Abstract: Abstract: Objective To study the predictive value of evaluation in oxygen partial pressure[p(O2)] and carbon dioxide partial pressure[p(CO2)] of pleural cavity to the closure of visceral pleura in primary spontaneous pneumothroax (PSP) pa⁃ tients. Methods Seventy-six hospitalized pneumothroax patients were divided into two groups: closed pneumothroax group (n=40) and open pneumothroax group (n=36), according to the radiographic information.To collect the expiratory gas by the device which we designed and produced, to collect the gas in the pleural cavity by thoracentesis. To detect the p （O2 ）and p （CO2 ）respectively, and the blood gas analysis of radial artery was done at same time. Results There was significantly low⁃ er value of p（O2 ）of the gas in the pleural cavity in patients of closed pneumothroax than that of open pneumothroax (P < 0.05). The level of p （CO2 ） was higher in patients of closed pneumothroax than that of open pneumothroax ( P < 0.05). There were no significant differences in values of p （O2 ） and p （CO2 ） in expiratory gas and the blood gas analysis between two groups （P＞0.05). There was significantly higher value of the expiratory gas / the pleural cavity gas p(O2) and a significantly lower value of p(CO2), in closed pneumothroax group than those of open pneumothroax group (P < 0.05). Logistic regression analy⁃ sis showed that values of the expiratory gas / the pleural cavity gas p(O2) and p(CO2) were the effective factors for the closure of visceral pleura. ROC curve showed that the areas under ROC curve (AUC) for the expiratory gas/the pleural cavity gas p(O2) and p(CO2) was 0.985 and 0.867, the sensitivities were 92.5% and 77.8%, the specificities were 100% and 85.0% and the reference values were 1.81 and 0.97. Conclusion To utilize the evaluation of gas partial pressure can predict whether the leakage of the visceral pleura is closed.

Key words: early diagnosis ；, sensitivity and specificity；visceral pleura, closure, open, oxygen partial pressure;, crbon dioxide partial pressure;, primary spontaneous pneumothorax