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Theoretical question about mouth breathing while using a nasal mask
Theoretical question about mouth breathing while using a nasal mask

I am trying to understand the impact of mouth breathing on OSCAR statistics while wearing a nasal mask. This is an interesting topic for me, as I suspect some of the statistics might be changed due to this and the CPAP machine may not be aware of it.

1) Pressure: If you open your mouth, you create an alternative and low pressure path for the air to go. That would mean less air going to your lungs and less oxygenation. Does the CPAP machine sense it and increase the pressure to counter this effect? I assume the CPAP machine can only sense the pressure in the CPAP hose+CPAP mask, so I don't see how it could make adjustments if it can't sense it. This could result in more obstructive events, due to inadequate pressure.

2) Tidal volume: I assume the machine calculates the volume sent by the motor, but if you are also mouth breathing, it means that you won't be taking deeper breaths, as some of the oxygen is coming from your mouth. This will result in a lower tidal volume than it is in reality and could be a reason for misdiagnosis.

3) False central events: I don't know if it is possible but if you start to mouth breath and don't use your nasal pathway for a period, the machine might think you are not berathing for this period, as there is no way for it to track if you are using your mouth. This would result in central apneas which are in fact false.

4) Irregular breathing pattern: If you are using your mouth and nose together, the emphasis can be on one or the other during certain periods of the sleep. This would result to an irregular pattern in nasal breathing, which is the only thing the machine is able to measure and can also be a reason for misdiagnosis. 

What do you think about those possibilities? If all of these claims are true, even occasional mouth breathing can be a problem for CPAP therapy and should probably be prevented by one of the usual methods (taping/chin strap/collar/etc...) or by changing to a full face mask.

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RE: Theoretical question about mouth breathing while using a nasal mask
I will be interested to see the answers you get to these questions, I have raised similar questions as a sub part to trying to find why my AHI numbers have been creeping upwards over the last several months.
- They are not spelling/grammar errors.. I live in Australia, we do it differently Down Under  Big Grin -
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RE: Theoretical question about mouth breathing while using a nasal mask
Strange things may happen in case of mouth breathing, see the screenshot below.  In the first half I've only breathed through my mouth, in the second half inspiration through nose, expiration through mouth.


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RE: Theoretical question about mouth breathing while using a nasal mask
1. The machine will maintain pressure until you reach large leak territory, then all bets are off.
2. Yes, TV does drop with mouth breathing. The exhale portion is not detected by the mask as it’s leaving the mouth.
3. Not sure, maybe, seems plausible
4. Not sure what the question is
Misdiagnosis is not an issue, you have a CPAP already presumably because you were diagnosed in testing. Mouth leaks are an issue if they are in large leak territory or waking you.
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