Intravital pathophysiologic comparison of frostbite and burn injury in a murine model

The breakdown of skin microcirculation and the leukocyte-endothelium interaction are assumed to play key roles in the pathophysiology of burn and frostbite injuries. Available data on frostbite and burn injuries were collected using different experimental models and setups, which limits direct comparisons of these thermal traumata significantly. To determine pathophysiologic similarities and differences, two comparable in vivo frostbite and burn models were used to assess microcirculatory and angiogenetic changes in burn and frostbite injuries.

Either deep partial thickness no-touch burns or frostbite injuries were inflicted to the ears of hairless mice (n = 40) by a hot or cold gas jet (117.0 ± 2.1°C for 1 s and -195.8 ± 2.7°C for 1.5 s, respectively) resulting in a necrotic, nonperfused area of about 1.56 ± 0.28 mm2. Intravital fluorescent microscopy was used in combination with fluorescent dyes in order to assess the microcirculation, angiogenesis, and leukocyte-activity over a 12-d period.

The angiogenesis occurred significantly faster after frostbite than after burn (16.4% ± 4.5% versus 30.6% ± 2.8% nonperfused area, compared with the baseline value on d 7 (P = 0.009)). The loss of functional vessel density was significantly more pronounced after frostbite (57.6% ± 2.2% versus 89.2% ± 4.9% (P < 0.001)). However, the area recovered faster. The edema formation, as a parameter for endothelial integrity, was significantly more pronounced and lasted longer after frostbite, compared with the burn injury, and reached its maximum level on d 7 after trauma (162.4% ± 4.2% versus 142.% ± 5.9%; P = 0.007). In contrast to the rolling leukocytes, which showed the same increase on d 1 and then a subsequent decrease in both groups, the number of adherent leukocytes after the burn was markedly higher on d 1 (480% versus 167%; P = 0.001) but decreased much faster. The number of adherent leukocytes after frostbite remained significantly higher than those of the burn group during the entire observation.

The comparison of analogous intravital burn and frostbite models indicates that despite the similarities, decisive microcirculatory differences in extension and recovery from these two types of thermal trauma exist.