Hind Limb Blood Flow During Immersion Hypothermia

¹ From the Arctic Aeromedical Laboratory, APO 731, Seattle, Washington

Femoral arterial blood flow was measured by means of an electromagnetic rotameter in 36 dogs prior to and during progressive immersion hypothermia. At a rectal temperature of 35°C a significant rise in blood flow occurred in all dogs. The augmented flow rate was the result of a fall in peripheral resistance since the flow increased as the mean arterial pressure fell. The vasodilatation could be blocked by intra-arterial injections of atropine or by a unilateral lumbar sympathectomy combined with a bilateral adrenalectomy. Thus, sympathetic cholinergic vasodilator fibers appeared responsible for this vascular response. At the point of maximal dilatation the femoral arteriovenous oxygen and temperature differences were negligible suggesting that the increased flow was handled by arteriovenous anastomoses. A secondary vasodilatation occurred at a rectal temperature of 28–25°C, apparently unrelated to nervous or local metabolic factors. The latter reaction seemed to be a cold-induced vasodilatation since a correlation existed between the increased blood flow and an extremely low muscle temperature.