Under standing AHI on pressure MyEncore Chart

george49 · Post by **george49** » Sun Jan 08, 2006 9:55 am

Have my next appointment next week and would like to know a little more about understanding AHI on pressure. Here are two of those charts a one week and a 24 day chart and a Daily AHI just for a quick ref. I guess i thought that by using the auto bipap biflex it would keep it under control but i am still having them but not as many. Can anyone put some light on this for me.
Thanks
George49

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CPAPopedia Keywords Contained In This Post (Click For Definition): bipap, AHI, auto

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CPAPopedia Keywords Contained In This Post (Click For Definition): bipap, AHI, auto

Ric · Post by **Ric** » Sun Jan 08, 2006 2:11 pm

It looks to me like the upper pressure limit is not quite high enough to compensate for the majority of obstructive events. I prefer to ignore the AHI numbers, since they combine two completely different clinical phenomenon which are not really equivalent quantitatively. It is useful and meaningful only when they are both "zero", meaning the pressures are sufficient to compensate for both obstructive apnea and hypopnea. Looking at the apnea and hypopnea separately on your graph tells me the hypopnea is extinguished at fairly low pressures, and the apneas are not fully compensated. What is the upper pressure? (if that's not obvious). You might check this another way, look at the EncorePro summary graph that shows "Non-responsive Apnea/Hypopnea Index", something like this"

If indeed the numbers are greater than zero, then you have a problem. The only other possibility that I can imagine is that if there were one more point on the second graph at 13, and it went to zero, then you might be ok. But we don't know that.

I think the "bimodal" shape of your "OAI" curve is interesting. I have a similar profile on my long-term graph of the apnea data (not the hypopnea). I have speculated that this might represent two different underlying phenomenon. My best guess is that the lower bump at around 6-7 represents sleeping on the side, and the higher bump 13-? occurs while facing the ceiling. I have no data to prove that, other than my original sleep study which actually recorded sleep posture, and tended to support that notion. But not enough data really for just one night.

Can you bump the upper pressure limit by one, just to see what happens?

george49 · Post by **george49** » Sun Jan 08, 2006 2:24 pm

I have attached my Daily AHI chart and i see in the first 5 days had three NR.
None since then.

I am using it on Auto pressure 4-20

thanks for your feed back it all helps

Ric · Post by **Ric** » Sun Jan 08, 2006 2:49 pm

I use the REMstar Auto with C-flex. I have no experience with the auto bipap biflex, and I'm not sure how it is different. Are there ramp times involved, or something else that would limit the pressure response, at least part of the time? I am puzzled at why there are non-responsive events at all. Is the response time so slow that it can't compensate fast enough? I can see I'm not really being helpful, just asking more questions. I am confident that somebody here has the expertise on the bipap and will set us both straight. Now I'm really curious.

george49 · Post by **george49** » Sun Jan 08, 2006 3:24 pm

Yes it does have a ramp and when in auto it is fixed.
I am not sure, but the NR that showed up where in the beginning of my treatment and i that might be why they are no longer showing up since it seems to be working somewhat.

The questions that you have ask make me wonder also.

Jerry69 · Post by **Jerry69** » Sun Jan 08, 2006 7:18 pm

george49 wrote:Have my next appointment next week and would like to know a little more about understanding AHI on pressure. Here are two of those charts a one week and a 24 day chart and a Daily AHI just for a quick ref. I guess i thought that by using the auto bipap biflex it would keep it under control but i am still having them but not as many. Can anyone put some light on this for me.
Thanks
George49

George, your charts don't make sense to me. You have one that shows an AHI of 42 vs.10 cm of pressure, but no where does an AHI of 42 show up on the daily charts of AHI. What is going on??!!

Jerry

george49 · Post by **george49** » Sun Jan 08, 2006 7:24 pm

Jerry

Yes that is the way i saw it also. My 24 day chart just does not look right and i don't know why. And the machine will only but out 20 so i really don't understand it. Maybe some one can but some light on it.

