RX-0335
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`APL_MAS_ITC_00023168
`RX-0335.0001
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`1
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`APPLE 1038
`Apple v. Masimo
`IPR2022-01291
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`5,830,137
`Page 2
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`U.S. PATENT DOCUMENTS
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`4,167,331
`4,266,554
`4,267,844
`4,357,105
`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
`
`9/1979 Nielsen .
`5/1981 Hamaguri .
`5/1981 Yamanishi .
`11/1982 Loretz .
`10/1983 Wilber .
`5/1984 Heinemann .
`2/1985 Gloima etal. .
`5/1986 Hamaguri.
`9/1987 Hamaguri .
`1/1989 Smith .
`2/1989 Malinouskas .
`2/1989 Hersh et al. .
`4/1989 Frick etal. .
`9/1989 Stone et al. .
`11/1989 Hausman et al. .
`3/1990 Corenman et al. .
`
`4,934,372
`4,997,769
`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
`
`6/1990
`3/1991
`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
`
`Corenman et al. .
`Lundsgaard .
`Schmitt et al. .
`Schweitzer et al. .
`Stone etal. .
`Clark et al. .
`Rother.
`Kohnoet al. .
`Chance .
`Polson .
`Hatschek .
`Minnich .
`Erdman .
`Takasugi et al.
`Mannheimer .
`Athan et al.
`.
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`.....
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`w 348/71
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`APL_MAS_ITC_00023169
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`RX-0335.0002
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`DISPLAY
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`U.S. Patent
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`Nov. 3, 1998
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`Sheet 2 of 7
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`5,830,137
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`Nov. 3, 1998
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`Sheet 3 of 7
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`Nov. 3, 1998
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`Sheet 4 of 7
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`U.S. Patent
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`5,830,137
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`U.S. Patent
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`Nov. 3, 1998
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`Sheet 5 of 7
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`U.S. Patent
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`Nov. 3, 1998
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`Sheet 7 of 7
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`5,830,137
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`INITIALIZE
`SYSTEM
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`FREQUENCY DOMAIN:
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`5,830,137
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`1
`GREEN LIGHT PULSE OXIMETER
`
`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.
`
`BACKGROUNDOF THE INVENTION
`
`10
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`2
`length and an infrared (800-940 nm) wavelength, (2) detect-
`ing the time-varying electromagnetic 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.
`
`Accritical 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 oflight 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
`known to 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 probes are 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 (e.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
`radiation. The electromagnetic radiation interacts with the
`blood and a residual optical signal is 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
`LFC produces a periodic electrical signal in the form of a
`pulse train having a frequency proportional
`to the light
`intensity. 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
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`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 thearterial system
`until it reaches the capillaries at which point a portion ofthe
`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 consciousness orsuffer permanent
`brain damageif 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 recommended as a standard of care for every
`general anesthetic.” Kevin K. Tremper & Steven J. Barker,
`Pulse Oximetry, Anesthesiology, January 1989, at 98.
`An oximeter determinesthe 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 maximum is 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 s
`saturation in arterial blood utilize the relative difference
`between the electromagnetic radiation absorption coefficient
`of deoxyhemoglobin, RHb, and that of oxyhemoglobin,
`HbO.,. The electromagnetic radiation absorption coefficients
`of RHb and HbO, are characteristically tied to the wave-
`length of the electromagnetic radiation traveling through
`them.
`
`60
`
`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 twoor
`more selected wavelengths, e.g., a red (600-700 nm) wave-
`
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`5,830,137
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`3
`silicon photodiode, a current-to-voltage converter (a tran-
`simpedance amplifier), a preamplifier, 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 theart.
`
`It is therefore an advantage ofthe present invention to
`provide a green-light
`reflectance-type pulse oximeter
`capable of measuring oxygen saturation at central body
`surfaces.
`
`is a further object of this invention to provide a
`It
`reflectance-type pulse oximeter using only green wave-
`lengths oflight to measure oxygen saturation.
`These and other advantages ofthe present invention shall
`become more apparent from a detailed description of the
`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 below serve to example the principles of
`this invention.
`
`is a block diagram of a pulse oximeter of the
`1
`FIG.
`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—4 of 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 viewof 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 How 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
`description which follows is to be understood as being a
`broad, teaching disclosure directed to persons of skill in the
`appropriate arts, and not as limiting upon the present inven-
`tion.
`
`two green light
`invention,
`According to the present
`sources alternatively illuminate a patient’s skin 2 and an
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`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 signal is 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 according to the
`present invention. The 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 (LEDs) 13, 15 in FIG. 1; however, other green light
`sources can be used, such as 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 oflight that can be used range
`from about 500 nm to about 600 nm.
`
`Depending on the particular green light sources chosen,
`green optical filters 16, 18 might be needed. For example, if
`the Toshiba Ltd. part nos. TLGA183P and TLPGA-183Pare
`used as green LEDs 13, 15 then narrow-bandoptical 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 TLGAI83P and
`TLPGA-183P are used, then one to four LEDs of each green
`frequency are needed.
