Increasing depth of propofol anesthesia is associated with increased collapsibility of the upper airway. This was associated with profound inhibition of genioglossus muscle activity. This dose-related inhibition seems to be the combined result of depression of central respiratory output to upper airway dilator muscles and of upper airway reflexes.

Rationale: Our understanding of how airway remodeling affects regional airway elastic properties is limited due to technical difficulties in quantitatively measuring dynamic, in vivo airway dimensions. Such knowledge could help elucidate mechanisms of excessive airway narrowing. Objectives: To use anatomical optical coherence tomography (aOCT) to compare central airway elastic properties in control subjects and those with obstructive lung diseases. Methods: After bronchodilation, airway lumen area (Ai) was measured using aOCT during bronchoscopy in control subjects (n 5 10) and those with asthma (n 5 16), chronic obstructive pulmonary disease (COPD) (n 5 9), and bronchiectasis (n 5 8). Ai was measured in each of generations 0 to 5 while airway pressure was increased from 210 to 20 cm H 2 O. Airway compliance (Caw) and specific compliance (sCaw) were derived from the transpulmonary pressure (PL) versus Ai curves. Measurements and Main Results: Caw decreased progressively as airway generation increased, but sCaw did not differ appreciably across the generations. In subjects with asthma and bronchiectasis, Caw and sCaw were similar to control subjects and the PL-Ai curves were left-shifted. No significant differences were observed between control and COPD groups. Conclusions: Proximal airway elastic properties are altered in obstructive lung diseases. Although central airway compliance does not differ from control subjects in asthma, bronchiectasis, or COPD, Ai is lower in asthma and the PL-Ai relationship is left-shifted in both asthma and bronchiectasis, suggesting that airways are maximally distended at lower inflating pressures. Such changes reflect alteration in the balance between airway wall distensibility and radial traction exerted on airways by surrounding lung parenchyma favoring airway narrowing. Clinical trial registered with Australian New Zealand Clinical Trials Registry (ACTRN12607000624482).

Summary Repetitive airway occlusion during sleep in patients with obstructive sleep apnoea (OSA) results in the generation of negative intrathoracic pressures and ends in arousal, both of which may predispose to reflux during sleep (nocturnal reflux). We aimed to determine and compare the prevalence of nocturnal reflux symptoms and their sleep‐associated risk factors in untreated OSA patients, OSA patients using continuous positive airway pressure (CPAP) therapy, and the general population. Gastro‐oesophageal reflux and sleep questionnaires were completed by 1116 patients with polysomnography diagnosed OSA and by 1999 participants of the 2007 Busselton population health survey. Of the OSA patients, 137 completed the reflux questionnaire before and after treatment. Risk of OSA in the general population was assessed using the Berlin score. The prevalence of frequent (>weekly) nocturnal reflux symptoms was increased (P < 0.001) in OSA patients (10.2%) versus the general population (5.5%), in individuals from the general population at high (8.7%) versus low risk (4.3%) of OSA and in patients with severe (13.9%) versus mild OSA (5.1%). Frequent nocturnal reflux symptoms were associated with high risk (general population) (OR 1.9, P < 0.01) and severity of OSA (OSA population) OR 3.0, severe versus mild OSA, P < 0.001) after correcting for age, gender and body mass index. Treatment with CPAP decreased the prevalence of reflux symptoms significantly. In conclusion, the prevalence of nocturnal reflux symptoms is increased in those with or suspected of having OSA. This association is independent of other risk factors including age, gender and body mass index, suggesting a causal relationship between OSA and nocturnal reflux.

Upper airway obstructive and nocturnal GER events are not directly related. The relatively low P (b) in these OSA patients raises the possibility of weakening of the gastroesophageal junction from repetitive strain associated with obstructed breathing events. The favourable effect of CPAP on nocturnal GER is possibly due to an increase in nadir P (b) and decrease in the duration for which the LES relaxes during swallow-induced and transient LESR.