Slope of the oxygen desaturation reflects the pharyngeal collapsibility in OSA.

Introduction: We recently demonstrated that patients with "deep" respiratory events (i.e., complete apneas, suggesting a more collapsible pharynx) were less likely to respond to oral appliance therapy. However, event depth, which requires accurate airflow measurements, can be difficult to determine due to movement of the nasal cannula or oral breathing. Oxygen saturation is an alternative signal for potentially characterizing respiratory event depth that is not impacted by these challenges in airflow measurement. In general, the reduction in ventilation during a respiratory event is proportional to the rate of change in oxygen saturation; deeper events cause a more rapid drop in oxygen saturation per unit time. Therefore, the aim of this abstract was to demonstrate that the slope of the oxygen desaturation curve is proportional to event depth and can be similarly associated with oral appliance treatment efficacy. Method(s): Eighty-one OSA patients (AHI>10 events/hr) were assessed via polysomnography during one night off and one night on treatment with oral appliance. Event depth and desaturation slope were measured from the "average" ventilatory and saturation profiles, respectively, as follows. The time-series signal (e.g. oxygen saturation) from all respiratory events were aligned at event termination and ensemble averaged to output a signal profile of the average respiratory event. Event depth was calculated as the mean reduction in ventilation from the ventilatory profile of the average respiratory event. Desaturation slope was measured as the change in oxygen saturation from the 10th (i.e. event start) to the 90th (i.e. event end) percentile of the saturation profile of the average respiratory event, divided by time between these points. Correlation between event depth and desaturation slope was assessed using Pearson's correlation. Bivariate logistic regression tested differences in both variables between oral appliance responders (>50% reduction in AHI from b