heartbeat: a headphone heart rate · pdf fileheartbeat: a headphone heart rate monitor ......
TRANSCRIPT
©2009 Buske 2
Overview
Non-technical background Current technology Project proposal and technical background Completed device Experimental results Future work
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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: 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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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