(01-15-2015, 10:31 AM)MR-ab Wrote: So I have a quandary. If the UAs are Obstructive increasing pressure may be a solution, if they are Central then reducing pressure may be a solution. How should I go about solving this?
Hi MR-ab, welcome to Apnea Board.
In ResMed machines like the S9 Elite, S9 AutoSet, S9 VPAP S and S9 VPAP Auto, which do perform the FOT to distinguish between obstructive apneas versus central apneas, whenever Leak is above 30 L/minute the ResMed machines do not attempt to perform the FOT, and all apneas are marked as being of Unknown type. To fix this, reduce Leak.
But on your machine, it looks to me like there was not excessive leak and all apneas are always of flagged as Unknown type.
This makes sense because the FOT takes about 6 to 10 seconds to work its magic, and ResMed machines with a back-up rate never take the time to perform the FOT. The machines jump right in without delay, treating the central event by automatically cycling between EPAP and IPAP.
Looks to me like the apneas in the data you posted might possibly be central apneas (these do look slightly similar to Cheyne-Stokes Respiration) but I think it much more likely that they are obstructive apneas, because the IPAP pressure pulses result in almost no Flow response, which is similar to the Flow during obstructive apneas. Therefore, I think a fix would likely be to increase both EPAP and IPAP equally, keeping Pressure Support (PS) unchanged, or perhaps it may help to increase both EPAP and PS.
(01-16-2015, 12:39 PM)MR-ab Wrote: b) Are there tell tail signs I should look for in the pressure waveforms that would indicate if the apneas are central or obstructive?
If no Flow results from an IPAP pressure pulse, the apnea is clearly obstructive.
If there is small Flow (non-zero) during IPAP and the IPAP pulses are being machine triggered (if the IPAP/EPAP pressure changes are occurring at the back-up rate), the apnea/hypopnea is likely central in type.
If the PS is 10 or higher, this usually would be high enough to do for us all the work of breathing during what would have become a central apnea. But a PS of 8 or 10 or higher would likely be excessive if used all the time, perhaps worsening unstable breathing or perhaps raising the amount of O2 in the blood to dangerously high levels. (Long periods of SpO2 of 98% or above are potentially dangerous, I think.)
So ST machines usually use values of PS which are too low to fully keep us ventilated if we stop all breathing effort, and therefore are usually only able to change central apneas into central hypopneas, unless the action of the machine cycling into IPAP manages to trigger some breathing effort by us.
In ASV machines, PS will automatically adjust only as high as needed to maintain an adequate amount of ventilation. Thus, during normal breathing PS may be small, but if we stop making effort to breathe PS will jump up high enough do for us all the work of breathing, keeping us ventilated adequately with no effort on our part. (Or at least, that's the concept.)
However, some patients with ASV machines are not able to handle high pressures (because of excessive and painful air-swallowing, or because of various problems with lungs or eyes or ears or jaw), so the ASV machine's Max Pressure setting has been severely limited until, like an ST machine, sometimes the ASV machine might only be able to change what would have become an apnea into an hypopnea, or change what would have become an hypopnea into a RERA event.