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`
`US 2(}0600848?9A1
`
`(19; United States
`(12) Patent Application Publication (10) Pub. No.: US 2006/0084879 A1
`Nazarian et at.
`(43) Pub. Date:
`Apr. 20, 2006
`
`(54)
`
`U5}
`
`3/IOTION Cz\NCELL;\Tl()N OF OPTIC.-'\L
`INPUT SIGNALS FOR PI-IYSIOLOGICAL
`PULSE MEASUREMENT
`
`ll1\-’(.'l1IL)l'SZ Richard A. Nazarian. lixcclsior. MN
`(US); Lori E. l.ucke. F,:11_1__aI1. MN (US):
`Susan S. Alfini. Fliutiiplin. MN (US):
`Mark J. Bina. Slioreview. MN (US);
`Don W. E. Evans. St. Paul. MN (US):
`Paul Harris. |)c1ta((.‘A); Michael w.
`Geat-.r.. Maple (irnve, MN (us)
`
`Correspondence Address:
`OPPE.\'Ill<3IMER WOLFF 3.: DONNELLY L[.P
`45 SOUTH SEVEN-T11 STREET, SUITE 3300
`MINNEAPOLIS‘ MN 55402 (US)
`
`(73) Assigmt Pulse-1-racer Tlbchmlugies Inch V-am.m1_
`W31. (CA)
`
`(211 App1_ Nu;
`
`11125114111
`
`(22)
`
`Filed:
`
`(Jet. 13. 2005
`
`Related US, Application Data
`
`(60) Prtwisimial application No. 60!’619.253, [ilcd on Oct.
`15. 2004. Prtwisioiial application No. 6():’68l.397.
`filed on May 16. 2005. Pmvisiotizll applicaition No.
`(T0t696.858. filed on Jul. 6. 2005.
`
`Publication Classification
`
`(51)
`
`Int- Cl-
`(2006.01)
`A613 5/02
`(52) U.S. Cl.
`............................................................ .. 600l500
`
`(57)
`
`ABS-1«RA(_--1«
`.
`.
`includes an accelemineter tor
`A pulse rate ‘sensor tliat
`nteasurtng periodic moltun and a pawn sensor for detecting
`erratic motion is capable 0|" more accurately determining
`pulse rate by accounting tor these types 01 [110t10l1. "the pulse
`rate sensor in accordance with the present inveiiticm dimin-
`ishes pulse rate signal dC‘g,I‘él(_liiT.l0ll due to erratic l‘l1L)llt‘|l1
`thmugh a combination of algorithins that control signal
`boosting. wan.-'::li:nrt11 refinement and signal noise suppres-
`sinn.
`
`E
`
`
`
`
`
`
`
`ACCELEROMETER
`ANDIOR DC
`COMPENSWON
`
`
`E
`
`PIEZOELECTRIC
`SENSOR
`
`
`
`
`connmoneo OPTICAL
`PULSE SIGNALS
`(PHOTODETECTOR)
`E
`
`TIME DOMAIN FILTER
`
`_5fl
`
`.
`
`
`FREQUENCY DOMAEN -
`FOURIER TRANSFORM
`if-3.
`
`FREQUENCY DOMAIN -
`FOURIER TRANSFORM
`E2
`
`
`
`
`
`PULSE RATE 50?
`
`
`
`0°‘
`
`U.S. Patent No. 8,923,941
`
`Apple Inc.
`APLIO46
`
`Apple Inc.
`APL1046
`U.S. Patent No. 8,923,941
`
`001
`
`

`
`Patent Application Publication Apr. 20, 2006 Sheet 1 of 6
`
`US 2006/0034379 A1
`
`
`0
`50
`100
`150
`200
`250
`300
`
`SAMPLE '#
`
`FIG. 1A
`
`NOISE
`
`SAMPLE #
`
`FIG. 1B
`
`SIGNAL + NOISE
`
`
`
`SAMPLE #
`
`FIG. 1C
`
`002
`
`002
`
`

`
`Patent Application Publication Apr. 20, 2006 Sheet 2 of 6
`
`US 200610084879 A1
`
`003
`
`003
`
`

`
`Patent Application Publication Apr. 20, 2006 Sheet 3 of 6
`
`US 200610084879 A1
`
`101
`
`E3.
