The association of Body Mass Index with airway obstruction in non-asthmatics : implications for the inaccurate differential diagnosis of asthma in obesity

Introduction: An association between obesity and asthma has been reported, with disparity between males and females in this association that is not fully explained. Studies investigating the association typically have not identified asthma using accepted objective diagnostic methods, possibly leading to the inaccurate diagnosis and management of asthma in those with obesity. Objective: This study investigated the association, including gender diflirences, between obesity and airway obstruction in non-asthmatics identified by spirometric protocols. Methods: The pulmonary function test results of non-asthmatic subiects were reviewed. Statistical analyses were employed to determine the association between pulmonary function measures and BMI. Results:Significant differences in the pulmonary function values, measured AS a percentage of predicted, existed between BMI images including FVC (p < 0.001), FEV,/FVC (p < 0.001),and FEFM», (p < 0.02). Gender différences were evident inFVC, FEVi, FEV,/FVC, FEFj,* , and FEF„«, (all p < 0.001). When age and smoking were controlled for, gender differences remained in the pattern of the effect of BMI on FVC. FVC was progressively compromised for females as BMl increased above normal range ( 2 25 kg/m^), and was diminished in males with a BMI > 30 kg/m^Conclusions: Clear association was not found between indices of airway obstruction and increasing BMI in this non-asthmatic group. The study findings suggest a restrictive pulmonary function profile in obesity which is specific to non-asthmatics and unique to each gender. The compromising effects of increasing adiposity on FVC may be experienced at a lower BMI in females than in males.