Journal of Applied Physiology
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J Appl Physiol 104: 394-403, 2008. First published November 8, 2007; doi:10.1152/japplphysiol.00329.2007
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Lung function in adults with stable but severe asthma: air trapping and incomplete reversal of obstruction with bronchodilation

Ronald L. Sorkness,1 Eugene R. Bleecker,2 William W. Busse,1 William J. Calhoun,3,4 Mario Castro,5 Kian Fan Chung,6 Douglas Curran-Everett,7 Serpil C. Erzurum,8 Benjamin M. Gaston,9 Elliot Israel,10 Nizar N. Jarjour,1 Wendy C. Moore,2 Stephen P. Peters,2 W. Gerald Teague,11 Sally E. Wenzel,7, for the National Heart, Lung, and Blood Institute Severe Asthma Research Program

1University of Wisconsin, Madison, Wisconsin; 2Wake Forest University, Winston-Salem, North Carolina; 3University of Pittsburgh, Pittsburgh, Pennsylvania; 4University of Texas Medical Branch, Galveston, Texas; 5Washington University, St. Louis, Missouri; 6Imperial College, London, United Kingdom; 7National Jewish Medical and Research Center, Denver, Colorado; 8Cleveland Clinic, Cleveland, Ohio; 9University of Virginia, Charlottesville, Virginia; 10Brigham & Women's Hospital, Boston, Massachusetts; and 11Emory University, Atlanta, Georgia

Submitted 23 March 2007 ; accepted in final form 7 November 2007

Five to ten percent of asthma cases are poorly controlled chronically and refractory to treatment, and these severe cases account for disproportionate asthma-associated morbidity, mortality, and health care utilization. While persons with severe asthma tend to have more airway obstruction, it is not known whether they represent the severe tail of a unimodal asthma population, or a severe asthma phenotype. We hypothesized that severe asthma has a characteristic physiology of airway obstruction, and we evaluated spirometry, lung volumes, and reversibility during a stable interval in 287 severe and 382 nonsevere asthma subjects from the National Heart, Lung, and Blood Institute Severe Asthma Research Program. We partitioned airway obstruction into components of air trapping [indicated by forced vital capacity (FVC)] and airflow limitation [indicated by forced expiratory volume in 1 s (FEV1)/FVC]. Severe asthma had prominent air trapping, evident as reduced FVC over the entire range of FEV1/FVC. This pattern was confirmed with measures of residual lung volume/total lung capacity (TLC) in a subgroup. In contrast, nonsevere asthma did not exhibit prominent air trapping, even at FEV1/FVC <75% predicted. Air trapping also was associated with increases in TLC and functional reserve capacity. After maximal bronchodilation, FEV1 reversed similarly from baseline in severe and nonsevere asthma, but the severe asthma classification was an independent predictor of residual reduction in FEV1 after maximal bronchodilation. An increase in FVC accounted for most of the reversal of FEV1 when baseline FEV1 was <60% predicted. We conclude that air trapping is a characteristic feature of the severe asthma population, suggesting that there is a pathological process associated with severe asthma that makes airways more vulnerable to this component.

airway closure; difficult asthma; fixed obstruction


Address for reprint requests and other correspondence: R. L. Sorkness, Univ. of Wisconsin, 777 Highland Ave., Madison, WI 53705 (e-mail: rlsorkne{at}wisc.edu)




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