Is photoplethysmography-derived pulse shape useful for fall detection?

Falls are a common source of serious injury for elderly people. The harm can be mitigated by using a fall detector. However they are far from ideal and produce a large number of false alarms for every real fall detected. This paper describes an experiment to examine whether the reliability of fall detectors might be improved by using photoplethysmography, which evaluates heart rate and blood flow in microvascular tissue, to make inferences about the body position. The results show a correlation between body position and pulse shape. However the effect is small and is of similar size to the effect of the position of the arm on which the sensor is mounted. Further work is needed to better understand how arm position affects pulse shape and the extent to which these results may be applicable to elderly people.