Comparison of effects and prognosis of ice water immersion and room temperature cooling treatments on lung inflammation in heat-induced rats

Objective To investigate the effects of ice water immersion, temperate-water immersion, and room temperature cooling treatments on constituent ratio of death, histology and related molecules in lungs of heat-induced rats. Methods One hundred and fifteen male SD rats were randomly divided into pulmonary injury-analyses group (n=70) and death-analyses group (n=45), and the former group included two groups: normothermic control group (NC, n=10) and heat stress group (HS, n=60). Rats in NC group were put in the room temperature chamber while rats in HS group were put in a folded heating pad with general anesthesia. When their core temperature (Tc) elevated to 42℃, cooling treatments were accomplished via room temperature (RT, n=20), temperatewater immersion (TWI, n=20) and ice water immersion (IWI, n=20). The heated rats in each group were sacrificed at the time of 15 min (n=10) or 3 h (n=10) after heat stress. The lung morphology was analyzed by hematoxylin and eosin staining, and the levels of related cytokines of the lung homogenate were analyzed by enzyme-linked immunosorbent assay. The constituent ratio of death in the death-analyses group was calculated 3 h after heat stress in HS+RT group (n=15), HS+TWI group (n=15), and HS+IWI group (n=15). Results Compared with HS+RT group, the constituent ratio of death in HS+TWI group and HS+IWI group decreased significantly (χ²=10.601, P=0.001). The heated rats in HS+IWI 3 h group displayed alveolar collapse, edema, hemorrhage and thickened interstitium, and the level of the pre-inflamatory cytokine TNF-α was higher than that of the NC group (P< 0.05) and the related TWI and RT groups (P< 0.05). Conclusion TWI and IWI can improve the prognosis of heat-induced rats, while IWI may aggravate the pulmonary inflammation and cause acute lung injury after heat stress, which suggests that it is necessary to redefine the cooling temperature and cooling time of water immersion.