Vasoconstrictor responsiveness during hyperbaric hyperoxia in contracting human muscle

• Published in: Journal of applied physiology (1985) 2013-01, Vol.114 (2), p.217-224
• Main Authors: Casey, Darren P, Joyner, Michael J, Claus, Paul L, Curry, Timothy B
• Format: Article
• Language: English
• Subjects: Adrenergic alpha-Antagonists - pharmacology; Adrenergic Uptake Inhibitors - pharmacology; Adult; Blood pressure; Blood Pressure - physiology; Exercise; Exercise - physiology; Forearm - blood supply; Humans; Hyperbaric Oxygenation; Hyperoxia - physiopathology; Male; Muscle Contraction - physiology; Muscle, Skeletal - physiology; Muscular system; Oxygen; Phentolamine - pharmacology; Receptors, Adrenergic, alpha - drug effects; Receptors, Adrenergic, alpha - physiology; Regional Blood Flow - physiology; Tyramine - pharmacology; Ultrasonic imaging; Vascular Resistance - physiology; Vasoconstriction - physiology
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.01197.2012

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 < 0.01). At rest, vasoconstriction to tyramine (% decrease from pretyramine values) did not differ between normoxia and hyperoxia (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.