as) United States
`a2) Patent Application Publication (0) Pub. No.: US 2010/0261986 Al
`(43) Pub. Date: Oct. 14, 2010
`
`Chinet al.
`
`US 20100261986A1
`
`(54) MOTION COMPATIBLE SENSOR FOR
`NON-INVASIVE OPTICAL BLOOD ANALYSIS
`
`(75)
`
`Inventors:
`
`Rodney Chin, Oakland, CA (US);
`Paul Mannheimer, Danville, CA
`(US); Ross Flewelling, Oakland,
`CA (US)
`
`Correspondence Address:
`NELLCOR PURITAN BENNETT LLC
`ATTN: IP LEGAL
`6135 Gunbarrel Avenue
`Boulder, CO 80301 (US)
`
`(73) Assignee:
`
`Nellcor Puritan Bennett LLC,
`Boulder, CO (US)
`
`(21) Appl. No.:
`
`12/822,898
`
`(22)
`
`Filed:
`
`Jun. 24, 2010
`
`Related U.S. Application Data
`
`(60) Continuation of application No. 11/827,858, filed on
`Jul. 13, 2007, which is a continuation of application
`No. 10/991,111, filed on Nov. 16, 2004, now Pat. No.
`
`7,260,425, which is a continuation of application No.
`10/080,433, filed on Feb. 21, 2002, now Pat. No. 6,845,
`256, whichis a division of application No. 09/348,437,
`filed on Jul. 7, 1999, now Pat. No. 6,374,129, whichis
`a division of application No. 08/722,443, filed on Oct.
`10, 1996, now Pat. No. 6,018,673.
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`(2006.01)
`AGIB 5/1455
`(52) US. C0. ceecccccccccccescssssssssssssssssnsvnnentnseesseseeee 600/324
`
`(57)
`
`ABSTRACT
`
`A non-invasive optical sensor which uses the motion signalto
`calculate the physiological characteristic being measured.
`For pulse oximetry, a least squares or a ratio-of-ratios tech-
`nique can be applied to the motion signalitself. This is made
`possible by selecting a site on the patient where variations in
`motion produce signals of two wavelengths which are suffi-
`ciently correlated. In particular, it has been determinedthat a
`sensorplaced on a nail, in particular a thumbnail, exhibits the
`characteristics of having the red and infrared signals corre-
`lated when used for pulse oximetry, and theresulting signals
`correlate to arterial oxygen saturation.
`
`
`
`
`
`TIME
`
`Log I
`
`APPLE 1075
`Apple v. Masimo
`IPR2022-01291
`
`1
`
`APPLE 1075
`Apple v. Masimo
`IPR2022-01291
`
`

`

`Patent Application Publication
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`Oct. 14,2010 Sheet 1 of 10
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`US 2010/0261986 Al
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`
`
`
`
`TIME
`
`FIG. 17
`
`red
`
`FIG. 2
`
`Log 1(t)
`
`IR-
`
`2
`
`

`

`Patent Application Publication
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`Oct. 14,2010 Sheet 2 of 10
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`US 2010/0261986 Al
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`32
`
`pa
`
`[*
`
`
`
`FIc. 4
`
`3
`
`

`

`Patent Application Publication
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`Oct. 14,2010 Sheet 3 of 10
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`US 2010/0261986 Al
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`
`
`FIG. 5
`
`
`Lomas 7
`FE
`
`
`4
`
`

`

`Patent Application Publication
`
`Oct. 14,2010 Sheet 4 of 10
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`US 2010/0261986 Al
`
`
`
` + issajous—Bandpass OOo
`
`Redof,
`
`NO MOTION
`HIGH SATURATION(100%)
`
`MOTION
`HIGH SATURATION(100%)
`
`LOW SATURATION(70%)
`
`NO MOTION
`LOW SATURATION(70%)
`
`MOTION
`
`FIG. &C
`
`FIG. &D
`
`5
`
`

`

`Patent Application Publication
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`Oct. 14,2010 Sheet 5 of 10
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`US 2010/0261986 Al
`
`
`
`
`STPA
`JNA?IWTere. 9
`PWNWN7h71ba
`$sppppepe
`
`FIG. 9B
`ReadingSp03 Control Sensor SpQ,
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`
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`TestSensor
`
`FIG. 10
`
`6
`
`

