Potential Hemodynamic Mechanisms for Gender Differences in AAA Formation

Abdominal aortic aneurysms (AAA) are a major cause of morbidity and mortality in the US. It is classically thought of as a disease of older men with the incidence approaching 30%. The most common place of AAA is infrarenal abdominal aorta where oscillatory shear stress (OSS) is present. OSS is known to initiate an inflammatory response in the endothelium. It is also known that females are at lower risk for developing AAA. The explanation for this difference is lacking. We recruited 8 healthy volunteers, 4 males and 4 females who underwent infrarenal abdominal aortic Magnetic Resonance angiography and phase contrast imaging. The collected data was used to calculate systolic forward and diastolic retrograde blood flow. Our results suggest that female infrarenal aortas are exposed to a 3-fold lower degree of OSS. It appears that the low resistance internal iliac arterial system may be in part responsible for such flow patterns. We conclude that female aortas are subjected to lower OSS and that low resistance internal iliac arterial system appears to play a protective role.