Dreamstation: AFLEX vs CFLEX

[Kyteflyer]

On my old machine (a Respironics Remstar Pro auto) CFLEX was the only option, so when I got the DS, I switched it from AFLEX (the default when it arrived) to CFLEX.  A couple of nights ago, I decided to change to AFLEX to see if my AHIs might improve (got worse but there may be other reasons).

Anyway, I guess my question is: why would anyone choose one over the other?

[Sleeprider]

I'll be out front with, I don't like Flex of any kind. I think Philips really missed the boat compared to Resmed's EPR. Flex predicts the timing of inhale and exhale in AFlex and exhale in CFlex, while EPR follows the respiration lead with changes in pressure that last through the entire inhale or exhale, just like bilevel. This anticipation by the Philips machines results in many people with much higher events, especially hypopnea, and a common inhale time that is longer than exhale time. That is not natural, and it doesn't match up with the flow rates on these individual's charts. I think this mis-timing of respiratory trigger and cycle is responsible for a lot of problems and sleep disruptions in more sensitive people. JMHO.

Cflex only reduces pressure for expiration, and returns pressure to the CPAP setting before exhale ends. In many people it returns that pressure to CPAP long before exhale is complete, and the machine records that moment as the start of inhale. (note CPAP pressure is the same as IPAP pressure in bilevel terms). This increase in pressure before exhale is over means many people feel like exhale has been cut-off and it reduces the volume of the subsequent breath. AFlex just doubles up on the errors since it provides pressure changes at both inhale and exhale transitions.

CFlex and AFlex works best for people with normal strong respiration that does not include a period of zero or near-zero flow near the end of expiration. For these people, Flex is comfortable and effective. For those with a longer zero flow at the end of expiration, before inspiration begins, Flex is a problem. This is based on many many observations, and I can predict who will have problems with Flex vs EPR based on the flow rate wave-form.

[Gideon]

My understanding of CFex and AFlex is that  AFlex and CFlex are the same EXCEPT CFlex was first and has a sharp/quick rise to Inspire pressure while AFlex has a slower/smoother rise to inspire pressure. 

I too prefer ResMeds EPR.

In answer to your question, for comfort.  You have the option of no flex or your choice of either CFlex or AFlex at any of 3 settings.  Like EPR it is there as a comfort setting for the user.  We have found, especially with ResMeds EPR that we can impact therapy by manipulating EPR similar to Pressure Support (PS) on a BiPap/Bilevel with the limit of the 3 cmH2O that the APAP can deliver.

CFlex/AFlex should have a similar impact but it does not act in the same manner as PS on a BiPAP.

[Kyteflyer]

Thanks for your explanations I've switched back to CFLEX... felt like AFLEX wasnt doing anything much (making things worse, my AHIs nearly doubled). Maybe I don't need it, but I wont switch it off (or start reducing, I am currently on level 3) until I have reached my optimum starting pressure (recommended as 6 in another thread) and am comfy with that.

[Steve.G]

On my old machine (a Respironics Remstar Pro auto) CFLEX was the only option, so when I got the DS, I switched it from AFLEX (the default when it arrived) to CFLEX.  A couple of nights ago, I decided to change to AFLEX to see if my AHIs might improve (got worse but there may be other reasons).

Anyway, I guess my question is: why would anyone choose one over the other?

If you don't mind my asking, how has the change to CFLEX been working out for you? I'm dealing with the VA so what I've been issues is what I get, and that's a Dreamstation. Its suspected that I'm dealing with upper airway resistance, but the VA hasn't responded to that so I'm playing with the settings. My charts are anything but clean. An Autosense 10 would be nice, I just don't have the cashflow to throw $800 at a maybe.

So, my Dreamstation arrived set on AFLEX. How has your change to CFLEX gone? I'm just wondering if there is precedence on CFLEX working better than AFLEX for someone. I suppose the simplest thing would be to simply change it, and spend another night crossing my fingers.

Steve

[nbritton]

I read about this the other day somewhere... the gist is that A-Flex works on both inspiration and expiration, while C-Flex only works on expiration.

[Pete G]

I'll be out front with, I don't like Flex of any kind. I think Philips really missed the boat compared to Resmed's EPR.  Flex predicts the timing of inhale and exhale in AFlex and exhale in CFlex, while EPR follows the respiration lead with changes in pressure that last through the entire inhale or exhale, just like bilevel.  This anticipation by the Philips machines results in many people with much higher events, especially hypopnea, and a common inhale time that is longer than exhale time.  That is not natural, and it doesn't match up with the flow rates on these individual's charts.  I think this mis-timing of respiratory trigger and cycle is responsible for a lot of problems and sleep disruptions in more sensitive people.  JMHO.  

I couldn't get used to the Dreamstation Flex.....Resmed EPR is soo much nicer

[Steve.G]

I read about this the other day somewhere... the gist is that A-Flex works on both inspiration and expiration, while C-Flex only works on expiration.

I was also reading that Aflex tries to anticipate the inhale and exhale, Cflex doesn't. Since I have nothing to lose at this point I went ahead and made the change, and slept a night. I'm mainly commenting this for general info at this point. Previously on my flow my inspiration had intermittent flat tops (indicating airway resistance) and under Cflex instead of Aflex those increased. The most remarkable change was on my expiration. The lower half of my flow under Aflex was a downward spike followed by a return to zero as if I was mouth-breathing. The entire night. When I switched the DS to Cflex, my expiration for the first time looks almost normal. If anyone is curious, the changes look like this (attached)

Anyway, I got the answer I was looking for, neither A nor C really addresses my sleep issue. I already believe Sleeprider is right about me being an EPR person, I'm just looking for proof so I can justify wanting to try a Resmed to the VA (and insurance, who already bought the Philips lol)

[Sleeprider]

Steve, the graphs are interesting and show how the timing of the Flex can affect both the inspirations and expiration wave form. I think the only way to find out about EPR is to use it. It should not take long for you to be a convert. One thing Resmed machines do is to provide a mask pressure that Sleepyhead can chart along with the flow rate. I wish we could see the actual delivered pressure for the Philips, but that is not data that it produces. The mask pressure wave-form show exactly how Resmed applies pressure transitions and why they work better.

[Gideon]

I read about this the other day somewhere... the gist is that A-Flex works on both inspiration and expiration, while C-Flex only works on expiration.

I was also reading that Aflex tries to anticipate the inhale and exhale, Cflex doesn't. Since I have nothing to lose at this point I went ahead and made the change, and slept a night. I'm mainly commenting this for general info at this point. Previously on my flow my inspiration had intermittent flat tops (indicating airway resistance) and under Cflex instead of Aflex those increased. The most remarkable change was on my expiration. The lower half of my flow under Aflex was a downward spike followed by a return to zero as if I was mouth-breathing. The entire night. When I switched the DS to Cflex, my expiration for the first time looks almost normal. If anyone is curious, the changes look like this (attached)

Anyway, I got the answer I was looking for, neither A nor C really addresses my sleep issue. I already believe Sleeprider is right about me being an EPR person, I'm just looking for proof so I can justify wanting to try a Resmed to the VA (and insurance, who already bought the Philips lol)

Steve.G I'm assuming these CFlex and Aflex closeups are yours.  If I'm right I would appreciate it if you would post the full daily chart for each day and repost these two charts and manually scale the charts to the same size.  I'm very likely to include those in a WIKI article or articles.

Thanks

Fred