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HeartBeat:A headphone heart

rate monitorOrion Buske, Chris Neils, Mike Regnier

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Overview

Non-technical background Current technology Project proposal and technical background Completed device Experimental results Future work

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The Issue

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The Issue

Prevalence of obesity (BMI ≥ 30) over last 22 years.[cdc.gov]

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The Issue

Overweight and obesity accounts for $51.5-$78.5billion in national costs in 1998 [CDC]

over 60% of Americans [CDC]

Heart disease #1 cause of death in USA [CDC]

467,000 coronary artery bypass surgeries in the US in2003 [AHA]

Average American watches over 4 hours of TV perday [A.C. Nielsen Co.]

Average American performs “moderate exercise”three hours per week [Gallup poll]

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The Solution

Healthy diet, exercise significant part ofsolution

Encourage personal responsibility for health Provide technologies to make this simple,

convenient

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Heart Rate Monitoring

Provides a goodmeasure of exerciseintensity

Useful for generalexercise, athletictraining, rehabilitation

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Current Technology

Reebok, Mio,Intervent, LifeSpan

Also, ear-lobe andforehead monitors

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The Competition

Pulsear: won 2008 prize for innovation in sport technologyhaving the potential to open up new market

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The Proposal

Take advantage of 110 million iPods: Use headphones to monitor heart rate Listen to music during exercise

Continuously record heart rate, vitals Put the validation in the hands of the

consumer

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The Proposal

Augment headphones with vital sign sensors Heart rate Respiration Body temperature

Build circuit to filter signals Import signals into computer Analyze and display in Labview UI

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The Background

Photoplethysmography (PPG) - use of lightabsorbance to measure properties of tissue

Signal: DC (bone, average blood volume,muscle) + AC (pulsatile blood)

Transmittance and reflectance orientationspossible, as with pulse oximetry

Device to use transmittance infrared (IR)PPG to detect pulse through ear concha

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The Prototype Ear-molded clay scaffold IR LED and phototransistor in

transmittance configuration Very low-power, high sensitivity Very sensitive to motion Uncomfortable

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The Result

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The Result: Device Embedded IR phototransistor

inside of Sony stereoheadphones

Attached LED to more stablesection of ear-clip

LED directed away fromreceiver, higher power

Much more resistant to motionthan prototype

More comfortable for most ears

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The Result: Circuit

Current to voltage converter Instrumentation amplifier (G = 85) Second-order Chebyshev high-pass filter (fc = 0.4 Hz) Second-order Chebyshev low-pass filter (fc = 1.3 Hz) Amplifier (G = 8)

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The Result: Circuit Analysis

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The Result: User Interface (UI)

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Testing

Devices: Two ear sensors Pulse oximeter ECG (control)

12 subjects Analyze effects of:

Blood pressure Motion Heart rate Headphone device variation Subject (height, weight,

sex, ear-structure) Variation with time

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Testing Regimen

5 min sitting still10 min general activity3 min rapping pulse oximeter fingers15 min tilt table (from horiz: -45, 0, +45)variable holding breath5 min sitting still after 5 min on stairs

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Data Processing

MATLAB scripts Filter data Classify heart beats w.r.t control Calculate accuracy and clean samples

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Data Processing: filter data

Pulse oximeter andear monitors: Filter Normalize Threshold

Ear data: raw (blue)and processed (red)

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Data Processing: filter

ECG (more work): High-pass filter Moving sum (low-pass) Normalize by stdev Threshold for failure Flip? Merge nearby peaks (R, S)

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Data Processing: classify

Identify reference data(ECG): Identify heartbeats in all data

streams Usually by thresholding Midpoint of above-threshold

block Moving window

2 ECG beats wide Classify others as TP, FP, FN

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Data Processing: accuracy

Calculate accuracy for each device, every 30 sec Trim tail to expected # of points - 1

Sample rate was faster than set Throw away if not enough measurements

Sample rate slower than set Throw away if accuracy below threshold (50%)

Assumed to be device failure Informally, accuracy seemed to be ~30% or ~80%

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Results: Summary Over all experiments, average accuracies (including

device failure: < 50%): Right headphone: 86.7% (85.9%) Left headphone:86.3% (84.2%) Pulse oximeter: 86.3% (81.6%)

Higher failure rate (usually < 10%, up to 40% on X7, vs <5% for ear monitors)

Left ear monitor significantly worse than right (p =0.02)

Ear monitors as accurate as pulse oximeter forunbiased experiments (1, 2, 8)

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Results: Experiment

Experiment affects accuracy Device closely matched pulse oximeter accuracy

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Results: Subject

Significant variation between subjects No significant difference between devices and pulse oximeter

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Results: Other

No significant affect of tilt-table tipping (indirect bloodpressure change)

No significant variation over time, although someinsignificant (p>0.05) increase Right ear: 0.3 [-0.1, 0.7] % / min Left ear: 0.4 [ 0.0, 0.8] % / min Pulse oximeter: 0.4 [-0.2, 0.9] % / min

Significant problem from inconsistent, slow samplerate

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Suggested Improvements

Increase sample rate (improve VI) Independent, automatic LED power Improve circuit filtering Improve headphone snugness of fit Music playlist generated from heart rate or

audio heart rate feedback

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Summary

Device able to measure heart rate throughconcha

Interfaces with real-time computer UI Utilized novel PPG orientation to improve

motion resistance Accuracy comparable to standard pulse

oximeter, but less failure

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Acknowledgements Chris Neils, Mike Regnier

Supervision, support, encouragement

Yung-Chun Chen, Trevor Fowler Technical aid

Wonderful, patient volunteers

Department of Bioengineering, University of Washington Funding, laboratory space

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Questions?