Ambient-light Photoplethysmography: - How can I tell your pulse from looking at your face?

Abstract

This thesis is an attempt to explore certain aspects of the subject called non-contact, ambient-light photoplethysmography, where we hope to reveal benecialproperties the technique may have. We have a clear focus on technical possibilitybut the medical relevance of it is also discussed and conrmed.Conclusions from previous work are exemplied { the ability we have with thismethod to compute an exact heart rate estimate, from the skin surface both onour face and in the palm of our hand, with and without the subject moving duringrecording; the presence of signal uctuations akin to those of breathing. Moreover,that the pulsations are strong enough to enable subdivision into smaller segmentsand a mapping of how the pulse amplitude is distributed among them.Other information is obtained: the phase information contained in the signalis robust enough that not only the average heart rate over some time but also itsshort time variability can be seen with more than a minimum of detail resolution.From a recording where both face and hand is in view, we further substantiate theclaim of phase robustness by estimating the phase delay, i.e. the dierence in bloodpressure wave travel time between forehead and palm.The concept of Independent Component Analysis has been suggested as a way ofimproving the output of the method|a procedure we investigate and nd limitedsupport for. Other, more simplistic signal processing approaches are found to havepositive traits in achieving overall signal clarity.