(12) United States Patent
`Ali et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,996,427 B2
`*Feb. 7, 2006
`
`US006996427B2
`
`(75)
`
`(54) PULSE OXIMETRY DATA CONFIDENCE
`INDICATOR
`
`.
`.
`.
`Inventors: Ammar A1 A11, Tustin, CA (US); Divya
`S. Breed, Laguna Niguel, CA (US);
`JEFOIHB J. Novak, A1150 VI€jO,
`(US); Massi E. Kiani, Laguna Niguel,
`CA (US)
`
`(73) Assignee: Masimo Corporation, Irvine, CA (US)
`( * ) Notice:
`Subject. to any disclaimer, the term of this
`patent 15 extended or adlusted under 35
`U‘S'C' 154(b) by 0 days‘
`.
`.
`.
`.
`.
`Thls patent IS Subject to a termmal d1S'
`Claim“
`(21) Appl. No.: 10/739,794
`(22)
`Filed:
`Dec. 18, 2003
`
`(65)
`
`Prior Publication Data
`
`Us 2004/0133087 A1 Jul’ 8’ 2004
`Related U.S. Application Data
`
`(63) Continuation of application No. 09/858,114, filed on May
`15, 2001, now Pat. No. 6,684,090, which is a continuation—
`in—part of application No. 09/478,230, filed on Jan. 6, 2000,
`now pat. No. 6,606,511.
`Provisional application No. 60/115,289, filed on Jan. 7,
`1999
`Int CL
`A61B 5/00
`
`(60)
`
`(51)
`
`(2006.01)
`
`...................................... .. 600/310; 600/324
`(52) U.s. Cl.
`(58) Field of Classification Search ......... 600/309-310,
`600/322-324, 330, 331, 336
`See application file for complete search history
`'
`
`(56)
`
`References Cited
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`OTHER PUBLICATIONS
`Webster’s New World Dictionary of AMerican English,
`Webster’s New World , Third College Edition, p. 30.*
`Michael W. Wukitsch et al., “Pulse Oximetryz Analysis of
`Theor
`Technolo
`and Practice ” Journal of Clinical
`Monit}o’ring, vol. 401110. 4, pp. 290-301 (Oct. 1998).
`* Cited by examiner
`
`Primary Examiner—Eric F. Winakur
`Assistant Examiner—Matthew Kremer
`(74) Attorney Agent or Firm—Knobbe Martens Olson &
`Bear LLP
`
`ABSTRACT
`(57)
`-
`1 M f h
`- d t
`-
`1 d
`fid
`A d t
`ence 1n ma Or, mc 11 ES a p ura y 0 p yS1'
`21 a Con
`ological data and a plurality of signal quality measures
`derived from a physiological sensor output, and a plurality
`of comparator outputs each responsive to one of the mea-
`sures and a corresponding one of a plurality of thresholds.
`An alert triggeroutput combines the comparator outputs. A
`low signal quality warning is generated in response to the
`jjjigfiggggzffigpfifigfieIZIILEZthgijgglfslfgfi Sfhtejg ‘gag:
`Confideice in the datag. The alerg may be in the form of a
`t d
`th
`1
`.
`t
`d.
`1
`t
`message genera e on
`e .pu Se Oxlme er
`lsp ay 0 Warn
`that the accuracy of saturation and pulse rate measurements
`may be compromised. A confidence-based alarm utilizes
`signal quality measures to reduce the probability of false
`alarms when data confidence is low and to reduce the
`
`probability of missed events when data confidence is high.
`
`24 Claims, 24 Drawing Sheets
`
`A
`
`INTEG
`COMPARATOR A<B
`B
`
`LOW INTEG
`
`401
`
`INTEG THRESHOLD
`15/2
`
`/610
`
`A
`
`FRD
`COMPARATOR A<B
`B
`
`
`
`LDW PRD
`
`ALERT TRIGGER
`
`
`
`
`PR DENSITY
`
`405
`
`PRD THRESHOLD
`/63?
