Reviewing data and how the S9 works

Well it has been almost 2 months since starting with my S9 and due to go in for a review in a couple of weeks.

I have started sitting down and looking at the reports etc in ResScan (and SleepyHead, great work Mark and the team) and will be the first to admit I still have a whole lot to learn about how things work with it all. From my understand there is the 10 second trigger to flag an event be it OA/CA, at that time if it is obstructive shouldn't the pressure be increased to compensate. What other conditions would stop the S9 increasing pressure at that point?

Here is a screen shot from last night and is similar to events I see on other nights. What I need clarification on is if the event starts at let's say 06:13:35 (not exact but not important), shouldn't it be flagged as an event at 06:13:45? and pressure increased yet there appears to be no increase until around 06:14:30



Isn't the S9 meant to stop this sort of thing? What else should I be looking at that would stop the machine doing something? Is this a 'normal' thing to happen?

As I said I am 'new kid on the block' and still learning so any advice is appreciated.

Cheers
Glen

It's gotta make you laugh! You can get 16 replies to dog farts but ask a simple question!

glenj

The Auto cpap machines don't actually increase pressure as an apnea occurs. In OSA it is normal to see 'pre-cursor' events (snores hypopneas, flattening of the curve) and these 'pre-cursor' events result in a slow increasing of the pressure over time (minutes). It is very very unusual to ever see a scored OSA apnea that had no snores or hypopneas or flattening taking place before it.

The Auto machine seeks to pre-empt OSA events.

Hope this helps explain one small part of the picture

Cheers DSM

The S9 will raise pressure after an obstructive apnea, not while it's happening.

The lag you're observing in you recorded data is probale a result of the data skew that happens on the SD card - google "S9 skew site:cpaptalk.com" to read more about that.

You can't really trust that time relationship between the charts, because the recording of all those real time data files seems tends to get a growing skew as the days go by. The combined data is probably at its most exact a after you format the SD card.

The bottom line: comparing the various traces gives you general an idea of what happened, and you can correct the skew mentaly. Don't use those relationships to understand precisely at which second when the algorithm causes a change in pressure.

Information about how the algorithm respond can by found on Resmed's site (see here for definitions), in patent applications, and in discussions on this forum.

glenj wrote:It's gotta make you laugh! You can get 16 replies to dog farts but ask a simple question!

Who said it's simple? And what makes you think those who know about dog farts know about the workings of the S9 and Rescan and vice versa?

I agree with ozij that what you are seeing is probably a problem with data skew. When this occurs the high sample rate flow data is offset in relation to the other slow rate data (events, pressure, etc). You can see this data offset if you look at how the data graphs line up at the beginning of the recording session. The high rate flow channel will start recording before the other channels. This time offset is constant throughout session.
I think reformatting the data card after downloading minimises this data offset. Reformatting will erase all data from the card, but the compliance data will be rewritten when the card is placed back in the machine.
Looking again at your data, there does appear to be some data skew, but its not too bad. I don't think ResMed starts increasing pressure until after the event, and I think that's one of the reasons some people don't like AutoSet machines and would prefer have a fixed higher pressure, or operate with a higher starting pressure. 13 second events are common, but 50 second obstructive event are getting a bit long.
How are your results for the rest of the night?

I sometimes see about a minute lag between an event and the response, and that's not from skew. I'm not sure why the S9 waits so long to respond. It could be that it's because the CEO's nephew wrote both the code for logging data and the code that controls the pressure. Scary thought.

OTOH, the machine controls my apnea very well, and after looking at the traces for a few nights breath by breath, I have a lot of confidence in the algorithm. It may be that it's designed not to respond to mild events unless there is at least a hint that there may be more to come. Unless you have another event in that minute between the first OA and the pressure increase, the machine didn't really let you down.

I have read about the skew and had reformatted the card once about 4-5 weeks ago but hadn't thought about it when looking at this event. Card now reformatted. How frequently to reformat is best to minimise the skew? (will go searching for that one in a sec)

Here is the entire night showing the other events etc. Although not appearing every night, events in the 30's are not uncommon



My current pressure settings are min 7 and max 14, my original prescription was for a set pressure of 9(had that re-written to get the Autoset and was done for 4-20cm), would it be worth trialling that(ie 9cm) for a few days, or even 11.1 (the 95% for the last fortnight)?

LOL, yes you are right ozij, no dogs here so I know nothing of dog farts seeping into my cpap and am working on my lack of knowledge of ResScan. Maybe one day I'll get a dog and able to post in both topics (hope not though....want the dog, not the farts)

It's interesting to see the full picture.

I reformat after most downloads, its just habit.

