interpreting & correlating graph data?

[Doubtful Tom]

If you please, I need a primer in graph and data interpretation (starting at kindergarten level). I'll try to sequence these Qs in a coherent manner:

1) When reading Pressure and Leak data, 95th % is key stat, correct? So if your Leak stat at 95 is high, then you have a Leak problem that needs fixing, correct?
2) What is considered good / acceptable score Leak data at 95%?
3) How do Leak and Pressure data correlate? Does a high 95 Leak score render 95 Pressure score unrealiable in any way? For ex., does high L require more P to control apneas? I'm assuming that high L lowers amount of P one breathes, correct? I'm trying to figure out if variations in P scores are affected by variations in L scores.
4) How does P & L correlation (assuming one exists) affect AHI? My AHI has been quite good -- generally below 1.0, sometimes as low as 0.1 and 0.0. But in trying to determine optimal P settings, I notice variations in the P data. Which got me wondering how much of this is being affected by L rates?

Is this making sense? Perhaps I'm trying to fine-tune the P settings too much. However, given the side effects of too much P -- aerophagia, aggravated reflux, in my own case -- I assume that ideally one would like to control AHI with lowest possible P. (and since titration report proved highly inaccurate, I've become increasingly fixated on this) All this preoccupation arose when I started spending more time reading summary graphs and not just relying on daily readings of machine, the latter having lulled me into sense that all was fine. As long as AHI was low, I figured the other data, especially re L, were not that significant. Now I'm thinking otherwise.

Thanks for your patience. tom

[jbenenson]

With my S9 set on APAP, if there is a leak then the machine goes right to the highest pressure to try to open my airway (unsuccessfully). It happens once or twice per night for me. My remedy is to re-adjust the mask to stop the leak at that pressure then restart the machine and go back to sleep. If you can, look at the air flow profile and you will see a definite correlation between the start of the leak and the increase in pressure. My rises quickly and stays high, then immediately drops to near the bottom and stays near there until another leak or actual event occurs. My AHI is really low when there are no leak events as it never takes the maximum pressure to open my airway.

[Doubtful Tom]

[quote=" If you can, look at the air flow profile and you will see a definite correlation between the start of the leak and the increase in pressure. .[/quote]


This sounds really helpful, j, but I'm not sure where to find "air flow profile." Is it in one of reporting options for ResScan data? Thanks for your help! tom

[robysue]

If you please, I need a primer in graph and data interpretation (starting at kindergarten level).

Since you ask for "a primer in graph and data interpretation (starting at kindergarten level)", I'll start with some really important key definitions so you know what these numbers actually mean. It's easiest to start with some examples. Since you didn't include any numbers except for AHI numbers in your post, I'll start by making some numbers up.

First, lets suppose that you slept with the S9 running for 7.5 hours and we're looking at the overnight data in ResScan or off the LCD for the numbers it shows. Now lets suppose that ResScan says that your Leak Rate data looks like this:

Median = 1.0 L/min
95% = 2.5 L/min
Max = 15 L/min

And lets suppose your pressure data looks like this:

Median = 7.5
95% = 9.8
Max = 10.2

And finally lets suppose that your AHI = 0.9, the AI = 0.6, and the CI = 0.1. [And so the OAI = 0.5 = 0.6-0.1 and the HI =0.3= 0.9-0.6].

First we can compute the number of events of each type without going into Rescan as follows:

(0.9 events per hour)x(7.5 hours) = 6.75, which equals 7 events that night (because Resmed truncates the decimal, always round UP)
(0.6 apneas per hour)x(7.5 hours) = 4.5, which equals 5 apneas that night
(0.1 central apneas per hour)x(7.5 hours) = 0.75, which equals 1 central apnea that night

A bit more arithmetic shows that there were likely 2 hypopneas (7 events - 5 apneas = 2 hypopneas) and 4 obstructive apneas (5 apneas - 1 central apnea = 4 obstructive apneas)

Now let's look at what the rest of those numbers actually mean.

The median leak rate = 1.0 L/min means that for 50% of the time the S9 was on, your leak rate was LESS THAN or EQUAL TO 1.0 L/min. And so for 50% of the night, your leak rate was also GREATER THAN or EQUAL TO 1.0 L/min. So in the 7.5 hours you slept with the machine, for 3.25 hours (3 hours and 15 minutes) you had a leak rate of LESS THAN or EQUAL TO 1.0 L/min.

The 95% leak rate = 2.5 L/min means that for 95% of the time the S9 was on, your leak rate was LESS THAN or EQUAL TO 2.5 L/min. And so for 5% of the night, your leak rate was GREATER THAN or EQUAL TO 2.5 L/min. Now it's important to realize that 5% of one hour is equal to three minutes. Since you slept for 7.5 hours, that means your leak rate was GREATER THAN or EQUAL TO 2.5 L/min for a grand total of (3 minutes)*(7.5 hours)=22.5 minutes. That 22.5 minutes of "high leak rates" might be in one giant half hour leak or it could be in several smaller leaks---the only way to know is that to look at the detailed graphs in ResScan. [You find the detailed graphs under the "Detailed Graphs" tab. If you only download "summary data" the detailed graphs won't be there.]

