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17-01-2010 | Respiratory | Article

Perception of bronchoconstriction similar between obese and normal-weight subjects


Free abstract

MedWire News: The perceptual responses to methacholine-induced bronchoconstriction and lung hyperinflation are similar in obese and normal-weight individuals with asthma, research shows.

The clinical implication is that frequent daily symptoms of obese asthma subjects "may not be directly related to abnormal airway sensitivity or behavior but may reflect other physiological effects of obesity," write Denis O'Donnell (Queen's University, Kingston, Ontario, Canada) and colleagues, in the American Journal of Respiratory and Critical Care Medicine.

Past research has suggested that obese subjects with asthma have more morbidity, greater resistance to therapy, and poorer asthma control than normal-weight subjects.

The differences between obese and normal-weight subjects, however, are still open to debate.

In the present study, O'Donnell and colleagues investigated the hypothesis that respiratory impairment associated with increased body mass index (BMI) would predispose these individuals to increased symptom intensity during acute airway narrowing.

In total, 51 normal-weight individuals with asthma and 45 obese subjects with asthma underwent a high-dose methacholine-challenge test designed to induce a maximum 50% decrease in FEV1.

Baseline plethysmographic end-expiratory lung volume (EELV) was lower, and inspiratory capacity (IC) was higher, in obese individuals compared with those of normal weight.

From baseline to PC20, where methacholine caused a 20% fall in FEV1, EELV increased more in obese participants (20% predicted) than normal-weight participants (13% predicted), with greater reductions in IC.

Dyspnea intensity increased similarly in obese and normal-weight subjects, from "very, very slight" at baseline to "slight" at PC20 and "somewhat severe" at the maximum response.

The dyspnea response to methacholine was not significantly different between groups for a given FEV1 or IC. In a mixed regression analysis, there was no interaction with BMI for induced dyspnea and changes in lung function.

Despite significant group differences in baseline respiratory mechanics, the perceived responses to bronchoconstriction and lung hyperinflation were similar in obese and normal-weight individuals with asthma, conclude the researchers.

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

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