First my disclaimer, I'm only another interested user who knows nothing about your personal situation.

I think you have way to many events, and I don't know why.

Your leaks are continuous but not that high, the machine should be able to cope, but it would be better to reduce them if possible.
I was reading an article the other day from an Australian manufacturer of custom nasal masks. These masks are only available in Australia, but I thought his comments on full face masks was worth reading. See the below link
http://www.acurest.com.au/truefit-custo ... face-mask/
Its much harder to get a perfect seal on a full face mask compared to nasal pillows, have you ever tried something like the ResMed Swift FX?

Your events are almost all obstructive, you haven't shown your Snore index or Flow limitation graph's, but as the pressure is staying within the high / low settings, I doubt if there is a problem there.

My only guess would be to close the pressure window by increasing your minimum pressure to about the median value and see what the effect is, or you could try running in CPAP mode with a pressure somewhere between your 95 percentile and maximum value. (I just noticed your current pressures are 7 - 14, I would give 12 - 14 a go and see what happens)

Please only make these adjustments if you feel confident to do so.

Have you ever tried looking at your SPo2 levels, is there an issue?

Firstly, I am happy to make changes to MY cpap settings and accept total responsibility.

Here are the other two graphs you mentioned. The snore index has prety much been the same since starting with cpap and is a VAST improvement on pre-cpap. As for the flow limitations, only just starting to read up on those.



Most of my leaks have been below the 24L/MIN lately with an exception here and there.



At my titration I initially tried a Swift FX then a nasal mask(with a chin strap for about 5 secs, hated it) but as I was opening my mouth I ended up with the FFM. I am interested in trying the Swift FX(or similar) again and use a chin-strap for a bit longer but the cost is holding me back at the moment. Starting to look OS though.

I have no idea what my SPo2 has been since my initial sleep study but that night it went down to 75%. I am seeing the Dr next Friday so I'll see how it went on the night of my titration but that was 2 months ago so I am only assuming it has improved with no way to check it at the moment.

As with most people all replies/assistance are greatly appreciated.

The central apneas have given me some concerns since I have been looking at ResScan. At my titration there was about 50/50 OA/CA.

On average I'd say I have been having more central apneas than obstructive. Some nights I will have 2-3 times as many CA and on other nights 2-3 times less(not so many of those nights though).

The ratio of OA/CA varies quite a bit night by night, and the numbers are seeming to still be coming down as I use the cpap more.

DEFINITELY something I will be discussing when I see the Dr. I will be far less than impressed if I was given a prescription for a machine that ends up not being the right one for me.

Personally I don't think the S9 is perfect at scoring centrals compared to obstructives. I think there have been a few comments to this effect on the forum, but they would be hard to find. Does anyone else have any opinions?

Again its my opinion, but I think people find it much easier to adapt to the Swift FX after they have been using another mask. You can buy them on Ebay for about half the RRP.

Your Flow Limitation and Snore Index graphs as expected don't show any problems.

It would be very handy to try and get hold of an SPo2 meter to see if your events are causing problems.

I hope the S9 AutoSet is the correct machine as the alternatives are very expensive.

You could also try playing with the EPR and see if anything changes. Try 3 and then 0. Its the only other variable

greg-g wrote:Personally I don't think the S9 is perfect at scoring centrals compared to obstructives. I think there have been a few comments to this effect on the forum, but they would be hard to find. Does anyone else have any opinions?

Perfect? No. Even Resmed doesn't say that. It seems to me that it does pretty well, but no machine will be 100% on this with just flow and pressure sensors.

The only thing I've noticed is a few waking events scored as OAs. I have a battered nose and seasonal allergies, hence sometimes my airway isn't all that great even when I'm awake. Also, without the ability to assess the state of the diaphragm, swallowing and squeezing out saliva to moisten a dry mouth would look exactly like an OA.

It wouldn't surprise me if some centrals with a partially occluded airway are scored as obstructive when I'm asleep, but my machine scores very few centrals now, and I'm fairly confident that the ones it does score aren't obstructive. I think a few apneas are probably misread the other way, but this doesn't trouble me. I'd be more concerned if the s9 didn't respond to obstructive events because it thought they were centrals.

Well, have been back and had my 2 month review and all is well and the Dr suggested another review in six months so now it is down to me tweaking here and there to fine tune things.

The SPo2 from my titration hovered around 96-97%.

Look out leaks, I have you in my sites!

I'm pleased the review went well, as you say, it is just a matter of tweaking, not that's there is much you can do. Apart from your events and leaks all the other graphs I think are perfect.
I would be interesting to see if adjusting the EPR has any effect, but I doubt if it will.

I see nothing out of the ordinary in all above graphs