RMV Spinoff from Accident & Incident Discussion - Northernone - aka Cameron Donaldson

[Joneill]

what animal uses its mouth as its main means of breathing

 

[BRT]

Since we are, sigh, once again back on the topic of skip breathing, let's look at the physiology.

1) you have a required "minute ventilation" (volume breathed per minute) that is a function of metabolic rate, body temperature and stimuli like drugs and CO2;
2) skip breathers do not have lower RMVs because they are "breathing less";
3) skip breathers may have fewer "wasted" breaths; wasted breaths being ventilation that wasn't really necessary for oxygenation or CO2 exchange, but because "you were thinking about your breathing." (See this post)

When you take an "extra" breath, a couple of things happen. You waste that volume of gas, and for a brief time, your alveolar CO2 drops because you have brought in fresh carbon-dioxide-free gas that has yet to exchange with the capillaries. That means that your body wants to breathe a little less in the minute that follows, to preserve CO2 and acid-base balance. At the same time, you used a bit more gas from your tank.
Perhaps sensing that you were breathing more than you really needed to, you try to "breathe less". This usually translates to smaller breaths. Smaller breaths work to preserve homeostasis, because with a larger dead space fraction, those breaths don't keep lowering your CO2, and your body gets back in balance (this is all very subtle - you can't feel it). But with the shallow breaths, you continue to waste gas and your RMV stays higher than physiologically required.

Skip breathers, on the other hand, actually try to breathe less.
Of course, it's not possible. Their bodies drives to respiration (increasing CO2 and decreasing oxygen) mandate that they have the same minute ventilation than they would without skip breathing. But what IS happening is in two parts: acute and chronic.

Acutely, as a skip breather tries to breathe less, his RMV is lower. But his CO2 is rising. His oxygen isn't falling because of all the extra oxygen molecules packed into a breath at depth.
As a result, he'll soon have to breathe MORE to lower his CO2 back to where it belongs.
OR...he/she can become acclimatized to slightly higher pCO2's. But at that point we switch to the chronic state.

At a chronic state of higher pCO2, his metabolic demands haven't changed, and he needs to have exactly the same minute ventilation than he'd required before he started skip breathing.
But at a higher pCO2. And that is where the risk lies. Diving at a higher chronic pCO2 for the benefit of that first couple of minutes when your RMV was briefly lower comes at the price of lower margin when gas density, workload and higher metabolic production of CO2 combine to make you hypercarbic. The skip breather is that much closer to a CO2 "hit" than a normal breather, and DOESN'T have a lower RMV. Gas density, CO2 production and your particular equipment may combine to result in unrecoverable hypercarbia and death.

Learning to breathe efficiently is the key. A brief pause at end inspiration to maximize exchange should be followed by a slow deep exhalation to exhaust the extra molecules of CO2 that accumulated during the pause. This is not a skip. It's just an altered pattern. The required minute ventilation is fixed. It may increase with exercise, and may decrease as a new diver gains experience, calmness and "Zen", but it won't change by breathing less or more.

So long as that "pause" isn't "skip breathing" then I don't know anybody that "skip breathes". I used to take that pause to the the point that I would have a headache after the dive.

 

[dmaziuk]

So long as that "pause" isn't "skip breathing" then I don't know anybody that "skip breathes". I used to take that pause to the the point that I would have a headache after the dive.

Presumably holding the pause by just the chest muscles and diaphragm, without closing off the airway -- just to be on the safe side?

 

[rsingler]

Presumably holding the pause by just the chest muscles and diaphragm, without closing off the airway -- just to be on the safe side?

Exactly. It's an inspiratory pause, not a breath hold.
Any headaches that might result are clearly CO2-related, and have crossed the line into skip breathing. Just not helpful to RMV, and risky as discussed above.

 

[Joneill]

panting dog is dissipating heat

That is certainly one reason dogs may pant - but not the only one...

 

[boulderjohn]

have crossed the line into skip breathing

..and where is the line? How long before a pause at the end of a breath turns into skip breathing?

The people I know who skip breathe and will talk about it ("Hell, yes! I skip breathe!" one said) maintain that they know where that line is. They are well aware of the danger of CO2 buildup, and they are sure they can avoid going too far.

 

[cerich]

It's called "Let's talk about something else" AKA red herring fallacy

before I have to learn a new term for what to me is intellectually dishonest, it's easier to state what I think and call it a day.

 

[rsingler]

..and where is the line? How long before a pause at the end of a breath turns into skip breathing?

The people I know who skip breathe and will talk about it ("Hell, yes! I skip breathe!" one said) maintain that they know where that line is. They are well aware of the danger of CO2 buildup, and they are sure they can avoid going too far.

An excellent question, John!
You can't feel it anymore, after you become a chronic CO2 retainer. We can see a guy with emphysema from across the street, pursing his lips and forcing out his breath against back pressure to maintain gas exchange with his smoke-damaged lungs. But he can't feel his pCO2 of 55 any more, because his body has elevated bicarbonate to keep his pH normal.
But a diver? My prejudice is that no matter how they pride themselves on their low RMV (and they should), they are also ignoring the subtle things that they just associate with diving, which are actually forced CO2 retention. A minor headache, the occasional big breaths back on land that they don't even notice any longer. They are the opposite of the relaxed Zen diver. They have developed a habit which they associate with their low RMV which is actually counterproductive, but they do not understand the physiology and have carried their altered pattern too far.
But they are not chronic CO2 retainers. You can't voluntarily do that all the time. Your body will correct, absent a disease process that produces more CO2 or impairs ventilation. So they have habituated themselves to feelings which they ignore, or which no longer are as severe (headaches) as the body acclimatizes. But they are at significantly increased risk, for ten minutes extra dive time.

I would say, listen to your body. Relax. Don't chase RMV. But perhaps just watch for wasted small breaths as you dive. Understand that your desire to "sip" just a little air from your tank actually made things worse, because you mostly exchanged dead space, and you'll be feeling the need to take a big breath soon when your body sees the rising CO2. Ignore that at your risk.
Then be happily surprised as your RMV improves naturally, with experience and calm.

 

[BRT]

..and where is the line? How long before a pause at the end of a breath turns into skip breathing?

The people I know who skip breathe and will talk about it ("Hell, yes! I skip breathe!" one said) maintain that they know where that line is. They are well aware of the danger of CO2 buildup, and they are sure they can avoid going too far.

We dove for years with a dive shop owner in Mexico who didn't seem to use any air. We wanted so badly to extend our dives and we learned to wait between breaths, call it what you want. I often waited long enough between breaths to have a good headache at the end of a dive. Now, a friend who often dives with us is really frustrated because he uses more air than us. He hangs above and watches. He says " all you guys that don't use much air are skip breathing, I can see it!" Naw, we are just waiting between breaths. Now I have to watch myself because I automatically "wait between breaths" and have to make sure I stop doing that while exercising. This February in Mexico I got a short tank. I didn't want a short dive so I "waited a little more between breaths" until my tank pressure was in line with my dive time. It works, very simply because each breath has less oxygen and more CO2 when exhaled. Pushed too far a person can get really narced and or a headache.

 

[BRT]

Presumably holding the pause by just the chest muscles and diaphragm, without closing off the airway -- just to be on the safe side?

Full disclosure, I close off the airway....I also know when I am going up or down.