What best describes the cause of pulmonary oxygen toxicity at low pressure?

• A. Breathing higher concentration of oxygen for short periods
• B. Breathing normal air at sea level
• C. Breathing higher concentration of carbon dioxide
• D. Breathing higher concentration of oxygen for extended periods, usually during hyperbaric chamber treatments

Answer: (D)

Oxygen toxicity in the lungs comes from excessive oxygen exposure over time. When the partial pressure of oxygen in the lungs stays high for a long period, the tissues generate reactive oxygen species that overwhelm the body's antioxidant defenses, causing inflammation, alveolar membrane damage, and edema. The key factor is how long you breathe a high oxygen concentration, not just the ambient pressure. That’s why breathing a higher concentration of oxygen for extended periods best describes the cause at low pressure. In practice, this is often seen during hyperbaric treatments where oxygen concentration is high; even at normal pressure, prolonged high FiO2 can produce the same toxic effect. The other options don’t fit because normal air at sea level isn’t highly oxygenated, carbon dioxide toxicity involves a different mechanism, and the essential danger is the duration of exposure to high oxygen, not a brief or unrelated scenario.