FUNCTIONAL ANATOMY OF CARDIAC PUMPING 



789 



fig. 23. Relationship of ventricular volume (VV) and body 

 weight (BW) in dogs. Ventricular volume measured at the 

 equilibrium state (zero transmural pressure). [See also fig. 2 

 (Horres et al., unpublished obser%'ations).] 



(77) the average functional residual capacity of the 

 left ventricle would be approximately 30 ml for 

 dogs weighing 12 kg. According to Gribbe et al. 

 (57), it is only 5 ml. The discrepancy between Holt's 

 and Gribbe's measurements in terms of ventricular 

 diastolic suction is illustrated in figure 24. If Holt's 

 data are correct, ventricular diastolic suction never 

 occurs under normal conditions. On the contrary 

 Gribbe's figures speak for the occurrence of diastolic 

 ventricular suction during all phases of diastole. 

 Obviously the controversy cannot be resolved on 

 the basis of presently available data. 



There has been some speculation about the pos- 

 sible nature of the frontal force, particularly whether 

 it originates from an active or a passive process. 

 An active process would be the contraction of muscle 

 fibers which, owing to their anatomical arrangement, 

 could widen the ventricular cavity during diastole 

 [Guasp (58)]. There is no experimental evidence to 

 support such a view. Another active process would 

 be the development of a force acting to lengthen the 

 muscle fibers upon completion of their contraction 

 ("active decontraction"). However, it has never 

 been satisfactorily demonstrated that processes of 

 energy conversion from chemical to kinetic energy 

 occur during muscular relaxation [Villa (152); 

 for review, Brecher (19, 20)]. The most acceptable 

 evidence is, at present, that the diastolic ventricular 

 vis a fronte is caused by passive processes, such as 

 one of the following, a) During systole an interfas- 

 cicular tension develops through shear forces be- 

 tween myocardial strands which contract to different 

 extents and asynchronously [details in Rushmer 

 (•39)]- f>) During systole noncontractile elements in 



the heart and possibly also some components of the 

 muscle fibers are elastically deformed beyond their 

 equilibrium state, thereby storing potential energy 

 which is released through elastic recoil during diastole 

 (see fig. 2). c) In the closed-chest mammal, additional 

 external forces residing in the elastic recoil of the 

 lungs exert their effect upon the heart by tending to 

 expand the cardiac cavities beyond the size these 

 cavities would assume in the absence of the lung 

 forces. 



In conclusion, some of the classical views concern- 

 ing the filling of the heart may need revision. The 

 ventricle acts as a reciprocating pump in which the 

 output stroke simultaneously provides energy for 

 the filling of the pump for the next stroke. In other 

 words, the heart does not act merely as a pressure 

 pump as William Harvey (66) believed, but it actu- 

 ally functions as a pressure-suction pump [see also 

 Gauer, (52, 53)]. The amount of energy necessary 

 for pump filling is, however, only a fraction of that 

 needed for ejection, since the filling occurs through a 

 fluid transfer into a low resistance system in which 

 small pressure differences will cause a rapid flow of 

 large amounts of blood. 



DIFFERENCES BETWEEN RIGHT AND 

 LEFT CARDIAC CAVITIES 



Functional differences between the right and left 

 cardiac cavities can be expected from their anatom- 

 ical characteristics. Yet it had long been tacitly 

 assumed that the two atria and the two ventricles 

 initiate and terminate their contraction simultane- 

 ously, and that a description of cardiac events on 

 both sides would be redundant. 



In fact, there are significant differences between 

 the left side and the right side chambers [see also 

 Katz (89), Hamilton et al. (62), Luisada & Fleischner 

 (103), Segers (145), Braunwald et al. (16), McKusick 

 (109)]. For instance, at equal pressures the right 

 atrium has a volume twice that of the left atrium, 

 which is thicker and less distensible than the right 

 (99). Experimentally, the volume-pressure curve 

 relationship in the left atrium has been found to be 

 linear only as long as the pressure remains within 

 the normal limits (pressure below 150 mm H 2 0). 

 When this limit is exceeded, a slight increase in 

 volume causes a much larger increase in pressure. 

 The normal level and patterns of pressure also 

 differ somewhat between the right and the left 

 atrium. The A wave of the right atrium, produced 



