US 9,241,676 B2
`(10) Patent No.:
`a2) United States Patent
`Lisogurskietal.
`(45) Date of Patent:
`*Jan. 26, 2016
`
`
`US009241676B2
`
`(54) METHODS AND SYSTEMS FOR POWER
`OPTIMIZATIONIN A MEDICAL DEVICE
`Inventors: Daniel Lisogurski, Boulder, CO (US);
`Clark R. Baker, Jr., Newman, CA (US)
`
`(75)
`
`(73) Assignee: Covidien LP, Mansfield, MA (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 128 days.
`.
`.
`.
`.
`.
`This patent is subject to a terminal dis-
`claimer.
`
`(2006.01)
`(2006.01)
`(2006.01)
`(2006.01)
`
`(51)
`
`(56)
`
`5,485,847 A
`5,515,847 A
`5,560,355 A
`ean A
`5,746,697 A
`5,766,127 A
`5,846,190 A
`5,924,979 A
`6,005,658 A
`
`1/1996 Baker, Jr.
`5/1996 Braiget al.
`10/1996 Merchantet al.
`Mitoos Ahan otal.
`5/1998 Swedlowetal.
`6/1998 Pologe etal.
`12/1998 Woehrle
`7/1999 Swedlowet al.
`12/1999 Kaluza etal.
`(Continued)
`
`FOREIGN PATENT DOCUMENTS
`
`WO
`WO
`
`WO 2006/080856
`8/2006
`WO 2006/083 180
`8/2006
`OTHER PUBLICATIONS
`Takada,H.et al., “Acceleration Plethysmography to Evaluate Aging
`Effect in Cardiovascular System,’ Medical Progress Through Tech-
`nology, vol. 21, pp. 205-210, 1997.
`(Continued)
`
`Primary Examiner — Mark Remaly
`(74) Attorney, Agent, or Firm — Shvarts & Leiz LLP
`
`(21) Appl. No.: 13/484,770
`(22)
`Filed:
`May 31, 2012
`(65)
`Prior Publication Data
`US 2013/0324856 Al
`Dec. 5, 2013
`Int. Cl.
`AGIB 5/00
`A6IB 5/021
`AGIB 5/024
`ABSTRACT
`(57)
`AGIB 5/1455
`A physiological monitoring system may use photonic signals
`(52) U.S. CL
`to determinephysiological parameters. The system may vary
`CPC wee AG61B 5/7285 (2013.01); A61B 5/021
`parametersof a light drive signal used to generate the photo-
`(2013.01); A61B 5/02416 (2013.01); A6IB
`nic signal from a light source such that power consumption is
`5/02433 (2013.01); A61B 5/14551 (2013.01)
`reducedor optimized. Parameters may includelightintensity,
`(58) Field of Classification Search
`CPC ween A61B 5/021; A61B 5/02416; A61B__firing rate, duty cycle, other suitable parameters, or any com-
`5/14551; A61B 5/7285
`bination thereof. In some embodiments, the system may use
`
`See application file for complete searchhistory. information fromafirst light source to generate a lightdrive
`.
`signal for a secondlight source. In some embodiments, the
`References Cited
`system may vary parameters in a way substantially synchro-
`nous with physiological pulses, for example, cardiac pulses.
`U.S. PATENT DOCUMENTS
`In some embodiments, the system may vary parameters in
`response to an external trigger.
`
`5,343,818 A
`5,349,952 A
`5,351,685 A
`
`9/1994 McCarthyetal.
`9/1994 McCarthy etal.
`10/1994 Potratz
`
`32 Claims, 30 Drawing Sheets
`
`
`
`
`
`
`
`
`Light Drive Circuitry
`
`Control
`
`UserInterface
`Circuitry
`180
`io
`
`
`UserInput
`102
`
`182
`Light Source
`
`
`
`
`
`130
`
`
`Front End Processing Circuitry 150
`
`Analog
`Analog-to-
`as
`Digital
`Conditioner
`Converter
`Back End Processing
`
`
`
`482 Circultry 170 ||Speaker154
`
`
`~
`186
`
`Detector
`Processor
`
`
`
`
`
`172
`Conditioner
`
`Demultiplexer
`Digital
`140
`el
`
`156
`158
`
`
`Memory
`Communication
`
`176
`interface
`
`Decimator/
`Dark
`120
`
`Interpolator
`Subtractor
`169
`162
`
`OMNI 2137 - IPR21-00453
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`
`
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`
`
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`
`
`
`
`
`
`
`
`
`Display
`
`184
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`Petitioner Apple Inc. — Ex. 1011, p. 1
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`OMNI 2137 - IPR21-00453
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`

