Epicardial Strains inEmbryonic ChickVentricle atStages 16Through 24

Embryonic cardiac development depends, inpart, onthelocal biomechanical environment. Tracking themotions ofmicrospheres attached totheembryonic chick ventricle, we computed two-dimensional epicardial strains atHamburger- Hamilton stages 16,18,21,and24(2.5, 3.5, 4.0, and4.5days, respectively, ofa21-day incubation period). First, inacross- sectional study, strains weremeasured inseparate embryos at eachstage (n.19perstage). Then, inalongitudinal study, strains weremeasured serially onthesameheart, withtheeggs resealed andreincubated between successive stages (n.4per stage). Although theheart undergoes major changes inmass, morphology, andloading during thestudied stages, both studies showedthatpeakcircumferential andlongitudinal strains relative toenddiastole weresimilar inmagnitude (0.13 to0.16) anddidnotchange significantly across thestage range. Thepeakprincipal strains also showed nosignificant changes, withmagnitudes ofz0.11 and0.18. Theshear strains were small, andtheir signs varied fromoneheart toanother. These results suggest that wall strain ismaintained within arelatively narrowrangeduring primary cardiac morphogenesis. (Circ Res.1994;75:896-903.)