Endothelial cell morphology around graded stenoses of the dog common carotid artery.

Graded stenoses (40-64% diameter reduction) were applied to dog common carotid arteries under anesthesia, and 27 days later the poststenotic velocity field was examined using transcutaneous pulsed Doppler velocimetry. Following in situ fixation, endothelial cell area, shape and orientation was measured by digitizing endothelial cell outlines in scanning electron micrographs. Endothelial cell area in the vicinity of the stenosis throat (within +/- 1 diameter) was reduced. No relation to stenosis hemodynamics was apparent. Cell area was increased 5 diameters downstream; in this region, there was turbulence due to jet break up. Cells were maximally rounded at the stenosis throat and gradually returned to upstream elongation by 5 diameters downstream. There was a region of flow separation and low velocity recirculation between the stenosis and the site of maximum turbulence, thus, downstream cell rounding was associated with flow separation. Subdivision of the experiments into four stenosis grades revealed little variation of the pattern of morphology between groups. It is possible that this is related to flow limitation with increasing grade. Elongation of endothelial cells through the entrance of the stenosis was apparent in only four experiments. Poststenotic dilatation of greater than 12% external diameter increase was noted in only four out of the sixteen experiments. In general, the relation of cell elongation to shear stress is supported, but this relationship does not fully explain endothelial cell shape at a stenosis.