Respiratory variations in the reflection mode photoplethysmographic signal. Relationships to peripheral venous pressure

Abstract

Photoplethysmography (PPG) is a non-invasive optical way of measuring variations in blood volume and perfusion in the tissue, used in pulse oximetry for instance. Respiratory-induced intensity variations (RIIVs) in the PPG signal exist, but the physiological background is not fully understood. Respiration causes variations in the blood volume in the peripheral vascular bed. It was hypothesised that the filling of peripheral veins is one of the important factors involved. In 16 healthy subjects, the respiratory synchronous variations from a PPG reflection mode signal and the peripheral venous pressure (PVP) were recorded. Variations of tidal volume, respiratory rate and contribution from abdominal and thoracic muscles gave significant and similar amplitude changes in both RIIV and the respiratory variation of PVP (p<0.01). The highest amplitudes of both signals were found at the largest tidal volume, lowest respiratory rate and during mainly thoracic breathing, respectively. The coherence between PVP and RIIV signals was high, the median (quartile range) being 0.78 (0.42). Phase analysis showed that RIIV was usually leading PVP, but variations between subjects were large. Although respiratory-induced variations in PVP and PPG showed a close correlation in amplitude variation, a causal relationship between the signals could not be demonstrated.

Fingertip photoplethysmographic waveform variability and systemic vascular resistance in intensive care unit patients

“…The HF band of PPGV represents the respiratory fluctuation in peripheral blood volume, secondary to the modulation of venous return and stroke volume by intrathoracic pressure change [5,6,11,18,26]. The LF band generally represents peripheral vasomotor activities, including those mediated by sympathetic control mechanisms [5,10,11,13,16,17,20,22,26].…”

The effect of vascular changes on the photoplethysmographic signal at different hand elevations

“…Although venous blood has generally been thought to be a static absorber of light, it has been shown that the venous blood volume does not in fact remain constant [Nilsson et al 2003]. In fact, the volume of the veins fluctuates in response to various physiological and physical effects, such as respiration [Phillips et al 2012].…”

Relations between ac-dc components and optical path length in photoplethysmography

“…1,6 Venous capacity corresponds with venous return that affects blood capacity of the heart in each contraction. If venous tone in consistent in the venous return curve, venous return decreases with the increase in central venous pressure and decreases stroke volume.…”

“…dc has many physiological meanings and correlates with the ac waveform. [1][2][3][4][5][6][7][8] According to the Lambert-Beer (or Beer-Lambert) law that explains mechanisms of PPG, PPG ac is generated by the optical path length ( d) that changes with the increase of volume in blood vessels as they pulsate. 9 Therefore, it can be said that PPG ac is in a consistent relationship generated by variations in dc and d.…”