Effect of respiratory alkalosis on hind limb and in situ skeletal muscle oxygen uptake in the dog

These experiments were conducted to determine whether changes in skeletal muscle metabolism contribute to the previously reported increase in whole-body O₂ uptake during respiratory alkalosis. Whole-body O₂ uptake was measured by the open-circuit method. The muscle metabolism studies were performed using the hind limb and in situ skeletal muscle preparations in anesthetized and paralyzed dogs. Oxygen uptake of the hind limb and in situ muscle was calculated from measurements of venous blood flow and arterial and venous O₂ concentrations (Van Slyke analysis) during the last 30 min of a 1-hr control period and 1-hr period of respiratory alkalosis. Minute ventilation (hence blood gases and pH) was controlled by a mechanical respirator.

Whole body O₂ uptake increased significantly (p<0.05) during alkalosis. When control muscle O₂ uptake values were 5.0 ml/kg per min or less, alkalosis resulted in a significant (p<0.05) increase in O₂ uptake over the control values. No increase was observed during alkalosis when the control O₂ uptake was greater than 5.0 ml/kg per min. In all experiments, arterial lactate concentration increased significantly (p<0.05) during alkalosis. Calculation of a positive venous-arterial lactate difference across muscle during the period of alkalosis indicates that skeletal muscle is a source of the elevated blood lactate.

The results of this study indicate that O₂ uptake of resting skeletal muscle is increased during states of respiratory alkalosis. Furthermore, it appears that skeletal muscle contributes to the elevation in whole-body O₂ uptake that also occurs during alkalosis. The increase in muscle O₂ uptake occurs only when the alkalosis is imposed on muscle in a true basal state.

The mechanism for the increase in O₂ uptake cannot be determined from the present data but some can be suggested. I have proposed that an increase in the rate of substrate cycling may contribute to the increased O₂ consumption observed in this study.