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`US 9,241,676 B2
` Page 2
`
`(56)
`
`References Cited
`
`11/2009 Andersonet al.
`7,623,990 B2
`4/2005 Smith et al.
`2005/0084202 Al
`5/2005 Stahmann et al.
`2005/0109339 Al
`11/2006 Chew etal.
`2006/0264720 Al
`2/2007 Huang
`2007/0038049 Al
`4/2001 Amanoet al.
`6,217,523 Bl
`6/2007 Sarussiet al.
`2007/0149871 Al
`5/2001 Potratz
`6,226,539 BL
`9/2007 Nordstrom etal.
`2007/0208240 Al
`2/2004 Sueppelet al.
`6.697.655 B2
`9/2011 Mathonnet
`2011/0213397 Al
`2/2004 Al-Ali
`6,697,658 B2
`9/2011 Lamegoetal.
`2011/0237911 Al
`5/2004 Turcott
`6,731,967 Bl
`10/2011 Lietal.
`2011/0245636 Al
`3/2005 Huangetal.
`6.863.652 B2
`6/2005 Rantalaet al.
`6,912,413 B2
`OTHER PUBLICATIONS
`2/2006 Diabetal.
`7,003,339 B2
`International Search Report andWritten Opinionofthe International
`Ieosee BS ae Naeetaletal.
`
`7.295.866 B2=-11/2007 Al-Ali Searching Authority for application No. PCT/US 2013/043338,
`7,382,247 B2
`6/2008 Welchet al.
`mailed on Oct. 2, 2013.
`
`U.S. PATENT DOCUMENTS
`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 2
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`OMNI 2137 - IPR21-00453
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`

`

`U.S. Patent
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`Jan. 26, 2016
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`Sheet 1 of 30
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`US 9,241,676 B2
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`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 3
`
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`OMNI 2137 - IPR21-00453
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`

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`U.S. Patent
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`Jan. 26, 2016
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`Sheet 2 of 30
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`US 9,241,676 B2
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`216
`
`218
`
`
`
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`j2uBisBAUIGRUBHIBUINDGJovIa1Eq
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`Time
`
`FIG. 2A
`
`214
`
`222
`
`Time
`
`FIG. 2B
`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 4
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`OMNI 2137 - IPR21-00453
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`

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`U.S. Patent
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`Jan. 26, 2016
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`Sheet 3 of 30
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`US 9,241,676 B2
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`Diastole
`
`ce
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`260
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`FIG. 2€
`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 5
`
`s Ls
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`

`

`U.S. Patent
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`Jan. 26, 2016
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`Sheet 4 of 30
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`US 9,241,676 B2
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`FIG.3
`
`Oooooog
`
`O
`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 6
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`OMNI 2137 - IPR21-00453
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`

`

`U.S. Patent
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`Jan. 26, 2016
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`Sheet 5 of 30
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`US 9,241,676 B2
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`ue)
`
`
`
`Generating a first light drive signal
`corresponding to a first photonic
`signal
`402
`
`
`
`
`Receiving a light signal
`corresponding to the first photonic
`signal
`404
`
`
`
`
`Analyzing the received light signa!
`to determine when to activate a
`second light source
`406
`
`
`
`
`
`
`
`Generating a second light drive
`signal corresponding te a second
`photonic signal
`408
`
`
`Determining a physiological
`parameter
`416
`
`FIG. 4
`
`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 7
`
`OMNI 2137 - IPR21-00453
`
`