`
`FIG. 2B
`
`004
`
`004
`
`

`
`Patent Application Publication Apr. 20, 2006 Sheet 4 of 6
`
`US 2006/0084879 A1
`
`FIG. 3
`
`005
`
`005
`
`

`
`Patent Application Publication Apr. 20, 2006 Sheet 5 of 6
`
`Us 2006/0034379 A}
`
`
`
`ACCELEROMETER
`ANDIOR DC
`COMPENSATION
`
`.50_3
`
`
`FOURIER TRANSFORM
`
`§.0_5
`
`
`
`FREQUENCY DOMAIN -
`
`
`PIEZOELECTRIC
`SENSOR
`
`
`
`_50_2
`
`
`
`CONDITIONED OPTICAL
`PULSE SIGNALS
`(PHOTODETECTOR)
`5_01_
`
`
`
`
`
`TIME DOMAIN FILTER
`
`§0_4
`
`I
`
`FREQUENCY DOMAIN -
`
`FOU RIER TRANSFORM
`ii
`
`
`
`PULSE RATE 507
`
`FIG. 4
`
`006
`
`006
`
`

`
`Patent Application Publication Apr. 20, 2006 Sheet 6 of 6
`
`Us 2006/0034379 A1
`
`
`
`ANALYZE DC
`
`
`
`COMPENSATION
`
`su3NAL
`
`404
`
`
`
`
`
`.4_03
`
`USE FREQUENCY
`
`ANALYSIS
`
`ALGORITHMS
`
`
`
`IS
`
`MOTION
`
`DETECTED?
`
`
`‘L99
`
`
`
`USE PEAK DETECTION
`
`ALGORITHMS
`
`410
`
`
`
`CALCULATE
`
`PULSE
`
`
`
`RATE 412
`
`
`
`
`FIG. 5
`
`007
`
`007
`
`

`
`US 200670084879 A1
`
`Apr. 20, 2006
`
`MOTION CANCEILATION OF OPTICAL INPUT
`SIGNALS FOR PHYSIOLOGICAL PULSE
`MEASUREMENT
`
`I3A(.‘KGROIJNl) 01'-' ’I'l-lli INVI'.iN‘I‘I()N
`
`[0001]
`
`1. Field of the Invention
`
`Tl1e present invention relates generally to the field
`[0002]
`ofsignai processing. More specilically. the present invention
`is related to pulse rate monitors capable of providing aceti-
`rate measurement and display of a user’s pulse rate during
`times of physical exercise or other 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 artifacts
`produced by body motion such as when the person is
`running or otherwise engaging in physical activity or exer-
`cise. Therefore, pulse rate monitors presently in the market
`utilize chest bands that are worn close to the heart
`to
`
`minimize the etfect of motion produced by exercise. Arti-
`facts produced by body motion are detected by pulse rate
`sensors as “noise" that masks the heart 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
`light source in the near infrared region into the tissue and
`measuring the returned signal
`intensity. Typically two or
`four light emitting diodes (i_.El)s) are employed with vary-
`ing intensity to establish the optimum optical window. The
`return signal strength will be modulated by the capillary
`blood fiow in the tissue and will vary with the physiologic
`pulse of the subject. This is a well ttnderstood and estab-
`lished principal that has been applied to pulse monitoring
`equipment for years. Pulse rate sensing taken at locations
`other than close to the heart. has not been successful because
`of the relatively low signal strength and relatively high
`“noisc" content. The low signal strength can be attributed to
`a number of factors including variations in skin and hair
`density. variations in vascularization. and optical alignment.
`Further. the rmived signal
`includes several components
`which can be generally classified as “noise“ when attempt-
`ing to sense pulse rate. These high “noise” levels are in
`addition to classical noise sources present within almost all
`electrical systems and primarily include inherent optical
`noise sources. interfering light sources. and motion artifact.
`
`"o illustrate. FIG. 1A depicts a signal of interest.
