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miltf
 
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Mask carbon dioxide levels - toxicity

Postby miltf on Tue May 06, 2014 4:09 pm

Hi,
This is my first post here. I am a relatively new CPAP user (6 months). Initially, I found that the silicone in most masks gave me nasal congestion, so I switched to Sleepweaver masks which are cloth. No congestion, but I sometimes had a shortness of breath feeling. I thought maybe the fixed vent rate on the mask was too low as it felt like my expired breath was not leaving the mask before I took a new breath. Well, long story short, the company and I had an email exchange which remains unresolved for me and I went ahead and measured the CO2 in the mask using a very sensitive and rapid sensor called a SprintIR (details upon request).

The measured CO2 in the mask air space ranges from 2-3.3% during use (air is less than 0.1%, exhaled breath is 3-5%). The US OSHA sets a limit on CO2 of 1% (time weighted average) and says that higher levels can lead to discomfort (!), headache, lethargy, etc. Levels above 3% are not allowed for any length of time. I made some holes in the mask wall to increase the vent rate and decrease the CO2 and, sure enough, my nights are far more comfortable. My ResMed S9 Autoset seems to adjust very well to this change and for the most part, this problem is solved for me.

However, I am still concerned about other users of CPAP. I have measured the two other masks I happened to have, a Respironics Profile Lite (2-3%) and a ResMed Swift FX (1.5-2.5%) and both of these have high CO2 levels. My guess is that most masks are not designed to achieve adequate venting of CO2, partly because of inadequate vent rate but mostly because of vent placement. I think this must contribute to the low compliance rate for CPAP among those who are prescribed this technology. After all, if you are feeling discomfort, headache and lethargy, you might as well just stick with OSA.

I'm putting this information out on this forum because I don't know what else to do with it. I'll be interested to hear your thoughts.

Milt

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Nozzelnut
 
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Re: Mask carbon dioxide levels - toxicity

Postby Nozzelnut on Tue May 06, 2014 4:34 pm

What would the CO2 be in the body without using APAP/CPAP therapy?

How long is that concentration of CO2 in the mask? Is it just in the mask volume and not in the hose? If it's just in the air volume in the mask (maybe .25L for FFM?) as compared to the tidal volume of your lungs what would the overall percentage be?

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Machine: S9 AutoSet™ CPAP Machine
Mask: Simplus Full Face CPAP Mask with Headgear
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miltf
 
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Re: Mask carbon dioxide levels - toxicity

Postby miltf on Tue May 06, 2014 4:42 pm

I don't know how to post the graph, but basically the CO2 level in the mask goes up to 3.3% when breathing out and down to 2.3 or so after breathing in. The sampling point is in the mask deadspace, not in the hose. The CO2 level of air entering the lungs during breathing is somewhere between these 2 levels. This is called rebreathing, as the expired CO2 is reentering the lungs.

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DeadlySleep
 
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Re: Mask carbon dioxide levels - toxicity

Postby DeadlySleep on Tue May 06, 2014 4:47 pm

I found that the silicone in most masks gave me nasal congestion


By what mechanism do you propose that silicone in a mask causes nasal congestion? The amount of VOCs emitted from silicone masks at room temperature are about zero.

Also, if you want to build some credibility about your CO2 statements, tell us what pressure settings you are using, the details of events you are experiencing and the details of what your leak line looks like before and after the cloth mask modifications.

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Re: Mask carbon dioxide levels - toxicity

Postby Julie on Tue May 06, 2014 4:50 pm

I'd like to straighten this out for you because you are going on mistaken premises.

First of all, I think it very possible your congestion was caused (as it is for so many others) by having the humidifier set too high, and that turning it down might well cure the problem. The silicone has almost no accounts of allergy or reactions to it in the literature or otherwise, and while you could be one in 100,000, it's far more likely a humidifier problem. The weaver mask probably did feel better because it's woven and therefore allows air to seep in and out, alleviating the extra humidity.

Second, CO2 goes out through the vents of all masks for all of us, and the only time it's a problem is if bedding is allowed to cover it, thus making us re-breathe it and causing symptoms.

