Safety Assessment Of New Helium-oxygen Decompression Procedures In Bama Swine

Maritime power,maritime Silk Road and other important national strategic layout of deepening reform and opening up are important fulcrums for our country to create a new pattern of all-round,multi-level and wide field opening under the new situation in a new way.They enhance the importance of the ocean in economic construction and national defense security,and promote the rapid development of the diving industry.Decompression sickness（DCS）is one of the main medical problems threatening the safety of diving operations,which is caused by improper decompression and the formation of air bubbles in the body of divers during ascending process.It has the characteristics of acute onset,serious condition and miscellaneous symptoms,etc.Its prevention is one of the core tasks of diving medical support.The most effective way to prevent DCS is to strictly implement the decompression procedure.With the continuous improvement of the decompression theory and the updated iteration of diving equipment,it is found that the present helium-oxygen conventional diving decompression procedures used in our country cannot longer meet the current diving practice.By optimizing the decompression algorithm,the research group calculated 206 new helium-oxygen conventional diving decompression procedures,and compiled a new helium-oxygen conventional diving decompression table,which must pass security verification before being applied in practice.It includes risk assessments for DCS and oxygen toxicity（OT）.However,the reliability of indexes selected for safety verification of decompression procedures needs to be further improved.Although the scientific and ideal decompression procedures can control the incidence of DCS within a reasonable range,in practice,due to the complex and changeable underwater environment,divers may encounter emergencies,so emergency decompression procedure needs to be developed for emergency decompression and getting out of the water.The traditional practice is often adjusted temporarily by diving medical experts with professional knowledge and experience who are responsible for on-site support.There is a certain scientificity,but its risk is also hard to control.In order to shorten the decompression time as much as possible and ensure that divers do not have serious DCS,the scientific approach is to clarify the safety limits of the decompression procedure in advance,that is,the critical conditions for DCS.This can not only provide a basis for developing emergency decompression procedures,but also provide support for further improvement of decompression procedures in the future.In this study,bama swine was selected as the research object to conduct simulated diving according to the new helium-oxygen conventional diving decompression procedures.The safety of the new helium-oxygen conventional diving decompression procedures was systematically verified through symptom and sign observation,bubble detection,theoretical calculation and biochemical index detection.And the safety assessment system was improved.On this basis,by adjusting the decompression algorithm and shortening the decompression time,the safe decompression limit of the new helium-oxygen conventional diving decompression procedure is explored,which provides an experimental basis for the formulation of emergency decompression procedure in emergencies and further improvement of decompression procedure in the future.PartⅠ:Safety verification of helium-oxygen decompression proceduresMethods:Firstly,the performance of the new hyperbaric chamber for large animals was tested to ensure that it can meet the environmental requirements of simulated helium-oxygen diving.On this basis,we conducted simulated diving according to the new helium-oxygen conventional diving decompression procedures.By observing the signs and symptoms of DCS in swine after exiting the chamber,detecting circulating bubbles in swine after exiting the chamber,testing the changes of the levels of serum endothelial injury indexes including endothelin-1（ET-1）,intercellular adhesion molecule-1（ICAM-1）,vascular cell adhesion molecule-1（VCAM-1）,and inflammatory factors including interleukin-1β（IL-1β）,tumor necrosis factor-α（TNF-α）,monocyte chemotactic protein-1（MCP-1）,and white blood cell（WBC）,red blood cell（RBC）and platelet（PLT）in the blood of the swine before and after simulated diving,we comprehensively assessed the DCS risk of decompression procedures.Through theoretical calculation of the unit of pulmonary oxygen toxicity dosage（UPTD）,observation of the behavioral changes in swine during simulated diving,and detection of the changes of serum oxidative damage indexes including hydrogen peroxide（H₂O₂）and malondialdehyde（MDA）levels in swine before and after simulated diving,we comprehensively assessed the oxygen toxicity（OT）risk of decompression procedures.Results:The new hyperbaric chamber for large animals had good performance,which can accurately control the temperature,humidity and gas concentration in the chamber to a given range.Simulated diving decompression was performed according to the new helium-oxygen conventional diving decompression procedures.No signs and symptoms related to DCS were observed 72 h after exiting the chamber in swine.No circulating bubbles were found after 6 h ultrasonic detection in swine.There were no significant changes in serum ET-1,ICAM-1,VCAM-1,IL-1β,TNF-α,MCP-1 and blood WBC,RBC and PLT levels before and after simulated diving in swine（P>0.05）.The UPTD of all the verified decompression procedures were less than 615.No OT-related behavior was observed in swine during the simulated dive.There were no significant changes in serum H₂O₂ and MDA levels before and after simulated diving in swine（P>0.05）.Conclusions:This study preliminarily proved the safety of the new helium-oxygen conventional diving decompression procedures from DCS and OT risks on the animal level,and laid a foundation for further human experiments.PartⅡ:Exploration of safety limits for helium-oxygen decompression proceduresMethods:A“radical procedure”with significantly shortened total decompression time was formed by adjusting the relevant parameters of the decompression algorithm to reduce the conservative degree of the decompression procedure.The DCS risk of the radical procedure was assessed by the same method in the first part study.If the bubble is detected in the animal but no DCS signs appear,the procedure is considered as the safe limit procedure.If no bubble is detected or DCS occurs,the algorithm parameters are adjusted again until the safe limit procedure is obtained.Finally,the relevant data of the safety limit procedure are used to explore the calculation method of the safety limit coefficient（that is,the ratio of the reduced decompression time of the radical procedure to the total decompression time of the original procedure）.Results:The bubble grades were divided into 3 groups:no bubble,low grade bubble and high grade bubble.When the high grade bubble was 4 or 5 grade,the Youden index of diagnosing DCS was the highest,which was 69.23%（Sensitivity of 100%）.In the no bubble group,simulated diving didn’t change the serum biochemical indexes in swine（P>0.05）.In the low grade bubble group（grade 1,2,3）,the serum levels of ET-1 and TNF-αwere significantly increased after simulated diving in swine（P<0.05）,but there were no significant changes in other indexes（P>0.05）.In the high grade bubble group（grade 4 and5）,the serum levels of ET-1,ICAM-1,VCAM-1,IL-1β,TNF-αand MCP-1 were significantly increased after exiting the chamber in swine（P<0.05）.The safety limit coefficient of decompression procedure had significant linear correlation and regression relationship with operation depth and animal weight,and the changes of the latter two could explain 82.1%of the variation of the former.The established regression equation for safety limit coefficient was statistically significant（P<0.001）.The results of residual analysis show that the residual satisfies normality,independence and homogeneity of variance.There was no multicollinearity between the different arguments.Bland-Altman diagram showed that the equation has a good fit with the original data.At the same time,the safety limit coefficient of the new helium-oxygen conventional diving decompression procedure is larger when the depth is smaller,while the safety limit coefficient of the decompression procedure decreases gradually as the depth increases.Conclusions:For bama swine,the safe decompression limit of the decompression procedure is when the amount of bubbles in the body reaches level 3.The regression equation established in this study can be used to calculate the safe limit decompression time of the new helium-oxygen conventional decompression procedure in swine models,which can provide a reference for human experiments,and then provide a basis for the formulation of emergency decompression procedures in practice.The variation of safety limit coefficient of different depth decompression procedures suggests that the greater the operating depth of the new helium-oxygen conventional diving decompression procedures,the smaller the safety redundancy,and more caution should be taken when making emergency decompression procedures.In addition,among the selected biochemical indicators for DCS risk assessment,ET-1 and TNF-αare highly sensitive,which can be used as important injury markers for safety assessment of decompression procedures.