,
`floating point coprocessors,etc. (all not shown) all in circuit
`communication, as is well known in the art. To be suitable,
`the processor 30 must be capable of being a signal analyzer.
`That
`is,
`the processor 30 must have the computational
`capacity to determine the saturation value from the collected
`data (LFC periodic pulses or ADC data, etc.).
`Interfacing the counter 34 and the processor 30 may be
`done in several ways. The counter 34 and processor 30 may
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`be configured to either (1) count the pulses generated by the
`LFC 28 during a given time period or (2) count the number
`of pulses of a free-running clock (corresponding to the
`amount of time) between the individual pulses of the LFC
`28. Either method will provide satisfactory data. The latter
`method can be implemented in several ways. For example,
`the counter can be reset at each period of the LFC signal. In
`the alternative, at each edge of LFC pulse train, the value in
`the counter can be saved to a register and subtracted fromthe
`value stored at the previous edge. Either way, the result is a
`counter value corresponding to the time difference between
`the two pulse edges. Manyother configurations are possible.
`‘The counter 34 can either count pulses or elapsed time
`between edges and the processor 30 either reads the value in
`the counter periodically by polling the counter, or the
`processor 30 reads the value whenever the counter 34
`generates an interrupt. Again, many other configurations are
`possible.
`Green light sources 12, 14 are driven along green light
`source power driver lines 35 by drivers 36. Although four
`green light source power driver lines 35 are shown for
`clarity, in the alternative there need be only two suchlines
`and they and the sources 12, 14 are electrically connected
`such that only one source emits green light if one of the two
`driver lines is grounded andthe other is at, e.g., +5 VDC
`(current limited), and vice versa. For example, if the sources
`12, 14 are diodes 13, 15, then the cathode of diode 13 is
`connected to the anode of diode 15, the anode of diode 13
`is connected to the cathode of diode 15, and the two nodes
`are connected via green light source powerdriverlines 35 to
`current-limited drivers 36.
`
`The drivers 36 drive the sources 12, 14 at the required
`voltage and current in an alternating manner, as known to
`those skilled in the art. If sources 12, 14 include LEDs13,
`15, then several suitable driver configurations, known to
`those skilled in the art, are available to drive the LEDs 13,
`15 at the required voltage and current. For example, a 74,
`74H,or 74S family buffer or inverter, such as a 7400 can be
`used to directly drive LEDs with suitable current limiting
`resistors (all not shown). As another example, it is common
`to drive LEDs from CMOS, NMOS, 74LS, or 74HC family
`devices with an NPN or PNPtransistor such as a 2N2222
`with suitable currentlimiting resistors (all not shown). Both
`drivers are widely known to those in the art. Additionally,
`constant current drivers 36 for LEDs 13, 15 will tend to
`produce a constant brightness from the LEDs 13, 15. The
`exact parameters of the driver will depend on the particular
`sources 12, 14 selected and are available from common
`sources.
`
`Whatiscritical about the drivers 24 is that they properly
`drive the sources 12, 14 and that they be interfaced with the
`processor 30 in such a way thal oximetry data is gathered.
`For example, the processor 30 might actually control the
`alternate Ulumination of the green sources 12, 14 by actively
`controlling the drivers 36. As another example, the drivers
`36 might have a local oscillator (not shown) that causes the
`sources 12 14to alternatively illuminate the patient’s skin 2
`and the processor would then receive a timing signalrelating
`to which source is currently illuminating.
`Some drivers 36 might need a normalizing function that
`increasesor decreases the intensily of electromagnetic radia-
`tion generated by the light sources 12, 14 in the system. For
`example,
`it might be desirable to be able use a single
`oximeter configuration to measure the oxygen saturation of
`an infant and later to use the same oximeter configuration to
`measure oxygen saturation levels of an adult. Since the
`nature of skin 2 and hair of an infant are different from that
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`US 6,330,468 B1
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`of an adult, it is generally accepted that an LED intensity
`calibrated to measure the oxygensaturation level of an adult
`will be too bright to measure the oxygen saturation level of
`an infant (the optical signal 24 is so bright that the photo-
`diode 26 saturates). Likewise, it is generally accepted that a
`light intensity calibrated to measure saturation of an infant
`will be too dim to provide adequate data to measure the
`oxygen saturation of an adult or a person with heavily
`pigmented skin 2. The normalizing function adjusts the
`intensities of the sources 12, 14 to provide a useful signal
`under most circumstances.
