How does CPAP actually work?

[morpheus1958]

I understand that CPAP puts air pressure so that airway does not collapse.
So far so good, but I don't understand 2 things

(1) If CPAP is pushing all this air through into the body through airway, 
      How do we exhale? wouldn't the incoming air being pushed by CPAP into the body block the exhalation?

(2) Where does all this air that is being pushed by CPAP go?
      It pushes the air through nose, so it is not going out through nose.
      I wear mouth tape, so it is not going out from mouth and while my other cavity is pushing some gases out, it is not quite at the same rate as that of a CPAP machine ( ). 


Thanks for your time and appreciate your help.

[HalfAsleep]

Great questions....

I'm thinking the way to answer is......you're still breathing. Your whole breathing apparatus is set up to go in both directions. And the xPAP is not making you breathe. Your body decides how much and when you need to breathe. Inhale, exhale, whatever.

You are exhaling the air. It's sometimes hard to exhale with an xPAP because you do have to push back against an incoming force of air. This is what EPR helps with, and why some folks need BPAP. It's to help with exhale.

If you're not exhaling air, you're swallowing. You will figure out the implications soon enough. 

[chill]

You are confusing volume (all that air!) with pressure.  CPAP therapy is all about pressure, not volume.  The amount of air that rushes out when the mask is off is not an indication of the actual air flow when you are wearing the mask.  When wearing the mask, the volume of air provided is a combination of: the amount that you normally breathe, the amount leaking form the mask vent (intentional leak), the amount leaking around your face (unintentional leak), and a tiny extra bit to increase the pressure.

You can exhale as the body's muscles are far, far, far stronger than the pressure a CPAP machine provides.  You can easily inflate a child's party balloon, a CPAP machine can't, even on max.  It just provides a very gentle, supporting push to the airway.  Gently puff out your cheeks a little bit, that is how much push it provides.

The air pushed in (see above) exists through the mask's vent.  You can hold your hand near it to get an idea of the actual airflow when using the machine.

[morpheus1958]

Thanks chill, that makes sense.

It is the pressure that is maintained by CPAP and there is no real transfer of air into the body.

and lungs are generally strong enough to exhale against the pressure of CPAP.

great explanation, mucho gracias.

[morpheus1958]

One followup question chill,

if the pressure is so low (compared to strength of our muscles), why do I sometimes get my tongue and chin pushed to one side in the morning?  I suspected that it was because all the air pressure coming in from only one of the nostrils ( as other nostril is blocked). But that does not make sense if CPAP pressure if too small compared to strength of tongue muscles or jaw muscles.
Would really appreciate if you can provide your thoughts on it, thanks in advance.

[chill]

I don't know the answer to that, but I doubt that it is the pressure.  But even mild pressure can aggravate nerves and that may be provoking the response that you are experiencing.  It could also be the mask pressing on a nerve or being tighter on one side than the other.  Seeing an ENT doc is probably a good idea.

[morpheus1958]

Thanks chill.