(12) Unlted States Patent
`(10) Patent No.:
`US 8,457,703 B2
`
`Al-Ali
`(45) Date of Patent:
`Jun. 4, 2013
`
`USOO8457703B2
`
`(54) LOW POWER PULSE OXIMETER
`
`~
`-
`_
`.
`Inventor. Ammar A1 A11, Tust1n, CA (US)
`(75)
`(73) Assignee: Masimo Corporation, Irvine, CA (US)
`( * ) Notice:
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U'S'C' 1540’) by 1603 days
`
`(21) APP1~ N0: 11/9393519
`
`(22)
`
`Filed:
`
`NOV. 13, 2007
`
`(65)
`
`Prior Publication Data
`US 2008/0064936 A1
`Mar. 13, 2008
`
`Related U.S. Appllcatlon Data
`
`(51)
`
`(63) Continuation of application No. 10/785,573, filed on
`Feb..24, 2004, now.Pat.. No. 7,295,866, which is a
`cont1nuatlon of apphcat1on No. 10/ 184,028, filed on
`Jun. 26, 2002: now Pat. No. 6,697,658.
`(60) Provisional applicationNo. 60/302,564, filed on Jul. 2,
`2001'
`Int Cl
`A6TB 5I/1455
`(52) us. Cl.
`USPC ............................ 600/323; 600/310; 600/322
`(58) Field of Classification Search
`USPC ................. 600/309, 310, 322, 323, 324, 333,
`600/473, 476; 356/41
`See application file for complete search history.
`
`(200601)
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
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`1
`avage e a .
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`
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`
`W0
`
`0 872 210 A1
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`
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`WO 99/63883
`OTHER PUBLICATIONS
`
`PCT International Search Report, App. No. PCT/USO2/20675, App.
`Dt:J .28,2002,4
`.
`a 6 un
`pages
`Primary Examiner 7 Eric Winakur
`Assistant Examiner 7 Chu Chuan (JJ) Liu
`(74) AHOY/’16)}, Agent, or Fll’m i Knobbe, Martens, OISOH &
`Bear LLP
`(57)
`
`.
`~
`~
`A 1311159 ox1meter .may “3911.03 POW? consumpt1on 1n the
`absence of overr1d1ng cond1tlons. Varlous sampl1ng mecha-
`nisms may be used individually or in combination. Various
`parameters may be monitored to trigger or override a reduced
`power consumption state. In this manner, a pulse oximeter
`can lower power consumption without sacrificing perfor-
`mance during, for example, high noise conditions or oxygen
`desaturations
`
`ABSTRACT
`
`24 Claims, 11 Drawing Sheets
`
`
`I
`3 2 SAMPLING CONTROLLER44o
`
`
`CONTROL
`
`
`ENGINE
`
`
`
`SIGNAL
`POWER
`
`
`STATUS
`STATUS
`
`
`CALCULATOR
`CALCULATOR
`
`452
`
`450
`
`
`
`
`
`DETECTOR
`
`FRONT-END
`
`PRE-
`PROCESSOR
`
`
`SENSOR
`
`L__'ETEREA_‘EF:__1
`
`L.
`
`SIGNAL PROCESSBR _________ 1
`
`1
`
`APPLE 1001
`
`APPLE 1001
`
`1
`
`

`

`US 8,457,703 B2
`
`Page2
`
`U.S. PATENT DOCUMENTS
`.
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`,
`,
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`,
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`~
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`12/1999 Diabetal.
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`“2000 Diab et 31'
`6’027’452 A
`”000 FlfihefiyetaL
`6’036’642 A
`”000 13131) et 31'
`a
`5
`~
`2822228 2
`”585888 61:1,: 2::
`6,081,735 A
`6/2000 Diab et a1.
`6’088’607 A
`”000 Diab et 31'
`6’110’522 A
`”000 LePPer’ 3' et 31'
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`9/2000 Minoz ........................... 600/309
`,
`,
`,
`,
`188888 Eifféda
`23222; 2
`11/2000 Kiani—Azarbayjany et al.
`6,151,516 A
`11/2000 Gerhardt et a1.
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`12/2000 Diabetal.
`6157 850 A
`.
