Relationship between diastolic shape (eccentricity) and passive elastic properties in canine left ventricle

This study was designed to investigate the relationship between left ventricular (LV) eccentricity, volume, and passive elastic properties. Eight open-chest fentanyl-anesthetized dogs were instrumented with an LV micromanometer, a remote-controlled mitral valve occluder, and two pairs of ultrasonic crystals to measure anterior-posterior and base-apex dimensions. We identified the presence of elastic recoil forces with negative LV diastolic pressure in nonfilling diastoles (end-systolic volume clamp). Using linear regression analysis we related midwall eccentricity to volume in nonfilling diastoles at the time of LVP(min) and at end diastole, and in normal beats at end systole at LVP(min) and at end-diastole. Intersection of the end-systolic and end-diastolic lines (transitional volume, V(t) = 38.0 + 6.4 ml) divides cycles with and without the presence of elastic recoil forces. V(t) is analogous to the equilibrium volume (V₀), determined as the volume intercept of the logarithmic passive pressure-volume (P-V) relationship using LV volume estimated from LV weights (V(0nl) = 37.6 + 4.4 ml), or the volume intercept of the linearized P-V relationship calculated from a prolate spheroidal model using measured minor and major diameters (V01 = 44.5 ± 3.5 ml). Linear regression analysis was also used to relate the square of peak mitral flow (MF²) with the corresponding atrioventricular pressure gradient (ΔP); the slope represents a dissipative constant for the cycles without, P = 0.00058(MF)² + 0.35 (n = 48, r = 0.73), and with elastic recoil P = 0.00035(MF)² + 0.21 (n = 24, r = 0.81). We conclude that shape changes are related to the elastic forces in the ventricle; V(t) is a manifestation of the V₀ on the eccentricity-volume plane; and the presence of elastic recoil forces in a small ventricle facilitates filling by decreasing the energy losses across the mitral valve.