Measurements of the viscoelastic and heterogeneous response of the passive stage 18 embryonic chick heart

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references (leaves 84-86).Issued also on microfiche from Lange Micrographics.During embryonic development, the heart undergoes remarkable morphological changes due to genetic programming and epigenetic influences such as mechanical loads. L.A. Taber and colleagues at Washington University have proposed mathematical models, based on theories of poroelasticity, nonlinear viscoelasticity, and finite elasticity, to aid in understanding the mechanics of cardiac development. Testing and refining these models, particularly the inherent constitutive relations, require data, however, which are scant. In collaboration with Prof. Taber, therefore, we have developed a computer-controlled system for quantifying the multi-axial regionally dependent mechanical response of the embryonic chick heart to controlled distension pressures, which has not been accomplished heretofore. The objectives of this study were to validate the use of this device for reliable data collection, and to identify characteristics of the multi-axial, regional mechanical response of the passive stage 18 embryonic heart. The first objective involved quantifying the viscous losses within the system, identifying the resolution of the collected data, and performing pilot studies on basilar arteries. Analysis of the device indicated that flow rates should be kept low (~0.5 [u]L/min) to avoid inaccuracies in the pressure measurements due to viscous losses. The resolutions of the strain and pressure measurements were adequate (~0.03 and 0.01 mmHg respectively) and the device performed reliably in the final configuration. The second objective involved quantifying the mechanical response of the hearts through step loading and cyclic inflation tests. The results from a cohort of 8 to 10 hearts indicate that the stage 18 heart exhibits marked viscoelasticity and heterogeneity, with smaller deformations occurring in the inner region of curvature of the looped heart than in the other regions. These experiments enhanced our understanding of the mechanics of the embryonic heart by delineating the general characteristics of its response to passive inflation, and suggested that the material assumptions of pseudoelasticity and homogeneity used in past models of the developing heart may not be valid. Evaluation of the material properties from these data, using finite element models to handle the complex geometry of the heart, should be the next step towards establishing a theoretical framework for future models of the embryonic heart