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[Equipment] Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
#31
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
(07-06-2017, 11:50 PM)bonjour Wrote: I disagree with modifying any part of the air delivery system, including the mask. The mask is engineered to deliver air and vent a certain amount of air to prevent CO2 rebreathing

What would be the problem with more air venting than the "engineered" rate. The only danger that I see is getting to too much venting for the machine to handle when inhalation is added to it.

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#32
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
Air in the system is designed to be balanced at some point and it must be balanced from 3cm H2O to 25cm H2O, the full range of pressures used for cpap treatment. This includes air delivered to the mouth/nose and the air vented. You can over vent which could result in the inability to deliver adequate air to the mouth/nose. Also you could under vent resulting in too much CO2 rebreathing.

Without a solid method of knowing how to measure this balance I cannot recommend encouraging anyone to make alterations.
Fred Bonjour - 0 - LAUNCH Project Manager and Lead Tester for OSCAR - Open Source CPAP Analysis Reporter 
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INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#33
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
Hulk:
Consider that when you use a diving hard hat, all the exhaled air and surface air mixes inside the helmet. Yet, not suffer any issues due to excess CO2..

normal CO2/O2 convergence would be ~5%, and consider the air we breath is 20% O2, and 80%N.. (discounting the inert gasses)
You could re-breath the same volume of air several time with no ill affect.  That is why AR is so effective.. Oh-jeez

...  Philip
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#34
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
bonjour,

What do you mean "balanced'? This is an open ended dynamic system and as long as you have at least enough venting then the person is safe. Since one would be increasing the venting from what is "engineered" to be safe, one would still be safe. It would be difficult to vent so much air that the machine could not keep up by just modifying the P10 diffuser with pin pricks or small cuts and one would feel it if the machine could not keep up. We have a number of people that use this kind of modification and they are still on the forum.

I do not promote modifying the vents but I think that too much emphasis has been placed on the "danger" of modifying the F10 vents.

Best Regards,

PaytonA

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PaytonA passed away in September 2017
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#35
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
Hey Hulk,

I'm another with extensive SCUBA, SCBA, AvOx and RPE experience. I find that the CPAP machines are most akin to a PAPR set-up. The PAPRs don't need the oral-nasal cup in them due to the constant flow of air (just like a CPAP). The increased dead air space and normal exhalation should not result in excessive build-up of CO2, assuming the diffusive vents are working properly.

You are correct that you can breathe out and feel the results of the excess backpressure (the vents can only clear so much in a fixed amount of time), but don't forget that they are constantly venting and the machine is constantly pushing air through them...it would take extraordinary circumstances for it to lead to a hypercapnia event (i.e. blocked vents).

Do you use a soft pillow? Side or tummy sleep, perhaps? Sleep on an arm? There are multiple potential ways to block/partially block the vents that could contribute to the symptoms you describe that may not be related to the normal operation of a CPAP (I actually have run the same set-up....S9, H5i and P10...and not had any issues).

Just putting a couple thoughts out there Smile

INFORMATION ON APNEA BOARD FORUMS OR ON APNEABOARD.COM SHOULD NOT BE CONSIDERED AS MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF A PHYSICIAN BEFORE SEEKING TREATMENT FOR MEDICAL CONDITIONS, INCLUDING SLEEP APNEA. INFORMATION POSTED ON THE APNEA BOARD WEB SITE AND FORUMS ARE PERSONAL OPINION ONLY AND NOT NECESSARILY A STATEMENT OF FACT.
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#36
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
Thanks to all who have contributed to this discussion.
 
Some points in reply:
1     Hard-hat divers were protected from re-breathing by an over-supply of air i.e. though a flushing action of a helmet.
I believe this should be the same in a system where there is no non-return valve and has been noted about the volumes of air produced by the CPAP machines.

2     Twin-hose SCUBA systems were engineered out because they relied on a full, deep evacuation of the lungs to blow out as much as possible of the CO2 from the hoses and then take in enough fresh air to for the diver to survive. Shallow breathing would result in CO2 poisoning.

3     The sleep disturbance I have experienced is all subconscious. Regardless of the mask I use, I fall straight to sleep within minutes of lying down. When I get any disturbance during the night I usually go straight back to sleep after attending to the problem. As this is happening continuously though the night I suspect that I am not achieving little, if any deep sleep?
This has been resulting in the daytime fatigue, cognitive function symptoms and so inability to work.

