Background: The clinical features, physiology, and pathology of severe asthma are poorly understood. Recently, the forced vital capacity (FVC) has been shown to be reduced in severe asthma compared to mild asthma, possibly due to air trapping. However, the natural history and risk factors of obstructive change for such asthmatic patients have not been fully elucidated. Methods: We examined the data of a retrospective analysis of lung function changes over a 10-year period in 54 severe asthma patients. Results: The faster obstructive changes detected by FEV1 (forced expiratory volume in one second) were accompanied by excessive loss of FVC (r = 0.85, p < 0.0001) and the reduction in FVC was 1.2 times larger than the FEV1 change. Age, baseline FVC, exacerbation rate and oral corticosteroids use showed significantly negative correlations with the rate of annual change in FVC. Conclusions: These data indicate that the decline in FVC is more evident than FEV1 in severe asthma, suggesting that small airway susceptibility may be the cause of rapid disease progression. Aging, exacerbations of asthma, and use of systemic corticosteroids are related to excess FVC decline, particularly if FVC is still normal.
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