`’
`’
`”/2000 M1115 et 31'
`6’165’005 A
`2882288 3 88881 $23231] 3””
`6,229,856 B1
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`6,232,609 B1
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`6,241,683 B1
`6/2001 Macklemetal.
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`6’263’222 B1
`“001 Diab et 31'
`6,278,522 B1
`8/2001 Lepper, Jr. et al.
`6,280,213 B1
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`6,285,896 B1
`9/2001 Tobleret a1.
`6’321’100 B1
`“/2001 Parker
`6,334,065 B1
`12/2001 Al-Alietal.
`6343 224 B1
`1/2002 Parker
`6:349:228 B1
`”002 Kimietal.
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`3/2002 Diab et al.
`6,368,283 B1
`4/2002 Xu etal.
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`4/2002 Caro etal.
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`6,515,273 B2
`6,519,487 B1
`6,525,386 B1
`
`.................... 600/323
`
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`10/2002 Kopotic et a1.
`12/2002 Diab etal.
`1/2003 Kolliasetal.
`2/2003 Al-Ali
`2/2003 Parker
`2/2003 Mills et a1.
`
`6,526,300 B1
`
`6,541,756 B2
`2288882 81
`6,584,336 B1
`6,595,316 B2
`6,597,932 B2
`228222? 8%
`’
`’
`6,632,181 B2
`2228822 8:
`6,643,530 B2
`6,650,917 B2
`6,654,624 B2
`6,658,276 B2
`6,661,161 B1
`6,671,531 B2
`6,678,543 B2
`6,684,090 B2
`2282282 8%
`6’697’657 B1
`6’697’658 B2
`,
`R3338,476 E
`6699194 B1
`6,714,804 B2
`163355492 E
`’
`6,721,582 B2
`2232882 8:
`6,728,560 B2
`6’735’459 B2
`6’745’060 B2
`6’760’607 B2
`6,770,028 B1
`6,771,994 B2
`6,792,300 B1
`6,813,511 B2
`28:22:41, 8%
`6,826,419 B2
`6,830,711 B2
`’
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`6,850,787 B2
`6,850,788 B2
`2822888 8%
`6’898’452 B2
`’
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`6,920,345 B2
`6,931,268 B1
`6,934,570 B2
`2828888 8%
`6,950,687 B2
`6’961’598 B2
`6’970’792 B1
`6’979’812 B2
`6,985,764 B2
`6,993,371 B2
`2992427 B2
`6’999’904 B2
`7,003,338 B2
`7’003’339 B2
`’
`’
`7,015,451 B2
`3838828 8%
`7’030’749 B2
`’
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`7821323 3%
`7’044’918 B2
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`,
`7,096,052 B2
`7,096,054 B2
`7,132,641 B2
`7,142,901 B2
`7,149,561 B2
`7,186,966 B2
`7,190,261 B2
`7,215,984 B2
`
`2/2003 Kianiet al.
`,
`_
`-
`4/2003 Schulzetal.
`2388; 30113832;
`6/2003 Ali et a1.
`7/2003 Cybulski et al.
`7/2003 Tian et a1.
`8,288; if“ e; 31'
`*
`‘eta'
`10/2003 Flahertyetal.
`$888; 338391“
`11/2003 D1:beta1
`“/7003 Diab et al,
`11/2003 Diab etal,
`12/‘7‘003 Kianlet a1
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`,
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`1.
`la et al.
`35004 D. b
`3/9004 Diab et al
`3/2004 Al-Ali et a1
`'
`4/‘7‘004 D' b
`7
`”1 “41'
`9
`4/2004 Trepagnleretal.
`2888:: 281:1?
`4/2004 Kolliasetal
`5,3004 P k
`65004 Digital
`75004 Al-Ali
`8/2004 Ali et a1
`8/2004 Kiani et a1.
`9/2004 Diab et al.
`9
`'
`11/2004 Diab etal.
`18:88:: 1281:“
`11/2004 Diab et a1
`12/2004 Mills et a1
`'
`‘
`2/2005 Weberetal.
`,
`2/2005 Al-Ali
`8,5882 21131? 31'
`5/2005 Al-Ali etal
`~
`2
`.
`7/2005 A1-A11eta1.
`8/2005 Kiani—Azarbayjany et al.
`8/2005 Kianietal.
