On a normoxic trimix course that I recently took I was told that "descending feet first reduces both nitrogen narcosis and the effects of CO2 because the orientation is more natural and lungs work better" I find this very difficult to believe. I wonder how anybody could have coined such an idea. Is this related to extremely fast descents in a wetsuit, where people may forget to vent out CO2 efficiently enough or what?
I do not believe the claim because:
- If I descend horizontally and watch forward, as I should to maintain contact with the team, then my head is about in the same position as it would be while descending feet first. The orientation thus shouldn't affect balance.
- In a vertical position, all the gas in the drysuit rushes up to the neck region and causes extra squeeze around the neck. Hardly pleasant nor good for circulation I guess.
- If I lay flat, then my lungs are at the same depth as the pressure regulating first stage and I can bearthe gas at ambient pressure. My head is also tilted back, thus opening the airway. If I descend feet first, then my lungs are deeper, and on each breath I must to some work to overcome this pressure difference. Further, I would need to look down, which puts my chin against my chest, which obstructs the airway. Breathing in an upright position should thus be harder.
What's the truth?
I do not believe the claim because:
- If I descend horizontally and watch forward, as I should to maintain contact with the team, then my head is about in the same position as it would be while descending feet first. The orientation thus shouldn't affect balance.
- In a vertical position, all the gas in the drysuit rushes up to the neck region and causes extra squeeze around the neck. Hardly pleasant nor good for circulation I guess.
- If I lay flat, then my lungs are at the same depth as the pressure regulating first stage and I can bearthe gas at ambient pressure. My head is also tilted back, thus opening the airway. If I descend feet first, then my lungs are deeper, and on each breath I must to some work to overcome this pressure difference. Further, I would need to look down, which puts my chin against my chest, which obstructs the airway. Breathing in an upright position should thus be harder.
What's the truth?
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