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`8
`desirable in clinical and health care environments. A suitable
`902-908 MHz or 2.4 GHz spread spectrum transmitter/
`receiver pair is available from common sources, such as
`Digital Wireless Corp., One Meczway, Norgrass, Ga., 30093
`(transmitter) and Telxon Pen-Based Computer, 3330 W.
`Market Street, PO. Box 5582, Akron, Ohio 44334-0582
`(receiver).
`Preferably, the transmitter 42 transmits the determined
`parameters, such as oxygen saturation, other gas saturation,
`pulse rate, respiration rate, etc.
`to the receiver 44, which
`requires a high level of digital signal processing capability
`In the oximeter 10 of the present invention, the normal-
`at the sensor location. However, in the alternative, different
`izing function might be not needed if an LFC is used. The
`data can be transmitted such as that has not been completely
`TSL235 has a dynamic range of approximately 118 dB.
`processed, e.g., the raw square-wave output 32 from the
`Moreover,
`the TSL230 is an LFC with a computer-
`LEC 28 or digital words from the high speed counter. This
`interfacable gain control for amplification or attenuation of
`alternative embodiment requires significantly less process-
`the opticalsignal, thereby providing an even higher dynamic
`ing powerat the sensor location.
`range. These very wide dynamic ranges allow the use of
`Referring now to FIG. 2, an alternative oximeter 60
`drivers 36 to be configured such that the intensities of the
`according to the present invention is shown. The use of
`light sources 12, 14 are set at fixed, predetermined values.
`green sources 12, 14 and drivers 36 are the same as FIG. 1.
`Said another way, these LFCs are so sensitive that an light
`The optical signal 24 with the time-varying intensity is
`intensity suitable for an infant mightstill generate a reflected
`detected by a photodiode 62. The photodiode 62 generates a
`optical signal 24 in an adult strong enough to determine the
`low-level current proportional to the intensity of the elec-
`saturation value of that adult. Thus, the drivers 36 might not
`tromagnetic radiation received by the photodiode 62. The
`need to have the ability to normalize the intensities of the ,
`current is converted to a voltage by a current to voltage
`sources 12, 14.
`converter 64, which may be an operational amplifier in a
`Preferably, the processor 30 is in circuit communication
`current to voltage (transimpedance) configuration.
`with a local display 38 to display a visual image correspond-
`The resulting signal 65 is then filtered with a filter stage
`ing to the oximetry data. The local display 38 can be any
`66 to remove unwanted frequency components, such as any
`display capable of displaying a visual image corresponding
`60 Hz noise generated by fluorescent lighting. The filtered
`to one or more oxygen saturation values at
`the desired
`signal 67 is then amplified with an amplifier 68 and the
`resolution. The local display 38 can display any numberof
`amplified signal 69 is sampled and held by a sample and
`different visual images; corresponding to the oximetry data.
`hold 70 while the sampled and held signal 71 is digitized
`For example, a simple numeric liquid crystal display (LCD)
`with a high-resolution (e.g., 12-bit or D higher) analog to
`can be used to numerically display the saturation value. In
`digital converter (ADC) 72. The digitized signal 73 is then
`the alternative, or in addition, a graphical LCD can be used
`read from the processor 30.
`to display the saturation value and display the pulse plethys-
`mograph waveform.In addition, discrete display LEDs (not
`Referring now to FIGS. 3-7, one embodiment of a probe
`shown) maybe used if the designer desires to display merely
`80 according to the present invention is shown. Surface
`mount LEDs 13¢-13d and 15a—15d and the LFC 28 are
`40
`a binary oxygen saturation level. For example, green,
`mounted onaprinted circuit board (PCB) 81. Surface mount
`yellow,and red discrete LEDs can be configured to represent
`LEDs 13a@-13d can be part no. SML-O1LOMTT86 (563 nm),
`safe, critical, and emergency conditions corresponding to
`saturation values of greater than 90 percent, 70 to 90 percent,
`from ROHM Corp., 3034 Owen Drive, Antioch, Tenn.
`37013, which are available from Bell Industries, Altamente
`arid less than 70 percent, respectively.
`Springs, Fla. Surface mount LEDs 15a—15d can be part no.
`Preferably, the processor 30 is also in circuit communi-
`SSL-LXISYYC-RP-TR from Lumex Optocomponents,Inc.
`cation with a remote display 40 to display a second visual
`(585 nm), which are available from Digikey Corp., 701
`image corresponding to the oximetry data. Like the local
`Brooks Avenue South, Thief River Falls, Minn. 56701-0677.
`display,
`the remote display 40 can have any number of
`The LEDs 13a—-13d and 13d and 15a—15d are surface
`configurations. In addition to the displa