The max leak rate=15L/min indicates that at some point when the S9 was sampling leak data, it detected a leak that was as large as 15L/min. It may have been a very short lived thing---when you broke the seal to scratch your nose for example. Or it could be that on one or two of the big leaks that you had, the leak pretty quickly went from in the neighborhood of 2.5 L/min to 15 L/min and stayed there. But you know for sure that you could not have leaked at a rate of 15L/min for more than about 22 minutes because of the 95% leak rate number and the time the machine was on.

The pressure numbers are similar:

The median pressure = 7.5 means that for 50% of the night (3.25 hours) the S9 was running at a pressure that was LESS THAN or EQUAL TO 7.5 cm. And for 50% of the night, the S9 was running at a pressure that was GREATER THAN or EQUAL TO 7.5 cm.

The 95% pressure = 9.8 means that for 95% percent of the night, the S9 was running at a pressure that was LESS THAN or EQUAL TO 9.8 cm. And so for 5% of the night, the S9 was running at a pressure that was GREATER THAN or EQUAL to 9.8cm. Again, it's useful to realize this means that the pressure was GREATER THAN or EQUAL TO 9.8 for about 22.5 minutes.

The max pressure = 10.2 means that at some point(s) during the night, the S9 reached a pressure of 10.2cm. You know (for sure) from the 95% data that the S9 was running at a pressure of 10.2 for less than about 22 minutes out of the night.
ou can also determine the number of events you had overnight by doing a simple multiply of the LCD's AHI, AI, and CI numbers if you want to---you don't need to go into ResScan to determine how many events the S9 scored unless you want to.

[robysue]

Now that you have an idea of what each of the numbers actually means, we can look at your questions:

1) When reading Pressure and Leak data, 95th % is key stat, correct? So if your Leak stat at 95 is high, then you have a Leak problem that needs fixing, correct?

That's what many people take to be the key stat for Pressure and Leak data. But it is worth looking at the median leak rate as well, in my opinion. The reason I look at both is that the median leak rate tells me whether I was leaking off and one all night long or not, where the 95% leak rate tells me if my worst leaks were bad ones or not. To illustrate what I mean, let's look at two examples:

Person A sleeps for 7.5 hours and is leaking off and on all night at a rate of 5.5 L/M and for about 25 minutes during the night, the leak rate actually is between 7 and 10 L/min. So A's leak numbers look like this:

median=5.5, 95%=7.0, and max=10.0

Now suppose Person B sleeps for 7.5 hours and has NO leaks at all for most of the night, but has ONE 25 minute leak where the leak rates are from 8 to 10 L/min during this leak. B's leak numbers look like this:

median=0.0, 95%=8.0, and max=10.0

Neither person's leak rates are grate enough to trigger the Red Frowny face in the short Sleep Quality menu on the LCD. But Person A is likely to be having more significant problems with comfort due to leaking all night long.

For Pressure, the usual rationale for looking at the 95% number is that it is theoretically high enough to prevent most of your apneas and hypopneas. And most people seem to tolerate this pressure rather well. But for auto-titrations, they usually want the 95% number over several nights in a row so they can see what pressure the S9 tends to settle at. During my week or so of auto-titration, the individual 95% numbers ranged from something like 7.4 (on the low end) to 8.2 on the high end. The whole week came in at something like 7.8 or so. So my straight titrated pressure is about 8cm. Folks around here seem to have several ideas on how to set the min and max ranges for an APAP range. But there does seem to be a consensus that the max needs to be set ABOVE the 95% and that the min needs to be set not much lower than that 95% number. But your mileage may vary.

2) What is considered good / acceptable score Leak data at 95%?

Well, the closer to 0, the better obviously. But the information from Resmed seems to indicate that leaks above 24 L/min (the RED LINE in ResScan's detailed graphs) are enough to cause problems with the algorithms the S9 uses in order to detect and respond to apneas, hypopneas, flow limitations, and snores. So in any case you really want your 95% leak rate under 24 L/min to insure that you're getting some kind of meaningful therapy. But comfort is as a much of an issue as therapy is in my opinion: Nasty leaks cause most people real discomfort and they frequently cause people to wake up multiple times during the night to fiddle with the mask even when the leak is well below 24 L/min. For me, I don't worry at all if my 95% leak rate is below 10 L/min unless I had to fiddle with my mask more than once in the night. And if I wake up multiple times needing to fiddle with my mask because of leaks, then the leak rate IS a problem regardless of how low the 95% leak rate is.

