Site of increased vascular resistance during isometric muscle contraction.

GRAY, SARAH D., ERIK CARLSSON, AND NORMAN C. STAUB. Site of increased vascular resistance during isometric muscle contraction. Am. J. Physiol. 213(3): 683-689. 1967.-We studied the intramuscular vessels during maximal tetanic contraction to localize the site of increased flow resistance. We examined the microcirculation of rats whose calf muscles were rapidly frozen before, during, or after maximal contraction. We found no evidence of compression of the microvasculature. Indeed, counts of functional capillaries per muscle fiber showed significantly more open capillaries within 5 set of the onset of a single maximal tetany compared to the resting condition. In anesthetized dogs we made arteriograms and venograms before, during, and after single maximal tetanic contractions of the calf muscles. We found numerous localized compressions and pinching of both arteries and veins as they entered the muscle or passed between muscle fasciculi. The defects were reproducible and were never seen when the muscle was relaxed. The evidence supports the view that the vascular resistance increase seen during strong muscle contraction is chiefly in the larger supplying vessels rather than in the microcirculation.