LAUSR

Esophageal and epiglottic pressure deflections are widely used to quantify ventilatory effort during sleep and the arousal threshold in patients with obstructive sleep apnea (OSA). However, changes in upper airway patency will fundamentally alter pressure gradients across the respiratory system with different airflow and volume dependent effects on esophageal versus epiglottic pressure. The magnitude of these obstruction effects on ventilatory effort assessed from pressure deflections has not been systematically investigated. This study sought to quantify the direct effect of airway occlusion on esophageal and epiglottic pressure deflections during sleep in patients with OSA compared to predictions based on classic respiratory mechanics. Pneumotachograph airflow and volume, and esophageal, epiglottic, mask and gastric pressures were measured throughout a non-occluded breath before and the first occluded breath after repeated external airway occlusions during sleep in 13 OSA patients on constant positive airway pressure (CPAP). Inspiratory pressure deflections were approximately doubled with epiglottic pressure, and increased by around 40% with esophageal pressure on the occluded compared to the pre-occluded breath. Differences in pressure between pre- and occluded breaths showed strong dependence on volume and flow, in line with theoretical models of respiratory mechanics. A relatively simple correction factor could account for these effects to provide more consistent measures of ventilatory effort from pressure, independent from measurement site and changing airflow conditions. These finding have important implications for interpreting ventilatory effort and arousal threshold measurements and for understanding relationships between underlying ventilatory drive and pressure deflections in the presence of airway obstruction during sleep.