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Effects of Obesity on Perceptual and Mechanical Responses to Bronchoconstriction in Asthma

¹ Department of Medicine, Queen's University and Kingston General Hospital, Kingston; ² Department of Community Health and Epidemiology, Queen's University, Kingston, Ontario, Canada

Correspondence and requests for reprints should be addressed to Denis O'Donnell, M.D., F.R.C.P. (I), F.R.C.P. (C), 102 Stuart Street, Kingston, ON, K7L 2V6 Canada. E-mail: odonnell{at}queensu.ca

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 FEV₁ were conducted in 51 NWA (BMI, 18.5–24.9 kg/m²; 29% male) and 45 OBA (BMI, 30.1–51.4 kg/m²; 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 PC₂₀, 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 FEV₁ 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.

Key Words: lung volumes • respiratory mechanics • methacholine bronchoprovocation • dyspnea

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject The nature and clinical consequences of the complex interactions between obesity, airway hyperresponsiveness, and dyspnea remain poorly understood. What This Study Adds to the Field Despite significant group differences in baseline respiratory mechanics, perceptual responses to methacholine-induced bronchoconstriction and lung hyperinflation were similar in obese and normal-weight individuals with asthma.