Flow Limitation

[nick2008]

What cause flow limitation? The last to night I've had limitation of ,85 and .93 this is much higher than I've been in a long time.

Thanks

[JDS74]

According to ResMed: (https://www.resmed.com/us/en/consumer/s ... aries.html)
Flow limitation
This refers to any event that limits the flow of air into your body, due to a blockage (or obstruction) in your upper airway.
Hypopnea
Hypopnea is a partial blockage of the airway. During a hypopnea, breathing is shallow at 50% less than baseline breathing, with partial upper airway obstruction lasting 10 seconds or longer.
OSA (Obstructive Sleep Apnea)
OSA is the most common type of SDB (sleep-disordered breathing). OSA is where an apnea or hypopnea occurs due to a complete or partial blockage (or obstruction) in the upper airway. See also: apnea; SDB; upper airway; hypopnea.

I take these definitions to mean that
An obstructive event has the airway completely closed.
An hypopnea event has the airway partially closed (~50% or so).
A flow limitation event has the airway partially closed but less than 50%.

So these are all the same thing going from milder to severer as one goes from flow limitation event to obstructive event.

[jnk...]

Personally, I consider these folks the experts on flow limitation:

While there is ample evidence that excessive flow limitation is abnormal and leads to pathologic changes in sleep and wakefulness, it is currently unclear whether including this in the diagnostic criteria for OSA would have any value. . . . Meurice et al. conducted an experiment in which two groups of patients diagnosed with OSA were treated with different CPAP pressures. The first group was treated with CPAP pressures targeted to eliminate flow limitation and the second group treated with CPAP pressures targeted to treat apneas, hypopneas and snores. The pressure requirements for the first group were higher than for the second group; however the first group had an increase in sleep time and more consistent improvement in maintenance of wakefulness testing. These results are suggestive that titration to eliminate flow limitation would lead to improved clinical outcomes. . . . Analysis of multiple indices for quantifying recorded SDB [sleep-disordered breathing] has shown that scoring flow limitation events in addition to apneas and hypopneas has a better sensitivity and specificity of correlating symptoms with their respiratory causes than currently used strategies. In particular, it is necessary to detect more subtle forms of SDB such as IFL [inspiratory flow limitation] in certain patient populations that do not present with frank apneas. Standardized IFL scoring should lead to better detection and characterization of IFL. A reasonable threshold to define abnormal IFL would be greater than 30% of sleep, however other quantifiable techniques should be considered. While there is data that IFL may be linked to clinical consequences in certain circumstances, more research is needed to establish guidelines in reproducible scoring of IFL. In addition, further evidence of its negative health associations are warranted before routinely incorporating into PSG interpretation. -- "The role of flow limitation as an important diagnostic tool and clinical finding in mild sleep-disordered breathing," Nevin Arora, Gerard Meskill, Christian Guilleminault; Stanford University Sleep Medicine Division, Redwood City, California, USA, September 2015. -- https://pdfs.semanticscholar.org/262b/4 ... 6d1dbc.pdf

My personal interpretation based on extending the application of those principles? For some of us, using PAP at a pressure higher than our APAPs give us, in order to smooth out more of the flattening of our waveforms, might actually improve our sleep. For others, not.

I believe that fact forms part of the basis of the benefits some patient populations receive from more unusual forms of PAP therapy by the likes, for example, of Dr. Krakow, who likes smoothing out a waveform beyond what many others shoot for, especially if a patient does not seem to be getting full benefit from standard-pressure PAP.

[palerider]

I take these definitions to mean that
An hypopnea event has the airway partially closed (~50% or so).
A flow limitation event has the airway partially closed but less than 50%.

That's not really correct.

A hypopnea is a result of reduced air *volume*. ie you're only able to inhale half as much as you normally were inhaling.... 50% tidal volume.

A flow limitation is a restriction in the air *flow*... like breathing through a straw. You can still inhale a full *volume* of air, but it takes longer and is more work.

[palerider]

What cause flow limitation? The last to night I've had limitation of ,85 and .93 this is much higher than I've been in a long time.

Thanks

a narrowing of the airway, it's like breathing through a straw...

This should help visualize what's happening in a FL, and other sleep disordered breathing issues:

https://www.youtube.com/watch?v=-gie2dhqP2c

[TASmart]

My personal experience is in line with the "Stanford dudes" above. My sleep study treated to the standard less than 5 AHI with similar Flow limitations. Over the last few months, unhappy with the flow limitations I was seeing I worked to lower/eliminate the FL as well as the AHI components. Results are much better sleep, and an AHI now generally about 1 rather than 3-5, and much more consistent results. My treatment pressure ended up being increased from 10 to 14.4. The downside is that leak control is more difficult.

[jnk...]

I think that historically speaking, definitions sometimes vary in exactitude, depending on number of signals and context. Especially for hypopneas, but even for apneas, in the context of home-machine, flow-signal, "scoring." Labs have their rules, which are constrained by agreements with payers. But some research docs use their own looser definitions.

From 2001:

Guilleminault initially proposed a liberal definition of a hypopnea as “a reduction—but not complete cessation—of air exchange.” More recent liberal definitions of a hypopnea have ranged all the way up to any visually discernible change in the appearance in the airflow signal or effort signals. This change may be a decrease in the amplitude or change in the shape of either the airflow signal (airflow flattening) or one of the two effort signals (abdominal or thoracic movement signals). Authorities agree that in order for a hypopnea to be clinically significant, it must be followed by either an arousal of some sort and/or an oxygen desaturation. [One] slide show presentation produced by the American Academy of Sleep Medicine . . . defines a hypopnea as any visually discernible reduction in the amplitude of either the airflow or the effort signals. This decrease in airflow must last for 10 seconds or longer. Also, in order to be counted as clinically significant, either an arousal of some sort and/or an oxygen desaturation of three points or more must follow the hypopnea. . . . I used to abide by the strict definition of an apnea argument (an apnea had to be an 80% to 100% reduction in airflow for the entire duration of the event). I have changed my mind to a more liberal interpretation of an apnea as being an event that contains the requisite 80% to 100% reduction in airflow but sometimes only during a portion of the event. The reason why I changed my mind is that nowhere in any of the definitions of an apnea does it specifically say that the entire apnea has to be an 80% to 100% reduction in airflow. They just say that there has to be an 80% to 100% reduction in nasal/oral airflow for 10 seconds or longer. Those 10 seconds could be anywhere within an event that would otherwise be counted as a hypopnea. Second, the shape and duration of the oxygen saturation level change parallel the duration of the entire apnea/hypopnea complex, not just the apnea portion of the event. . . . -- http://www.sleepreviewmag.com/2001/04/t ... hypopneas/

From a historical overview from 2009:

The operational definition for hypopnea remains controversial. One problem stems from recording technique; that is, most sleep laboratories measure flow qualitatively, and such measures do not proportionally estimate tidal volume. Therefore, couching airflow changes in terms of percentage decrease from baseline is problematic. Guilleminault et al.'s original definition of hypopnea as a reduction in airflow without complete cessation of breathing adhered closely to the general principle but left open the question of how much decrease in airflow was minimally required to score a hypopnea. A wide assortment of definitions were developed using different cutting scores for percentage of airflow decrease. Then in 2001, the AASM Clinical Practice Review Committee defined hypopnea largely based on the definition used in the Sleep Heart Health epidemiologic studies. -- https://www.sciencedirect.com/topics/me ... y/hypopnea