`

`Patent Application Publication
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`Oct. 14,2010 Sheet 6 of 10
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`US 2010/0261986 Al
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`
`
`paNP|etfaye
`
`NOI
`
`aee|a
`
`FIG. 114
`
`(PRIOR ART)
`
`7
`
`

`

`Patent Application Publication
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`Oct. 14,2010 Sheet 7 of 10
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`US 2010/0261986 Al
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`
`
`
`1 AK
`_i...
`AASNaPit—
`i
`
`
`
`FIG. 118
`
`8
`
`

`

`Patent Application Publication
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`Oct. 14,2010 Sheet 8 of 10
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`US 2010/0261986 Al
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`
`
`FIG. 16
`
`FIG. 15
`
`9
`
`

`

`Patent Application Publication
`
`Oct. 14,2010 Sheet 9 of 10
`
`US 2010/0261986 Al
`
` CALCULATE
`
`OXYGEN
`SATURATION
`
` MOTION
`
`
`
`
`
`
`DISPLAY
`SELECT &
`SELECT &
`DISPLAY
`PULSE & OXYGEN
`
`ACTIVATE
`
`
`ACTIVATE
`OXYGEN
`
`
`SATURATION
`
`SATURATION
`REFLECTANCE
`TRANSMITTANCE
`
`
`
`
`SENSOR
`SENSOR
`
`
`
`
`FIG. 17
`
`
`
`
`MONITOR 120
`
`SENSOR
`DRIVE
`CIRCUIT
`
`CONTROLLER
`
`GEN.
`
`12
`
`PUMP
`CONTROL
`
`FIG. 18
`
`
`
`DETECTOR
`
`
`
`
`
`110 FREQ,|~} BANDPASS we
`FILTER
`
`
`oceN
`CALC.
`PROCESSOR
`
`
`itd
`
`118
`
`10
`
`10
`
`

`

`Patent Application Publication
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`Oct. 14,2010 Sheet 10 of 10
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`132
`
`134
`
`140
`
`
`
`FIG. 19
`
`11
`
`11
`
`