3) How do Leak and Pressure data correlate? Does a high 95 Leak score render 95 Pressure score unrealiable in any way? For ex., does high L require more P to control apneas? I'm assuming that high L lowers amount of P one breathes, correct? I'm trying to figure out if variations in P scores are affected by variations in L scores.

Not really. If the 95% leak rate is based on one half-hour leak when you're basically wide awake and trying to fix the leak, that's not likely to effect the readings of the other seven hours the machine was running---if you had the mask on for 7.5 hours total. On the other hand, if you are leaking enough to make the Green Smiley face turn into a RED Frowny, that indicates your 75% leak rate is AT or ABOVE 24 L/min and Resmed's litertature indicates that at that point therapy can and probably is being compromised.

4) How does P & L correlation (assuming one exists) affect AHI? My AHI has been quite good -- generally below 1.0, sometimes as low as 0.1 and 0.0. But in trying to determine optimal P settings, I notice variations in the P data. Which got me wondering how much of this is being affected by L rates?

First congratulation on the greate AHI numbers. How are you feeling with those numbers? If you've got lots of daytime energy, no daytime sleepiness, and overall feel like you're getting good qualtiy sleep, you might want to leave well enough alone on the pressure settings and just concentrate on getting the leaks down to where they are not bothering YOU at night. Just how high are your 95% leak rates anyway?

My anecdotal evidence is that my 95% leak rates have little or nothing to do with either my 95% pressure level or my AHIs. But that may be because I typically have leak rates numbers like these: median leak = 0.0 (always), 95% leak = 0.0 to 5.0, max = 0.0--20.0, but most of the time it's below 10.

How I feel seems to depend on both max/95% pressure and AHI. I didn't do as well when my pressure range allowed the S9 to go above 9cm, which was my first titrated prescription. [That's since changed.] The AHI's were great at 95% pressures of 9cm, but I was bloated, had dried out eyes, couldn't sleep well, and felt like something the cat drug in all day. At somewhat lower pressure levels, my AHI's are not consistently below 1.5 any more, I'm still tired, but not as exhausted, and how I feel on a day-to-day basis now has a bit of a correlation with my overnight AHI. But how I feel is still more strongly correlated with how many times I wake up at night, which is most definitely NOT correlated with my AHI rates. My sleep doc has decided to prescribe a bi-level in hopes that will help me finally get over the hump and really start feeling better than I did before CPAP---or at least get back to feeling no worse that I did before CPAP.

Is this making sense? Perhaps I'm trying to fine-tune the P settings too much. However, given the side effects of too much P -- aerophagia, aggravated reflux, in my own case -- I assume that ideally one would like to control AHI with lowest possible P. (and since titration report proved highly inaccurate, I've become increasingly fixated on this) All this preoccupation arose when I started spending more time reading summary graphs and not just relying on daily readings of machine, the latter having lulled me into sense that all was fine. As long as AHI was low, I figured the other data, especially re L, were not that significant. Now I'm thinking otherwise.

You may be doing too much fiddling with the P settings. How often do you change them? It takes some time for me to adjust to each new pressure setting and I'm very reluctant to change them unless it's because of pressure-related side affects. Since you say you've had aerophagia and the pressure has aggravated your reflux, I can understand your desire to fiddle with the pressure range.

Have you tried to figure out where the line for too much pressure for the stomach to tolerate actually is? In my case, I really can't seem to tolerate 9cm, but do "ok" with a max of 8cm and a median at or below 7cm. My stomach would really prefer to go even lower, but then I do seem to run into problems with inconsistent AHI numbers where the high ones corresponding to days I feel even worse than normal.

So now that I've rattled on way to long with far more detailed information than you probably wanted in the first place, what do your leak numbers look like and what is the pressure range you're currently using?

[Doubtful Tom]

robysue,
Do you know the Little Feat song "Rock n Roll Doctor" -- "two degrees in bebop, a Piaget of swing, he's a master of rhythm and a rock n roll king."

You are clearly the "Cpap Data Doctor." If I were musically inclined, I would compose an encomium of lyrics in your honor. In the meantime, I will settle for printing off and studying this valued dissertation in data interpretation. Followup study session Qs sure to follow, I'm sure.

My admiration of your knowledge is exceeded only by my gratitude for your generosity in sharing it.

Humbly yours,
tom

[robysue]

robysue,
Do you know the Little Feat song "Rock n Roll Doctor" -- "two degrees in bebop, a Piaget of swing, he's a master of rhythm and a rock n roll king."

You are clearly the "Cpap Data Doctor." If I were musically inclined, I would compose an encomium of lyrics in your honor. In the meantime, I will settle for printing off and studying this valued dissertation in data interpretation. Followup study session Qs sure to follow, I'm sure.

My admiration of your knowledge is exceeded only by my gratitude for your generosity in sharing it.

Humbly yours,
tom

It's the math professor in me: I love teaching and I love helping folks understand quantitative data related things.

Glad that you found my posts helpful!