Experimental frost-bite in Hanford Miniature Swine. I. Epithelial 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: pyknosis, vacuolation, individualization of cells, and degeneration were graded from 0-5; 0, no change; 5, severe change. Necrosis, new epithelium, and microabscesses were recorded as present or absent. Early changes of vacuolation of keratinocytes, individualization of cells and pyknosis increased with biopsy time until 1 week, at which time more severe changes predominated. Intermediate changes of advanced degeneration and dermoepidermal microabscesses were seen at 48 h and 1 and 2 weeks. Late changes of necrosis and epithelial regeneration occurred, both separately or together in the same tissue, at 1 and 2 weeks. Regeneration occurred either as complete replacement of epithelium, or as crescents of new epithelium beneath degenerating epithelium. The results show that necrosis is a late development, so prognosis based on early skin biopsies must be guarded to unfavourable. Furthermore, these findings suggest that cold has a direct effect on epithelial cell membranes.