111111
`
`1111111111111111111111111111111111111111111111111111111111111111111111111111
`US 20060084879A l
`
`(19) United States
`(12) Patent Application Publication
`Nazarian et al.
`
`{10) Pub. No.: US 2006/0084879 Al
`Apr. 20, 2006
`(43) Pub. Date:
`
`(54) MOTION C ANCELLATION OF OPTICAL
`INPUT SIGNALS FOR PHYSIOLOGIC AL
`PULSE MEASUREMENT
`
`(75)
`
`Inventors: Richard A. Naz arian, Excelsior. MN
`(US); Lori E. Lucke, Eagan. MN (US);
`Su san S. Alfini. Champlin, MN (US):
`M a rk J. Bina, Shoreview, MN (US);
`Don W. E. Evans, St. Paul, MN (US);
`Paul Barris, Delta (CA): Michael W.
`Geatz, Maple Grove, MN (US)
`
`Correspondence Address:
`OPPENHEIMER WOLFF & DONNELLY LLP
`45 SOUTH SEVENTH STRE ET, SUITE 3300
`MINNEAPOLIS, MN 55402 (US)
`
`(73) Assignee: PulseTracer Technologies Inc., Va ncou(cid:173)
`ver (CA)
`
`(21) Appl. No.:
`
`11/250,011
`
`(22) Filed:
`
`Oct. 13, 2005
`
`Relate d U.S. Applicat ion Dat a
`
`(60) Provisional appl ication No. 60/619,253, filed 011 Oct.
`15, 2004. Provisional appl ication No. 60/68 1,397,
`filed on May 16, 2005. Provisional application No.
`60/696,858, fi led on Jul. 6, 2005.
`
`Publication C lassification
`
`(51)
`
`Int. C l.
`(2006.01)
`A6JB 5102
`(52) U.S. C l. .............................................................. 600/500
`
`ABSTRACT
`(57)
`A pulse rate sensor tha t includes an accelerometer for
`measuring periodic motion and a piezo sensor for detecting
`erratic motion is capable of more accurately detenniujng
`pulse rate by accouuting for these types of motiou. The pulse
`rate sensor in accordance wi th the present invention dinlin(cid:173)
`ishcs pulse ra te signal degrada tion due to erratic motion
`through a combination of algorithms that control signal
`boosting, wavefonu refinement and signal noise suppres(cid:173)
`sion.
`
`CONDITIONED OPTICAL
`PULSE SIGNALS
`(PHOTODETECTOR)
`501
`
`PIEZOELECTRIC
`SENSOR
`
`502
`
`ACCELEROMETER
`AND/OR DC
`COMPENSATION
`503
`
`TIME DOMAIN FILTER
`504
`
`FREQUENCY DOMAIN -
`FOURIER TRANSFORM
`505
`
`FREQUENCY DOMAIN -
`FOURIER TRANSFORM
`505
`
`BAND
`REJECT
`FILTER
`
`PULSE RATE 507
`
`001
`
`Apple Inc.
`APL1031
`U.S. Patent No. 9,289,135
`
`

`

`Pa tent Application Publication Apr. 20, 2006 Sheet 1 of 6
`
`US 2006/0084879 AJ
`
`SIGNAL
`
`0
`
`50
`
`100
`
`200
`
`250
`
`300
`
`150
`SAMPLE#
`
`FIG. 1A
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`200
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`300
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`300
`
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`100
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`200
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`I
`
`250
`
`I
`
`150
`SAMPLE#
`
`FIG. 1 C
`
`002
`
`

`

`Patent Applica tion Publication Apr. 20, 2006 Sheet 2 of 6
`
`US 2006/0084879 AJ
`
`-
`
`-
`
`-
`-
`--
`
`-
`--
`110
`-
`
`112
`--
`
`114 --
`
`102
`-
`
`104
`--
`
`106
`-
`
`108
`- -
`
`101
`
`FIG. 2A
`
`003
`
`

`

`Patent Application Publication Apr. 20, 2006 Sheet 3 of 6
`
`US 2006/0084879 A1
`
`FIG. 28
`
`004
`
`

