as) United States
`a2) Patent Application Publication 10) Pub. No.: US 2015/0018647 Al
`(43) Pub. Date: Jan. 15, 2015
`
`MANDEL etal.
`
`US 20150018647A1
`
`(54)
`
`METHOD AND APPARATUS FOR
`MONITORING A SUBJECT FOR BLOOD
`OXYGEN SATURATION
`
`5/7282 (2013.01); A61B 5/742 (2013.01);
`A61B 5/0022 (2013.01)
`USPC oieecccc cece cee senene creer cscs eneensenees 600/323
`
`(71)
`
`Applicant: Xerox Corporation, Norwalk, CT (US)
`
`(72)
`
`Inventors: Barry P. MANDEL,Fairport, NY (US);
`Peter Johan NYSTROM,Webster, NY
`(US); Lalit Keshav MESTHA,Fairport,
`NY (US)
`
`(73)
`
`Assignee:
`
`XEROX CORPORATION,Norwalk,
`CT (US)
`
`(21)
`
`Appl. No.: 13/937,782
`
`(22)
`
`Filed:
`
`Jul. 9, 2013
`
`Publication Classification
`
`(51)
`
`(52)
`
`Int. Cl.
`A6IB 5/1455
`A6IB 5/00
`US. Cl.
`
`(2006.01)
`(2006.01)
`
`CPC wee A61B 5/14552 (2013.01); A61B 5/681
`(2013.01); A61B 5/6829 (2013.01); A61B
`
`(57)
`
`ABSTRACT
`
`Whatis disclosed is a system and method for monitoring a
`subject of interest for functional blood oxygen saturation
`using an apparatus that can be comfortably worn by the sub-
`ject aroundan area of exposed skin where a photoplethysmo-
`graphic (PPG)signal can be registered. In one embodiment,
`the apparatusis a reflective or transmissive wrist-worn device
`with emitter/detector pairs fixed to an inner side of a band
`with at least two illuminators, each emitting source light at a
`different wavelength band. Each photodetector comprises
`sensors that are sensitive to a wavelength bandofits respec-
`tive illuminator. Each photodetector measuresan intensity of
`sensed light emitted by a respective illuminator. The signal
`obtained by the sensors comprises a continuous PPG signal.
`The continuous PPG signal analyzed for functional blood
`oxygen saturation levels and communicated to a remote
`device. Various embodimentsare disclosed.
`
`fo
`
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`
`c NETWORK
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`

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`116
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`4
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`Jan. 15,2015 Sheet 4 of 10
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`US 2015/0018647 Al
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`Patent Application Publication
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`Jan. 15,2015 Sheet 6 of 10
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`704 705 706
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`” 707
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`FIG. 7
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`7
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`Patent Application Publication
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`Jan. 15,2015 Sheet 7 of 10
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`US 2015/0018647 A1
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`Patent Application Publication
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`Jan. 15,2015 Sheet 8 of 10
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`US 2015/0018647 Al
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`METHEMOGLOBIN
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`

`

`Patent Application Publication
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`Jan. 15,2015 Sheet 9 of 10
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`US 2015/0018647 Al
`
`f
`{
`
`START
`
`\
`poo 1000
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`FUNCTIONAL BLOOD OXYGENATION SATURATION
`
`ACTIVATE AN APPARATUS COMPRISING AT LEAST
`ONE EMITTER/DETECTOR PAIR FIXED TO AN
`INNER SIDE OF ABAND WORN CIRCUMFERENTIALLY
`AROUND AN AREA OF EXPOSED SKIN BY A
`SUBJECT BEING MONITORED FOR
`
`;
`
`1002
`
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`ANALYZE THE CONTINUOUS PPG SIGNAL
`FOR A DETERMINATION OF FUNCTIONAL
`BLOOD OXYGENATION SATURATION LEVELS
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`

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`Patent Application Publication
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`Jan. 15,2015 Sheet 10 of 10
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`RECORDS
`
`PATIENT
`
`11
`
`11
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`

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`US 2015/0018647 Al
`
`Jan. 15, 2015
`
`METHOD AND APPARATUS FOR
`MONITORING A SUBJECT FOR BLOOD
`OXYGEN SATURATION
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`[0001] This patent application is related to concurrently
`filed and commonly owned U.S. patent application Ser. No.