`[0006]
`FIG. 1B depicts noise caused by motion artifact. interfering
`lights sources. random noise and the like. FIG. 1C illustrates
`how the signal of interest is masked by noise due to low
`signal strength. as an example.
`
`[0007] While conventional signal processing techniques
`may be able to reduce “out of band" 11oise: 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 w|:ticl1 is motion.
`
`[0008] Various pulse rate detection systems are known in
`the art. U.S. Pat. No. 4.338.950 to Barlow. Jr. et al. discloses
`an instrument comprised of wrist-mounted unit. which con-
`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 Mathews discloses a
`device which may be worn on the wrist or hand during
`physical activity. The device contains a light sensor to
`measure pulse and light sensor or accelerometer for mea-
`suring movement. Mathews discloses that a noise cancella-
`tion circuit takes the values from these sensors to give a true
`pulse signal that is free of pedornetry vihratiorl or noise.
`
`[0010] US. Pat. No. 5.807.267 to Bryars et al. discloses an
`apparatus which can be combined in a single 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
`Ll1e noise from local body motion. Signals fro111 this back-
`ground sensor are digitaliy subtracted from the primary
`pulse sensor thus allegedly reducing the effects of random
`body noise.
`
`[0011] U.S. Pat. No. 6.099.478 to Aoshima et al. disclosse
`a pulse wave detecting means comprising an I,I-El). photo
`transistor. or piezoelectric microphone. Body motion detect-
`ing means detect body motion using an acceleration sensor.
`Aoshima et al. disclose that 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-
`vides similar disclosures.
`
`[00l2] U.S. Pat. No. 6.129.676 to Odagiri et al. discloses
`a pulse rate monitor that can be assembled into a wrist
`watehband and used during activities. such as mnning. 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 spectrum is subtracted from the pulse wave
`spectrum. which 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 B1 to Amano et al. dis-
`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 motion data from corrected pulse
`wave data. Body motion waves are detected by an accel-
`eration sensor. This device may be incorporated into a
`pedometer.
`
`to
`[0014] U.S. Patent Appln. Publn. 200570116820 Al
`Gold:-eich discloses a wrist mounted device that detects
`
`pulse rates. The vibration sensor is a piemo ceramic sensor
`that measures movement of the wrist and may include an
`accelerometer. A physiologic sensor detects the blood pres-
`sure pulse rate. and may be fiber optic. Ambient sensors may
`also be present.
`
`[0015] Whatever the precise merits. features. and advan-
`tages of the above cited references. none of them achieves
`or fuifills the purposes of the present invention. For these
`reasons it would be desirable to provide an improved device
`and method for accurately measuring pulse rate during
`physical exercise and other activities.
`
`008
`
`008
`
`

`
`US 2006:’0084879 A1
`
`Apr. 20, 2006
`
`SUMMARY OF THE INVENTION
`
`it is therefore an object of the present invention to
`[0016]
`provide a device and method for accurately monitoring and
`detecting pulse rate.
`
`is an object of the present
`it
`[0017] More particularly.
`invention to provide a solution to that allows for adequate
`removal of inherent optical noise sources. interfering ambi-
`ent
`light sources and motion artifact
`in optical signals
`especially under intense physical activity.
`
`It is yet another object of the present invention to
`[0018]
`provide a pulse rate monitor that 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. IC.
`
`[0019] These and other objects are accomplished in accor-
`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
`tisstte, a photo detector for receiving reflected light from the
`body tissue and producing a photo detector output signal
`indicative of the reflected light; an accelerometer for mea-
`suring regular motion of the individual and producing an
`accelerometer output signal indicative ofthe regttlar 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 the photo detector output signal, the accelerometer
`output signal, and the Contact
`type motion sensor output
`signal. and determining the pulse rate of the individual.
`where t.l1e pulse rate is determined by conditioning the photo
`detector output signal and removing portions of the condi-
`tioned photo detector output caused by regular motion and
`erratic motion of the individual.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0020] FIG. IA illustrates a desired optical signal to be
`measured.
`
`[0021] FIG. 1B illustrate noise typically caused by
`motion.
