Bear with me on this one folks.  It may be necessary to humor me and pretend to be interested.  

What if you (like a machine) were asked to maintain a constant positive air pressure?  Assume you have to do it by exhaling air from your lungs.  You will probably generate pressure by controlling the expansion and contraction of the space in the passageway through which the air will pass.  You will also need to control the velocity of air passing through the space.

Now you don’t have a gauge to measure your accuracy and thus will have a problem maintaining constant pressure.  Purse your lips and blow into a small juice glass to the extent that you feel the air blow back from the glass.  Now do the same but use the juice pitcher as the receptor rather than the glass.  Would you notice a change in effort to achieve the same positive air pressure?  Would it be true that the airflow velocity must change as the receiving chamber changes its size?

Translate that knowledge to the CPAP machine.  Would it not follow that the CPAP machine needs to change its velocity on a variable basis to maintain constant pressure?  While you are sleeping, the size of your juice container changes all the time because of the variability of your breathing, right?  Breath deep, breath shallow, breathe slow, breath faster.  Don’t breath.  Breath.

So would it be true that constant positive air pressure requires a variable velocity delivery system?  The point of all this will be made clear in a subsequent posting.  I just need some assurance right now.

Don't think so.  your lungs are a closed system so to speak.  A CPAP is a passthru.  Has a seperate inlet and outlet.

Here's what I've been searching for in both related posts regarding air pressure.  Since I just started on this new RESMED S8, I going to assume I got one of the "late August" new ones with the EPR feature.

Quoted from CPAP.COM

Resmed is preparing S8 machines for a late August launch that have EPR (Exhalation Pressure Relief). The Resmed version specifics are largely secret but it is known that the specific pressure drop in centimeters at the initiation of expiration is adjustable.

I think (pending verification) this closes my issue.  Thanks for putting up with me in both recent posts. What a mystery this has been to me thinking I had a defective unit.

Sounds very similar to Cflex...

The irony in this is that I had a conversation earlier this year with a rep from one of the manufacturers and he told me it was a fad.... LOL!

<<COMMERCIAL LINK REMOVED>>

                          You broke the code!  This is quoted from the CPAP July Newsletter:

             Easy Breathing Technology Heats Up: C-Flex, SoftX and EPR

C-Flex is a feature that makes breathing back against CPAP pressure easier to do by creating momentary pressure drops as a patient begins exhaling. Respironics invented C-Flex and holds patents for its exclusive use.

Other manufactures are now bringing products to market with their own versions of easy breathing technology. Some time ago Invacare released the Invacare Polaris EX CPAP with SoftX that uses a valve system to bleed pressure off at the beginning of expiration.

Resmed is preparing S8 machines for a late August launch that have EPR (Exhalation Pressure Relief). The Resmed version specifics are largely secret but it is known that the specific pressure drop in centimeters at the initiation of expiration is adjustable.

We have been big supporters of C-Flex from the start. We said in our November 2002 CPAP Newsletter that we were:

"convinced that C-Flex will soon make fixed pressure CPAPs obsolete. Anyone who has had an opportunity to breath on standard CPAP vs C-Flex is almost sure to strongly prefer C-Flex"

This trend is a good one for an industry built on improving patient's lives.


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Success Nourishes Hope