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Flow limit and AHI's

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ittiandro +0 points · almost 3 years ago Original Poster

I am trying to understand the relationship between Flow Limit and obstructive apneas. It may appear just an academic exercise because my therapy has been working well since I first started and O.A.’s have practically disappeared, but it is nevertheless something I want to clarify because I always like to understand things. I submit two daily records, one showing 0.00 AHI’s and one showing 6.05 AHI’s . The Flow Limit patterns are different . On the one showing 6.05 AHI’s the Flow Limit spikes up close to 1, the maximum value on the Y axis, whereas the report with 0.00 AHI’s has a much flatter F.L. profile .Am I correct in understanding that a flatter F.L. profile points to a better sleep pattern in terms of apneas and viceversa?



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Sierra +0 points · almost 3 years ago Sleep Patron

This is a fairly complex area of sleep apnea. Women in particular tend to have higher levels of flow limitations prior to having any full apneas. ResMed makes a special machine (AirSense 10 AutoSet for Her) that has a mode which is more sensitive to flow limitations and increases pressure earlier in response to flow limitations. See the graphic below. A flow limitation is said to be a flat spot on the top of each inhale breath on the flow graph. You may be able to see it in SleepyHead if you expand the scale to see each individual breath during a period of time when flow limitation is high.

It should also show up in a higher RERA score, which are events which are not apneas but may cause arousal and sleep disturbances.

Keep in mind that all this AutoSet for Her machine can do to address these events is to increase pressure earlier. You can do the same thing by simply increasing your minimum pressure. Another option is to go to a fixed pressure instead of auto pressure control.

Looking at that second graphic of yours the main flow limitation is occurring during the time when your maximum pressure is limited. It may be necessary to increase your maximum pressure allowed in auto pressure control mode.

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