`
`I550
`HR
`COMPARATOR A<B
`5
`
`/550
`
`A
`
` HARMONIC RATIO
`
`
`HR THRESHOLD
`/552
`
`0001
`
`Apple Inc.
`APLIO64
`
`U.S. Patent No.
`
`8,923,941
`
`Apple Inc.
`APL1064
`U.S. Patent No. 8,923,941
`
`0001
`
`

`
`US 6,996,427 B2
`Page 2
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`$331 $343“? 1‘; e‘ ‘*1’
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`°“‘~
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`
`g’$‘6"§§(1) :1
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`6,830,711 B2
`6,850,787 B2
`6,850,788 B2
`6,852,083 B2
`6,861,639 B2
`6,898,452 B2
`
`0002
`
`0002
`
`

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`U.S. Patent
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`Feb. 7, 2006
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`Sheet 1 of 24
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`US 6,996,427 B2
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`US 6,996,427 B2
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`1
`PULSE OXIMETRY DATA CONFIDENCE
`INDICATOR
`
`This application is a continuation of application Ser. No.
`09/858,114, filed May 15, 2001, now U.S. Pat. No. 6,684,
`090, which is a continuation-in-part of application Ser. No.
`09/478,230, filed Jan. 6, 2000, now U.S. Pat. No. 6,606,511,
`which claims the benefit of U.S. Provisional Application No.
`60/115,289, filed Jan. 7, 1999.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`This application generally relates to devices and methods
`for measuring physiological data, and more particularly to
`devices and methods of presenting this data.
`2. Description of the Related Art
`Oximetry is the measurement of the oxygen status of
`blood. Early detection of low blood oxygen is critical in the
`medical field, for example in critical care and surgical
`applications, because an insufficient supply of oxygen can
`result in brain damage and death in a matter of minutes.
`Pulse oximetry is a widely accepted noninvasive procedure
`for measuring the oxygen saturation level of arterial blood,
`an indicator of oxygen supply. A pulse oximeter typically
`provides a numerical readout of the patient’s oxygen
`saturation, a numerical readout of pulse rate, and an audible
`indicator or “beep” that occurs in response to each pulse. In
`addition, a pulse oximeter may display the patient’s plethys-
`mograph waveform, which is a visualization of blood vol-
`ume change in the illuminated tissue caused by pulsatile
`arterial blood flow over time. The plethysmograph provides
`a visual display that is also indicative of the patient’s pulse
`and pulse rate.
`Apulse oximetry system consists of a sensor attached to
`a patient, a monitor, and a cable connecting the sensor and
`monitor. Conventionally, a pulse oximetry sensor has both
`red and infrared (IR) light-emitting diode (LED) emitters
`and a photodiode detector. The sensor is typically attached
`to a patient’s finger or toe, or a very young patient’s patient’s
`foot. For a finger, the sensor is configured so that the emitters
`project light through the fingernail and into the blood vessels
`and capillaries underneath. The photodiode is positioned at
`the fingertip opposite the fingernail so as to detect the LED
`transmitted light as it emerges from the finger tissues.
`The pulse oximetry monitor (pulse oximeter) determines
`oxygen saturation by computing the differential absorption
`by arterial blood of the two wavelengths emitted by the
`sensor. The pulse oximeter alternately activates the sensor
`LED emitters and reads the resulting current generated by
`the photodiode detector. This current is proportional to the
`intensity of the detected light. The pulse oximeter calculates
`a ratio of detected red and infrared intensities, and an arterial
`oxygen saturation value is empirically determined based on
`the ratio obtained. The pulse oximeter contains circuitry for
`controlling the sensor, processing the sensor signals and
`displaying the patient’s oxygen saturation and pulse rate. A
`pulse oximeter is described in U.S. Pat. No. 5,632,272
`assigned to the assignee of the present invention.
