THE CONTROL OF THE FUNCTION OF THE HEART 



507 



1 r 



C.S.*48 



9u 



I 



E 



O CONTROL 



• STELL STIM 



H.R 154 /miN 



10 15 20 25 30 5 10 15 20 



INDICATED CHANGES IN FIBER LENGTH (LVE D ) 



FIG. 15 



1 1 1 r 



STELLATE STIMULATION 



► END-OIASTOLIC 



I END-DIAST0LIC-0050tns 



k ENO-DIASTOLIC -0-070 ms 



5 10 15 20 25 



INDICATED CHANGES IN FIBER LENGTH 



tricular contraction and the \cntricle will, under these 

 influences, contract more forcefully from any given 

 filling" or end diastolic pressure as shown in figures 1 3 

 and 14. The early studies of Anrep (3) and other 

 more recent studies (28, 29, 55, 96, 105) indicate 

 that a changed myocardial extensibility cannot, of 

 itself, account for the increased ventricular contrac- 

 tion. However, wliether or not the augmented stroke 

 work is produced solely by a more forceful contraction 

 from a given end diastolic fiber length, or whether a 

 change in the relation between \entricular end dias- 

 tolic pressure and fiber length contributes to the 

 observed augmentation, has only recently been es- 

 tablished (67). In figure 15 (left) cur\'es are shown 

 comparing the relation between changes in left 

 ventricular diastolic pressure and simultaneous 



changes in myocardial segment length at the end of 

 diastole (after atrial systole) before and during stel- 

 late stimulation in four dogs. Figures on abscissae 

 represent millimeter deflection on tracing. \ i-mm 

 segment length change was equal to a 6-mm tracing 

 deflection. The relation between left \entricular end 

 diastolic pressure and segment length is unmodified 

 by stellate stimulation at the heart rates studied. 

 The same results were obtained when plotting the 

 pressure-length curves from points in diastole prior 

 to atrial systole (at or near equilibrium) before and 

 during stellate stimulation when an adequate dias- 

 tolic period was present (67). 



It must, however, be emphasized that the rela- 

 tion between ventricular pressure and myocardial 

 segment length at end diastole may involve factors 



