Calling all doctors... real ones, not tv characters

[avra cohen]

In bed, you are at essentially std pressure, 14.7 psi, (no dirty jokes here). You would not be breathing O₂ at higher partial pressure so it will should not affect you 24 hr. exposure.

I use a CPap every night. Great device.
It uses air but I would love to know how anyone here has a similar device that upps the pO2 or fO2 at 1 ATA. I have never heard of that.
If I did use one that added to my O2 clock while I slept I would be worried about my diving. Are there tables for that? I don't think so.

NOT a doctor, just a diver. Closest I've come to CPAP is diving my positive pressure full face mask (AGA) which is a must for diving in potentially contaminated environments. But as I'm taking advanced nitrox, I thought this was an interesting academic problem.

Any device like a CPAP that increases the pressure of an inspired gas mixture, necessarily increases the partial pressure of all its components (Gas Laws: Dalton's Law), so of course your pO2 will be raised. With supplemental oxygen being added, either by O2 concentrator or compressed gas source, the pO2 will be even that much greater proportional to the increase in fO2.

The pertinent question is: can this possibly amount to exposures that would be of concern for diving under any circumstances?

What is the high end pressure of a CPAP? It seems this does not usually exceed 20mmH2O. Converting to atmospheres
(Online Conversion - Pressure Conversion), we find this equals 0.002 or 1.002 ATA's. That is the equivalent of diving in 0.8 inches of seawater, albeit for eight hours. Help, I fell in a puddle and can't get up! Luckily I am wearing my scuba gear!

So suppose we now add in the supplemental O2? Even 100% O2 delivered by oronasal mask (as opposed to demand valve) has only an efficiency range of 50>70%. So (.70)x(1.002)=pO2 .7014, the equivalent of diving at 3.34 ATAs (.7014/.21) or 77fsw (2.34atm x 33)!
I dreamed I was in DECO! Of course we are not AT that pressure, we are asleep in bed! That is just the equivalent depth we would need to go to ON AIR to reach this level of oxygen partial pressure. So how do we compute our Oxygen Toxicity Units?
___________________________________
Nitrox FAQ:
What is the oxygen clock?
The oxygen clock is a mechanism for monitoring oxygen exposure over time.
The theory behind the oxygen clock has been around for about 30 years and concerns pulmonary oxygen toxicity (aka whole body toxicity or the Lorrain Smith Effect). It is measured in units of pulmonary toxic dose (UPTD)... Dr Bill Hamilton has suggested that we use the term OTU as he feels it gives more positive vibes. The OTU is based on empirical data from which the following best fit formula has been derived:

OTU = t * [(PO2 - 0.5) exponent 0.83]/0.5
where:

t is the exposure time in minutes
PO2 is the partial pressure of oxygen in Bar
0.5 is the threshold below which no significant pulmonary oxygen toxicity has been observed.
0.83 is the exponent which gives the best fit to experimental observations.
However, very roughly, 1 OTU is equivalent to 1 Bar exposure per minute.
(1 bar = 1.02 atmosphere [technical])

Period Dose/day Total
(days) (units) (units)
1 850 850
2 700 1400
3 620 1860
4 525 2100
5 460 2300
6 420 2520
7 380 2660
_____________________________________

So... 8 hours= 480minutes, pO2 is 0.7

Using the formula, 0.7 - 0.5 = 0.2, raised to the power of .83= .26
.26 x 480 = 124.8, 125/0.5= 250 OTU's

Well, IF my arithmetic is correct, and supposing an fO2 0.7 for eight hours at 1.0 ATA (we neglected the +.002 CPAP), that's more than a quarter of your allowable daily dose. Would the fO2 EVER likely be that high? I don't know! From what I've gleaned, actual fO2 would likely not be more than half or this. Now we need a REAL doctor. So I wrote to DAN Europe where I have had better luck getting timely responses. Here is what I asked:

Question: My dive buddy has been prescribed a CPAP machine w/ supplemental O2
supplied from a concentrator for the treatment of obstructive sleep apnea.
No other respiratory impairment was diagnosed. Depending on the fraction
and pressure, will this have to be accounted for in our dive planning as far
as oxygen toxicity units are concerned. We are currently doing
decompression dives using a popular dive table planner. Do the actual O2
exposures during sleep need to be factored in? Should we simply raise the
setting on the conservatism factor?
If the CPAP were just using ambient air, would there still be any concern
due to the increased pO2?
Thank you for any information about sleep apnea and diving.