`

`US 2010/0261986 Al
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`Oct. 14, 2010
`
`MOTION COMPATIBLE SENSOR FOR
`NON-INVASIVE OPTICAL BLOOD ANALYSIS
`
`CROSS-REFERENCES TO RELATED
`APPLICATIONS
`
`[0001] This application is a continuation of U-S. applica-
`tion Ser. No. 11/827,858, filed on Jul. 11, 2007, which is a
`continuation of U.S. application Ser. No. 10/991,111 filed
`Nov. 16, 2004, now U.S. Pat. No. 7,260,425, which is a
`continuation of U.S. application Ser. No. 10/080,433, filed
`Feb. 21, 2002, now U.S. Pat. No. 6,845,256, whichis a divi-
`sion of U.S. application Ser. No. 09/348,437, filed Jul. 7,
`1999, now U.S. Pat. No. 6,374,129, whichis a division ofU.S.
`application Ser. No. 08/722,443, filed Oct. 10, 1996, now
`USS. Pat. No. 6,018,673, which disclosures are incorporated
`by reference for all purposes.
`
`BACKGROUNDOF THE INVENTION
`
`[0002] The present invention relates to optical sensors for
`non-invasive determination of physiological characteristics,
`and in particular to sensors for making such determinationsin
`the presence of motion.
`[0003] Many types of optical sensors are used to measure
`physiological characteristics ofa patient. Typically, an optical
`sensor provides emitted light which is then scattered through
`tissue and detected. Various characteristics of a patient can be
`determined from analyzing such light, such as oxygen satu-
`ration, pulse rate, pH,etc.
`[0004]
`Pulse oximetry is typically used to measure various
`blood characteristics including, but not limited to, the blood-
`oxygen saturation of hemoglobin in arterial blood, the vol-
`umeofindividual blood pulsations supplying the tissue, and
`the rate of blood pulsations corresponding to each heartbeat
`of a patient. Measurementof these characteristics has been
`accomplished by use of a non-invasive sensor whichscatters
`light through a portion of the patient’s tissue where blood
`perfuses the tissue, and photoelectrically senses the absorp-
`tion of light in such tissue. The amountof light absorbed is
`then used to calculate the amount of blood constituent being
`measured.
`
`[0005] The light scattered through the tissue is selected to
`be of one or more wavelengthsthat are absorbed by the blood
`in an amount representative of the amount of the blood con-
`stituent present in the blood. The amountoftransmitted light
`scattered through the tissue will vary in accordance with the
`changing amount of blood constituent in the tissue and the
`related light absorption. For measuring blood oxygenlevel,
`such sensors have typically been provided with a light source
`that is adapted to generate light of at least two different
`wavelengths, and with photodetectors sensitive to both of
`those wavelengths, in accordance with knowntechniques for
`measuring blood oxygensaturation.
`[0006] Known non-invasive sensors include devices that
`are securedto a portion of the body, such asa finger, an ear or
`the scalp. In animals and humans, the tissue of these body
`portions is perfused with blood and the tissue surface is
`readily accessible to the sensor. A photoelectric pulse trans-
`ducer from World Precision Instruments is described as even
`recording signals through the fingernail.
`[0007] Optical sensors are typically either reflective or
`transmissive. Transmissive sensors have the emitter and
`detector on opposite sides ofa finger, toe, nose or othertissue.
`They measure light transmitted through the tissue from one
`
`side to the other. Reflectance sensors, on the other hand, have
`the emitter and detector side-by-side, such as placement on
`the forehead, or on a fetus where it is difficult to position a
