Nitrox + Asthma = Question?

[DeputyDan]

My daughter has mild asthma but has been cleared to dive and is OW certified.

My question would be - If she were to take a Nitrox course, are there any issues related to asthma?

 

[diverlady]

I'm not a doc but I have mild asthma and am EANx certified. I've used Nitrox and not had any issues. Humidity bothers my asthma so dry air of any mix is pure heaven!

Diverlady

 

[diver_paula]

Ditto for me on Diverlady's experience.

 

[Big-t-2538]

The asthma is triggered more by the dry-ness of the contents of the tank, not the O2 content inside.

If she is cleared to dive, that should have no effect on EANx certs....but there is always something that shocks me.

 

[large_diver]

I sent a similar question to DAN recently -- see the end of my post below for my original question and DAN's answer.

A technical instructor I spoke to recently about this issue actually said that use of Nitrox underwater could be beneficial to an asthmatic due to improved beathing capacity vs. air. He cited a study that compared use of Triox vs. air -- the decrease in breathing capacity when using Triox is 0% at a depth of 50 feet (vs. 40% on air) and 14% at 100 feet (vs. 50% on air). The person I received this information from went on to postulate that Nitrox, while not providing all of the breathing capacity benefits of Triox, would at least marginally increase breathing capacity at depth vs. air.

I haven't been able to find any other data on this breathing capacity topic. I asked DAN about it -- although they did confirm that breathing capacity using air is significantly reduced at depth (they cited a 30% reduction in breathing capacity at 33 feet and a 50% reduction at 100 feet -- largely matching the figures above), they did not provide any information on the effect of Nitrox vs. air on breathing capacity.

-Chris

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My original question sent to DAN:
Does DAN have an opinion on whether use of Nitrox is dangerous by someone who has mild asthma? Would Nitrox represent an advantage over air (other than the "usual" benefit of longer NDL times)?

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DAN's reply:

Chris

Thanks for the inquiry

The concerns with asthma are not the percentage of Oxygen in the mix but the fact that breathing any air mix at depth with a potential for air trapping and then ascending could create a lung expansion injury.

Scuba diving can be dangerous for asthmatics for two reasons. First, during scuba diving there is normally a reduction in breathing capacity due to immersion and an increase in breathing resistance caused by the higher gas density at depth. At 33 feet, the maximum breathing capacity of a normal scuba diver is only 70% of the surface value, and at 100 feet it is only one half. If a diver's breathing capacity is already reduced because of asthma, there may be insufficient reserve to accommodate the required increase demanded by exertion. Second, both narrowing of the bronchi and excessive mucus production can inhibit exhalation of air during ascent, and could predispose to pneumothorax, pneumomediastinum or air embolism.

For these reasons, almost all physicians trained in diving medicine previously recommended that people with asthma should never dive. However, a consensus of experts at a 1995 workshop held under the auspices of the Undersea and Hyperbaric Medical Society (UHMS) proposed more liberal guidelines. A range of medications is available for asthma treatment, and can often return lung function to normal. Specific breathing tests (often referred to as "pulmonary function tests" or "PFTs") can be used to determine the response to therapy. The UHMS workshop panel felt that the risk of diving with asthma is probably acceptable if, both before and after a provocative test such as exercise, the diver has normal PFTs. Even if divers with asthma fulfill this criterion, they must also be free of respiratory symptoms before each dive.

[The consensus at the UHMS Workshop on diving and asthma was that the provocative test should be exercise, rather than histamine/methacholine inhalation. I would highly recommend obtaining the full workshop report entitled: Are Asthmatics Fit to Dive (DH Elliott, Ed), 1996, Undersea and Hyperbaric Medical Society, Kensington, MD. The book can be obtained via the UHMS web site: www.uhms.org. ]

So the concerns are not the mix but the fitness to dive for asthmatics.

I hope this is helpful.

Laurie Gowen, NREMT-B, DMT
DAN Medical Services
Department of Anesthesiology
Duke University Medical Center
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[Saturation]

large_diver once bubbled...
Nitrox underwater could be beneficial to an asthmatic due to improved beathing capacity vs. air. He cited a study that compared use of Triox vs. air -- the decrease in breathing capacity when using Triox is 0% at a depth of 50 feet (vs. 40% on air) and 14% at 100 feet (vs. 50% on air). The person I received this information from went on to postulate that Nitrox, while not providing all of the breathing capacity benefits of Triox, would at least marginally increase breathing capacity at depth vs. air.

Breathing gases are denser with depth, thus the work of breathing compressed gas increases. It doesn't become apparent until you buildup c02 by exerting onself then periods of shortness of breath last longer, if not persist. The work of breathing can be reduced by reducing N2 and 02 BY USING He as much as possible in the mix and using the best low work of breathing regulator available. A problem is not during inhalation, as pressurized gas is pushed into the lungs in open circuit SCUBA, all you do is trigger it with a brief negative pressure on the 2nd stage. However, to exhale, you need to force the gas through your airways by chest compression and this is where a problem lies. A reduction is breathing resistance would benefit all divers, however this isn't noticable compared to air without heavy work, deep depth or a bad regulator or combinations of them.

