Muscle blood flow and flow heterogeneity during exercise studied with positron emission tomography in humans

Blood flow is the main regulator of skeletal muscle's oxygen supply, and se veral studies have shown heterogeneous blood flow among and within muscles. However, it remains unclear whether exercise changes the heterogeneity of flow in exercising human skeletal muscle. Muscle blood flow and spatial flo w heterogeneity were measured simultaneously in exercising and in the contr alateral resting quadriceps femoris (QF) muscle tomography. The relative di spersion (standard deviation/mean) of blood flow was calculated as an index of spatial flow heterogeneity. Average muscle blood flow in QF was 29 (10) ml . (kg muscle)(-1) min(-1) at rest and 146 (54)ml . (kg muscle)(-1) min( -1) during exercise (P = 0.008 for the difference). Blood flow was signific antly(P < 0.001) higher in the vastus medialis and the vastus intermedius t han in the vastus lateralis and the rectus femoris, both in the resting and the exercising lees. Flow was more homogeneous in the exercising vastus me dialis and more heterogeneous (P < 0.001) in the exercising vastus laterali s (P = 0.01) than in the resting contralateral muscle. Flow was more homoge neous (P < 0.001) in those exercising muscles in which flow was highest (va stus intermedius and vastus medialis) as compared to muscles with the lowes t flow (vastus lateralis and the rectus femoris). These data demonstrate th at muscle blood flow varies among different muscles in humans both at rest and during exercise. Muscle perfusion is spatially heterogeneous at rest an d during exercise, but responses to exercise are different depending on the muscle.