[Treatment] Autoset mystery

[GDB2222]

I have been on CPAP treatment for 20 years, and I have just completed a 7 day follow-up sleep study using a Resmed S9 Autoset loaned by the hospital. I did sleep slightly better with the S9 than with my old machine, so I was happy to splash out on buying an S9 as a replacement.

So, now I have a brand new Resmed S9 Autoset, to replace my ageing S8 Autoset. For the first time, I have the ability to look at all the detailed graphs, using the ResScan software, and I'm hoping to fine-tune my treatment. That's really the point of my post. And to say thank you for this wonderful website. It's a terrific resource.

My AHI is about 1.5 at the moment, almost all AI. What is troubling me is that the machine is registering most of the AI events as Centrals, even in circumstances where I'm pretty sure they must be obstructive. It's a mystery to me. Let me explain:-

I have the min pressure set at 10, max= 20. My treatment pressure is about 15.

5 minutes after going to sleep I had a series of four apneas lasting around 20 seconds each. I vaguely remember them, so I wasn't fast asleep. Looking at ResScan, all four events are classified as centrals. Yet, I can see that the CPAP pressure was low, around 10, and I thought that central apneas tend to be associated with high pressure?

Anybody here can explain this please?

[zonk]

Central apnea can occur at any pressure, not all are pressure induced
The machine have no way knowing whether you were awake or asleep, apnea scored while you,re awake are meaningless and can be discarded for true AHI value

[trish6hundred]

Hi GDB2222,
WELCOME! to the forum,!
Glad you were able to get an S9AutoSet, CONGRATULATIONS.!
Hang in there for more answers to your question and best of luck to you.

[GDB2222]

Thanks, both of you!

Zonk, do you know how the machine distinguishes central and obstructive apneas?

In my case, I don't have any neurological symptoms to explain the central apneas. I think it's solely related to the CPAP treatment.

[archangle]

Some people use the term "SWJ" Sleep Wake Junk.

Weird stuff happens as you fall asleep or wake up. As long as they're not too long or severe, it's not a big deal. Centrals are pretty common kinds of SWJ. 4 centrals at 20 seconds each wouldn't give me a second thought.

Also don't get too concerned about the word "central." They're not necessarily more dangerous than obstructives, they're just harder to get rid of.

Also, look at the airflow waveform and see how "real" the apneas are.

[zonk]

Thanks, both of you!

Zonk, do you know how the machine distinguishes central and obstructive apneas?

In my case, I don't have any neurological symptoms to explain the central apneas. I think it's solely related to the CPAP treatment.

The scoring criteria to score apnea is apnea have to be 10 seconds or more
When the machine detect an apnea, send a small puff of air in the first 4 seconds
If closed airways detected ... obstructive apnea scored
If open airways detected ... central apnea scored

Let me find you some links explain it better and in details

[archangle]

Zonk, do you know how the machine distinguishes central and obstructive apneas?

In my case, I don't have any neurological symptoms to explain the central apneas. I think it's solely related to the CPAP treatment.

The S9 uses a sequence of air pulses at about 4 per second called the "Forced Oscillation Technique" (FOT). They then measure the airflow changes to try and see how big a volume of air it's "pushing against." Simplified answer about FOT, but you can Google it if you want more info.

Anyone can have a small number of central apneas, even without any CPAP pressure at all.

[zonk]

1- CSA detection
Central Sleep Apnoea (CSA) detection is now available in both S9 AutoSet and S9 Elite.
It uses the Forced Oscillation Technique (FOT) to determine whether the airway is open or closed during an apnoea.
Small oscillations in pressure are added to the current device pressure. The CSA algorithm uses the resulting flow and pressures to measure whether the airway is open or closed
http://www.s9morecomfort.com/s9morecomfo...toset.html

2- Central Sleep Apnea Detection and the Enhanced AutoSet Algorithm
Abstract
The ability to detect central apneas is a useful addition to an automatic algorithm for the treatment of OSA. The ResMed
AutoSet algorithm has recently been enhanced to include a Central Sleep Apnea Detector (CSAD). This paper describes the
CSAD as part of the enhanced AutoSet algorithm on the S9 flow generator and documents the process of validation which
included early human testing, bench testing and clinical trial results. The enhanced AutoSet algorithm and CSAD showed
that it identified and appropriately treated the different types of apneas with a very high degree of accuracy leading to better overall therapy
Read more http://www.resmed.com/au/assets/document...-paper.pdf

[robysue]

My AHI is about 1.5 at the moment, almost all AI. What is troubling me is that the machine is registering most of the AI events as Centrals, even in circumstances where I'm pretty sure they must be obstructive. It's a mystery to me. Let me explain:-

I have the min pressure set at 10, max= 20. My treatment pressure is about 15.

5 minutes after going to sleep I had a series of four apneas lasting around 20 seconds each. I vaguely remember them, so I wasn't fast asleep. Looking at ResScan, all four events are classified as centrals. Yet, I can see that the CPAP pressure was low, around 10, and I thought that central apneas tend to be associated with high pressure?

These sound like sleep transition "centrals" that would NOT be scored on an in-lab sleep test.

When we are transitioning to sleep, the control of our breathing must be passed from the voluntary nervous system to the autonomous nervous system. As part of this transition, the CO2 "trigger" for inhalations must be reset---i.e. in normal night breathing it takes a (slightly) higher level of CO2 in the blood to trigger an inhalation. During this transition process it is relatively common to have a "central apnea" because the process of resetting the CO2 trigger is not completely "smooth" in some people. This kind of central apnea is NOT considered part of sleep disordered breathing and they are not scored on in-lab sleep tests unless it is so problematic that it prevents a timely transition a real sleep state.

In other words, if the CAs scored by your Resmed S9 are largely confined to the period when you are actively transitioning to sleep, they probably are normal sleep transition centrals that would not be scored on a sleep test. Your S9's FOT algorithm for detecting the patency of the airway is correctly determining that the airway is NOT obstructed when these events are happening.

[GDB2222]

Many thanks for all the help.

After the first night, I changed the pressure range from 10-20 to 12-18. I have had a few more nights data, and things have not improved. In fact they have worsened. My AHI has gone from 1.5 to 3.9. I am inclined to go back to 10-20 pressure range.

Last night, for example, I had very few events for the first 5 hours of sleep (less than 1/hour). Then, 3 apneas and 6 hypopneas over a space of 10 minutes. Then, an hour after that, 7 apneas and 1 hypopnea over a space of 15 minutes. That woke me up. 9 apneas were classified as central, and 1 as obstructive. Mask leaks increased at about this time. Flow limitation is shown mostly as rounded, rather than flat.

I assume these events are when I go into REM sleep? Is that likely? Is there anything to be done about it?

Thanks so much for your help so far. I am so grateful!