Hyperventilation and human calf blood flow

Abstract

Calf blood flow was measured in normal subjects by venous occlusion plethysmography, and capillary blood flow by the disappearance rate of an intramuscular injection of Na ll31 before and during hyperventilation at 30 breaths/min. for 3 min. Hyperventilation with room air produced a significant increase in plethysmographie calf blood flow, a decrease in vascular resistance, and an increase in the disappearance rate of Nal131. Hyperventilation with 5% CO2 in O2 produced no significant change in calf blood flow, vascular resistance, or Nal131 disappearance rate. After 10 mg propraniolol was injected intravenously, a significant decrease occur red in calf blood flow but not in vascular resistance; the vasodilatation previously induced by intravenous epinephrine was replaced by vasoconstriction. Propranolol failed to completely block the increase in calf blood flow and decrease in vascular resistance during hyperventilation, although a significant but small attenuation did occur. It is concluded that hyperventilation produces an increase in muscle capillary blood flow which is partially but not entirely mediated by stimulation of beta receptors.