`sensor over a finger, etc. Reflectance sensors detect light
`whichis scattered back to the same surface.
`
`is to determine the
`the goal
`In pulse oximetry,
`[0008]
`amount of oxygen in arterial blood, as distinguished from
`venous blood or the tissue itself. The light emitted can be
`absorbed byall three, however, and they need to be distin-
`guished among. FIG.1 illustrates a plot ofthe logarithm ofthe
`detected intensity signal versus time. Solid line 10 is the
`detected infrared signal in a pulse oximeter, shown varying
`with time. Dotted line 12 is the detected red wavelength
`signal. As can be seen, the value moves up and down with the
`heartbeat frequency, due to the pulsing of the blood through
`the arteries. The portion of the signal below line 14is repre-
`sentative of light absorbed by the tissue, venous blood, and a
`baseline componentofthearterial blood.
`[0009] Using appropriate signal analysis, the DC portion
`can be climinated, leaving an extracted AC portion whichis
`due to absorption by arterial blood. As can be seen in FIG.1,
`and more clearly in FIG. 2, the red and infrared signals,
`although varying by different amounts, are in phase. FIG. 2
`illustrates a plot over an epochof timeofthe red logarithmic
`signal versus the infrared logarithmic signal, and is com-
`monlyreferred to as a Lissajous plot. As can be seen,a line is
`formed, indicating they are in phase.
`[0010] This characteristic of the red and infrared signals
`allows the determination of oxygen saturation through two
`methods. In a first method, the “ratio of ratios” is calculated,
`whichis the ratio, between red andinfrared,ofthe logarithms
`of the quotients obtained by dividing the maximum signal
`intensity and the subsequent minimum signalintensity. This
`ratio-of-ratios is then used in a predetermined formula to
`calculate arterial oxygen saturation. This is described more
`fully in U.S. Pat. No. 4,653,498.
`[0011]
`In a second method, referred to here as “least
`squares,” a least squares regression analysis is performed on
`the above-mentionedLissajousplot to determine the slope of
`the ensemble of data points taken during an epoch oftime.
`This slope is then used in a predetermined formula to deter-
`minearterial oxygen saturation. Other techniquesare set forth
`in a co-pending application entitled “Method and Apparatus
`for Estimating Physiological Parameters Using Model-Based
`Adaptive filtering,” filed Jun. 7, 1996, Ser. No. 08/660,510,
`the disclosure of which is hereby incorporated by reference.
`[0012]
`Insomecases, it is desirable to measure the oxygen
`saturation of the venousbloodin orderto get an indication of
`how much oxygen is being used by the body. Thearterial
`blood, on the other hand, gives an indication of how much
`oxygenis being delivered to the body. In Shiga U.S. Pat. No.
`4,927,264, the oxygen saturation in venous bloodis deter-
`mined by inducing a venous pressure with a pressure cuff.
`This effectively varies line 14 of FIG. 1 at a frequencydiffer-
`ent from the heart rate, so that it can be separatelyfiltered and
`isolated and comparedtothe arterial pulse. The non-varying
`portion is then assumedto be thetissue absorption and can be
`distinguished from the slowly varying pressure induced
`venous blood absorption. An alternate approach can be used
`in extracorporeal monitoring where the blood is actually
`pumpedout of the body and then back in. Such a techniqueis
`set forth in an article by Odell et al., entitled “Use of Pulse
`Oximetry to Monitor Venous Saturation During Extracorpo-
`real Life Support”Critical Care Medicine,vol. 22, no. 4 (Apr.
`
`12
`
`12
`
`