`
`[0022] FIG. 1C illustrates the combined optical signal and
`noise.
`
`[0023] FIG. 2A diagramtuatically illustrates a pulse rate
`sensor in accordance with the present invention.
`
`[0024] FIG. 2]} 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-
`lion.
`
`[0026] FIG. 4 illustrates a flowchart depicting the motion
`discrimination process i11 accordance with the present inven-
`tion.
`
`[0027] FIG. 5 illustrates a flowchart depicting steps fol-
`lowed to calculate pulse rate in accordance with the present
`invention.
`
`DESCRIPTION OF THE PREFERRED
`liMI30l)IMliN'I‘S
`
`[0028] While this invention is illustrated and described in
`a preferred embodiment. the device may be produced in
`
`many different 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 the present disclosure is to be considered
`as an exemplification of the principles ofthe 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 an 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 (eg.
`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 the reflected light from the tissue. Pulse rate sensor
`.10] uses the inli'ared optical 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 tl1ree-di-
`mensional accelerometer. that detects periodic or constant
`motion ofthe user. and a contact type motion sensor 106 that
`measures inconsistent or erratic motion ofthe user. and other
`
`movement related sources that effect 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 output may
`also be used as input for step counter or pedometer 114.
`Microprocessor ll0 performs signal conditioning functions
`on the pulse signals received from the photo detector 104.
`and also samples and filters signals from accelerometer 108
`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 picao 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-
`nents.
`
`[0030] Pulse rate sensor 101 may be encapsulated in a
`watch module 120 as slrovvn in FIG. 2B with an optional
`rechargeable battery in one embodiment of the present
`invention. However. other caniersfmodules are envisioned
`as usable with the present
`invention such as pendants.
`jewelry. bracelets. patches, music players, etc. which may
`also contain standard watch ftmctions to include timefdate
`
`and a stopwatchftimer. These other carriers may be posi-
`tioned anywhere on the am’: of an individual or in the case
`of a pendants around the neck of an individual. The pulse
`rate sensor in accordance with the present invention may
`also include capabilities for firmware updates through the
`impleinentation of a software boot loader. Other additions
`may include a communication module such as universal
`serial bus (USE) port or an RI-‘
`t'E!(:Cl\tt2l'll1t’Ell't5t'l1lllCf
`to
`autolnatically upload data to a web pI.‘lt‘tal. Additionally, the
`pulse rate sensor may include radio frequency identification
`(RFID} to uniquely identify each watch sold to the web
`portal.
`
`[003]] The pulse rate sensor in accordance with the pre-
`ferred 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
`
`O09
`
`009
`
`

`
`US 2006:’0084879 A1
`
`Apr. 20, 2006
`
`applied to the optical sensor by automatically adjusting the
`ligltt entitting diode otttpttt to maintain the optimal signal
`strength. controlling the amplification of tlte received signal.
`and atttontalically removing the direct cttrrent bias of the
`received signal. The conditioned optical sensor otttpttt and
`the accelerometer and piezo sensor outputs are sampled as
`ittput to two different pulse rate calculators. one used when
`there is no tttotiott present and the other used whett tltere 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-
`radation due to amt motion and skin vibrations is diminislted
`
`througlt a combination of algoritlutts that control signal
`boosting. waveiiarm refinement and signal noise suppres-
`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 pltotodetector 10. which may be a
`reflective infra-red sensor. is filtered tltrouglt low pass filter
`12 and is provided to input 1 of the microprocessor 110.
`which includes an intental analog to digital converter 14.
`Naturally. analog to digital converter [4 could also be a
`component separate fl't.‘Jl11 microprocessor 110. Tltrottgh this
`connection microprocessor 110 is able to monitor the output
`from photo detector 10 and to determine the appropriate
`intensity for an infra-red ligltt etttitting diode 16. which
`transmits optical signals into body tissue. The intensity of
`infra-red light emitting diode I6 is programmable using an
`output 8 front a digital
`to analog converter
`I8 within
`microprocessor 110 (again, digital to analog convcner 18
`could also be a component separate litont ttticroprocessor
`110). As further discussed below. an internal closed loop
`control function within the microprocessor 110 maintains
`the proper intensity of the infra-red light emitting diode 16
`using the feedback from the photodeetor 10 at input 1 to
`control output 8. Using this control fiinction, the output
`signal from photodetoctor 10 is in an appropriate range for
`direct cttrrent compensation and other related functions.
