Validation of different methods to compare isovolumic cardiac function in isolated hearts of varying sizes

Functional comparison of isolated hearts with different sizes has been difficult because function varies at different ventricular volumes. To date, no standard volume has been established. To determine the most accurate experimental approach, we tested five different methods to standardize volume in control hearts with different sizes but similar papillary muscle function and in hearts with concentric hypertrophy: intracardiac balloon volume (VB) = 120 microliters (M1). VB at diastolic pressure = 10 mmHg (M2) or diastolic wall stress = 4 kdyn/cm2 (M3), V1 = 25 microliters/100 g body weight (M4) and VB = 50% of volume at peak developed pressure (Vmax; M5). Systolic and diastolic functions of control groups were different using M1 and comparable using M2 or M5. M3 and M4 showed borderline significant differences. We concluded that M5 and M2 were suitable to compare function among hearts of different sizes. If diastolic compliance is of interest, as in concentric hypertrophy, parameter-volume curves should be normalized by Vmax to compare function at corresponding points of the Frank-Starling curve (e.g., at 50% of Vmax, M5).