THE EFFECT OF DIGITALIS ON THE VENOUS PRESSURE

Abstract

The action of digitalis on the circulation-in man is not yet clearly understood. There can be no doubt that it benefits most patient-s with congestive heart failure, but beyond this there is no certainty. McKenzie (1905) believed that its value was -greatest in cases of congestive heart failure with auricular fibrillation and could then be attributed to slowing of the ventricular rate; Lewis (1937) agreed, maintaining that improvement was infrequent in patients with normal rhythm, because slowing of the heart rate was often inconspicuous. Dock and Tainter (1930) and Katz et al. (1938) suggested that digitalis might act primarily by constricting the hepatic vein, a throttle mechanism that was demonstrated in anesthetized dogs; they claimed that the venous pressure was lowered by means of a bloodless venesection, blood being dammed back in the. liver and portal system. Such a theory harmonized with other findings, e.g. digitalis reduced the cardiac output ofnormal dogs (Harrison and Leonard, 1926) and decreased the size of the heart in normal human beings (Stewart et al., 1938). In 1940, however, one of us was able to show that digitalis lowered the venous pressure in 90 per cent of cases of heart failure with normal rhythm, and that this was due neither to slowing of the heart rate nor to any hepatic yein throttle mechanism; for the venous pressure fell as sharply when cardiac slowing was prevented, and the liver and spleenshrank simultaneously (Wood, 1940). More recently, McMichael and Sharpey-Schafer (1944),showed that mechanical lowering of the right auricular pressure by means of cuffs on the thighs produced effects on the cardiac output in man similar to those resulting from digitalis: in cases of congestive heart failure the right auricular pressure fell and the cardiac output rose; in normal subjects the right auricular pressure fell and the cardiac output fell. They suggested that digitalis might have a primary action in lower-