  Remote photoplethysmography (rPPG) allows for noncontact monitoring of blood
volume changes from a camera by detecting minor fluctuations in reflected
light. Prior applications of rPPG focused on face videos. In this paper we
explored the feasibility of rPPG from non-face body regions such as the arms,
legs, and hands. We collected a new dataset titled Multi-Site Physiological
Monitoring (MSPM), which will be released with this paper. The dataset consists
of 90 frames per second video of exposed arms, legs, and face, along with 10
synchronized PPG recordings. We performed baseline heart rate estimation
experiments from non-face regions with several state-of-the-art rPPG
approaches, including chrominance-based (CHROM), plane-orthogonal-to-skin (POS)
and RemotePulseNet (RPNet). To our knowledge, this is the first evaluation of
the fidelity of rPPG signals simultaneously obtained from multiple regions of a
human body. Our experiments showed that skin pixels from arms, legs, and hands
are all potential sources of the blood volume pulse. The best-performing
approach, POS, achieved a mean absolute error peaking at 7.11 beats per minute
from non-facial body parts compared to 1.38 beats per minute from the face.
Additionally, we performed experiments on pulse transit time (PTT) from both
the contact PPG and rPPG signals. We found that remote PTT is possible with
moderately high frame rate video when distal locations on the body are visible.
These findings and the supporting dataset should facilitate new research on
non-face rPPG and monitoring blood flow dynamics over the whole body with a
camera.
