79° 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



fig. 24. Functional residual capacity 

 of the clog's ventricle and its relation to 

 ventricular diastolic suction. Lejt: data 

 derived from Holt (77), assuming that a 

 functional residual capacity of 50 ml in 

 a 20.9-kg dog corresponds to 30 ml in 

 a 12-kg dog (regression line of fig. 23). 

 Right: data of Gribbe et al. (56) for a 

 12-kg dog. Center: elastic equilibrium 

 state of the ventricle in a 12-kg dog 

 (Horresf/ al., unpublished observations). 



FUNCTIONAL RESIDUAL CAPACITY 



HOLT 

 (in vivo) 



t 



NO 



SUCTION 



I 



I 

 I 



NEUTRAL POSITION 



I 



(ELASTIC EQUILIBRIUM; 



I 



I 

 SUCTION 



HORRES et al, 

 (in vitro) 



FUNCTIONAL RESIDUAL CAPACITY 



GRIBBE et al . 

 (in vivo) 



ml 

 30 



by atrial systole, is often not so steep and tall as that 

 of the left atrium, and normally precedes it slightly. 

 The peak of the right atrial V wave is usually lower 

 than that of the left atrial V, and the mean right 

 atrial pressure is usually less than the left atrial 

 pressure. 



At the level of the ventricles the bundles of myo- 

 cardial fibers which encircle the two cavities, much 

 as the windings of a turban, belong to a common 

 anatomical structure. The combined effect of their 

 contraction is to wring blood out of the ventricular 

 chambers into the respective arteries. Yet the mus- 

 cular arrangement is such that contraction of the 

 left ventricle produces primarily a reduction in the 

 lateral diameter with only a moderate shortening 

 along the vertical axis, whereas on the right side 

 there is much ventricular shortening between apex 

 and base with relatively less pulling of the free wall 

 toward the septum. The mechanical effects of left 

 ventricular contraction occur a trifle earlier than 

 those of right ventricular contraction, since the rise 

 in right ventricular pressure usually lags by 0.01 

 to 0.02 sec behind the rise in left ventricular pressure 

 (see also fig. 19). It is, therefore, understandable 

 that mitral valve closure usually precedes tricuspid 

 valve closure. Nevertheless, it is by no means es- 

 tablished whether the later start of right ventricular 

 contraction is the only cause of asynchronicity. 

 Other factors could also operate, such as a faster 

 rate of contraction of the left ventricular wall or a 

 quicker reaction of the mitral cusps to the rising 

 wave of pressure in comparison with the tricuspid 

 valve. The characteristics of the vascular bed into 



which ejection proceeds cause differences in the se- 

 quence of pumping events on the right and on the 

 left side. Since the pressure in the pulmonary artery 

 is low (low resistance to flow in the pulmonary vas- 

 cular bed), the pulmonary valve opens first. Indeed, 

 for an interval of about 0.02 sec, the ventricular 

 contraction produces an ejection on the right side 

 while there is still an isovolumetric pressure rise 

 on the left side. Similarly, right ventricular ejection 

 continues well after cessation of left ventricular ejec- 

 tion. In other words, the end of left ventricular 

 systole precedes that of the right and closure of the 

 aortic valve precedes closure of the pulmonary valve. 

 On the other hand, because of a much longer phase 

 of isovolumetric relaxation in the left ventricle as 

 compared to the right, the opening of the mitral 

 valve is thought to follow that of the tricuspid, as 

 seen in table 1, which is borrowed from Luisada & 

 Liu (104) and summarizes the sequence of events of 

 right and left ventricular contraction (see also figs. 

 18 and 19). 



Because of these differences in the pumping action 

 of the ventricles, reference is often made to right 

 and left ventricles as being a ''volume pump" and 

 "pressure pump," respectively. Implied in this no- 

 menclature are the facts that the right ventricle 

 can easily handle an increase in volume output with- 

 out apparent strain, whereas it is not so well equipped 

 for raising its pressure to a high level. On the con- 

 trary, the left ventricle, with a much larger mass 

 of active musculature and a more nearly spherical 

 geometry is better able to face an increase in out- 

 flow resistance than the right ventricle. What is 



