Distributed mechanics of the canine right ventricle: effects of varying preload

Fundamental questions in the mechanics of the right ventricle (RV) include: what are the distributions of diastolic and systolic strains across the RV epicardium and how do these strains change with increasing preload? Arrays (approximately 4 x 4 cm) of 25 to 30 lead markers were sutured to the epicardium of the RV anterior free wall in 6 open-chest, anesthetized dogs. Biplane cinéradiography (16 mm, 120 fps) was used to track marker positions throughout the cardiac cycle as loading conditions were altered by intravenous volume infusion. Continuous two-dimensional nonhomogeneous deformations were estimated across the region by fitting high-order finite element surfaces to the three-dimensional marker coordinates in successive ciné frames. End-systolic strains referred to end-diastole did not change with increasing preload, but did exhibit considerable longitudinal variation, e.g. the principal strain associated with maximal shortening (E1) was more than twice as great nearer the apex (E1 = -0.18 +/- 0.08) than in more basal (E1 = -0.09 +/- 0.05) regions. However, large amounts of lengthening occurred during diastolic inflation. End-diastolic extensional strains referred to an unloaded configuration were moderate at low pressure (E2 = 0.13 +/- 0.08) but increased to large values at high preloads (E2 = 0.28 +/- 0.11). End-diastolic strains also showed considerable longitudinal variation, i.e. near the base lengthening (E2 = 0.31 +/- 0.13) tended to be much greater than near the apex (E2 = 0.15 +/- 0.12). These results indicate that both diastolic sarcomere lengths and systolic sarcomere shortening increase in proportion to diastolic loading leaving end-systolic sarcomere strains unchanged.