Flow patterns and preferred sites of atherosclerotic lesions in the human aorta – I. Aortic arch

Objectives To elucidate the role of fluid mechanical factors in the localized genesis and development of atherosclerotic lesions in man. Methods Flow patterns and preferred sites of atherosclerotic lesions in the human aortic arch were studied in detail using isolated transparent aortic trees prepared from humans postmortem and by means of flow visualization of tracer polystyrene microspheres, using cinemicrographic techniques. Results Under the condition of steady flow that simulated mid-systole, the flow in the aortic arch consisted of three major components; (i) a straight flow to the brachio-cephalic artery located close to the right dorsal wall of the ascending aorta; (ii) a quasi-parallel undisturbed flow located close to the common median plane of the aortic arch and its side branches, and (iii) a clockwise slow, spiral secondary flow located dominantly near the left ventral wall of the aortic arch. Thus, looking down the aorta from its origin, the flow in the aortic arch appeared as a single helical flow revolving in a clockwise direction. Conclusions Atherosclerotic lesions were found mainly in regions of low wall shear stress such as the proximal lip of the orifice of each side branch where a slow recirculation flow formed, and the left ventral wall of the aortic arch where a slow spiral secondary flow formed.