Association of obstructive sleep apnea with thoracic fluid volume and small airways narrowing in asthma during sleep

Abstract

<b>Background:</b> Obstructive sleep apnea (OSA) is prevalent in asthma patients and is related to asthma severity. This suggests a pathophysiological link between the two. Since exaggerated negative pleural is generated during obstructive apneas, it could draw more fluid into thorax that could cause small airway narrowing. Previously, we showed that generation of negative pleural pressure during Mueller maneuvers to simulate obstructive apneas, drew fluid into the thorax, and narrowed small airways. We therefore hypothesized that patients with asthma and co-existing OSA (apnea-hypopnea index≥10) will have a larger overnight increase in thoracic fluid volume (TFV) and a greater degree of small airway narrowing, than those without OSA. <b>Methods:</b> Participants underwent overnight polysomnography. Before and after sleep, we measured TFV and respiratory system reactance at 5Hz (X₅), as an index of small airway narrowing, using oscillometry. Changes in all variables between the two groups were compared using analysis of covariance (ANCOVA). <b>Results:</b> Compared to the non-OSA group, participants with coexisting OSA had significantly greater overnight increases in TFV and greater narrowing of small airways (Fig 1). <b>Conclusion:</b> These results suggest that increases in TFV resulting from exaggerated negative pleural pressure swings during obstructive apneas are one mechanism by which OSA could worsen asthma at night.