THE CIRCULATORY CHANGES AFTER FULL THERAPEUTIC DOSES OF DIGITALIS, WITH A CRITICAL DISCUSSION OF VIEWS ON CARDIAC OUTPUT 1

Abstract

A critical review has been made of older and current views of the action of digitalis on the circulation and an attempt has been made to correlate its influence on the heart and peripheral vessels with diminution in cardiac output. Previous studies, by many observers, have shown that digitalis is a very effective heart stimulant and increases the efficiency of systolic contraction, while recent observations on normal men and animals have indicated that the drug diminishes cardiac output. In the authors'' experiments on dogs a fall of venous pressure regularly accompanied the diminished cardiac output following a full therapeutic dose of digitalis. This is convincing evidence that the change in blood flow was a result of peripheral, and not cardiac, actions of the drug. These facts are in agreement with the generally accepted view that the output of the normal heart is governed largely by the venous return. Following a single therapeutic intravenous dose of digitalis, there was a gradual rise of blood pressure, sometimes sustained during several hrs. in intact animals, and simultaneously there were constriction of the vessels of the skin and intestine, and an increase in the volume of the liver and spleen, due to hepatic vein constriction and to a pooling of blood in these viscera. Consequently, these changes must have resulted in the diminished venous return to the heart, and a diminished output and heart size. The work of previous investigators has shown that the heart contracts with increased efficiency after therapeutic doses of digitalis, but that the effect on cardiac output varies with the functional state of the circulation. The action of the drug, in man, probably varies in the same way, i.e., the output of the normal heart is reduced, but, in such pathological states as heart failure with passive hyperemia, digitalis would tend to increase the cardiac output and to restore the venous pressure to a normal level.