The role of differential oxygen distribution between the brain and peripheral tissues on tolerance to induced central hypovolemia

Abstract

BackgroundMaintenance of cerebral perfusion and oxygenation is essential for survival from hemorrhage. As individuals vary in tolerance to reduced blood volume (e.g., central hypovolemia), we hypothesized that subjects with high tolerance (HT) will maintain cerebral oxygenation compared to low tolerant (LT) subjects, which will be associated with greater peripheral vasoconstriction.Methods13 human subjects were instrumented for cerebral (ScO2) and muscle (SmO2) oxygenation (near‐infrared spectroscopy, NIRS), then completed a step‐wise presyncopal‐limited lower body negative pressure (LBNP) protocol. Total hemoglobin (HbT) was calculated as an index of local peripheral resistance (inverse relationship) at the muscle.ResultsProgressive decreases in ScO2 were observed in LT subjects (n=5) from −45 mmHg LBNP (P≤0.01 compared to baseline), while ScO2 did not change throughout LBNP for the HT subjects (n=8; P≥0.44). SmO2 decreased at −30 and −60 mmHg LBNP (P≤0.01) in the HT group with concomitant increases in resistance (decreases in HbT; P≤0.03). In contrast, both SmO2 (P=0.01) and HbT (P=0.06) only decreased at −60 mmHg LBNP in the LT group.ConclusionsIn support of our hypothesis, increased tolerance to progressive central hypovolemia was associated with maintained cerebral oxygenation, due, in part, to earlier onset of peripheral vasoconstriction.Source of Funding: US Army MRMC