Alterations in pulmonary and peripheral vascular resistance in immersion hypothermia.

The effects of immersion hypothermia on the systemic and pulmonary circulations were investigated in anesthetized, closed-chest, untreated dogs, cold-adapted dogs and in dogs receiving sympathomimetic and sympatholytic agents. Evidence is presented that both pulmonary and systemic vascular resistances are increased progressively during hypothermia, the former to a greater extent than the latter. It is felt that the primary causes for the increase in vascular resistance are progressive diminution in the cardiac output and the local effect of low blood temperature on the vasculature.