VENOUS RETURN 



I I I 7 



fic. 19. Analysis of decompensated heart 

 disease, showing a greatly depressed cardiac 

 output curve and a progressive shift of the 



venous return curves to the right until death 



occurs, as explained in the text. 



-4 + 4 



RIGHT ATRIAL 



+ 8 +12 »I6 



PRESSURE (mm Hq) 



Figure 20 depicts recompensation of the animal 

 that had been almost dead from decompensated 

 heart disease. The lower curve illustrates a cardiac 

 output curve of a decompensated heart, showing that 

 after a period of time the venous return curve had 

 already reached the far right curve with equilibrium 

 occurring at point A. Then, upon instituting appropri- 

 ate treatment, such as the administration of digitalis 

 (117), the heart becomes considerably stronger, and 

 the cardiac output curve rises to the upper curve. If 

 this rise is relatively rapid, the venous return curve 

 will not be immediately affected. Therefore, the new 

 equilibrium point becomes point B, which represents 

 a cardiac output greater than that required for normal 

 renal function. As a consequence, the output of urine 

 now becomes actually far greater than normal, which 

 is a well-known effect of digitalis when a decompen- 

 sated state is converted into a compensated state. The 

 output of urine causes a decrease in mean circulatory 

 pressure and a progressive shift in the venous return 

 curves toward the left. Thus, during the ensuing days, 

 the equilibrium points in figure 20 shift from point 

 B to C, to D, and finally E. At point E the venous 

 return curve becomes stable because now the cardiac 

 output has fallen back to a value that is just sufficient 

 to maintain a renal output equal to the daily intake 

 of fluid and salts. One can see that we now have three 

 different curves equating with each other, the cardiac 

 output curve, the venous return curve, and a straight 

 line which is a curve representing the level required 

 for normal renal function. It is where these three 



-4 -t +9 +12 1-I6 +20 +24 



RIGHT ATRIAL PRESSURE (mm Hq) 



fig. 20. Analysis of recompensation after a bout of cardiac 

 decompensation. The lower cardiac output curve represents 

 the decompensated heart and the upper curve the recom- 

 pensated heart. The sequence of events is explained in the 

 text. 



curves equate that the circulatory system finally es- 

 tablishes its steady-state equilibrium. 



A heart can also be recompensated without in- 

 creasing the cardiac output curve at all but simply 

 by lowering the level required for normal function. 

 For instance, in figure 20, if this were lowered down 

 to a value of 700 ml per min, then point A would be 

 approximately 1 00 ml per min greater than the level 

 required for normal renal function. As a result fluid 



