FL Score (Flow Limitation Score)

The FL Score is computed by the WAT (Wobble Analysis Tool) engine and measures flow limitation at the population level across all breaths in a session. For each breath window, it calculates the ratio of tidal volume variance in the top half of the signal versus the total variance.

In normal breathing, airflow ramps up smoothly and rounds off naturally, distributing variance across the full waveform. In flow-limited breathing, the airflow hits a ceiling because the airway is partially narrowed, creating a flat-topped pattern where most of the variance is concentrated at the peaks.

A higher FL Score means more of your breaths show this flat-topped pattern. An FL Score of 60 means 60% of breath windows showed significant flow limitation characteristics. Unlike the Glasgow Index (which scores individual breath shapes) or NED (which measures specific peak-to-mid flow drops), FL Score provides a broader population-level view of how much flow limitation is present across your entire session.