Relation of oxygen saturation and blood flow in different structural parts of the microvscular system of the human skin

The most important function of the human cardiorespiratory system is the supply tissues by oxygen and the microvascular system plays a key role in this process. To date, the physiologically important relationship between tissue oxygen saturation and blood flow remains insufficiently studied. The aim of this study is to estimate the relationship between blood flow fluctuations in the microvessels and tissue oxygen saturation in skin as a function of blood flow velocity and microvessel type under native conditions and during local heating. This work utilizes measurements published in an open database obtained with the EPOS method, which combines a probe for measuring tissue perfusion differentiated by microvessel type, a sensor for determining tissue oxygenation, and a heater. The data collected during the test with local heating up to 40°C were selected from the database. It was obtained that unlike perfusion spectra, tissue oxygenation spectra are concentrated in the low-frequency region. The peculiarities of the relationship between the oxygen saturation level and blood flow fluctuations in human skin microvessels depending on their type have been demonstrated. The oxygenation signal is modulated by blood flow in a wide range of frequencies, with low-frequency modulations corresponding to endothelium-dependent, neurogenic, and myogenic oscillations having a stronger relationship between SO2 level and perfusion fluctuations. Such oscillations are functionally significant, related to oxygen extraction processes. Higher correlation of low-frequency SO2 fluctuations and blood flow fluctuations is typical for perfusion components associated with capillary blood flow and small arterioles.