A pneumothorax occurs under what circumstance related to lung injury?

A pneumothorax occurs when air enters the pleural space, which can happen as a result of a lung injury that allows air to escape from the lung into the chest cavity. The phrase "when air from a lung collapses a lung" accurately describes this process, as the presence of air in the pleural space can lead to a collapse of the lung (atelectasis). This condition is usually associated with trauma or injury to the lung, such as a penetrating wound, rib fracture, or certain medical conditions that compromise lung integrity.

Understanding the mechanics of a pneumothorax is essential for divers and those involved in advanced diving practices, as changes in pressure during dives can increase the risk of lung injury. In contrast, dehydration, cold water immersion, and high blood pressure are not directly related to the mechanism of air entering the pleural space, which confines the context of lung injury specifically to the escape of air resulting from trauma or other stresses on lung tissue.