`

`U.S. Patent
`
`Jan. 26, 2016
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`Sheet 6 of 30
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`US 9,241,676 B2
`
`Ln
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`
`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 8
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`OMNI 2137 - IPR21-00453
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`
`
`
`

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`U.S. Patent
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`Jan. 26, 2016
`
`Sheet 7 of 30
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`US 9,241,676 B2
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`600
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`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 9
`
`OMNI 2137 - IPR21-00453
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`

`

`U.S. Patent
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`Jan. 26, 2016
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`Sheet 8 of 30
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`US 9,241,676 B2
`
`ECG
`
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`FIG. 7
`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 10
`
`OMNI 2137 - IPR21-00453
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`

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`U.S. Patent
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`Jan. 26, 2016
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`Sheet 9 of 30
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`US 9,241,676 B2
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`R18
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`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 11
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`OMNI 2137 - IPR21-00453
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`

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`U.S. Patent
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`Jan. 26, 2016
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`Sheet 10 of 30
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`US 9,241,676 B2
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`OS boa oo
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`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 12
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`OMNI 2137 - IPR21-00453
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`

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`U.S. Patent
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`Jan. 26, 2016
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`Sheet 11 of 30
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`US 9,241,676 B2
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`900
`
`Generating a light drive signal, in
`part correlated to physiological
`pulses
`902
`
`
`
`
`
`
`
`
`
`
`
`Receiving a signal related to the
`light drive signal
`304
`
`Determining a physioloigcal
`parameter
`306
`
`FIG. 9
`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 13
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`OMNI 2137 - IPR21-00453
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`

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`U.S. Patent
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`Jan. 26, 2016
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`Sheet 12 of 30
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`US 9,241,676 B2
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`1660
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`
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`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 14
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`OMNI 2137 - IPR21-00453
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`U.S. Patent
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`Jan. 26, 2016
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`Sheet 13 of 30
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`US 9,241,676 B2
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`L102
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`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 15
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`OMNI 2137 - IPR21-00453
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`
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`Jan. 26, 2016
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`Sheet 14 of 30
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`US 9,241,676 B2
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`
`
`PPG
`
`1204 ~y
`
`
`
`Signal
`
`
`Light
`Drive
`
`Time
`
`FIG. 12
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`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 16
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`OMNI 2137 - IPR21-00453
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`Sheet 15 of 30
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`US 9,241,676 B2
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`1302
`
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`
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`
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`
`Diastole
`
`Time
`
`FIG. 13
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`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 17
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`OMNI 2137 - IPR21-00453
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`Sheet 16 of 30
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`US 9,241,676 B2
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`1400
`
`1496
`
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`
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`
`FIG. 14
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`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 18
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`OMNI 2137 - IPR21-00453
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`Sheet 17 of 30
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`US 9,241,676 B2
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`1500
`
`Diastole
`
`Systole
`
`Diastole
`
`we©SSmo=ge3On
`
`Diastale
`
`Time
`
`Diastole
`
`FIG. 15
`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 19
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`OMNI 2137 - IPR21-00453
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`

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`Sheet 18 of 30
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`US 9,241,676 B2
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`1600
`
`1610-~\y
`
`1612 ~y
`
`Signal
`
`PPG
`
`Light
`Drive
`
`Time
`
`FIG. 16
`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 20
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`OMNI 2137 - IPR21-00453
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`Sheet 19 of 30
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`US 9,241,676 B2
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`1780
`
`
`
`Receive a signal and sample ata
`first rate
`
`
`
`
`
`1702
`
`
`
`Receive a signal and sample ata
`second rate
`
`
`
`
`
`1704
`
`
`
`
`
`
`
`Decimate or interpolate to output
`signals at a constant rate
`1786
`
`FIG. 17
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`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 21
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`OMNI 2137 - IPR21-00453
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`Sheet 20 of 30
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`1800
`
`1802
`
`1804
`
`1806
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`
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`
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`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 22
`
`OMNI 2137 - IPR21-00453
`
`

