Blood flow elevation increases V̇O₂ maximum during repetitive tetanic contractions of dog muscle in situ

Blood flow through the gastrocnemius-plantaris muscle of the dog in situ was increased by a pump in the arterial supply during a 30-min period of 1/s isotonic tetanic contractions. Compared with a control series of experiments with normoxemia and spontaneous flow, the pump increased flow 84%, from 1.51 ± 0.08 to 2.78 ± 0.15 ml · g^-1 · min^-1. The perfusion pressure was increased from 125 to 196 mmHg. The pump hyperemia increased maximal O₂ uptake (V̇O₂) at 5 min of contractions by 31%, from 8.97 ± 0.44 to 12.89 ± 0.30 μmol · g^-1 · min^-1. The extraction was decreased, and venous PO₂ (PV(O₂)) was increased. Fatigue, measured as a drop in power production from the highest level at 10 s to 30 min, was 49% during pump hyperemia and 54% in the control conditions. V̇O₂ decreased 30% from the 5-min value to the 30-min value with pump hyperemia and 28% over the same time in the control conditions. At maximal V̇O₂, the ratio V̇O₂/Pv(O₂) was increased by pump hyperemia compared with control conditions, suggesting an increased O₂ diffusing conductance of the muscles. We conclude that the elevated perfusion pressure of pump hyperemia increased flow to raise maximal V̇O₂ mainly in areas of the muscle that had restricted flow under control conditions.