Abstract: Objective To investigate the mitochondrial damage and its effect in early stage of pressure ulcer in a rat. Methods 40 rats were randomly divided into 5 groups(n=8), control group(Con group) rats without stress, the experimental group was treated with a special pressure equipment compress (170 mmHg) 2 h and relax 0.5 h is one cycle(1C), experimental group was divided into 3C , 6C , 9C and 12C group. The pathological changes of the compressed muscle tissue of the rats in each group were observed by HE staining, Western blot methods to detect the expression of Bcl-2 and Bax in the compressed tissue, and the ultrastructure of muscle fibers and mitochondria were observed by transmission electron microscope. Results There are pathological damage and gradually increased in the experimental groups, with the increase of compression cycle; the expression of Bcl-2 in each experimental group was significantly increased compared with the control group（P＜0.05）, in the 3C group reached the peak, and then decreased; the expression of Bax was increased gradually with the increase of compression cycle（P＜0.05）, and in the 12C group reached the peak; with the increase of the compression cycle the muscle fibers of each experimental group appeared gradually increased pathological damage: disorder, dissolution and fracture, the ridge of the mitochondria disappeared, vacuolar degeneration, et al. Conclusions In the early stage of pressure ulcer in a rat occurred mitochondrial damage and induced apoptosis.

Key words: pressure ulcer, ischemia/reperfusion injury, mitochondria, apoptosis