Authors:
Timothy Burton
1
;
Gennadi Saiko
2
and
Alexandre Douplik
2
;
3
Affiliations:
1
Department of Biomedical Engineering, Ryerson University, Toronto, Canada
;
2
Department of Physics, Ryerson University, Toronto, Canada
;
3
iBest, Keenan Research Centre of the LKS Knowledge Institute, St. Michael Hospital, Toronto, Canada
Keyword(s):
Photoplethysmography, Microvasculature, Hemodynamics, Contactless, Remote, Bioimaging.
Abstract:
Introduction: The photoplethysmographic (PPG) signal contains information about microvascular hemodynamics, including endothelial-related metabolic, neurogenic, myogenic, respiratory, and cardiac activities. The present goal is to explore the utility of a consumer-grade smartphone camera as a tool to study such activities. Traditional PPG is conducted using a contact method, but the resultant contact pressure can affect venous flow distribution and distort perfusion examination. This motivates us to develop a remote PPG method (rPPG) to study such activities. Methods: We used an imaging setup composed of a stand-mounted consumer grade camera (iPhone 8) with on-board LED illumination. The camera acquired 1920x1080 video data at 60 frames per second (fps); 90 second videos were captured for a hand in rest and elevated positions. Spatial averaging was performed to extract rPPG, which was filtered using continuous wavelet transform to analyse frequency ranges of interest. Results: The da
ta demonstrated a plurality of observed patterns, which differed between rest and elevation positions. In addition to cardiac and respiratory activities, we noticed another two distinct low frequency patterns: oscillations that we conclude are likely Mayer waves, and monotonic reflection increase (gravitational venous outflow). In some cases, these two patterns are combined. Conclusions: rPPG demonstrated potential for venous compartment examinations.
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