Authors:
David Western
1
;
John Eveness
1
;
Beshoy Agayby
2
;
Xicai Alex Yue
3
;
Timothy Cox
1
;
Alistair Foster
2
and
Nick Gompertz
2
Affiliations:
1
Institute of BioSensing Technology, UWE Bristol, Bristol, U.K.
;
2
Earswitch Ltd, U.K.
;
3
Institute of BioSensing Technology, UWE Bristol, Bristol, U.K
Keyword(s):
Photoplethysmography, Pulse Oximetry, Ear Canal, Skin Tone, Earables.
Abstract:
Photoplethysmography (PPG) is a well-established form of physiological sensing, but persistent challenges include skin-tone-dependent variations in performance and trade-offs between performance and acceptance factors in site selection. We propose that the inner, bony portion of the ear canal may offer several advantages over established sites, including reduced sensitivity to skin tone. We support this position through a combination of anatomical analysis, colorimetry, and the first examples of PPG data collected from the bony ear canal, including pulse oximetry calculations during voluntary breathholds. Colorimetry revealed no statistically significant differences in lightness, chroma, or hue of the bony canal between subjects with lighter versus darker external skin tones. The commonly used ratio-of-ratios (R) method for pulse oximetry was sensitive to de-oxygenation from breathholds, showing statistically significant correlation with breathhold duration. Our results show that the
bony ear canal is not pigmented, and that PPG signals can be obtained from this site, even in the presence of idiosyncracies such as earwax and myringosclerosis.
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