`the
`Whichever particular green light sources are used,
`green light 20 emitted from the 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 nmare preferred due to current
`commercial availability.
`Whichever peak wavelengths and wavelength bandsare
`used, what is important is that electromagnetic radiation 20
`from the first source 12 must have an absorption coefficient
`with respect to oxyhemoglobin that is substantially different
`(i.e., 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
`detected that
`is substantially different
`(i.e., measurably
`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
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`5,830,137
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`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 LFCsignal line 32. The LFC signal is
`input into a counter 34, which is in circuit communication
`with the processor 30.
`The LFC28 produces a periodic electrical signal in the
`form ofa pulse train having a frequency corresponding to
`the intensity of the broadband optical signal received by the
`LFC 28, One suitable LPC 52 is the TSL235, 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-vollage 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 shown in 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 34 is 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 known in 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 EPROM microcontroller, which is
`available from Microchip Technology Inc., address 2355
`West Chandler Blvd., Chandler, Ariz. 85224-6199, (602)
`786-7668. Another suitable processor is the TMS320C32
`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), and associated
`control circuitry, such as decoders and multi-phase clocks,
`floating point coprocessors, etc. (all not shown)all in circuit
`communication, as is well knownin 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
`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
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`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 from the
`value storedat the previous edge. Either way, the result is a
`counter value corresponding to the time difference between
`the two pulse edges. Many other configurationsare possible.
`The counter 34 can either count pulses or elapsed time
`between edges andthe 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 powerdriver 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 such lines
`and they and the sources 12, 14 are electrically connected
`such that only one source emits green lightif one of the two
`driver lines is grounded and the otheris at, e.g., +5 WDC
`(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 LEDs 13,
`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 748 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 current limiting 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.
`
`What is critical about the drivers 24is that they properly
`drive the sources 12, 14 and that they be interfaced with the
`processor 30 in such a way that oximetry data is gathered.
`For example,
`the processor 30 might actually control the
`alternate illumination 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 14 to alternatively illuminate the patient’s skin 2
`and the processor would then receive a timing signal relating
`to which source is currently illuminating.
`Somedrivers 36 might need a normalizing function that
`increases or decreasesthe intensity of electromagnetic radia-
`tion generatedby thelight 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
`of an adult, it is generally accepted that an LED intensity
`calibrated to measure the oxygen saturation 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
`
`12
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`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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`5
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`20
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`The transmitter 42 transmits a signal 46 using an antenna 48.
`The receiver 44 receives the signal 46 using a second
`antenna 50 and passes the information to the display circuit
`40. The transmitter 42, receiver 44, and the two antennas 48,
`50 can be any suitable radio frequency or other wireless
`telemetry system, including infrared, biomedical (49 MHz),
`or microwave systems. These telemetry systems are well
`known in the art and widely available from common
`sources. Additionally, spread spectrum technology (~900
`MHz or 2.4 GHz) provides a highly secure link, a high noise
`immunity, and a high informational capacity, all of which are
`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, P.O. Box 5582, Akron, Ohio 44334-0582
`(receiver).
`
`5
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`5
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`60
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`65
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`In the oximeter 10 of the present invention, the normal-
`izing function might be not neededif an LFC is used. The
`TSL235 has a dynamic range of approximately 118 dB.
`Moreover,
`the TSL230 is an LFC with a computer-
`interfacable gain control for amplification or attenuation of
`the optical signal, thereby providing an even higher dynamic
`range. These very wide dynamic ranges allow the use of
`drivers 36 to be configured such that the intensities of the
`light sources 12, 14 are set at fixed, predetermined values.
`Said another way, these LFCs are so sensitive that an light
`intensity suitable for an infant might still generate a reflected
`optical signal 24 in an adult strong enough to determine the
`saturation value of that adult. Thus, the drivers 36 might not
`need to have the ability to normalize the intensities of the
`sources 12, 14.
`Preferably, the processor 30 is in circuit communication
`with a local display 38 to display a visual image correspond-
`ing to the oximetry data. The local display 38 can be any
`display capable of displaying a visual image corresponding,
`to one or more oxygen saturation values at the desired 2
`resolution, The local display 38 can display any number of
`different visual images corresponding to the oximetry data.
`For example, a simple numeric liquid crystal display (LCD)
`can be used to numerically display the saturation value. In
`the alternative, or in addition, a graphical LCD can be used
`to display the saturation value and display the pulse plethys-
`mograph waveform. In addition, discrete display LEDs (not
`shown) may be used if the designer desires to display merely
`a binary oxygen saturation level. For example, green,
`yellow, and red discrete LEDs can be configured to represent
`safe, critical, and emergency conditions corresponding to
`saturation valuesof greater than 90percent, 70 to 90percent,
`and less than 70 percent, respectively.