`

`U.S. Patent
`
`Jan. 26, 2016
`
`Sheet 21 of 30
`
`US 9,241,676 B2
`
`
`
`Perform a physiological
`measurement ina first mode
`
`4902
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`Detect a physiological condition
`1904
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`
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`Perform a physiclogical
`measurement ina second mode
`
`1306
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`FIG. 19
`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 23
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`OMNI 2137 - IPR21-00453
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`

`

`U.S. Patent
`
`Jan. 26, 2016
`
`Sheet 22 of 30
`
`US 9,241,676 B2
`
`2083
`
`2008
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`2016
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`2018
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`intensity
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`FIG, 20
`
`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 24
`
`OMNI 2137 - IPR21-00453
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`

`

`U.S. Patent
`
`Jan. 26, 2016
`
`Sheet 23 of 30
`
`US 9,241,676 B2
`
`2108
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`2116
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`PPG
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`rseseeatratetetetaitatettetratenes
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`
`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 25
`
`OMNI 2137 - IPR21-00453
`
`

`

`U.S. Patent
`
`Jan. 26, 2016
`
`Sheet 24 of 30
`
`US 9,241,676 B2
`
`2200
`
`
`
`Recieve a first signal
`2202
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`Calculate a second signal related to
`the first signal
`2204
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`identify features of the second
`signal
`2206
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`signal with the first signal
`2208
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`FIG. 22
`
`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 26
`
`OMNI 2137 - IPR21-00453
`
`

`

`U.S. Patent
`
`Jan. 26, 2016
`
`Sheet 25 of 30
`
`US 9,241,676 B2
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`2306
`
`oot
`
`ca]
`
`2302 wo
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`oS
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`FIG. 23
`
`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 27
`
`OMNI 2137 - IPR21-00453
`
`

`

`U.S. Patent
`
`Jan. 26, 2016
`
`Sheet 26 of 30
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`US 9,241,676 B2
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`2400
`
`FIG. 24
`
`OMNI 2137 - IPR21-00453
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`Petitioner Apple Inc. — Ex. 1011, p. 28
`
`OMNI 2137 - IPR21-00453
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`

`

`U.S. Patent
`
`Jan. 26, 2016
`
`Sheet 27 of 30
`
`US 9,241,676 B2
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` oS4Wy
`
`Cd
`
`FIG. 25
`
`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 29
`
`OMNI 2137 - IPR21-00453
`
`

`

`U.S. Patent
`
`Jan. 26, 2016
`
`Sheet 28 of 30
`
`US 9,241,676 B2
`
`
`
`Q
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`FIG. 26
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`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 30
`
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`OMNI 2137 - IPR21-00453
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`

`

`U.S. Patent
`
`Jan. 26, 2016
`
`Sheet 29 of 30
`
`US 9,241,676 B2
`
`re
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`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 31
`
`OMNI 2137 - IPR21-00453
`
`

`

`U.S. Patent
`
`Jan. 26, 2016
`
`Sheet 30 of 30
`
`US 9,241,676 B2
`
`oo
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`FIG. 28
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`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 32
`
`OMNI 2137 - IPR21-00453
`
`

