M-Shape (Breath Pattern)
A characteristic inspiratory flow pattern with two peaks and a mid-inspiratory dip, suggesting upper airway oscillation or dynamic obstruction.
What Is M-Shape (Breath Pattern)?
An M-shaped breath is a characteristic inspiratory flow pattern where the waveform shows two distinct peaks with a dip in between, resembling the letter M. The mid-inspiratory dip (valley below 80% of peak flow in the middle 50% of inspiration) indicates that the upper airway is oscillating or briefly collapsing and reopening during a single breath.
M-shaped breaths are a specific marker of dynamic upper airway obstruction. Unlike the flat-topped pattern detected by NED and Flatness Index (which indicates steady airway narrowing), M-shapes suggest the airway is unstable, alternating between more and less restricted states within each inspiration.
AirwayLab tracks M-shaped breaths as a percentage of total breaths, reported separately from general flow limitation metrics. A high M-shape percentage, especially combined with elevated NED or Glasgow scores, suggests the airway is not just narrowed but actively oscillating, which may respond differently to therapy adjustments than simple steady-state flow limitation.
How AirwayLab Measures This
The NED engine identifies M-shaped breaths by checking whether any flow valley in the middle 50% of inspiration drops below 80% of peak inspiratory flow. The percentage of M-shaped breaths is reported on the NED Analysis tab.
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What causes M-shaped breaths?
M-shaped breaths occur when the upper airway briefly narrows or oscillates during inspiration, causing flow to dip before recovering. This pattern suggests dynamic airway instability rather than steady narrowing, and may indicate the airway is on the verge of collapsing during each breath.
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Medical Disclaimer
AirwayLab is not a medical device and is not FDA-cleared or CE-marked. It is provided for educational and informational purposes only. The analysis results should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult qualified healthcare providers regarding your sleep therapy and any changes to PAP settings.