Baseline plethysmographic signal of arterial pulse during polysomnography: a potential insight into venous return and its clinical implications

Pulse oximetry is based on the technique of photoplethysmography. It is known that the pulsatile arterial component can provide a range of information, such as arterial blood oxygen saturation, the response to fluid infusion, and the nature of respiratory events during sleep. Until now, little importance has been given to the venous component of the plethysmographic signal, which is non-pulsatile but subject to volumetric variations in relation to changes in endopleuric pressure. Respiratory-induced intensity variations contained in the baseline of the photoplethysmographic signal have been well documented. We hypothesize that in polysomnography, variations in the baseline of the plethysmographic signal (referred to as the BPS, baseline plethysmographic signal) reflect variations in venous return induced by respiration, and that these variations present morphological aspects that could have clinical utility in the interpretation of polysomnographic signals, particularly regarding respiratory effort associated with respiratory events, their nature (central or obstructive), and the hemodynamic alterations associated with them. This article presents a selection of polysomnographic traces and images with physiopathological considerations that support our hypothesis.