`

`US 9,241,676 B2
`
`1
`METHODS AND SYSTEMS FOR POWER
`OPTIMIZATION IN A MEDICAL DEVICE
`
`The present disclosure relates to power optimization, and
`moreparticularly relates to conserving and optimizing power
`in a photoplethysmography system or other medical device.
`
`SUMMARY
`
`Systems and methods are provided for optimizing power
`consumption in an optical physiological monitoring system.
`
`2
`trigger, vary the light intensity, duty cycle, light source firing
`rate, any other suitable parameter, or any combination
`thereof.
`
`BRIEF DESCRIPTION OF THE FIGURES
`
`15
`
`25
`
`35
`
`40
`
`45
`
`The above and other features of the present disclosure, its
`nature and various advantages will be more apparent upon
`consideration of the following detailed description, taken in
`conjunction with the accompanying drawings in which:
`FIG.1 is a block diagram ofan illustrative physiological
`monitoring system in accordance with some embodiments of
`the present disclosure;
`FIG. 2A showsanillustrativeplot ofa light drive signal in
`accordance with some embodiments of the present disclo-
`In some embodiments, reducing power consumption may
`sure;
`allow for increased battery life in portable systems or
`FIG. 2B shows anillustrative plot of a detector signal that
`increased portability. In some embodiments, varying light
`may be generated by a sensor in accordance with some
`output during a cardiac cycle may reduce heating effects of
`embodiments of the present disclosure;
`the emitters. Parameters that may be varied include light
`FIG. 2C showsillustrative timing diagramsofa drive cycle
`intensity,firing rate, duty cycle, other suitable parameters, or
`modulation and cardiac cycle modulation in accordance with
`any combination thereof. The generated signals may be used
`some embodiments of the present disclosure;
`to determined physiological parameters suchas blood oxygen
`FIG.3 is a perspective view of an embodimentof a physi-
`saturation, hemoglobin, bloodpressure, pulse rate, other suit-
`ological monitoring system in accordance with some embodi-
`ments of the present disclosure;
`able parameters, or any combination thereof.
`FIG. 4 is a flow diagram showingillustrative steps for
`In some embodiments, the system may use information
`determining a physiological parameter in accordance with
`fromafirst light source to control a secondlight source. The
`some embodiments of the present disclosure;
`system may generatea first light drive signal for activating a
`FIG. 5 showsan illustrative timing diagram of a physi-
`first light source to emita first photonic signal. Thefirst light
`ological monitoring system in accordance with some embodi-
`source and secondlight source may each include one or more
`ments of the present disclosure;
`emitters. The system mayreceive a light signal attenuated by
`FIG. 6 shows another illustrative timing diagram of a
`the subject, wherein the light signal comprises a component
`physiological monitoring system in accordance with some
`corresponding to the first photonic signal. The system may
`embodiments of the present disclosure;
`analyze the componentofthe light signal to determine when
`FIG. 7 shows another illustrative timing diagram of a
`to activate a second light source. The system may generate a
`physiological monitoring system in accordance with some
`second light drive signal, based on the analysis ofthe first
`embodiments of the present disclosure;
`component, for activating the secondlight source to emit one
`FIG. 8A shows anotherillustrative timing diagram of a
`or more second photonic signals. The system may determine
`physiological monitoring system in accordance with some
`one or more physiological parameters based on the light
`embodiments of the present disclosure;
`signals.
`FIG. 8B showsanotherillustrative timing diagram of a
`In some embodiments, the system may vary a light drive
`physiological monitoring system in accordance with some
`signal in a way substantially synchronous with physiological
`embodiments of the present disclosure;
`pulses, for example, cardiac pulses. The system may generate
`FIG. 9 is a flow diagram showingillustrative steps for
`a light drive signal for activating a light source to emit a
`determining a physiological parameter in accordance with
`photonic signal, wherein at least one parameter of the light
`some embodiments of the present disclosure;
`drive signal is configuredto vary substantially synchronously
`FIG. 10 shows anotherillustrative timing diagram of a
`with physiological pulses of the subject. The system may
`physiological monitoring system in accordance with some
`receive a light signal attenuated by the subject, wherein the
`embodiments of the present disclosure;
`signal comprises a component corresponding to the emitted
`FIG. 11 shows anotherillustrative timing diagram of a
`photonic signal. The system may determine physiological
`physiological monitoring system in accordance with some
`parameters based on the signal. In some embodiments, the
`embodiments of the present disclosure;
`system may vary light levels with other periodic (or mostly
`FIG. 12 shows anotherillustrative timing diagram of a
`periodic) physiological changes. For example, venous return
`physiological monitoring system in accordance with some
`changes with intrathoracic pressure during a respiration cycle
`embodiments of the present disclosure;
`can affect the baseline level of the photoplethysmography
`FIG. 13 shows anotherillustrative timing diagram of a
`waveform. The system may vary the emitter output such that
`physiological monitoring system in accordance with some
`similar signal quality is available at the detector over time
`embodiments of the present disclosure;
`varying volumes of venousblood present in the path oflight.
`FIG. 14 shows anotherillustrative timing diagram of a
`In some embodiments, the system may vary a light drive
`physiological monitoring system in accordance with some
`signal based on a received external trigger. The system may
`embodiments of the present disclosure;
`receive an external trigger based on a signal otherthan a light
`FIG. 15 shows anotherillustrative timing diagram of a
`signal received by the physiological monitor. The trigger may
`physiological monitoring system in accordance with some
`
`includeasignal received from an ECG sensor, an ECG sensor embodiments of the present disclosure;
`configured to detect an R-wave, a blood pressure sensor, a
`FIG. 16 shows anotherillustrative timing diagram of a
`respiration rate sensor, any other suitable sensor, or any com-
`physiological monitoring system in accordance with some
`bination thereof. The system may, in responseto the external
`embodiments of the present disclosure;
`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 33
`
`OMNI 2137 - IPR21-00453
`
`

