It was probably the position you were in not the reg.
Overbreathing my regulator
- Thread starter Hatul
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Bubbletrubble
Contributor
What was the cracking pressure of the second stage that you were using at the time?
When you were on your back at the surface, you could have done a very simple test to demonstrate whether it was the second stage or first stage that was limiting. While "over-breathing" your reg, you could have tried purging your backup/octo reg. If air came out of the purged reg, then the first stage wasn't limiting.
I suspect that you were hyperventilating. When a wave submerged your face in the water, your supine position effectively increased the cracking pressure of the second stage. All of this combined to increase your work of breathing.
It's possible that your reg just needs a little tune-up.
To answer your question, any high end second stage reg can be tuned to have a very high cracking pressure. That could give the diver a false perception of "over-breathing" the reg.
When you were on your back at the surface, you could have done a very simple test to demonstrate whether it was the second stage or first stage that was limiting. While "over-breathing" your reg, you could have tried purging your backup/octo reg. If air came out of the purged reg, then the first stage wasn't limiting.
I suspect that you were hyperventilating. When a wave submerged your face in the water, your supine position effectively increased the cracking pressure of the second stage. All of this combined to increase your work of breathing.
It's possible that your reg just needs a little tune-up.
To answer your question, any high end second stage reg can be tuned to have a very high cracking pressure. That could give the diver a false perception of "over-breathing" the reg.
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OP
Hatul
Contributor
It's a good idea to do the purge test and I'll try it next time. My reg has the adjustment knob and I keep it set just before it freeflows.
I'm sure I hyperventilate at times and a certain amount is inevitable in some situations when diving. My overall air consumption is at least on par with others I dive with.
By the way there is small flaw in your reasoning I need to point out (I'm an anesthesiologist). When you hyperventilate your CO2 in your blood drops rather than going up. What may happen is when excited you may take rapid shallow breaths that are inefficient and may appear like hyperventilation.
Also for these shore dive that require a lot of swimming I'm going take my snorkel, as I used up lots of tank air just for swimming on the surface.
Adam
Bubbletrubble
Contributor
Oops! Yeah. I posted too quickly without double-checking. Huge mistake. I'll fix that. Hyperventilation actually decreases arterial CO2 concentration. Hypoventilation increases PaCO2. My physiology professor would not be happy.
As a side note, it's possible that your hyperventilation was caused by exceeding your VO2max during exercise. I wonder if a respiratory alkalosis developed.
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oldmossback
Contributor
All above are good examples of what could be causing your problem........and yes, breathing on your back on the surface is easier without the regulator.......remember you are also pushing against the water with your lungs and the sensation caused by the small exhaust and 2nd stage spring compound the experience.......
Underwater, if you are vertical in any respect, (head toward the surface) your lungs are in deeper water ( which translates to pressure) than your regulator.......so again you have the sensation of overbreathing.......especially if you have just done or are doing hard swiming........
The cure, again as stated above, is to slow down your breathing and keep your reg. below your lungs............
Underwater, if you are vertical in any respect, (head toward the surface) your lungs are in deeper water ( which translates to pressure) than your regulator.......so again you have the sensation of overbreathing.......especially if you have just done or are doing hard swiming........
The cure, again as stated above, is to slow down your breathing and keep your reg. below your lungs............
I agree with the notion that you are not really overbreathing the regulator but were just not breathing correctly. A couple of other factors here, you were on the surface; regulators are designed to be used under water. You were on your back; regulators are designed to be used when you are not on your back.
Most likely, you were stressed, and breathing in short gasps --which is also more likely on your back. That lead to a C02 build up and made it feel as if you could not catch your breath.
Learn to control your breathing --that means all the time, on land, in the water, in stressful situations --that really makes all the difference. A good technique is to practice taking six seconds to inhale, really exercising the stretch of your lungs. Then take another six seconds to exhale.
Jeff
Most likely, you were stressed, and breathing in short gasps --which is also more likely on your back. That lead to a C02 build up and made it feel as if you could not catch your breath.
Learn to control your breathing --that means all the time, on land, in the water, in stressful situations --that really makes all the difference. A good technique is to practice taking six seconds to inhale, really exercising the stretch of your lungs. Then take another six seconds to exhale.
Jeff
Bubbletrubble
Contributor
Come to think of it, I wonder if heightened lactic acid build-up (due to strenuous exercise) decreased blood pH enough to cause central and peripheral chemoreceptors to increase the respiratory rate.