`13/937,740, “Method And Apparatus For Monitoring A Sub-
`ject For Atrial Fibrillation”, by Mestha et al. (Attorney
`Docket 20121584-US-NP), and U.S. patent application Ser.
`No. 13/
`, “Method And Apparatus For Monitoring A
`Subject For Fractional Blood Oxygen Saturation”, by Mestha
`et al. (Attorney Docket 20121584Q1-US-NP), which are
`incorporated herein in their entirety by reference.
`
`TECHNICAL FIELD
`
`[0002] The present invention is directed to an apparatusthat
`can be worn circumferentially around an area of exposed skin
`of a subject being monitored for a functional blood oxygen
`saturation level.
`
`BACKGROUND
`
`BRIEF SUMMARY
`
`[0005] What is disclosed is a method and apparatus for
`monitoring a subject of interest for functional blood oxygen
`saturation. Methods are disclosed for determining a func-
`tional oxygenation saturation level using eithera reflective or
`a transmissive sensing apparatus. Each embodiment com-
`prises emitter/detector pairs fixed to an inner side of a band
`worn circumferentially around an area of exposed skin of a
`subject with at least two illuminators each emitting source
`light at a different wavelength band. In one embodiment
`wherethe present apparatus comprises a transmissive sensing
`device, each photodetector measures an intensity of light
`emitted from its respective paired illuminator which has
`passed through a chord ofliving tissue. In another embodi-
`ment where the present apparatus comprises a reflective
`device, each photodetector measures an intensity of light
`emitted from its respective paired illuminator which has
`reflected off a surface of the skin. In each configuration, a
`time-series signal is generated by the continuous sensing of
`light intensities. The time-series signal comprises a continu-
`ous PPG signal of the subject. In another embodiment, the
`time-series signal is processed to extract the continuous PPG
`signal. Both embodiments are disclosed herein. The continu-
`ous PPG signal is analyzed to determine functional blood
`oxygensaturation levels. Alert signals can be communicated
`to one or more remote devices such as, a smartphone,if the
`monitored levels fall outside a limit of acceptability pre-set
`for this subject.
`[0006] Many features and advantages of the above-de-
`scribed apparatus will becomereadily apparent from the fol-
`lowing detailed description and accompanying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0003] Hemoglobin, also spelled haemoglobin, (Hb, also
`written Hgb) is the iron-containing oxygen transport metal-
`loprotein in red blood cells of most vertebrates and some
`invertebrates. Hemesites within a blood cell contain ferrous
`[Fe?*] ion which has an affinity to oxygen (binds lightly to
`oxygen). The mammalian Hb molecule has a complex qua-
`ternary structure with each Hb molecule having two alpha
`chain and two beta chain polypeptides. Each Hb chain con-
`tains a single molecule of heme (a heme unit). Each unit of
`heme holds an Fe*? ion (also written Fe?*) in such a waythat
`the iron can interact with an oxygen molecule to form oxy-
`genated hemoglobin or oxyhemoglobin (O,Hb, also written
`HbO,). If the hemoglobinis fully saturated then it can trans-
`port four oxygen molecules from the respiratory organs
`(ungsorgills) where the oxygenis received, to body tissues
`where the hemesites release the oxygen they are carrying.
`Oxygenated bloodis bright red dueto the iron being bound to
`oxygen. The oxygen is used by the cells to burn nutrients
`which,in turn, provide energy to powercellular metabolisms.
`The hemesites collect carbon dioxide (CO,) and returns these
`gases back to the respiratory organs to be expelled into the
`surrounding environmentvia a process of exhalation or expi-
`ration. Deoxygenated blood hasa bluish color. There is a need
`for a device that can provideabilities to continuously monitor
`patient’s functional oxygen level seamlessly without imped-
`ing their mobility, causing discomfort or limiting the use of
`their hands using reflective or transmissive sensing arrange-
`ment. The device can be worn on the wrist, ankle, arm orleg.
`The information gathered from the device can be transmitted
`to a smart phone using wireless (e.g. Bluetooth or NFC) or
`wired technology, where it can be analyzed, displayed and
`further transmitted to a central monitoring station via the
`internet.
