Decompression sickness is characterized by which mechanism and timing?

• A. Oxygen toxicity during prolonged exposure to cabin air
• B. Allergic reaction to air
• C. Gas bubbles form in tissues due to gradual pressure changes
• D. Gas bubbles form in tissues due to rapid pressure changes; risk during unplanned rapid ascent or ascent with diving history

Answer: (D)

Decompression sickness occurs when a rapid drop in ambient pressure causes dissolved inert gas, usually nitrogen, to come out of solution and form bubbles in tissues and blood. These bubbles disrupt microcirculation and trigger inflammation, leading to joint and muscle pain, neurologic symptoms, and sometimes skin changes. The timing matters: symptoms typically appear soon after a rapid ascent, often within minutes to hours, and are more likely if the ascent was unplanned or involved a diving history. It is not caused by oxygen toxicity or an allergic reaction to air, and it’s the rapid pressure change, not a gradual one, that drives the problem.