Vasoconstrictor responsiveness during hyperbaric hyperoxia in contracting human muscle

This study demonstrates that functional sympatholysis is impaired slightly in contracting muscles under conditions of increased O2 availability. However, when considered in the context of the substantial reductions in skeletal muscle blood flow and vasodilation (̃20-25%) observed during hyperbaric hyperoxic exercise, the contribution of the exaggerated vasoconstrictor responsiveness (̃5% difference compared with normoxia) does not appear to be a major contributor. This idea is further supported by the fact that muscle blood flow remains substantially reduced (̃15%) during hyperoxic exercise compared with normoxic exercise with α-adrenergic blockade. Identifying other potential mechanisms and determining how they interact during hyperoxic exercise warrants further study.