Difference between A-Flex and C-Flex ?

Can someone please explain the difference between A-flex and C-flex ? Apparently, my machine has option for both in the setup menu. It is currently set to A-Flex "3", and I understand that helps ease the pressure on exhale, providing a comfort factor. My machine is a Phillips Respironics System One Autopap.

thanks

http://flexfamily.respironics.com/

Above link has some excellent information and links to detailed information about all the "flex" options in the PR System One machines.

While I do not have this machine, I do have the older M series APAP. One has AFlex and one has CFlex. I personally felt the AFlex suited my needs the best.

It is a comfort feature and different folks will likely have different needs. You can play around with either at different setting to find which one suits you the best.

I have the same machine and, yes it the Flex feature does drop the pressure during exhalation.

I have mine set at A-Flex 1. I like A-Flex better because, to me, it feels more natural. A setting of 1 seems to be enough for me. I have the machine set in auto mode - 10.5 cm to 13 cm and my 90% pressures is 11 or 12 cm. I have AHIs below 2 (and often below 1) with this setting.

You need to choose the flex setting that works best for you though. Try them all!

We should probably define the three different pressures found right at the mask to make this explanation make sense. The first pressure to consider is baseline pressure. The baseline pressure is what the machine is set for and what it is trying to hold constant to the best of it's ability (measured at the mask) since there is a person involved that is needing more VOLUME as they breathe in and less VOLUME as they breathe out. If you had a manikin head with a CPAP mask on it that wasn't breathing the baseline pressure would be the only pressure to consider, but we have people to deal with of course. Inhale and exhale pressure are the two others to discuss since we are breathing in and out. Inhale and exhale are modifiers of baseline pressure since the pressure, measured at the mask, will tend to drop slightly as the machine fills the lungs (inhale) and must work harder to do that. Exhale pressure at the mask is the last to consider. The pressure will have a tendancy to return to baseline (go up in relative terms) since there is less of a volume need on the motor of the machine while the person is exhaling.

Now to the original question - The A-Flex feature should probably be called "C-Flex while the machine is in auto mode" because that's all it is. When A-Flex first came out in the Remstar line years ago the machine had four modes: CPAP, CPAP with exhale relief in three levels, APAP, and APAP with exhale relief in three levels. Modes 2 & 4 where named C-Flex and A-Flex just for simplicity. Most people understand the difference between CPAP and APAP. CPAP is always at the same (constant) inhale and exhale pressure and baseline pressure, or the tightest constant the machine is capable of producing measured at the mask. APAP mode is always the same inhale and exhale pressure, or the tightest constant the machine is capable of producing measured at the mask, but has the capability to raise or lower the baseline pressure the next breathing cycle, or depending on what the software algorhythm is programmed to do. The flex feature is just a controlled leak (of three different sizes) turned on electronically INSIDE the machine at the exact right moment (top of inhale curve) to soften the exhale pressure at the mask.

I have not had very much luck using either the A/flex or C/flex. I end up having to increase my pressure to compensate and then am right back to where I was beforehand. So even though I have these features I do not use them and would probably not get another machine with it. For some people I am sure it is a wonderful thing.