Adjusting Leak Rate to increase CO2

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cnaumann
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Adjusting Leak Rate to increase CO2

Post by cnaumann » Sat Dec 20, 2014 8:37 am

I recently purchased a Nasal Aire II mask. It has a much higher leak rate than the mask I was recently using, a Nuance Pro. Since moving to the Nasal Aire II, my AHI has gone up from about 0.5 to about 2, and my respiration drops down to the preset back up rate of 8BPM sometimes for up to an hour.

One thing that I have noticed is that the total leak rate on the Nasal Aire II is much higher than the Nuance Pro. The best pressure setting I found on the the Nuance Pro were minimal, a fixed EPAP of 4 and a very low PS min (sometimes 0, sometimes 3, it did not make much diffference as far as AHI went, but I found a PS min 3 more comfortable.) With these settings, the leak rate on the Nuance Pro was anout 10 lpm, and the Nasal Aire II was about 20 lpm. My minute vent rate is 7-8 lpm.

My current theory is that I a re-breathing more CO2 with the Nuance Pro and that is making my numbers better.

I am seriously considering adjusting the leak rate on the Nasal Aire II to see if that makes a difference. Has anyone else ever done something like this? Is my thinking on this nuts?

The issue I was having with the Nuance pro is that the mask only works well in one sweet spot. If I move, the mask slips a little and I either cannot breath through it or it blows air in my face. I have to re-adjust it several times a night. I have been tempted to tape it in place. There are several things I do not like about the Nasal Aire II, but it absolutely stays in place the entire night. I do not wake up and adjust it. Oddly, it is not the nasal prongs that I object too, it is the bulky hose running up and over my ear and the loud vent ports. I wish I could get a hybrid mask. One that uses nasal pillows to make the actual seal but has some prongs to act as guides.
Last edited by cnaumann on Sun Dec 21, 2014 9:44 am, edited 1 time in total.

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cnaumann
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Re: Adjusting Leak Rate

Post by cnaumann » Sun Dec 21, 2014 9:43 am

I plugged one of the two vent hole on the Nasal Aire II last night. As expected, the total leak rate dropped from about 24lmp to 12lpm compared with the previous night. My AHI also dropped from 7.05 to 0.58. My spO2 levels were about the same on both nights but there were fewer desats with the lower AHI. With the hole plugged, my respiration rate stayed around 12 bpm most of the night and only bottomed out to the backup rate of 7 BPM for about 10 minutes. Two of the three AHI events were recorded during this low respiration event. With both vent holes open, my repiration rate bottomed out to the back up rate severel times during the night with one incident lasting nearly an hour.

My ears are ringing a little this morning, but otherwise I feel pretty good. Obviously, I can make any conclusion based on one night's worth of data. I am not sure deliberately plugging vent holes is a good idea, but it is interesting.

I am tempted to try just the mask and the hose with no machine.

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palerider
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Re: Adjusting Leak Rate

Post by palerider » Sun Dec 21, 2014 10:10 am

cnaumann wrote:I plugged one of the two vent hole on the Nasal Aire II last night. As expected, the total leak rate dropped from about 24lmp to 12lpm...

My ears are ringing a little this morning,... I am not sure deliberately plugging vent holes is a good idea,
well, given that most all masks vent around 20lpm @4cm (rising to around 50lpm@20cm)... I wonder if you weren't poisoning yourself with excess co2 last night.
let us know if you try plugging up the other hole too.

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Sludge
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Re: Adjusting Leak Rate

Post by Sludge » Sun Dec 21, 2014 12:03 pm

cnaumann wrote:I am tempted to try just the mask and the hose with no machine.
If you do, can I have your stuff?

Is your wife "hot"?
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cnaumann
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Re: Adjusting Leak Rate to increase CO2

Post by cnaumann » Sun Dec 21, 2014 4:41 pm

well, given that most all masks vent around 20lpm @4cm (rising to around 50lpm@20cm)... I wonder if you weren't poisoning yourself with excess co2 last night.
let us know if you try plugging up the other hole too.


I don't think I was anywhere near the poisoning threshold. There were no other signs of CO2 poisoning such as high respiration rate or high heart rate, just a mild increase in respiritory effort which is what I was trying to achieve. I am more concerned about long term effects of slightly increased CO2 than short term poisoning.

The Nuance Pro that I had been using only vents about 17lpm at 4cmH2O according to the manual. According to the total leak rate of reported by my machine the mask only vents between 10-12lpm at 4cmH2O in actual use. The instructions for the Nuance actually say that some rebreathing my occur at low pressures. Blocking one port of the Nasal Aire II did not really reduce its reported vent rate below the reported vent rate of the Nuance Pro.

I calculated the deadspace of the entire hose to be around 360ml (15cm x 2m). My normal tidal volume is around 650ml while asleep. While awake it in around 2,000ml and can certainly go higher if stressed, so even with both vent ports blocked and the machine off, it would be easy to overcome the deadspace in the hose. As it is, there is really no reason to block the other vent port deliberately, but an accidental blockage shouldn't cause a major problem even if the machine fails at the same time.

Unlike oxygen deprivation or CO poisoning where you just sort of fade out, you don't go quietly with CO2 poisoning. CO2 build up causes increased respiratory effort and a number of other reactions. If things got really out of hand, the increased effort should either overcome the deadspace in the hose, trigger mouth breathing, and/or wake me up. It is hard to see that any of this would be any more dangerous that using the Nuance pro or having a power failure in the middle of the night. I would be dead long ago if my body didn't respond to increased CO2 level by increasing respiratory effort.