`8,2882 Elfifilyjt 31'
`9/5005 A1)-Ali
`11/2005 Diab
`11,3005 Diab
`12,5005 Al-Ali
`1/2006 Mason et a1
`1/2006 Kianietal
`'
`2,5006 Ali etal
`2/2006 Webere't 31
`2/2006 Weber etal,
`2,3006 Diabetal
`'
`7
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`3/2006 Da1keetal.
`:83882 2112521.
`4,3006 Al-Ali
`g
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`7:382 3121:8611
`55006 Diab
`1
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`6/;006 M.“
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`1 56 3~
`8/2006 Mason et al.
`8/2006 Abdul-Hafiz et a1.
`11/2006 Sc_hu1zeta1.
`11/2006 Klametal.
`12/2006 Diab
`3/2007 Al-Ali
`3/2007 Al—Ali
`5/2007 Diab
`
`'
`
`'
`
`'
`
`'
`
`'
`
`2
`
`

`

`US 8,457,703 B2
`
`Page 3
`
`7,215,986 B2
`7,221,971 B2
`7,225,006 B2
`7,225,007 B2
`RE39,672 E
`7,239,905 B2
`7,245,953 B1
`7,254,431 B2
`7,254,433 B2
`7,254,434 B2
`
`5/2007 Diab
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`5/2007 Al-Ali et al.
`5/2007 Al-Ali
`6/2007 Shehada et al.
`7/2007 Kiani-Azarbayjany et al.
`7/2007 Parker
`8/2007 Al-Ali
`8/2007 Diab et 211.
`8/2007 Schulz et a1.
`
`7,272,425 B2
`7,274,955 B2
`D554,263 S
`7,280,858 B2
`7,289,835 B2
`7,292,883 B2
`7,295,866 B2
`zoos/0234317 A1
`
`9/2007 Al-Ali
`9/2007 Kiani et al.
`10/2007 Al-Ali
`10/2007 Al-Ali et al.
`10/2007 Mansfield et 31.
`11/2007 De Felice et a1.
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`10/2005 Kiani
`
`* cited by examiner
`
`3
`
`

`

`US. Patent
`
`Jun. 4, 2013
`
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`US 8,457,703 B2
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`

`1
`LOW POWER PULSE OXIMETER
`
`US 8,457,703 B2
`
`2
`
`FIG. 2 illustrates a sleep-mode pulse oximeter 200 utilizing
`conventional sleep-mode power reduction. The pulse oxime-
`ter 200 has a pulse oximeter processor 210 and a power
`control 220. The power control 220 monitors the pulse oxime-
`ter output parameters 212, such as oxygen saturation and
`pulse rate, and controls the processor power 214 according to
`measured activity. For example, if there is no significant
`change in the oxygen saturation value over a certain time
`period, the power control 220 will power down the processor
`210, except perhaps for a portion of memory. The power
`control 220 may have a timer that triggers the processor 210
`to periodically sample the oxygen saturation value, and the
`power control 220 determines if any changes in this param-
`eter are occurring. Ifnot, the power control 220 will leave the
`processor 210 in sleep mode.
`There are a number ofdisadvantages to applying consumer
`electronic sleep mode techniques to pulse oximetry. By defi-
`nition, the pulse oximeter is not functioning during sleep
`mode. Unlike consumer electronics, pulse oximetry cannot
`afford to miss events, such as patient oxygen desaturation.
`Further, there is a trade-offbetween shorter but more frequent
`sleep periods to avoid a missed event and the increased pro-
`cessing overhead to power-up after each sleep period. Also,
`sleep mode techniques rely only on the output parameters to
`determine whether the pulse oximeter should be active or in
`sleep mode. Finally, the caregiver is given no indication of
`when the pulse oximeter outputs were last updated.
`One aspect of a low power pulse oximeter is a sensor
`interface adapted to drive a pulse oximetry sensor and receive
`a corresponding input signal. A processor derives a physi-
`ological measurement corresponding to the input signal, and
`a display driver communicates the measurement to a display.
`A controller generates a sampling control output to at least
`one of said sensor interface and said processor so as to reduce
`the average power consumption ofthe pulse oximeter consis-
`tent with a predetermined power target.
