Influence of prolonged hypothermia and hyperthermia on cardiac response to injected potassium

Abstract

Left ventricular Na, K, Cl and H₂O and plasma Na, K and Cl have been measured in normothermic dogs, animals cooled to a rectal temperature of 25°C for 2 hours, and dogs maintained at a rectal temperature of 41.5°C for 1 hour. These three main groups are subdivided into a control group killed with pentobarbital sodium prior to obtaining cardiac tissue, and dogs that received an intravenous injection of 11.2% KCl at a rate of 0.5 ml/kg/min. until ventricular fibrillation or cardiac arrest occurred. The method employed to measure cardiac sensitivity to K is criticized. Despite the criticisms, the data suggest a reduced sensitivity of hypothermic hearts and an increased sensitivity of hyperthermic hearts to injected KCl. The rapid rate of injection of KCl employed in these experiments resulted in a high incidence of ventricular fibrillation except in one group of hypothermic dogs in which cardiac arrest was predominant. It is concluded that this predominance was the result of a slowed rate of supply of the injected KCl to cardiac tissue probably resulting from reduced coronary blood flow.