Capillary Ultrastructure in Thermally Stressed Paired Digital Biopsies in Man

Two digital biopsies were removed from the fingertips of each of 5 subjects--one in a cold environment and the other in a warm environment. Electronmicroscopic examination of the capillaries within the dermis revealed a pleated, contracted endothelial lining in the cold, with encroachment of the lumen by projecting nuclei and cytoplasm. Biopsies from the warm fingertips were dilated in appearance and had more microvillous processes and vesicles.Contraction and dilation of capillaries under physiologic thermal variation would appear to result from swelling of endothelium and consequent occlusion of the lumen.