`In one embodiment, a calculator derives a signal status
`output responsive to the input signal. The signal status output
`is communicated to the controller to override the sampling
`control output. The signal status output may indicate the
`occurrence of a low signal quality or the occurrence of a
`physiological event. In another embodiment, the sensor inter-
`face has an emitter driver adapted to provide a current output
`to an emitter portion ofthe sensor. Here, the sampling control
`output determines a duty cycle of the current output. In a
`particular embodiment, the duty cycle may be in the range of
`about 3.125% to about 25%.
`In another embodiment, the sensor interface has a front-
`end adapted to receive the input signal from a detector portion
`of the sensor and to provide a corresponding digitized signal.
`Here, the sampling control output determines a powered-
`down period of the front-end. A confidence indicator respon-
`sive to a duration of the powered-down period may be pro-
`vided and displayed.
`In yet another embodiment, the pulse oximeter comprises a
`plurality ofdata blocks responsive to the input signal, wherein
`the sampling control output determines a time shift of suc-
`cessive ones of the data blocks. The time shift may vary in the
`range of about 1.2 seconds to about 4.8 seconds.
`An aspect of a low power pulse oximetry method com-
`prises the steps of setting a power target and receiving an
`input signal from a pulse oximetry sensor. Further steps
`include calculating signal status related to the input signal,
`calculating power status related to the power target, and sam-
`pling based upon the result ofthe calculating signal status and
`the calculating power status steps.
`
`REFERENCE TO RELATED APPLICATIONS
`
`The present application is a continuation of US. applica-
`tion Ser. No. 10/785,573, entitled “Low Power Pulse Oxime-
`ter,” filed Feb. 24, 2004, which is a continuation ofapplication
`Ser. No. 10/184,028, entitled “Low Power Pulse Oximeter,”
`filed Jun. 26, 2002, now US. Pat. No. 6,697,658, which
`claims priority benefit under 35 U.S.C. §119(e) from US.
`Provisional Application No. 60/302,564, entitled “Low
`Power Pulse Oximeter,” filed Jul. 2, 2001. The present appli-
`cation incorporates each of the foregoing disclosures herein
`by reference.
`
`BACKGROUND OF THE INVENTION
`
`Pulse oximetry is a widely accepted noninvasive procedure
`for measuring the oxygen saturation level of a person’s arte-
`rial blood, an indicator of their oxygen supply. Oxygen satu-
`ration monitoring is crucial in critical care and surgical appli-
`cations, where an insufficient blood supply can quickly lead
`to injury or death. FIG. 1 illustrates a conventional pulse
`oximetry system 100, which has a sensor 110 and a monitor
`150. The sensor 110, which can be attached to an adult’s
`finger or an infant’s foot, has both red and infrared LEDs 112
`and a photodiode detector 114. For a finger, the sensor is
`configured so that the LEDs 112 project light through the
`fingernail and into the blood vessels and capillaries under-
`neath. The photodiode 114 is positioned at the finger tip
`opposite the fingernail so as to detect the LED emitted light as
`it emerges from the finger tissues. A pulse oximetry sensor is
`described in US. Pat. No. 6,088,607 entitled “Low Noise
`Optical Probe,” which is assigned to the assignee of the
`present invention and incorporated by reference herein.
`Also shown in FIG. 1, the monitor 150 has LED drivers
`152, a signal conditioning and digitization front-end 154, a
`signal processor 156, a display driver 158 and a display 159.
`The LED drivers 152 alternately activate the red and IR LEDs
`112 and the front-end 154 conditions and digitizes the result-
`ing current generated by the photodiode 114, which is pro-
`portional to the intensity of the detected light. The signal
`processor 156 inputs the conditioned photodiode signal and
`determines oxygen saturation based on the differential
`absorption by arterial blood of the two wavelengths emitted
`by the LEDs 112. Specifically, a ratio of detected red and
`infrared intensities is calculated by the signal processor 156,
`and an arterial oxygen saturation value is empirically deter-
`mined based on the ratio obtained. The display driver 158 and
`associated display 159 indicate a patient’ s oxygen saturation,
`heart rate and plethysmographic waveform.
