Effects of obesity on perceptual and mechanical responses to bronchoconstriction in asthma.

Rationale: The influence of obesity on the perception of respiratory discomfort during acute bronchoconstriction in asthma is unknown.
Objectives: We hypothesized that the respiratory impairment associated with an increased body mass index (BMI) would predispose to greater perceived symptom intensity during acute airway narrowing. We therefore compared relationships between induced changes in dyspnea intensity and lung function during methacholine (MCh) bronchoprovocation in obese (OBA) and normal-weight (NWA) individuals with asthma of mild to moderate severity.
Methods: High-dose MCh challenge tests to a maximum 50% decrease in FEV(1) were conducted in 51 NWA (BMI, 18.5-24.9 kg/m(2); 29% male) and 45 OBA (BMI, 30.1-51.4 kg/m(2); 33% male) between 20 and 60 years of age. Serial spirometry, inspiratory capacity (IC), plethysmographic end-expiratory lung volume (EELV) and dyspnea intensity using the Borg scale were measured throughout bronchoprovocation.
Measurements and Main Results: Spirometry and airway sensitivity were similar in both groups; baseline EELV was lower (P < 0.0005) and IC was higher (P = 0.007) in OBA compared with NWA. From baseline to PC(20), EELV increased more in OBA (20% predicted) than NWA (13% predicted) (P = 0.008) with concomitant greater reductions in IC (P < 0.0005). Dyspnea ratings were not different for a given FEV(1) or IC across groups. By mixed effects regression analysis, relationships between induced dyspnea and changes in lung function parameters were not influenced by BMI, sex, or their interaction.
Conclusions: Perceptual responses to MCh-induced bronchoconstriction and lung hyperinflation were similar in obese and normal-weight individuals with asthma despite significant group differences in baseline lung volumes.