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 μg. 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.