`
`SUMMARY OF THE INVENTION
`
`Increasingly, pulse oximeters are being utilized inportable,
`battery-operated applications. For example, a pulse oximeter
`may be attached to a patient during emergency transport and
`remain with the patient as they are moved between hospital
`wards. Further, pulse oximeters are often implemented as
`plug-in modules for multiparameter patient monitors having
`a restricted power budget. These applications and others cre-
`ate an increasing demand for lower power and higher perfor-
`mance pulse oximeters. A conventional approach for reduc-
`ing power consumption in portable electronics, typically
`utilized by devices such as calculators and notebook comput-
`ers, is to have a “sleep mode” where the circuitry is powered-
`down when the devices are idle.
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`US 8,457,703 B2
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`3
`In one embodiment, the calculating signal status step com-
`prises the substeps of receiving a signal statistic related to the
`input signal, receiving a physiological measurement related
`to the input signal, determining a low signal quality condition
`from the signal statistic, determining an event occurrence
`from the physiological measurement, and indicating an over-
`ride based upon the low signal quality condition or the event
`occurrence. The calculating power status step may comprise
`the substeps of estimating an average power consumption for
`at least a portion of the pulse oximeter, and indicating an
`above power target condition when the average power con-
`sumption is above the power target. The sampling step may
`comprise the substep of increasing sampling as the result of
`the override. The sampling step may also comprise the sub-
`step of decreasing sampling as the result of the above power
`target condition, except during the override.
`Another aspect of a low power pulse oximetry method
`comprises the steps of detecting an override related to a
`measure of signal quality or a physiological measurement
`event, increasing the pulse oximeter power to a higher power
`level when the override exists, and reducing the pulse oxime-
`ter power to a lower power level when the override does not
`exist. The method may comprise the further steps of prede-
`termining a target power level for a pulse oximeter and
`cycling between the lower power level and the higher power
`level so that an average pulse oximeter power is consistent
`with the target power level.
`In one embodiment, the reducing step comprises the sub-
`step ofdecreasing the duty cycle of an emitter driver output to
`the sensor. In another embodiment, the reducing step com-
`prises the substep of powering-down a detector front-end. A
`further step may comprise displaying a confidence indicator
`related to the duration of the powering-down substep. In yet
`another embodiment, the reducing step comprises the sub step
`of increasing the time-shift of post-processor data blocks.
`Another aspect of a low power pulse oximeter comprises a
`sensor interface adapted to receive an input signal from a
`sensor, a signal processor configured to communicate with
`the sensor interface and to generate an internal parameter
`responsive to the input signal, and a sampling controller
`responsive to the internal parameter so as to generate a sam-
`pling control to alter the power consumption of at least one of
`the sensor interface and the signal processor. The signal pro-
`ces sor may be configured to generate an output parameter and
`the sampling controller may be responsive to a combination
`of the internal and output parameters so as to generate a
`sampling control to alter the power consumption of at least
`one of the sensor interface and the signal processor. The
`internal parameter may be indicative of the quality of the
`input signal. The output parameter may be indicative of oxy-
`gen saturation.
`In another embodiment, the sampling controller is respon-
`sive to a predetermined power target in combination with the
`internal parameter so as to generate a sampling control to alter
`the power consumption of at least one of the sensor interface
`and the signal processor. The signal processor may be con-
`figured to generate an output parameter and the sampling
`controller may be responsive to a combination of the internal
`and output parameters and the power target so as to generate
`a sampling control to alter the power consumption of at least
`one of the sensor interface and the signal processor. The
`sensor interface may comprise an emitter driver and the sam-
`pling control may modify a duty cycle of the emitter driver.
`The sensor interface may comprise a detector front-end and
`the sampling control may intermittently power-down the
`detector front-end. The processor may generate a plurality of
`data blocks corresponding to the input signal, where each of
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`the data blocks have a time shift from a preceding one of the
`data blocks, and where the sampling control may determine
`the amount of the time shift.
