Combined FL Percentage

The Combined FL Percentage reports the proportion of all breaths in a night that are classified as flow-limited by either of two methods: NED above 34% (indicating significant peak-to-mid flow drop) or Flatness Index above 0.85 (indicating a very flat-topped breath pattern). By combining both detection criteria, it catches flow limitation that either method alone might miss.

NED and Flatness Index detect overlapping but distinct aspects of flow limitation. NED is sensitive to progressive airway narrowing during inspiration (mid-flow dropping below peak). Flatness Index is sensitive to the overall rectangularity of the breath. Some flow-limited breaths show one pattern without the other, so the combined metric provides the most complete per-breath picture.

Below 20% indicates well-controlled therapy. Between 20 and 40% is borderline. Above 40% suggests significant residual flow limitation. This metric is particularly useful as a single summary number when communicating results to clinicians, as it directly answers the question "what percentage of breaths are flow-limited?"