Impairment of Gas Transport and Gas Exchange in Dogs During Acute Hypothermia

¹ From the Department of Physiology, State University of New York, College of Medicine at New York City, Brooklyn, New York

Respiratory and circulatory responses were studied in anesthetized dogs during acute hypothermia produced in a cold-air bath. In four control animals, the constancy of rectal and heart temperatures, total ventilation, cardiac output, arterial carbon dioxide tension and hydrogen ion concentration was established. Two types of responses occurred after cooling began (12 animals): a) cooling with shivering which resulted in a temporary increase in body temperature, ventilation and cardiac output; b) cooling without shivering which resulted in a decrease in body temperature, ventilation and cardiac output. During shivering, ventilation increased with an increase in the ventilatory equivalent for oxygen. Cardiac output increased but the circulatory equivalent for oxygen decreased at high levels of oxygen consumption. A respiratory alkalosis occurred. In cooling without shivering, the decrease in cardiac output was brought about by a reduction in heart rate; the stroke volume increased precipitously when the heart temperature dropped below 30°C. The circulatory equivalent for oxygen increased at low levels of oxygen consumption. The diminution of the total ventilation, which was brought about by a decrease in both tidal volume and respiratory rate, resulted in an increase in the arterial CO₂ tension and H⁺ concentration (respiratory acidosis). In all experiments with hypothermia, the animal had a primary respiratory failure followed by circulatory failure. The heart temperature of these dogs at death averaged 24.8°C.