Hypercapnia

[Mr. Bubble]

I have started deeper diving (below 130) and I have learned that I suffer from hypercapnia. Retention of CO2. Some of my instructional books say that some people are just more prone to CO2 retention. Is there a way to find out, a test that would indicate that I have this build-up moreso than others? I had some difficulty in the 120-130 rang a few years ago, under exersion, rapid decent and depth, I became highly anxious. It has taken me several dives to regain my confidence in the lower limits of recreational diving, regulating my breathing and exhailing forcefully. I realize that learning to extend my range, I will need to begin tri-mix, but at around 165, I begain feeling the anxiety and nausia again. Is this normal? The other divers I was with expressed no ill feelings and were at 180 (for a few min.) How does trimix and hypercapnia work? If I am predisposed to CO2 retention, is trimix going to solve that problem, or is is going to be something of greaster concern for me at greater depth?

Thanks

 

[diverdoug1]

Using Trimix will not change your minute ventilation (Resp. rate X tidal volume), so it should not change your pCO2 (serum carbon dioxide). Trimix may very well help the anxiety if it is being caused by nitrogen narcosis. The most common cause of hypercapnia in divers is "skip breathing", or voluntarily limiting their minute ventilation, in an attempt to minimize gas comsumption (bad idea for many reasons). Hope this helps!

 

[DevonDiver]

This seems to fall into the catagory of understanding your limitations and expanding your depth progressively.

It is most likely that narcosis and anxiety is playing a key role in increasing your stress. That results in a shallower, quicker, breathing pattern...failure to refresh dead air spaces, coupled with increased air density (and maybe some increased breathing resistance from the reg)...hence hypocapnia.

Trimix is the ultimate solution to narcosis (some agencies recommend an END of 30m) and that may, in turn, allow you to maintain a more regular breathing pattern at depth.

The other, immediate, solution is to accept that your progression in deeper diving may be forcing you too far outside your comfort zone. Spend more time diving intermediate depths, get happy and comfortable with them, before progressing. We all progress at different speeds and there is no shame in accepting that you are not yet comfortable to progress. What matters most is that you are happy and comfortable with the dives you undertake.

I've never heard of divers being more or less physiologically susceptible to hypocapnia.... but am sure there are members of this forum with the appropriate medical knowledge to confirm or deny that.

 

[diverdoug1]

Some people are "CO2 retainers" who rely on their hypoxic drive to regulate respirations, not pCO2 (as is normal). It is my medical opinion that anyone with such severe respiratory pathology should consider not diving. I don't think hypOcapnia is an issue we are discussing here, but is usually a result of hyperventilation. HypOcapnia more frequently becomes an issue in diving medicine with relation to free divers, and increasing the risk of shallow water black out.

 

[Mr. Bubble]

Thanks for the notes. I guess I need to figure out if its narcosis or CO2 retention that is the problem. I do not recall high anxiety as being a narcosis affect, but spelled out under CO2 retention. I recall being a new diver, that I always had bad headaches after every dive. I learned to live with it and presumed it was something you just had to put up with in diving. Then I learned about CO2 retention. I begain clearing my lungs on a regular basis, and my headaches disappeared while diving.
I totally agree about taking it progressively. I am just more intune with my "feelings" than ever before, and pay close attention to my symptoms to avaiod a full blown situtation. I would hate to be moving into the trimix mode and having a predisposition to CO2 retention, then be 250 down and feeling like I need to scramble. My last air dive to 170 left me feeling nausious (narced) closing in (narced) and anxious (Co2 retention) It seems that they can always messure the PPO2, PPN2 but never the level of CO2 at depth.
like you say, one step at a time, easy does it.

Thanks

 

[diverdoug1]

Anxiety can be caused by nitrogen narcosis in the absence of hypercarbia.

 

[DevonDiver]

Anxiety is definitely a symptom of narcosis....as is Excessive Confidence. Narcosis can really exagerate your moods/feelings on the dive.