EPICARDIAL STRAINS IN EMBRYONIC CHICK VENTRICLE AT STAGE-16 THROUGH STAGE-24

Embryonic cardiac development depends, in part, on the local biomechan ical environment. Tracking the motions of microspheres attached to the embryonic chick ventricle, we computed two-dimensional epicardial str ains at Hamburger-Hamilton stages 16, 18, 21, and 24 (2.5, 3.5, 4.0, a nd 4.5 days, respectively, of a 21-day incubation period). First, in a cross-sectional study, strains were measured in separate embryos at e ach stage (n greater than or equal to 19 per stage). Then, in a longit udinal study, strains were measured serially on the same heart, with t he eggs resealed and reincubated between successive stages (n greater than or equal to 4 per stage). Although the heart undergoes major chan ges in mass, morphology, and loading during the studied stages, both s tudies showed that peak circumferential and longitudinal strains relat ive to end diastole were similar in magnitude (0.13 to 0.16) and did n ot change significantly across the stage range. The peak principal str ains also showed no significant changes, with magnitudes of approximat e to 0.11 and 0.18. The shear strains were small, and their signs vari ed from one heart to another. These results suggest that wall strain i s maintained within a relatively narrow range during primary cardiac m orphogenesis.