Effect of Change in Air Temperature Upon Systemic Small and Large Vessel Resistance

Journal/Book: Circulation Research Vol. V No. 1 January 1957. 1956/1957;

Abstract: From Army Medical Research Laboratory Fort Knox Ky. Received for publication August 27 1956 Direct resistance measurements in the foreleg of the anesthetized dog show that the rise in total resistance following reduction of air temperature is due predominately to small vessel constriction and is based upon at least three different mechanisms. The large arteries and veins also constrict and evidence is presented which suggests that the venous and possibly the arterial resistance responses are predominately due to changing levels of circulating epinephrine norepinephrine or both. Summary Observation were made upon small and large vessel resistance iu the foreleg of the pentobarbital anesthetized dog in relation to 10 and 15 min. exposures to air temperatures of 20 and 0 C. respectively. Studies were made with nerves intact blocked and blocked plus local phentolamine infusion. Upon 0 C. exposure total resistance of the intact leg increased to 143 per cent of the 20 C. value. Eighty-three per cent of the rise was due to small vessel constriction. Arterial and venous resistance elevations were not necessarily related in terms of time direction or pattern to that observed in the small vessel segment. Venous resistance sometimes continued to rise during the rewarming period at a time when small vessels were dilating. At least three mechanisms contributed to changes in total and small vessel resistance. These include changing activity in nonlocally distributed nerves changing levels of circulating or locally released epinephrine and a direct effect of temperature change on blood vessel musculature. The changes in venous and possibly arterial resistance are interpreted as due predominately to changing levels of epinephrine norepinephrine or both. schö

Zurück | Weiter