Sincerely, Avra Cohen

Dr R. Cali-Corleo MD MSc MMCFD replies:

Dear Mr Cohen

The small extra amount of Oxygen provided by the CPAP should not be a problem if you are doing air diving, If you are doing Nitrox or Trimix diving with many dives where you will be sailing close to the UPTD max permitted levels then yes I would calculate the night as a 'dive' on the pp of oxygen he will be using and add it to the 'load' of the diver

I hope this answers your question

Regards

Dr R. Cali-Corleo MD MSc MMCFD
d/Chief Medical Officer, DAN Europe
Specialist in Baromedicine & Public Health

Oddly, the exact same question posed to DAN US, got a different response:

Dear Avra,
Thanks for your inquiry and your support as a DAN member. We know of no reason to think the supplemental O2 supplied by a concentrator on a CPAP machine is sufficient to warrant consideration for dive planning. Please donÃÕ hesitate to contact us again if you have any further questions.
Best regards,
Brian Harper, EMT, DMT
Medical Information Specialist
Divers Alert Network
(919) 684-2948 ext. 234

Personally, I think the doctor's answer was more accurate. I realize you are not at present diving gas mixes or profiles that would cause concern, and I certainly do not mean to raise any. But if you do start doing live-a-boards and diving multiple exposures using high O2 mixes, I expect by that time you'll have no trouble keeping tabs on your oxygen clock!

Good luck getting tested and going forward with treating this. It can only improve your diving and probably all areas of your life.

For all you CPAP divers, I suspect you are familiar with all or most of the sites I looked at, but for anyone else interested here are some of the best:

Sleep Apnea - symptoms, causes, and treatment of central and obstructive sleep apnea on MedicineNet.com
American Sleep Apnea Association
Obstructive Sleep Apnea (OSA) - sleepdisorderchannel
Apnea Board - Sleep Apnea forums, helps, CPAP advice
Sleep Apnea Information & Resources
www.cpaptalk.com • CPAP and Sleep Apnea Community
Instruction: CNS Oxygen Toxicity | Scuba Diving Magazine
Pulmonary Oxygen Toxicity
Hypoxemia: Causes, Symptoms and Treatment
Effects of Continuous Positive Airway Pressure Versus Supplemental Oxygen on 24-Hour Ambulatory Blood Pressure -- Norman et al. 47 (5): 840 -- Hypertension

Best of luck Wendy, hope I can dive Lake Minnewaska with you soon... Avra

 

[hobodiver]

Wow Avra. That's impressive. You should email that to Bernie and ask if you can get extra credit for it

 

[Flea Dog]

Avra,

You missed some specific points to Wendy's case. Wendy does not know if she will have supplemental O₂ yet. I am speaking only of use machine use w/o supplemental O₂.

Wendy, as you might guess by her screen name lives 1000+ feet above sea level, so she already is at a lower psi, significant maybe, maybe not. Interestingly, going home from a dive, she has to be careful of going home too soon after N₂ exposure

Wendy does not know what machine or settings she will have. I speak specifically of VPAP usage, not CPAP. A CPAP will cause significantly higher pressure in her lungs tan will a VPAP. I once tried a CPAP it was awful. A VPAP will adjust to your breathing rate and volume with constant recalculations being done, it's far superior!

(Please recalculate for air at say 1200 feet. )

You make a very good point, anyone using a breathing machine should not push their daily O₂ exposure, I have never exceded 50% dispite using Nitrox below 100+ for 4 dives in a day. My N2 levels were high to say the least, (day off tomorrow).