Dr. Stasha Gominak states “We all know that you can make someone “crazy” by sleep depriving them, we’ve seen it used as a form of torture”
http://drgominak.com/sleep/

and Discusses:-
Sleep and Vitamin D (All Parts Combined)
https://www.youtube.com/watch?v=xF24xmJQK1k


4     So, with SleepyHead reporting the AHI down to between 2 and 2.5 (was 24 at the Sleep Study) and the Obstructive Index between 0.86 and 1.22, I thought it probable that the debilitating fatigue I was experiencing was due to the actual mechanics of the CPAP equipment and my subconscious acclimatisation to having to wear this equipment.
So, a week ago I changed to a RESMED AirFit F20:
a.    There was a huge improvement in my waking state, I felt fitter and alert.
b.    Each day it this has improved.
c.    There are longer periods of undisturbed sleep.
d.    There is continual flow though the mask and the air always feels fresh.
e.    I note there is a ‘non-return’ valve in the nose-piece. While it does not seal against a seat it does provide a resistance against exhaust. Note when washing it the water runs one-way easily but the other way it runs out the vents.
f.     I feel relaxed and confident in this mask. I think this is largely due to my BA and Dive Training.
g.    The tension on the straps is critical to balance between ‘blowout’ prevention and impingement of the hard-plastic mask on my face.
h.    As the CPAP pressure changes this balance is lost so the seal unrolls and I have to re-tuck it or adjust the tension on the head gear. (I suppose something like what happens on hovercraft to keep the skirt inflated and the bottom of the hovercraft airborne?)
i.     I am keen to try the RESMED AIRTOUCH F20 to see it solves the leakage problems. My CPAP supplier has advised it is not available yet.
j.     I believe there is still a lot of fine tuning that can be done so I am looking forward to my next visit to the Sleep Physician.

5     I find Dr. Stasha Gominak’s talks interesting, as, through her link between sleep and headaches, she makes the distinction between the management (of which CPAP is one tool) and the causes of sleep apnoea.

6     This leads to the question of solving the cause of Sleep Apnoea? Is Dr. Stasha Gominak’s correct that Vitamin D, being a hormone is pivotal in maintaining the correct level of paralysis?
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#37
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
(07-07-2017, 07:12 PM)PsychoMike Wrote:
Hey Hulk,

I'm another with extensive SCUBA, SCBA, AvOx and RPE experience. I find that the CPAP machines are most akin to a PAPR set-up. The PAPRs don't need the oral-nasal cup in them due to the constant flow of air (just like a CPAP). The increased dead air space and normal exhalation should not result in excessive build-up of CO2, assuming the diffusive vents are working properly.

You are correct that you can breathe out and feel the results of the excess backpressure (the vents can only clear so much in a fixed amount of time), but don't forget that they are constantly venting and the machine is constantly pushing air through them...it would take extraordinary circumstances for it to lead to a hypercapnia event (i.e. blocked vents).

Do you use a soft pillow? Side or tummy sleep, perhaps? Sleep on an arm? There are multiple potential ways to block/partially block the vents that could contribute to the symptoms you describe that may not be related to the normal operation of a CPAP (I actually have run the same set-up....S9, H5i and P10...and not had any issues).

Just putting a couple thoughts out there Smile

Hey PsychoMike,

To answer your questions:
I use a CPAP, scolloped pillow (have done since the end of the 1st week after I became concerned about the issues of blocking mask vents)
I side sleep.
As far as am aware, I don't arm sleep, maybe a bit of hand under the pillow?
I generally nose breath.
However, even though the leakage reports were regarded as 'acceptable' by the CPAP Technician, I started using a chin strap, after number of times awaking with my mouth open, getting sore throat and ear ache.

This seemed to work well and not having it too tight, meant I could open my mouth if I needed to.

The scary thing was when waking, noting the pressure was low and feeling as though I had been re-breathing. I would cover the exhaust vents by putting my fingers over the vents when breathing out.
There was no difference in breathing back pressure with them covered or un-covered!
So it was quite clear, that the path of least resistance was back down the tube.

In SleepyHead, these events co-encided with the times that the EPAP Pressure dropped off the scale!
The RESMED S9 Manual advises it will not let the pressure drop below 4 i.e. if Min Auto pressure is set to 6 and the EPR is 3, it will NOT drop the pressure to 3.


Except when during the week when I was on constant pressure 10 less 3 for EPR. Sleepyhead shows just a flatline of 10?

Of note 'Mask Pressure' data on SleepyHead only started appearing a couple of weeks ago?
Any idea of if this an anomaly or is the data hidden?

