NED stands for Negative Effort Dependence -- a specific breathing characteristic where increasing respiratory effort produces less inspiratory airflow rather than more.
What Is Negative Effort Dependence?
In a normal breath, effort and airflow move together: breathe harder, get more air. In a breath with NED, that relationship inverts. The harder the respiratory muscles work, the more the airway resists, and the less air flows through. The "negative" in NED refers to this inverted relationship between effort and output.
NED is a property of individual breaths, calculated per breath from the shape of the inspiratory flow waveform.
What AirwayLab's NED Engine Measures
NED Score
Calculated as: (peak flow - mid-inspiration flow) / peak flow x 100. A higher percentage means a larger drop in flow during the mid-inspiratory phase -- the waveform signature of effort-dependent restriction.
Flatness Index (FI)
The ratio of mean inspiratory flow to peak flow. Lower values indicate a more flattened waveform overall.
Tpeak/Ti ratio
How early the peak flow occurs within the total inspiration time, expressed as a fraction. An early peak followed by declining flow is characteristic of flow-limited breathing.
M-shape detection
Identifies breaths where the flow curve shows a double-dip pattern during mid-inspiration -- a valley that drops below 80% of peak flow in the central portion of the breath. This waveform shape is associated with flow limitation.
RERA detection
Sequences of 3-15 consecutive breaths showing progressive flow limitation features, followed by a recovery breath, are flagged as potential Respiratory Effort-Related Arousals (RERAs). AirwayLab uses NED slope, recovery breath shape, and sigh detection to identify these sequences.
Estimated Arousal Index (EAI)
A derived metric based on spikes in respiratory rate and tidal volume relative to a rolling two-minute baseline. It is a proxy measure for breathing-related sleep fragmentation, not a clinical arousal count.
Night summary (H1/H2 split)
Results are split into H1 and H2 (first and second halves of the night) to show whether flow limitation patterns shift across the session.
Where to Find It in AirwayLab
NED metrics appear in the Flow tab alongside the WAT metrics. The night summary includes H1/H2 split and the combined flow limitation percentage across all scored breaths.
What NED Does NOT Tell You
NED describes the shape of your inspiratory waveforms. It is not a diagnostic instrument and does not confirm whether a specific airway condition is present. RERA detection in AirwayLab is based on flow signal heuristics from EDF data -- it is not equivalent to polysomnography-based RERA scoring by a sleep clinician.
Discuss your data with your clinician for clinical interpretation.
See Your NED Analysis
Upload your ResMed SD card data for full NED analysis in your browser -- NED score, flatness index, RERA detection, and H1/H2 split. No data uploaded.
Related reading
What Is the Glasgow Index in CPAP/BiPAP Data? -- nine-component breath shape scoring.
What Is the WAT Score in CPAP Data? -- FL Score, regularity, and periodicity bundle.
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.