Vasomotor Responses in the Human Arm During Leg Exercise

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Abstract
Blood flow was measured in the hands and forearms of recumbent subjects by venous occlusion plethysmography during leg exer cise on a bicycle ergometer. In three highly practiced subjects, exercise resulted in a small fall in forearm flow and a moderate rise in arterial pressure. Resistance to blood flow was therefore considerably increased. Blocking the vasomotor fibers to forearm skin did not affect this, but blocking the deep nerves to the muscle vessels prevented the increase in vascular resistance during exer cise. Treating the forearm with bretyliurn tosylate had the same effect as deep nerve block. It was concluded that vasoconstrictor tone in muscle is increased during exercise. Since treating the forearm with atropine did not affect the normal response, it was concluded that activation of vasodilator fibers to muscle is not an integral part of the gen eral vasomotor response to exercise. Evidence was also found that the vasodilator outflow to a specific muscle group is not specifically activated when the muscle group in question is exercised. During fairly heavy exercise, vasodilatation occurred in both hand and forearm skin. In the hand this was preceded by vasoconstric tion. Evidence was found that the vasodila tation in the hand was due to release of vaso constrictor tone, whereas that in the forearm was mediated through vasodilator fibers. It is likely that the increase in heat production during exercise was responsible for the reflex vasodilatation in skin.