HeartBeat: A headphone heart rate monitor

Transcription

1 HeartBeat: A headphone heart rate monitor Orion Buske, Chris Neils, Mike Regnier 2009 Buske 1

2 Overview Non-technical background Current technology Project proposal and technical background Completed device Experimental results Future work 2009 Buske 2

3 The Issue 2009 Buske 3

4 The Issue Prevalence of obesity (BMI 30) over last 22 years. [cdc.gov] 2009 Buske 4

5 The Issue Overweight and obesity accounts for $51.5-$78.5 billion 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 in 2003 [AHA] Average American watches over 4 hours of TV per day [A.C. Nielsen Co.] Average American performs moderate exercise three hours per week [Gallup poll] 2009 Buske 5

6 The Solution Healthy diet, exercise significant part of solution Encourage personal responsibility for health Provide technologies to make this simple, convenient 2009 Buske 6

7 Heart Rate Monitoring Provides a good measure of exercise intensity Useful for general exercise, athletic training, rehabilitation 2009 Buske 7

8 Current Technology Reebok, Mio, Intervent, LifeSpan Also, ear-lobe and forehead monitors 2009 Buske 8

9 The Competition Pulsear: won 2008 prize for innovation in sport technology having the potential to open up new market 2009 Buske 9

10 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 2009 Buske 10

11 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 2009 Buske 11

12 The Background Photoplethysmography (PPG) - use of light absorbance to measure properties of tissue Signal: DC (bone, average blood volume, muscle) + AC (pulsatile blood) Transmittance and reflectance orientations possible, as with pulse oximetry Device to use transmittance infrared (IR) PPG to detect pulse through ear concha 2009 Buske 12

13 The Prototype Ear-molded clay scaffold IR LED and phototransistor in transmittance configuration Very low-power, high sensitivity Very sensitive to motion Uncomfortable 2009 Buske 13

14 The Result 2009 Buske 14

15 The Result: Device Embedded IR phototransistor inside of Sony stereo headphones Attached LED to more stable section of ear-clip LED directed away from receiver, higher power Much more resistant to motion than prototype More comfortable for most ears 2009 Buske 15

16 The Result: Circuit Current to voltage converter Instrumentation amplifier (G = 85) Second-order Chebyshev high-pass filter (f c = 0.4 Hz) Second-order Chebyshev low-pass filter (f c = 1.3 Hz) Amplifier (G = 8) 2009 Buske 16

17 The Result: Circuit Analysis 2009 Buske 17

18 The Result: User Interface (UI) 2009 Buske 18

19 Testing Devices: 12 subjects Two ear sensors Pulse oximeter ECG (control) Analyze effects of: Blood pressure Motion Heart rate Headphone device variation Subject (height, weight, sex, ear-structure) Variation with time 2009 Buske 19

20 Testing Regimen 5 min sitting still 10 min general activity 3 min rapping pulse oximeter fingers 15 min tilt table (from horiz: -45, 0, +45) variable holding breath 5 min sitting still after 5 min on stairs 2009 Buske 20

21 Data Processing MATLAB scripts Filter data Classify heart beats w.r.t control Calculate accuracy and clean samples 2009 Buske 21

22 Data Processing: filter data Pulse oximeter and ear monitors: Filter Normalize Threshold Ear data: raw (blue) and processed (red) 2009 Buske 22

23 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) 2009 Buske 23

24 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 2009 Buske 24

25 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% 2009 Buske 25

26 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 for unbiased experiments (1, 2, 8) 2009 Buske 26

27 Results: Experiment Experiment affects accuracy Device closely matched pulse oximeter accuracy 2009 Buske 27

28 Results: Subject Significant variation between subjects No significant difference between devices and pulse oximeter 2009 Buske 28

29 Results: Other No significant affect of tilt-table tipping (indirect blood pressure change) No significant variation over time, although some insignificant (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 sample rate 2009 Buske 29

30 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 2009 Buske 30

31 Summary Device able to measure heart rate through concha Interfaces with real-time computer UI Utilized novel PPG orientation to improve motion resistance Accuracy comparable to standard pulse oximeter, but less failure 2009 Buske 31

32 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 2009 Buske 32

33 Questions? 2009 Buske 33