`

`US 2010/0261986 Al
`
`Oct. 14, 2010
`
`4, 1994). In Odell, the venous blood being pumpedoutof the
`body passesthe sensor, and the pumping mechanism provides
`an artificial pulse allowing the use of pulse oximetry tech-
`niques.
`[0013] Motion artifact can degrade a pulse oximetry signal
`relied upon by a physician, without the physician’s aware-
`ness. This is especially true if the monitoringofthe patient is
`remote, the motionis too small to be observed, or the doctor
`is watching the instrumentor other parts of the patient, and
`not the sensorsite. Thus, typically techniques are employed to
`reduce the effects of motion or compensate for motion.
`[0014]
`In one oximeter system described in U.S. Pat. No.
`5,025,791, an accelerometer is used to detect motion. When
`motion is detected, readings influenced by motionare either
`eliminated or indicated as being corrupted. In a typical
`oximeter, measurements taken at the peaks and valleys of the
`blood pulse signal are used to calculate the desired character-
`istic. Motion can cause a false signal peak andvalley, result-
`ing in a measurement having an inaccurate value and one
`whichis recorded at the wrong time. In U.S. Pat. No. 4,802,
`486, assigned to Nellcor Puritan Bennett, the assignee of the
`present invention, an EKGsignal is monitored and correlated
`to the oximeter reading to provide synchronizationto limit the
`effect of noise and motion artifact pulses on the oximeter
`readings. This reduces the chances of the oximeter locking
`onto a periodic motion signal. Still other systems, such as the
`one described in U.S. Pat. No. 5,078,136, assigned to Nellcor
`Puritan Bennett, use signal processing in an attemptto limit
`the effect of noise and motion artifact. The ’136 patent, for
`instance, uses linear interpolation and rate of change tech-
`niques to analyze the oximeter signal. U.S. Pat. No. 5,337,744
`sets forth sensor modifications used to improve the immunity
`of the signal from motionartifacts.
`the measurement
`[0015] The motion signal
`impedes
`because it obscures the cardiac signal. The motion signal can
`have many components, such as, for example, the emitter or
`detector physically moving away from the body, or a volume
`of venous andarterial blood sloshing around in response to
`the motion, or the signal path being shortened or lengthened
`by expansion or compression of the tissue due to motion.
`[0016] Contrary to conventional practice, signal analysis
`mightbe able to directly use the time-varying motionsignal to
`calculate oxygen saturation. Under some conditions,
`the
`ratio-of-ratios (or least squares) resulting from a motion-
`induced signal has the same valueasthe ratio-of-ratios (or
`least squares) for the cardiac induced signal. The red and
`infrared intensity signals are often not in phase, and can limit
`the use ofthe motionsignalfor calculating oxygen saturation.
`Oneofthe factors that may cause thisis illustrated in FIG.3.
`As FIG.3 illustrates, light from emitter 28 can pass through
`skin 13, fat 15, muscle 16, and bone 18, on its way to a
`detector 30. Light of one wavelength may, on average, take
`path 32, while light of another wavelength may penetrate
`deeper and take path 34. Motion will cause disproportionate
`variancesin the path lengths of the two wavelengthsoflight,
`resulting in out-of-phase signals of the detector.
`
`BRIEF SUMMARY OF THE INVENTION
`
`[0017] The present invention provides a non-invasiveopti-
`cal sensor which uses the motionsignal to calculate the physi-
`ological characteristic being measured. For pulse oximetry, a
`least squaresor a ratio-of-ratios technique can be applied to
`the slope of the motion signalitself. This is made possible by
`selecting a site on the patient where motion producessignals
`
`at two wavelengths which are adequately correlated with each
`other. Adequately correlated signals have a “closed” or
`“nearly closed” Lissajous. In particular, it has been deter-
`minedthat a sensor placed on a nail, in particular a thumbnail,
`exhibits the characteristics of having the red and infrared
`signals in phase when usedfor pulse oximetry.
`[0018] The present invention also provides an optical sen-
`sor whichfits entirely ona nail. No adhesive orother securing
`mechanism aroundtherestofthe finger is necessary, resulting
`in the entire sensor moving with the nail. The use ofthe nail
`site reduces the likelihood of out-of-phase motion signals for
`red and infrared wavelengths, and takes advantage of the
`predominantly arterial blood saturation characteristic of the
`blood present beneath the nail. In addition, the nail is an
`advantageous surface for adhering the sensor to, and at this
`location the method of attachmentallowsa low profile, low
`masssensorto be used whichfurtherlimits differential phase
`errors due to motion.
`
`Preferably, the sensor on a nailof the present inven-
`[0019]
`tion is a reflectance-type sensor. In one embodiment, a closer
`spacing is used than in typical prior art sensors, preferably
`less than 5 mm, more preferably approximately 4 mm.It has
`been empirically determined that the physiological charac-
`teristics at a nail site produce an improved signal with closer
`spacing. In addition, the sensor preferably has a curvature
`which conformsto the shape ofthe nail, and is attached with
`an adhesive.
`
`Inalternate embodimentsof the invention, artificial
`[0020]
`motion may be induced with an air bag or otherwise to pro-
`duce a motion signal which can be used with the sensorofthe
`invention. In particular, this could be used for patients with
`low perfusion, a weak heartbeat or no heartbeat such asis the
`case during heart bypass surgery.
`[0021] Fora further understanding ofthe nature and advan-
`tages of the invention, reference should be madeto the fol-
`lowing description taken in conjunction with the accompany-
`ing drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a graph ofthe log ofthe infrared and red
`[0022]
`intensity signals for pulse oximeters.
`[0023]
`FIG. 2 is a graph of the red and IR signals showing
`correlation.
`
`FIG. 3 isa diagram ofthe different average paths of
`[0024]
`different wavelength light through a patient.
`[0025]
`FIG. 41s a perspective view of a nail sensor accord-
`ing to the present invention on a thumb.
`[0026] FIG.5 is across-sectional, cutaway view of a thumb
`showing its components.
`[0027]
`FIG. 6isaend, cutaway view of one embodimentof
`a conformable nail sensor according to the present invention.
`[0028]
`FIG. 7 is a diagram of a sensor according to the
`present invention placed longitudinally to span the lunula of
`the nail.
`
`FIGS. 8A-8Dare Lissajousplots of the output of a
`[0029]
`sensor according to the invention with and without motion,
`and at low and high saturation.
`[0030]
`FIG. 9A is a plot of the red and infrared frequency
`distribution (FFT of time signals) showing experimental
`results from a thumbnail sensor according to the invention.
`[0031]
`FIG. 9B is a plot of the Lissajous for the results of
`FIG.9A.
`
`13
`
`13
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`

