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Dynamic Hyperinflation with Bronchoconstriction

Differences between Obese and Nonobese Women with Asthma

¹ Respiratory Research Unit, Department of Medical and Surgical Sciences, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand

Correspondence and requests for reprints should be addressed to Professor D. Robin Taylor, M.D., Otago Respiratory Research Unit, Dunedin School of Medicine, University of Otago, P.O. Box 913, Dunedin, New Zealand. E-mail: robin.taylor{at}stonebow.otago.ac.nz

Rationale: Symptoms and respiratory function tests may be difficult to assess and interpret in obese patients with asthma, particularly if the asthma is severe. It is unclear whether the dynamic changes that occur during bronchoconstriction differ between obese versus nonobese patients with asthma.

Objectives: To explore whether the changes in airway caliber and lung volumes that occur with acute bronchoconstriction are different in obese and nonobese patients with asthma and whether any differences contribute to the quality and intensity of symptoms.

Methods: Thirty female patients with asthma were studied. Spirometry, lung volume measurements, and dyspnea scores were obtained before and immediately after bronchoconstriction induced by methacholine, aiming to provoke a reduction in FEV₁ of 30%.

Measurements and Main Results: Body mass index was independently associated with changes in lung volume after adjustment for baseline airway caliber and hyperresponsiveness. Increases in functional residual capacity and decreases in inspiratory capacity were significantly greater in obese participants (P < 0.001 and P = 0.003, respectively).

Conclusions: Changes in respiratory function, notably dynamic hyperinflation, are greater in obese individuals with bronchoconstriction. This may potentially alter the perception and assessment of asthma severity in obese patients with asthma.

Key Words: asthma • hyperinflation • methacholine challenge • obesity

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Obesity affects respiratory function independently of asthma. Obese patients with asthma are often classified as having more severe asthma. Whether this is due to independent additive effects or a dynamic effect of obesity on asthma is unclear. What This Study Adds to the Field This study has shown that dynamic hyperinflation in response to acute bronchoconstriction is greater with increasing body mass index, and this may contribute to an enhancement of perceived symptoms in obese subjects with asthma.

 

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