Experimental frost-bite in Hanford Miniature Swine. II. Vascular changes.

Frost-bite lesions were produced in five Hanford Miniature Swine exposed to - 75 degrees C air for 1, 3, 5, 10, or 20 min. Biopsies were taken at 0, 3, 6, 12, 24, and 48 h, and 1 and 2 weeks. Two hundred slides were evaluated microscopically: superficial and deep hyperaemia, vascular inflammation, medial degeneration, and thrombosis were graded from 0 to 5; 0, no change; 5, severe change. Haemorrhage was recorded as present or absent. Hyperaemia was the earliest change seen, both grossly and microscopically. Leucocyte emigration and vasculitis were intermediate stages seen most commonly in the 6, 12, and 24 h biopsies. Medial degeneration and thrombosis, the most severe vascular changes, were not seen until 1-2 weeks following frost-bite injury. These findings show that the outcome of frost-bite can not be accurately predicted from early frost-bite lesions, because thrombosis and medial degeneration are not evident in early lesions.