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Biomechanical perspective on the porcine pulmonary root prior to Ross remodeling.

BACKGROUND AND AIM OF THE STUDY
Pulmonary autograft dilation can lead to aortic insufficiency requiring reoperation. Remodeling occurs when the pulmonary root is subjected to systemic pressure. It is unknown whether a regional variability of the material properties exists within the root, resulting in unequally distributed wall stress prior to remodeling after the Ross procedure. The study aim was to determine differences in regional pulmonary root material properties, and to identify changes in wall stress at both pulmonary and systemic pressure.


METHODS
Five regions of the porcine pulmonary root--anterior and posterior artery, and each sinus--were subjected to displacement-controlled equibiaxial stretch testing. The stress-strain data recorded were used to determine stiffness at 35% strain. Separate finite element simulations of the root were performed using each of the five regional material properties. Tissue dilation and wall stress were compared at pulmonic and systemic pressures.


RESULTS
The pulmonary artery (PA) demonstrated tissue anisotropy, and was stiffer in the circumferential than the longitudinal direction (p < 0.001), whereas the sinuses demonstrated no differences in stiffness between the circumferential and longitudinal directions (p = 0.73). Overall, the PA was significantly more compliant than the sinuses, both circumferentially (p = 0.04) and longitudinally (p = 0.007). However, no regional differences in stiffness were found between the anterior and posterior PA (circumferential, p = 0.37; longitudinal, p = 0.06), or among the sinuses (circumferential, p = 0.22; longitudinal, p = 0.38) at 35% strain. Based on finite element simulations, the PA dilated from 35.14 +/- 1.67 cm to 45.98 +/- 2.56 cm, and the sinuses from 35.05 +/- 1.39 cm to 40.02 +/- 2.17 cm from pulmonic to systemic pressure. The maximum wall stress increased from 41.07 +/- 4.17 to 287.06 +/- 31.84 kPa in the PA, and from 55.87 +/- 4.38 to 295.64 +/- 32.97 kPa in the sinuses.


CONCLUSION
Significant inherent differences in compliance were demonstrated between the PA and pulmonary sinuses. These results suggest that the artery dilates more than the sinuses, but is subjected to equally large wall stresses when the systemic pressure is applied prior to remodeling.