Ventricular Compliance

As the ventricle fills with blood, the pressure and volume that result from filling are determined by the compliance of the ventricle. Normally, compliance curves are plotted as the change in volume (ΔV) over the change in pressure (ΔP). For the ventricle, however, it is common to plot ΔP versus ΔV (see Figure). Therefore, the slope of the relationship is the reciprocal of the compliance, which is sometimes referred to as ventricular "stiffness."

The compliance of the ventricular is determined by the physical properties of the cardiac muscle and other tissues making up the ventricular wall as well as by the state of ventricular contraction and relaxation. For example, in ventricular hypertrophy the ventricular compliance is decreased (i.e., the ventricle is "stiffer"), therefore, ventricular end-diastolic pressure (EDP) is higher at any given end-diastolic volume (EDV) (see Figure). Alternatively, at a given EDP, a less compliant ventricle would have a smaller EDV (i.e., filling will be impaired). If ventricular relaxation is impaired (as occurs in some forms of heart failure), the functional ventricular compliance is also reduced (because of residual active tension), which will also impair ventricular filling. In a disease state such as dilated cardiomyopathy, the ventricle becomes very dilated without appreciable thickening of the wall. This dilated ventricle will have increased compliance as shown in the figure; therefore, although the EDV may be very high, the EDP may not be greatly elevated.

Revised 04/04/07