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Why don't these flow rate curves count as flow-limited?
RE: Why don't these flow rate curves count as flow-limited?
As I posted over in my thread about communicating with my sleep doctor, last night I sent a MyChart message requesting an update to my chart and giving them the serial number to my vauto.


When I was collecting my thoughts and data to talk about how the vauto works so much better than the autoset, I created this document:


I realized that this is a really nice clean illustration of how the autoset stacks up against the vauto. And also, I think that what I'm seeing is that the ResMed algorithm is not properly flagging hypopneas in somebody like me who has long continuous runs of flow-limited breathing. (So a better title of this thread has morphed into "Why don't these severely flow-limited flow rate curves count as hypopnea?")

I think that ultimately the answer goes back to my crack about "that's not an event, that's a lifestyle". Sleep apnea medicine is all about counting discrete events. Because the ResMed algorithm treats flow limits, with the logic that they are a sign of impending events, it is set up to treat flow limits as it treats hypopnea. And so when it sees the flow limits, it tries to do the right hypopnea thing without needing to see the hypopnea.

However, if you are going to use the machine summary reports to decide whether the patient's sleep-disordered breathing is being successfully treated, then an algorithm which is blind to a whole bunch of hypopnea that is going on is going to seriously mislead you!
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RE: Why don't these flow rate curves count as flow-limited?
Cathy, I have the advantage that I don't need to sell my doctor on the benefits of the Vauto over CPAP for my therapy. Like you, I have to hope he can persevere through the inevitable denials from Medicare, and appeal the decisions to help me get the machine I need.
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RE: Why don't these flow rate curves count as flow-limited?
I have been using my vauto for a bit now and compared flow rates and pressure between autoset data and vauto data. I don't see any noticeable difference nor do I feel any when using the different machines on similar settings.

Reviewing your examples posted you can't compare individual cases like this because there are too many factors. I know you are noticing improvement on average but just for argument sake when looking at individual cases that autoset night could have been because you were sleeping in a different more restrictive position whereas the vauto data was just a short restriction.

One thing to note is that of course no hypopneas were flagged. A hypopnea is a 50% reduction for 10 seconds or more. Your flow restrictions occur too slowly to be considered a hypopnea. They are real restrictions though and worth treating.

I believe I commented on it earlier and I am going to stick with my theory. I believe your vauto data is better because you have restrictive breathing that gets worse as your body attempts to mouth breath (opening mouth/dropping chin which unfortunately creates more restriction due to positional issues). Your vauto provides higher pressure support which helps maintain enough breathing that your body doesn't start opening mouth and so you don't degrade into these periods of worsening flow limitations caused by mouth opening/chin tucking. Jmo.
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RE: Why don't these flow rate curves count as flow-limited?
Ok, so I'm not at all sure what happened here -- how could the cpap miss this?


It really missed -- the flow limit score was tiny, and the pressure didn't budge. Sometimes it's obvious why the miss -- weird confusing noise in the signal, usually -- but this was a pretty straightforward.
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RE: Why don't these flow rate curves count as flow-limited?
Cathyf: It's been fascinating to read about your transition from APAP to the Vauto. I'm a newbie so still learning. If I understand correctly, it looks like the transition really helped the flow limitations.
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RE: Why don't these flow rate curves count as flow-limited?
I have an appointment with the sleep dr on Thursday, and I've spent 2 weeks back on autoset collecting data. I've noticed two striking comparisons -- On autoset I have lots and lots of higher respiration rate periods, and the flow rate curves on autoset are noticeably wider and noisier than on vauto. I screen-shotted two weeks on autoset, and the previous two weeks on vauto, with autoset on the left and vauto on the right, respiration rate on the first page, flow rate on the second page.


I'm not sure what this means, but maybe explains why on autoset I wake up stiff and sore like I've been exercising all night?
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RE: Why don't these flow rate curves count as flow-limited?
To me the Autoset spikes in RR look like an attempt to get the same ventilation need you get from the VAuto where eachTV benefit is greater due in part to longer inspiration time and the greater efficiency from reduced impact of dead space. At the higher RR you breathe faster to make up a TV short fall.  But that is less efficient because each TV is smaller due to dead space losses and longer I-times (the latter I'd guess at lower FRs than for the VAuto?). Longer I-times are an indicator of increased work of breathing.

I'm not saying this is applicable to you, but it may be. Google and review some research by searching something like "NED in breathing". NED is a condition where, strangely, upstream from an airstream choke point there is also a reduction in the effective cross section of the airway. The possibility it could apply to your case came to mind as I scanned the matter briefly earlier today. Planned to look at it more closely.

Hope this makes sense. At first NED did not seem to for me. It just happens, don't know why. A lot to has been written to read more about it.
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.  (Disclaimer use permitted by sheepless)

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RE: Why don't these flow rate curves count as flow-limited?
Look closer at the flow rate waveforms during those previous high respiration rates and then read through the below thread. My guess is it is paradoxical breathing due to respiratory effort required to overcome your flow limitations, they don't occur on the vauto due to the extra PS decreasing respiratory effort required.

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RE: Why don't these flow rate curves count as flow-limited?
Amazing -- I have kind of noticed this before, and focused on the cardiogenic oscillations which I can understand are innocuous. The issue with cardiogenic oscillations is that they will cause the respiratory rate to be wildly mismeasured because all those little bumps get counted as breaths and they aren't. (This is the breathing that I call "marching llama's" because the jaggy oscillations kind of look like the pattern on a serape that would be worn by a llama in Andean folk art.)

But what I didn't see until elliotg's pictures is that the entire freaking inhale is a wildly oscillating flow rate.

This is last night:
2-minute closeup around midnight:
2-minute closeup around 3:40:

Now go back a year ago when I wasn't paying attention to this:
2-minute closeup around 2:30:

2 minutes back in 2019:

Hey, I make elliotg look like an amateur!

These are all pictures from when I wasn't wearing a cervical collar, but NOT having clusters of positional apnea.
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RE: Why don't these flow rate curves count as flow-limited?
Just further confirmation you have restrictions and benefit from the higher PS.
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