`

`US 9,241,676 B2
`
`3
`FIG. 17 is a flow diagram showing illustrative steps for
`decimating and interpolating a signal in accordance with
`some embodimentsof the present disclosure;
`FIG. 18 showsan illustrative timing diagram of a physi-
`ological monitoring system including samplingrate variation
`in accordance with some embodimentsofthe present disclo-
`sure;
`FIG. 19 is a flow chart showing steps to adjust a cardiac
`cycle modulation based ona physiological condition in accor-
`dance with some embodimentsof the present disclosure;
`FIG.20is an illustrative timing diagram of a system oper-
`ating in a first and second mode following detection of a
`physiological condition in accordance with some embodi-
`ments of the present disclosure;
`FIG.21 is another illustrative timing diagram of a system
`operating in a first and second modefollowing detection of a
`physiological condition in accordance with some embodi-
`ments of the present disclosure;
`FIG. 22 is a flow diagram showing illustrative steps for
`identifying features in a signal in accordance with some
`embodiments ofthe present disclosure;
`FIG.23 is an illustrative plot of a waveform showing iden-
`tification of fiducials in accordance with some embodiments
`ofthe present disclosure;
`FIG.24 is another illustrative plot of a waveform showing
`identification of fiducials in accordance with some embodi-
`
`ments of the present disclosure;
`FIG.25 is another illustrative plot of a waveform showing
`identification of fiducials in accordance with some embodi-
`
`ments of the present disclosure;
`FIG.26is an illustrative plot of waveforms showing pulse
`identification in accordance with some embodiments of the
`present disclosure;
`FIG. 27 is an illustrative plot of waveforms showing
`dicrotic notch identification in accordance with some
`embodiments ofthe present disclosure; and
`FIG.28 is an illustrative plot of waveforms showing PPG
`signals in accordance with some embodimentsofthe present
`disclosure.
`
`DETAILED DESCRIPTION OF THE FIGURES
`
`The present disclosure is directed towards poweroptimi-
`zation in a medical device. A physiological monitoring sys-
`tem may monitor one or more physiological parameters of a
`patient, typically using one or more physiological sensors.
`The system may include, for example, a light source and a
`photosensitive detector. Providing a light drive signal to the
`light source may account for a significant portion of the
`system’s total power consumption. Thus, it may be desirable
`to reduce the power consumption of the light source, while
`still enabling high quality physiological parameters to be
`determined. The system may reduce the power consumption
`by modulating parameters associated with the light drive
`signal in techniques correlated to the cardiac cycle or other
`cyclical physiological activity. For example, the system may
`decrease brightness during a particular portion of the cardiac
`cycle. It may also be desirable to reduce the power consump-
`tion by thelight drive signal to reduce heating effects caused
`by an emitter.
`An oximeter is a medical device that may determine the
`oxygen saturation of an analyzed tissue. One commontype of
`oximeteris a pulse oximeter, which may non-invasively mea-
`sure the oxygen saturation of a patient’s blood (as opposed to
`measuring oxygen saturation directly by analyzing a blood
`sample taken from the patient). Pulse oximeters may be
`includedin patient monitoring systems that measure anddis-
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`60
`
`4
`play various blood flow characteristics including, but not
`limited to, the oxygen saturation of hemoglobin in arterial
`blood. Such patient monitoring systems may also measure
`and display additional physiological parameters, such as a
