Obesity and airway hyper-responsiveness

RATIONALE: Data on the relationship between airway hyper-responsiveness (AHR) to methacholine and obesity are conflicting. OBJECTIVE: To assess the relationship between obesity, morbid obesity and objectively determined methacholine AHR in 1000 unselected methacholine challenge tests. METHODS: We reviewed data from 1000 unselected methacholine tests from a hospital-based pulmonary function laboratory; tests were performed in subjects with respiratory symptoms and non-diagnostic spirometry. We assessed the prevalence of obesity and morbid obesity, defined as BMI >= 30 and >= 40 kg/m(2), respectively, in subjects with (PC20 <= 8 mg/mL) and without (PC20 > 8 mg/mL) AHR. RESULTS: Obesity was present in 34.6% of the 1000: this included 40.6% of the 315 subjects with AHR vs. 31.8% of those without AHR (p = 0.007). Morbid obesity was present in 5.8% including 9.5% vs. 4.1% of those with and without AHR respectively (p = 0.0006). Results were significant in females but not in males. Log PC20 (artificially extrapolated in the 685 subjects with PC20 > 8 mg/mL) correlated negatively with BMI (r = -0.105, p = 0.0009) and positively with FEV1% (r = 0.28, p < 0.0001). BMI correlated negatively with FEV1% (r = - 0.15, p < 0.0001); however, the correlation of log PC20 vs BMI remained significant when adjusted for FEV1%. CONCLUSIONS: Obesity was more prevalent among those with methacholine AHR than those without; the relationship was more evident in females and in morbidly obese vs. obese. Reduced FEV1 due to chest wall restriction may be a contributing factor.