The effect of local temperature on the reactivity to noradrenaline of digital vessels.

Abstract

The effect of local temperature on the in vivo reactivity of vascular smooth muscle was studied. Reactivity was measured as the increase in critical opening pressure (COP) of digital vessels caused by intravenous infusion of 5 μg of noradrenaline per minute. With one hand cool (22 °C) and the other warm (34 °C) in test experiments or both hands either cool or warm in control experiments, simultaneous measurements were made of the increase in COP of vessels in both middle fingers in response to the noradrenaline. In control experiments the mean increase in COP was similar in right and left fingers, but in test experiments the mean increase was greater in the warm finger than in the cool one. Warm vessels were more reactive to noradrenaline than cool ones (p < 0.01). Because a short period of ischemia is involved in the measurement of COP, other experiments were performed in which the effect of duration of ischemia on the COP, with and without a continuous intravenous infusion of noradrenaline, was ascertained. They suggested that the estimated COP would, in most cases, be about 3 mm Hg less than the COP existing just before the measurement. These results also indicated that although the rate of fall of COP during ischemia was slightly greater for a higher initial COP, the ischemia involved did not invalidate the comparison of the increases in COP caused by noradrenaline in warm and cool fingers, as an index of relative arteriolar reactivity in the test reactivity experiments.