ABSTRACT
Ventricular diastolic function is a complex process. Three of its major components are relaxation, passive filling, and atrial contraction. Relaxation is an active, energy-requiring process during which calcium is removed from the actin-myosin filaments, causing contracted muscle to return to its original length. Relaxation properties are dynamic and are normally transiently enhanced during physical exertion. In disease states (eg, hypertension, ischemia), relaxation rates may not be able to augment or may even worsen. After active relaxation, filling of the ventricle continues along the pressure gradient from the left atrium to the left ventricle (passive filling). The amount of filling during this phase is determined by left atrial pressure and left ventricular compliance; compliance is the increase in ventricular volume per unit of driving pressure. Thus, abnormally low compliance impairs filling and produces high end-diastolic pressure. Ventricular filling is also affected by the duration of diastolic filling. The contribution from atrial contraction further increases ventricular volume by as much as 15% to 20% in normal subjects and 45% to 50% in those with abnormal ventricular relaxation and passive filling (Table 3-30).
