FUNCTIONAL ANATOMY OF CARDIAC PUMPING 



79' 



table i . The Cardiac Cycle. Time Intervals Between 

 Valvular Motions (Normal Dogs) 



Event 



Q wave (ECG) 

 Closure of mitral valve 

 Closure of tricuspid valve 

 Opening of pulmonic valve 

 Opening of aortic valve 



Closure of aortic valve 

 Closure of pulmonic valve 

 Opening of tricuspid valve 

 Opening of mitral valve 

 Rapid filling of right ventricle 

 Rapid filling of left ventricle 



Each peak of rapid ventricular filling follows A-V valve 

 opening by 0.08-0.10 sec, and the closure of the respective 

 semilunar (i.e., pulmonary or aortic) value by 0.12-0. 18 

 sec. This table shows the sequence of events in normal, 

 large dogs, whose figures are probably very close to those of 

 normal man. [From Luisada & Liu (104).] 



meant by the terms "volume pump" and "pressure 

 pump" is actually "low-pressure head pump" and 

 "high-pressure head pump." 



There is no fundamental difference in the pump- 

 ing action of the two ventricles before birth. They 

 both receive blood from a common atrial chamber, 

 their walls are of the same thickness, they have the 

 same capacity, and they both eject their contents 

 into a common aortic chamber via either the ductus 

 arteriosus or the ascending aorta. The pressure against 

 which the fetal ventricles eject their contents is lower 

 than that in the adult systemic circuit, but after 

 birth the resistance in the lesser circuit drops sud- 

 denly with the first breath, whereas that in the sys- 

 temic circuit gradually increases. The difference 

 in pumping action that prevails in the normal adult 

 exists essentially because of the difference in resist- 

 ance to flow. 



In the adult the resistance to flow in the pulmonary 

 vascular bed is estimated to be only about one- 

 eighth of that in the systemic circulation. On the 

 other hand, it is estimated that a sizable amount of 

 the mechanical energy, both pressure and kinetic, 

 imparted to the blood by left ventricular ejection 

 is still available at the point of venous inflow into 

 the right ventricle, and is partly responsible for right 

 ventricular filling and distention during diastole 

 (vis a tergo). Connecting these two observations, 

 one may wonder whether right ventricular contrac- 

 tion is necessary at all, or whether the left ventricle 

 alone could not only circulate the blood through the 

 systemic vascular bed but also through the pulmonary 



vascular bed. The problem has been approached in 

 different ways. It was first observed that major de- 

 struction of the right ventricular wall (by cauteriza- 

 tion, for instance) causes but slight changes in sys- 

 temic venous and arterial pressure [Bakos (5), 

 Kagan (86)]. Yet a doubt remains, since some inner 

 layers of the right ventricular wall are left intact 

 in such experiments, and conceivably contractions 

 of muscular bundles, which belong to the left ven- 

 tricular wall, could still pull on passive strands of 

 the remaining right ventricular wall and thus in- 

 directly eject blood through the pulmonary ostium. 

 In such a case, the noncontracting cauterized re- 

 mainder of the right ventricular wall would passively 

 compress the half-moon-shaped right ventricular 

 cavity. Also, the still intact, powerful ventricular 

 septum could contribute to the right ventricular 

 systolic pressure rise. Acute experiments in which the 

 entire heart is arrested and only the left ven- 

 tricle, but not the right, is replaced by a mechanical 

 pump, indicate that apparently stable circulatory 

 conditions in both the systemic and the pulmonary 

 vascular beds can be maintained using a single "left 

 ventricle" pump [see also Rodbard & Wagner 

 (137), Jamison et al. (85), Warden et al. (154), 

 Patino (•/ al. (127), Xuland et al. (121), Monod- 

 Broca (115), Glenn (55)]. Obviously, the pressure 

 in the vena cava is then raised to maintain sufficient 

 pressure for the pulmonary circulation, and there 

 may be an impairment to cerebral, coronary, and 

 hepatic venous outflow. However, the conditions are 

 compatible with survival of the animal. The question 

 is not solely of academic interest, since it is not im- 

 possible to envision that some day surgical tech- 

 niques will be devised to drain the entire systemic 

 venous return directly into the pulmonary artery, 

 thereby placing the entire load of circulation on the 

 left ventricle. 



the pericardium 



The function of the pericardium in the cardiac 

 pumping process has been the subject of much de- 

 bate. Some authors consider that the pericardium 

 does not affect cardiac performance, because con- 

 genital absence of this structure in man is compat- 

 ible with maintenance of a seemingly normal cardiac 

 function [see Ellis et al. (43) and Hering et al. (74)]. 

 Others have speculated that the primary function of 

 the pericardium is to confine in space the pumping 

 structures which are characterized by their expansi- 



