Exceptionally poor ASV night. What might have caused it please?

[Asjb]

May I have some advice please?

Background - Diagnosed 10/2014, minimal home testing. <Severe> sleep apnoea (AHI 58). OSA (rhinitis, laryngeal cysts, deviated septum) + intermittent allergic asthma + intermittent flaccid muscle paralysis (genetic disorder; attacks last for up to a few hours at a time). I didn't do very well on CPAP/APAP (fatigue unchanged, AHI up to 15, treatment-induced centrals from diagnostic zero to 3/hr), so was changed to ASV (never had a titration study).

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: 2 screenshots at different levels of detail (sorry - I still can't work out from Imgur how to post a thumbnail, only links)

http://imgur.com/s362kp0

http://imgur.com/aOMrmAk

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).

As luck would have it, it was not one of the occasional nights that I wear an oximeter.

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).

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?

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 would be very grateful for any advice. Thank you.

[Sleeprider]

As you said, the events were focused on a relatively short period just before waking. Your pressure support is limited in settings to 7.2 and it appears that was insufficient to overcome the resistance in your airway to cause you to adequately ventilate. It seems as though the pressure pulses resulted in small increases in flow, but not full breaths. The patterned breathing seems to show a series of arousals and breathing between periods of apnea with a cycle time of about 1-minute.

If everything has been working out for you, I don't know that a change is in order, but it appears more maximum pressure support will be required to break these cycles if they recur. You will have to experiment to find what that threshold is, but you might try increasing max PS to 8.0.

[vsheline]

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).

Hi Asjb,

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.)

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.)

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.

Take care,
--- Vaughn

[Sleeprider]

Vaughn, I agree with your analysis. Assuming the apnea and hypopnea is obstructive, this is probably more of a low EPAP problem than lack of pressure support. I think what I missed is that for some reason, EPAP is fixed not auto, and at 9.5 if OA gets going, pressure support is probably not going to break it. Is this model capable of automatic increase of EPAP, or is it fixed bilevel with an ASV function?

[vsheline]

... for some reason, EPAP is fixed not auto, and at 9.5 if OA gets going, pressure support is probably not going to break it. Is this model capable of automatic increase of EPAP, or is it fixed bilevel with an ASV function?

I think the AirCurve ASV is the model sold in USA, and AirCurve CS is sold in other regions but has same features. So, yes, I think Asjb's machine has the ASVAuto therapy mode.

Now that I think of it, perhaps changing to a narrow range in ASVAuto mode would be best for characterizing and treating those obstructive events. The machine itself would raise EPAP as needed to avoid obstructive events.

Perhaps Min EPAP of 9 or 10, and Max EPAP of 11 or 12, to start.

The automatic adjustments in EPAP would provide Asjb with a mini titration every night, showing when the machine is reacting to obstructive conditions.

I think Asjb should discuss these approaches with her doctor, if feasible, and find out her doctor's reasons for the low pressure limits which were prescribed.

In addition, Asjb's sleep study or titration study may indicate whether her OSA is positional.

[Asjb]

Dear Sleeprider and Vsheline,

Thank you very much for such excellent information and advice. It all makes much more sense to me now and thanks to your expertise I have a Good Plan now for my settings. Your comments included -

Quote < I've no idea whether "body paralysis" could result in obstructive collapse of the airway, which is what happened during the zoomed-in period > end quote

My paralytic attacks (muscular genetic disorder) affect all voluntary muscles and my throat and mouth muscles do weaken during the episodes so it makes sense I would have more airway obstruction. My chest muscles also weaken during the paralysis so I tend to hypoventilate, which doesn't help the situation of course. I have found the 'forced-rate puffs' of an ASV machine to be very comfortable and reassuring during paralytic episodes.

Quote: <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?> . And <I think Asjb should discuss these approaches with her doctor, if feasible, and find out her doctor's reasons for the low pressure limits which were prescribed> end quote

Ah! - complex situation (as appears to be typical here in France...). After many mostly unsatisfactory months (symptoms and AHI) using an Airsense 10 CPAP/APAP on a variety of different settings, I thought I needed to try a bipap machine to allow me to tolerate the much higher pressures my Sleepyhead data clearly suggested I often needed. So I politely made my case for a Resmed Aircurve bi-pressure to three different sleep doctors. All of them told me my AHI of up to 15 on treatment was 'entirely satisfactory' and that my ongoing fatigue 'must be due to something else', and they refused to prescribe or trial any Resmed/Respironics bi-pressure machine (although the last doctor did offer me Sefam bi-pressure Brick, which I refused). They all also refused to arrange a bipap and ASV titration study (I never had any titration study at diagnosis either).

So as a last resort I asked my excellent muscle doctor for help. He is not trained in sleep apnoea but he wanted me to feel less tired and to reduce my cardiac risk. He trusted my analysis of my APAP Sleepyhead data and the explanations that I gave him. He approved my request for a Resmed Aircurve VAuto but the technician then arrived instead with a Pacewave ASV (I think there must have been admin confusion between the Vs in 'VAuto' and 'ASV' - Resmed machines seem to have slightly different 'type names' in Europe c.f the USA). When he realised the mistake, the technician, knowing my medical history, suggested ASV might be better for me anyway (I have echo-cardiogram proof I don't have cardiac failure). So I accepted the ASV machine - and I'm never giving it back! It's been brilliantly effective.

Thus since 10/2015 I haven't been under the care of a sleep doctor so the technician set the machine for me. He is very good but he did struggle to choose pressures - he told me he has no other clients using ASV who aren't under the close supervision of a medical specialist. And I had never tolerated a pressure of more than 12 before the the ASV. But now thanks to your advice, I feel confident about continuing to adjust the ASV settings myself.

Quote: <Although raising the Max PS may marginally help, I think Obstructive events are best treated by avoiding positional sleep apnea, which usually means taking precautions to make it impossible for us to roll into our worst sleeping position> end quote.

My diagnostic test showed sleeping on my back and on my left side were equally awful, sleeping on my right side was a 70% improvement. I have largely trained myself to stay on my right side I think.

And quote: <So, yes, I think Asjb's machine has the ASVAuto therapy mode> end quote.

Yes, it does do auto-EPAP and I shall now try that as you suggest, and then look at changing the PS too if needed.

Thank you very much again for your advice, I am very grateful.