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Event Duration
#1
Just pondering the duration of events as it relates to pressure settings. With pressure set at 8/14, and an AHI around 1, my event duration ranges between 10 and 25 with an occasional hypopnia around 45. I'm wondering whether the event duration could be reduced by tweaking the lower pressure setting to a higher number. It seems logical that the system could stop the event more quickly if the needed pressure could be reached more quickly.

BTW, is there a way to see duration as an average?

Once again, the propensity to tweak launches a needless quest. I am doing just fine as is.
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#2
Jim, i am certainly not the expert on this but it seems to be the opposite end of the range that might be suspect. When you are having an event, the machine jacks up the pressure to the upper limit to open you up so you can breathe.

It drops to the lower limit when you are breathing well and don't need the higher pressure. Look at your flow graph and see if it is hovering at the max at the same time as your events. If it is maxing out then maybe the upper limit should be raised a bit.

If your limits are set right, your flow should gently fluctuate between the high and low without hitting and staying.
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#3
(04-12-2014, 09:46 AM)drgrimes Wrote: Jim, i am certainly not the expert on this but it seems to be the opposite end of the range that might be suspect. When you are having an event, the machine jacks up the pressure to the upper limit to open you up so you can breathe.

It drops to the lower limit when you are breathing well and don't need the higher pressure. Look at your flow graph and see if it is hovering at the max at the same time as your events. If it is maxing out then maybe the upper limit should be raised a bit.

If your limits are set right, your flow should gently fluctuate between the high and low without hitting and staying.
Thanks DR. That certainly makes sense but...I have settled on my upper pressure limit as the best trade off between AHI and aerophagia so I hesitate to change it. I'm getting almost perfect therapy so am merely nitpicking about lowering event duration.

I was just idly theorizing that a smaller gap between lower and upper pressure limit would result in a faster response to a developing event. I suppose one could test that theory by simply going straight CPAP set at the upper limit.

I am also wondering what duration most people experience.

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#4
As far as the duration, the minimum registered as an event is 10 seconds, so anything down close to 10 is good. 45 seconds seems a bit long. One thing i notice when i have the occasional long event, is a major leakage at the same time, so i discount those as not meaning very much.

I think it's possible for the machine to misinterpret what's happening when major leaks occur. OR maybe even a long but minor leak. Sometimes my nasal pillow shifts a bit and lightly leaks, but not enough to wake me. Maybe the machine thinks i am not breathing fully for that period of time.
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#5
Does your machine score the duration of a hypo-apnea?
Based on what you've said, and my novice understanding, you seem to be doing rather well.

As for event durations. Last night I slept 7 hours with 5 Apnea events of duration:
13, 18, 11, 10, 23 plus one central apnea of 10 seconds and zero hypo-apnea.
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#6
My S8 does not distinguish apneas and does not give a duration for hypopneas (at least not in ResScan), but the apneas (probably centrals) are normally near 10 seconds with an occasional excursion to the low 20s

Best Regards,

PaytonA
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#7
(04-12-2014, 11:02 AM)justMongo Wrote: Does your machine score the duration of a hypo-apnea?
Based on what you've said, and my novice understanding, you seem to be doing rather well.

As for event durations. Last night I slept 7 hours with 5 Apnea events of duration:
13, 18, 11, 10, 23 plus one central apnea of 10 seconds and zero hypo-apnea.
Thanks justMongo. My night was 6:51 with OA events of 10, 14, 26, 10, 11 and one hypopnea of 24 so my experience is about the same as yours. I'm thinking that's pretty good and not worth messing with.

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#8
(04-12-2014, 10:42 AM)JimZZZ Wrote: I was just idly theorizing that a smaller gap between lower and upper pressure limit would result in a faster response to a developing event. I suppose one could test that theory by simply going straight CPAP set at the upper limit.

Hi JimZZZ,

If you zoom in around an apnea event, I think you will find from looking at the Flow and the High Rate Pressure, is that the EPAP pressure never adjusts to cut short the apnea event. This is because the machine will respond to Snore and Flow Limitation (which stop when we stop breathing) and to clusters of apneas or hypopneas, but I think the machine will not respond to single events. Even when there are clusters of events, I think the machine waits for the current apnea to end before responding.

If we are using EPR and an apnea begins while EPR has lowered the pressure, then after a time the EPR will end and the pressure will return to normal, but the IPAP pressure the machine returns to will be the same IPAP setting as was used before the current apnea started. I think only machines like ASV models which have a "back up respiration rate" will respond to the start of an apnea (and thereby prevent an apnea from lasting as long as 10 seconds).

If you raise the minimum EPAP setting this would likely reduce the likelihood of obstructive events, but I am not sure whether this would have any influence on duration of apnea events. I think it may affect duration of apneas which happen to occur when the Pressure is bottomed out at its minimum pressure setting.


Take care,
--- Vaughn


Added:

From Zonk's post below, it sounds like even a single obstructive apnea will result in the AutoSet pressure being raised, after the apnea has ceased.




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#9
Thanks for the info. Looking at my SleepyHead data, I can see you are right.
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#10
From ResMed http://www.resmed.com/au/clinicians/comp...clinicians

How does a ResMed AutoSet device respond to flow limitation?
* If flow limitation is detected, AutoSet Spirit responds by gradually increasing pressure to bring the airway back to normal. Typically, this helps prevent snoring and apneas
* If no further events occur, AutoSet Spirit gently decreases the pressure, towards the minimum set pressure

How does a ResMed AutoSet device respond to apnea?
* Typically prevents apneas, by treating flow limitation and snore. These usually act as early signals for more severe apneic events
* In the event of a sudden apnea that occurs without any preceding flow limitation or snore, AutoSet Spirit increases the pressure after the apnea has ceased to prevent further apneic events
* Pressure response is based on the duration of the apnea
* If no further events occur, AutoSet Spirit gently decreases the pressure, towards the minimum set pressure




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