Cough reflex sensitivity to capsaicin is decreased in patients with obstructive sleep apnea

Abstract

The cough reflex is as an effective and rapidly responding defense mechanism protecting the lungs against inhaled irritants and foreign substances, and facilitating the expulsion of mucus. Although cough is a common symptom in patients with obstructive sleep apnea (OSA), the effect of OSA on cough reflex sensitivity is unknown. Aim of the study was to evaluate cough reflex sensitivity to capsaicin in patients with OSA and the correlation between OSA severity and cough reflex sensitivity. Methods: fifty-seven non-smokers with normal spirometry and chest radiograph referred for evaluation of OSA were studied. Patients were diagnosed with OSA (n=30) when apnea-hypopnea index (AHI), obtained from full-night polysomnography, was greater when 15/h. Subjects with AHI lower when 15 were classified as non-OSA patients (n=27). All patients underwent cough reflex provocation test with capsaicin. Capsaicin aerosol was given in order of ascending concentration until the concentration inducing 2 (C2) and 5 or more coughs (C5) was attained. Results: patients with and without OSA did not differ in terms of age, gender and body mass index. C2 and C5 were significantly higher (i.e., cough reflex sensitivity lower) in patients with OSA (log C2 1.58±0.15; log C5 2.35±0.16µM mean ± SEM) than in non-OSA patients (log C2 1.01±0.14µM; log C5 1.63±0.19; p=0.009 and p=0.007 respectively). A significant positive correlation was obtained between AHI and log C 2 (r=0.42, p=0.001) and log C5 (r=0.51, p<0.001). Conclusion: our data demonstrated that cough reflex sensitivity to capsaicin is decreased in patients with OSA and positively correlates with OSA severity.