`
`SUMMARY OF THE INVENTION
`
`2
`physiological conditions including heart stroke volume,
`pressure gradient, arterial elasticity and peripheral resis-
`tance. The ideal waveform 100 displays a broad peripheral
`flow curve, with a short, steep inflow phase 130 followed by
`a 3 to 4 times longer outflow phase 140. The inflow phase
`130 is the result of tissue distention by the rapid blood
`volume inflow during ventricular systole. During the out-
`flow phase 140, blood flow continues into the vascular bed
`during diastole. The end diastolic baseline 150 indicates the
`minimum basal tissue perfusion. During the outflow phase
`140 is a dicrotic notch 160, the nature of which is disputed.
`Classically, the dicrotic notch 160 is attributed to closure of
`the aortic valve at the end of ventricular systole. However,
`it may also be the result of reflection from the periphery of
`an initial, fast propagating, pressure pulse that occurs upon
`the opening of the aortic valve and that precedes the arterial
`flow wave. A double dicrotic notch can sometimes be
`
`observed, although its explanation is obscure, possibly the
`result of reflections reaching the sensor at different times.
`FIGS. 2-4 illustrate plethysmograph waveforms 200, 310,
`360 that display various anomalies. In FIG. 2, the waveform
`200 displays two arrhythmias 210, 220. In FIG. 3,
`the
`waveform 310 illustrates distortion corrupting a conven-
`tional plethysmograph 100 (FIG. 1). FIG. 4 shows a filtered
`waveform 360 after distortion has been removed through
`adaptive filtering, such as described in U.S. Pat. No. 5,632,
`272 cited above. FIG. 4 illustrates that, although the wave-
`form 360 is filtered, the resulting pulses 362 have shapes that
`are distorted in comparison to the pulses illustrated in FIG.
`1.
`
`A desirable feature of pulse oximeters is an audible
`“beep” tone produced to correspond to the patient’s pulse.
`Conventionally, the beep is triggered from recognition of
`some aspect of the plethysmograph waveform shape. Such
`a waveform-triggered beep may indicate an arrhythmia, like
`those displayed in FIG. 2, but may also generate false pulse
`indications as the result of motion-artifact or noise induced
`waveform distortion, as illustrated in FIGS. 3 and 4. This
`characteristic results because both distortion and arrhyth-
`mias result in anomalies in the plethysmograph waveform
`shape on which this beep mechanism is dependent.
`Alternatively, the beep can be triggered from a time base set
`to the average pulse rate. Signal processing can generate an
`average pulse rate that is resistant to distortion induced error.
`A pulse beep based on average pulse rate is relatively
`insensitive to episodes of distortion, but is likewise insen-
`sitive to arrhythmias.
`An example of the determination of pulse rate in the
`presence of distortion is described in U.S. Pat. No. 6,002,
`952, filed Apr. 14, 1997, entitled “Signal Processing Appa-
`ratus and Method,” which is assigned to the assignee of the
`current application and incorporated by reference herein.
`Another example of pulse rate determination in the presence
`of distortion is described in U.S. patent application Ser. No.
`09/471,510, filed Dec. 23, 1999, entitled “Plethysmograph
`Pulse Recognition Processor,” which is assigned to the
`assignee of the current application and incorporated by
`reference herein.
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`One aspect of the present invention is a processor having
`a decision element that determines if the waveform has little
`
`or no distortion or significant distortion. If there is little
`distortion, the decision element provides a trigger in real-
`time with physiologically acceptable pulses recognized by a
`waveform analyzer. If there is significant distortion, then the
`decision element provides the trigger based synchronized to
`an averaged pulse rate, provided waveform pulses are
`detected. The trigger can be used to generate an audible
`
`FIG. 1 illustrates the standard plethysmograph waveform
`100, which can be derived from a pulse oximeter. The
`waveform 100 is a display of blood volume, shown along the
`y-axis 110, over time, shown along the x-axis 120. The shape
`of the plethysmograph waveform 100 is a function of
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`is insensitive to episodes of significant
`pulse beep that
`distortion, but is capable of responding to arrhythmia events.