Avra, a point everyone including me missed is the increased N2 exposure. I wonder if that should be considered in deep diving, (or shallow) and using a positive pressure breathing device. Thinking about it the use of PP breathing at sea level must increase your N₂ tissue level.

In particular, the very slow compartments could be significantly affected by the small pressure increase.

Now that would be interesting to calculate, (at sea level). As per Wendy and N₂ it would not be as great as she really does live in the mountains, however when she is returning home from an ocean dive it may be a concern. For me at 140 feet I probably get a higher N₂ exposure then Wendy, but I don't know to what degree it would be significant if at all. It is interesting that DAN has not mentioned that. You use PP breathing for roughly 8 hours a day for 365 days etc. For me 4 years of use, (man that's a lot of days.)

Can you recalculate, (seriously this time) using the same parameters and as you did, but include N₂ and use sea level and 1000 and 2000 feet. If you can, would you put it in a spreadsheet and post it on this thread.

This is getting to be a great dive theory discussion.

Only once did I leave home w/o my VPAP. I when to FLA and after a few days I went diving seasick at 125 feet. It was the only time I ever gotten narc'd and was so weak on surfacing; I could not make it up the boat ladder w/o help. I won't go any where without my VPAP

John

 

[SkipperJohn]

Wendy, there's an oil based spray you spray onto the back of your throat to help with the snoring thing. It's supposed to work for 7+ hours. I use it and although I don't get 7 hours of relief, it does seem to help for 1 or 2 hours. I have been putting off that mask thing for years. The thought of sleeping with it just doesn't work for me. I am about to try that new mouthpiece thing. It looks like a boxers mouthpiece but it reorients your lower jaw to make snoring more difficult.

 

[avra cohen]

Avra, You missed some specific points to Wendy's case. Wendy does not know if she will have supplemental O₂ yet. I am speaking only of use machine use w/o supplemental O₂.
...
Avra, a point everyone including me missed is the increased N2 exposure. I wonder if that should be considered in deep diving, (or shallow) and using a positive pressure breathing device. Thinking about it the use of PP breathing at sea level must increase your N₂ tissue level.

As I stated I was intrigued by the question as an academic exercise. I was not really trying to address Wendy's specific case since as you point out that is far from settled.
I have little doubt that anyone using CPAP knows a great deal more about this subject than I could absorb from a self guided tutorial on the internet. But I was curious to see HOW one would go about calculating the effects rather than just relying on someone's general advice to 'not worry about it'.

I pointed out that CPAP by definition raises the partial pressure of all inspired gases, both nitrogen and oxygen. It simply turns out for AIR, that the amount is so negligible, less than 0.03 psi, as to be of no consequence for diving. Breathing high fractions of O2 for extended periods is another matter, and it appears to be one that should be accounted for IF your diving profiles and exposures are pushing the oxygen clock limits.

As to the altitude factor, that is another set of calculations that should be considered.
The actual equations (Barometric formula - Wikipedia, the free encyclopedia) are too mathematically complicated for me. But conversion tables ease the problem. New Paltz is a modest 250' above sea level, not much different than coastal New York City. But hopping up to nearby Lake Minnewaska for a dive will quickly bring us to 1650'. This is an altitude dive. What is the air pressure here? Pressure Altitude Calculator gives us approximately 715 mmHg, or 13.8 psi or .97 atm.
Diving will have to be conducted using altitude tables, but I don't see any additional complications here for the use of CPAP or supplemental O2 even if it is being used at altitude. Am I missing something here?

Avra

 

[Flea Dog]

You are 100% correct. I am still interested in the N2 of the very slow compartments. As you say the pressure change is not huge it can have an effect on the body.

I am very interested in what your thinking is in regards to using a positive pressure (PP) breathing device and the N2 level in very slow compartments, as you have done quite a bit of research on this.

You got me thinking that your N2 exposure while not under high pressure like a dive to 10, 20 or 30 feet. I am exposed to a slight elevation in pressure for say 8 hours a day seven days a week; where as a diver might have say 2 to 4 hours in a day. The shallow dives can cause quite a build up in very slow compartments.