`

`Patent Applica tion Publication Apr. 20, 2006 Sheet 4 of 6
`
`US 2006/0084879 AJ
`
`12
`
`14
`
`1
`
`9
`
`6
`
`8
`L-------------------------------~
`
`18
`
`110
`
`FIG. 3
`
`005
`
`

`

`Patent Application Publication Apr. 20, 2006 Sheet 5 of 6
`
`US 2006/0084879 A1
`
`CONDITIONED OPTICAL
`PULSE SIGNALS
`(PHOTODETECTOR)
`501
`
`PIEZOELECTRIC
`SENSOR
`
`502
`
`ACCELEROMETER
`AND/OR DC
`COMPENSATION
`503
`
`t t
`
`TIME DOMAIN FILTER
`504
`
`FREQUENCY DOMAIN(cid:173)
`FOURIER TRANSFORM
`505
`
`FREQUENCY DOMAIN -
`FOURIER TRANSFORM
`505
`
`BAND
`REJECT
`FILTER
`
`506
`
`PULSE RATE SO?
`
`FIG. 4
`
`006
`
`

`

`Patent Application Publication Apr. 20, 2006 Sheet 6 of 6
`
`US 2006/0084879 Al
`
`USE FREQUENCY
`ANALYSIS
`. ALGORITHMS
`
`408
`
`ANALYZE DC
`COMPENSATION
`SIGNAL 404
`
`USE PEAK DETECTION
`ALGORITHMS
`410
`
`CALCULATE
`PULSE
`RATE
`
`412
`
`FIG. 5
`
`007
`
`

