Posted by SGS on February 13, 2003 at 12:29:05:

In Reply to: Re: Optimum pressure caveats, indeed!! posted by BigGuy on February 13, 2003 at 06:05:43:

OK I see your point. After having a read I can see your point.

I think what we're talking about is lung restriction. This is where the lungs don't or can't stretch as well as they used to (your obesity example is a good example of extra-pulmonary restriction where the lungs can't stretch because of weight pushing down and upward). At night this can result, as you say, in hypoxemia due to low lung volume. Kryger calls this 'hypoxemia with no demonstrable change in breathing pattern". The picture in people such as this can be muddied by the presence of OSA and of periodic breathing (AKA Pickwickian syndrome)

So you might have a problem where a person has both OSA and restricted lung capacity at the same time. So they might have a generally low O2 saturation caused by lung restriction and then periodic dips caused by obstructive episodes.

My own postulation is that CPAP isn't nearly as powerful as your respiratory pressure so it isn't going to help inflate you lungs very much (especially when the pressure is being used up overcoming the collapsing upper airway. I know the use BiPAP machines in some people like this as it seems to trick them into breathing regularly and more strongly (preventing hypoventilation which as you say will lead to generally low 02 levels)

Good question I had to go and read the textbook and get a better idea. Kryger M, Restrictive Lung Disorders (2000). In Principles and Practice of Sleep Medicine (3rd Ed.) Kryger Roth and Dement (eds.).

Follow Ups:

• Re: Optimum pressure caveats, indeed!! BigGuy 05:02 2/14/03 (0)

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