C02 building up while racing underwater to figure out working SAC?

[Soakedlontra]

Today my buddy and I wanted to figure out our working SAC so we decided to swim as fast as we could for 5 minutes keeping a depth of 27 ft. After kicking for about 2 minutes I began to feel that something 'funny' was going on with my breathing. There was no current and we were diving at a site that we dive regularly. The visibility was not too bad. I don't know how to put it into words exactly but all at sudden one part of me kept telling me to stop and go to the surface. I felt, maybe, I was not getting enough oxygen or something like that, the regulator seemed to be working fine. While I kept swimming I thought that I had two choices 1) stop swimming like a maniac and hover just above the bottom to regain control of my breathing or signal my buddy to go back up to the surface. I decided to do a controlled ascent and off we went going to surface in the water column and even stopped at 15 ft to do a safety stop. On the surface I took several deep breaths and then I felt normal again. Then we discussed whether to go back down and try it again or not and we decided to skipped it and do some skills that we had planned to do. Every went OK. We shared air hovering above the bottom and took turns in deploying the surface marker buoy.

I am wondering if that uncomfortable sensation was caused buy a building up of CO2. Is there a particular way of breathing while swimming vigorously that can help to prevent the increasing of CO2 in your body?
Or was it caused by something else?

 

[g1138]

You nailed it on the head. CO2 buildup, there really is no way to prevent it or fix it when swimming vigorously. If you keep to a shallower depth, you can either relieve or prolong the eventual CO2 hit; since there's an increased partial pressure of CO2 at depth that's greater than at the surface. The main priority however, should be to keep strenuous activities to a minimum

For what it's worth, your working SAC rate should not be an all out sprint, but rather what you would normally feel when you are "working".
Keep it to a swim pace just a tad above normal. You shouldn't be working on a dive to the point that you're even nearing a CO2 hit.

Edit:
Ok, so there is one other way that may help to relieve a CO2 hit. This should be done in addition to stopping all strenuous activity. There have been times were I have been close to a CO2 hit. Once was when I was in the pool harassing and drilling students on problem solving skills during a scientific diver training class. (things like ripping masks off and unhooking tank straps etc)The class was swimming in a circle and I was excitedly swimming around the group to fiddle with things. Got really winded in the process.

A second time was during a sci dive where I became pinned between two boulders while surveying the bottom. The surge pounded me back and forth and I started hyperventilating.

Both times, I got to a place where I could fin pivot and relax; if you can't stabilize in a fin pivot then just forget about the bottom and kneel or lay down. I then kept my reg on a light purge and just breathed deep breaths, trying to get my breathing back to a normal pace. Purging the reg kept me from having to activate the cracking pressure, which at that point seemed like an awful lot.
Doing this helped me to catch my breath a lot faster and calm down. But if you're already close to the surface and have a safe way to ascend, I would just go for that after you get your breathing somewhat under control, rather than trying to sort the entire situation underwater.

 

[Soakedlontra]

Thanks!

You nailed it on the head. CO2 buildup, there really is no way to prevent it or fix it when swimming vigorously. If you keep to a shallower depth, you can either relieve or prolong the eventual CO2 hit; since there's an increased partial pressure of CO2 at depth that's greater than at the surface. The main priority however, should be to keep strenuous activities to a minimum"
For what it's worth, your working SAC rate should not be an all out sprint, but rather what you would normally feel when you are "working".
Keep it to a swim pace just a tad above normal. You shouldn't be working on a dive to the point that you're even nearing a CO2 hit.

Well I pushed it too hard, my buddy was fine, though...darn! I guess different people react in a different way...But what if you don't have any choice because, for instance, you want to get out from a strong current that you did not expect? It did happen to me once. In that case we drifted and surfaced...thankfully the boat captain was able to see us! Maybe we should have climbed the bull kelp stipes instead like a couple of divers did...

, so there is one other way that may help to relieve a CO2 hit. This should be done in addition to stopping all strenuous activity. There have been times were I have been close to a CO2 hit. Once was when I was in the pool harassing and drilling students on problem solving skills during a scientific diver training class. (things like ripping masks off and unhooking tank straps etc)The class was swimming in a circle and I was excitedly swimming around the group to fiddle with things. Got really winded in the process.

A second time was during a sci dive where I became pinned between two boulders while surveying the bottom. The surge pounded me back and forth and I started hyperventilating.

Both times, I got to a place where I could fin pivot and relax; if you can't stabilize in a fin pivot then just forget about the bottom and kneel or lay down. I then kept my reg on a light purge and just breathed deep breaths, trying to get my breathing back to a normal pace. Purging the reg kept me from having to activate the cracking pressure, which at that point seemed like an awful lot.
Doing this helped me to catch my breath a lot faster and calm down. But if you're already close to the surface and have a safe way to ascend, I would just go for that after you get your breathing somewhat under control, rather than trying to sort the entire situation underwater.