`

`US 2006/0084879 Al
`
`Apr. 20, 2006
`
`MOTION CANCELLATION OF OPTICAL l NPUT
`SIGNALS FOR PHYSIOLOGICAL PULSE
`MEASUREMENT
`
`BACKGROUND OF HIE INVENTION
`
`(0001) 1. Field of the Invention
`
`[0002) Tbe present invention relates generally to tbe field
`of signal processing. More specifically, the present invention
`is related to pulse rate monitors capable of providing accu(cid:173)
`rate measurement and display of a user's pulse rate dt1ring
`times of physical exercise o r o ther activity.
`
`(0003) 2. Background of the Related Art
`
`(0004) The accurate measurement of an active person's
`pulse rate at the wrist is complicated due to the artifucts
`produced by body motion such as when the person is
`mnning or otherwise engaging in physical activity or exer(cid:173)
`cise. Therefore, pulse rate monitors presently in the market
`utilize chest bands that arc worn close to the hear1 to
`minimize tl1e effect of motion produced by exercise. Arti(cid:173)
`facts produced by body motion are detected by pulse rate
`sensors as "noise" that masks the beart rate pulse signal
`being measured. In order to mitigate the effects of these
`artifacts. it is necessary to filter out and cancel as much of
`the noise signal occurring in the pulse rate frequency band
`as possible while retaining the desired pulse signal.
`
`(0005) Signals of interest are generated by transmitting a
`ligbt source in the near infrared region into the tissue and
`measuring the returned signal intensity. Typically two or
`four light emining diodes (LEOs) are employed with vary(cid:173)
`ing intensity to establish the optimum optical window. The
`return signal strength will be modulated by the capillary
`blood flow in tbe tissue and will vary with the physiologic
`pulse of the subject. Tbis is a well understood and estab(cid:173)
`lished principal that has been applied to pulse monitoring
`equipment for years. Pulse rate sensing taken at locations
`otl1er than close to Lbe beart, bas not been successful because
`of the relatively low s ig11al strength and relafively high
`" noise" content. The low s ignal strength can be attributed to
`a number of factors including variations in skin and bair
`density. variations in vascularization, and optical alignment.
`Further. the received signa l includes several components
`which can be generally classified as "noise" when attempt(cid:173)
`ing to sense pulse rate. These hjgb "noise" levels are in
`addi tion to classical noise sources present within almost all
`electrical systems and primarily include inherent optical
`noise sources. interfering light sources, and motion artifact.
`
`(0006] To illustrate, FIG. lA depicts a signal of in terest.
`FIG.lB depicts noise caused by motion artifact. interfering
`lights sources, random noise and tbe like. FIG.lC illustrates
`how the signal of interest is masked by noise due to low
`signal strengtl1. as an example.
`
`(0007) While conventional signal processing techniques
`may be able to reduce "out of band" noise: that is, noise not
`found within the frequency of interest, they are challenged
`to address noise that mimics the signal of interest and that is
`non-random. the most common of wbich is motion.
`
`[0008) Various pulse rate detection systems are known in
`the art. U.S. Pat. No. 4,338,950 to Barlow. Jr. eta!. discloses
`an instnrment comprised of wrist-mounted mut, which con(cid:173)
