The role of blood flow in limiting maximal metabolic rate in muscle

To determine the role of blood flow in limiting maximal metabolic rate, the contralateral femoral artery was cannulated and the blood passed through a pump (controlled flow perfusion) or a bypass (self perfusion) to the artery feeding the canine gastrocnemius-plantaris muscle group (N = 15). After a period of self perfusion, the pumped flow was set at the spontaneous level. The muscle was stimulated at 4 or 5 twitches per second to produce a maximal metabolic rate and the pumped flow increased until the precontraction perfusion pressure was reached. After 5 minutes, the flow was increased (perfusion pressure around 200 mm Hg) and then the flow was returned to initial levels and subsequently decreased below this. Oxygen uptake (Vo2) was determined in the fifth minute at each flow level. Isometric tension was measured with a myograph. When the flow was increased above that during the initial contraction period, tension and Vo2 increased above their initial levels. When returned to initial levels, tension and Vo2 followed. Flows below this level resulted in Vo2 and tension decreasing below initial levels. Autoregulation transients were present before and after contraction. It appears that maximal metabolic rate and contractile performance of in situ dog muscles with autoregulating vascular beds are normally limited by blood flow.