Wall stress as a possible mechanism for the development of transverse intimal tears in aortic dissections

ln aortic dissection intimal tear develops in a transverse direction. Since dissection is associated with the aneurysm of the aorta, its mechanism was investigated by analysing the pressure induced wall stress as a function o f 'growth' of the aneurysm. The stresses were determined using a finite ele ment analysis where the aorta was modelled as an isotropic, nonlinear, hype relastic material. Growth of the aneurysm was simulated by dilating an aort ic segment in increments of 10% of the initial diameter. At each dilation l uminal pressure of 120 mm Hg was applied and stress determined. In the aneu rysm bulb, longitudinal stress increased significantly as the bulb became l arger, while circumferential stress changed only a little. In the undilated segment both the longitudinal and circumferential stresses remained relati vely unchanged. The increase in the longitudinal stress in the bulb occurre d primarily clue to change in shape of the aorta from cylindrical to ellips oidal to spherical. Hence, as the aneurysm 'grows' the longitudinal stress in the bulb increases rapidly and could be responsible for the transverse t ear in the aortic dissection.