`tains a piezoelectric transducer for detecting pulse rate and
`
`an accelerometer for detecting body motion during physical
`activity. The instrument further includes a processor for
`subtracting the body movement component from the signal,
`thus yielding the true heart beat signal.
`
`(0009) U.S. Pat. No. 5,431.170 to Matbews discloses a
`device wbich may be worn on the wrist or hand during
`physical activity. The device contains a light sensor to
`measure pulse and ligbt sensor or accelerometer for mea(cid:173)
`suring movement. Mathews discloses that a noise cancella(cid:173)
`tion circuit takes the values from these sensors to give a true
`pulse s ignal that is free of pedometry vibration or noise.
`
`(0010) U.S. Pat. No. 5,807.267 to Bryars et al. discloses an
`apparatus which can be combined in a si~ngle unit with a
`wrist watch to display the user's heart pulse rate during
`physical exercise. A primary piezo sensor detects the heart
`rate pulse of a user and a background piezo sensor detects
`the no ise from local body motion. Signals from tl1is back(cid:173)
`grotmd sensor are digita lly subtracted from the primary
`pulse sensor thus a llegedly reducing tbe effects of random
`body noise.
`
`[0011] U.S. Pat. No. 6,099,478 to Aosl1ima et a l. disclosse
`a pulse wave detecting means comprising an LED, photo
`transistor. or piezoelectric microphone. Body motion detect(cid:173)
`ing means detect body motion using an acceleration sensor.
`Aosbima e t al. disclose thai pulse wave extracting means
`subtract the output of the two sensors to give an accurate
`pulse rate. Assignee related U.S. Pat. No. 5,776,070 pro(cid:173)
`vides similar disclosures.
`
`[0012] U.S. Pat. No. 6,129,676 to Odagiri et al. discloses
`a pulse rate monitor that can be assembled into a wrist
`watchband and used during activities, such as running. The
`wrist watchband contains an acceleration sensor to detect
`action noise and a piezoelectric microphone to detect pulse.
`When constant motion such as running is detected, the
`action noise spectnrm is subtracted from the pulse wave
`spectnr m, wbich is depicted in FIGS. 6A-C. Running speed
`and distance may also be obtained. U.S. Pat. Nos. 5,697,374
`and 6,023,662 provide similar disclosures.
`
`[0013) U .S . Pat. No. 6,361,501 B l to Amano et al. dis(cid:173)
`closes a pulse wave diagnosing device formed of device
`main body having a wristwatch structure, and pulse wave
`detection sensor unit. A body motion component remover
`subtracts corrected body motio n data .from corrected pulse
`wave data. Body motion waves are detected by an accel(cid:173)
`eration sensor. This device may be incorporated into a
`pedometer.
`
`(0014) U.S. Patent Appln. Publn. 2005/0116820 AI to
`Goldreich discloses a wrist mounted device that detects
`pulse rates. The vibration sensor is a piezo ceranuc sensor
`that measures movement of the wrist and may include an
`accelerometer. A physiologic sensor detects the blood pres(cid:173)
`sure pulse rate, and may be fiber optic. Ambient sensors may
`also be present.
`
`[0015) Whatever the precise merits. features, and advan(cid:173)
`tages of the above cited references, none of them achieves
`or ful fills the purposes of the present invention. For these
`reasons it would be desirable to provide an improved device
`and method for accurately measuring pulse rare during
`pbysical exercise and other activities.
`
`008
`
`