`

`US 2010/0261986 Al
`
`Oct. 14, 2010
`
`FIG. 10 is a graph showinga plot of oxygen satura-
`[0032]
`tion readings of a sensor according to the present invention
`comparedto a standardprior art sensor.
`[0033] FIGS.11A and11B compare the priorart sensor and
`the present invention. The output waveforms and Lissajous
`plot are shownfor each.
`[0034]
`FIG. 12 is a diagram ofan alternate embodiment of
`the invention showing a combinationreflective and transmis-
`sive sensor.
`
`FIG. 13 is a diagram ofan alternate embodiment of
`[0035]
`the invention showing a self-contained nail sensor with its
`owndisplay.
`[0036]
`FIG. 14 is a diagram ofa nail sensor with a motion
`inducing mechanism accordingto the present invention.
`[0037]
`FIGS. 15 and 16 are top andside viewsofthe motion
`stimulating mechanism of FIG. 14.
`[0038]
`FIG. 17 is a flowchart of one embodimentofa pro-
`gram for responding to whether motion or a cardiac pulse is
`used for calculating saturation.
`[0039]
`FIG. 18 is a block diagram of one embodiment of
`portions of an oximeter using controlled generation of
`motion.
`[0040] FIG.19 is adiagram of an embodimentofthe sensor
`using a cylindrical lens and a tinted adhesive.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`maybelimited by the presence of bone 52, preventing one of
`the wavelengths from going deeper into tissue and having a
`different distance to travel. This effect is provided by the
`selection of the thumbnail asa site, and the use of reflectance
`oximeter sensor as opposed to a transmissive sensor. In a
`transmissive sensor, light would have to travel around the
`bone deep through the tissue, and the red and infrared may
`travel different lengths and be affected differently by motion.
`[0046] Connective tissue layer 54 is thin and apparently
`strongly connective. Thus, the expansion and compression of
`tissues, particularly fatty tissues, which may cause out of
`phase motionartifacts for other sites and types of sensors, is
`apparently greatly reduced here. Because the thumbnail 56
`itself provides a strong mounting platform, the sensor can be
`securely attachedto it with adhesive, avoiding the emitter and
`detector from separating from the patient and causing gaps
`that may cause corrupt ratio-of-ratio values.
`[0047] The region beneath nail 56 also provides a region
`which appears to be concentrated with oxygen saturated
`blood similar to the saturation ofarterial blood. Oxygen con-
`sumption beneath the nail appears to be small relative to the
`circulationthere,or the relative volume of venous blood may
`be negligibly small.
`[0048] The presence of many small capillaries, rather than
`large vessels, makes the region more homogeneous, and thus
`lessens the likelihood that two different light wavelengths
`would be affected differently by passing through differing
`regions. In the absence of motion,the high perfusion allows a
`normalpulse oximetry reading to be made. During the occur-
`rence of motion, the large amountof blood present allows a
`strong motion signal to be obtained, since a lot of blood is
`moved around by the motion. In experiments conducted by
`the inventors, motion artifact signals greater than 50 times
`that of a normal pulsatile plethysmograrn signal have been
`observed. The nail site also appears to have a nailbed-tissue
`boundary that is optically phase-matchedfor the wavelengths
`of the sensor.
`
`FIG. 4 illustrates a sensor 40 according to the
`[0041]
`present invention preferably mounted on a nail 42 (a thumb-
`nail or any other digit may be used). The sensoris held on with
`adhesive, and has an emitter 44 and a detector 46. A flexible
`circuit 48 provides the electrical connections to the emitter
`and detector, and may be accordion-shaped betweenthe sen-
`sor and a securing band 50 to provide additional strain relief.
`This isolates the sensor from tugging or pulling on the elec-
`trical connection cord from either the sensor side or the other
`direction. Band 50 maybe,for instance, an elastic band, cloth
`wrap secured with Velcro™, or another device. Flexible cir-
`Inaddition to measuring oxygensaturation, the nail-
`[0049]
`cuit 48 could be electrical wires or fiber optic cables. The
`bed is a good site for other optical sensors. For example,
`different 25 wavelength light could be premixed using the
`glucose detection which requires the use of a near infrared
`fiber optic cable.
`wavelength could be used. Among the blood properties or
`[0042] The placementonthetop ofthe nail allows the cable
`constituents that can be measuredare blood gases (CO,, O,),
`to extend alongthe topof the finger or other digit, without the
`pH,glucose, drug concentrations, or other analytes (THb,
`sensoror the cable being on the palmarside ofthe digit where
`Het, lactate, K*, Na*, Ca,*,etc.).
`it would interfere with grasping or other functionality of the
`hand.
`[0050]
`FIG. 6 is an end, cutaway view of one embodiment
`[0043] As can be seen, the emitter 44 and detector 46 are
`of a sensor 40 according to the present invention. Emitter 44
`and detector 46 are shown mounted onaflexible circuit board
