EAI (Estimated Arousal Index)

The Estimated Arousal Index (EAI) provides an estimate of how many times per hour the brain briefly wakes during sleep, based on breathing pattern changes detected in the flow waveform. True cortical arousals can only be measured with EEG (brain wave monitoring), but the respiratory patterns that accompany arousals can be detected from flow data.

AirwayLab detects arousal-like events by identifying breaths where respiratory rate spikes more than 35% above a 120-second rolling baseline and tidal volume spikes more than 50% above baseline simultaneously, with at least 2 of the preceding 5 breaths showing flow limitation (NED above 20% or Flatness Index above 0.85). A 30-second refractory period prevents double-counting.

Important context: EAI is a secondary marker. Research from Dr. Avram Gold and others suggests that flow limitation itself drives symptoms via the limbic and HPA axis stress response, independent of arousals. AirwayLab presents EAI alongside primary flow limitation metrics (Glasgow Index, FL Score, NED) because flow limitation may be the more important clinical indicator for understanding symptoms.