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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



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RIGHT ATRIAL PRESSURE (mm Hg) 



fig. 15. Effect of rapid transfusion of blood on venous 

 return and cardiac output curves, showing the result to be an 

 elevated venous return and cardiac output and also a con- 

 siderably elevated right atrial pressure. 



pressure and cardiac output is not always even 

 directionally the same (169), for in some circulatory 

 conditions the cardiac output rises while the right 

 atrial pressure falls; at other times, as in figure 15, 

 the right atrial pressure can rise very greatly while 

 the venous return and cardiac output change rela- 

 tively little. 



EFFECT OF SHOCK ON VENOUS RETURN, CARDIAC OUT- 

 PUT, and right atrial pressure. Figure 1 6 depicts 

 by the dashed curves the normal equating of venous 

 return and cardiac output curves and then by the 

 solid curves the effects immediately after hemorrhage 

 in the so-called compensated stage of shock. In this 

 instance, the hemorrhage has reduced the mean 

 systemic pressure considerably, shifting the venous 

 return curve to the left (99). Immediately, however, 

 circulatory reflexes have become active, causing the 

 heart to become hypereffective and greatly elevating 

 the cardiac output curve. The decreased blood volume 

 also causes the slope of the venous return curve to 

 decrease. Therefore, for two reasons, /) decreased 

 mean systemic pressure, and 2) increased resistance 

 to venous return, the venous return curve is shifted 

 to the left, and its plateau is reduced. Therefore, the 

 venous return and the cardiac output curves equate 



-8 -4 +4 +8 +12 



RIGHT ATRIAL PRESSURE (mm Hg) 



fig. 1 6. Effect of shock on the venous return and cardiac 

 output curves, showing in the early compensated stage of 

 shock a low venous return and cardiac output but also a 

 greatly depressed right atrial pressure (point A). In irrever- 

 sible shock the cardiac output becomes greatly depressed as 

 illustrated by the dash-dot curve; venous return and cardiac 

 output become greatly reduced while the right atrial pressure 

 rises (point B). 



at point A, the cardiac output and venous return 

 falling to about one-half normal and the right atrial 

 pressure falling to —5 mm Hg. These are typical 

 effects observed following acute hemorrhage (90, 

 160, 161, 167). Very similar effects occur in persons 

 with vasomotor collapse except that the partial reflex 

 compensation which occurs following hemorrhage is 

 absent (147). 



In the irreversible stage of shock an entirely differ- 

 ent situation ensues, because the heart then begins 

 to deteriorate. This has been shown especially by the 

 work of Crowell (92), but also by measurements made 

 in Wiggers' laboratory (61, 150, 197, 198) and by 

 Remington (161). The cardiac output curve falls to 

 the lower curve of the figure, and the new equilibrium 

 point is now point B. Thus, the venous return and 

 cardiac output fall to a still lower value while the 

 right atrial pressure begins to rise; these are typical 

 events in the irreversible and terminal stage of shock. 

 As a result of this additional decrease in cardiac out- 

 put, the heart deteriorates still more, and a vicious 

 cycle of cardiac deterioration develops, causing a 

 progressive rise in right atrial pressure and a pro- 

 gressive fall in venous return and cardiac output. 



