Which statement best distinguishes evolved gas dysbarism from trapped gas?

Which statement best distinguishes evolved gas dysbarism from trapped gas?

• A. Evolution gas results from increased pressure
• B. Trapped gas occurs only in the lungs
• C. Evolved gas results from a reduction in ambient pressure causing gas to come out of solution
• D. Evolved gas happens only in deep water diving

Answer: (C)

The key idea is how gas forms bubbles when pressure changes. Evolved gas dysbarism happens when ambient pressure falls—such as during ascent—causing dissolved inert gas (mainly nitrogen) to come out of solution and form bubbles in tissues or the bloodstream. This exsolution from solution is what defines evolved gas. Trapped gas, by contrast, refers to gas already present in a closed space and not arising from dissolved gas coming out of solution; it isn’t limited to the lungs and isn’t caused by a drop in ambient pressure producing new bubbles. It can occur in other noncommunicating gas pockets, and the mechanism isn’t about gas solubility changing with pressure. So the correct distinction is that evolved gas results from a reduction in ambient pressure causing gas to come out of solution.

The key idea is how gas forms bubbles when pressure changes. Evolved gas dysbarism happens when ambient pressure falls—such as during ascent—causing dissolved inert gas (mainly nitrogen) to come out of solution and form bubbles in tissues or the bloodstream. This exsolution from solution is what defines evolved gas. Trapped gas, by contrast, refers to gas already present in a closed space and not arising from dissolved gas coming out of solution; it isn’t limited to the lungs and isn’t caused by a drop in ambient pressure producing new bubbles. It can occur in other noncommunicating gas pockets, and the mechanism isn’t about gas solubility changing with pressure. So the correct distinction is that evolved gas results from a reduction in ambient pressure causing gas to come out of solution.