Wondering1 wrote: ↑Sat Dec 03, 2022 11:31 am
Whew, back after several grueling days at hospital, worked like a rented mule!
Data is pretty much spot on in assuming that my thought is that tidal volume plays a significant role in detecting a hypopnea.
Take a look at the OSCAR chart that I posted way-back:
Since you won't take the time to draw the horizontal lines that Rubicon and I both suggested that you need to draw, I've taken the time to download your image and edit it by putting in the appropriate horizontal lines that indicate the baseline amplitude in the flow graph and the amplitude of the breaths that triggered the hypopnea being scored. I've also added vertical lines that indicate the beginning and end of the event.
Here's the edited image, slightly blown up to show both the scale in the y-direction and the hypopnea in a bit more detail:
That baseline amplitude is about 28 L/min. That's the blue dotted line at the tops of the regular sleep breathing before the big breath that ends at 5:55:40.
The amplitude of the breaths that caused the machine to flag a hypopnea shown by the red dotted line: The amplitude of those breaths in the hypopnea are at 14 L/min. Last time I checked, a decrease from 28 L/min to 14 L/min is in fact a 50% reduction in the amplitude of the flow graph---which meets (just barely) the first part of the criteria for a Resmed machine to score a hypopnea.
As for the length of the event: The start of the hypopnea is around the green vertical line at approximately 5:55:50. The end is the purple line that I've extended over the purple line with the H that Oscar drew for you. It's at 5:56:11. That means this event lasted about 21 seconds, which is more than enough to meet the part of the definition that says the reduced flow has to last at least 10 seconds.
The final criteria that a Resmed machine uses to decide when to score a hypopnea is evidence of a flow limitation. You have not included the flow limitation graph in your screenshot. But if you look very carefully at the shapes of the inhalations in the hypopnea, there is some evidence of flow limitation in 1st, 3rd, and 4th breaths of the hypopnea. It would not surprise me at all if there was a
minor flow limitation visible in the flow limitation graph that lines up precisely with this hypopnea.
It's no surprise that your machine flagged this as a hypopnea: It meets all the criteria Resmed uses to decide something is worth flagging as a hypopnea.
You don't need the tidal volume graph to understand why this got flagged as an H. You do need to take the time to do what Rubicon suggested that you do on page 1 of this thread and that I suggested way back on page 2 of this thread.
There doesn't appear to be much change in the peak amplitude of the inhalations before the big breath and after, at not so as to be immediately discernable.
But there is: As I've shown with my horizontal lines, there is a reduction in flow that is right around 50% for those flagged breaths. If you changed the y-axis on the graph to go from -36 to +36, the reduction in height would be much, much clearer. The distortions in the shape of the inhalations (i.e. the flow limitations) in the flagged breaths would also become much clearer if you use -36 to +36 for the y-range of this part of the flow graph.
However, looking at the TV chart, a significant change is clear (before big breath and after).
The big bump
up in the TV graph is a temporary increase caused by the large inhalation that ends at 5:55:40. That one breath does not substantially change the baseline amplitude of the normal sleep breathing before that breath occurred. But the size of that one breath does cause the bump in the much lower resolution TV graph. In other words, the "decrease" in TV that you are so attached to thinking is relevant is made much
larger because TV is dropping from the amount of air you inhaled in the big breath that ends at 5:55:40 to the much smaller inhalations in the hypopnea. You should also notice that the TV graph "lags" the flow graph: In other words, there appears to be some "averaging" going on in that graph. It would not surprise me if what that graph was actually plotting was the
average TV calculated over a running 2 minute window rather than the actual TV for each individual inhalation.
But more importantly, the evidence that your airway
might be partially collapsed is drawn from the decrease in the amplitude in the flow graph combined with the distortions in the small inhalations that are flagged as the hypopnea.
I will add: If this were in my data, I'd be inclined to think this was a post arousal event specifically because it follows a big breath of the sort that is often, but not always, associated with an arousal. If this were my data and I was really, truly interested in trying to figure out whether this event could/should/would have been scored on a PSG, I'd be cross checking this with my FitBit data to see if there was a red dot "wake" relatively around 5:55:30-5:56:00. If there was, that would be enough to convince me this was a post arousal hypopnea that most likely would not "count" on a PSG. If not, I'd be writing this off as a possible arousal or possible marginal H or a possible "false negative" and I would not lose any additional sleep over it.
In other words, you have spent an enormous amount of time trying to use this example to prove an idea (that TV is relevant to scoring Hs) that the entire world of sleep medicine long ago decided was not relevant at all.
Frankly, I don't know if the Resmed engineers only look at the peak height of an inhalation and use that as the yardstick to evaluate subsequent breaths for possible hypopneas.
They don't. They also look at flow limitations. And to get technical, they more than likely are using something called "root square mean" analysis for analyzing a whole bunch of things connected to the idea of "peak-to-peak" differences in amplitude. But informally and for a non-math audience, all that fancy numerical stuff boils down to what's happening to the amplitudes of the peaks over time.
And they focus on the peak-to-peak differences in amplitude and a drop from the running baseline amplitude specifically because the sleep medicine community community long ago decided that a sudden decrease in the
flow of air into the lungs, along with with appropriate other data channels on a PSG, indicates the airway is partially collapsed and that while the person continues to make an
effort to breathe, the air flow into the lungs is compromised.
But it would appear that the TV of subsequent breaths is a clearer indication that the patient has "diminished" ventilation.
Ventilation is not what sleep disordered breathing is all about. Flow and flow limitation are the name of the game because that's what the sleep medicine community decided was important many decades ago.
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