Inside the pleural cavity, the significance of negative pressure is that the lungs are always in a state of expansion, so that the lungs maintain good ventilation and air exchange function. The pleural cavity is a closed structure formed by the visceral pleura and the wall pleura, when the lung atrophies when breathing, there will be a negative pressure in the pleural cavity, the negative pressure will attract the lungs to make the lungs reexpand again, so that the lungs are always in the state of expansion, which is conducive to the lungs to carry on the exchange of gases, and is conducive to keeping the cardiorespiratory function normal. When suffering from pneumothorax, due to the rupture of pulmonary blisters, the gas in the lungs overflows into the pleural cavity to compress the lung atrophy, the effective respiratory area of the lungs decreases and the phenomenon of chest tightness and shortness of breath occurs, and at this time it is necessary to give the closed chest drainage, so as to make the positive pressure in the pleural cavity return to negative pressure, and make the lungs reexpand again to be conducive to the respiratory function of the lungs.