Most CPAP analysis stops at AHI: total respiratory events per hour. WAT looks at what is happening in the intervals between flagged events -- moments when your machine counts everything as fine, but your breathing patterns may be showing subtle instability.
What Is the WAT Score?
WAT stands for Wobble Analysis Tool -- a bundle of three independent metrics that AirwayLab calculates from your inspiratory flow data. Each metric measures a different aspect of breathing stability during PAP therapy.
The Three WAT Metrics
FL Score (Flow Limitation Score)
A percentage from 0 to 100 measuring how much of your inspiratory waveform shows flattening compared to a normal rounded profile. Higher means more flow limitation was present across the night. A score of 0 means no detectable waveform flattening. A score of 100 means fully flattened waveforms throughout.
This is AirwayLab's own continuous score, calculated breath by breath from the raw EDF data. It is independent of ResMed's firmware and gives more granular resolution than the categorical 0/0.5/1.0 FL channel you may have seen in OSCAR.
Regularity (Sample Entropy)
A statistical measure of how irregular your minute ventilation is from breath to breath. Higher entropy means more variable, inconsistent breathing patterns. Lower values indicate stable, regular ventilation. Sample Entropy is borrowed from nonlinear dynamics -- it quantifies unpredictability in the breathing signal.
Periodicity Index
Uses Fourier analysis to detect cyclical breathing patterns that repeat on a 30-100 second cycle. A higher Periodicity Index suggests your breathing is oscillating in a regular pattern rather than staying stable throughout the night. This frequency band is associated with periodic breathing patterns.
Where to Find It in AirwayLab
WAT metrics appear in the Flow tab of the AirwayLab dashboard. All three numbers are shown alongside the NED metrics for the selected night.
What WAT Does NOT Tell You
WAT metrics describe characteristics of your breathing waveforms from a single night of data. They are not diagnostic and do not indicate whether therapy adjustment is needed. A high FL Score is one data point among many -- it describes a pattern, not a cause or a solution.
Discuss your data with your clinician for clinical interpretation.
See Your WAT Score
Upload your ResMed SD card data to see your FL Score, Regularity, and Periodicity Index. Everything runs in your browser -- nothing uploaded.
Related reading
CPAP Flow Limitation Score: What 0, 0.5, and 1.0 Mean -- how ResMed's categorical FL channel relates to AirwayLab's continuous score.
What Is NED (Negative Effort Dependence)? -- a companion metric calculated in the same Flow tab.
AirwayLab Glossary -- definitions of all metrics used in AirwayLab.
AirwayLab is a free, open-source tool for analysing PAP flow data. Your data never leaves your browser. Nothing on this page constitutes medical advice -- always discuss your results with a qualified sleep specialist.