`
`[0007] The foregoing and other features and advantages of
`the subject matter disclosed herein will be made apparent
`from the following detailed description taken in conjunction
`with the accompanying drawings, in which:
`[0008]
`FIG. 1 illustrates an anterior and dorsal view of a
`subject ofinterest to show various locations where the present
`apparatusis likely to be worn;
`[0009]
`FIG. 2 illustrates the anterior and dorsal views ofthe
`subject of FIG. 1 showing that the present apparatus can also
`be worn circumferentially around the neck and circumferen-
`tially around an area of the subject’s mid-section;
`[0010]
`FIG. 3 shows an embodimentof the present appa-
`ratus being worn circumferentially arounda finger of each of
`the subject’s left and right hands;
`[0011]
`FIG. 4 shows one embodiment of a transmissive
`device worn circumferentially around an area ofexposed skin
`as shownin any of FIGS. 1-3;
`[0012] FIG.5 shows one embodimentofa reflective device
`worn circumferentially around the area of exposed skin of
`FIGS. 1-3;
`[0013]
`FIG. 6 showsthe angularrelationships of the emit-
`ter/detector pair of the reflective device of FIG. 5;
`[0014]
`FIG. 7 shows one embodiment of a control panel
`fixed to an outer side of the bands of each of the transmissive
`andreflective devices of FIGS. 4 and 5;
`[0004] Accordingly, what is needed in this art is a method
`
`[0015] FIG. 8 illustrates Beer’s Law inatissue layer con-
`and apparatus for monitoring a subject of interest for func-
`taining venousandarterial structures;
`tional blood oxygen saturation levels which can be comfort-
`ably worn by the subject circumferentially around an area of
`[0016]
`FIG. 9A plots extinction coefficients for RHb,
`exposed skin.
`HbO,, COHb, and MetHb;
`
`12
`
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`US 2015/0018647 Al
`
`Jan. 15, 2015
`
`FIG. 9B plots extinction coefficients of RHb and
`[0017]
`in regions of red and infrared wavelengths;
`HbO,
`FIG. 10 isa flow diagram of one embodimentof the
`[0018]
`present method for monitoring a subject of interest for func-
`tional blood oxygen saturation; and
`[0019]
`FIG. 11 isa block diagram illustrating one example
`networked system for performing various aspects of the
`teachings hereof;
`
`DETAILED DESCRIPTION
`
`[0020] Whatis disclosed is a system and method for moni-
`toring a subject of interest for functional blood oxygen satu-
`ration using an apparatus which can be comfortably worn
`around an extremity. The present apparatus is disclosed in two
`embodiments, 1.e., a reflective sensing device and a transmis-
`sive sensing device.
`
`Non-Limiting Definitions
`
`[0021] A “subject of interest” refers to a subject having a
`cardiac function. Although the term “human”, “person”, or
`“patient” may be used throughoutthis disclosure, it should be
`appreciated that the subject may not be human.Assuch, use
`of the terms “human”, “person” or “patient” is not to be
`viewedaslimiting the scope ofthe appendedclaimsstrictly to
`human beings.
`[0022] An “area of exposed skin”refers to a circumferen-
`tial region of the subject where a photoplethysmographic
`(PPG) signal can be obtained by various embodiments of the
`apparatus disclosed herein. FIG.1 illustrates an anterior view
`101 of a subject of interest and a dorsal view 102. Various
`circumferential areas of exposed skin are shown where the
`present apparatus is likely to be wom. For example, the
`present apparatus can be worn circumferentially around the
`upper left or right arms at 104 and 105, respectively. Or,
`aroundtheleft or right forearms at 106 and 107; around the
`left or right wrists at 108 and 109; around the upperleft and
`right thigh at 110 and 111; aroundthe left and right calf at 112
`and 113; or aroundthe left and right ankle at 114 and 115.
`FIG.2 illustrates the anterior and dorsal views of the subject
`of FIG. 1 showingthat the present apparatus can also be worn
`circumferentially around the neck 103 and around an area of
`the mid-section 116 where PPGsignals can be registered. The
`illustrations ofFIGS. 1 and 2 should not be viewed as limiting
`the scope hereofto the areas shown, as other embodiments of
`the present apparatus can be worn circumferentially around
`the finger, toe, forehead, hand, and foot. FIG. 3 shows an
`embodimentof the present apparatus being worn circumfer-
`entially around a finger 302 of the subject’s left hand or
`around a finger 303 of the subject’s right hand.