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`A further aspect of a low power pulse oximeter comprises
`an interface means for communicating with a sensor, a pro-
`cessor means for generating an internal parameter and an
`output parameter, and a controller means for selectively
`reducing the power consumption of at least one of the inter-
`face means and the processor means based upon the param-
`eters. In one embodiment, the interface means comprises a
`driver means for determining the duty cycle of emitter current
`to the sensor, the driver means being responsive to the con-
`troller means. In another embodiment, the interface means
`comprises a detector front-end means for receiving an input
`signal from the sensor, the power for the detector front-end
`means being responsive to the controller means. In yet
`another embodiment, the processor means comprises a post-
`processor means for determining a time shift between data
`blocks, the post-processor means being responsive to the
`controller means. In a further embodiment, the controller
`means comprises a signal status calculator means for gener-
`ating an indication ofa low signal quality or a physiological
`event based upon at least one of an internal signal statistic and
`an output physiological measurement, and a control engine
`means in communications with the signal status calculator
`means for generating a sampling control responsive to the
`indication. In yet a further embodiment, the controller means
`comprises a power status calculator means for generating a
`power indication of power consumption relative to a power
`target, and a control engine means in communications with
`the power status calculator means for generating a sampling
`control responsive to the power indication.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of a conventional pulse oximeter
`sensor and monitor;
`FIG. 2 is a block diagram of a pulse oximeter having a
`conventional sleep mode;
`FIG. 3 is a top-level block diagram of a low power pulse
`oximeter;
`FIG. 4 is a detailed block diagram of a low power pulse
`oximeter illustrating a sensor interface, a signal processor and
`a sampling controller;
`FIG. 5 is a graph of emitter drive current versus time
`illustrating variable duty cycle processing;
`FIG. 6 is a graph of oxygen saturation versus time illus-
`trating intermittent sample processing;
`FIGS. 7A-B are graphs of data buffer content versus time
`illustrating variable data block overlap processing;
`FIG. 8 is a graph of power versus time illustrating power
`dissipation conformance to an average power target using
`variable duty cycle and intermittent sample processing;
`FIG. 9 is a state diagram of the sampling controller for
`variable duty cycle and intermittent sample processing;
`FIG. 10 is a graph of power versus time illustrating power
`dissipation using variable data block overlap processing; and
`FIG. 11 is a state diagram of the sampling controller for
`variable data block overlap processing.
`
`DETAILED DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`FIG. 3 illustrates one embodiment of a low power pulse
`oximeter. The pulse oximeter 300 has a sensor interface 320,
`a signal processor 340, a sampling controller 360 and a dis-
`play driver 380. The pulse oximeter 300 also has a sensor port
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`US 8,457,703 B2
`
`5
`302 and a display port 304. The sensorport 302 connects to an
`external sensor, e.g. sensor 110 (FIG. 1). The sensor interface
`320 drives the sensor port 302, receives a corresponding input
`signal from the sensor port 302, and provides a conditioned
`and digitized sensor signal 322 accordingly. Physiological
`measurements 342 are input to a display driver 380 that out-
`puts to the display port 304. The display port 304 connects to
`a display device, such as a CRT or LCD, which a healthcare
`provider typically uses for monitoring a patient’s oxygen
`saturation, pulse rate and plethysmograph.
`As shown in FIG. 3, the signal processor 340 derives the
`physiological measurements 342, including oxygen satura-
`tion, pulse rate and plethysmograph, from the input signal
`322. The signal processor 340 also derives signal statistics
`344, such as signal strength, noise and motion artifact. The
`physiological measurements 342 and signal statistics 344 are
`input to the sampling controller 360, which outputs sampling
`controls 362, 364, 366 accordingly. The sampling controls
`362, 364, 366 regulate pulse oximeter power dissipation by
`causing the sensor interface 320 to vary the sampling charac-
`teristics of the sensor port 302 and by causing the signal
`processor 340 to vary its sample processing characteristics, as
`described in further detail with respect to FIG. 4, below.
`Advantageously, power dissipation is responsive not only to
`output parameters, such as the physiological measurements
`342, but also to internal parameters, such as the signal statis-
`tics 344.
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`FIG. 4 illustrates further detail regarding the sensor inter-
`face 320, the signal processor 340 and the sampling controller
`360. The sensor interface 320 has emitter drivers 480 and a
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`detector front-end 490. The emitter drivers 480 are responsive
`to a sampling control 362, described below, and provide emit-
`ter drive outputs 482. The emitter drive outputs 482 activate
`the LEDs of a sensor attached to the sensor port 302 (FIG. 3).
`The detector front-end 490 receives an input signal 492 from
`a sensor attached to the sensor port 302 (FIG. 3) and provides
`a corresponding conditioned and digitized input signal 322 to
`the signal processor 340. A sampling control 364 controls
`power to the detector front-end 490, as described below.
