Mechanism of Increased Femoral Arterial Flow During Body Warming.

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Abstract
Westin et al showed that in the nonshivering hypothermic dog anesthetized with pentobarbital, immersion of the body in warm water (40-45[degree]C) evoked an immediate and striking rise in the femoral artery blood flow at a time when the blood and body temperatures were still falling. This study was undertaken to investigate possible active reflex vasodilatation to explain this phenomenon. Arterial pressure, skin and body temperature, femoral arterial blood flow and cardiac output were monitored during immersion cooling and rewarming. After control measurements on intact animals, 2 experi-. mental variables were (1) hind limbs skinned or (2) transperitoneal abdominopelvic sympathectomy. The vasodilation which doubled femoral flow 30 seconds after immersion in warm water was not changed by skimming. After sympathectomy the femoral flow was much increased but subsequently did not respond significantly to cooling or rewarming. The changes in arterial pressure and cardiac output were comparatively insignificant. The fact that this reflex does not arise in the skin of the leg and that the vasodilatation occurs primarily in muscle is shown. This femoral vasodilatation reflex can operate despite the effect of cold blood still bathing the vasomotor control centers. The change may be brought about by a sensitivity to temperature trend rather than to absolute value. The function of this response is not clear and it may be peculiar to nonshivering animals as it was not observed in Sernyl : anesthetized animals. The results indicate that the fall in femoral flow during immersion hypothermia and the rise in flow on immersion in warm water are due to changes in sympathetic vasoconstrictor tone triggered upon contact of the body with warm water.

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