Which statement accurately describes an open pneumothorax?

An open pneumothorax occurs when there is a direct communication between the pleural space and the external environment, usually due to a penetrating injury such as a puncture wound. This allows air to enter the pleural cavity during inhalation, which can lead to a collapse of the lung on the affected side. The presence of a hole in the chest wall differentiates an open pneumothorax from a closed pneumothorax, where there isn't such an opening.

In this context, the correct statement highlights the mechanism by which an open pneumothorax occurs. The wound allows for abnormal airflow, which directly impacts the lung's ability to expand and function properly, thereby affecting breathing. This understanding is crucial for a combat medic in identifying and managing such injuries effectively on the battlefield or in any emergency medical situation.