`As shown in FIG. 4, the signal processor 340 has a pre-
`processor 410 and a post processor 430. The pre-processor
`410 demodulates red and IR signals from the digitized signal
`322, performs filtering, and reduces the sample rate. The
`pre-processor provides a demodulated output, having a red
`channel 412 and an IR channel 414, which is input into the
`post-processor 430. The post processor 430 calculates the
`physiological measurements 342 and the signal statistics 344,
`which are output to a signal status calculator 450. The physi-
`ological measurements 342 are also output to a display driver
`380 (FIG. 3) as described above. A pulse oximetry signal
`processor is described in US. Pat. No. 6,081,735 entitled
`“Signal Processing Apparatus,” which is assigned to the
`assignee of the present invention and incorporated by refer-
`ence herein.
`
`Also shown in FIG. 4, the sampling controller 360 has a
`control engine 440, a signal status calculator 450 and a power
`status calculator 460. The control engine 440 outputs sam-
`pling controls 362, 364, 366 to reduce the power consumption
`of the pulse oximeter 300. In one embodiment, the control
`engine 440 advantageously utilizes multiple sampling
`mechanisms to alter power consumption. One sampling
`mechanism is an emitter duty cycle control 362 that is an
`input to the emitter drivers 480. The emitter duty cycle control
`362 determines the duty cycle of the current supplied by the
`emitter drive outputs 482 to both red and IR sensor emitters,
`as described with respect to FIG. 5, below. Another sampling
`mechanism is a front-end control 364 that intermittently
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`removes power to the detector front-end 490, as described
`with respected to FIG. 6, below. Yet another sampling mecha-
`nism is a data block overlap control 366 that varies the num-
`ber of data blocks processed by the post processor 430. These
`various sampling mechanisms provide the flexibility to
`reduce power without sacrificing performance during, for
`example, high noise conditions or oxygen desaturation
`events, as described below in further detail.
`The sampling controls 362, 364, 366 modify power con-
`sumption by, in effect, increasing or decreasing the number of
`input samples received and processed. Sampling, including
`acquiring input signal samples and subsequent sample pro-
`cessing, can be reduced during high signal quality periods and
`increased during low signal quality periods or when critical
`measurements are necessary. In this manner,
`the control
`engine 440 regulates power consumption to satisfy a prede-
`termined power target, to minimize power consumption, or to
`simply reduce power consumption, as described with respect
`to FIGS. 8 and 10, below. The current state of the control
`engine is provided as a control state output 442 to the power
`status calculator 460. The control engine 440 utilizes the
`power status output 462 and the signal status output 452 to
`determine its next control state, as described with respect to
`FIGS. 9 and 11, below.
`Further shown in FIG. 4, the signal status calculator 450
`receives physiological measurements and signal statistics
`from the post processor 430 and determines the occurrence of
`an event or a low signal quality condition. An event determi-
`nation is based upon the physiological measurements output
`342 and may be any physiological-related indication that
`justifies the processing of more sensor samples and an asso-
`ciated higher power consumption level, such as an oxygen
`desaturation, a fast or irregular pulse rate or an unusual
`plethysmograph waveform to name a few. A low signal qual-
`ity condition is based upon the signal statistics output 344 and
`may be any signal-related indication thatjustifies the process-
`ing of more sensor samples and an associated higher power
`consumption level, such as a low signal level, a high noise
`level or motion artifact to name a few. The signal status
`calculator 450 provides the signal status output 452 that is
`input to the control engine 440.
`In addition, FIG. 4 shows that the power status calculator
`460 has a control state input 442 and a power status output
`462. The control state input 442 indicates the current state of
`the control engine 440. The power status calculator 460 uti-
`lizes an internal time base, such as a counter, timer or real-
`time clock, in conjunction with the control engine state to
`estimate the average power consumption of at least a portion
`of the pulse oximeter 300. The power status calculator 460
`also stores a predetermined power target and compares its
`power consumption estimate to this target. The power status
`calculator 460 generates the power status output 462 as an
`indication that the current average power estimate is above or
`below the power target and provides this output 462 to the
`control engine 440.
`FIG. 5 illustrates emitter driver output current versus time.
`The graph 500 depicts the combination of a red LED drive
`current 510 and an IR drive current 560. The solid line graph
`502 illustrates drive currents having a high duty cycle. The
`dashed