Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The luminal geometry of blood vessels at bifurcations is a critical determinant of blood flow. We have undertaken a detailed analysis of the geometry of cerebral bifurcations using a computer-based, video analysis system and frozen section techniques. The luminal surfaces of twenty bifurcations from whole brains obtained at autopsy from three human subjects were digitized at 10.00 (+OR-) 0.16 (mu)m increments. The property of natural fluorescence of the internal elastic lamina and of adventitial collagen was used in conjunction with episcopic, ultra-violet irradiation to map both the luminal and adventitial boundaries. White light illumination was used in conjunction with contrast materials to selectively map the luminal boundary. The digitized coordinate sets were analyzed to obtain luminal, dimensional data at 10 (+OR-) 0.16 (mu)m trunk increments from the parent to the daughter branches. The dimensional data for each section included; diameters, cross-sectional area, centroid coordinates and perimeter.;All specimens exhibited a linear increase in luminal cross-sectional area as the point of branching was approached. The magnitude of the increase in cross-sectional area ranged from 50% to 122%. All specimens exhibited a linear decrease in the summed cross-sectional areas of the daughter branch sections beyond the branch point. This decrease ranged from 66% to 35%. The observed changes in luminal cross-sectional area would account for a uniform decrease in mean flow velocity in the parent trunk at the approach to the flow divider and a uniform increase in the mean flow velocity beyond the point of branching. The location of the region of transition from increasing to decreasing cross-sectional area occurred within 300 (mu)m of the flow divider. This region of geometric transition coincides with the locations of saccular aneurysms, medial defects and intimal cushions. It is postulated that flow disturbances arising from an abrupt change in the acceleration of the flow in this apical region may contribute to the development of these early vascular lesions.



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