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Re: Problemsexhaling wih C-PAP machine

Posted by Greg Harper on May 03, 1998 at 19:49:33:

In Reply to: Problemsexhaling wih C-PAP machine posted by BAS4 on May 02, 1998 at 07:27:47:

BAS4,

This is a very common problem that occurs in the initial stages of CPAP therapy.

It occurs because when your titration sleep study was done the pressure was set at the highest level that was needed to keep your airway open while you were sleeping. Let's use 10 cmH2O as an example.

When you are awake but trying to go to sleep the CPAP unit is still at the 10 pressure level. Because you are awake with your airway open, the 10 pressure level is being transmitted down into your lower airways and over-inflating your lungs. The medical term for this is "increasing the functional residual capacity" of the lungs. So now, while you are trying to go to sleep your lungs are "over-inflated" more than you are accustomed to. This stimulates the stretch receptors within the lung tissue. These receptors send a message to your brain that something is not right. This is one of the reasons that people report having "anxiety" or "claustrophobia" when first starting out on CPAP therapy.

The second thing that happens is that the muscles that you breathe with are also stretched passed their normal resting levels. This puts these muscles at what I call "a mechanical disadvantage for breathing". This theory is based on Starling's law of muscle functioning.

Starling's law states that the more strech that is placed on a muscle, the less functional it becomes. This is what happens with initial stages of CPAP therapy. As the pressure is transmitted down into the lower airway the muscles become more streched out and become less functional. This leads to an increase in the work of breathing and makes it uncomfortable for CPAP users at first.

Now, what do you do about all of this...

When you have the sensation of "shortness-of- breath" when you put the mask on at night:

1. Hit the "ramp feature" on your machine to lower the pressure.

2. Take a few deep breaths through your mouth and nose to "reset" the strech receptors in your lungs and stretch out you muscles for breathing. This also flushes out any carbon dioxide from your mask and airway. Carbon dioxide is a respiratory stimulant at low levels. You don't need any stimulation of this sort when you are trying to go to sleep.

If all goes well it will take 10 to 14 days to develop the muscular strength that you will need to overcome the extra work-of-breathing that is associated with CPAP therapy. In about three weeks it may feel like the machine is not delivering the correct pressure. This is because you have developed the muscular strength that you need to overcome the extra work-of-breathing. The stretch receptors will not be stimulated because your breathing muscles will be able to maintain your lung volume at the proper functional residual capacity.

In a few weeks you probably will not have to use the ramp feature every night.

Hope this info helps.

Good night!

Greg Harper, RRT, RCP

Respiratory Care Practioner

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