Asthma is identified by the presence of reversible airflow obstruction; however, irreversible airflow obstruction also develops in some asthmatic patients. Peat et al described a greater decline in lung function, as measured by height-adjusted FEV1, in a cohort of asthmatic patients when compared to normal subjects (50 mL/yr vs 35 mL/yr) followed up for 18 years. These observations have been confirmed by Lange et al,2 who reported on a Danish cohort followed up over 15 years, and by Sears et al in a New Zealand population-based birth cohort. The degree of loss in lung function has been shown to be related to asthma duration.
The mechanisms of the loss in FEV1 may result from the development of airway remodeling; however, no prospective studies have been conducted to test this hypothesis. Nonetheless, one study suggested that the decline in FEV1 may be related to the persistence of airway inflammation, albeit neutrophilic inflammation. Some studies have suggested that early treatment with inhaled corticosteroids may prevent the development of the accelerated decline in FEV1. read more
Agertoft and Pedersen and Haahtela et al reported that the early introduction of inhaled corticosteroids in newly diagnosed asthma in children or adults results in a greater improvement in lung function than when introduced as little as 2 years later. These results suggest that a delay in treating airway inflammation early in the course of the disease can result in airway abnormalities, which are less amenable to inhaled corticosteroid treatment later. The Childhood Asthma Management Program (CAMP) study prospectively evaluated the effects of inhaled corticosteroids (budesonide, 400 ^g/d) on lung function in children with a mean duration of asthma of 5 years. No significant difference between budesonide and placebo was found in the degree of change in the postbronchodilator FEV1 percentage of predicted; however, the mean postbronchodilator FEV1 value at baseline was > 100% of predicted normal in all treatment arms, and no significant decline over time was seen in the postbronchodilator FEVj percentage of predicted in the placebo group, making a treatment effect difficult to demonstrate. In addition, the children who received budesonide had a significantly smaller decline in the ratio of FEV1 to FVC before the administration of a bronchodilator.