Robert P. Thompson

HH Stage 22 chick heart inflated ex ovo with perfusate containing propidium iodide (red) and 3000 MW dextran (green), viewed here in left sagittal plane by confocal microscopy of acrylamide slab sections. Stretch‐sensitive membrane leaks were conspicuous along subendocardial trabeculae near the apex of the looped ventricle (bottom) and along inner wall of AV canal (inset), indicating peak strain of inner wall myocytes as modeled and measured by Damon et al., Developmental Dynamics 238:1535–1546.

The hypothesis that inner layers of contracting muscular tubes undergo greater strain than concentric outer layers was tested by numerical modeling and by confocal microscopy of strain within the wall of the early chick heart. We modeled the looped heart as a thin muscular shell surrounding an inner layer of sponge‐like trabeculae by two methods: calculation within a two‐dimensional three‐variable lumped model and simulated expansion of a three‐dimensional, four‐layer mesh of finite elements. Analysis of both models, and correlative microscopy of chamber dimensions, sarcomere spacing, and membrane leaks, indicate a gradient of strain decreasing across the wall from highest strain along inner layers. Prediction of wall thickening during expansion was confirmed by ultrasonography of beating hearts. Degree of stretch determined by radial position may thus contribute to observed patterns of regional myocardial conditioning and slowed proliferation, as well as to the morphogenesis of ventricular trabeculae and conduction fascicles. Developmental Dynamics 238:1535–1546, 2009.