What do you think about the idea of a theoretical build up in very slow compartments using (PP)?

John

PS. Come on up to Minne this Sat.

 

[scubamountaingirl]

wow you guys. this is just what i was afarid of....that there really is some gas math to take into consideration....but as John said i am above 1200 ft. everyday...??? hummm i will print this out and take it with me to the mask thingy....and yes i have been putting it off for ten or more years because of the mask. as for snoring i have lots of earplugs for the very rare lover, but the more important issue is my heart health from holding my breath while sleeping.

if i want to be as good a diver as i can, i need all the normal lung and brain function i can muster up...will keep reading these posts. and thank you so much Avara for going the distance for me...you get extra points i will tell Bernie...LOL

w

 

[avra cohen]

Guys, just to clarify, I'm a WOODWORKER! I have no expertise in ANY kind of medicine, hyperbaric, sleep disorders, or otherwise. Nor in decompression theory, nor in diving generally, beyond being a lowly freshly minted NAUI instructor. But I am always curious to learn more. Anything I've posted is only my imperfect understanding of things I've learned or read, often from the internet. Whenever appropriate I try to provide links so you may view those same sources and draw your own conclusions. One of the reasons I post, is so that I may stand corrected by someone having actual expertise. With that caveat in mind...

there really is some gas math to take into consideration....

There is always gas math. How much do I need to go as deep as I want for as long as I want, and how much do I need to reserve to return safely with my buddy from the deepest point of the dive, when my buddy has a catastrophic OOG emergency.
That's EVERY dive.
If you're able to do that then you can figure out OTU's pretty easily. And that you will only need to do IF you will be diving repeatedly utilizing high O2 content gasses. IF you have been prescribed supplemental O2 for use during sleep, you will simply factor that in. Not really a big deal.

but as John said i am above 1200 ft. everyday...

If you are diving up there, you should be using altitude tables and certainly should take an Altitude Diver course.

i have been putting it off for ten or more years because of the mask.

As noted on many of the sites I posted links to, there are other methods of delivery besides oronasal mask, such as nasal 'pillows'.
But it seems that most folks who are provided a well fitting mask at the outset, soon adapt to it. My best friend has used one for years.

as for snoring i have lots of earplugs... but the more important issue is my heart health from holding my breath while sleeping.

Snoring is only a symptom. Apnea is the problem. It doesn't affect only your heart. If your O2 saturation rates are as low as you've indicated, it only seems prudent that you be thoroughly tested to see exactly where you stand and what your options are.

you get extra points i will tell Bernie...LOL

HA! Hobodiver (Mats) was kidding because he and I are both taking the same Advanced Nitrox/ Deco Procedures course with Bernie Chowdhury. Incidentally, besides being a wonderful gentleman, an acclaimed author, legendary diver, inspiring instructor, and Fellow of the Explorers Club... Bernie is also a Certified Hyperbaric Technician. This stuff ought to be right up his alley. I am certain he will offer the same advice to be tested, but he might have more expert advice on the theoretical effects of CPAP and supplemental O2, on diving.

I am still interested in the N2 of the very slow compartments. As you say the pressure change is not huge it can have an effect on the body...
What do you think about the idea of a theoretical build up in very slow compartments using (PP)?

Here is where my complete lack of expertise leaves me short.
So far as I can tell, the CPAP increase beyond ambient is SO slight, that there are no implications for either the metabolized O2 or the inert N2. If my math was nearly correct, the MAXIMUM usual pressure is equivalent to 0.03 psi or diving in 0.8 INCH
of water! So yes, it affects your body. Yes, if you go diving soon after arising, your slow tissues are 'pre-loaded' with this very slight increase in N2 saturation. But it is never advisable to dive right up to, or even close to, the outside limits of any dive table or algorithm generated decompression table. The increase you would experience from CPAP seems far below the bounds of the margin you should be allowing under normal circumstances for reasonably safe diving practice. If you are in fact diving your tables to the edge, you might indeed want to increase the conservatism factor if you know you have this slight N2 load at the outset.
That is my INEXPERT opinion, for what it's worth. I just don't know enough about the theoretical aspects of tissue gas loading to be able to quantify the CPAP effect.
I'd love to hear from someone knows more. Bernie?

