# US 9,433,386 B2 · Method and apparatus for monitoring a subject for atrial fibrillation

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- Number: US 9,433,386 B2
- Document ID: US9433386B2
- Status: Granted
- Kind: B2
- Application number: 13/937,740
- Filed: 2013-07-09
- Published: 2015-01-15
- Granted: 2016-09-06
- Earliest claimed: 2013-07-09
- Assignees: Xerox Corporation
- Applicants: Xerox Corporation
- Inventors: Lalit Keshav Mestha; Survi Kyal; Barry P. Mandel; Peter Johan Nystrom
- Web page: https://patentgrep.com/patent/US9433386B2

## CPC

- A61B 5/7282: {Event detection, e.g. detecting unique waveforms indicative of a medical condition (cough events A61B5/0823; seizures A61B5/4094; sleep apnoea A61B5/4818)}
- A61B 5/0024: {for multiple sensor units attached to the patient, e.g. using a body or personal area network}
- A61B 5/02427: {Details of sensor}
- A61B 5/6831: {Straps, bands or harnesses}
- A61B 5/0022: {Monitoring a patient using a global network, e.g. telephone networks, internet}
- A61B 5/746: {Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms}
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)

## Abstract

What is disclosed is a method for monitoring a subject for cardiac arrhythmia such as atrial fibrillation using an apparatus that can be comfortably worn by the subject around an area of exposed skin where a photoplethysmographic (PPG) signal can be registered. In one embodiment, the apparatus is a reflective or transmissive wrist-worn device with emitter/detector pairs fixed to an inner side of a band with at least one illuminator emitting source light at a specified wavelength band. The illuminator is paired to a respective photodetector comprising one or more sensors that are sensitive to a wavelength band of its paired illuminator. The photodetector measures intensity of sensed light emitted by a respective illuminator. The signal obtained by the sensors comprises a continuous PPG signal. The continuous PPG signal analyzed for peak-to-peak pulse points from which the existence of cardiac arrhythmia such as atrial fibrillation event can be determined.

## Claims

### Claim 1

A method for monitoring a subject of interest for atrial fibrillation, the method comprising:
activating an apparatus comprising one of a transmissive device, or a reflective device, each with a plurality of emitter/detector pairs with at least one illuminator emitting source light at a specified wavelength band, and fixed to an inner side of a band worn circumferentially around an area of exposed skin by a subject of interest being monitored for the presence of cardiac arrhythmia, each detector comprises at least one sensor that is sensitive to a wavelength band of the illuminator, the detector measuring an intensity of received light emitted by an illuminator, said measurements comprising a continuous photoplethysmographic (PPG) signal for said subject, said apparatus comprising a control panel with a LED which is activated when the device is turned ON, an alert LED which is activated in response to an alert condition, a LED which is activated when atrial fibrillation is not present, and a speaker providing an audible alert in response to a presence of atrial fibrillation, said controller
(i) turning said emitter/detector pairs ON/OFF for a desired length of time,
(ii) receiving said measured intensities from each of said detectors, and
(iii) communicating said intensities to a wireless handheld device executing a downloadable application for analyzing said continuous PPG signal measured intensity for a determination of the presence of atrial fibrillation, said wireless handheld device signaling said controller to perform at least one of: turning ON said alert LED to indicate a presence of atrial fibrillation, and emitting a sound through said speaker.

### Claim 2 (depends on 1)

The method of claim 1, wherein said cardiac arrhythmia is atrial fibrillation.

### Claim 3 (depends on 1)

The method of claim 1, wherein said apparatus is a transmissive device said illuminator and paired detector defines a chord of living tissue through which said emitted source light passes, the detector measuring an intensity of light passing through said chord of living tissue.

### Claim 4 (depends on 3)

The method of claim 3, wherein each illuminator is separated from its paired detector by a distance D, said distance being less than 75% of a diametrical distance of the area where said band is being worn, each detector measuring an intensity of light passing through said chord of living tissue.

### Claim 5 (depends on 1)

The method of claim 1, wherein said apparatus is a reflective device, distance D is a distance between each illuminator and paired detector as measured around said circumference, said emitted light impacting said skin surface at an angle θL, each detector measuring an intensity of light reflecting off a surface of skin at an angle θR, where 0°<(θL, θR)<90°.

### Claim 6 (depends on 1)

The method claim 1, further comprising a plurality of illuminators each illuminator separated from its paired detector by a distance D.

### Claim 7 (depends on 6)

The method of claim 6, wherein a wavelength band of a first illuminator is centered about 660 nm and a wavelength band of a second illuminator is centered about 940 nm.

### Claim 8 (depends on 1)

The method of claim 1, wherein a wavelength band of said illuminator is centered at one of 660 nm or 940 nm.

### Claim 9 (depends on 1)

The method of claim 1, wherein multiple emitter/detector pairs are fixed circumferentially around an inner side of said band.

### Claim 10 (depends on 1)

The method of claim 1, wherein multiple emitters and multiple detectors form an emitter/detector pair.

### Claim 11 (depends on 10)

The method of claim 10, wherein each emitter/detector pair is configured to emit/detect a different wavelength band.

### Claim 12 (depends on 1)

The method of claim 1, wherein said peak-to-peak pulse points are detected in the continuous PPG signal using an adaptive threshold technique with successive thresholds being based on variations detected in previous magnitudes of said pulse peaks.

### Claim 13 (depends on 1)

The method of claim 1, further comprising using a Poincare diagram of said peak-to-peak pulse dynamics to determining a relationship between consecutive beats.

