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Flow Limitation Confusion
#1
Question 
Flow Limitation Confusion
I have read on this board in the Wiki and discussion that Apneas can be broken down into
1.    Apnea (80-100%) 10 seconds or more. Breaks down into
                Central Apnea if forced oscillation technique (FOT) diagnoses the airway open but not breathing
                Obstructive Apnea if FOT diagnoses the airway is blocked
2.      Hypopnea (50-80%) 10 seconds or more
3.      Flow Limits (0-50%) not timed

I am confused if this is just a reporting limitation of AirSense or if I don’t fully understand the above. I have 2 charts below.
1.      One shows at 1:47:05 through 1:47:17 an almost 90%+ full Flow limitation. That is almost 12 seconds. Why is this not an OA?
2.      Wow I had a great night. The only Apnea was a CA at 1:53:39 through1:53:50 which is 11 seconds. So, do CAs and OAs just not show the Flow Limitation or should it be showing the 80% + blockage?

Huhsign

   

   
-- Bill
Struggling to keep the air moving like everyone else …  ?

Standard Disclaimer:
I'm just a CPAP user like you. I can't give medical advice. 
  Sleep-well
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#2
RE: Flow Limitation Confusion
The numbering system for FLs on ResMed machines does not indicate a percentage of blockage. Instead, it indicates relative limitation, with a higher number corresponding to greater limitation. More information from the Board's Wiki:

ResMed also determines flow limitation. S8 AutoSet defines flow limitation using flatness of an inspiratory breath. The flatness index is calculated by the RMS deviation from unit scaled flow calculated over the middle 50% of a normalized inspiratory breath. From the S9 onward, flow limitation is calculated using a combination of flatness index, breath shape index, ventilation change, and breath duty cycle. Ventilation change is the ratio of the current breath ventilation to recent 3-minute ventilation. Breath duty cycle is the ratio of current breath time of inspiration to total breath time of recent 5 minutes. If a breath is severely flow limited, the flow limitation index will be closer to one and when the breath is normal or round, the flow limitation index will be zero
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#3
RE: Flow Limitation Confusion
Thanks @Dormeo for that clarification.  I took the 0.9 to be like 90% blocked and not just a relative number for the flatness of the flow curve. Geezzzz

My periodic breathing has patterns that are flat on tops of flow curves but keep getting progressively smaller. I do question my flow curves since the typical restriction looks sort of like a chair pattern with spike then flat before final drop. All of mine are reverse. I have the spike after the flat. 

Thanks
-- Bill
Struggling to keep the air moving like everyone else …  ?

Standard Disclaimer:
I'm just a CPAP user like you. I can't give medical advice. 
  Sleep-well
Post Reply Post Reply
#4
RE: Flow Limitation Confusion
FLs have several kinds of shapes in the inspiration traces. One is a dent, or sometimes several; another is a plateau, and yet another is a lop-sided peak (chair-pattern, as you describe it). The chair can be facing either way. And come to think of it, a peak could be in the middle of what would otherwise be a plateau. These are all indications that you are exerting a little extra effort to complete your inhalation.
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