Site of increased vascular resistance during isometric muscle contraction

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Abstract
The intramuscular vessels were studied during maximal tetanic contraction to localize the site of increased flow resistance and the microcirculation of rats whose calf muscles were rapidly frozen before, during, or after maximal contraction was examined. No evidence of compression of (he micro -vasculature was seen. Counts of functional capillaries/muscle fiber showed significantly more often open capillaries within 5 sec. of the onset of a single maximal tetany compared to the resting condition. In anesthetized dogs arteriograms and venograms before, during, and after single maximal tetanic contractions of the calf muscles were made. Numerous localized compressions and pinching of both arteries and veins as they entered the muscle or passed between muscle fasciculi were seen. 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.

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