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

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In this thread we have the benefit of two highly trained breathing specialists. They are Drs specializing in anesthesiology and we are blessed to have them as our two newest staff members. Welcome to the staff, our longtime board members @rsingler and @Compressor
 
No I mean slow shallow breathing, never deep breathing. Deep breathing or over breathing narrows the air ways and reduces oxygen transfer.
Respectfully and gently disagree. Please see @rsingler 's post above.
For more information please see the classic book in respiratory physiology. I don't want to say more as @rsingler did it perfectly and it will detract from thread topic.
 
Do you mean narcosis rather than DCI?
No.
Elevated carbon dioxide can cause not only narcosis but DCI. Why? Because elevated levels of carbon dioxide can cause blood vessels to dilate enhancing delivery of inert gas to tissues. Also elevated levels can lower the threshold for oxygen toxicity. Factors that can increase the divers' carbon dioxide levels include the increased dead space of breathing equipment and the additional work of breathing dense gas underwater, and activity level among other things.
 
I'm reluctant to reply, lest we derail this thread. But from an A&I perspective, gas management for a dive to possibly 150' is an appropriate topic. Therefore breathing technique as it relates to gas management is also relevant.





A few terms have been put together that don't quite go together, physiologically.
We've got slow, shallow, deep, overbreathing, calm, narcosis, CO2 retention, airways and oxygen transfer, all in three sentences. Let's sort this out, with all due respect to the cumulative experience of the divers above.

Slow is good, up to (and maybe even including) the point of skip breathing. Without rehashing that argument, a slow rate with a hint of a pause at end-inhalation maximizes the time that oxygen is extracted from the alveoli and CO2 is discharged into them.

Calm is good, but shallow is bad. Period. If shallow makes you feel calm then there's a tradeoff happening.
Why is shallow bad? Dead space. You have pulmonary and equipment passages that are used but do not contribute to oxygen/CO2 exchange. The higher the percentage of your breath that you waste on dead space exchange, the more gas from your tank you are going to use. Why? Because to avoid hypoxia and CO2 retention, you must breathe some minimum amount. Any dead space ventilation is on top of that, but still pulls from your tank. From a dead space exhange standpoint, the most efficient technique might be one large breath per minute, large enough to dump all your CO2 and inhale all your next minute's oxygen at once, with long pauses at end-inhalation to allow the transfer to take place. But this is not physically possible. So we need a compromise.

Deep is good, overbreathing is bad. Slow breaths minimize the turbulent flow which is problematic at high gas density. Deep breaths minimize dead space exchange. Overbreathing (specifically, rapid exhalation) can contribute to airway collapse, which, while it doesn't affect oxygen transfer per se, does affect gas transfer, and therefore CO2 retention (and possibly hypoxemia) especially at depth (high gas density).

What are we left with?
A need to minimize dead space ventilation (bigger breath).
A need to minimize wasted ventilation (calm, Zen breathing).
A need to minimize turbulence at high gas density (slow breathing).
A need to maximize gas exchange (some sort of "pause" at end inspiration which won't screw up your buoyancy, but adds time for gas exchange at the alveolar/capillary interface), but which doesn't become skip breathing to the extent that your CO2 climbs from breath to breath.

Relatively Slow, Calm, Relatively Deep, and only what you need. That's how you minimize RMV.
Ok i should not have used the word shallow, should have said light and from the abdomen. A person breathing through the mouth, which divers do, could be exhaling 50% of the oxygen they just inhaled. To much oxygen resulting in to little co2 will narrow the airways, limit the body's ability to oxygenate and constrict the blood vessels.
 
Because elevated levels of carbon dioxide can cause blood vessels to dilate enhancing delivery of inert gas to tissues.
So you are saying that respiration affects on-gassing, that our deco models need to know more than time and depth?
 
Factors that can increase the divers' carbon dioxide levels include the increased dead space of breathing equipment and the additional work of breathing dense gas underwater, and activity level among other things.

I’d speculate that the most common dead space that enables carbon dioxide retention is the divers lungs. Especially when skip breathing or using shallow breathing to limit Gas usage..

I too know folks with rediculous SAC rates...they are all skip breathers. As said earlier in this thread, they won’t admit it...but I can see an OC diver breathe...they are skip breathing.

It’s fair to theorize that Cam had some level of increased CO2 retention if his SAC was that low. Maybe a level he was comfortable with when chilling on a scooter. But when already retaining, add some level of exertion(read wicked current) and things can start going south quick. Breathing rate goes sky high, the narcosis, the anesthesia, Increased risk of sudden Unconsciousness, increased risk of OxTox...all of which have and will again happen to experienced, young and fit divers.

Like I said earlier, we won’t know unless we find him...or his gear.

Side note: has there been a search effort in the area where he would or could have likely been doing deco? I’ve seen or heard of as many incidents start during deco as I have on the bottom.
 
So you are saying that respiration affects on-gassing, that our deco models need to know more than time and depth?
you just hit the nail on the head, a divers breathing habits has a directly affects on that persons decompression penalty.
 
So you are saying that respiration affects on-gassing, that our deco models need to know more than time and depth?
Decompression illness is caused by multiple factors (as you know) and respiration has effects on in-gassing as well as off gassing. Deco models do need to account for multiple factors if they want to be accurate.

In honor of Cameron, let's not change the content of this thread. Questions about DCI can be raised in the appropriate forum. I appreciate your kindness and understanding in this matter.
 
Ok i should not have used the word shallow, should have said light and from the abdomen. A person breathing through the mouth, which divers do, could be exhaling 50% of the oxygen they just inhaled. To much oxygen resulting in to little co2 will narrow the airways, limit the body's ability to oxygenate and constrict the blood vessels.

I don't understand this. Oxygen to CO2 ratio would not change when you inhale through your mouth or your nose. If you breathe air, the O2 would be about 20.5% and CO2 would be about 0.04%.​
 
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