Asthmatics would have the added benefit of breathing highly filtered gas and reduced chances for allergens in the gases, but no other added benefits apart from normal people: asthmatics have near normal pulmonary function when not in an attack. An asthmatic attack at depth, a great fear for sometime but very rare, would be near fatal regardless of gas breathed, and not because of the gas, but because of embolism or a pneumthorax. Because its recommended asthmatics continue to take maintenance medications during dives, some of which contrain epinephrine like analogs, there is a theoretical increased risk of a lowered oxygen toxicity threshold with high 02 mixtures.

[error! not NITROX] TRIOX or trimix may aid mild COPD patients throughout a dive, who have permanent impairments. However, if the same COPD patients can exercise without issues on the surface, the vast majority do not experience dyspnea at depth. The only time one would notice the differences between mild COPD patients and normal divers at depth is during the performance of some work: lifting, using tools etc., or heavy swimming. Otherwise, if COPD patients have some impairment at the surface, they may not pass the open water physical requirements.

 

[large_diver]

Saturation,

Thanks for responding.

A few questions.

First -- please define COPD.

Second -- you mention that Nitrox can reduce the work required to breathe (during exhalation)...I assume this is due to differing gas densities?

Third -- you discuss the build-up of CO^2 due to the work of breathing at depth. You state that Nitrox may reduce (marginally) breathing resistance/effort. What about breathing CAPACITY? Does Nitrox affect breathing capactiy and would an improvement in breathing capacity play a role in reducing CO^2 levels?

Thanks,

-Chris

 

[Saturation]

large_diver once bubbled...
Saturation,

Thanks for responding.

A few questions.

First -- please define COPD.

welcome ...
chronic obstructive pulmonary disease, a combination of emphysema and bronchitis, most patients who have classic emphysema have some amount of bronchitis and vice versa, the balance of which determines whether you are mostly an 'emphysema' patient or a 'bronchitis' patient; COPD has many causes, #1 common cause is smoking...

Second -- you mention that Nitrox can reduce the work required to breathe (during exhalation)...I assume this is due to differing gas densities?

I MADE A MISTAKE. The answer should be NO, I said YES previous. THIS IS A CORRECTION. See next post by me following below.

Third -- you discuss the build-up of CO^2 due to the work of breathing at depth. You state that Nitrox may reduce (marginally) breathing resistance/effort. What about breathing CAPACITY? Does Nitrox affect breathing capactiy and would an improvement in breathing capacity play a role in reducing CO^2 levels?
-Chris

SORRY CHRIS, MEA CUPLA. Mistake. Nitrox will not reduce the gas density at depth compared to air.

Breathing capacity which I presume to mean the capability to inhale and exhale? In indirect ways yes, once you reduce N2 AND 02, it reduces the work of breathing and it enhances overall all lung functional measures including "capacity" [the medical term is different, if I understand your meaning.]. However, your capacity cannot exceed what your are physically capable of doing on the surface [less the lungs burst.]

After N2 and 02 reduction, c02 elimination is done best by reducing the resistance to exhalation in the 2nd stage, meaning keeping the exhaust vents as short as possible.

 

[large_diver]

I'm referring to capacity in the same context referred to in the DAN reply above...which I take to mean the amount of gas you can take into your lungs.

Using air, this capacity is reduced depending on depth by the %s cited above. I am curious to know if Nitrox has any effect on this. All else held equal, I would think that being able to inhale/exhale more gas (in this case Nitrox) means your body is getting more O^2 and expelling more CO^2....still reduced vs. lung function on the surface, but better than breathing air at depth.

-Chris

 

[Saturation]

large_diver once bubbled...
I'm referring to capacity in the same context referred to in the DAN reply above...which I take to mean the amount of gas you can take into your lungs.
Using air, this capacity is reduced depending on depth by the %s cited above. I am curious to know if Nitrox has any effect on this.

Hi Chris, thanks I think I understand.

The answer would be no, you won't increase maximum breathing capacity by using nitrox over air [I believe DAN is using a lung function also known as maximum voluntary ventilation, MVV].

The density of pure 02 is actually greater than nitrogen, so even if you breathed 100% 02, if at all possible, it would be slightly worse than breathing pure Nitrogen, if that was possible. Air is a mixture of both gases, trace gases and water vapor to dilute both gases to reduce its density to less than either gas alone.

Here is a link to a periodic table, see the physical properties of each gas, under DENSITY.
http://environmentalchemistry.com/yogi/periodic/

All else held equal, I would think that being able to inhale/exhale more gas (in this case Nitrox) means your body is getting more O^2 and expelling more CO^2....still reduced vs. lung function on the surface, but better than breathing air at depth.
-Chris

Yes, but to move gas more easily at depth by breathing gas alone is to add He to the mix. Other practical ways are to increase the IP of your reg to its maximum, and remove any impediments to exhalation. Technique wise, breath SLOWLY and deeply. As regulator IP increases, or breathing rate increases, the turbulence of gas mixing actually increases gas resistance, so at some point, breathing rapidly or increase IP produces negative results. The net results is a build up of C02. There is little reduction of 02 since at depth one is breathing a very hyperoxic mixture compared to the surface but c02 buildup is proportionate for a given work.

I've also made a correction to my previous post, the best way to reduce gas density in mixtures is to use He such as trimix but not triox, which contains too much 02.