`[0023]
`“Photoplethysmography” is the study of signals
`containing relative blood volume changes in vessels which
`are closeto the skin surface. Sensors of the present apparatus
`using sequentially captured pulsating signals provide a con-
`tinuous time-series signal which, in one embodiment,is the
`subject’s PPG signal. In other embodiments, the time-series
`signal is processed to extract the PPG signal. In this alterna-
`tive embodiment, a sliding windowis used to define consecu-
`tive time-sequential segments of the time-series signal. Each
`signal segmentoverlaps a previous segmentby atleast a 95%.
`Each of the consecutive time-series signal segments is
`detrended to remove low frequency variations and non-sta-
`tionary components. The detrended signal segments are fil-
`tered such that frequencies of the subject’s cardiac beat are
`
`retained. In one embodiment, the filter comprises a higher-
`order band-limited Finite Impulse Response (FIR) Filter
`which constrains band width to a desired range of the sub-
`ject’s heart. Thefiltered time-series signal segments are then
`upsampledto a pre-selected sampling frequencyto increase a
`total numberof data points in order to enhance an accuracy of
`peak-to-peak pulse point detection. In one embodiment,
`upsampling involves an interpolation technique using a cubic
`spline function and a pre-selected sampling frequency. The
`upsampled time-series signal segments are then smoothed
`using any of a variety of smoothing techniques. These pro-
`cessed signal segments are then stitched together to obtain a
`continuous PPGsignalfor the subject. Method for obtaining
`a continuous PPGsignal are disclosed in: “Continuous Car-
`diac Pulse Rate Estimation From Multi-Channel Source
`Video Data”, U.S. patent application Ser. No. 13/528,307, by
`Kyalet al., “Continuous Cardiac Pulse Rate Estimation From
`Multi-Channel Source Video Data With Mid-Point Stitch-
`
`ing”, U.S. patent application Ser. No. 13/871,728, by Kyalet
`al., and “Continuous Cardiac Signal Generation From A
`Video OfA Subject Being Monitored For Cardiac Function”,
`USS. patent application Ser. No. 13/871,766, by Kyaletal., all
`of which are incorporated herein in their entirety by refer-
`ence.
`
`[0024] An “emitter” refers to an illuminator which emits
`source light at a desired wavelength band. An emitter may
`comprise one or more illuminators. Functional oxygen satu-
`ration determination requiresat least two illuminators. In one
`embodiment, a wavelength bandofa first illuminatoris cen-
`tered about 660 nm and a wavelength band of a secondillu-
`minatoris centered about 940 nm.
`
`<A “photodetector” or simply “detector” is a light
`[0025]
`sensing element comprising one or more sensors or sensing
`elements which are sensitive to a wavelength band of a
`respective illuminator system. Each photodetector continu-
`ously measures an intensity of received light emitted by its
`illuminators and outputs, in response thereto, a time-series
`signal. To improve signal to noise ratio in the time-series
`signal, in one embodiment,all the emitters at similar wave-
`length bandare illuminated and photodetector outputs com-
`bined to produce a single time-series signal. The photodetec-
`tors are fixed to an innerside of the band with each emitter/
`detector pair being separated by a distance D, as discussed
`with respect to FIGS. 4-6.
`[0026] A “transmissive device” is one embodimentof the
`present apparatus where the distance D separating each illu-
`minator and paired detector defines a chord ofliving tissue
`through which the emitted source light passes. The distance D
`is less than 75% of a diametrical distance of the area around
`
`which the apparatus is worn. The respective paired photode-
`tector measures an intensity of light passing through the
`chord of living tissue. FIG. 4 shows one embodimentof a
`transmissive device 400 worn circumferentially around an
`area of exposed skin. Band 401 has a plurality of emitter/
`detector pairs fixed to an innerside thereof. Emitters 402A-D
`are paired, respectively, to detectors 403A-D. Emitter 402A
`comprises a single illuminator which emits light at a desired
`wavelength band. Emitters 402B and 402C each comprise
`twoilluminators, which may emitlight at the sameor differ-
`ent wavelength bands. Emitter 402D is shown comprising
`three illuminators which mayall emit sourcelight at a same or
`different wavelength bands. The band 401 may comprise any
`configuration ofemitter/detectorpairs. FIG. 4 is one example.
