Airway Responsiveness Measured by Forced Oscillation Technique in Severely Obese Patients, before and after Bariatric Surgery

Background. The influence of obesity on airway responsiveness remains controversial. Objective. This study was designed to investigate airway responsiveness, airway inflammation, and the influence of sleep apnea syndrome (SAS), in severely obese subjects, before and after bariatric surgery. Methods. A total of 120 non-asthmatic obese patients were referred consecutively for pre-bariatric surgery evaluation. Lung function, airway responsiveness to methacholine, exhaled nitric oxide measurement, and sleep studies were performed. Airway hyperresponsiveness (AHR) was defined as a 50% or greater increase in respiratory resistance measured using the forced oscillation technique in response to a methacholine dose <= 2000 mu g. Forced expiratory volume in 1 second (FEV1) was measured after the last methacholine dose. Airway responsiveness was reevaluated after weight loss in patients with a pre-surgery AHR. Results. AHR was found in 16 patients. The percent FEV1 decrease or percent respiratory resistance increase in response to methacholine was related to baseline expiratory airflow (forced expiratory flow at 50%) (r = 0.26, p < .006 and r = 0.315, p =.0005, respectively) but not to body mass index (BMI) or exhaled nitric oxide. Both airway responsiveness parameters were significantly related to forced expiratory flow at 25-75%/forced vital capacity, a measure of airway size relative to lung size (r = 0.27, p < .005 and r = 0.25, p < .007, respectively). Sleep apnea was not significantly associated with AHR or airway inflammation. About 11 patients with AHR were reevaluated 18 months to 2 years after surgery, with no change in AHR associated with weight loss. Conclusion. Airway responsiveness is not related to BMI or to SAS. AHR in severely obese patients might be related to distal airway obstruction or low relative airway size.