Bipap is Respironics brand name for their bilevel pressure machines. Their exhale relief is called BiFlex.
VPAP is ResMed brand name for their bilevel pressure machines. They don't have a special exhale relief
unless using CPAP mode and then you get EPR.
So same animal called different names. BiPap has become sort of a generic name though.
Bilevel pressure machines offer 2 separate pressures. One for inhale and one for exhale. In straight bilevel mode these pressures are fixed. In Auto adjusting mode these pressures will auto adjust as needed.
Bilevel machines also offer straight CPAP mode.
There are bilevel machines that are strictly fixed pressures (so 2 machines in one straight cpap mode and fixed bilevel mode) and there are Bilevel Auto machines that offer auto adjusting pressures along with the other modes (so like 3 machines in one...cpap mode, fixed bilevel mode and auto adjusting mode)
APAP/CPAP machines offer a single pressure and the associated exhale relief with those machines.
Respironics calls their exhale relief "Flex"... it is a flow based relief and not a dramatic per cm drop in pressure. It doesn't feel the same as EPR in a ResMed machine. Hard to describe how it feels but for me it was more of a rhythm thing. A setting of 3 seemed "fast" to me...made me feel like it was trying to make me breathe too fast.
You can read about Flex here...http://aflex.respironics.com/
upper right lets you see each individual Flex explanation. To be honest, kinda hard to understand.
ResMed calls their exhale relief EPR... pretty simple relief, just a drop in pressure during exhale and a per cm drop for each setting with the setting of 3 being the greatest drop.
One can sort of get an idea what a Bilevel machine will feel like with EPR of 3. It isn't the same timing but it is a close feeling. I tested my ResMed VPAP in CPAP mode with EPR of 3...pressure 10...so 10 inhale and 7 exhale.
Pretty darn comfortable. I then tested it in straight bilevel mode with 10 IPAP (inhale) and 7 EPAP (exhale) so that gives a PS (pressure support..which is the difference between IPAP and EPAP) of 3 which is essentially what using cpap mode with 3 EPR is. For me it felt "close" but not quite the same...when using bilevel mode the machine actually waits longer if it needs to before changing from EPAP to IPAP. It will wait till I want to actually start the inhale before it increases to IPAP.
CPAP mode with EPR...the machine didn't wait. There is an option to change the response time for EPR if the timing is a problem. For me it wasn't a problem. I could tell the difference but it was every so slight of a difference and not a big deal. Just a minor "difference" in how something "feels" or is perceived by someone.
For this reason we sometimes refer to the use of ResMed with EPR of 3 a sort of "poor man's" bilevel. Technically it isn't but it is close in how it feels.
Now of course true bilevel machines offer more than 3 cm difference or what we call PS. It is this difference that actually offers the comfort. Believe it or not but using bilevel with PS of 4 is more comfortable than PS of 2.
I tried it by setting EPAP at 9 and IPAP at 11...so PS of 2 and EPAP at 9 and IPAP at 13 so PS of 4...and PS of 4 is much more comfortable than PS of 2 (for me).
Bilevel machines do produce a bit of a different sound because of the dramatic change in pressures so the motor or fan noise will change. How it is perceived is going to depend on the person's hearing and sensitivity to various tones and sounds. My husband says that maybe a teeny tiny bit of more "noise" with the bilevel machine when compared to my APAP PR S1 machine. He says he has to strain really hard to hear it and it is not a big deal. I can't hear any difference because I only "hear" the inhale and exhale. This has always been the way for me. It is more of a conducted hearing...if I plug up my ears with my fingers I still "hear" the inhale and exhale pretty much the same. It only takes me 2 or 3 minutes for my brain to tune it out and then I don't hear anything.
I happen to own both brands of bilevel machines...the S9 VPAP Auto and the Respironics PR S2 BiPap auto.
I have a thread where I discussed how I came to use the bilevel machine here. It may also answer some questions a person might have.http://www.cpaptalk.com/viewtopic/t71442/viewtopic.php?f=1&t=71067&p=656179&hilit=+Hybernite#p656179
When to use Bilevel pressures...who might do better? Well, remember that there are "plain" bilevel machines that mainly do just the exhale relief thing and people who have aerophagia problems or simply problems exhaling against the pressures (could be high or low really) usually do well with those "plain" machines and there are bilevel machines that are used for people with a problem with centrals these are the ASV type of machines and there are many models in that line. My machines are what I call "plain" bilevel because I am comparing them to the high dollar ASV type of bilevel machines that are used for people with problems with centrals and such and that is a whole different discussion. Sometimes a plain bilevel machine is sufficient to keep centrals low enough to not be a problem...sometimes it isn't and someone has to move on to the high dollar ASV models.
I don't have a problem with centrals. When I used APAP machine I would see 18 cm at times during the night and I never had any more centrals than what would be considered normal and sometimes never had any centrals.
Higher pressures don't automatically create centrals. Some people will have centrals pop up at low pressures of 7 or 8...
Why do I sleep better and feel better using a bilevel machine over the APAP? Don't really know. I had no aerophagia issues to speak of and no problems exhaling against my APAP pressures. All I know is that I noticed a difference in how I felt and how long I slept and for me it works and that is all that I really care about.
I have recently began to wonder if maybe I had a UARS component to my OSA and wondered if maybe the higher IPAP has helped. There is no way to know for sure. Maybe my body and brain just like the "comfort".
Before anyone asks...which brand do I prefer? It really is a toss up but in my thread above I explain why I lean towards the VPAP. If I was prone to aerophagia issues I suspect I would like the roaming PS of the PR S1 BiPap over the fixed PS of the VPAP. The VPAP can also be set to mimic APAP..so not an official APAP mode IPAP and EPAP can be set the same and still allow auto adjusting. The BiPap won't let you set IPAP and EPAP the same...there is minimum default 2 cm PS...still very close to APAP if someone wanted to go that way.
Roaming PS and fixed PS is discussed in my thread above. I have no idea when or where one might be preferred over another based on medical needs. I have looked but never found the answer to that question.