Observations on the Heart-Lung Preparation in the Rat

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Abstract
A technique for producing and studying a heart-lung preparation in the rat is described. The relationship between filling pressure and cardiac output was found to remain constant for 60 to 90 minutes after the start of the extracorporeal circulation. The influence on this relationship of alterations in pulmonary ventilation, arterial pulse pressure, and heart rate has not been found to be critical. The mechanisms underlying deterioration of the preparation have been investigated, but no firm conclusions have been reached. Deterioration was not prevented by the introduction of fresh blood into the circulation. During prolonged experiments, the extracellular-fluid content of the heart was found to increase, the intracellular potassium was unaltered, and the intracellular sodium was reduced. Acute elevation of the sodium concentration in the circulating blood lowered, whereas potassium raised, the cardiac output for a given filling pressure. These opposing actions were found to summate. Slowing of the heart brought about by high concentrations of potassium was antagonized by sodium.