`Another desirable feature for pulse oximeters is a visual
`indication of the patient’s pulse. Conventionally,
`this is
`provided by an amplitude-versus-time display of the
`plethysmograph Waveform, such as illustrated in FIG. 1.
`Some monitors are only capable of a light-bar display of the
`plethysmograph amplitude. Regardless, both types of dis-
`plays provide a sufficient indication of the patient’s pulse
`only when there is relatively small distortion of the plethys-
`mograph Waveform. When there is significant distortion,
`such as illustrated in FIG. 3A, the display provides practi-
`cally no information regarding the patient’s pulse.
`Yet another desirable feature for pulse oximeters is an
`indication of confidence in the input data. Conventionally, a
`visual display of a plethysmograph Waveform that shows
`relatively small distortion would convey a high confidence
`level in the input data and a corresponding high confidence
`in the saturation and pulse rate outputs of the pulse oximeter.
`However, a distorted Waveform does not necessarily indicate
`low confidence in the input data and resulting saturation and
`pulse rate outputs, especially if the pulse oximeter is
`designed to function in the presence of motion-artifact.
`Another aspect of the current invention is the generation
`of a data integrity indicator that is used in conjunction with
`the decision element trigger referenced above to create a
`visual pulse indicator. The visual pulse indicator is an
`amplitude-versus-time display that can be provided in con-
`junction with the plethysmograph Waveform display. The
`trigger is used to generate a amplitude spike synchronous to
`a plethysmograph pulse. The data integrity indicator varies
`the amplitude of the spike in proportion to confidence in the
`measured values.
`
`Yet another aspect of the present invention is a processing
`apparatus that has as an input a plethysmograph Waveform
`containing a plurality of pulses. The processor generates a
`trigger synchronous with the occurrence of the pulses. The
`processor includes a Waveform analyzer having the Wave-
`form as an input and responsive to the shape of the pulses.
`The processor also includes a decision element responsive to
`the Waveform analyzer output when the Waveform is sub-
`stantially undistorted and responsive to pulse rate when the
`Waveform is substantially distorted. The trigger can be used
`to generate an audible or visual indicator of pulse occur-
`rence. A measure of data integrity can also be used to vary
`the audible or visual indicators to provide a simultaneous
`indication of confidence in measured values, such as oxygen
`saturation and pulse rate.
`A further aspect of the current invention is a method of
`indicating a pulse in a plethysmograph Waveform. The
`method includes the steps of deriving a measure of distortion
`in the Waveform, establishing a trigger criterion dependent
`on that measure, determining Whether the trigger criterion is
`satisfied to provide a trigger, and generating a pulse indica-
`tion upon occurrence of the trigger. The deriving step
`includes the sub-steps of computing a first value related to
`the Waveform integrity, computing a second value related to
`the recognizable pulses in the Waveform, and combining the
`first and second values to derive the distortion measure. The
`
`trigger criterion is based on Waveform shape and possibly on
`an averaged pulse rate.
`One more aspect of the current invention is an apparatus
`for indicating the occurrence of pulses in a plethysmograph
`Waveform. This apparatus includes a Waveform analyzer
`means for recognizing a physiological pulse in the Wave-
`form. Also included is a detector means for determining a
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`measure of distortion in the Waveform and a decision means
`for triggering an audible or visual pulse indicator. The
`decision means is based the physiological pulse and possibly
`the pulse rate, depending on the distortion measure.
