Photoplethysmogram signal analysis for detecting vital physiological parameters: An evaluating study

The photoplethysmogram (PPG) is the signal resulting from local variations of blood volume in tissues. It reflects the peripheral pulse wave modulated by heart activity, respiration and other physiological effects. This signal is detected through optical devices set up as a transducer fixed on a vascular path, in which light is transmitted using LEDs in red and/or infra-red wavelengths and the reflected or transmitted lights are detected through photodiodes or phototransistors. This signal is then amplified and processed to provide the desired output: the PPG signal. PPG is applied for detecting and assessing different vital physiological parameters in different situations which can be classified as: the Monitoring of Clinical Physiological Parameter such as: Blood Oxygen Saturation, Heart Rate, Respiration and Cardiac Output, Blood Pressure.; the Vascular Assessment such as Arterial Compliance, Arterial Disease and Ageing, Venous Assessment, Vaso-Spastic Conditions, Endothelial Function.; the Autonomic Function assessment such as: Thermoregulation and Vasomotor Function, Orthostatic Intolerance, Blood Pressure and Heart Rate Variability, Neurology, and further Cardiovascular Variability Assessments such as arterial stiffness. In fact different approaches are developed in order to analyze the PPG signal and determine indices which are used in evaluating and assessing these vital physiological parameters. As for example, the pulse transit time PTT defined as the time duration from a reference point of time, for the pulse pressure wave to travel to any specified point on the periphery which is used in assessing Blood Pressure changes, Heart Rate and the compliance of the arterial walls. Furthermore, the amplitude, slope or duration variations of the PPG can also be used for Blood oxygen saturation assessment, arterial disease and ageing and arterial stiffness evaluation. The objectives of this paper is a review and evaluating study of the different methods which are developed in order to analyze the PPG and extract different parameters which are used in assessing vital physiological situations.