Severe Asthma Uniquely Marked By Air Trapping

Occurs regardless of degree of airway inflammation

MONDAY, Feb. 4 (HealthDay News) -- Air trapping is a characteristic feature of severe asthma and occurs regardless of the degree of airflow limitation, suggesting that severe asthma has separate pathophysiological features and is not simply an extreme form of the asthma, according to an article published online in November in advance of publication in the Journal of Applied Physiology.

Ronald L. Sorkness, Ph.D., of the University of Wisconsin-Madison, and colleagues evaluated spirometry, lung volumes and reversibility with bronchodilation in 287 patients with severe asthma and 382 with non-severe asthma participating in the Severe Asthma Research Program.

Patients with severe asthma exhibited prominent air trapping, evidenced by reduced forced vital capacity (FVC) seen over the entire range of airflow limitation (FEV1/FVC). This was confirmed in a subset of patients with ratios of residual volume to total lung capacity. In contrast, prominent air trapping was not seen in patients with non-severe asthma, even in those with FEV1/FVC less than 75 percent predicted, indicative of airflow limitation. In addition, compared to those with non-severe asthma, individuals with severe asthma had more prominently reduced FEV1 after maximal bronchodilation.

These data "show a statistically and physiologically significant shift of the study population classified as Severe Asthma toward more air trapping at all levels of airflow limitation -- these results suggest that there may be a pathophysiological process present commonly in severe asthma that contributes to air trapping."

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