Quantifying the magnitude of pharyngeal obstruction during sleep using airflow shape

Rationale and objectives: Non-invasive quantification of the severity of pharyngeal airflow obstruction would enable recognition of obstructive versus central manifestation of sleep apnoea, and identification of symptomatic individuals with severe airflow obstruction despite a low apnoea-hypopnoea index (AHI). Here we provide a novel method that uses simple airflow-versus-time ("shape") features from individual breaths on an overnight sleep study to automatically and non-invasively quantify the severity of airflow obstruction without oesophageal catheterisation. Methods: 41 individuals with suspected/diagnosed obstructive sleep apnoea (AHI range 0-91 events.h(-1)) underwent overnight polysomnography with gold-standard measures of airflow (oronasal pneumotach: "flow") and ventilatory drive (calibrated intraoesophageal diaphragm electromyogram: "drive"). Obstruction severity was defined as a continuous variable (flow: drive ratio). Multivariable regression used airflow shape features (inspiratory/expiratory timing, flatness, scooping, fluttering) to estimate flow: drive ratio in 136264 breaths (performance based on leave-one-patient-out cross-validation). Analysis was repeated using simultaneous nasal pressure recordings in a subset (n=17). Results: Gold-standard obstruction severity (flow: drive ratio) varied widely across individuals independently of AHI. A multivariable model (25 features) estimated obstruction severity breath-by-breath (R-2=0.58 versus gold-standard, p<0.00001; mean absolute error 22%) and the median obstruction severity across individual patients (R-2=0.69, p<0.00001; error 10%). Similar performance was achieved using nasal pressure. Conclusions: The severity of pharyngeal obstruction can be quantified non-invasively using readily available airflow shape information. Our work overcomes a major hurdle necessary for the recognition and phenotyping of patients with obstructive sleep disordered breathing.