`Another aspect of the present invention is a data confi-
`dence indicator comprising a plurality of physiological data
`and a plurality of signal quality measures derived from a
`physiological sensor output. A plurality of comparator out-
`puts are each responsive to one of the measures and a
`corresponding one of a plurality of thresholds. An alert
`trigger output combines said comparator outputs, and a low
`signal quality Warning is generated in response to said alert
`trigger output. The thresholds are set so that the Warning
`occurs during a time period when there is low confidence in
`the data.
`In one embodiment,
`the Warning is a display
`message that supplements a visual pulse indicator,
`the
`display message specifies a low signal quality when the
`visual pulse indicator has an amplitude that is less than
`one-third full-scale. In another embodiment, the signal qual-
`ity measures are an integrity measure, a pulse rate density
`measure and a harmonic ratio measure.
`In a particular
`embodiment, the thresholds may have an integrity value of
`less than 0.3, a pulse rate density value of less than 0.7 and
`a harmonic ratio value of less than 0.8.
`
`In yet another embodiment a filter for the data generates
`a smoothed data output. An adjustment for the smoothed
`data output is a function of at least one of the signal quality
`measures so that smoothing at the smoothed data output
`increases when at least one of the signal quality measures
`decreases. An alarm trigger is responsive to the smoothed
`data output so as to generate an alarm when the smoothed
`data output is outside of a predetermined limit. In a particu-
`lar embodiment the filter comprises a buffer having a buffer
`input and a delay output. The buffer input corresponds to the
`data and the delay output is time-shifted according to the
`adjustment. A first filter comparator output is responsive to
`the data and a data threshold, and a second filter comparator
`output is responsive to the delay output and a delay output
`threshold. The comparator outputs are combined so as to
`provide the alarm trigger.
`A further aspect of the present invention is a data confi-
`dence indicator comprising a processor configured to derive
`a time-dependent physiological data set and a plurality of
`time-dependent signal quality measures from a physiologi-
`cal signal. Abuffer is configured to time-shift the data set by
`a delay to generate a delayed data set, Where the delay is a
`function of at least one of the signal quality measures. The
`indicator has a threshold setting a limit for the delayed data
`set. A Warning is generated when the levels of the data set
`and the delayed data set are beyond that threshold. In one
`embodiment, a first comparator output is responsive to the
`data and the threshold, and a second comparator output is
`responsive to the delayed data set and the threshold. A
`combination of the first and second comparator outputs
`provides an alarm trigger for the Warning. The data confi-
`dence indicator may also comprise a combination of the
`signal quality measures providing an alert trigger to generate
`Warning when confidence in the data set is low.
`An additional aspect of the present invention is a data
`confidence indication method comprising the steps of
`acquiring a signal from a physiological sensor, calculating a
`physiological data set from the signal, calculating signal
`quality measures from the signal, and indicating on a display
`the confidence in the data set based upon at least one of the
`signal quality measures. The indicating step may have the
`substeps of utilizing the signal quality measures to detect a
`low signal quality period during which time the data set may
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`5
`be compromised, and writing an alert message on the display
`during at least a portion of that period. Additional utilizing
`substeps may include comparing each of the signal quality
`measures to a corresponding one of a plurality of thresholds
`to generate a plurality of trigger inputs and combining the
`trigger inputs to trigger a low signal quality warning. Addi-
`tional steps may include setting an alarm limit for the data
`set, filtering the data set to generate an alarm trigger based
`upon the alarm limit and adjusting the characteristics of the
`filtering step according to at least one of the signal quality
`measures so that more filtering is applied during the low
`signal quality period. In one embodiment, the filtering step
`comprises the substeps of time-shifting the data set to create
`a delayed data set, comparing the data set to a threshold to
`generate a first trigger input, comparing the delayed data set
`to the threshold to generate a second trigger input, and
`combining the trigger inputs to generate the alarm trigger.
