Spatial orientation of arterial sections determined from aligned vascular smooth muscle.

The alignment of the arterial axis can be used as the required reference for three-dimensional (3-D) measurements of structures within the artery wall. Our hypothesis is that this alignment reference may be derived mathematically if one uses medial smooth muscle, a tissue component we have found to have a circumferential organization in human cerebral and coronary arteries. We tested this hypothesis for angles of sectioning up to 60 degrees, using arteries fixed at normal distending pressure. These segments of artery were sectioned at precisely measured angles, using a specially designed mitre box, and the sections were stained to enhance birefringence of the smooth muscle. Arteries from eleven autopsies were obtained from the heart and brain, and measurements of 3-D orientation on medial smooth muscle were made with a polarizing light microscope equipped with a four-axis Universal stage. By comparing the cutting angle, we deduce that we can determine the obliqueness of cut relative to the arterial axis to within 4.6 degrees. The application that is important to us, and possibly to other laboratories, is that the necessary direction reference for an artery is completely contained within a single tissue section.