`arranged laterally across the width of the nail. However, a
`longitudinal arrangement(discussed morefully below) or any
`60. An electrical cord 62 provides the connection to the elec-
`other arrangement on a nail is possible. The spacing of the
`trical components of circuit board 60. The body of the sensor
`emitter and detector may be varied, but an optimum spacing
`is preferably a semi-rigid piece of black poron foam. A metal
`was experimentally foundto be less than 10 mm,preferably
`strip could be imbeddedto give extra rigidity. An adhesive is
`less than 5 mm, more preferably approximately 4 mm.
`attached to underside 64 of the sensor to attach it securely to
`the nail. The underside is also curved to conform to the shape
`[0044] Thenailbedmakes a goodsite for the sensor because
`of the nail, but is slightly flexible to allow adaptation to
`it has been observed that motion generates artifact signals for
`differing nail shapes. Different curvature sensors could be
`the red and infrared wavelengthsthat are largely correlated to
`one another. The inventors have observedthat this results in a
`provided for different sizes and shapes of nails to provide
`optimum fit, or the bottom surface could be fabricated from a
`ratio-of-ratios (or least squares) which correlates well with
`softer, more conforming material.
`the arterial oxygen saturation.
`[0051] One characteristic of the nail as a site is that the nail
`[0045] Referring to FIG. 5, a cross-sectional view of the
`thumb is shown. Ascan be seen, the thumb includes a bone 52
`itself could act as a light pipe, shunting light between the
`with a thin layer ofconnective tissue 54 between the bone and
`emitter and the detector. Preferably, the light travels through
`thumbnail 56. A numberof characteristics may contribute to
`the tissue beneath the nail along a path 66. However, some
`the improved signal and the motion inducedartifact being in
`light could bounce back andforth throughthe nail itself ona
`phase. The different wavelength paths illustrated in FIG. 3
`path 68 between the emitter and detector in a manner not
`
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`US 2010/0261986 Al
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`Oct. 14, 2010
`
`present, sensor 74, which may be moresensitive to the cardiac
`pulse signal, could be used. Alternately, a single pair of red
`and infrared emitters could be used, with a reflectance detec-
`tor on the nail, and a transmissive detector off the nail.
`Depending on the mode, a switch in the sensor, or in an
`intermediate amplifier module, or in the oximeter monitor
`could select between the detectors. In another embodiment, a
`single detector is used, with one pair of emitters on the nail,
`and another pair of emitters off the nail. Alternately, a com-
`pletely separate transmissive sensor could be used.
`[0060]
`In somepatients, in particular those with low blood
`perfusion, it may be difficult to lock onto a pulse waveform.
`The additional transmissive sensor could be used to enable
`
`unlike a waveguide. To limit this shunting, the sensor body is
`madeto absorb light, or at least the region between the emitter
`and detector is madeat least partially absorbing to the wave-
`lengths of interest. In this way, each timelightstrikesthe side
`of the nail adjacent the absorbing layer, it will be absorbed,
`rather than propagating along the nail.
`[0052]
`Shunting can also be limited by recessing the emit-
`ter and detector and providing a narrow numerical aperture.
`Because ofthe rigidity of the sensor body, recessing will not
`producevariationsin distance during motion. By limiting the
`numerical aperture of the emitter and detector to values less
`than 0.9, preferably to valuesless than 0.5, the emitter will not
`directly launch light into the nail “waveguide,” and light
`which docs potentially travel path 68 will be outside the
`acceptance angle of the detector.
`[0053] The nail also provides advantages for adhering the
`sensor to the patient since the nail does not have the quantity
`of oils or sweat as present on the skin.
`[0054]
`FIG. 7 is a diagram of a sensor 700 arranged longi-
`tudinally along a nail 706. The sensor has an emitter 702 and
`a detector 704 which are not both onthe lunulaofthe nail. The
`
`lunula is the light colored area of the nail below line 708 in
`FIG.7. It is believed that if both the emitter and detector are
`
`located on the lunula, more undesirable shunting oflight will
`occur.
`
`locking on for such patients. In addition, a transmissive sen-
`sor could be used to calibrate the nail sensor “on-the-fly.”
`Because of shunting and other unique aspects ofthe nailsite,
`a predetermined calibration may be off. A measurement of
`saturation using the transmissive and the nail reflectance sen-
`sors could be donein the absence ofmotion, with a correction
`factor appliedto the reflectance sensor. The correction could
`be a constant which is added or a multiplicative factor, or
`both. If measurements are done at different saturations, a
`calibration line or curve could be determined by the oximeter
