ACUTE HYPOTHERMIA IN GUINEA PIGS

Abstract

Severe reductions of body temp. were produced in 30 un-anesthetized mature guinea pigs by partial immersion in ice water. The early phases of cooling were characterized by increased struggling, hyperpnea, enhanced metabolism, and cardiac slowing. Regardless of the rate of cooling or rewarming, heart rates varied linearly with colonic temp. between 23[degree] and 35[degree]C, falling 17.5 beats per min. for each decrement of one Centigrade degree. Below 23[degree]C, the drop was erratic and often precipitous. Premature beats of auricular and ventricular origins, A-V and intraventricular blocks, and reversible ventricular fibrillation were all noted. When cooling at 0.2[degree] to 0.3[degree] per min., maximal pulmonary ventilation occurred at 35[degree]C (33[degree]-37[degree]) and averaged 170% of pre-immersion rates. At this point, O2 consumption was maximal at 170% of pre-immersion values or 250% of estimated basal rates. Below 33[degree]C ventilation and O2 uptake diminished progressively with temp. Relative to O2 uptake, however, the ventilation rate remained high to the stage of terminal apnea. Therefore the progressive fall in O2 consumption cannot be ascribed to failure of external respiration. Some animals survived after colonic temp. of 17.5[degree]C, others succumbing at as high as 21[degree]C. This large variation in lethal temp. is unexplained. Sublethal cooling appeared to damage the guinea pig''s capacity to restore a normal body temp. spontaneously in room air. The latter died within 10 to 15 hrs. of chilling, even though colonic temps. were then within a few degrees of normal. It appears that the derangements operative in delayed fatalities differ from those responsible for death in deep hypothermia.