A scuba diver breathing air ascends rapidly from 30 meters. The diver develops sudden dyspnea and frothy sputum within minutes of surfacing. Arterial PaO2 is 45 mmHg. Which mechanism explains this presentation?
- A Decompression sickness causing nitrogen gas emboli in pulmonary vessels
- B Pulmonary barotrauma from breath-holding on ascent causing alveolar rupture and pulmonary edema ✓
- C Oxygen toxicity from high PO2 at depth causing reactive oxygen species lung injury
- D Hypercapnic respiratory failure from CO2 retention during the dive
Explanation
Rapid ascent from 30 meters while breath-holding causes gas in the lungs to expand (Boyle's law — pressure decreases from ~4 atm to 1 atm, volume quadruples). If the diver cannot exhale fast enough, excessive alveolar pressure causes pulmonary barotrauma — alveolar rupture, pneumothorax, mediastinal emphysema, or arterial gas embolism (frothy sputum, acute hypoxemia). Decompression sickness (option A) primarily causes musculoskeletal and neurological symptoms and develops minutes to hours after surfacing from prolonged dives. Oxygen toxicity (option C) occurs after prolonged exposure to high PO2, not acute ascent. CO2 retention (option D) is unrelated.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.