CARDIOVASCULAR RESPONSE OF THE DOG TO IMMERSION HYPOTHERMIA

Abstract

When the intracardiac temp, of the pentothalized or etherized dog immersed in an iced bath reached 20[degree]C, the following (average) progressive changes occurred (1) pulse rate decreased from 150 to 35 per min., (2) mean blood pressure fell from 125 to 70 mm. Hg., (3) blood viscosity increased 3 x, due largely to hemoconcentration, (4) the "activity phase" (systole plus isometric relaxation) increased in duration 6 x that at normal temp., (5) the several segments of the EKG were lengthened, those representing repolarization being influenced more than those representing excitation. The characteristic sequence preceeding death was: Bursts of indioventricular beats of diminishing effectiveness; a rise in right atrial pressure, which signalled a failing myocardium; and ventricular fibrillation. It is suggested that failure is caused by a decreased rate of coronary flow (occasioned by the drop in blood pressure, the increased blood viscosity, and the increased time during which the myocardium exhibits tension) coupled with a greatly diminished metabolic rate. Thus in the face of an adequate arterial O2 tension there occurs at some critical temp an incomplete metabolic restitution between beats. A failing aspiration may help to determine that temp.