FUNCTIONAL ANATOMY OF CARDIAC PUMPINC 



779 



in the next lower band, where P.S. stands for proto- 

 systole and P.D. for protodiastole. The lowest band 

 of the upper margin, R, illustrates the time difference 

 between the activities of the right and left heart. A 

 number of points warrant brief comments. For all 

 intracardiac and arterial pressures a common zero is 

 used. The "low" pressure events (left atrium, right 

 ventricle, and pulmonary artery) are plotted on a 

 scale from o to 45 mm Hg (left), whereas the "high" 

 pressure events (left ventricle and aorta) are graphed 

 on a scale from o to 150 mm Hg (right). The use of 

 two different pressure scales for correlating simul- 

 taneous events on the same time basis results in 

 different slopes. The casual viewer may hastily con- 

 clude that the rate of pressure rise during isovolu- 

 metric contraction is greater in the right ventricle 

 than in the left ventricle, which is actually not the 

 case. Correspondingly, the pressure drop during 

 ventricular isovolumetric relaxation appears to occur 

 faster on the right than on the left side, which does not 

 happen either. The ascending limbs of the aortic and 

 pulmonary arterial pressure curves have been obtained 

 from overdamped recording systems, such as often 

 happens with long catheters. This might explain 

 why the tracings of the arterial pressures have gentle 

 slopes and remain considerably below the summits of 

 the ventricular pressure curves. An interesting 

 innovation is the protosystolic phase (P.S.) which 

 apparently extends from the leveling off of the left 

 atrial A wave until the beginning of the left ventricu- 

 lar pressure rise. It seems to correspond to the con- 

 ventional Z point. According to the tracings in figure 

 19, the protosystolic phase appears to be timewise 

 closely related to the electrocardiogram. It seems to 

 last from the beginning of the Q wave until the tip of 

 the R wave. The usefulness of introducing this 

 distinctly different phase seems to lie in the easy 

 correlation of certain characteristics of the phono- 

 cardiogram and vibrocardiogram with the cardiac 

 cycle during this time interval. 



A number of other cyclical events occurring in the 

 circulatory system also can be more or less accurately 

 correlated with the cardiac cycle. Examples would 

 be: various peripheral arterial and venous pressure 

 pulse curves as well as flow pulse curves; intra- 

 myocardial pressures (96); the ballistocardiogram; 

 electrokymogram (42, 163, 135); angiokymogram 

 ( 147); angiocardiogram; cardiorheogram (3, 68); and 

 heart sounds [Luisada et al. (105)]. In all cases the 

 previously mentioned difficulties in precise timing 

 must be given serious scrutiny. A discussion of all 



events which lend themselves to correlation would 

 exceed the scope of this chapter. 



FUNCTION OF THE HEART VALVES 



Valves are essential for efficient action of all 

 reciprocating pumps in order to maintain unidirec- 

 tional flow. Valves must offer a minimal impedance 

 to flow, yet be able to close abruptly with minimal 

 leakage and minimal displacement. The heart dif- 

 fers from a mechanical pump in that a perfect seal 

 must be obtained in orifices which are continuously 

 changing in shape, size, and position throughout 

 the cardiac cycle. Therefore, the valves must be 

 somewhat larger than the area to be covered in order 

 to remain competent under all normal working 

 situations. The heart valves are also located in 

 orifices beyond which the blood enters wider 

 chambers. This provides for a rapid stream along 

 the axis of the orifice, with decrease in lateral pressure 

 at, and just beyond, the restricted valvular plane 

 (Bernoulli effect) and possibly the production of 

 eddy currents. This mechanism keeps the valves 

 floating in the blood stream and insures rapid ap- 

 proximation of the valve leaflets as soon as the axial 

 stream of blood ceases. 



The movements of the atrioventricular and semi- 

 lunar valves are passive since the valve leaflets do 

 not contain muscle fibers [see also Moritz (116)]. 

 The consideration of this aspect is important because 

 it is easier to replace passive structures by protheses 

 than it is to create protheses for active structures 

 such as muscles. It is also possible to investigate the 

 forces involved in the movement of passive structures 

 by observing the function of a prothesis which simu- 

 lates a natural organ in suitable physical analogues. 

 Davilla (36) summarizes this trend of thought as 

 follows: "The most successful protheses have been 

 those which fulfill a passive role in the functional 

 complex: a metal plate on the skull, a nail in a long 

 bone, steel or plastic mesh in a weak abdominal wall, 

 a tube of cloth to replace a blood vessel. . . . Fortu- 

 nately, the role of the cardiac valves in hemodynamics 

 is a passive one. They are not parts that move but 

 parts which are moved. Their role is identical to that 

 of a simple check valve. It is their environment which 

 complicates the matter. They are immersed in flowing 

 tissue which is chemically unstable but which must 

 not be subjected to extreme unbalance; which pos- 

 sesses a clotting mechanism that must not be activated 

 by the valve; and which transports vital cells that 



