Vascular smooth muscle orientation in curved branches and bifurcations of human cerebral arteries.

Two approaches were developed for determining reference axes and positions associated with bending tubular arteries and bifurcations from the human middle cerebral branching system. In the region of the bifurcation the orientation of groups of two-dimensional nuclear vectors was determined by the method of roses and average alignment. The reference axes and positions for these groups were determined from physical reconstructions of two bifurcations. The overall pattern in the bifurcation region was found to be random but there were significant differences between group orientations. The three-dimensional arterial direction vectors for three sections, from the bending arteries of one bifurcation, were determined. By taking the dot product of the three-dimensional nuclear vectors and these direction vectors, the pitch of individual nuclei was determined. The average pitch was 2.45 degrees +/- 3.20 (SD for N = 8) with the largest mean pitch (6.14 degrees) in the branch with the greatest curvature. Possible use of the three-dimensional approach for determination of smooth muscle orientation at bifurcations is discussed in general terms.