`

`US 2006/0084879 Al
`
`Apr. 20, 2006
`
`2
`
`SUMMARY OF THE lNVENTION
`It is therefore an object of the present invention to
`[0016]
`provide a device and method for accurately monitoring and
`detecting pulse rate.
`
`[0017) More particularly, it is an object of the present
`invention to provide a solution to that allows for adequate
`removal of inherent optical noise sources, imerfering ambi(cid:173)
`ent light sources and motion artifact in optical signals
`especially under intense physical activity.
`
`(0018)
`It is yet another object of the present invention to
`provide a pulse rate monitor ibat can distinguish between
`noise artifact and an individual's true pulse from a signal
`representing a composite of pulse and noise artifact as
`illustrated in FIG. lC.
`[0019) These and other objects are accomplished in accor(cid:173)
`dance with the present invention, a system and method for
`measuring a user's pulse rate during physical exercise or
`activity. that includes a pulse rate sensor having one or more
`emitters capable of transmitting a light source into body
`tissue, a photo detector for receiving reflected light from ibe
`body tissue and producing a photo detector output signal
`indicative of the reflected light; an accelerometer for mea(cid:173)
`suring regular motion of the individual and producing an
`accelerometer output signal indicative of the regular motion;
`a contact type motion sensor for measuring erratic motion of
`the individual and producing a piezo sensor output signal
`indicative of the erratic motion; and a microprocessor for
`receiving tht: photo <.lt:tector output signal, the acceleromett:r
`output signal. and tbe contact type motiou sensor output
`signal, and detennining the pulse rate of the individual,
`where the pulse rate is determined by conditioning the photo
`detector output signal and removing portions of the condi(cid:173)
`tioned photo detector output caused by regular motion and
`erratic motion of the individual.
`
`BRIEF DESCRJIYflON OF TI-lE DRAWINGS
`[0020] FIG. lA illustrates a desired optical signal to be
`measured.
`
`illustrate noise typically caused by
`
`[0021] FIG. lll
`motion.
`[0022) FIG. 1C illustrates tbe combined optical signa l and
`noise.
`
`[0023] FIG. 2A diagrammatically illustrates a pulse rate
`sensor in accordance with the present invention.
`
`(0024] FIG. 2B illustrates a pulse rate sensor encapsulated
`in a watch module in accordance with the present invention.
`
`(0025] FIG. 3 illustrates the signal conditioning process
`for an optical signal in accordance with the present inven(cid:173)
`tion.
`
`(0026) FIG. 4 illustrates a flowchart depicting the motion
`discrimination process in accordance with the present inven(cid:173)
`tion.
`(0027) FIG. 5 illustrates a flowchart depicting steps fol(cid:173)
`lowed to calculate pulse rate in accordance with the present
`invention.
`
`DESCRIPTION OF THE PREFERRED
`EMBODl MENTS
`[0028) While this invention is illustrated and described in
`a preferred embodiment, the device may be produced in
`
`maJlY di:l}(::rent configurations, forms and materials. There is
`depicted in the drawings, and will hereinafter be described
`in detail, a preferred embodiment of the invention. with the
`understanding that tbe present disclosure is to be considered
`as an exemplification of the principles of the invention and
`the associated functional specifications for its construction
`and is not intended to limit the invention to the embodiment
`illustrated. Those skilled in the art will envision many other
`possible variations within the scope of the present invention.
`
`[0029] FIG. 2A illustrates a pulse rate sensor 101 in
`accordance with the present invention. Emitters 102 (e.g.
`LED, light emitting diodes) transmit a light source in the
`near infrared (IR) region into body tissue and a photo
`detector such as a reflective infra-red sensor 104 that
`receives tbe reflected light from the tissue. Pulse rate sensor
`101 uses the infrared optica l processes from which body
`volume displacement is analyzed to detect and store pulse
`rate data, which is indicative of heart rate. Pulse rate sensor
`101 also comprises an accelerometer 108, preferably a
`two-dimensional accelerometer and optionally a three-di(cid:173)
`mensional accelerometer, that detects periodic or constant
`motion of the user, and a contact type motion sensor 106 that
`measures inconsistent or erratic motion of the user. and other
`movement related sources that ellect the optical pulse. The
`contact type motion sensor can be a piezo sensor or other
`types of sensors capable of measuring erratic motion such as
`vibration. The accelerometer or optical sensor o utput may
`also be used as input for step counter or pedometer 114.
`Microprocessor 110 performs signal conditioning f11nctions
`on the pulse signals received from the photo detector 104,
`and also samples and filters signals from accelerometer l 08
`and piezo sensor 106. Pulse rate detector 112 calculates the
`pulse rate of a user by using conditioned optical pulse
`signals received by microprocessor 110, filtered signals from
`accelerometer 108, and piezo sensor 106. While pulse rate
`detector 112 is shown as being part of microprocessor 110,
`it is understood that these could also be separate compo(cid:173)
`nents.
`
`(0030] Pulse rate sensor 101 may be encapsulated in a
`watch module 120 as shown in FrG. 2B with an optional
`rechargeable battery in one embodiment of the present
`invention. However, other carriers/modules are envisioned
`as usable with the present invention such as pendants.
`jewelry. bracelets, patches. music players, etc. which may
`also contain standard watch functions to include time/date
`and a stopwatcbltimer. These o ther carriers may be posi(cid:173)
`tioned auywhere on the ann of an individual or in the case
`of a pendants around the neck of an individual. The pulse
`ra te sensor in accordance with the present invention may
`also include capabilities fo r firmware updates through the
`implementation of a software boot loader. Other additions
`may include a communication module such as universal
`serial bus (USB) port or an RF receiver/transmitter to
`automatically upload data to a web portal. Additionally, the
`pulse rate sensor may include radio frequency identification
`(RFID) to uniquely identii)r each watch sold to the web
`portal.
`
`[0031) The pulse rate sensor in accordance with tbe pre(cid:173)
`timed embodiment of the present invention consists of an
`optical emitter including of one or more light emitting
`diodes, an optical receiver, active signal conditioning, an
`accelerometer and a piezo sensor. and a microprocessor. The
`microprocessor controls the active signal conditioning
`
`009
`
`

