Flow Limitations on AirCurve 10 ASV

[mmannari99]

I recently switched back to the AirCurve from a PR Dreamstation ASV. Doing much better with the AirCurve. I still get a moderate number of Hypopneas (average of 4/hour for last week). I get no OSAs and only an occasional "unspecified apnea". My pressures are: EPAP min/max = 4.0/6.0, Pressure Support min/max = 0 - 5.0, max pressure 11.0. The IPAP and EPAP pressures during the night do not reach these maximums, but come close (EPAP max 5.9, IPAP max 10.9). It appears I quite often see Flow Limitations exceed 0.50, maxing up to 0.90. My 95th percentile leak rate is good at about 14, and Oscar reports no LL events. 

My question is, are these above 0.50 flow limitations contributing to the Hypopneas? 

Thanks

[Gideon]

Event Definition Apnea, Hypopnea, Flow Limitation[edit]

• Apnea: 80% to 100% reduction in airflow for >= 10 seconds
  
  
• Hypopnea: 50% to 80% reduction in airflow for >= 10 seconds
  
  
• Flow Limitation: <50% reduction in airflow for >= 10 seconds
  

so a similar cause is possible for all these event types.

[sheepless]

I don't trust my flow limitations stats and graph. with the autoset I used to get lots of low flow limitations with a figure almost always showing up in the 95% and med columns. with asv, I get lots of high, 1.0 flow limitations with 0.0 in the 95% and med columns. IDK if it's a difference in effectiveness of the two machines or simply inaccurate data.

I seem to remember Sleeprider talking a while back about how asv functions in some way that itself produces these high flow limitations, maybe implying they aren't real? sorry I can't remember more but maybe someone else does?

[jaswilliams]

if your still seeing hypopneas normal answer is to increase pressure support max yours is low and if your using oscar the max pressure stat in the left column is a 95th percentile not absolute max. Your asv hands are tied preventing it from fixing the hypopneas

[Sleeprider]

Flow limitation is a common characteristic of pressure support induced inspiration. When you don't make the spontaneous effort to breathe, the ASV pressure support does ensure a volume of air is inspired; however as the lung fills, resistance increases, and this gives the appearance of flow limitation. This is not upper airway resistance, but a function of resistance in the lung itself. We see this on nearly every individual that has posted close-ups of the respiratory flow wave during ASV and ST non-invasive ventilation intervention. We don't try to treat this form of flow limitation, but rather accept that it is a common result of non-invasive ventilation.

The check for whether flow limitation is upper airway or a result of ventilation is to look at pressure support when it occurs. If the flow limitation mostly occurs during higher pressure support, it is pulmonary. If the flow limitation occurs during minimum or low pressure support, it may be upper respiratory, and a higher minimum pressure support or higher minimum EPAP may help.

[mmannari99]

Thank you Sleeprider. That is one of the best explanations I have gotten in my 6 months of ASV use. I will look into that.