OSCAR Graph Question Events Flags/AHI

[Bob Cali]

Can someone please explain the AHI graph per attached as it corresponds to the events flag graph above. I understand the event flag can trigger the AHI, but the lines on the AHI graph start with the event but seems to go on for a time per the timelines. Thanks

[clan]

Hi Bob,

The AHI number is an hourly average of how many obstructive events (OA+UA+H) you have had during the night.

The AHI chart is a rolling AHI count (OA+UA+H) over the last hour.

You had an Hypopnea(H) at 05:00 so the line went up to 1 and it decreased with -1 at 06:00
You had an Hypopnea(H) at 05:10 so the line went up to 2 and it decreased with -1 at 06:10
You had an Unclassified Apnea(UA) at 06:47 so the line went up to 1 and the chart ends

You used your device for 06:41:54 hours

You had 0 OA - good for you.
You had 1 UA divided by 06:41:54 which is 0.15 (average per hour)
You had 2 H divided by 06:41:54 which is 0.30 (average per hour)

OA+UA+H averages = 0 + 0.15 + 0.30 = 0.45

or

OA+UA+H count = 0 + 1 + 2 = 3 events during the night.

And if you followed the math you will notice that you will be a little skewed if you simply divide by 6.42.

To be precise you need to calculate in seconds.

3,600 seconds on the hour.
60 seconds on the minute

Duration 06:41:54 in seconds (6*3,600)+(41*60)+54 = 21,600 + 2,460 + 54 = 24,114

We divide the AHI count with the duration to get the average. AHI averages are always in hours. So if we divide with the seconds we need to multiple with the number of seconds in a hour to adjust back to hours.

AHI average per hour is then (3 / 24,114) * 3,600 = (3 * 3,600) / 24,114 = 10,800 / 24,114 = 0.4478726051256531

This is then rounded to 0.45 which is your AHI.

And while we are here: Remember that your device not necessarily classifies all events correctly which means that your AHI might not be quite accurate. If you sleep worse than what your AHI might suggest you would start looking at the flow rate. If you have many LL (large leaks) the machine might not be able to sense an obstruction and it will not be flagged.

Hope this makes a little sense.

Kind Regards,
clan

[Bob Cali]

[Gideon]

an OA, CA, or H event increases the AHI chart by 1 for one hour when it then decreases the chart by 1. Subsequent events do the same resulting in a 1 hr rolling AHI.

The Experts ignore this chart as we get that info directly from the events chart, the more clustered events are the worse the AHI is.