`

`US 2006/0084879 Al
`
`Apr. 20, 2006
`
`3
`
`applied to the optical sensor by automatically adjusting the
`light emitting diode output to maintain the optimal signal
`strength. controlling the amplification of the received signal,
`and automatically removing the direct current bias of the
`received signal. The conditioned optical sensor output a nd
`the accelerometer and piezo sensor outputs are sampled as
`input to two different pulse rate calculators. one \!Sed when
`there is no motion present and the other used when there is
`motion present. The piezo sensor is used to detect erratic
`motion while the accelerometer is used to detect periodic
`motion.
`
`(0032) As further described below, pulse rate signal deg(cid:173)
`radation due to arm motion a nd skin vibrations is diminished
`tlu·ough a combination of algorithms that control signal
`boosting, waveform refinement and signal noise suppres(cid:173)
`sion.
`[0033) Referring to FIG. 3. the process to achieve signal
`conditioning of the pulse signal output from photo detector
`10 in accordance with the present invention is illustrated. A
`pulse signal output from photodetector 10, wh.ich may be a
`retlective infra-red sensor, is filtered through low pass fi lter
`12 and is provided to input 1 of the microprocessor 110,
`which includes an internal analog to digital convertor 14.
`Naturally, analog to digital converter 14 could also be a
`component separate from microprocessor 110. Through this
`connection, microprocessor 110 is able to monitor tl1e output
`from photo detector 10 and to determine the appropriate
`intensity for an in:ti'a-red light emitting diode 16, which
`transmits optical signals into body tissue. 111e intensity of
`infra-red light emitting diode 16 is programmable using an
`output 8 from a digital to a nalog converter 18 within
`microprocessor 110 (again, digital to analog converter 18
`could also be a component separate from microprocessor
`110). As further discussed below. an internal closed loop
`control func tion with.in the microprocessor 110 maintains
`the proper intensity of the infra-red light emitting diode 16
`using the feedback from the photodector 10 at inplll 1 to
`control output 8. Using this control function, the output
`signal from photodetector 10 is in an appropriate r<tnge for
`direct current compensation and other related functions.
`Further, tills intensity control allows the microprocessor 110
`to periodically adjust the system to account for different
`environmental and physiological conditions, including vary(cid:173)
`ing ambient light levels. long term blood flow changes and
`varying responses from user to user. The pulse signal
`trans milled from photodetector 10 is filtered through a
`lowpass filter 12 of approximately I 0 Hz to reduce inherent
`noise.
`
`[0034) 11Je pulse signal from photodetector 10 generally
`includes a large direct current component that represents
`gross blood flow, and a small altemating current component
`that represents tme pulse. Because it is desirable to accu(cid:173)
`rately measure tme pulse, active signal conditioning includ(cid:173)
`ing additional amplification of the alternating current com(cid:173)
`ponent and compensation of tl1e direct current component is
`necessary. Compensation of the direct current component
`occurs in two stages. The first stage is accomplished using
`an amplifier 28 to achieve a fixed signal gain. lbe output
`from this first stage is provided to microprocessor 110 at
`input 2. The second stage is the programmable gain stage
`utilzing a second amplifier 30 with output to microprocessor
`110 shown at 3. A fixed direct current compensation voltage,
`shown at output7, is subtracted from the filtered pu lse signal
`
`provded from filter 12. Amplifier 28 has a fixed gain and is
`output to t11e microprocesser 110 at 2. The amplification and
`DC adjustment provided by amplifier 28 moves the signal
`level of its output to the midrange of second operational
`amplifier 30 and a11ows for a second stage of amplification.
`The amplification gain 32 associated with second amplifier
`30 is programmable to allow for adjust necessary to deal
`with varying pulse strengths. The gain 32 is periodically
`adjusted by the microprocessor 110 to maintain signal
`integrity. A programmable direct current compensation sig(cid:173)
`nal from output 6 is also applied to second ampl ifier 30 by
`miroprocessor IJO. It is during this second stage that the
`sensor signal is significantly amplified. The prograllllllable
`direct current compensation at output 6 is adjusted with
`every sample of the first stage gain signal or input 2 of the
`analog to digital convertor. The microprocessor calculates
`the direct current value of the optical pulse signal. and
`applies that value using output 6 as the reference at the input
`of the amplifier stage 30. This is a fine adjustment and allows
`for tl1e quick recovery of the pulse signal during and after
`motion. As significant amplification is applied to the input
`singal a t second amplifier 32, the programmable direct
`current compensation further helps to center the signal at the
`amplifier input, and prevents second amplifier 32 from
`saturating during periods of motion by the user. Thus, the
`pulse can be more accurately tracked during periods of
`motion.
`[0035) Referring again to FIG. 4, the steps used to control
`the direct current compensation signal 6 and the optical
`emitter supply signal 8 are described below.
`l) 111e optical sensor output signal, first amplifer
`(0036)
`output signal, and second amplifer output signal are all
`oversampled at inputs 1. 2. and 3 as shown in FIG. 2
`to generate samples x1(i). x2(i), x3(i) where i repre(cid:173)
`sents the irn san1ple.
`[0037) 2) The signals are all filtered to produce a
`smoother signal at a lower sample rate. More specifi(cid:173)
`caUy, the oversampled signals are processed as follows:
`
`X
`smoorl~d(J) = (1 / X )• Lxl(i); X= number of poims
`j:l
`
`smoorlu:2(;) = (I f X ) • L x2(i); X = number of points
`j • ;
`
`X
`
`smoorltt3(;) = (1 / X )• LxJ(ll; X = number of points
`
`X
`
`j "<i
`
`[0038) The filtered sample signal (smoothxl G)) is used
`for the automatic optical emitter control at signal 8. 1l1e
`filtered first amplifier output signal (smoothx2(j)) and
`the
`filtered
`second
`amplifier
`output
`signal
`(smoothx3G)) are used for automatic direct current
`compensation at signal 6 and for pulse detection,
`respectively.
`
`[0039) 3) Automatic control of optical emitter 16 is
`based on the filtered second amplifier output signal at
`input 1, and is applied as foUows on a periodic basis.
`If smoothlG)>expected
`range.
`then
`[0040] a)
`decrease output at signal 8.
`
`010
`
`