`Band 401 is worn circumferentially around an area the skin
`
`13
`
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`
`Jan. 15, 2015
`
`406 covering a plurality of subcutaneoustissues (collectively
`at 407) which surround deeper tissues such as muscles,
`organs, bones, and the like (collectively at 408). Distances D,,
`D,, D, and D, define a chord ofliving tissue through which
`light emitted by illuminators 402A-D passes and which, in
`turn,is detected by paired photodetectors 403A-D. Although
`notillustrated exactly to scale, distance D,, D,, D3, D, are less
`than 75% of a diametrical distance 409 of the area around
`which the apparatus is worn. Distances between respective
`emitter/detector pairs do not have to be equal. It should be
`appreciated that the subcutaneoustissues include a plurality
`of blood vessels and other tissue structures. Other embodi-
`ments of the transmissive device hereof comprise multiple
`emitter/detector pairs fixed to an inner side of the band.
`[0027] A “reflective device” is one embodiment of the
`present apparatus where each photodetector measures an
`intensity reflecting offa surface of skin 406. FIG. 5 shows one
`embodimentof a transmissive device 500 worn circumferen-
`
`tially aroundan area of exposed skin as shown in any of FIGS.
`1-3. Band 401 hasa plurality of emitter/detectorpairs fixed to
`an inner side thereof. Emitters 502A-D are paired, respec-
`tively, to detectors 503A-D. Emitter 502A comprises a single
`illuminator which emits light at a desired wavelength band.
`Emitters 502B and 502C each comprise two illuminators,
`which may emit light at the same or different wavelength
`bands. Emitter 502D is shown comprising three illuminators
`which mayall emit source light at a sameor different wave-
`length bands. The band 401 may comprise any configuration
`of emitter/detector pairs. FIG. 5 is one example. Band 401 is
`worn circumferentially around an area the skin 406 covering
`aplurality of subcutaneoustissues (collectively at 407) which
`surround deeper tissues such as muscles, organs, bones, and
`the like (collectively at 408). It should be appreciated that the
`subcutaneoustissues include a plurality of blood vessels and
`othertissue structures. In FIG. 6, the source light emitted by
`each illuminators 502 impacts the surface of the skin 406 at
`angle 0, andreflects off the skin surface at angle 0,, where
`0°<(8,, 82)<90°. Distance D is a distance measured between
`each illuminator 502 andits paired photodetector 503.
`
`Example Control Panel
`
`[0028] Reference is now being madeto FIG. 7 which shows
`one embodimentof a control panel 700 fixed to an outer side
`ofthe bands of eachofthe transmissive andreflective devices
`
`of FIGS. 4 and 5. The control panel allowsthe user to effec-
`tuate various aspects of the functionality of the embodiments
`disclosed herein.
`
`would read the removable card including uploading execut-
`ing machine readable program instructions contained thereon
`for performing any of the functionality described herein.
`[0030] Directional buttons 703, are shownto enable a vari-
`ety of functions including increasing/decreasing a volume
`being played through speaker 704. The up/down buttons may
`be configured to increase intensities of any of the emitters
`fixed to an inner side of band 401 or to adjust the sensitivities
`of any of the sensor elements of the photodetectors. Buttons
`704 maybe usedto tune the present apparatus to standards set
`by the FDA or other regulatory agencies. USB port 704
`enables the connection of a USB cordto the present appara-
`tus. Such a connection can enable any of a variety of func-
`tions. For example, the USB device may be used to program
`a microprocessor or configure the present apparatus specifi-
`cally to a particular patient and set threshold levels for blood
`oxygen saturation detection and monitoring.
`[0031]
`Speaker 705 enables an audible feedback for the
`visually impaired. Such as an audible alert may beinitiated in
`response to the detected blood oxygen saturation being out-
`side a pre-defined limit ofacceptability. The audible alert may
`be varied in volume, frequency, and intensity, as desired,
`using the up/down buttons 703. LEDs 706 enable any of a
`variety of visual feedback for the hearing impaired. Visual
`feedback may take the form of, for instance, a green LED
`being activated whenthe device is tumed ON. Ared LED may
`be activated in responseto an alert condition. A blue LED can
`be activated whenthe a physiological even is not present. The
`LEDscan beactivated in response to a communication occur-
`ring between the present apparatus and a remote device via a
`wireless communication protocol. The LEDs maybeacti-
`vated in combination. Button 707 turns the device ON/OFF.
