Effect of sympathetic stimulation on dog paw volume

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Abstract
Small vessel pressures and flows and changes in volume of the dog hind paw were recorded simultaneously to study the responses to various rates of sympathetic stimulation. Although a progressive change in small vessel responses occurred as the stimulation frequency was increased, the responses could be grouped into three categories. At the lowest stimulation frequencies (1–2/sec, and less) the constrictor response was predominantly arteriolar. During the stimulation period metatarsal vein pressures and paw volumes did not exceed prestimulation levels. At stimulation frequencies of 1–2/sec to 15–20/sec an initial arteriolar constriction was followed by appreciable arterial and venous constriction. Increases in venous resistance, coupled with continued arterial inflow, produced increased paw volume and pooling of blood in minute vessels. At stimulation frequencies of 20–25/sec marked arterial and venous constriction occurred. Arterial inflow was stopped and paw volumes were decreased even though venous resistance was increased.