I'm not sure how the search on the community works (or doesn't), but I could not get this thread to come up when I did a search and I knew the title.
I have been trying to understand the graph. It has now gone from 2 lines to 4 lines. And there is actually another important horizontal value line, making there a total of 5 lines that we can not get a definition from Fitbit from and that are not labeled.
The top and bottom lines seem to represent the 'RANGE' limits on the graph. as it is EOV and not actual SpO2, it is hard to define these 'RANGE' limits. From the bottom, there is the invisible 'ERROR' line, a solid 'AVERAGE' line and then the dotted '% VARIATION' line is what I am guessing. And honestly, these are wild guesses as Fitbit insists on keeping us in the dark and that seems to extend as well to the support reps.
I see the ERROR line when all too often, my sensor seems unable to determine what the SpO2 is, or so it would seem. Fitbit has kind of acknowledged they are aware of the issue but nothing beyond the kind of state. It isn't a zero and nothing points to it being an average, it is kind of a null variation that appears many nights and at varying times through the night. It may simply be an artifact of the algorithm they apply to the SpO2 data.
The new solid line in the middle of the graph appears to be the 'AVERAGE' SpO2 and may not be a true average or median but rather a rolling average. It would be nice to get some feedback from Fitbit on this. As the devices now offer an mean nightly SpO2 (i.e. average) it would make sense that this is a reference point on the EOV graph.
In tracking SpO2, the absolute number is not what the medical community focuses on. If folks do research, they will read that for most individuals, it is anticipated that the SpO2 will be 95% or a bit more, suggesting that lungs and circulation are working at a normally high level. But whether it is 94% or 96% or 98% doesn't much matter and is individual and dependent on external factors. Hence it is easiest not no focus on that absolute number in determining overnight changes. If anyone has asked a technician about the readings on a sleep apnea test, the concern is not the absolute %, but rather the concern is a fluctuation from the average, or more so a variation from the current or rolling average. Different groups suggest using either a 3% or a 4% variation over a short period of time as indicating an apnea event (i.e. an event that oxygen saturation drops enough to count). The community accepts that this normally happens overnight and I they discount a small number (6?) then assess mild, moderate or severe apnea to users with a higher count of apnea events.
I interpret the EOV graph presented by Fitbit to mean that when variation appears to exceed 3% or 4%, that it crosses the dotted line and is flagged as a concern that there may be an apnea during those periods. Hence I have identified the dotted line as '% VARIATION' to indicate that the line may represent 3% or 4% variation from the rolling average SpO2.
It would be nice to get some feedback from Fitbit on this interpretation.
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