`The device is capable of wirelessly communicating text,
`email, picture, graph, chart, and/or a pre-recorded message to
`a remote device such as, for example, a smartphone, a Wi-Fi
`router, an I]-Pad, a Tablet-PC, a laptop, a computer, and the
`like. Such communication mayutilize a Bluetooth protocol.
`The communication may utilize network 710 shown as an
`amorphouscloud.
`the embodiments
`[0032]
`It should be appreciated that
`describedare illustrative for explanatory purposes and are not
`to be viewed as limiting the scope of the appended claims
`solely to the elements or configuration of FIG. 7.
`[0033]
`“Oxygen saturation”refers to the amountof oxygen
`that is dissolved in arterial blood (written SpO2, SO2 or
`SaO,). It is a measure of the percentage of hemoglobin bind-
`ing sites in the bloodstream that, at the time of the observa-
`tion, are transporting oxygen. A normal oxygen saturation
`range in human bloodis around 94-98% at sea level, 92-94%
`at 5,000 ft., and <92% at higher elevations. Supplementary
`oxygen is highly desirable if blood oxygen saturation falls
`below 90% to counter the effects of hypoxemia.
`[0034]
`“Functional oxygen saturation”is the ratio of oxy-
`hemoglobin (HbO,) to the sum of HbO,+RHb (hemoglobin
`that is not carrying oxygen, called reduced hemoglobin). If
`the functional oxygen saturation is from arterial hemoglobin
`thenit is called functional arterial oxygen saturation. Func-
`tional SO, is given by:
`
`In FIG.7, the control panel 700 has a female adaptor
`[0029]
`701 for receiving male counterpart of a power supply, as are
`normally understood, to charge one or more batteries (not
`shown). In some embodiments, a separate power supply com-
`prising a battery pack is kept in a pocket and a cord is con-
`nected to the control pattern via adaptor 701. The power
`supply may be a transformer pluggedinto a wall socket with
`a cord which provides continuous powerto the present appa-
`ratus. Also shown is a slot 702 for insertion of amemory chip
`or MicroSD cardasare typically found in cellular smartphone
`devices. Such a removable memory card records signals
`obtained from the photodetectors, and may contain device
`specific parameters which are usedto set powerlevels, adjust
`()
`HbO2
`intensity values, provide data, formulas, threshold values,
`Functional SO, =RHbHBO? x 100.
`patient information, and the like. Once inserted into the
`device, the present apparatus reads the data as needed. A
`microprocessor (CPU)or ASIC internal to the control panel
`
`14
`
`14
`
`

`

`US 2015/0018647 Al
`
`Jan. 15, 2015
`
`[0035]
`follows:
`
`This can be expressed in terms of concentrations as
`
`Functional SO, =
`
`Cro,
`C(RHb+Hb0>)
`
`x 100,
`
`(2)
`
`where Cyy,0, 1s the concentration ofHbO3, and Czz44270,) 18
`the total concentration of RHb and HbO,in the blood.
`[0036] According to Beer’s Law (also known as Beer-Lam-
`bert-Bouguer’s law), as light travels through a media, the
`intensity | decreases exponentially with distance. FIG.8 illus-
`trates Beer’s Law in a tissue layer containing venous and
`arterial structures whichreflect light. Ife(A) is the wavelength
`dependent extinction coefficient or absorptivity coefficient
`then:
`
`T=[geet
`
`(5)
`
`where I, is the detected intensity of incident light, c is the
`concentration in mmol/L (or g/dL), and d is the optical path
`length in cm.
`[0037] The transmittance T is theratio of transmitted light
`I to the amountof detected incidentlight I,.
`
`pat a preted
`Io
`
`[0038] The absorbance A is given by:
`A=-In(T)=€(ned=a(A)d
`
`(6)
`
`7)
`
`where a(A) is a measure ofthe rate of decrease in the intensity
`of light as it passes through a substance.