`Further. this intensity control allows the microprocessor 110
`to periodically adjust the system to account for dillerent
`environmental and pltysiologcal conditions. including vary-
`ing ambient light levels. long term blood flow changes and
`varying responses front user to user. The pulse signal
`transmitted from photodettctor 10 is liltered through a
`lowpass filter 12 of approximately 10 [In to redttce inherent
`noise.
`
`[0034] The pulse signal front photodetector 10 generally
`includes a large direct current component that represents
`gross blood flow. and a small alternating current component
`that represents true pulse. Because it is desirable to aceti-
`rately measure true pulse, active signal conditioning inclttd—
`ing additional amplification of the alternating current com-
`ponent and compensation of the direct current component is
`necessary. (Toittpcitsation of the direct current component
`occurs in two stages. The first stage is accomplished using
`an amplifier 28 to achieve a fixed signal gain. The output
`from this first stage is provided to microprocessor 110 at
`input 2. The second stage is the programmable gain stage
`utilziug a second amplifier 30 with output to microprocessor
`110 shown at 3. A fixed direct current compensation voltage.
`shown at output 7. is subtracted from the filtered pulse signal
`
`provded from filter 12. Atttplifier 28 has a fixed gain and is
`output to the tnicroprocesser 110 at 2. The amplification and
`DC‘ adjustment provided by amplifier 28 moves the signal
`level of its output to the tuidrange of second operational
`amplifier 30 attd allows 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-
`nal frorn output 6 is also applied to second anlplilier 30 by
`ntiroprocessor 110.
`It is during this second stage that the
`sensor signal is significantly amplified. The programmable
`direct current compettsation at output 6 is adjusted with
`every sample of the first stage gain signal or input 2 ofthe
`analog to digital converter. 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
`olthe amplifier stage 30. This is a line adjustment and allows
`for the quick recovery ofthe pulse signal during and after
`motion. As significant amplification is applied to the input
`singal at second amplifier 32.
`the programmable direct
`current cotttpensation further helps to center the signal at the
`amplifier input, and prevents second amplifier 32 front
`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)'Ihe optical sensor output signal. first ainplifer
`[0036]
`output signal, and second arnplifer otttpttt signal are all
`oversampled at inputs 1. 2. and 3 as shown in FIG. 2
`to generate samples xI(i). x2(f). x3(i') where i repre-
`sents the i”‘ sample.
`
`filtered to produce a
`2) The signals are all
`[0037]
`smoother signal at a lower sample rate. More specifi-
`cally. tbe oversampled signals are processed as follows:
`
`I
`
`.sritoot.lt.rlt;'J = t1,tXt: Z.tiiti_l‘. X = number of points
`F.
`.\'
`
`.srnoor.tu:2t_.il = 11 IX): 2:.r2tr'l'. X = number of points
`j .'
`.\'
`
`.r:.Itoorilr_t'.3[j] = [1 ,lXltZ.t.'.'l'{fl'. X : rtumher of points
`ft
`
`[0038] The filtered sample signal (sntootltxl|’_i)) is used
`for the automatic optical emitter control at signal 8. The
`filtered first amplifier otttpttt signal {sntoothx2{i)) and
`the
`filtered
`second
`amplifier
`output
`signal
`(smoothx3(i)) are used for automatic direct current
`contpensation at signal 6 and for pulse detection.
`respectively.
`
`3) Automatic control of optical emitter 16 is
`[0039]
`based on the filtered second amplifier output signal at
`input 1, and is applied as follows on a periodic basis.
`
`smootl1l(i)>expected
`If
`a)
`[0040]
`decrease output at signal 8.
`
`range.
`
`then
`
`010
`
`010
`
`

`
`US 2006:’0084879 A1
`
`Apr. 20, 2006
`
`sniootltltj)-cexpected
`If
`b)
`[0041]
`increase output at signal 8.
