Final answer:
The condition with trapped air in the pleural space that cannot escape and results in lung collapse is known as a spontaneous pneumothorax. This affects the normal passive expiration by preventing proper lung expansion and altering intrapleural pressure.
Step-by-step explanation:
The condition described, where air builds up in the pleural space and is unable to escape, causing lung collapse on the affected side and pressure on the mediastinum, is known as a spontaneous pneumothorax. This can occur due to abnormalities in connective tissue or other factors causing the pleural spaces to accumulate air. In this state, normal expiration, which is usually passive and relies on the elasticity of lung tissue and the relaxation of the diaphragm and intercostal muscles, becomes compromised. As the thoracic cavity and lungs are supposed to decrease in volume and create a pressure gradient for air to leave the lungs, in pneumothorax, the presence of air in the pleural space prevents proper lung expansion and leads to decreased pulmonary function. Additionally, diseases like respiratory distress syndrome and pulmonary fibrosis show a decrease in lung compliance, affecting the intrapleural pressure and further complicating the exhalation process.