`[0039]
`If multiple materials that absorb light at a given
`wavelength are present in the sample, the total absorbance A,
`at wavelength A is the sum ofall absorbers:
`Ame, (Acidteo(A)codates(A)czdsteg(A)cada
`
`(6)
`
`€, are respectively for
`€,,
`€,,
`whereextinction coefficients €,,
`RHb, HbO,, COHb, and MetHb components selected at
`wavelength »% and are obtained using the extinction plot of
`FIG. 9A. Concentrations c,, ¢,, ¢3,4, correspond to RHb,
`HbO;, COHb,
`and MetHb, 1e.,
`¢)=Crzyy, Co-Cypo,s
`€3=C Copp, aNd C4=Cy70,774- Lhe alternating part of absorbance
`allows pulsatile and non-pulsatile components to be differen-
`tiated.
`
`[0040] During diastole, the reflected light from the arterial
`walls is retransmitted. There is absorbance again dueto arte-
`rial and venousblood. Using Beer’s law, considering multiple
`absorbers, peak intensities during diastole and systole can be
`written as follows. Light reflected from theliving tissue (nor-
`mally about 1 to 2% each way)is ignored. Peak intensity, I,;;,
`during diastole,(1.e., the minimum reflected light intensity) is
`given by:
`
`Toy = Inefaede*4ac(HoMerbHO, MEH» }24in)
`
`)
`
`whered,,,,,. 18 the diameterof arteries whenit is minimal(i.e.,
`diastole) where the absorbance dueto arterial hemoglobin is
`minimal and corresponding intensity is at a maximum inten-
`sity 1,,. It is to be noted that for transmission arrangement,
`effective transmission of light path will be once through the
`
`venous blood and oncethroughthe arterial blood. Hence the
`scalar value “2” will be replaced by “1” in Eqn.(7).
`[0041]
`Peak intensity, I,,, during systole, (i.e., the reflected
`light intensity in the return path), is given by:
`
`let = IneBdeeae*acHEHoH**HbO2 WeHbO> !24max)
`
`(8)
`
`whered,,,,., 1S the diameter ofarteries whenit is maximum and
`the correspondinglight intensity is at a minimumintensity I,.
`It is to be noted that for transmission arrangement, effective
`transmission of light path will be once through the venous
`blood and once through the arterial blood. Hence the scalar
`value “2” will be replaced by “1” in Eqn.(8).
`[0042]
`Substituting d,,,=d,,,,,+6d in Eqn. (8), where 8d is
`the change in diameter ofarteries during one cardiac cycle,
`and using Eqn.(7), we get:
`
`Tgp, = [pefateO°ae*acHbHb+0)HBO, )*4nin)
`eoEHOHb *£HO “CHO, 26d
`
`(9)
`
`[0043] Dividing Eqn. (6) by Eqn.(7) we get, the normalized
`transmitted signal due to variations in path length, T,,, where:
`
`ae te
`— Fre = HMHetSHO, WeHD0, !26d
`Try
`
`(10)
`
`[0044] By the same argumentas before, scalar value “2”
`will be replaced by “1”in Eqn. (10) for transmission arrange-
`ment. Ratio of systolic and diastolic peaks in Eqn. (10)
`removes the dependence onlight intensities from illumina-
`tors at different wavelengths, if two or more LEDsare used.
