OUTPUT OF HEART AND VENOUS INFLOW 



217 



have to become more dilated (i.e., more stretched) during diastole than 

 would a normal heart. If this condition is maintained, the muscle hyper- 

 trophies with the result that less diastolic dilatation becomes necessary 

 because of the cumulative effect of the larger number of fibers. Increase 

 in arterial pressure within certain limits does not affect the amount of 

 the systolic discharge so long as the inflow is kept constant. 



It will be observed in the preceding paragraph that nothing is said 

 about the tension of the musculature at the beginning of systole; only its 

 length is considered to be important. More recent work by Straub and 

 Wingers 61 shows however that in this particular Starling has erred and 



BP 



VP 



Fig. 63. It will be observed that when V.P. is suddenly increased, the cardiac volume im- 

 mediately becomes greater (indicated by a general fall in the level of C), and that, although the 

 contractions of the ventricle also become more vigorous, they do not do so with sufficient prompti- 

 tude to maintain the systolic volume constant. In other words the output of the heart does not at 

 first keep pace with the inflow, so that the mean volume of the heart becomes progressively 

 greater, and it is onjy after some moments that the contractile power -increases sufficiently so 

 that the output equals the inflow and the mean volume becomes steady. 



the latter investigator has pointed out that this is probably due to the 

 fact that a heart-lung preparation is too artificial (e.g., the coronary 

 blood flow is certainly abnormal and the pericardium is usually opened) 

 to represent the conditions actually obtaining in the intact animal. The 

 advantage claimed for the preparation was that the rate of heart could 



