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Call for Excel VBA help: to support effort to clarify/understand FL
RE: Call for Excel VBA help: to support effort to clarify/understand FL
fyi, I for one appreciate your efforts and updates. I hope you get some useful feedback. unfortunately, I have nothing to offer but moral support as this level of detail is way beyond me.
  Shy   I have no particular qualifications or expertise with respect to the apnea/cpap/sleep related content of my posts beyond my own user experiences and what I've learned from others on this site. Each of us bears the burden of evaluating the validity and applicability of what we read here before acting on it.  
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RE: Call for Excel VBA help: to support effort to clarify/understand FL
An update that shows a bit more progress zig-zagging toward a better understanding of what ResMed flow limit (FL) flags can or do reflect in my own breathing. There are few surprises in the graphs, but the varying volumes do show applicabilty of FL flags while suggesting other factors Resmed patents and algorithm cover.

In a nutshell the alternative approach being taken is to present examples of inspiratory volume reductions in relationship both to flow limitations (lower case "fl", those limitations below the Resmed FL flag threshold level) and to those flagged limitations above that minimum threshold. My present comments about the graphs are only three. 1) M-tipped inspirations are accompanied, as is usual for me, by a trailing FL flag that starts late in that breath's exhalation; moreover, there are two successeive M-tips which present a stacked FL with a seond step. Yes, there is a flow drop there but I believe the M-tip gets special Resmed attention to shape and flagging; 2) A few tiny cardiogenic flows show along the 0-axes; 3) I'm curious why, at about 09:47:25, there is no FL as there is at 09:47:00 (I see the former form frequently and without FL. The algorithm may "see" it as breath-holding?

I show in the attachment's top-most graph a crude representation of the loss of Tidal Volume (TV) due both to restriction from flow limitations and from "false-losses" that arise from natural/normal/usual breathing variations--simple changes of respiratory rate and other sleep metrics that vary during sleep. Accordingly, the baseline in the upper graph arbitrarily presents drop bars from a fictitious constant baseline, one chosen to be near a fictitious steady Miinute Volume (MV) of 5 to 7 liters/min. In other words, if the "drops baseline" is set at 7 L/min for TV and the breathing is actually 4 L/min then the drop would be 7 minus 4 L/min--it would be 3 L/min. Unlike the ease of showing real TV from the zero baseline in the data, there is no fixed volume baseline for computing inspiratory loss.  

In theory--and as could have been presented much more clearly--the upper graph and the third graph down should have the same vertical scale that would mate together along their bottom and top edges respectively like two pieces of paper would match after tearing the sheet in two.

Three side notes: 1) Re the bottom attachment in post no. 10 above: some days after posting, it struck me that the seeming absence of flow limitations (according to the cruder approach there) was likely due to oblivious  filtering out of  the largest flow limitations which would be expected there, given what SleepyHead presented as FL. I intend to check that out as I blunder along this path. 2) Those numbers in the 16 thousands along my graphs' axes in the attachment are the seconds past midnight. It is a big hassle to deal with conversion of them--as they are used in files underlying OSCAR presentations to usual clock numbers. They could be divided by 86400 (seconds in a day) and then be formatted as time values in Excel if I weren't too lazy or if space for presenting clock time wouldn't be crowded when showing and dealing with logged times in fractions of seconds. The graphs are closely, if not perfectly, synchronized, though crudely presented.

Readers' constructive and provocative observations would be helpful.

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RE: Call for Excel VBA help: to support effort to clarify/understand FL
I have to admit this is so far over my head right now, but good luck with your continued research and I hope that (one day) I'll have some informed opinions to share. Smile

See my comparison of Viatom/Wellue and CMS50F oximeters here.

Not a doctor, definitely not your doctor, all advice is given as-is and represents simply my own understanding as a fellow patient and OSCAR user.
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RE: Call for Excel VBA help: to support effort to clarify/understand FL
2SleepBetta, this is over my head, too, at this point, but my husband the theoretical physicist says that these time-series data analyses that we are doing are inherently the same sorts of things he does in his research.

If you have access to a Mac, there is a tool called DataGraph which he says is the hands-down best tool for doing this kind of analysis.
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