BLOOD-FLOW ELEVATION INCREASES VO2 MAXIMUM DURING REPETITIVE TETANIC CONTRACTIONS OF DOG MUSCLE INSITU

Blood flow through the gastrocnemius-plantaris muscle of the dog in si tu was increased by a pump in the arterial supply during a 30-min peri od of 1/s isotonic tetanic contractions. Compared with a control serie s of experiments with normoxemia and spontaneous flow, the pump increa sed flow 84%, from 1.51 +/- 0.08 to 2.78 +/- 0.15 ml . g-1 . min-1. Th e perfusion pressure was increased from 125 to 196 mmHg. The pump hype remia increased maximal O2 uptake (VO2) at 5 min of contractions by 31 %, from 8.97 +/- 0.44 to 12.89 +/- 0.30 mumol . g-1 . min-1. The extra ction was decreased, and venous PO2 (Pv(O2)) was increased. Fatigue, m easured as a drop in power production from the highest level at 10 s t o 30 min, was 49% during pump hyperemia and 54% in the control conditi ons. VO2 decreased 30% from the 5-min value to the 30-min value with p ump hyperemia and 28% over the same time in the control conditions. At maximal VO2, the ratio VO2/Pv(O2) was increased by pump hyperemia com pared with control conditions, suggesting an increased O2 diffusing co nductance of the muscles. We conclude that the elevated perfusion pres sure of pump hyperemia increased flow to raise maximal VO2 mainly in a reas of the muscle that had restricted flow under control conditions.