`to allow adjustments anywhere along the calculated curve.
`FIG. 8 has FIGS. 8A-8D which show the Lissajous
`[0055]
`Subsequently, in the presence of motion, the nail sensor will
`plots and calculated saturations for a sensor according to the
`be more accurately calibrated.
`present invention during four conditions: motion and no
`[0061]
`FIG. 13 illustrates an alternate embodiment of the
`motion at high and low saturation. As can be seen in FIGS. 8A
`invention in whichaself-contained sensor 80 accordingto the
`and 8B at high saturation, the calculated saturation 100% is
`present invention includes the processing circuitry on one or
`equivalent with or without motion. In FIG. 8B, the motion
`more semiconductorchips inside, and has its own display 82,
`signal is seen to be more than 10 timeslarger than the cardiac
`which may be a liquid crystal display, for instance. In one
`signal of FIG. 8A (FIGS. 8A and 8C are magnified by 10).
`Similar results occurat low saturation as seen in FIGS. 8C and
`embodiment, a button 84 allows switching between modes,
`8D where the saturation valuesare calculated to be 70% under
`such as between displaying a pulse and oxygensaturation.In
`both conditions.
`an alternate embodiment,a flex connection 86 to a module 88
`attached on a band 90 maybe used. Module 88 might contain
`the battery, or alternately the processing circuitry, or the dis-
`play. Additionally, either embodiment could be used for a
`wireless transmission to an oximeter, with the transmitting
`circuit either being in module 88 or sensor body 80.
`[0062]
`FIG. 14 illustrates another embodiment of the
`present invention in which a stimulatoris used to generate an
`artificial pulse. A stimulator could electrically stimulate the
`nerves to cause motion of an appendage, or could use a
`pneumatic pressure cuffto stimulate an artificial pulse; or use
`electro-mechanical stimulation or any other mechanism
`which generates a pulse characteristically different (e.g.,
`amplitude, frequency, shape, etc.) than the cardiac pulse so
`that the cardiac pulse need not be used. Such an apparatus
`would be particularly advantageous for patients with low
`blood perfusion or a weak heartbeat. FIG. 14 is one embodi-
`ment showing a sensor 92 mounted on a thumbnail, with an
`airbag 94 mounted to the bottom of the thumb andheld in
`place with a band 96. A hose 98to the airbag periodically
`inflates and deflates it, causing a pressure wave throughthe
`thumb, giving artificially induced motion. This pressure
`induced motion providesthe variation neededfor sensor 92 to
`measure the oxygensaturation using eitherthe ratio-of-ratios
`or a least squares technique. If the motion is in the frequency
`range of a heartbeat, the sensor can be backward compatible
`with existing oximeter monitors, even those that look for a
`cardiac signal.
`
`FIG. 9A is a graph of the frequency distribution of
`[0056]
`the detected red and infrared signals for a sensor ofthe present
`invention in an experiment with an 8 Hzartificial motion
`pulse applied. The cardiac signature can be seen at the lower
`frequencies below 5 Hz, while the 8 Hz driven motion signal
`is also visible. FIG. 9B is a graph ofthe red versus infrared
`intensity signals for the experimentillustrating that both sig-
`nals are correlated and representative of the same saturation.
`[0057]
`FIG. 10 illustrates the oxygensaturation readings of
`a sensor according to the present invention in experimental
`tests without motion comparing it with a standard priorart
`transmissive sensor at another site. A close agreement was
`noted, indicating the calibration of this sensor on the nailbed
`site is similar to a conventional transmission sensor.
`
`FIGS. 11A and 11B show a comparisonofthe out-
`[0058]
`put waveform and Lissajous, in the presence of motion, of a
`sensor according to the present invention (FIG. 11B) with a
`standard prior art transmissive sensor at another site (FIG.
`11A).
`FIG. 12 illustrates an alternate embodiment of the
`[0059]
`present invention in which a nail sensor 70 according to the
`present invention is attached via a flexible circuit 72 to a
`transmissive sensor 74 which wraps aroundthe finger and has
`an emitter 76 and detector 78 positioned on top and on the
`bottom of the finger. Such a combination sensor could allow
`the oximeter monitor with its program to choose between the
`sensors depending upon motion conditions. When motion is
`present, nail sensor 70 could be used, and when motionis not
`
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`US 2010/0261986 Al
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`Oct. 14, 2010
`
`FIG. 15 illustrates airbag 94 in a top view, showing
`[0063]
`hose 98 connected to a diaphragm pump 100. FIG. 16 shows
`aside view ofthe airbag 94 of FIG. 15, showingthatit is wide
`butflat.
`
`FIG. 17 isa flowchart of one embodimentof a por-
`[0064]
`tion of a program for operating an oximeter so that either
`cardiac pulses or motion pulses can be used to calculate
`oxygen saturation. The oxygen saturation is calculated in a
`known manner(step A). In a first alternative, the signal is
`analy