`

`US 2006/0084879 A 1
`
`Apr. 20, 2006
`
`4
`
`If smooth I G)<expected
`[004 1) b)
`increase output at signal 8.
`
`range.
`
`then
`
`where a non-tero value indicates a peak in the
`[ 0055)
`filtered signal and a zero indicates no peak.
`
`[0042) 4) Direct current compensation is applied at
`output 6 as follows at the update rate of the smoothing
`fillers as follows.
`
`[0056) 4) ll1c instantaneous pulse rate is calculated in
`block 412 as the difference between peaks in the filtered
`signal.
`
`(0043) a) If smooth3U)>(max value of smooth3(j)(cid:173)
`threshold),
`then Direct current compensations)•
`smooth2(j)
`
`[0044) b) Else
`if smooth3G)<(min value of
`smooth3(j)+thresbold). then Direct current compen(cid:173)
`sations )•smoot h2(j)
`
`(0045] c) Else direct current compensationU)-direct
`current compcnsationU-1 ).
`
`[0046) During periods of motion, the signal applied for
`direct current compensation at output 6 by the microproces(cid:173)
`sor is corrclatc.'CI to the motion of the user. As as result, the
`direct current compensation can also be used as an indicator
`of motion as shown in FIG. 5. The direct current compen(cid:173)
`sation sigmtl is first analyzed in step 404. and this analysis
`is used to detect motion in step 406. If the direct current
`compensation is stable or lacks change this indicates a lack
`of motion and then the peak detection algoritJun 410
`described below is used to calculate the pulse rate 412. Tb.is
`allows for a fast recovery of the pulse rate after periods of
`motion. If the direct current compensation is correcting the
`signal. tllis indicates that motion is present and the frequency
`bas~:d algoritlun 408 dt.:scribcd below is ust:d to calculat~: th~:
`pulse rate 4 12.
`
`(0047) The direct current compensation(j) signal is used
`for motion discrimination in block 406 and determines
`whether peak detection algorithms can be used. for example
`during periods of no motion, or if frequency analysis is
`necessary for example during periods of motion. Stated
`alternatively, the direct current compensationU) signal is
`used to determine whether to apply peak detection algo(cid:173)
`rithms in block 408 or frequency analysis in block 410 to
`determine the pulse rate. More specifically, if direct c urrent
`compensationU) has not changed for the past 3x(llpulse
`rate) seconds during which pulse rate is being measured,
`then the peak detection algorithm described below is used.
`If direct current compensations) has changed during the past
`3x(l/ pu1se rate) seconds during which pulse rate is being
`measured the frequency analysis algorithm described below
`is used.
`
`Peak detection is calculated as follows:
`
`(0048)
`I) A first derivative calculated as dilfi (i)•
`smoothx2(i)-smoothx2(i-l ) is taken over the filtered
`signal.
`
`(0049) 2) A second derivative. difi2(i):diHl (i)-diiD (i-
`1 ). is calculated or computed from the first derivative.
`
`(0050) 3) Peak detection is analyzed using the first and
`second derivatives to find the peaks within the filtered
`signal.
`
`(005 1]
`
`If diO'I (i)•O and dilf2(i)<O then
`
`[0052) peak(i)•i
`
`(0053] Tf diO'I (i) docs uot•O and dift2(i)>0 then
`
`(0054) pcak(i)-0
`
`lnstn.ntruJcous pulse rote(i)-sample mre (in hz)/Period·
`(pcu(i)-prc,·ious non·7ero(peu(1)))060 sec/minute.
`
`(0057) Referring back to FlG. 3, the pulse detection
`system also includes an accelerometer 20 and piezo sensor
`22. Signals from accelerometer 20 and piezo sensor 22 are
`filtered th rough lowpass filters 24, 26 at analog to digi tal
`inputs 5 and 4, respectively before being sampled. The
`accelerometer 20 is used in the motion mitigation fast
`1buricr transform (PFT) a lgorithms and the piezo sensor is
`an indicl'nor o ferratic motion as shown in FIG. 4. Generally
`speaking, the accelerometer 20 and piezo sensor 22 are used
`to remove the mo tion artifacts from the optical sensor output
`present during motion of the user. When substantial erratic
`or momentary motion is detected us ing the piezo sensor 22,
`the information is used to filter the optical sensor output in
`the time domain so that the signal is not used for pulse rate
`calculations during the erratic motion 504. Additional fil(cid:173)
`tering may also be applied to the instantaneous pulse rate to
`provide a more stable pulse rate output. Periodic motion is
`detected by analyt"jng the accelerometer output signal in the
`frequency domain 505 and this information is used to
`generate a band reject filter which is applied to the optical
`sensor output in the frequency domain 506.
`[0058)
`If it is determined that motion is present. a fre(cid:173)
`quency algorithm as shown in FlG. 4 is used. ll1e signals
`that undergo frequency analysis are the smoothed first
`amplifier output signal (smoothx2) and the smoothed second
`amplifier output signal (smoothx3) in step 501. Signals from
`the accelerometer 20 and direct current compensation are
`also provided in step 503 so tbat funher frequency analysis
`can be done. Frequency analysis may include all or a subset
`or the loregoing signals. T he frequency bins will be ana(cid:173)
`lyzed to determine whether motion (r(:quencies a re present.
`Again, motion frequencies are determined by the acceler(cid:173)
`ometer output o r the direct current compensation signal. The
`motion frequencies arc then removed from the sensor sig(cid:173)
`nals. smoothx2 and smoothx3 to allow for discrimination of
`the pulse rate as lo llows:
`
`ten second window filter
`( 0059) a) Apply a
`to
`smoothx2. smoothx3, accelerometer. and direct current
`compensation
`
`[ 0060) b) Remove data as necessary if erratic motion is
`detected in the time domain at step 504
`
`[ 006 1) c) Apply frequency translation to all or a subset
`of windowed smoothx2, smoothx3, accelerometer. and
`direct current compensation in step 505;
`
`(0062) d) Band pass filter all signals in the range of 0.5
`liz to 4 117 at step 506:
`
`in smoothx2,
`frequency peaks
`(0063) e) Identify
`smoothx3, accelerometer. and DC compensation:
`
`f) Using the frequency peaks from the acceler(cid:173)
`(0064]
`ometer o f direct current compensation to determine the
`fn;:qucncics to rqject, using band reject filter. from
`smoothx2 ond smoothx3 at step 506;
`
`011
`
`