`patient’s pulse rate and blood pressure.
`An oximeter may include a light sensor that is placed at a
`site ona patient,typically a fingertip, toe, forehead orearlobe,
`or in the case of a neonate, across a foot. The oximeter may
`use a light source to pass light through blood perfusedtissue
`and photoelectrically sense the absorption ofthe light in the
`tissue. In addition, locations which are not typically under-
`stood to be optimalfor pulse oximetry serve as suitable sensor
`locations for
`the blood pressure monitoring processes
`described herein, including any location on the body that has
`a strong pulsatile arterial flow. For example, additional suit-
`able sensor locations include, without limitation, the neck to
`monitor carotid artery pulsatile flow, the wrist to monitor
`radial artery pulsatile flow, the inside of a patient’s thigh to
`monitor femoral artery pulsatile flow, the ankle to monitor
`tibial artery pulsatile flow, and aroundorin front of the ear.
`Suitable sensors for these locations may include sensors for
`sensing absorbed light based on detecting reflected light. In
`all suitable locations, for example, the oximeter may measure
`the intensity of light that is received at the light sensor as a
`function of time. The oximeter may also include sensors at
`multiple locations. A signal representing light intensity ver-
`sus time or a mathematical manipulation ofthis signal(e.g., a
`scaled version thereof; a logarithm taken thereof, a scaled
`version of a logarithm taken thereof; a derivative taken
`thereof, a difference taken thereof, etc.) may be referred to as
`the photoplethysmograph (PPG)signal. In addition, the term
`“PPGsignal,” as used herein, mayalso refer to an absorption
`signal (i.e., representing the amountof light absorbed by the
`tissue), a transmission signal(i.e., representing the amount of
`light received from the tissue), any suitable mathematical
`manipulation thereof; or any combination thereof. The light
`intensity or the amountoflight absorbed maythen be used to
`calculate any of a number of physiological parameters,
`including an amountof a blood constituent (e.g., oxyhemo-
`globin) being measuredas well as a pulse rate and when each
`individual pulse occurs.
`In someapplications, the photonic signal interacting with
`the tissue is selected to be of one or more wavelengths that are
`attenuated by the blood in an amountrepresentative of the
`blood constituent concentration. Red and infrared (IR) wave-
`lengths may be used because it has been observedthat highly
`oxygenated blood will absorb relatively less red light and
`moreIR light than blood with a lower oxygen saturation. By
`comparing the intensities of two wavelengths at different
`points in the pulse cycle, it is possible to estimate the blood
`oxygen saturation of hemoglobin in arterial blood.
`The system may process data to determine physiological
`parameters using techniques well known in the art. For
`example, the system may determine blood oxygensaturation
`using two wavelengths of light and a ratio-of-ratios calcula-
`tion. The system also mayidentify pulses and determine pulse
`amplitude, respiration, blood pressure, other suitable param-
`eters, or any combination thereof, using any suitable calcula-
`tion techniques. In some embodiments, the system may use
`information from external sources(e.g., tabulated data, sec-
`ondary sensor devices) to determine physiological param-
`eters.
`
`In some embodiments, it may be desirable to implement
`techniques to optimize power consumption in an oximeter or
`other system. For example, in a battery powered system,
`reducing the power requirements may allow for smaller
`devices, longerlife, or both. In some embodiments, powering
`OMNI 2137 - IPR21-00453
`
`Petitioner Apple Inc. — Ex. 1011, p. 34
`
`OMNI 2137 - IPR21-00453
`
`

