Wondering1 wrote: ↑Thu Dec 01, 2022 7:24 pm
robysue1 wrote: ↑Thu Dec 01, 2022 3:49 pm
The problem, such as it is, is that Oscar (and SleepyHead before) (and SleepHQ as well) misnames the graph with the redundant phrase "Flow Rate" instead of the simpler, yet just as accurate, "Flow".
To get to a better understanding I asked the folks over at Apneaboard about the misnaming of the graph:
The flow rate graphs displays the instantaneous respiratory flow in mL/second (flow rate) for the time shown in the graph... Any given point on the graph is the flow-rate per second, but the graph represents the flow-rate in mL/second over time. It is properly named.
First, whoever posted that last quote hasn't bothered to actually look at the units of an Oscar Flow Rate graph: The units for Flow Rate in Oscar are L/min, not mL/sec. And mathematically "flow rate" and "flow" mean the same thing: Flow is the measure of the
instantaneous rate of change in volume of the air in the lungs.
Since you are still unwilling to accept that "flow" itself is a
rate function, how about we look a screenshot of ResScan, the official Resmed software? Here's how ResScan displays the data:
You can find the original of this image on the official ResScan webpage itself at
https://resscan.software.informer.com/. It's labeled Screenshot (1). Click on it and you'll see the large version which I took a screenshot of.
As you can clearly see, there is no graph in ResScan that is called
Flow Rate. But the graph labeled
Flow is, in fact, the graph that Oscar calls the Flow Rate graph.
So the dimensions are: Y-axis = mL/sec, X-axis = time of day
Almost, but not quite correct.
Yes the x-axis units are time of day. But the y-axis is not mL/sec in either ResScan or Oscar or SleepHQ. The units in the Flow/Flow Rate graph are L/min. Now if you want to, you can convert L/min to mL/sec:
1 L/min = 1000 mL/min = (1000/60) mL/sec
But the fact is that regardless of whether you are looking at the data in ResScan, Oscar, or SleepHQ, the units for the Flow (or Flow Rate) graph are labeled as L/min.
AlIf you integrate one inhalation curve by seconds, I think you should get a single mL value for that inhalation.
That would be a volume (mL) for that breath.
Technically if you integrate the Flow curve over one inhalation, you get the volume of air inhaled in one inhalation measured in
Liters because you are integrating with respect to time and because the flow curve is measured in L/min and you are integrating over time measured in minutes.
The technical definition of tidal volume (TV) is "volume of air inhaled in one inhalation" and, yes, usually TV is usually measured in mL, not Liters. So in terms of the math:
TV = (integral over the time for one inhalation of the flow curve) * 1000 mL
That is the volume that is graphed in the tidal volume graph.
Yes, but this has nothing to do with the definition of a hypopnea---regardless of whether we're talking about the AASM definition or the Resmed xPAP machine definition.
So what I've been trying to say here is that, if the hypopnea determination is based on reduction in volume (ml) then the TV graph is an important tool.
But the definition of hypopnea is NOT based on a reduction in
volume. It is based on a reduction in
flow and
flow is measured in L/min.
I know I'm not going to convince you. But it's important for others who are reading this thread to understand:
Mathematically there is no difference between "flow" and "flow rate" and "rate of flow", just like there is no difference between "speed" and "rate of speed".
And the AASM definition of hypopnea as well as the definitions used by the engineers and programmers who designed the Resmed and PR machines and the algorithms they use to flag hypopneas are all based on reductions in
flow, not tidal volume, and
flow is measured as a rate---i.e. in L/min.
Joined as robysue on 9/18/10. Forgot my password & the email I used was on a machine that has long since died & gone to computer heaven.
Correct number of posts is 7250 as robysue + what I have as robysue1
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