Quote: (Originally Posted by
Drmike)
Retained CO2 from over exersion/stress:
RMV probably I would imagine well over 50 before finally stop trying to convince myself im not having a problem
Bail to OC.
RMV will continue to rise it wont drop unless activity is stopped and I calm myself down. (on or off the loop recovery just as fast if retained CO2, key is to stop activity and calm down)
This battle to calm down breathing (retained co2 is almost as much mental as physical)
With all activity stopped and thinking happy thoughts RMV drops to levels where I feel ok again (no panic/stress feeling) after less than say 2 mins (this has been my experience) I go back to the loop and see if it was retained or scrubber failure.
I have had more retained CO2 issues than CO2 hits but the recovery time (at those times) for me was similar in both cases. But I think its really a matter of how bad the hit is (or how bad you let it get before you bail) leave it long enough and recovery would i imagine be much longer too.
But I seriously seriously doubt your RMV will be in the low 20s for quite some time after you bail (other stress raisers like being on limited bail out vol would likely kick in)
If I was to guess Id say maybe expect inital RMV 50+ then recovery (of main CO2 symptoms) after maybe 2-3 mins with RMV reducing steadily to slightly highet than normal levels over say a 10-15min period (this is just my guess based on my limited experience - it may be complete bol1ocks)
Mike's answer is near perfect in my view. Importantly, he reminds us that there are two potential causes of hypercapnia: CO2 retention because more is produced than eliminated from the body, and scrubber failure. The former usually arises in the context of over-exertion and we are particularly prone to this problem at extreme depths when the inspired gas is dense.
In scrubber failure the problem cannot be resolved unless you bail off the loop (or invoke some sort of semi-closed mode). In retention, the problem is unlikely to be resolved unless you rest and concentrate all attention and energy on just breathing. In reality, you cannot really tell what is causing your problem (scrubber failure or retention) so as Mike implies the correct approach is to invoke both restorative procedures simultaneously: that is, bail out and rest immediately. As he also suggests, if you are strongly suspicious that overexertion and retention caused the problem, then a cautious return to the loop to see if the problem recurs is sometimes appropriate.
I agree with Mike's estimates for recovery times. The drive to breathe will fall rapidly as CO2 is eliminated, and breathing rates / volumes will quickly fall. However, the potential complication in very deep diving is that the work of breathing itself can become a significant contributor to CO2 production. The more this is so, then the slower CO2 levels will fall because the breathing process itself (which is what gets rid of your CO2) will also be producing it. Indeed, it is possible that one can get into a vicious spiral in which so much CO2 is being produced by the work of breathing that it is impossible to rest and ventilate it off. The CO2 drives greater effort to breathe, which produces more CO2 and so on. This is what we think happened to David Shaw, and anyone interested in learning more about this frightening possibility should read our paper in Aviation Space and Environmental Medicine. Thus, Mike's estimates are fine, but there is some contextual influence of depth, gas density, and almost certainly of the resistance to breathing in the equipment. The deeper you are, the denser the gas, and more resistance in your equipment, the closer you are to an unrecoverable problem.
Warm regards,
Simon M