Time Course of Vascular Resistance and Venous Oxygen Changes following Brief Tetanus of Dog Skeletal Muscle

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Abstract
The time courses of vascular resistance and venous blood oxygen (O2) saturation following a brief tetanus of isolated dog calf muscle were studied during free-flow (constant-pressure), high constant-flow (>30 ml/100 g min-1), and low constant-flow (-1) perfusion. A monophasic decrease in resistance followed a 1-second tetanus during either free-flow or high constant-flow perfusion. The transient decrease in vascular resistance during high constant-flow perfusion returned to control before the return of the decrease in end-capillary oxygen tension. Thus, it seems unlikely that the vascular response to a brief tetanus during free-flow or high constant-flow perfusion was controlled by a factor related to oxidative metabolism. A biphasic resistance response followed a brief tetanus during low constant-flow perfusion. This vascular response had a longer duration than the response during free-flow or high constant-flow perfusion. It returned to control with approximately the same time course as that for tissue O2 consumption and could therefore be controlled by factors related to oxidative metabolism. These findings support the hypothesis that exercise hyperemia is due to multiple factors. Moreover, they indicate that, under the conditions of free-flow perfusion or high constant-flow perfusion, the vascular response to a brief tetanus is not solely controlled by factors directly associated with tissue oxidative metabolism.