Hyperbaric hyperoxia slightly increased vasoconstrictor responsiveness during exercise compared to normoxia (-22% vs -17%), but this did not fully explain the 20-25% reduction in forearm blood flow.
Does hyperbaric hyperoxia alter functional sympatholysis and vasoconstrictor responsiveness during forearm exercise in healthy young men?
The substantial reductions in skeletal muscle blood flow during hyperbaric hyperoxic exercise are not primarily explained by an attenuation of functional sympatholysis or greater alpha-adrenergic vasoconstriction.
Absolute Event Rate: -22% vs -17%
p-value: p=<0.05
Large increases in systemic oxygen content cause substantial reductions in exercising forearm blood flow (FBF) due to increased vascular resistance. We hypothesized that 1) functional sympatholysis (blunting of sympathetic α-adrenergic vasoconstriction) would be attenuated during hyperoxic exercise and 2) α-adrenergic blockade would limit vasoconstriction during hyperoxia and increase FBF to levels observed under normoxic conditions. Nine male subjects (age 28 ± 1 yr) performed forearm exercise (20% of maximum) under normoxic and hyperoxic conditions. Studies were performed in a hyperbaric chamber at 1 atmosphere absolute (ATA; sea level) while breathing 21% O(2) and at 2.82 ATA while breathing 100% O(2) (estimated change in arterial O(2) content ∼6 ml O(2)/100 ml). FBF (ml/min) was measured using Doppler ultrasound. Forearm vascular conductance (FVC) was calculated from FBF and blood pressure (arterial catheter). Vasoconstrictor responsiveness was determined using intra-arterial tyramine. FBF and FVC were substantially lower during hyperoxic exercise than normoxic exercise (∼20-25%; P 0.05). During exercise, vasoconstrictor responsiveness was slightly greater during hyperoxia than normoxia (-22 ± 3 vs. -17 ± 2%; P < 0.05). However, during α-adrenergic blockade, hyperoxic exercise FBF and FVC remained lower than during normoxia (P < 0.01). Therefore, our data suggest that although the vasoconstrictor responsiveness during hyperoxic exercise was slightly greater, it likely does not explain the majority of the large reductions in FBF and FVC (∼20-25%) during hyperbaric hyperoxic exercise.
Casey et al. (Fri,) conducted a other in Healthy (n=9). Hyperbaric hyperoxia vs. Normoxia (1 ATA while breathing 21% O2) was evaluated on Vasoconstrictor responsiveness to tyramine during exercise (% decrease in forearm blood flow) (p=<0.05). Hyperbaric hyperoxia slightly increased vasoconstrictor responsiveness during exercise compared to normoxia (-22% vs -17%), but this did not fully explain the 20-25% reduction in forearm blood flow.