Schwartz et al. The Contribution of Red Blood Cell Desaturation to Exercising Skeletal Muscle Vasodilation Heterogeneity. Manuscript Data

Experimentally challenging muscle blood flow during exercise requires cardiovascular compensation to protect the matching of oxygen delivery to oxygen demand; however, certain individuals may fail to protect this matching due to an absence of compensatory vasodilation at the local vasculature. We investigated whether red blood cell (RBC) desaturation explains the underlying presence of compensatory vasodilation. Further, prior studies were completed in males, and we sought to elucidate whether biological sex impacts this relationship. The University of Toronto Health Sciences research ethics board approved this study (#41525) according to the terms of the Declaration of Helsinki and all participants provided written informed consent before their participation. 40 healthy individuals (23±5 yrs, 50% female) completed four-minutes of submaximal forearm handgrip exercise at 30% maximum voluntary contraction both with and without brachial artery compression reducing forearm blood velocity by 30% and challenging muscle blood flow. Measures of forearm blood flow (ml/min), blood pressure (mmHg) and RBC desaturation (skeletal muscle oxygen saturation, %) were obtained throughout. Forearm vascular conductance (FVC, ml/min/100mmHg) following challenged exercise greater than 1.96 the coefficient of variation of unchallenged exercise represented the presence of compensatory vasodilation. Data are ∆ from rest (mean±SD). 26 individuals responded with compensatory vasodilation while 14 individuals did not (49±20 vs. 0±4 %FVC, p<0.001). RBC desaturation was greater in individuals responding with compensatory vasodilation (-22±9 vs. -5±4 %oxygen, p<0.001) and was negatively correlated with FVC (rs=-0.819, p<0.001). Sex had no effect on the presence of compensatory vasodilation (p=0.507), nor on the extent (p=0.506) or rate (p=0.857) of RBC desaturation during the muscle blood flow challenge. The presence/absence of compensatory vasodilation following a muscle blood flow challenge appears to be proportional between sex and associated with local RBC desaturation.