Abstract： Objective:To observe the changes of plasma nitric oxide (NO) and desmosine (DES) concentrations in animals under different decompression pressure loads, and to explore the role of NO and DES in quantitative evaluation of diving decompression injury.Methods:A total of 50 male SD rats were divided into five groups with 10 rats in each group by the random table method. Rats in Group 1 were not pressurized and were given air ventilation, and left the cabin after 120 min; after pressurized to 70 m for 70 min, 40 rats in the other four groups were decompressed at a constant rate to the normal pressure in 40 min (Group 2), 30 min (Group 3), 20 min (Group 4) and 10 min (Group 5), respectively. The changes of plasma NO and DES concentrations in rats after leaving the cabin were observed. A total of 40 male rabbits were divided into four groups with 10 rabbits in each group by the random table method. The rabbits were used to simulate fast buoyancy ascent escape from the depth of 150 m and the compression pressure doubled every four seconds. The four groups were decompressed at a constant rate of 6 m/s after being given different bottom time, i. e., 4 s (Group 1), 60 s (Group 2), 180 s (Group 3), and 300 s (Group 4). The changes of plasma NO and DES concentrations in the rabbits after leaving the cabin were analyzed.Results:Compared with the rats in the Group 1, the plasma NO and DES concentrations of the rats of the Group 5 significantly increased, with statistically significant differences ( P<0.05 or P<0.01), and the plasma DES concentration of the rats in the Group 4 also increased, with a statistically significant difference ( P<0.05). The plasma NO and DES concentrations in rats were positively correlated with the reciprocal of the decompression time at a constant rate (NO: r=0.683, P<0.01; DES: r=0.535, P<0.01) and showed significant linear regression relationships (NO: r2=0.467, P<0.01; DES: r2=0.287, P<0.01). Compared with the values before escape, the plasma NO concentrations in the rabbits of the Group 3 and 4 increased significantly, with statistically significant differences ( P<0.01), and the plasma DES concentrations in all four rabbit groups increased significantly, with statistically significant differences ( P<0.01). After leaving the cabin, compared with the rabbits in the Group 1, the plasma NO and DES concentrations in rabbits of the Group 3 and 4 increased significantly, with statistically significant differences (NO: P<0.05 or P<0.01; DES: P<0.01). After leaving the cabin, the plasma NO and DES concentrations in rabbits were positively correlated with the bottom time (NO: r=0.672, P<0.01; DES: r=0.702, P<0.01)and showed significant linear relationships (NO: r2=0.452, P<0.01; DES: r2=0.493, P<0.01). Conclusion:The plasma NO and DES concentrations can quantitatively indicate the damage caused by decompression pressure loads, which makes it possible to design decompression protocol and safety evaluation. The severity of decompression injuries is linearly related to the reciprocal of decompression time (or rate) that determines the decompression pressure load, which have reference value for the decompression rate control in the theoretical model of decompression.