Regional Mechanical Properties of Human Pulmonary Root Used for the Ross Operation

Background and aim of the study: Significant dilation of the pulmonary autograft after the Ross operation is problematic and requires reoperation. Autograft remodeling occurs in response to the immediate rise in pressure and consequent wall stress. The stressstrain response of the pulmonary root plays an important role in understanding the structural and functional changes of the autograft following the Ross procedure. At present, limited data are available on the mechanical properties of fresh human pulmonary roots; hence, the study aim was to determine the regional mechanical properties of human pulmonary roots. Methods: Eighteen fresh healthy specimens of human pulmonary root were obtained from the California Transplant Donor Network (Oakland, CA, USA). Five regions of the pulmonary root - anterior and posterior pulmonary artery (PA), and each of the three sinuses - were subjected to displacementcontrolled equibiaxial stretch testing within 24 h of cross-clamp time. Comparisons between the different regions of the pulmonary root were made based on tissue stiffness at physiologic stress. Histologic analyses were also performed of the fibrous structures of the PA and sinuses. Results: Human PA and sinuses demonstrated a nonlinear response to loading, with no directional dependency to biaxial loading. The anterior PA was significantly more compliant than the posterior PA and the three sinuses in both circumferential and longitudinal directions (p 0.43), or among the three sinuses (p >0.30) in the two directions. A tight, more dense weave of elastin was found in the anterior PA than in either the posterior PA or the sinuses. Conclusion: Significant inherent differences in compliance were demonstrated among different regions of the human pulmonary root. These regional differences may impact upon pulmonary autograft remodeling following the Ross operation, and also influence late autograft dilation.