Biomechanical comparison of human pulmonary and aortic roots

OBJECTIVE: Significant dilation of the pulmonary autograft is problematic after the Ross operation and may require reoperation. Pulmonary autograft remodelling occurs in response to the immediate rise in pressure and consequently wall stress. Stress–strain response of the pulmonary root plays an important role in understanding autograft function and remodelling following the Ross procedure. However, limited data are available on mechanical properties of fresh human pulmonary roots. The aim of this study was to compare mechanical properties of fresh human pulmonary and aortic roots prior to the Ross operation. METHODS: Fresh healthy human hearts (n= 21) were obtained from California Transplant Donor Network (Oakland, CA). Five regions of pulmonary and aortic roots, anterior and posterior artery and three sinuses, were subjected to displacement-controlled equibiaxial stretch testing within 24 h of cross-clamp time. Different regions of pulmonary and aortic roots were compared using a paired-comparison approach based on tissue stiffness at systemic pressure. Furthermore, histologic analysis was performed to compare the fibrous structure of pulmonary and aortic roots. RESULTS: Human pulmonary and aortic roots demonstrated nonlinear response to biaxial loading in both circumferential and longitudinal directions. Pulmonary artery was found to be significantly stiffer than ascending aorta at systemic pressure in the two principal directions (P< 0.001). Similarly, pulmonary sinuses were significantly stiffer than the aortic sinuses at systemic pressure in the two directions (P< 0.001). Histological analysis revealed that aortic roots had tight denser weave of elastin than pulmonary roots. CONCLUSIONS: Significant differences were found in the compliance and fibrous structure of human pulmonary and aortic roots. These regional differences may impact pulmonary autograft remodelling and influence late autograft dilation.