The 7 day chart makes more since to me,

Jerry69 · Post by **Jerry69** » Sun Jan 08, 2006 7:56 pm

george49 wrote:Jerry

Yes that is the way i saw it also. My 24 day chart just does not look right and i don't know why. And the machine will only but out 20 so i really don't understand it. Maybe some one can but some light on it.

The 7 day chart makes more since to me,

I agree. Change your machine to 8-12 cm and see what happens. Just guessing that you are missing some events by starting at 4 cm. (Actually, been reading posts on this forum.

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Hey, just checked out your machine. You have a Cadilac!! I don't know about Bi-flex machines. But, change something and see what happens. Can't hurt.

Jerry

george49 · Post by **george49** » Sun Jan 08, 2006 9:25 pm

Yes i could raise the lower end up to six and see how that works out.

I have to go and see them on tuesday and i will try and see if they would read that chart also.

Ric · Post by **Ric** » Sun Jan 08, 2006 9:53 pm

The two graphs in question are not actually inconsistent. Since there are no OAI events with pressures greater than 9 recorded in the first week of 2006, that tells me that the 10-12 cm pressure events occurred in the last 2 weeks of Dec 2005. The OAI at pressures 10, 11, 12 (40, 26, 30 respectively) are RATES, and not a raw tally for any given day. There's no point in looking for a peak of 40 for any given day on the OAI-HI vs date graph.

Here's a hypothetical: say there are 10 OAI events during a 15 minute period on any given day which were resolved at 10 cm-H2O pressure. That represents a RATE of 40 events/hr. If that were the only time spent at that pressure, then that is what you would see on the OAI vs. PRESSURE curve. The actual number you see there represents all the OA events at that pressure divided by the total cumulative hours AT THAT PRESSURE.

Now to complete the calculation, bring up yet another graph, under the "HOURS" tab. It shows the cumulative time spent at a given pressure. That is the denominator in the RATE calculation, that is, the OAI. Unfortunately there is no chart or graph in either EncorePro or MyEncore that shows the cumulative EVENTS at a given pressure. You could arrive at this rather tediously if you wanted to look at all the DAILY detailed reports in EncorePro that shows the OA and H events juxtaposed with the pressure graph. Or if you trust the RATE graph in MyEncore you could calculate it backwards by multiplying the OAI times the cumulative hours, although in this case it doesn't prove anything since that is a completely circular argument. But that would tell you what the numerator OUGHT to be. Nevertheless, I am willing to believe the graphs you displayed are not really inconsistent. It's a matter of understanding what they trying to convey.

george49 wrote:And the machine will only put out 20 so i really don't understand it. Maybe some one can but some light on it.

The machine you are describing will deliver up to 20 cm-H2O pressure. I think that is the "20" that you are referring to. But there is no limit to the number of OSA events you can have at a given pressure. It will record as many as you can throw at it. And likewise there is no limit to the RATE that derives from those events, depending on how FAST you can throw them at it. That's entirely up to you.

Hope that helps.

george49 · Post by **george49** » Sun Jan 08, 2006 10:36 pm

So if i have this right, you are saying that in 197.7 hrs. i had 40 OAI at pressure 10 and so on.

Thank you
George

Guest · Post by **Guest** » Mon Jan 09, 2006 1:01 am

You're getting close. Understand that OAI is an INDEX, not a count. In plain english I suppose you might say as the pressures adjust up and down, the time the machine spends at each pressure is recorded in its own "bucket". Sorting the OSA events into a pressure bucket is slightly more complicated, but roughly if an event fails to resolve at 9, say, but resolves at 10, it is thrown into the 9 bucket. If it it fails to resolve at 10, it will be thrown into a 10 or higher bucket, but never a 9 or lower. (nevermind the details, the method is actually more complicated than that). If a given pressure bucket has lots of events and very few hours, it will have a very high INDEX. Whereas other pressures have many many hours and very few events, so it will have a low index. If all the events are resolved at some pressure, let's say 13, then there will be no events above that and the OAI will be uniformly zero. (don't EVEN try to divide those ZERO events by ZERO hours)