`
`ra1tge.
`
`then
`
`where a non-zero value indicates a peak in the
`[0055]
`filtered signal and a zero indicates no peak.
`
`4) [)irect current compensation is applied at
`[0042]
`output 6 as follows at the update rate of the smoothing
`filters as follows.
`
`a) If sn1ooth3(}}:-(max value of sn1ooth3{i)-
`[0043]
`threshold).
`then Direct current cotnpensations)-
`s:nooth2(i]
`
`value of
`smooth3(j)<(tnin
`if
`lilsc
`b)
`[0044]
`sn1ootl13(i)+tl1reshold). then Direct current compen-
`sations}=smooth2(i)
`
`c) Else direct current compensation(j}-direct
`[0045]
`current coinpensation{}-1).
`
`[0046] During periods of tnotion. the signal applied for
`direct current compensation at output 6 by the microproces-
`sor is correlated 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-
`sation signai 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 algurithnt 410
`described below is used to calculate the pulse rate 412. This
`allows for a first recovery of the pulse rate after periods of
`motion. If the direct current compensation is correcting the
`signal. this indicates that motion is present and the frequency
`based algorithm 408 described below is used to calculate the
`pulse rate 412.
`
`[0047] The direct current compensation(i) signal is used
`for motio11 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 compensation[j) signal
`is
`used to determine whether to apply peak detection algo-
`rithms in block 408 or frequency analysis in block 410 to
`determine the pulse rate. More specifically. if direct current
`compensatiort(j) has not changed for the past 3x[ll'pulse
`rate) seconds during which pulse rate is being measured.
`then the peak detection algorithm described below is used.
`Ifdirect current compensations) has changed during the past
`3x(lr’pulse rate) seconds during which pulse rate is being
`measured the frequency analysis algorithm described below
`is used.
`
`Peak detection is calculated as follows:
`
`1) A first derivative calculated as difi‘l(i)-
`[0048]
`smoothx2[i)—smoothx2(i—1) is taken over the filtered
`signal.
`
`2) A second derivative. dill2(i)=diI'fl (i}—di[f1 (i-
`[0049]
`1), is calculated or computed from the first derivative.
`
`3) Peak detection is analyred using the first and
`[0050]
`second derivatives to find the peaks within the filtered
`signal.
`
`[0051]
`
`If ditfl (i)-0 and dili‘2{i)<0 then
`
`[0052]
`
`peak(i)=i
`
`[0053]
`
`If diff1 (i) does not=0 and difl2(i)>0 then
`
`[0054]
`
`peak(i)=0
`
`4) The instantaneous pulse rate is calculated in
`[0056]
`block 412 as the diflerence between peaks in the filtered
`signal.
`lrtstantsneous pulse r:1tetiI=ssrnple rate tilt |1;cJ.rl’eried—
`{peskt t I- previous non-zcrotpcrtlzt t l l1"Gl1 secfiminnle.
`
`the pulse detection
`[0057] Referring back to FIG. 3.
`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 digital
`inputs 5 and 4. respectively before being sampled. The
`accelerometer 20 is used in the motion mitigation last
`fourier transform (FFT) algoritluns and the piezo sensor is
`an indicator nferratic motion as shown in FIG. 4. Generally
`speaking. the accelerometer 20 and piezo sensor 22 are used
`to remove the motion artifacts from the optical sensor output
`present during motion of t.l1e user. When substantial erratic
`or momentary motion is detected using 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 Inotion 504. Additional lil-
`tering may also be applied to the instantaneous pulse rate to
`provide a more stable pulse rate output. Periodic motion is
`detected by analyzing t.he 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 li'equency domain 506.
`
`if it is determined that motion is present. a fre-
`[0058]
`quency algorithm as shown in FIG. 4 is used. The signals
`that undergo frequency analysis are the smoothed first
`amplifier output signal (smootlix2) and the smoothed second
`amplifier output signal (smootl1x3) i11 step 501. Signals from
`the accelerometer 20 and direct current compensation are
`also provided in step 503 so that further frequency analysis
`can be done. Frequency analysis may include all or a subset
`of the foregoing signals. The frequency bins will be ana-
`lyzed to determine whether motion frequencies are present.