### Claim 14 (depends on 1)

The method of claim 1, further comprising normalizing said peak-to-peak pulse points to a frequency between 60-70 bpm to reduce pulse variations.

### Claim 15 (depends on 1)

The method of claim 1, further comprising determining whether a time interval between consecutive beats of said signal is outside an acceptable limit for said subject.

### Claim 16 (depends on 1)

The method of claim 1, further comprising communicating said continuous PPG signal measured intensities to any of: a smartphone, a Wi-Fi router, an I-Pad, a Tablet-PC, a laptop, and a computer.

### Claim 17 (depends on 1)

The method of claim 1, further comprising initiating an alert signal in response to said cardiac arrhythmia such as atrial fibrillation being outside a pre-defined limit of acceptability.

### Claim 18 (depends on 12)

The method of claim 12, wherein said signal comprises any of: text, email, picture, graph, chart, and pre-recorded message.

### Claim 19

An apparatus for monitoring a subject of interest for cardiac arrhythmia, the apparatus comprising:
one of a transmissive device or a reflective device, each with a plurality of emitter/detector pairs with at least one illuminator emitting source light at a specified wavelength band, and fixed to an inner side of a band worn circumferentially around an area of exposed skin by a subject of interest being monitored for the presence of cardiac arrhythmia, each detector comprises at least one sensor that is sensitive to a wavelength band of the illuminator, the detector measuring an intensity of received light emitted by an illuminator, said measurements comprising a continuous photoplethysmographic (PPG) signal for said subject, said apparatus comprising a control panel with a LED which is activated when the device is turned ON, an alert LED which is activated in response to an alert condition, a LED which is activated when atrial fibrillation is not present, and a speaker providing an audible alert in response to a presence of atrial fibrillation, said controller (i) turning said emitter/detector pairs ON/OFF for a desired length of time, (ii) receiving said measured intensities from each of said detectors, and (iii) communicating said intensities to a wireless handheld device executing a downloadable application for analyzing said continuous PPG signal measured intensity for a determination of the presence of atrial fibrillation, said wireless handheld device signaling said controller to perform at least one of: turning ON said alert LED to indicate a presence of atrial fibrillation, and emitting a sound through said speaker.

### Claim 20 (depends on 19)

The apparatus of claim 19, wherein said cardiac arrhythmia is atrial fibrillation.

### Claim 21 (depends on 19)

The apparatus of claim 19, wherein said apparatus is a transmissive device said illuminator and paired detector defines a chord of living tissue through which said emitted source light passes, the detector measuring an intensity of light passing through said chord of living tissue.

### Claim 22 (depends on 21)

The apparatus of claim 21, wherein each illuminator is separated from its paired detector by a distance D, said distance being less than 75% of a diametrical distance of the area where said band is being worn, each detector measuring an intensity of light passing through said chord of living tissue.

### Claim 23 (depends on 19)

The apparatus of claim 19, wherein said apparatus is a reflective device, distance D is a distance between each illuminator and paired detector as measured around said circumference, said emitted light impacting said skin surface at an angle θL, each detector measuring an intensity of light reflecting off a surface of skin at an angle θR, where 0°<(θL, θR)<90°.

### Claim 24 (depends on 19)

The apparatus of claim 19, further comprising a plurality of illuminators each illuminator separated from its paired detector by a distance D.

### Claim 25 (depends on 24)

The apparatus of claim 24, wherein a wavelength band of a first illuminator is centered about 660 nm and a wavelength band of a second illuminator is centered about 940 nm.

### Claim 26 (depends on 19)

The apparatus of claim 19, wherein a wavelength band of said illuminator is centered at one of 660 nm or 940 nm.

### Claim 27 (depends on 19)

The apparatus of claim 19, wherein multiple emitter/detector pairs are fixed circumferentially around an inner side of said band.

### Claim 28 (depends on 19)

The apparatus of claim 19, wherein multiple emitters and multiple detectors form an emitter/detector pair.

### Claim 29 (depends on 28)

The apparatus of claim 28, wherein each emitter/detector pair is configured to emit/detect a different wavelength band.

### Claim 30 (depends on 19)

The apparatus of claim 19, wherein said peak-to-peak pulse points are detected in the continuous PPG signal using an adaptive threshold technique with successive thresholds being based on variations detected in previous magnitudes of said pulse peaks.

### Claim 31 (depends on 19)

The apparatus of claim 19, further comprising using a Poincare diagram of said peak-to-peak pulse dynamics to determining a relationship between consecutive beats.

### Claim 32 (depends on 19)

The apparatus of claim 19, further comprising normalizing said peak-to-peak pulse points to a frequency between 60-70 bpm to reduce pulse variations.

### Claim 33 (depends on 19)

The apparatus of claim 19, further comprising determining whether a time interval between consecutive beats of said signal is outside an acceptable limit for said subject.

### Claim 34 (depends on 19)

The apparatus of claim 19, further comprising communicating said continuous PPG signal measured intensities to any of: a smartphone, a Wi-Fi router, an I-Pad, a Tablet-PC, a laptop, and a computer.

### Claim 35 (depends on 19)

The apparatus of claim 19, further comprising initiating an alert signal in response to said cardiac arrhythmia such as atrial fibrillation being outside a pre-defined limit of acceptability.

### Claim 36 (depends on 35)

The apparatus of claim 35, wherein said signal comprises any of: text, email, picture, graph, chart, and pre-recorded message.