A NONLINEAR POROELASTIC MODEL FOR THE TRABECULAR EMBRYONIC HEART

A theoretical model is presented for the primitive right ventricle of the stage 21 chick embryo. At this stage of development, the wall of t he heart is trabecular with direct intramyocardial blood flow. The mod el is a pressurized fluid-filled cylinder composed of a porous inner l ayer of isotropic myocardium and a relatively this nonlinear poroelast icity theory, modified to include residual strain and muscle activatio n. Correlating theoretical and experimental pressure-volume loops and epicardial strains gives first-approximation constitutive relations fo r stage 21 embryonic myocardium. The results from the model suggest th ree primary conclusions: (1) Some muscle fibers likely are aligned in the compact layer, with a fiber angle approximately + 10 deg from the circumferential direction. (2) Blood is drawn into the wall of the ven tricle during diastolic filling and isovolumic contraction and is sque ezed out of the wall during systolic ejection, giving a primitive intr amyocardial circulation before the coronary arteries form. As the hear t rate increases, the transmural blood flow velocity increases, but th e volume of blood exchanged with the lumen per beat decreases. (3) Res idual strain affects transmural stress distributions, producing nearly uniform stresses in the porous layer, where the peak end-systolic str ess occurs. These results improve our understanding of the relation be tween form and function in the developing heart and provide directions for biological experiments to study cardiac morphogenesis.