An example from my EncorePro "Sleep Therapy Daily Details" report from last night (daily events per hour chart at the bottom of the page) I find, aside from spending most of the night at the baseline pressure of 6, there were 23.5 minutes at 7, with a calculated OAI of 5.1, which represents (23.5 x 5.1)/60 = 2 events charged to pressure bucket 7. I spent only 3 minutes at 9, but was assigned an OAI of 40, which equates to (3 x 40)/60 = 2 lousy events that gave me a FORTY. (the 60 is there to convert minutes to hours)

Working it backwards, If I see I had spent 3 minutes at pressure 9, and I could independently discover there were 2 events in those 3 minutes, I would calculate my OAI index as (2/3) x 60 = 40, which is exactly what the EncorePro did.

Look at your cumulative hours at the 10, 11, 12 pressures under the MyEncore HOURS tab, and the OAI from your graph (above). From that you can calculate how many "events" you have accumulated at each pressure, using (minutes x OAI) /60. That's hard to verify over a long time interval, but pretty easy to do for a single day where you can see the events (tick marks) as they occur.

Another observation is that a "tick mark" on the EncorePro "sleep therapy flags graph does NOT NECESSARILY equate to an "event". Some events span multiple ticks, or just one, depending on what else is going on with the pressure response.

Does that help?

(I hope somebody understands my babbling)

Ric · Post by **Ric** » Mon Jan 09, 2006 1:05 am

That was ME, dawgonnit.

GRRRRRRRRRRRRRRRRR...

(oh wait! maybe i should check the math before I claim credit)

Ric · Post by **Ric** » Mon Jan 09, 2006 1:35 am

george49 wrote:So if i have this right, you are saying that in 197.7 hrs. i had 40 OAI at pressure 10 and so on.

OAI is "Obstructive Apnea Index", not to be confused with OSA "Obstructive Sleep Apnea", which is a diagnosis, nor OSA events, which are the breathing obstructions that occur. The TLAs* tend to blur together.

My second observation is that, SUPPOSE for those 197.7 hours in your example, you had spent a mere 3 minutes of that at a pressure of 10. And SUPPOSE that during those 3 minutes you had exactly 2 OSA events. And SUPPOSE all you did was just sneeze once or twice. YES, there would be a tick mark on the graph showing an OAI of 40. And it would display very prominently on the graph. Statistically it would not be that significant. And clinically it might not be all that important. Or it might be too. That begs for some reality checks and some serious head-scratching before reaching conclusions based on a single graph.

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*TLA = three-letter acronym

Snoredog · Post by **Snoredog** » Mon Jan 09, 2006 3:06 am

George:

9cm appears to be your ideal pressure. Based upon your reports, you cannot really go any higher than that 9cm pressure or your NR apneas increase dramatically.

Again those are thought to be central apneas and if they increase in frequency with pressure then they are pressure induced therefore you should establish a pressure ceiling on the machine so that doesn't happen. I'm not sure if any machine can read those accurately. Shallow breathing and using a cannula style mask can cause the machine to record them.

My suggestion would be to set the bottom pressure at 6cm and the high to 9cm and use it within that range for a while. I'd put the machine in cpap mode with a 6cm starting ramp and see how you do. Why did they issue you an auto/bipap?

The only chart that really means anything is the AHI indice, as that is the SUM of both Hypoapnea +Apnea events seen together. Your goal should be to end up with the lowest AHI score and the lowest NR. Most flow limitations turn into hypoapneas, most hypoapneas turn into snores or apneas. Some machines like the Spirit like to trigger off snore and as a result eliminate the follow-on apnea. So when you look at those reports you might see zero AI's and a dozen or so HI's as a result.

If you increased your bottom pressure from 4cm to 6cm, it might eliminate or pre-treat many of your hypoapneas preventing them from turning into apneas later on.

What does your snore index look like? It would be interesting to see if that also went up at 10cm pressure, if the snores continued to go up then its the increased air pressure causing an increase in snores.

What does the Snore chart show in relation to your AHI score? Do they go down at 9cm also?

Under standing AHI on pressure MyEncore Chart