Which of the following is NOT an example of extrapulmonary air?

Airway obstruction does not involve the presence of air outside the lungs, which distinguishes it from the other options listed. It refers to a blockage within the respiratory system that restricts airflow, typically occurring in conditions such as asthma, foreign body aspiration, or swelling. This blockage originates inside the airway itself and does not signify the presence of air in abnormal locations within the body.

On the other hand, pneumothorax, pneumoperitoneum, and pneumomediastinum are all conditions that involve the presence of air in areas outside the normal lung structures. Pneumothorax involves air in the pleural space surrounding the lungs, pneumoperitoneum is the presence of air within the peritoneal cavity, and pneumomediastinum refers to air in the mediastinum, the central compartment of the thoracic cavity. These conditions are termed extrapulmonary because they are characterized by air accumulation outside of the lungs.