Posted by Peter on September 30, 2002 at 07:29:15:

In Reply to: Aclaim Without Diffuser? posted by Steven on September 29, 2002 at 17:01:57:

I first thought I would try to give you an alternative “home-made” solution but realized soon that the text would be very long and won’t probably work anyway. Let’s just say that there are several reasons why these “diffusers” are made by firm, elastic, “sound dead” material.

But what I can try to do is to give you at least an explanation of the principles involved. You may know this all ready but it doesn’t hurt to be remind. Be aware this become a long text.

So,…

What a xCPAP does is to push air using a circular fan with large area into a smaller area (about the same size than “cross section of the hose”). That will increase the air pressure. Every fixed rotation speed of the fan will give you a certain pressure.

Just remember that this works both ways. If you for example suddenly increase the cross section of the hose the pressure will decrease.

The design of xCPAPs gives us a large amount of air, much more than we really need for breathing during the sleep. That is an important part of the design btw and partly the reason why the pressure changes so little when you’re using longer hoses and/or different hose sizes - it’s kind of smart.

When you’re inhaling, a “small” amount of this incoming air goes into your lungs, and when exhaling you’re using your muscles to create a pressure to get rid of the used air from your lungs though the “diffuser” hole/s.

(At the same time you’re working against the CPAP pressure but because your muscles are so much stronger than the relatively low pressure from the CPAP that doesn’t normally mean a thing. If it does “BiPAP”s solve the problem at least partly.)

So far more or less basic physical principles.

Now, if we’re getting more air from the xCPAP than we need, where does that all goes? out through the diffuser holes, where else. At the same time this rich air flow will clear the air inside your mask and prevent you from breathing “old” air. A downside is that your body can’t keep the humidity inside you nose/sinus/lungs/throat/mouth etc. at the desirable 100% relative humidity. But that’s where the heated humidifier comes in, and at least decrease the problem.

All xCPAPs are designed a certain range of leakage in mind. If you go outside this range they can’t keep the correct pressure. A CPAP sees the diffuser holes and what we apnea patients normally call leaks as the same thing. A good mask designer knows the market of all xCPAPs and therefore adjust the diffuser holes that in mind. Because different is not better, just different, “all” masks I’ve seen and used during the years are very similar in this context.

So, finally we’ve come to the fact what happens when you have too large diffuser holes (or in your case can’t find the silicone diffuser). The equipment sees that as a HUGE leak. The pressure inside your mask will fall and you’ll probably get more apneas/hypopneas than before. Compensating by increasing the CPAP pressure won’t probably help neither. And you’re also getting serious problems with the large increasing amount of air blowing “everywhere” and drying everything in its way.

That was a long text for so little - you probably have to swallow the bitter pill and dig deeper in your pocket.

Sorry for rattling so much - Peter

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