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1 Cardiac Sciences, University of Calgary, Calgary, Canada; Physiology and Biophysics, University of Calgary, Calgary, Canada; Libin Cardiovascular Centre, University of Calgary, Calgary, Canada
2 Civil Engineering, University of Calgary, Calgary, Canada
* To whom correspondence should be addressed. E-mail: kcagibbo{at}ucalgary.ca.
During pulmonary artery constriction (PAC), an experimental model of acute RV pressure overload, the inter-ventricular septum flattens and inverts. Finite Element (FE) analysis shows that the septum is subject to axial compression and bending when so deformed. This study examines the effects of acute PAC on the LV freewall, and the role the pericardium may play in these effects. In 8 open-chest anaesthetized dogs, LV, RV, aortic, and pericardial pressures were recorded under control conditions and with PAC. Model dimensions were derived from 2-D echocardiography minor-axis images of the heart. At control (pericardium intact), FE analysis showed that the septum remained concave to the LV, stresses in the LV, RV and septum were low, and the pericardium was subject to circumferential tension. With PAC, RV end-diastolic pressure exceeded LV pressure and the septum inverted. Compressive stresses developed circumferentially in the septum out to the RV insertion points, forming an arch-like pattern. Sharp bending occurred near the insertion points, accompanied by flattening of the LV free wall. With the pericardium removed, the deformations and stresses were different. The RV became much larger, especially with PAC. With PAC the arch-like circumferential stresses still developed in the septum, but their magnitudes were reduced, compared with the pericardium-present case. There was no free-wall inversion and flattening was less. From these FE results, the pericardium has a significant influence on the structural behaviour of the septum, the LV and RV free-walls. Further, the deformations of the heart are dependent on the presence or absence of the pericardium.
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