You have had trouble exhaling against pressure, which many others do, but there's a feature you can activate on most machines called either EPR or something similar, and it allows you to exhale without a problem. You need to try that feature on your machine to see if it helps, before assuming it's all about CO2.

miltf
 
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Re: Mask carbon dioxide levels - toxicity

Postby miltf on Tue May 06, 2014 4:59 pm

I don't have a mechanism for why I get congestion -- I just know that I don't get it when I don't use a silicone mask. I can certainly smell the silicone though so it must have some volatile content.

As to other details -- The air in the mask is sampled through a flange fitting in the mask wall. A vacuum pump set to 1 L/min (calibrated by flow meter) pulls air out of the mask and into the flow through sensor chamber. The sensor is calibrated with a range of 0-5% (v/v).

The S9 is set at 5 cm constant pressure. The vent rate of the mask is supposed to me 16 L/min. The leak rate during the experiment is minimal.

Re: Julie's comments.

None of your comments, though worthy of respect, can change the fact that I am measuring high CO2 levels in 3 CPAP masks, levels that are above that set by OSHA as tolerable in a workplace.

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Re: Mask carbon dioxide levels - toxicity

Postby HoseCrusher on Tue May 06, 2014 5:10 pm

According to this study:

http://www.archbronconeumol.org/en/comp ... /13087086/

your readings are a bit low...

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Humidifier: HumidAire H4i™ Heated Humidifier
Additional Comments: Retired my Swift FX
Machine is an S8 Autoset II. SpO2 96+% and holding...

miltf
 
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Re: Mask carbon dioxide levels - toxicity

Postby miltf on Tue May 06, 2014 5:24 pm

HoseCrusher wrote:According to this study:

http://www.archbronconeumol.org/en/comp ... /13087086/

your readings are a bit low...


Thanks for the observation. This is one of the only studies published on CPAP rebreathing and it points out that placing the vent on the elbow or tubing (still common) is not good design.The measurements reported in this paper are End Tidal, meaning they are measured at the nostril and only represent and highest CO2 during the breathing cycle. They reflect only indirectly the CO2 in the air that is breathed in. The numbers I am measuring are in the mask dead space -- not the same, but certainly consistent.
Last edited by miltf on Tue May 06, 2014 5:29 pm, edited 1 time in total.

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Todzo
 
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Re: Mask carbon dioxide levels - toxicity

Postby Todzo on Tue May 06, 2014 5:28 pm

The actual volumes inside the mask are low so you will be rebreathing very little additional air (keep in mind that we do not totally purge our systems and do rebreath some air as part of normal healthy breathing). And indeed a more common problem with CPAP use is carbon dioxide maintenance so some have come up with ways to help this which include enhancing the rebreathing space[1] or adding carbon dioxide at critical phases in the breathing process[2].

If the mask vent is working properly I would not worrry about it.

[1]: Gilmartin G, McGeehan B, Vigneault K, Daly RW, Manento M, Weiss JW, Thomas RJ.
Treatment of positive airway pressure treatment-associated respiratory instability with enhanced expiratory rebreathing space (EERS).
Source: J Clin Sleep Med. 2010 Dec 15;6(6):529-38. Division of Pulmonary, Critical Care and Sleep Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA.
Link: http://www.ncbi.nlm.nih.gov/pubmed/21206741

[2]: Dynamic CO2 therapy in periodic breathing: a modeling study to determine optimal timing and dosage regimes
Yoseph Mebrate, Keith Willson, Charlotte H. Manisty, Resham Baruah, Jamil Mayet, Alun D. Hughes, Kim H. Parker and Darrel P. Francis
J Appl Physiol 107:696-706, 2009. First published 23 July 2009; doi: 10.1152/japplphysiol.90308.2008
Link: http://www.ncbi.nlm.nih.gov/pubmed/19628721
May any shills trolls sockpuppets or astroturfers at cpaptalk.com be like chaff before the wind!