`Egn. (7) represents changesto reflected light caused by the
`pulsation of the bloodin the arteries. The normalized absorp-
`tion can be obtained using Eqn. (3) as follows:
`
`A, = -In(T,,)
`
`qb
`
`I
`= -h(7)
`= (En cup + €nn0, ACHpo, 26d
`
`[0045] By the same argumentas before, scalar value “2”
`will be replaced by “1”in Eqn. (11) for transmission arrange-
`ment. If we use two wavelengths, (i.e., red at 660 nm and IR
`at 940 nm), (FIG. 9B) and assumethatthe optical path lengths
`are the same,(i.e., both light passes through samesize veins,
`arteries or arterioles), then the ratio of the absorbanceat the
`red and IR wavelengths depends on the absorbers present in
`those components. Thus, we can write the ratio R as follows:
`
`
`_ Aired
`Aur
`
`InUrrred / IRH,red)
`InUenir/ Trae)
`
`(12)
`
`15
`
`15
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`

`

`US 2015/0018647 Al
`
`Jan. 15, 2015
`
`[0046]
`
`Substituting Eqn. (11) in Eqn. (12), we get a ratio:
`
`_ tb ARed Cb + EHO, ARed CHbO, )
`~ &xp(Air Cup + Etb0, Air )CHbO,)
`
`(13)
`
`[0047] Concentrations for hemoglobin and oxygenated
`hemoglobin can be expressed in terms of SO, using a revised
`version of Eqn. (2) in Eqn. (13). From Eqn. (2), we get the
`concentrations of HbO, and Hbas follows:
`Ceo-SO2(Cuno+x)
`
`(14A)
`
`Cp=(1-SO3)(Cxp0°+x)
`
`(14B)
`
`Substituting Eqns. (14A & 14B) into Eqn. (13), we
`[0048]
`get a ratio:
`
`E40 (Area SO2(CHpo, + CHD)
`
`Ce —SO2)(CHb0, +CHb) + |
`~ eo —SO2)(CHpo, +CH) + |
`
`£1607 Air )SO2(CHbo, + CH)
`
`(15)
`
`Further simplification leads to cancellation of terms
`[0049]
`associated with hemoglobin concentrations. Rearranging
`terms, we can obtain the equation for the arterial oxygen
`saturation in percent:
`
`50> =
`>
`
`
`leup(Area) — Rey (Ayr) x 100
`(EnOrea) £107 Ared)) + (Expo, (Air) — Enpo(AirIR
`
`(16)
`
`tion, the illuminators emit their source light which,in turn,is
`sensed by each emitters paired photodetector. A continuous
`PPGsignal is generated thereby.
`[0054] At step 1004, receive a continuous PPG signal from
`the detectors of the activated apparatus.
`[0055] Atstep 1006, analyze the continuous PPG signal for
`a determination of functional blood oxygen saturation level
`(s). Embodiments for determining a functional blood oxygen
`saturation level are discussed herein in detail.
`
`[0056] At step 1008, a determination is made,as a result of
`having determined the functional blood oxygenation level in
`step 1006, whether a boundary limit has been exceeded.If so
`then, at step 1010, an alert signalis initiated. Thealert signal
`or notification can be sent to a technician, nurse, medical
`practitioner, and the like, using, for example, antenna 1108
`(of FIG. 11). In one embodiment,the alert signal is commu-
`nicated via network 710 of FIG. 7. Such a signal may take the
`form of a messageor, for instance,a bell tone, ring, or sonic
`alert being activated at a nurse’s station. The alert signal may
`take the form ofinitiating a visible light which provides an
`indication suchas, for instance, a blinking colored light such
`as the LEDs 706 of FIG.7. If, at step 1008, a boundary limit
`has not been exceededthen processing repeats with respect to
`step 1004 wherein the PPG signal is continuously received
`and analyzed for functional blood oxygen saturation. Pro-
`cessing repeats in a similar manner. In another embodiment,
`further processing stops. The apparatus hereofis intended to
`be used for continuous monitoring while the device is ON.
`[0057] The flow diagrams depicted herein areillustrative.
`Oneor moreof the operationsillustrated in the flow diagrams
`may be performed in a differing order. Other operations may
`be added, modified, enhanced, or consolidated. Variations
`thereof are intendedto fall within the scope of the appended
`claims.
`
`[0050] Eqn. (16) can also be written in simplified form as
`follows:
`
`Example Networked System
`
`Itis to be noted that we use SO2 and SaO2 mean the
`[0051]
`same. In Eqn. (17), extinction coefficients are replaced by
`constants determined from clinical studies to produce a best
`fit between measured arterial functional oxygen saturation
`S,O, using, for example, a FDA approved sensing method or
`in-vitro measurementof S,O,, andthe ratio R of Eqn. (16).
`
`[0058] Reference is now being made to FIG. 11 which
`illustrates a block diagram of one example signal processing
`
`(17)
`ky —kyR
`ky —k4R
`100
`S,O2 = ——_ 00 =
`system 1100 for performing various aspects of the teachings
`
`wt=eh) + (ke kak kkk
`hereof.
`[0059]
`In FIG. 11, the control panel 700 of the present
`apparatus fixed to band 401 utilizes ante