`Again. motion frequencies are determined by the acceler-
`ometer output or the direct current compensation signal. The
`motion frequencies are then removed from the sensor sig-
`nals, smoothx2 and srnoothx3 to allow for discrimination of
`the pulse rate as follows:
`
`to
`ten second window filter
`:1) Apply a
`[0059]
`smootlu-:2. smoothx3. accelerometer. and direct current
`contpertsation
`
`1)) Remove data as necessary if erratic motion is
`[0060]
`detected in the time domain at step 504
`
`c) Apply frequency translation to all or a subset
`[0061]
`of windowed stnoothx2. srnootl1x3. accelerorneter. and
`direct current compensation in step 505;
`
`G1) Band pass filter all signals itt the range of0.5
`[0062]
`Hz to 4 Hz at step 506;
`
`smoothxll.
`in
`Identify frequency peaks
`e)
`[0063]
`smoothx3. accelerottteter, and DC compensation:
`
`i) Using the frequency peaks from the acceler-
`[0064]
`ometer of direct current compensation to determine the
`frequencies to reject. using hand reject" lilter.
`front
`smoothx2 and srnoothx3 at step 506;
`
`011
`
`011
`
`

`
`US 2006:’0084879 A1
`
`Apr. 20, 2006
`
`g) Remove peaks from smoothx3 that are not
`[0065]
`common with those in smoothx2: and
`
`ll) Pulse rite equals the lowest frequency peak in
`[0066]
`smooth)-:3 (block 507)
`
`If no peaks are remaining the pulse rate is not updated.
`
`it is anticipated that 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-
`ometer is filtered. It‘ the motion detected is a “step.“ i.e. loot
`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 liindaniental lrequeiicies of motion.
`Peaks are detected using the first and second derivative
`methods described above.
`
`[0068] The pulse rate is otttput using a digital signal which
`transitions at tl1e rate of the pulse rate. The pedometer is
`output using a digital signal wl1icl1 transitions once for each
`step detected.
`
`[0069] A system and method for the effective implemen-
`tation of motion cancellation of optical input signals for
`physiological pulse measurement
`in accordance with the
`present invention has been disclosed herein. While various
`preferred embodiments have been shown and described, it
`will be understood that
`there is no intent
`to limit
`the
`
`is intended to
`it
`invention by such disclosure. but rather.
`cover all modifications and alternate constructions falling
`within the spirit and 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 from said
`body tissue and producing :1 photo detector output
`signal indicative of reflected light;
`
`an accelerometer for measuring regular motion of the
`individual and producing an accelerometer output sig-
`nal indicative of the regular Iuotion:
`
`a contact type motion sensor for measuring erratic motion
`of the user and producing a contact type motion sensor
`output signal indicative of the erratic motion: and
`
`a microprocessor for receiving the photo detector output
`signal. the accelerometer output signal. and the contact
`type motion sensor output signal. and detemiining the
`pulse rate of the individual. wherein the pulse rate is
`determined by conditioning the photo detector output
`signal and removing portions of the conditioned photo
`detector output caused by regular motion and erratic
`motion of the individual.
`
`2. Tlie pulse rate sensor of claim 1 wherein said trans-
`mitted light source lies in the near infrared region.
`3. The pulse rate sensor of claim 1 wherein said emitter
`comprises a plurality of light emitting diodes.
`4. The pulse rate sensor of claim 1 wherein said photo
`detector is a reflective infra—red sensor.
`
`5. The pulse rate sensor of claim l wherein said acceler-
`ometer is a two-dimensional accelerometer.
`
`6. The pulse rate sensor of claim 1 wherein said sensor is
`encapsulated in a watch module for wrist-based sensing.
`7. The pulse rate sensor of claim 6 wherein said watch
`module includes a universal serial bus port to automatically
`upload data, a radio lrequeiicy identification tag to uniquely
`identify said watch module. wherein said watch module is
`further capable of receiving firmware updates.
`8. The pulse rate sensor of claim 1 wherein said contact
`type motion sensor comprises a p