`Yet a further aspect of the present invention is a data
`confidence indication method comprising the steps of
`acquiring a signal from a physiological sensor, calculating a
`physiological data set from the signal, calculating a plurality
`of signal quality measures from the signal, setting an alarm
`threshold for the data set, and delaying an alarm trigger
`when the data set exceeds the threshold as a function of at
`
`least one of the signal quality measures so as to reduce the
`probability of false alarms. In one embodiment, the delaying
`step comprises the substeps of time-shifting the data set by
`a delay to generate a delayed data set, where the delay is a
`function of at least one of said signal quality measures, and
`comparing the data set to the threshold to create a first limit
`output. Further substeps include comparing the delayed data
`set to the threshold to create a second limit output and
`combining the limit outputs to generate the alarm trigger.
`The data confidence indication method may further com-
`prise the steps of comparing each of the signal quality
`measures to a corresponding one of a plurality of thresholds
`to generate a plurality of trigger inputs and combining the
`trigger inputs to trigger a low signal quality warning.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 illustrates a standard plethysmograph waveform
`that can be derived from a pulse oximeter;
`FIG. 2 illustrates a plethysmograph waveform showing an
`arrhythmia;
`FIG. 3A illustrates a plethysmograph waveform corrupted
`by distortion;
`FIG. 3B illustrates a filtered plethysmograph correspond-
`ing to the distortion-corrupted plethysmograph of FIG. 3A;
`FIG. 4 illustrates the inputs and outputs of the pulse
`indicator according to the present invention;
`FIGS. 5A—B illustrate the generation of one of the pulse
`indicator inputs;
`FIG. 6 is a top-level block diagram of the pulse indicator;
`FIG. 7 is a detailed block diagram of the “distortion level”
`portion of the pulse indicator;
`FIG. 8 is a block diagram of the infinite impulse response
`(IIR) filters of the “distortion level” portion illustrated in
`FIG. 7;
`FIG. 9 is a detailed block diagram of the “waveform
`analyzer” portion of the pulse indicator;
`FIG. 10 is a detailed block diagram of the “slope calcu-
`lator” portion of the waveform analyzer illustrated in FIG. 9;
`FIG. 11 is a detailed block diagram of the “indicator
`decision” portion of the pulse indicator;
`FIG. 12 is a display illustrating a normal plethysmograph
`and a corresponding visual pulse indicator;
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`FIG. 13 is a display illustrating a distorted plethysmo-
`graph and a corresponding high-confidence-level visual
`pulse indicator;
`FIG. 14 is a display illustrating a distorted plethysmo-
`graph and a corresponding low-confidence-level visual
`pulse indicator;
`FIG. 15 is an input and output block diagram of a signal
`quality alert;
`FIG. 16 is a functional block diagram of a signal quality
`alert;
`FIG. 17 is an input and output block diagram of a
`confidence-based alarm;
`FIG. 18 is a functional block diagram of a confidence-
`based alarm; and
`FIGS. 19A—D are saturation versus time graphs illustrat-
`ing operation of a confidence-based alarm.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`
`FIG. 4 illustrates a pulse indicator 400, which can be
`incorporated into a pulse oximeter to trigger the occurrence
`of a synchronous indication of each of the patient’s arterial
`pulses. The indicator 400 operates on an IR signal input 403
`and generates a trigger output 409 and an amplitude output
`410. The trigger output 409 can be connected to a tone
`generator within the pulse oximeter monitor to create a
`fixed-duration audible “beep” as a pulse indication.
`Alternatively, or in addition,
`the trigger output can be
`connected to a display generator within the pulse oximeter
`monitor to create a visual pulse indication. The visual pulse
`indication can be a continuous horizontal trace on a CRT,
`LCD display or similar display device, where vertical spikes
`occur in the trace synchronously with the patient’s pulse, as
`described in more detail below. Alternatively,
`the visual
`pulse indication can be a bar display, such as a vertically- or
`horizontally-arranged stack of LEDs or similar display
`device, where the bar pulses synchronously with the
`patient’s pulse.
`The amplitude output 410 is used to vary the audible or
`visual indications so as to designate input data integr