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Severe exacerbations predict excess lung function decline in asthma

¹ James Hogg iCapture Centre, St Paul's Hospital, University of British Columbia, Vancouver, BC, Canada. Depts of ² Epidemiology, and ³ Pulmonology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.

CORRESPONDENCE: T. R. Bai, Respiratory Division, University of British Columbia, Rm 166, St Paul's Hospital, 1081 Burrard Street, Vancouver V6Z1Y6, BC, Canada. Fax: 1 6048068351. E-mail: tbai{at}mrl.ubc.ca

Keywords: Airways remodelling, exacerbations, prognosis, treatment of asthma

Received: December 19, 2006
Accepted May 7, 2007

Severe asthma exacerbations are periods of intense airway inflammation that have been hypothesised to contribute to structural changes in the airways. If so, accelerated lung function decline over time should be more prevalent in adult patients with asthma who have frequent exacerbations than those without, but to date this has not been demonstrated.

A cohort study was performed in order to investigate the effect of severe exacerbations on the progression of airway obstruction in 93 nonsmoking asthmatics with moderate-to-severe disease prior to treatment with inhaled corticosteroids. Subjects were followed for 5 yrs (median follow-up 11 yrs).

In total, 56 (60.2%) subjects experienced at least one severe exacerbation (median rate 0.10·yr^–1). Oral corticosteroid use and more severe airway obstruction at baseline were associated with a higher exacerbation rate. Independent of these variables, asthma patients with frequent exacerbations had a significantly larger annual decline in forced expiratory volume in one second (FEV₁; median difference (95% confidence interval) 16.9 (1.5–32.2) mL·yr^–1). Exacerbation rate significantly predicted an excess decline in FEV₁, such that one severe exacerbation per year was associated with a 30.2 mL greater annual decline in FEV₁.

These data support the hypothesis that exacerbations, indicating intermittent periods of worsening airway inflammation, are associated with excess lung function decline in asthma.