`

`US 2006/0084879 Al
`
`Apr. 20, 2006
`
`5
`
`[0065) g) Remove peaks from smoothx3 that are not
`common with those in smoothx2: and
`
`[0066) h) Pulse rate equals the lowest frequency peak in
`smoothx3 (block 507)
`If no peaks are remaining, the pulse rate is not updated.
`
`It is anticipated thai the present invention may also
`[0067]
`be used as a pedometer. To use the pulse rate monitor wrist
`watch as a pedometer, the data from the two-axis acceler(cid:173)
`ometer is filtered. Jfthe motion detected is a "step," i.e. foot
`motion, the filter applied to the Y-axis accelerometer data
`should be one-half that applied to the X-axis accelerometer
`data. Peak detection, i.e. detecting the intervals between the
`peaks of the signals from the X and Y accelerometers, is
`used to determine the 1imdamental frequencies of motion.
`Peaks are detected using the first and second derivative
`methods described above.
`
`[0068) Tile pulse rate is output using a digital s ignal which
`transitions at the rate of the pulse rate. The pedometer is
`output using a digital signal which transitions once for each
`step detected.
`
`[0069] A system and method for the efl'ective implemen(cid:173)
`tation of motion cancellation of optical input signals for
`physiological pulse measurement in accordance with the
`present invention has been disclosed herein. Whi.le various
`preferred embodiments have been shown and described, it
`will be understood that there is no intent to limit the
`invention by such disclosure. but rather, it is intended to
`cover all modifications and altemate constructions falling
`within the spirit :ll1d scope of the invention, as defined in the
`appended claims.
`
`We claim:
`1. A pulse rate sensor for measuring a physiological
`parameter of an individual comprising:
`
`an emitter for transmitting a light source into body tissue;
`
`a photo detector for receiving reflected light :fi·om said
`body tissue and producing a photo detector output
`signal indicative of reflected light;
`
`an accelerometer fo r measuring