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Association of effective circulating blood volume with sublingual RBC velocity and microvessel pressure difference in anesthetized individuals: A clinical investigation and computational fluid dynamics modeling

Background: Although changes in effective circulatory volume may affect microcirculatory red blood cell (RBC) velocity and oxygen extraction ratio, no systemic variable has been consistently associated with hemodynamic coherence. We therefore evaluated the association between mean circulatory filling pressure and microcirculatory perfusion and oxygenation. Methods: This analysis included anesthetized individuals in steady-state physiology. We assessed the correlation of mean circulatory filling pressure analogue (Pmca) with sublingual microcirculation and RBC velocity using SDF+ imaging and a modified optical flow-based algorithm. We also reconstructed the 2D microvessels and applied Computational Fluid Dynamics (CFD) to evaluate the correlation of Pmca and RBC velocity with the obtained pressure and velocity fields in microvessels from CFD [pressure difference ({Delta}p)]. Results: Twenty adults were included in the study, of whom 12 (60%) were men and 8 (40%) were women, with a median age of 39.5 years (IQR 35.5-44.5). Sublingual velocity distributions were similar and followed a log-normal distribution. A constant Pmca value of 14 mmHg was observed in all individuals with sublingual RBC velocity of 6-24 m sec-1, while a Pmca <14 mmHg was observed in those with RBC velocity >24 m s-1. When Pmca ranged between 11 mmHg and 15 mmHg, {Delta}p fluctuated between 0.02 Pa and 0.1 Pa. Conclusions: These data suggest that the intact regulatory mechanisms may maintain a physiological coupling between systemic hemodynamics and tissue perfusion and oxygenation when Pmca is 14 mmHg.