Dive safe... Avra

 

[DocVikingo]

Hi Scubamountaingirl,

You're off to a good start. After specifically asking for only doctor's opinions, 4 pages of thread have been generated and you have yet to hear directly from a single one. LOL.

Also amusing is the amount of "gas math" that has been generated when at the moment it is not clear at what pressure your CPAP will be set nor if 02 supplementation will be prescribed or not and if so at what concentration.

But, you did start some lively and occasionally cerebral discussion.

Given typical CPAP pressures and 02 concentrations (when prescribed), by the time a land-based diver gets off the machine, performs his or her morning toilet, eats breakfast, gets to the boat, gets to the dive site, suits up and enters the water, it seems quite unlikely that either N2 or 02 "loadings" are going to be significantly different than if the diver had no CPAP exposure at all.

Avra Cohen has been so kind as to supply opinions on this issue from two knowledgeable and reputable sources. In the case of the typical recreational diver, I find DAN's remark that "We know of no reason to think the supplemental O2 supplied by a concentrator on a CPAP machine is sufficient to warrant consideration for dive planning" to be entirely reasonable.

Dr. R. Cali-Corleo opined that (bold words mine), "If you are doing Nitrox or Trimix diving with many dives where you will be sailing close to the UPTD max permitted levels then yes I would calculate the night as a 'dive' on the pp of oxygen he will be using and add it to the 'load' of the diver." This, of course, arguably is not typical recreational diving and appears to be a very conservative recommendation in any event. However, given how little is known about CPAP and SCUBA, the recommendation is worth entertaining if you're planning on these sorts of profiles.

Please keep the forum updated on exactly what CPAP regimen you will be on.

Helpful?

Regards,

DocVikingo

This is educational only and does not constitute or imply a doctor-patient relationship. It is not medical advice to you or any other individual and should not be construed as such.

 

[HBO MD]

Hi,
The issue of sleep apnea as pertains to diving relates in part to the cause, potential complications and therapy.
In terms of the cause, this may be either central, ie related to the central nervous system. Here the respiratory center control of ventilation fluctuates with resultant increasing levels of CO2 as there are "respiratory pauses"; very frightening for partners who witness this. There may also be accompanying O2 desaturations, if these pauses are prolonged and severe.
Peripheral sleep apnea, or obstructive sleep apnea, is more common, where parts of the airway collapse and obstruct. This is not uncommon in our "growing" American population and nocturnal support is often initiated.
When the lungs experience changes in O2 or CO2 tension there are compensatory physiological changes. These may be acute and fluctuate through the night, but with time, they may become chronic, and manifest as increased pressure within the pulmonary circulation. This is known as pulmonary hypertension, ( you're familiar with systemic hypertension; well this is in the lungs). As such pressures are transmitted back to the right side of the heart. In this scenario, diving may have theoretical problems due to pressure changes between right and left sides, the risk of worsening oxygenation etc.
I personally would recommend reviewing the diagnosis ; and I apologize if I missed part of this within the thread. Sleep apnea is a complex issue, and review by someone who specializes in this field is very important so as not to be inappropriately labeled for the rest of your life.
In the absence of long term sequalae, such as pulmonary hypertension ; it has already been noted that there are numerous options, from CPAP to BiPAP etc, depending on whether this is primarily oxygenation or ventilation related. Baffling for many of us physicians let alone patients. Additionally the FiO2, or amount of oxygen they provide also varies, particularly if positive end expiratory pressure is applied.
I would not anticipate that these interventions would impact significantly upon diving in the absence of complications from long term sleep apnea.
At your age, I have to wonder about the diagnosis and if true, severity.
I'm not sure if this helps or merely confuses things.
Let me know.

"Medical disclaimer; not responsible, don't listen, not real medical directives, just thoughts, yada yada yada"