I don't think I was hyperventilating (like one time several years ago when the current freaked me out and somehow I lost control of my buoyancy and my buddy got hold of my fin and dragged me down . In that particular case surfacing did not seem to be the best option so I sank to the bottom and kept breathing deeply until it was under control and ended the dive according to plan without further problems).
Maybe my breathing was too shallow...even if I thought otherwise...

 

[TSandM]

What happens when you overexert on scuba is that your breathing becomes rapid and shallow -- the increased work of breathing through a regulator prevents you from increasing your minute ventilation to the extent that you can do it on land. The exertion creates increased CO2 production, but because so much of the breathing you're doing is only ventilating your trachea and major bronchi, and less is getting deep into the lungs where it actually participates in gas exchange, you are removing CO2 less efficiently. The result is CO2 buildup, and a feeling of shortness of breath or even panic. The only solution is to reduce CO2 production by becoming still, and making your breathing pattern deeper and slower again, to make it more efficient.

It is not surprising that you had more CO2 buildup than your buddy. Two people moving at the same speed may be working at entirely different levels, depending on fitness, strength, resistance to the water, fin type and kick efficiency.

 

[MXGratefulDiver]

As you know, Betty ... I do that exercise in my AOW class. But I'm curious ... why 27 feet? Granted, you can calculate your SAC rate at any depth by dividing actual consumption by ATAs at that depth ... but the math is much easier if you go a few feet deeper and do it at 33 fsw.

Next time, as soon as you feel the onset, signal your buddy to slow down a little bit ... and concentrate on modulating your breathing to a slower, deeper pattern. If the feeling persists more than a few seconds, discontinue the exercise, relax, and get your breathing back under control ... you don't want to push it to the point of a feeling of "I can't get enough air" ... that imposes a powerful urge to bolt to the surface.

... Bob (Grateful Diver)

 

[Kellykins]

lactic acid buildup?!
Like when you run too fast, and then you feel that horrible sensation in your lungs making you breath funny

 

[clownfishsydney]

Swimming as hard as you can will probably always bring on some sort of problem. Always swim as slow as you can. SAC = normal air consumption.

 

[MXGratefulDiver]

Swimming as hard as you can will probably always bring on some sort of problem. Always swim as slow as you can.

As a general practice, I would agree with you. But the purpose of what Betty is describing is a class exercise designed to simulate swimming against a hard current (i.e. "worst case" situation) for the purpose of checking your "working" air consumption rate.

This is useful information for those who choose to make air management a part of their dive planning process, as described in Understanding Gas Management

Swimming fast as part of a normal diving practice is not something I would recommend ... unless conditions dictate that you have to. It is, however, not a bad idea to know where your limits are in this regard ... at least for those of us who shore dive on a regular basis, and have to end our dive at a specific location ... because sometimes you WILL have to ...

... Bob (Grateful Diver)

 

[HowardE]

I think this perfectly illustrates the CO2 cycle, and the dangers of CO2 buildup, "retention."

This cycle is especially dangerous to rebreather divers as well, which is why you may hear that working on a rebreather isn't wise.

The thing about CO2 is that the buildup of CO2 drives us to breathe more to ultimately get rid of the CO2, as TS&M explains. The need to breathe more when you're already exerted often causes us to breathe heavily and inherently not as deep, which causes more CO2, which causes us to need to breathe more, and the cycle gets worse and worse.

When you're breathing more, and often harder, you end up breathing more shallowly. When we're on scuba or any other system that requires us to breathe through a tube, (snorkel, rebreather, etc) there is anatomical dead space in the line, where inevitably we are re-breathing gas with elevated CO2 in it. For Scuba divers, this can be overcome by attempting to resume your normal breathing pattern, as the anatomical dead space in the trachea and your second stage is relatively small, and can easily be overcome by full "normal" deep breaths... Shallow breathing makes us rebreathe the gas in our lungs, and thus the elevated CO2 as explained. (this is why skip breathing doesn't work)

To a rebreather diver. This cycle can be deadly, because if you "overbreathe" you can ultimately make up more CO2 than your rebreather can handle, and the diver can potentially "go to sleep" from the lack of fresh O2, and the higher levels of CO2, which obviously - going to sleep on the bottom isn't a good idea.

 

[boulderjohn]

..But what if you don't have any choice because, for instance, you want to get out from a strong current that you did not expect? It did happen to me once. In that case we drifted and surfaced...thankfully the boat captain was able to see us! Maybe we should have climbed the bull kelp stipes instead like a couple of divers did...

If you are in such a circumstance, the best thing to do is to find something to hold on to while you get some rest. It does not take much. I have hooked a single finger over dead coral. and I have dug my fingers into sand. Perhaps you were in a situation where nothing was available, but if you have anything to get your claws on, that's the best thing to do.

If there is any chance you will need to drift and surface, you should carry a SMB and spool/reel so you can send a signal before you surface and drift away.