(01-31-2016, 06:16 AM)Asjb Wrote: I've been using ASV for 2 months and delighted. Fatigue much improved. AHI average 0.8. Desaturation events reduced from 120/night to fewer than 10. No obstructives or centrals ever reported - just a few hypos and <unknown apnoeas>.
Settings unchanged recently - min EPAP 10, pressure support 1.4 to 7.2.
Last night: ... The AHI was 4.4 - exceptionally high for me since using ASV. More than 95% of the events were within an hour with a max AHI during this hour of 28. I was definitely asleep at the time, not just dozing. The events were not associated with flow limitation on the graphs and no leaks were recorded at the time (95% leak for the night was zero).
I am not concerned about this one-off result but I am intrigued as to why it happened and whether or not I might need to change anything.
Could it be that I somehow blocked the expiratory plate? (I do tend to burrow in the duvet).
No, that's not it. If the mask vents had been blocked, that would not have caused the Flow to be small while the Pressure Support was max'ed out, large. (Below, "Flow" and "Pressure Support" are defined.)
Quote:I can't work out from the Sleepyhead graphs if the hypopneas and unknown apnoeas (? central) were caused by high pressure points, or the pressure spikes came as a response to the events. So maybe my max pressure of 17.2 is too high - or not high enough? Or, if nights like this become more frequent, do I need to increase the pressure support? If so, to what?
None of the apneas or hypopneas during the zoomed-inperiod look like central events, all look obstructive.
Central events start gradually and end gradually.
Obstructive events may start gradually or suddenly but all tend to end very suddenly with "recovery breaths" after we have managed to arouse ourself enough to take some large breaths before again gradually falling more deeply asleep, perhaps allowing our airway to progressively close off again, allowing the obstructive apnea or hypopnea to return.
Also, in an ASV or ST or other machine which has a backup respiration rate (as yours does), during an obstructive apnea the Flow will nearly stop, even though the Pressure Support has raised itself as much as is allowed by the Max PS setting. (Below, this is discussed further.)
Quote:But my main 'diagnosis' is that I had an episode of body paralysis (which affects my respiratory muscles too), probably worsened by just-before-waking REM sleep. I often wake up during my nocturnal paralyses (which is helpful as I can then take extra treatment to abort them) but not this time Would the Sleepyhead data be compatible with that?
I've no idea whether "body paralysis" could result in obstructive collapse of the airway, which is what happened during the zoomed-in period. But if you are thinking perhaps paralysis was causing central apneas, no, that's not it.
The Flow waveform shows that all the events during the zoomed-in period were Obstructive.
The Flow waveform is the estimated rate of airflow into (positive Flow) and out of (negative Flow) our lungs. "Flow" is different from the airflow in the hose, which includes the "Flow" plus the airflow exiting through the mask vent holes plus airflow from leaking.
By definition, the Flow waveform shows the rate of airflow in our lungs/airway. The Tidal Volume waveform shows the total volume of airflow into (or out of) our lungs/airway per breath
. The Minute Volume waveform shows the total volume of air breathed in (or out of) our lungs/airway per minute
Pressure Support (PS) is the difference (the amount the pressure is boosted) between the lower pressure (EPAP) used during exhalation, versus the boosted pressure (IPAP) used during inhalation. When we see this difference (PS) increase or decrease, this shows the ASV machine is automatically adjusting PS in an attempt to keep the Minute Volume nearly unchanged. If the airway is open and if the lungs are healthy (normal), by the time the PS gets as high as around 10 cmH2O, the machine will be doing just about all the work of breathing for us, keeping us nearly fully ventilated even though we are making no effort to breathe. This is how the machine is able to treat/prevent Central Apneas.
The machine reacts the same way to obstructive apneas and obstructive hypopneas as it does to central apneas and central hypopneas: it raises the PS as much as needed to maintain nearly the same Minute Volume as existed before the sudden decrease in Flow / Tidal Volume / Minute Volume.
Obstructive apneas often are strong enough, however, that even a large increase in Pressure Support may result in negligible increase in Flow, which is what we see in the Pressure and Flow waveforms during the zoomed-in period.
If your PS had been higher (perhaps somewhere in the range 10 to 15, I think), perhaps such a very large PS might have been able to fully overcome the Obstructive Apneas, or instead perhaps the higher PS might have been able to eliminate the hypopnea events we see when PS was max'ed out at 7.2, and might have been able to reduce the severity of the apneas by converting them into hypopneas. We cannot know, but a higher Max PS would make this more likely.
But at the same time, it is likely that very high PS like 15 may be so intolerably bothersome (at least at first) that you would have difficulty falling asleep at all, or it may cause excessive air swallowing (aerophagia) or may cause some other problem. (Personally, I think it is crazy that in the new AirCurve ASV machine the default Max PS setting is 15; I think 10 would be a better default upper limit and, if needed, higher values for Max PS could be achieved by gradual adjustments of the Max PS setting.)
In your case, apparently your doctor has prescribed a relatively low value for Max PS. I suggest you discuss why with him/her. Is this based only on experience with other patients, or is your doctor concerned about something special in your case?
If you want to make an adjustment based on the obstructive events you posted, I would suggest considering upping EPAP to 11 and seeing how it goes. A large hike in EPAP (of course implemented gradually, to avoid a larger EPAP than necessary, and to allow you to become gradually acclimated to the higher EPAP) might be needed to avoid the type of events in the zoomed-in period. However, as good or better results might be obtained simply by avoiding certain sleep positions.
Although raising the Max PS may marginally help, I think Obstructive events are best treated by
(1) avoiding positional sleep apnea, which usually means taking precautions to make it impossible for us to roll into our worst sleeping position, which for most users means preventing ourselves from rolling flat onto our back while asleep, and
(2) if avoiding bad sleep positions doesn't help or is not feasible, then raising the EPAP pressure (better than raising the Max PS) would likely result in a decrease in the number of obstructive events.
By the way, for ResMed machines which provide Central Apnea Detection, I think the setup manual (Clinical Guide) will say that apneas are classified as being of Unknown type when the Leak is higher than 30 Liter/minute, which is around when the ResMed Forced Oscillation Technique (FOT) becomes unreliable. But our ASV machines never wait or delay reacting to an apnea (never take the approximately 10 seconds or so which would be needed to perform the FOT), so all apneas on ResMed ASV machines will be of type Unknown.