Effects of cryotherapy after contusion using real-time intravital microscopy

Purpose: To examine effects of local tissue cooling on contusion-induced microvascular hemodynamics and leukocytes behavior using real-time intravital microscopy. Methods: Male Wistar rats (N = 21, 130-150 g) were randomly assigned to intensive cooling group (3°C, N = 7), a moderate cooling group (27°C, N = 7), or control group (37°C, N = 7). Contusion was induced by dropping a plastic ball on exposed cremaster muscle. After 5 min, the cremaster muscle was superfused with a saline solution for 10 min at controlled temperature of either 3°C (cooling), 27°C (moderate cooling), or 37°C (control). Microvascular hemodynamics (vessel internal diameter, blood flow rate and erythrocyte velocity) and leukocyte behavior (rolling and adhesion) were measured from recorded videotapes in the same venules before and after contusion, and after cooling. Results: Cooling-induced vasoconstriction was marked at 3°C and moderate at 27°C compared with that at 37°C. Blood flow rate and erythrocyte velocity were markedly lower at 3°C compared to 37°C. At 27°C, erythrocyte velocity was higher than that at 37°C, but blood flow rate was maintained at a level similar to that at 37°C. The number of rolling and adhering leukocytes at 3°C and 27°C were significantly less than at 37°C. Conclusion: Our results suggest that local tissue cooling, similar to cryotherapy, improves edema and inflammatory reaction, and may be useful for reducing inflammatory response without inhibiting blood flow after contusion.