Hypopnea - Resmed scoring

[Opus1]

IIRC, a hypopnea is  marked if there is a >30% reduction in air flow of the baseline for 10 seconds or more.

The first and most obvious question is what parameters define the baseline.

Consider this flow rate:
[img][/img]

 Is the Hypopnea marked at 04:16:11 a legitimate hypopnea (the beginning of the 10 seconds would be at 04:16:01) ?
It seems to my unpracticed eye that it depends on if the baseline includes/excludes the large inhalations at 04:15:34 and 04:15:43

So, the legitimacy of the 04:16:11 hypopnea may well depend on what is considered baseline (either time or # of inhalations). 

Does anyone know what Resmed considerers baseline? 

[BoxcarPete]

I have no idea, but I have tricked the machine into marking hypopnea by doing something similar to that while awake - taking several deep breaths and then resuming normal breathing does the trick sometimes. I've also tricked it into marking a CA by inhaling for more than 10 seconds straight. It lined up my air intake flow line to the zero point and called the rest of the airflow a mask leak. It's really neat that these machines give us so much data to play with, but they aren't perfect and it takes a little judgement to see if any changes need to be made to our settings as a result of flags it posts to mark areas of suspected disorder.

[Opus1]

While I'm asking questions to better understand,

Consider this flow rate plot:
[img][/img]

Should the area above the zero flow line and under the zero flow line be approximately equivalent ?

Would this area (either red or blue) be considered the tidal volume for that breath?

[BoxcarPete]

1. They should be, but the machine has only one airflow sensor, and air potentially goes many places before eventually going back to atmosphere: out the mask vent, into your lungs, back out, then out the mask vent, out the side of the mask, out your open mouth, etc. Bear in mind that air is continuously passing this one sensor all the time. The machine is trying its best to figure out how much of that air made it into your lungs and back out with each breath based on the subtle changes in flow rate and pressure along with its own known inputs to the system. As I said above, it can be fooled pretty easily because it really has no idea what's happening to the air once it goes past the machine's intake. It doesn't try to balance them perfectly, if there is a major discrepancy it can write a bunch of air off to mask leaks to try and keep it close.

2. Red+blue should be the volume, since tidal volume is the peak-peak volume exchanged with the atmosphere from normal respiration.

[dataq1]

Tidal volume is a measure of the amount of air a person inhales during a normal breath.

TV is either the red OR blue component, not both.

[BoxcarPete]

Yes, I stand corrected. Red = blue = tidal volume, which is inhaled and exhaled alternately. I get a bit mixed up sometimes considering the implications of the curves representing flow, with the right hand side of the top curve being air still going in but slower, rather than starting to go out.

[dataq1]

No problem… mixed up is my middle name ! 

Now, I’d really like the experts here to weigh in on the question about the baseline.
In fact an associated question could be, when computing a baseline to compare, is the volume (the area under the curve) used or are just the peaks (maximum rate for each breath) used?

In the OPs example, that big inhalation (@ 04:15:39) is not only is twice the peak rate of previous inhalation but (by eyeball) two or three times the volume of the prior breaths.

[Opus1]

Please help,
Is the baseline defined by time, if so how much time?

[Gideon]

Only the peaks or inhales are looked at for events.
On hypopneas it is a moving average, I'm not sure how long, and a 50%-80% reduction. 80-100% are an apnea.

On flow rate, the volumes/ area for both inhale and exhale should be the same, and while the chart is a flow rate you can sort of think of it as a poor representation of tidal volume but there is a chart for tidal volume.

The flow rate chart represents what should be a closed system, if volumes are different where and why did it go?

[Opus1]

Thanks, 
To summarize, we don't know if the moving average (baseline?) would have included the large inhalation peaks at 04:15:34 and 04:15:43.

But if we suspect that those peaks were included in the baseline, that would explain why the hypopnea is marked for the period of 04:16:01 to 04:16:11.

So, in your opinion, is this hypopnea legitimate?*

(in my, far less experienced opinion, it is NOT; the scoring having been unduly influenced by a prior large inhalation)

*the reason for my inquiry is because I seem to have many such similar "events" that dominate the AHI nightly, and I fear are giving my sleep doc an incorrect impression of my nightly experience.

Many thanks.