494 HANDBOOK OF PHYSIOLOGY -^ CIRCULATION I 



250 



AP 



w 



OL 

 10 



LVO 



600 

 400 

 200 



1 



- V-' U' 



, 05;^ , 



FIG. 3.-1, B, C. AP = aortic pressure in mm Hg; LVD = left ventricular diastolic pressure in cm 

 HjO; TCF = total coronary How in ml/min. CF = total coronary How in ml/min. 



rose to the level shown in the second panel. No 

 change in contractility was observed. Shortly there- 

 after, in the same experiment, the aortic resistance 

 was lowered and the spontaneous, unrestricted 

 coronary flow observed (third panel). Coronary flow- 

 was then pumped (fourth panel) at the unrestricted 

 flow rate which had been observed when aortic 

 resistance and pressure were high. Once again, a 

 change in ventricular contractility was not apparent. 

 These data are not construed as indicating that ati 

 adequate coronary flow is unimportant since, in any 

 heart, a restriction of coronary flow below a critical 

 lc\el will decrease contractility (23). Rather, the.se 

 data indicate that when coronary flow is adequate, a 

 change in contractility can take place in which a 

 change in coronary flow is not the primary deter- 

 minant. 



Figure 4.4 shows the resuhs of an experiment in 



which changes in the end diastolic length of a selected 

 segment of left ventricular myocardium were re- 

 corded simultaneously with changes in L\'ED 

 pressure (58, 103). The left ventricular stroke work 

 was increased over a comparable range either by 

 increasing stroke volume while keeping aortic sys- 

 tolic pressure approximateh constant (solid lines), or 

 by increasing aortic pressure while keeping stroke 

 \olume approximately constant (dashed lines). When 

 stroke work was increased by increasing stroke 

 volume, both end diastolic pressure and end diastolic 

 segment length rose. When work was increased by 

 increasing aortic pressure there was little rise in end 

 diastolic pressure and a slight decrease in end diastolic 

 segment length. These data indicate that the ven- 

 tricular myocardium had, if anything, become 

 slightly less extensible, not more so, and that when 

 work was increased by increasing aortic pressure, the 