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Re: Mask carbon dioxide levels - toxicity

Postby TangledHose on Tue May 06, 2014 5:33 pm

Your hypothesis is over simplified, your not taking into account the volume of air/gas in the very small space of a full face or any other mask. There may very we'll be a higher level of CO2 in the mask space but the volume of air in the mask is insignificant and there is a constant flow of fresh air being forced into the mask from the cpap machine, so the amount of rebreathed CO2 is of little consequence. Many of us, including me, use overnight oximeters to measure the actual amount of oxygen present in the blood. These oxygen levels increase with the use of cpap verses not using the cpap. This would prove that the masks are not causing cpap users to increase their levels of CO2 in the respiratory system, actually quite the opposite.

I also think it is naive of you to assume that multi-million dollar companies that produce this medical equipment haven't thoroughly tested these results with each new mask design. There are thousands of test hours behind products like cpap masks before any are certified for production.

_________________
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Todzo
 
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Re: Mask carbon dioxide levels - toxicity

Postby Todzo on Tue May 06, 2014 5:47 pm

miltf wrote:Hi,
This is my first post here. I am a relatively new CPAP user (6 months). Initially, I found that the silicone in most masks gave me nasal congestion, so I switched to Sleepweaver masks which are cloth. No congestion, but I sometimes had a shortness of breath feeling.


Hypocapnea seems to be more often associated with increased air hunger while using CPAP. Keep in mind that the pressures used are ALWAYS above atmospheric. If not the CPAP has failed.

miltf wrote: I thought maybe the fixed vent rate on the mask was too low as it felt like my expired breath was not leaving the mask before I took a new breath. Well, long story short, the company and I had an email exchange which remains unresolved for me and I went ahead and measured the CO2 in the mask using a very sensitive and rapid sensor called a SprintIR (details upon request).


“SprintIR (details upon request)” Details requested.

miltf wrote:The measured CO2 in the mask air space ranges from 2-3.3% during use (air is less than 0.1%, exhaled breath is 3-5%). The US OSHA sets a limit on CO2 of 1% (time weighted average) and says that higher levels can lead to discomfort (!), headache, lethargy, etc. Levels above 3% are not allowed for any length of time. I made some holes in the mask wall to increase the vent rate and decrease the CO2 and, sure enough, my nights are far more comfortable. My ResMed S9 Autoset seems to adjust very well to this change and for the most part, this problem is solved for me.


Requested data from you. What are your current leak rates with the additional holes. What are they without the holes. If you can make your own manometer (a hose and a ruler!) and what is the actual measured pressure at the mask with and without the additional holes (note: painters tape makes a wonderful temporary cover and tends to leave not residue).

miltf wrote:However, I am still concerned about other users of CPAP. I have measured the two other masks I happened to have, a Respironics Profile Lite (2-3%) and a ResMed Swift FX (1.5-2.5%) and both of these have high CO2 levels. My guess is that most masks are not designed to achieve adequate venting of CO2, partly because of inadequate vent rate but mostly because of vent placement. I think this must contribute to the low compliance rate for CPAP among those who are prescribed this technology. After all, if you are feeling discomfort, headache and lethargy, you might as well just stick with OSA.

I'm putting this information out on this forum because I don't know what else to do with it. I'll be interested to hear your thoughts.

Milt


To deal with my own issues of respiratory instability I have found that INCREASING the rebreathing space can be very helpful. I do this only as necessary but am not at all concerned about the natural rebreathing space in the mask which is probably much less than what naturally occurs within my own body during each breath. We do not fully purge all the air we breath. We always rebreath some.