Your concern and Sludge's concern is noted, and I certainly do not recommend anyone else try this. While deliberately plugging vent holes may seem reckless and idiotic, I am putting some thought into what I am doing and I don't think I am being a total idiot.
Last edited by cnaumann on Sun Dec 21, 2014 6:49 pm, edited 1 time in total.

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Krelvin
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Re: Adjusting Leak Rate to increase CO2

Post by Krelvin » Sun Dec 21, 2014 4:44 pm

CO2 poisoning can lead to confusion among a number of other memory problems.
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archangle
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Re: Adjusting Leak Rate to increase CO2

Post by archangle » Sun Dec 21, 2014 4:55 pm

If you modifiy your mask, be sure no one else can end up with it somehow, for instance, if you die suddenly. Destroy it or remove your modifications if you throw it away.

Sufficiently high CO2 rebreathing can lead to unconsciousness and death with very little warning.

That said, in theory, if the mask vents enough air to be safe at 4 cmH2O, it should be safe to reduce the leak rate to the same level by blocking some of the holes at a higher pressure. The problem comes if you get it wrong, if whatever you did to block up some holes shifts around and blocks some holes, if your CPAP pressure drops and lets the leak rate get too low, etc.

Google EERS to see about working with retaining CO2.

Realize if you screw it up, you could die quietly in your sleep.

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Re: Adjusting Leak Rate to increase CO2

Post by palerider » Sun Dec 21, 2014 5:05 pm

Krelvin wrote:CO2 poisoning can lead to confusion among a number of other memory problems.
may be too late.

btw, love the new avatar

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Re: Adjusting Leak Rate to increase CO2

Post by TangledHose » Sun Dec 21, 2014 5:32 pm

He never answered Sludge's question about his wife..........?


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palerider
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Re: Adjusting Leak Rate to increase CO2

Post by palerider » Sun Dec 21, 2014 5:45 pm

TangledHose wrote:He never answered Sludge's question about his wife..........?
she may be the one plugging up the other hole.

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Re: Adjusting Leak Rate to increase CO2

Post by TangledHose » Sun Dec 21, 2014 5:55 pm

Good Point!


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Re: Adjusting Leak Rate to increase CO2

Post by cnaumann » Sun Dec 21, 2014 11:30 pm

archangle - all good points. The mask mods are obvious (q-tip stub in vent hole) so no worries there. But that is an excellent point about foisting modified and potentially dangerous equipment on unsuspecting users.

There is a good bit if debate if high CO2 levels will wake you up. Occasionally campers die in tents that get buried under snow. However, most seem to wake up. Well, at least the ones that post about it woke up. There is probably some bias there.

From the articles on EER, it looks like I need to start with about 150ml of deadspace. I think I will open a vent hole in my non-heated hose 150ml away from the mask and give it a try.

Sludge, my stuff consists of a few million LEGO pieces. Sure you want it?

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Re: Adjusting Leak Rate to increase CO2

Post by Sludge » Mon Dec 22, 2014 7:41 am

cnaumann wrote:Sludge, my stuff consists of a few million LEGO pieces.
Is that Street for "My ho has big cans"?
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Re: Adjusting Leak Rate to increase CO2

Post by cnaumann » Mon Dec 22, 2014 8:25 am

Well, I am still here.

Here is what I tried. I took my spare unheated hose and put a couple of layers of 2" packing tape around 39cm from the mask end. The packing tape prevents the hose from compressing or bending at that point and provides structural support. I then burned two 0.125" hole through the packing tape and hose using a hot drill rod. This produced a leak rate of 15 lpm at 4 cmH20 according to the PR960. That was a little below target so I burned a third hole. This produced a leak rate of 20 lpm at 4cmH2O which was acceptable. The calculated deadspace is pi*(1/2 *22mm^2)*390mm = 148 ml plus the volume of the mask and mask hose. I plugged both vent hole in the Nasal Aire II mask using cut off Q-tips. I used EPAP fixed at 4cm with a PS of 4cm - 21cm. Backup rate was set to 7 BPM.

The results were very encouraging. Unfortunately, I did not properly re-seat the SD card properly after verifying the leak rate so I am missing the breath-by-breath data.

PR960 data:
Total AHI: 0.19 - one reported OA event. This ties my previous record which was an AHI of 0.18 with one reported Hypopnea.
Flow Limit: 4 events
Timed Breaths: 13 - near my low of 11, Typical is around 100.
V Snore: 5 events. This is much higher than normal. I believe this was due water guggling in the hose at the vent ports.

Pulse Ox data:
Desat Events: 6 - Average is 27. tied for a record low.
Base spO2: 94.4 - Average is 93.3. This is a record high since using only my left pinkie for measurement.
Min spO2: 91 - Average is 89. This is a record high since using only my left pinkie for measurement.
Average Heart Rate: 62.5 - Average is 70.

These early results look extremely encouraging to me. Repiratory effort is up, cardiovascular effort is down. I want to get several more nights of data to see if this setup continue to produce good results and get an idea of how I feel during the day. If the results hold, I may have to find a doctor that is working with EERS.

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Re: Adjusting Leak Rate to increase CO2

Post by archangle » Mon Dec 22, 2014 2:39 pm

cnaumann wrote:There is a good bit if debate if high CO2 levels will wake you up.
The actual problem is low O2, not high CO2, but they are linked. There are lots of dead people in industrial settings who have passed out and died from this and never felt anything before passing out. Google "Confined space training" for info.

Yes, most of us do wake up if our CPAP quits or our vent gets blocked, but the dead confined space victims argue it's not a sure thing.

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