`

`US 9,241,676 B2
`
`5
`the light source may include a large amountofthe powerload
`a device may experience.
`
`
` wa
`
`6
`amplitudes that are large may saturate an analog to digital
`convertor. In response to a signal with high amplitudes, the
`system may reduce emitter brightness. In a further example,
`the quality of a low amplitude signal may be degraded by
`quantization noise by an analog to digital converter. In
`response, the system mayincrease the emitter brightness.
`
`For example, the
`brightness of a light source may be decreased during a less
`important period and increased during a more important
`period. In some embodiments, parameter variation may
`reduce the impact of heating effects caused by a light source
`on a subject. Techniques to vary the amountof timea light
`source is turned on, to vary the brightness ofthe light source,
`other techniques, or any combination thereof, may be
`employed to modify power consumption.
`In some embodiments, the brightness of one of morelight
`sources may be modulated in a technique that is related to the
`cardiac cycle. The cardiac cycle is the substantially periodic
`repetition of events that occur, for example, during heart-
`beats. The cardiac cycle may include a systole period and
`diastole period. The cardiac cycle may include pressure
`changes in the ventricles, pressure changesin the atria, vol-
`ume changes in the ventricles, volume changesin the atria,
`opening and closing of heart valves, heart sounds, and other
`cyclic events. In some embodiments, the heart may enter a
`non-periodicstate, for example, in certain types ofarrhythmia
`and fibrillation.
`
`As usedherein, “cardiac cycle modulation”will refer to the
`modulation techniques generally correlated to the cardiac
`cycle. It will be understood that cardiac cycle modulation
`may include modulation aligned with pulses of the heart,
`pulses ofa particular muscle group, other suitable pulses, any
`other suitable physiological cyclical function, or any combi-
`nation thereof. In some embodiments, the system may use a
`cardiac cycle modulation with a period on the order of the
`cardiac cycle period. For example, the cardiac cycle modula-
`tion may repeat every cardiac cycle. In some embodiments,
`the system mayuse a cardiac cycle modulation with a period
`on the order of some multiple of the cardiac cycle period. For
`example, the cardiac cycle modulation mayrepeat every three
`cardiac cycles. In some embodiments,
`the cardiac cycle
`modulation may relate to both a cardiac cycle and a respira-
`tory cycle. The cardiac cycle and the respiratory cycle may
`
`have a time varying phaserelationship.
`
`As used herein, “drive cycle modulation” (described
`below)will refer to a relatively higher frequency modulation
`technique that the system may use to generate one or more
`wavelengths of intensity signals. Cardiac cycle modulation
`may havea period of, for example, around 1 second, while
`drive cycle modulation may have a period around,
`for
`example, 1.6 milliseconds.
`In some embodiments, conventional servo algorithms may
`beusedin addition to any combination of cardiac cycle modu-
`lation and drive cycle modulation. Conventional servo algo-
`rithms may adjust thelight drive signals due to, for example,
`ambient light changes, emitter and detector spacing changes,
`sensor positioning, other suitable parameters, or any combi-
`nation thereof. Generally, conventional servo algorithms vary
`parametersat a slowerrate than cardiac cycle modulation. For
`example, a conventional servo algorithm may adjust drive
`signal brightness due to ambient light every several seconds.
`The system may use conventionalservo algorithmsin part to
`keep received signal levels within the range of an analog to
`digital converter’s dynamic range. For example, a signal with
`
`m wa
`
`For example
`a drive cycle modulation cycle may include the system turn-
`ing on a first light source, followed by a “dark”period, fol-
`lowedby a secondlight source, followed by a “dark”period.
`The system may measure the ambient light detected by the
`detector during the “dark”period and then subtract this ambi-
`ent contribution from the signals received duringthe first and
`second “on” periods. In some embodiments, drive cycle
`modulation may be implemented using time division multi-
`plexing as described above, code division multiplexing, car-
`rier frequency multiplexing, phase division multiplexing,
`feedback circuitr