[1]: Gilmartin G, McGeehan B, Vigneault K, Daly RW, Manento M, Weiss JW, Thomas RJ.
Treatment of positive airway pressure treatment-associated respiratory instability with enhanced expiratory rebreathing space (EERS).
Source: J Clin Sleep Med. 2010 Dec 15;6(6):529-38. Division of Pulmonary, Critical Care and Sleep Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA.
Link: http://www.ncbi.nlm.nih.gov/pubmed/21206741

[2]: Dynamic CO2 therapy in periodic breathing: a modeling study to determine optimal timing and dosage regimes
Yoseph Mebrate, Keith Willson, Charlotte H. Manisty, Resham Baruah, Jamil Mayet, Alun D. Hughes, Kim H. Parker and Darrel P. Francis
J Appl Physiol 107:696-706, 2009. First published 23 July 2009; doi: 10.1152/japplphysiol.90308.2008
Link: http://www.ncbi.nlm.nih.gov/pubmed/19628721
May any shills trolls sockpuppets or astroturfers at cpaptalk.com be like chaff before the wind!

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Todzo
 
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Re: Mask carbon dioxide levels - toxicity

Postby Todzo on Tue May 06, 2014 5:52 pm

It is interesting to see how if issues which deal with air hunger and carbon dioxide maintenance come up here the shills, trolls, and their sock puppets also appear. Sometimes you can tell them because they tend to use very gross avatars.
May any shills trolls sockpuppets or astroturfers at cpaptalk.com be like chaff before the wind!

JDS74
 
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Re: Mask carbon dioxide levels - toxicity

Postby JDS74 on Tue May 06, 2014 6:26 pm

miltf:

Your concerns appear to be about 2 different things.
1) Congestion fwhen using a silicone mask and none when using a fabric one.
And
2) The amount of CO2 being rebreathed during therapy.

Although the first seems to be rare, for you its real and no amount of naysaying can change that. You've found a solution that allows you to continue therapy. So from my point of view, that problem is personal to you and solved.

On the CO2 issue, some discussion is in order. What is missing in the discussion so far is consideration is dead space in the mask.
My mask has a dead space of 16 mL and my average tidal volume of about 650 mL so with a 3% CO2 level in the dead space, the increase in CO2 above ambient is 2% of 3% or .06% which in the grand scheme of things is negligible. And that assumes that 100% of the dead space volume is inhaled. But my mask has a leak rate of about 40 L/ min so the dead space is constantly being flushed.

Masks with different dead spaces and different leak rates will have different calculations but the mask makers have done it in their designs.

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Oracle 452 Lessons Learned Updated
AutoSV 960 with HC150 extra humidifier and Hibernite heated hose
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Re: Mask carbon dioxide levels - toxicity

Postby Wulfman... on Tue May 06, 2014 6:53 pm

miltf wrote:I don't have a mechanism for why I get congestion -- I just know that I don't get it when I don't use a silicone mask. I can certainly smell the silicone though so it must have some volatile content.

As to other details -- The air in the mask is sampled through a flange fitting in the mask wall. A vacuum pump set to 1 L/min (calibrated by flow meter) pulls air out of the mask and into the flow through sensor chamber. The sensor is calibrated with a range of 0-5% (v/v).

The S9 is set at 5 cm constant pressure. The vent rate of the mask is supposed to me 16 L/min. The leak rate during the experiment is minimal.

Re: Julie's comments.

None of your comments, though worthy of respect, can change the fact that I am measuring high CO2 levels in 3 CPAP masks, levels that are above that set by OSHA as tolerable in a workplace.


I'm thinkin' that your pressure is your primary problem. If you're using a high humidity level, that might be the second culprit. It's been discussed at length in the past that pressures of 6 cm. or below may not be sufficient to flush the CO2 from the mask (also confirmed by manufacturers' warnings/recommendations).

Another discussion I was also part of about 7 years ago had to do with certain masks also not sufficiently clearing CO2. I had that suspicion with a ResMed Mirage Quattro mask.......and I've used a 12 cm. pressure setting. Using it, I just never seemed to get a "rested" feeling. So, I have stuck with my old original/standby......the Ultra Mirage Full Face.


Den

.

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Re: Mask carbon dioxide levels - toxicity

Postby kona0197 on Tue May 06, 2014 6:56 pm

I am pretty sure in Co2 re-breathing was an issue the CPAP mask makers would have been sued already, several times over. Besides, I feel great in the morning after using my CPAP machine and I wasn't killed by re-breathing CO2, if I did at all.

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