Flow Limitation (Inspiratory Flow Limitation)

Flow limitation is the partial narrowing of the upper airway during inspiration that restricts airflow without causing a complete airway collapse. On a flow waveform, it appears as a flattened inspiratory peak rather than the normal rounded shape. It is the central phenomenon that AirwayLab was built to detect and quantify.

Flow limitation exists on a spectrum between normal breathing and complete obstruction (apnea). While AHI only captures events at the severe end of this spectrum, flow limitation can cause significant sleep disruption at any level. The increased respiratory effort required to breathe through a narrowed airway triggers the body's stress response, potentially fragmenting sleep even without full arousals.

Research from Dr. Avram Gold and others suggests that flow limitation drives symptoms through the limbic and HPA axis stress response, independent of cortical arousals. This explains why many people with a normal AHI and even a low arousal index still experience fatigue, unrefreshing sleep, and other symptoms of sleep-disordered breathing. AirwayLab uses four independent engines (Glasgow Index, WAT, NED, Oximetry) to detect and quantify flow limitation from multiple angles.