The Effects of a Variety of Hemodynamic Changes on the Rapid and Slow Components of the Circulation in the Human Forearm1

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Abstract
Various experimental procedures were utilized to study their effects on the relationship between the rapid and slow components of blood flow in the human forearm. Local hyperemia produced by intraarterial injection of tolazoline, reactive hyperemia, or local exercise increased the flow and volume in the rapid component relative to that in the slow component. Venous congestion resulted in marked but nearly proportionate prolongation of mean circulation times. The relative flows and volumes of the 2 components were not significantly changed. Local (intraarterial) infusion of either epinephrine or norepinephrine and systemic administration of epinephrine produced no obvious changes in these parameters although the number of cases, especially those with paired controls, was insufficient to rule out small changes. Systemic infusion of norepinephrine produced characteristic changes in the time-concentration curve of the dye, indicating a relative increase in blood flow of the rapid component. It is suggested that the latter was due to the hypertension plus vasoconstriction in the forearm occurring in response to significant elevation of mean pressure. These observations demonstrate that the biphasic system of forearm blood flow and volume is dynamic, the relative proportion of the rapid and slow components changing under appropriate stimuli. The data also suggest that under normal resting conditions the ratios f1/f2 and v1/v2 are near the lower levels of their possible range.