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
Authors: Chalkias Athanasios , Xenos Michalis 
Published: May 2022

ABSTRACTBackgroundAlthough 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.MethodsThis 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 (Δp)].ResultsTwenty 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 μm sec-1, while a Pmca <14 mmHg was observed in those with RBC velocity >24 μm s-1. When Pmca ranged between 11 mmHg and 15 mmHg, Δp fluctuated between 0.02 Pa and 0.1 Pa.ConclusionsThese 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.HIGHLIGHTSChanges in effective circulatory volume may affect microcirculatory red blood cell (RBC) velocity and oxygen extraction ratio, but no systemic variable has been consistently associated with hemodynamic coherenceWe found that a mean circulatory filling pressure analogue (Pmca) value of 14 mmHg maintains sublingual RBC velocity at 6-24 μm s-1A Pmca <14 mmHg is observed in individuals with RBC velocity >24 μm s-1Microvessel pressure difference is maintained constant when Pmca ranges between 11 mmHg and 15 mmHgThese findings imply that tissue oxygenation can be maintained in very low RBC velocitiesTherapeutic strategies and translational research beyond optimizing macrohemodynamics and microcirculatory flow are required, including normalizing red blood cell velocityBRIEF COMMENTARYBackgroundHemodynamic coherence is not well-investigated and no systemic hemodynamic variable has been consistently correlated with microcirculatory perfusion and tissue oxygenation.Translational SignificanceThe present study provides a novel method to monitor hemodynamic coherence and tissue perfusion, which can aid in the identification of novel hemodynamic phenotypes and enhance microcirculation-guided therapeutic strategies, optimizing local delivery of oxygen. Our findings also imply that (1) tissue oxygenation can be maintained in very low red blood cell velocities; and (2) therapeutic strategies and translational research beyond optimizing macrohemodynamics and microcirculatory flow are required, including normalizing red blood cell velocity.