Microscopic structure of disturbed flows in the arterial and venous systems, and its implication in the localization of vascular diseases.

A novel technique to prepare isolated transparent natural blood vessels was developed and used to investigate the connection between blood flow and the localization of vascular diseases in man. Transparent segments of arteries and veins were prepared from dogs and humans postmortem, and the flow patterns in various regions of the circulation were studied in detail by means of flow visualization and cinemicrographic techniques. It was found that under normal physiological conditions, complex spiral secondary flows and recirculation zones form in various regions of the arterial and venous systems such as the aortic arch, aortic T-junctions, carotid artery bifurcations, the major branching sites of the intracranial cerebral arteries and venous valve pockets. Incipient saccular aneurysms were found at the flow divider of the anterior communicating-anterior cerebral artery junction where the flow directly impinged on the vessel wall. In human cerebral arteries, atherosclerotic thickenings of the vessel wall were found to be localized on the outer wall (hip) of one or both daughter vessels at bifurcations and T-junctions, and at the inner wall of arterial bends, at the very places where secondary and recirculation flows were dominant and wall shear stress was low. The results clearly indicate that there is a strong correlation between the sites of flow disturbance and the preferred sites for the genesis and development of vascular diseases clinically found in man.