Perhaps this is more a conditioning issue than a reg issue.
halocline
Contributor
The lungs/reg relative position is not the cause of increased breathing resistance. This is very common misconception that's repeated over and over. This is very easy to prove; on a dive with a conventional 2nd stage try breathing vertically head up and then vertically head down; you'll find that it's about the same, even though those two positions represent the most extreme difference in lung/reg depth.
Then try positioning horizontal facing down and horizontal facing up, these are far lower pressure differentials between lungs and reg, yet they present by far the most dramatic differences in breathing resistance.
I am more and more convinced that the reason for this has to do with the relative depth of the mouthpiece and the diaphragm, and to a certain extent the relative depth of the exhaust valve and the diaphragm. The former is very easy to demonstrate with a double hose reg, in which you can easily change the relative depth of the mouthpiece and diaphragm simply by moving the mouthpiece around. The latter is a result of case fault geometry; somewhat simplified, the exhaust valve acts as a limiting factor on how much pressure can be present in the 2nd stage case; when it is deeper than the diaphragm, the pressure in the case is somewhat higher, which I believe is a contributor to the increase in cracking pressure.
I've experimented quite a bit with my D series 2nd stages; those have a coaxial diaphragm/exhaust valve arrangement in which there is never significant difference in depth between the two. Those regs are far less sensitive to position changes in breathing resistance than conventional 2nd stages.
But, I think that the strongest contributing factor is the relative depth of the mouthpiece exit point and the diaphragm. Another easy demonstration of this is a freeflowing 2nd stage can be stopped simply by turning it mouthpiece down. The effect is dramatic, and of course, there are no lungs involved in that one.
If you experience a little difference in breathing resistance between vertical heads up and vertical head down, it's because the mouthpiece is not inline with the center of the diaphragm, and so with head down it's a little deeper. On my conventional 2nd stages (G250/109) there is almost no difference. I attribute that to the slight increase in mouthpiece depth being offset by the slightly shallower exhaust valve lowering the pressure limit in the 2nd stage.
Then try positioning horizontal facing down and horizontal facing up, these are far lower pressure differentials between lungs and reg, yet they present by far the most dramatic differences in breathing resistance.
I am more and more convinced that the reason for this has to do with the relative depth of the mouthpiece and the diaphragm, and to a certain extent the relative depth of the exhaust valve and the diaphragm. The former is very easy to demonstrate with a double hose reg, in which you can easily change the relative depth of the mouthpiece and diaphragm simply by moving the mouthpiece around. The latter is a result of case fault geometry; somewhat simplified, the exhaust valve acts as a limiting factor on how much pressure can be present in the 2nd stage case; when it is deeper than the diaphragm, the pressure in the case is somewhat higher, which I believe is a contributor to the increase in cracking pressure.
I've experimented quite a bit with my D series 2nd stages; those have a coaxial diaphragm/exhaust valve arrangement in which there is never significant difference in depth between the two. Those regs are far less sensitive to position changes in breathing resistance than conventional 2nd stages.
But, I think that the strongest contributing factor is the relative depth of the mouthpiece exit point and the diaphragm. Another easy demonstration of this is a freeflowing 2nd stage can be stopped simply by turning it mouthpiece down. The effect is dramatic, and of course, there are no lungs involved in that one.
If you experience a little difference in breathing resistance between vertical heads up and vertical head down, it's because the mouthpiece is not inline with the center of the diaphragm, and so with head down it's a little deeper. On my conventional 2nd stages (G250/109) there is almost no difference. I attribute that to the slight increase in mouthpiece depth being offset by the slightly shallower exhaust valve lowering the pressure limit in the 2nd stage.
My guess is that this has more to do with increased work of breathing than any actual limitation of flow. I just finished reading a fascinating paper from the DAN Symposium on Technical Diving, which was talking about respiratory mechanics and gas flow in the lungs. When you are trying to maximize your minute ventilation, as you are with heavy exertion, increased work of breathing becomes a significant factor. The respiratory center doesn't want to do the work, so it allows the CO2 level to climb a little, and that may have been quite enough to make you uncomfortable.
I can say that with my old MK14/R190 while chasing an eagle ray for a picture at 80 fsw I nearly panicked because it did not seem I was able to get enough air. I ascended to ~60', held onto the wall and breathed as deeply as I could while concentrating on the idea that I was over exerting and I would survive (nearing blackout). I was solo at the time and over 3000' off shore, so I have been quite a bit more cautious about chasing fish in similar situations.
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