mgrunk wrote:I am having trouble understanding the scales on the graphs for the SmartLink Software:
AHI - what is the vertical scale measuring? It says Length of AHI - but for hyponeas (that's most of my issues) they begin to be measured at 10 seconds.
I think you're misreading the vertical axis. But I also have to admit that as a mathematician, this graph doesn't seem in sync with the data presented later on in the Events graph. Typically the
AHI is the average number of apneas+hypopneas that occur in one hour of time the machine is running. In other words, the overnight AHI is computed as follows:
AHI = (total number of events)/(time machine ran in hours)
For PR machines, like the one I use, there's no such thing as an AHI graph. For Resmed machines, the AHI graph measures the "number of events since the top of the hour"---i.e. on the Resmed graphs, the AHI is reset to zero at the beginning of every clock hour. Hence it gives you a visual of how many events occurred each hour during the night. It appears that this AHI graph is not like the Resmed ones since the "resets" to zero don't occur on the hour every hour. At first I though that this might be plotting a running "AHI" based on the last hour of data every time an event is recorded. But there are at least two times that it appears that you had at least 7 events in one clock hour of time, but the AHI never goes that high in this graph. So this graph's meaning has indeed stumped me.
Pressure - I understand - I have a range of 5 - 10
Yep, the pressure graph is pretty easy to understand. It just traces the pressure setting at any point during the night. You should notice that the big bump in the pressure graph happens to correspond to the hour when you had the most frequent occurrences of hypopneas. In other words, this graph shows how your machine responded to that set of hypops shown in the Events table that starts just before the 2:26 tick mark.
Leaks - is is the volume of the leak?
Not quite the volume. Rather the units are L/min = Liters per minute. And so this graph measures
how fast you were losing air in the semi-closed system formed by the PAP machine, the hose, the mask, your nose (and mouth), your upper airway, and your lungs. I'd need more details from the user manual for the machine to make more sense of this graph. On both the PR machines and the Resmed machines, leak is represented by a single curve. But there are two here. And without additional written material I really don't know what is being plotted for "average leak" vs. time and what's being plotted as "maximum leak" vs. time. Also needed to properly interpret this graph is knowing whether or not this graph represents
Total leak rate or just
Unintentional leak rate. All masks have a built-in intentional leak rate to prevent us from rebreathing our own CO2. Some manufacturers report Total leak rate, which includes both the intentional leak rate and the unintentional leak rate. But some (such as Resmed) report only the Unintentional leak rates. I believe that DeVilbass shows total leak rate. So to interpret this graph, you need to look at your mask's owner's manual to find out what its intentional leak rate at your pressures are. Then you want your leak rate graph (at least the "average leak rate" part of it) to stay pretty close to that expected intentional leak rate for your mask. My guess is that the bump in the average leak rate between 2:26 and 2:56 is mostly made up of additional
intentional leak because that's also when your pressure level went from roughly 5cm to just over 10cm of pressure. That would certainly increase the intentional leak rate quite a bit.
Events - I don't know at all if where the dot is means anything other than the frequency of the events - oh wait, I see now the ASHEL - means apneas, snores, etc - so if it were black and white, you could still see what event it was:
This is indeed a table that shows
when each event occurred and
what kind of event it was. So you had about 19 hypopneas, one apnea (presumably an obstructive one), and two NRIs (non responsive incident---i.e. most likely a "central") during the night. It looks like you had the machine running for around 4.5 to 5 hours. So the overnight AHI is somewhere between 22/5 = 4.4 and 22/4.5 = 4.9. The worst period of the night was a thirty minut period from roughly 2:26 to 2:56, where you had 7 hypops plus an NRI.
NOTE: If you ever had events that happened right on top of each other---i.e. a pair of back to back OAs with just a few breaths between them, you might not be able to just count the dots to find out how many events occurred. That's because those dots are huge compared to the time scale. And if two events of the same type occur within 30 seconds of each other, then their corresponding dots are going to land on top of each other. And you'll only see one dot instead of two.
FWIW, most nights it seems like the event starts and the pressure ramps up and the mask can't handle the higher flow rate (sleepweaver mask) - but in general my events are under 4. So, last night was unusual - I rarely have apnea's or NRI's.
When you say your events are under 4, do you mean your overnight AHI is usually less than 4? Or do you mean you usually see four or fewer dots on the events table?
Also---as I explained earlier, it could be that what that leak line is showing is that as the pressure goes up, the expected leak from the sleepweaver mask also goes up. The rest of your "average leak rate" line looks pretty good to me---in terms of it being flat. What's the expected, intentional leak rate for the sleepweaver at 5cm? What's its expected, intentional leak rate at 10cm?
