Decompression Sickness and Pressure-Related Disorders
Why decompression sickness happens
When ambient pressure falls, dissolved nitrogen can come out of solution as bubbles in blood and tissue. In aviation this follows rapid decompression or flying soon after diving. Symptoms include joint pain (the bends), skin mottling, chest pain, visual disturbance and neurological signs. Symptoms may be delayed by hours, so a pilot who has dived must respect the no-fly interval before ascending to altitude.
Prevention and treatment
Prevention means adequate surface intervals after diving, avoiding flying with a cold, and using oxygen after a decompression event. Treatment is descent, 100 per cent oxygen, and medical assessment; recompression may be needed on the ground. The condition is distinct from barotrauma, which is mechanical damage from pressure differences across body cavities.
Traps in questions
Examiners test the difference between decompression sickness (bubbles, systemic) and barotrauma (squeeze, local). They also test the direction of the pressure gradient: on ascent gas expands and may cause barodontalgia or gastric discomfort; on descent it contracts and causes ear and sinus squeeze. Another trap is the belief that symptoms always appear immediately.
Worked example
A pilot dives in the morning and plans an afternoon flight at 8,000 ft. The safe rule is to observe the recommended surface interval (commonly at least 12 hours after a no-decompression dive, longer after repetitive or decompression dives) and to seek advice when unsure. Rule of thumb: if you have dived, do not fly until the interval has passed.