Pressures within Right and Left Ventricles. 145 



can be increased beyond their normal capacity either (a) by an 

 increased initial pressure overcoming the inherent tendency of 

 the ventricles to resist stretching, or (b) by a reduction of this 

 inherent power of the ventricle to resist stretching, i.e., by a 

 reduction of tonus. 1 



According to the hypothesis of Patterson, Piper and Starling 

 it would be necessary to assume that an augmented venous return, 

 for example, causes a prompt reduction of tonus. Our entire 

 experience teaches us, however, that the degree of tonus in a 

 muscle of any type is not capable of being rapidly changed; on 

 the contrary, such changes occur very slowly. The results of 

 Patterson, Piper and Starling, corroborated in my own work, 

 indicate, however, so prompt a response on the part of the ventricle, 

 as to make this almost presumptive evidence against the view 

 that tonus changes are primarily or chiefly concerned. To supply 

 quite certain proof that such changes are, on the other hand, 

 associated with and probably due to simultaneous changes in 

 initial tension requires a careful study of the pressure changes in 

 the right and left ventricles during the early response of the right 

 heart to changes in venous inflow and arterial resistance. 



II. Experimental Results. 



The venous inflow into the right heart of intact animals was 

 increased by allowing a graded inflow of normal saline into the 

 jugular vein. Increased arterial resistance was produced, in 

 experiments here reported, by partial compression of the thoracic 

 aorta. Records of right and left intraventricular pressures were 

 synchronously recorded by optical manometers. The results of 

 17 such experiments may be briefly summarized: 



1. Effects of Saline Infusion. — Beginning with the very first 

 beat when the initial (diastolic) volume of the heart increases, 

 after such saline infusion has started, the initial tension in the 



1 To prevent misunderstanding, it should be noted that I define the term "tonus" 

 as that partial state of contraction which persists during diastolic rest, and by virtue 

 of which muscle resists stretching. The statement of Patterson, Piper and Starling, 

 that tonus is "synonymous with the physiological condition or fitness of the muscle 

 and its measure is the energy set free per unit length of muscle fiber at each contrac- 

 tion of the heart," I believe, expresses the end effects of tonus changes but does not 

 describe the nature of the tonus phenomenon itself. 