Re above, some theory to consider and questions for those who know a lot more about this stuff than I:
When sleeping, what is the pressure of exhaust breath?
The pressure back down the delivery tube is Exhaust breath pressure - Mask Vent back pressure.
Is this pressure back down the supply tube sensed by the S9 so, it will wind itself back to meet the minimum pressure?
Hence, making it quite easy to blow back against the CPAP pump?


I question why doesn't it have a valve similar to the one in the F20 Mask?

Next week I see the Sleep Physician for a full review of the 6 week Trial.
I am hoping the SleepPhjysican's Technician has the equipment to measure the back-pressure resistance and then compare it to the pressure Data?
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#38
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
Further to Dr Stasha Gominak's views, she talks about how CPAP is a 'Patch' not a cure!

Also how Vitamin D is not the only factor.

https://www.youtube.com/watch?v=uj8FTWCb010&t=676s
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#39
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
(07-15-2017, 04:07 AM)HULK Wrote: I question why doesn't it have a valve similar to the one in the F20 Mask?

Well you guys made me curious. I got to thinking about my F20 mask and the anti- asphyxia valve in the elbow. The way that it is designed makes it look like it might have a dual purpose. One being as a check valve that opens the mask to the atmosphere when the CPAP is not operating and the other to keep air from being pushed down the tube from an exhalation. So I grabbed my mask and tried a test.

I removed the elbow from the mask and covered the vents on the side of the elbow (anti-asphyxia vents that the flapper valves close off when the CPAP is connected and operating) with my thumb and forefinger. I then blew into the elbow from the mask side and the air easily came out the tubing side of the elbow. I think that this demonstrates clearly that the valves in question do not prevent air from going back down the tube.

The answer to the above question is as follows. The nasal and nasal pillow masks do have their own anti-asphyxiation valve. It is called.......your mouth. Sorry I could not resist. The logic is that if your machine quits operating while you are asleep you will open your mouth to prevent asphyxiation. Since the full face mask seals off both the mouth and nose it was felt that they needed their own method for preventing inadvertant asphyxiation.

Best Regards,

PaytonA

Admin Note:
PaytonA passed away in September 2017
Click HERE to read his Memorial Thread

~ Rest in Peace ~
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#40
RE: Rebreathing causing Hypercapnia (CO2 – Carbon Dioxide Poisoning)
Interesting as this probably take us to the point where 'normal' and 'abnormal' operation need to be considered sepetatelly.

'Normal' being where the equipment is all operating to the settings as per the Sleep Physician's Prescription.

'Abnormal' being where the has been a failure of some sort e.g. power, hose kink, vent blockage etc

Looking at the valve in the elbow of the RESMED F20 mask, it appears to be designed to allow free flow towards the mask and limit the back down the tube to the CPAP pump.
The difference in resistance due to the design of the valve can easily be tested by disconnecting the elbow and from the CPAP end blow out and suck back.

So, in 'normal' operation the resistance it provides PLUS the CPAP air pressure ensure expelled air plus any surplus air is exhausted out the mask vents, hence there is protection form re-breathing. i.e. for air to go back down the tube the air pressure of the CPAP machine PLUS the resistance of pushing of the valves through the closed positon and the to being open the other way, (which is against their designed position), would have to be overcome.


In the 'abnormal' situation of the CPAP pump failing it appears to be deigned to provide a resistance higher than the mask's vents, thereby providing protection from re-breathing.

In the 'abnormal' situation of the CPAP pump failing AND the mask vents being blocked, as the valve has no seat, it is possible to breath through the valve (as PaytonA correctly points out) but this would cause Hypercapnia due to the length of the hose and the internal air volume of the CPAP machine.

With regard to the RESMED P10 Nasal Pillows - my question still remains - "in 'normal' operation is expelled air going down the supply tube and so being re-breathed?"

I agree with PaytonA, there is an anti-asphyxia valve - i.e. your mouth.
So, as a nose breather, perhaps this is why I had incidents of opening my mouth?
Don't we all have a natural mechanism that when there is no or poor quality air through the nose, we instinctively/subconsciously go the back-up i.e. mouth?
As the appliance used to manage the mouth opening was a chin strap (just one of the number of commercially available ones specifically for this purpose), did this make the issue worse be limiting the ability to open my mouth?
Of note, it was suggested that strips off tape could be placed across my lips!
I believe this could be highly dangerous as the anti-asphyxia valve is your mouth.
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