Flow limitation as compared with hypopnea

Recently I got asked about the difference between the 'Flow Limitation' data coming from EncorePro vs the hypopnea data.

It got me thinking on the topic & in doing some looking around I found an old 2001 post that had some interesting remarks about the older Autos being divided into two types, 1) measure using flow limitation data and 2) Machines that did not measure using flow limitation data.

I had not really heard such definitions before & so thought it would prompt some interesting discussions.

I also dug up these defs ...
Flow Limitation – the partial closure of the upper airway impeding the flow of air into the lungs.
Hypopnea - shallow breathing in which the air flow in and out of the airway is less than half of normal--usually associated with oxygen desaturation.

(I know that here we have discussed that a flow limitation will usually preceed a hypopnea & that a hypopnea is when air flow drops by 50% in a 10 sec period & also that some respiratory people will say that a real hypopnea also means that a desat has occured at the same time).

Also as an aside, in this 2001 article the poster mentions the SommnoSmart machine & its use of FOT to determine if the sleeper's throat/airway is open or closed based on the ability to send a sonar signal (I am assuming it is FOT the poster is discussing). I recall SWS mentioning this type of use of FOT to explore the throat whereas some recent discussions (SAG) mentioned using FOT to try to force the airway open by 'tickling' the muscles with the low frequency oscillations (SommnoSmart II).

Here is the post I was reading http://www.sleepnet.com/apnea69/messages/694.html

The main topic then is ...

> Flow limitation score vs Hypopnea score - what is Encore Pro telling us

> What was the purpose of machines that measured flow limitations & those that didn't ?



DSM

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CPAPopedia Keywords Contained In This Post (Click For Definition): Encore Pro, Hypopnea

Originally most autopap designs were based on snore mic sensors rather than airflow sensors. This first category of APAP was often referred to as "snore based" and the second category was frequently referred to as "flow based" (despite also mathematically deriving snore signals from the flow sensors).

These latter machines, that were sometimes said to be based on "detecting flow limitations", also detected apneas and hypopneas (which were also cited in medical and manufacturer literature as "flow limitations", in a much broader sense of the definition). When cited in this manner, the term "flow limitations" included everything up to and including full fledged apneas. It was thus very confusing to many people that the term "flow limitations" was, and still is, used in these two ways: 1) a lesser air restriction than a hypopnea, and 2) all categories of air restriction, including hypopnea and apnea.

Today most APAP machines are of the "flow based" variety rather than the "snore based" (or even less employed FOT). Again, the machines with "flow based" sensors still mathematically derive snore signal from the flow channel itself. That snore signal is one of many "signals" embedded in the single flow channel. As a side note, "flow analysis" and "embedded signal analysis" are two different things. Flow analysis and discrete data channel analysis occur during the PSG. Embedded signal analysis is conceived by an APAP design team (think delta-oriented testing-type algorithms and trend-based quantitative wave shape analysis, with an entirely different time-domain based subset of "signal objectives" than those relied on by sleep techs who are titrating fixed pressures).

Then, aside from the above machine category definitions, there was and still is the issue of manufacturers defining and scoring hypopneas and flow limitations differently. So do we think the industry has been a bit ambiguous over the years, Doug? Yup... standardization of definitions and event scoring, at the very least, would be nice.

SWS thanks

as always, a wealth of rich data. Plenty to work through there.

When I saw the ref to the sommnoSmart I recalled your comment that FOT was originally used as an exploratory device (sonar) & that link is exactly how it was described.

It later occured to me (after making the post) that the non-flow limitation sensing units were probably what I knew as acoustical sensing & again you have clarified that well.

I think I may have mentioned having a PB Cloud Nine & am sure it is an acoustic based auto but I have no data on it (still haven't worked out how to change its settings else I would have tried it out )

DSM

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CPAPopedia Keywords Contained In This Post (Click For Definition): auto