Data available on the ResMed S9's LCD

The ResMed S9 AutoSet and S9 Elite have a wealth of efficacy data available right on the machine's LCD. The available on-screen data runs rings around the woefully inadequate data provided by the PR System One's LCD. (Note that if you are willing to download the System One data into Sleepy Head or Encore, all the bells and whistles of full efficacy data are there. It's just the System One's on-board data that sucks.)

But many newbie users of the Resmed S9 are not shown how to access the LCD's efficacy data by the DME that sets up their machine.

So---if you are using a Resmed S9 Elite or a resmed S9 AutoSet and you want to know how to get to the LCD's efficacy data and what that efficacy data tells you about the quality of your therapy, this post should answer your questions.

Step-by-step instructions on how to get to the Sleep Quality Report on your S9's LCD

1. Press the info button on the S9 to get into the Short Sleep Quality Report. You should see your Usage for the night, an icon indicating Mask Fit for the night, and the AHI for the night. Note that Mr. Red Frowny Face shows up if your excess leak rate is AT or ABOVE 24 L/min for at least 30% of the night. If you only see the Usage data, your DME has locked you out of the full Sleep Report Data. Take the machine back to theDME and demand that they change the setting for Sleep Quality from Usage to On. Or learn how to get into the clinical menu and set Sleep Quality to On yourself.
   
2. If you want more detailed information, you can go from the short Sleep Quality Report to the more detailed Long Sleep Quality Report by holding both the info and the double check buttons down at the same time for three seconds or so. You may notice a brief flash.
3.  Use the large round knob to scroll down ONE icon on the left hand list of icons. You should now see the top of the detailed Sleep Quality menu. And then CLICK the round button to select the detailed Sleep Quality menu. This will now let you scroll all the way through the detailed Sleep Quality menu to see the AHI, AI, and CAI, which are at the bottom of this menu. It will also allow you to change the data period from 1 Day to 1 Week to 1 Month to 3 Months to get an idea of the averages of the data over longer time frames than over night.

Information on what data is available on the S9's LCD in the Long Sleep Quality Report

 

The S9's software detects four types of respiratory events: Obstructive apneas, central apneas, unknown apneas, and hypopneas. The unknown apneas are events that the S9's algorithm detects as apneas, but cannot tell whether the apnea is obstructive or central with enough certainty to classify them.

The AHI number is the Apnea/Hypopnea Index for the reporting period, which on the S9 LCD is typically the overnight number. For overnight (one day) data, the AHI is computed by the S9 as follows: It takes the number of all detectable events (obstructive apneas, central apneas, unknown apneas, and hypopneas detected) and divides that number by the time the machine was running. In other words, the AHI is the average number of apneas and hypopneas that occurred each hour the machine was on. The LCD display number on the S9 is simply truncated at one decimal place without any rounding as near as I can tell. I believe that for longer reporting periods (such as five days), ResScan simply averages the nightly AHI numbers to compute the one in the report. But I don't know for sure.

The AI number is the Apnea Index for the reporting period. It only counts the obstructive, central, and unknown apneas. In other words, the S9 computes this number by dividing the number of detected apneas (includes obstructive, central, and unknown apneas) by the time the machine was running. In other words, the AI is the average number of apneas that occurred each hour the machine was on. Again, the S9's LCD display number seems to simply be truncated at one decimal place instead of being rounded to one decimal place.

An example might help.  Suppose that on a given night the S9 detects 15 total events---let's say there are 9 obstructive apneas, 2 central apneas, and 4 hypopneas---and that the machine was run for a total of 6.6 hours.

The S9's LCD's overnight AHI, AI, and CAI numbers are computed as follows:

AHI = 15/6.6 = 2.272727 = 2.2 (due to truncating the decimal)
AI = 11/6.6 = 1.666667 = 1.6 (due to truncating the decimal)
CAI = 2/6.6 = 0.303030 = 0.3 (due to truncating the decimal)

Note that we can use the LCD's overnight data to estimate the number of apneas, central apneas, obstructive apneas, and hypopneas by doing some quick multiplication of the LCD's overnight indices by the usage number. Here's a typical example:

Let's suppose you look at the detailed Sleep Quality Data one morning and this is what you see:

Usage: 7.3
Pressure: 12.4
Leak: 9.6
AHI: 1.8
AI: 1.4
CAI: 0.3

The Usage number indicates you used the machine 7.3 hours overnight.

The Pressure number is the 95% pressure level. For example, if the LCD says the Pressure = 12.4, that means that your pressure was AT or BELOW 12.4 cmH2O for 95% of the night. It also means that your pressure was AT or ABOVE 12.4 cmH2O for 5% of the night.   Note: If you are using an S9 Elite or if you are using an S9 AutoSet in CPAP mode, the Pressure number will just be your Pressure setting and it will remain the same every day.

The Leak number is the 95% excess leak rate in Liters per minute (L/min). Since the LCD says the Leak = 9.6, that means that your unintentional leak rate was AT or BELOW 9.6 L/min for 95% of the night. It also means that your unintentional leak rate was AT or ABOVE 9.6 L/min for 5% of the night.

And how long is 5% of the night? Well, 5% of one hour = 3 minutes. So you can multiply the Usage time by 3 minutes to get an idea of how long your leaks were above the reported leak rate: In our example, leaks were ABOVE 9.6 L/min for a total of no more than 7.3 * 3 = 21.9 minutes and the Pressure was above 12.4 for a total of no more than 7.3 * 3 - 21.9 minutes.

Since the usage was about 7.3 hours, we can also estimate the number of events you had and what type they were from the LCD's AHI, AI and CAI numbers as follows:

Total number of apneas and hypopneas:
AHI x Usage = (1.8 events per hour) x (7.3 hours) = approx. 13.14 events = 14 events (round UP since there's a fraction)

Total number of apneas (all types):
AI x Usage = (1.4 apneas per hour) x (7.3 hours) = approx. 10.22 apneas = 11 apneas (round UP since there's a fraction)

Total number of central apneas:
CAI x Usage = (0.3 CAs per hour) x (7.3 hours) = aprox. 2.19 central apneas = 3 central apneas (round UP since there's a fraction)

Estimated Total number of obstructive apneas:
First, an estimate of the OAI is simply OAI = AI - CAI. Note that if your S9 detects any Apneas of Unknown type, that will throw this calculation off, but it's still a good estimate. So here we go:

OAI = AI - CAI = 1.4 - 0.3 = 1.1 and
OAI x Usage = (1.1 OAs per hour) x (7.3 hours) = 8.03 obstructive apneas = 8 apneas (since we truncate to one decimal and because 8 + 3 = 11 apneas)

Total number of hypopneas:
First, an estimate of the HI is simply HI = AHI - AI. So here we go:

HI = AHI - AI = 1.8 - 1.4 = 0.4
HI x Usage = (0.4 Hypopneas per hour) x (7.3 hours) = 2.93 hypopneas = 3 hypopneas (Which make since because 11 apneas + 3 hypopneas = 14 events.)

Of course, to get more detailed information about when the events happened and how long each of the apneas lasted, you will need to download the data into ResScan (or Sleepy Head) and look at the graphs for the night.