ABSTRACT
Heart valve function is primarily governed by the pressure gradients across the valves during dierent cardiac phases, although other active mechanisms have been implicated. During diastole, the ventricular lling phase, the mitral and tricuspid valves open due to higher atrial pressure than the pressure in the relaxed ventricle, thus allowing diastolic lling of both the ventricles. e aortic and pulmonary valves are closed in this phase due to higher pressure in the aorta and pulmonary artery, respectively. Next, as the ventricles contract, ventricular pressure builds up, reaching rst the pressure required for closing the atrioventricular valves, and then the pressure required to open the semilunar valves. e period of build up between these two pressures is the isovolumetric contraction phase, where all four valves are closed. During systole, high pressures in the ventricles open the aortic and pulmonary valves, allowing ejection of blood into the arterial tree and the lungs, respectively. Following this, the ventricles relax, reducing pressures, rst, to that slightly lower than in the arteries, when the semilunar valves close, and then second, to that slightly lower than that in the atria, when the atrioventricular valves open. e period of reduction of pressures between these two points is known as the isovolumetric
9.1 Introduction ...................................................................................... 9-1 9.2 Aortic Valve ....................................................................................... 9-3
Valve Structure • Valve Function • Valve Disease and Treatment 9.3 Pulmonary Valve ............................................................................ 9-10
Valve Structure • Valve Function 9.4 Mitral Valve ..................................................................................... 9-12
References .................................................................................................... 9-24
relaxation, when, again, all four valves are closed. e typical pressure and ow curves and the relative durations of all the phases in the cardiac cycle for the aortic and mitral valves are shown in Figure 9.2.
