VENOUS RETURN 



I 103 



Grodins (78) and also to Chapter 50 by Warner in 

 this Handbook, as well as to the paper presenting his 

 algebraic analysis (192). The algebraic method of 

 circuit analysis depends upon expressing the functions 

 of the individual segments of the circulation in terms 

 of mathematical equations. Then, for a composite 

 analysis of the entire circulation, the equations are 

 solved by standard methods for simultaneous equa- 

 tions. 



SIMPLIFIED GRAPHICAL ANALYSIS OF VENOUS RETURN, 

 CARDIAC OUTPUT, AND RIGHT ATRIAL PRESSURE 



A simplified method for graphical analysis of venous 

 return, cardiac output, and right atrial pressure de- 

 pends upon dividing the circulatory system into two 

 major segments. The first segment is a composite of 

 the right heart, the lungs, and the left heart. The 

 second segment is the systemic circulation. By studying 

 flows and pressures at different points while stressing 

 the circulation in any one of many different ways, one 

 can analyze the circulatory functions of the heart- 

 lung segment in a) the heart-lung preparation, or b) 

 the intact animal. On the other hand, the functional 

 characteristics of the systemic circulation can be 

 studied a) in an isolated systemic system in which the 

 entire heart or part of the heart is replaced by a pump 

 (98), or b) in the intact circulation by measuring 

 pressures and flows at different points while stressing 

 the circulation. These studies yield graphical function 

 curves that are complements to each other. These 

 complementary curves can then be plotted on the 

 same coordinates and thus solved by their points of 

 intersection. The function curves depicting function 

 of the heart-lung segment are called "cardiac output 

 curves," and they are one form of Starling's curves of 

 the heart. The curves depicting function in the 

 systemic circulation are called "venous return curves." 

 Before we can procede further with this analysis we 

 must now characterize the various types of cardiac 

 output and venous return curves that occur in differ- 

 ent circulatory conditions. 



Cardiac Output Curves 



In figure 2, the middle curve represents the normal 

 cardiac output curve of the heart of a 10-kg dog. The 

 shape of this curve has been confirmed by numerous 

 investigators, beginning with Patterson & Starling 

 (154) in 1 91 4 and extending through studies by Katz 

 (123), Krayer (131), and especially Sarnoff and his 



4000 



3600 



3200- _ 



2800- 



1600- 



800 



fig. 2. Cardiac output curves for the normal heart, for 

 hyper- and hypoeffective hearts, and for hearts subjected to 

 increased or decreased resistive loads. 



colleagues (18-20, 38, 120, 171, 172). The quantita- 

 tive values used in this graph were derived princi- 

 pally from the original quantitation made by Patter- 

 son and Starling, data presented by Sarnoff and his 

 colleagues, and many measurements made in our own 

 laboratories. 



A particular problem in determining the quantita- 

 tive values for the cardiac output curves has been the 

 fact that almost all such curves have been recorded in 

 open-chest animals. Yet, in circuit analysis we need to 

 know the quantitative values for the cardiac output 

 curves in the normal closed-chest animal rather than 

 in the open-chest animal. We shall see below that the 

 quantitative values for the curves change markedly 

 upon opening the chest. The figures expressed in this 

 chapter will be for the closed-chest animal unless 

 otherwise specified, and the quantitative values that 

 are presented are based upon curves obtained in 

 open-chest animals but extrapolated to the closed- 

 chest animal on the basis of unpublished determina- 

 tions that we have made in this laboratory while 

 stressing the circulation with rapidly increasing or 

 decreasing blood volume. 



Basically, three different groups of factors determine 



