Difference Between Flow Limitations and Hypops

[skjansen]

Can someone define what flow limitation is as it relates to the Resmed machine? My AHI was 2.8 last night and AI was 0.0. This looks good to me but I am just wondering about hypopneas. I saw in another thread that the Resmed machine really does not recognize hypopneas. I am so confused. I thought hypopneas were a reduction in the air flow for less than 10 seconds and after that they turned into apneas. Is that not the case?

Does that mean a AHI of 2.8 is not as good as I think it is? Can I really have hypopneas that last for minutes without the machine picking up on that?

Just wondering.

[Velbor]

Can someone define what flow limitation is as it relates to the Resmed machine?

ResMed AutoSet Clinical Manual wrote:
Inspiratory flow limitation indicates silent partial obstruction. When your patient is breathing normally, the inspiratory flow measured by the unit as a function of time shows a typically rounded curve for each breath. As the upper airway begins to collapse, the shape of the inspiratory flow/time curve changes and the central section flattens. The AutoSet algorithm analyzes the shape of the central part of the curve for each breath and assigns a value as the amount of flattening. Inspiratory flow limitation, or partial airway closure, usually precedes snoring and obstruction. Detection of this flow limitation enables the unit to increase the pressure before obstruction occurs, making treatment pre-emptive. The Flattening Index is a measure of silent inspiratory airflow limitation.

I saw in another thread that the Resmed machine really does not recognize hypopneas. I am so confused.

Perhaps you are referring to viewtopic/t34091/Hypopneas--almost-igno ... esmed.html

This is absolutely false. ResMed machines "recognize" hypopneas. They sense them. They compute the hourly frequency. They report them on the LCD screen and in their software. What they do NOT do is DIRECTLY respond with pressure change to hypopneas themselves. ResMed machines DO respond to FLOW LIMITATION as measured by FLATTENING.

I thought hypopneas were a reduction in the air flow for less than 10 seconds and after that they turned into apneas. Is that not the case?

That is not accurate. There are a variety of definitions of hypopnea, used in different situations for different purposes. From the perspective of ResMed machines, "A hypopnea is defined as a 50 to 75% drop in ventilation. A hypopnea is scored if the 8-second moving average ventilation drops below 50%, but not below 25%, of the recent average for 15 consecutive seconds."

Yes, indeed, that sounds like gobeldygook, and you have every justification for being confused. But if you're looking at your own response to therapy from night to night, the technical details of the definition don't really matter very much, since whatever the definition is, it's the same each night. (By the way, even the definition of "apnea" for the machine is considerably more complex than one would expect, but again, it just doesn't really matter.)

Does that mean a AHI of 2.8 is not as good as I think it is?

I don't know how good you think it is. I would think that it's great!!

Can I really have hypopneas that last for minutes without the machine picking up on that? Just wondering.

No. The machine WILL sense it, will count it, will report it. It will also RESPOND to the FLOW LIMITATION that will likely accompany the hypopnea. Don't let the WORDS get you bent out of shape.

The ResMed auto machines, just like all of the other auto machines (and just like all medications), are proven to be safe and effective for MOST people.

Velbor