Photoplethysmography and its application in clinical physiological measurement

Abstract

Photoplethysmography (PPG) is a simple and low-cost optical technique that can be used to detect blood volume changes in the microvascular bed of tissue. It is often used non-invasively to make measurements at the skin surface. The PPG waveform comprises a pulsatile ('AC') physiological waveform attributed to cardiac synchronous changes in the blood volume with each heart beat, and is superimposed on a slowly varying ('DC') baseline with various lower frequency components attributed to respiration, sympathetic nervous system activity and thermoregulation. Although the origins of the components of the PPG signal are not fully understood, it is generally accepted that they can provide valuable information about the cardiovascular system. There has been a resurgence of interest in the technique in recent years, driven by the demand for low cost, simple and portable technology for the primary care and community based clinical settings, the wide availability of low cost and small semiconductor components, and the advancement of computer-based pulse wave analysis techniques. The PPG technology has been used in a wide range of commercially available medical devices for measuring oxygen saturation, blood pressure and cardiac output, assessing autonomic function and also detecting peripheral vascular disease. The introductory sections of the topical review describe the basic principle of operation and interaction of light with tissue, early and recent history of PPG, instrumentation, measurement protocol, and pulse wave analysis. The review then focuses on the applications of PPG in clinical physiological measurements, including clinical physiological monitoring, vascular assessment and autonomic function.

Contact‐Free Screening of Atrial Fibrillation by a Smartphone Using Facial Pulsatile Photoplethysmographic Signals

“…In addition to handheld ECG devices, smartphones are capable of detecting pulsatile photoplethysmographic signals related to cardiac‐induced fluctuations in tissue blood volume using the built‐in cameras and LED (light‐emitting diode) smartphone flash 14, 15. To date, the photoplethysmographic signal is typically recorded by placing a finger over the smartphone camera lens, which measures changes in reflected light intensity from the LED caused by blood volume changes in the fingertip.…”

Measuring venous oxygenation using the photoplethysmograph waveform

“…The necessary conditions for using spectroscopic measurements to infer the oxygen saturation in a given vascular compartment are: (1) pulsatile flow, and (2) differential spectral absorbance [3,4]. The pulsatile flow allows the spectral absorbance to be measured at two different states of tissue perfusion (maximum perfusion and minimum perfusion).…”

Investigation of peripheral photoplethysmographic morphology changes induced during a hand-elevation study

“…Photoplethysmography (PPG) is a non-invasive optical technique that exploits the variation in light absorption due to blood volume changes in the vessels close to the skin during the cardiac cycle [1]. It is widely used in pulse oximetry for calculation of heart rate and estimation of blood oxygen saturation using PPGs recorded at two wavelengths simultaneously [2].…”

“…The PPG signal consists of a slowly varying (dc) baseline and a pulsatile (ac) component [1]. This cardiac-synchronous pulsatile component is assumed to depend solely on the arterial inflow of blood into a monitoring site such as the finger or earlobe [4].…”

“…As the ac PPG signal is similar in morphology to the arterial blood pressure waveform [5], it has been suggested that they are both influenced by similar vascular mechanisms [6]. Therefore, the PPG signal has been explored as a method to extract further circulatory and cardiovascular information from patients [1].…”