The evolution of heart beat rate measurement techniques from contact based photoplethysmography to non-contact based photoplethysmography imaging

Heart is the central organ of the blood circulation system where blood starts to flow from. It is essential to observe heart functions because it helps to prevent life-threatening conditions that could be present. The easiest way to examine the heart functions is started by assessing the heart beat rate (HBR). Electrocardiogram (ECG), oscillometric method and photoplethysmography (PPG) are typical methods used in hospital for continuously acquiring patient's HBR. Among these three methods, only the development of PPG method has been evolved from contact sensory based to contactless imaging based. Thence, the theory, concept, research and evolution of the PPG method are presented in this study. The motivation in developing noncontact imaging based PPG methods for HBR measurement not only limits to avoid direct attachment of the sensors on specific body positions, but also very benefits in the remote health care monitoring which is the future trend in medicine. Furthermore, the advancement of the technology especially in the smart device development also incites the researchers to develop the PPG imaging method as mobile app which is competent for HBR measurement.