VENOUS RETURN 



1119 



In order to equate the events that take place in 

 the left heart with those that take place in the right 

 heart, we now need to transpose the direction of the 

 scale for left atrial pressure. Figure 22 illustrates this 

 transposition, showing now the left atrial pressure 

 rising from right to left rather than from left to right. 



2800 



E 

 u 



o. 

 I- 



o 



tr 



< 

 -I 

 z> 

 u 

 or 

 1- 

 z 



Id 



> 



2400- 



2000 



1600- 



W 1200 



O 



z 

 < 





UJ 400- 



3 

 O 



800- 



T 

 ► 20 



w +50 +40 +30 +20 +J0 -10 



LEFT ATRIAL PRESSURE (mm Hg) 



pig. 22. Transposition of the curves illustrated in fig. 21. 

 This transposition allows the left heart analysis to be correlated 

 with the right heart analysis in the following figures. 



-4 -2 »2 «-4 +6 



RIGHT ATRIAL PRESSURE (mm Hg) 



+ 50 +40 .30 +20 +10 -10 

 LEFT ATRIAL PRESSURE (mm 1+)) 



fig. 23. Simultaneous analysis of left and right heart 

 function, showing that in the steady state the venous returns 

 and outputs of the two sides of the heart are all in equilibrium 

 with each other. 



Finally, we superimpose the analysis for the left 

 heart onto a simultaneous analysis for the right heart, 

 as shown in figure 23. In this superimposition, we 

 place the left atrial and right atrial pressure scales 

 so that the 7 mm Hg level of one coincides with the 

 7 mm Hg level of the other. The reason for this is 

 that our preliminary measurements of mean pulmo- 

 nary pressure show it to be almost identical in the 

 normal state with the mean systemic pressure, that 

 is, almost exactly 7 mm Hg. Now, we can explain 

 the composite analysis of the two sides of the heart. 



Note in figure 23 that the right ventricular output 

 curve and the right ventricular venous return curve 

 equate at the 1200 ml per min level. Likewise, the left 

 ventricular output curve and the left ventricular 

 venous return curve also equate at this same level. 

 Therefore, under normal circumstances the two 

 venous returns and the two ventricular outputs are 

 all equal to each other, and the circulation is in a 

 steady state, without any momentary transference 

 of blood from one of the circulatory segments to 

 another. 



BALANCE OF THE TWO VENTRICULAR OUTPUTS WITH 



each other. Proceeding to figure 24, we see the 

 normal situation again depicted by the solid curves. 

 However, the dotted venous return curves represent 

 a situation in which excess blood has momentarily 

 been transferred from the pulmonary circulation to 

 the systemic circulation. Note especially that the two 

 venous return curves intersect the zero venous return 



-4 -2 t2 +4 +6 



RIGHT ATRIAL PRESSURE (mm Hg) 



+ 8 



► 50 »40 +30 .20 .10 -10 

 LEFT ATRIAL PRESSURE (mmHg) 



pig. 24. An analysis showing the manner in which the two 

 sides of the heart automatically balance their outputs. The 

 sequence of events is explained in the text. 