`Preferably, the processor 30 is also in circuit communi-
`cation with a remote display 40 to display a second visual
`image corresponding to the oximetry data. Like the local
`display,
`the remote display 40 can have any number of
`configurations. In addition to the displays listed above in
`connection with the local display 38, the remote display can
`be an integral part of a nurses’ station receiver or some other
`personal data receiver. In the alternative, the remote receiver
`can be a standard personal computer (not shown) configured
`to display the desired image and numerical values.
`The processor 30 and the remote display 40 are placedin
`circuit communication via a transmitter 42 and receiver 44.
`
`30
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`35
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`AC
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`45
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`8
`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
`at the sensor location. However, in the alternative, different
`data can be transmitted such as that has not been completely
`processed, e.g., the raw square-wave output 32 from the
`LFC 28 ordigital words from the high speed counter. This
`alternative embodiment requires significantly less process-
`ing power at the sensor location.
`Referring now to FIG. 2, an alternative oximeter 60
`according to the present
`invention is shown. The use of
`green sources 12, 14 and drivers 36 are the same as FIG. 1.
`The optical signal 24 with the time-varying intensity is
`detected by a photodiode 62. The photodiode 62 generates a
`low-level current proportional to the intensity of the elec-
`tromagnetic radiation received by the photodiode 62. The
`current is converted to a voltage by a current to voltage
`converter 64, which may be an operational amplifier in a
`current to voltage (transimpedance) configuration.
`The resulting signal 65is then filtered with a filter stage
`66 to remove unwanted frequency components, such as any
`60 Hz noise generated by fluorescent lighting. The filtered
`signal 67 is then amplified with an amplifier 68 and the
`amplified signal 69 is sampled and held by a sample and
`hold 70 while the sampled and held signal 71 is digitized
`with a high-resolution (e.g., 12-bit or higher) analog to
`digital converter (ADC) 72. The digitized signal 73 is then
`read from the processor 30.
`Referring now to FIGS. 3-7, one embodimentof a probe
`80 according to the present
`invention is shown. Surface
`mount LEDs 13a—13d and 15a—15d and the LFC 28 are
`mountedon a printed circuit board (PCB) 81. Surface mount
`LEDs 13@—13d can be part no. SML-OLOMTTS86 (563 nm),
`from ROHM Corp., 3034 Owen Drive, Antioch, Tenn.
`37013, which are available from Bell Industries, Altamente
`Springs, Fla. Surface mount LEDs 15a—15d can be part no.
`SSL-LXISYYC-RPTR from Lumex Optocomponents, Inc.
`(585 nm), which are available from Digikey Corp., 701
`Brooks Avenue South, Thief River Falls, Minn. 56701-0677.
`The LEDs 13a—13d and 15a—15d are surface mounted in a
`roughly circular pattern around the LFC 28. The PCB 81 is
`mountedin a cylindrical housing 82 having an annular lip 83
`projecting from one end. PCB 81 is held in place between a
`PCB spacer 84 and a housing spacer 85. A housing cap 86
`closes off the other end of the housing 82. A light shield 87
`shields the LFC 28 from direct illumination by the LEDs
`13a—13d and 15a—15d. The PCB spacer 84 and the shield 87
`engage a clear face 88, with the PCB spacer 84 engaging an
`outer surface 89 of the face 88 and the shield 87 positioned
`within an annular channel 90 cut into the face 88.
`
`The face 88 comprises three sections: a clear, colorless
`area 91, a first filtered area 16, and a secondfiltered area 18.
`The filters 16, 18 are glued along a seam 92 with an
`appropriate optically clear adhesive,
`leaving a circular
`region into which the clear, colorless area 91 is glued at a
`circular seam 93. In the alternative, the face 88 can be made
`in a single piece (including pieces 16, 18, and 91) and
`coatings 94 and 95 can be used to implementthe filters 16
`and 18. Although shownasflat surfaces, face pieces 16, 18,
`and 91 can alternatively be shaped to form discrete lenses
`(not shown) to focus the radiant energy from the LEDs
`13a—13d and 15a—15d onto the skin 2 and into the blood 4
`and from the skin 2 onto the photodiode 26, 62. The face 88
`steps down at an annular shoulder 96 to a thinner portion 89,
`which engages the lip 83 of the housing 82.
`The PCB 81 can be made of common materials including
`fiberglass PCB material. The housing 82, PCB spacer 84,
`
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`9
`housing spacer 85, housing cap 86, and light shield 87 can
`all be injection molded of an opaque plastic such as several
`of the opaque injection-moldable plastics sold under the
`trademark “ZELUX.” If made of one piece, the face 88 can
`be made of glass, which can endure the high temperature
`processing required to apply some narrowband coatings.
`One appropriate coating for coatings 94, 95 is a multilayer
`dielectric coating dep