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Original Research |

A Multivariate Analysis of Risk Factors for the Air-Trapping Asthmatic Phenotype as Measured by Quantitative CT Analysis

Ashley Busacker, PhD*; John D. Newell, Jr, MD, FCCP; Thomas Keefe, PhD; Eric A. Hoffman, PhD; Janice Cook Granroth, BS; Mario Castro, MD, FCCP; Sean Fain, PhD; Sally Wenzel, MD, FCCP
Author and Funding Information

*From the Department of Environmental and Radiological Health Sciences (Drs. Busacker and Keefe), Colorado State University, Fort Collins, CO; Division of Radiology (Dr. Newell), National Jewish Medical and Research Center, Denver, CO; Department of Radiology (Dr. Hoffman and Ms. Granroth), University of Iowa Carver College of Medicine, Iowa City, IA; Division of Pulmonary and Critical Care Medicine (Dr. Castro), Washington University School of Medicine, St. Louis, MO; University of Wisconsin (Dr. Fain), Madison, WI; and Division of Pulmonary, Allergy, and Critical Care Medicine (Dr. Wenzel), University of Pittsburgh Medical Center, Pittsburgh, PA.

Correspondence to: Ashley Busacker, PhD, Department of Environmental and Radiological Health Sciences, Campus Delivery 1681, Colorado State University, Fort Collins, CO 80523; e-mail: Ashley.Busacker@colostate.edu

Dr. Busacker is recipient of the American Academy of Allergy, Asthma, and Immunology Strategic Training in Allergy Research (ST*AR) Award.

Grant support was provided by National Institutes of Health HL69149, HL64368, HL69349, HL69170, HL-69155, HL69174, HL69130, HL69167, HL69116, and HL69174–05.

The authors have no conflicts of interest to disclose.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).


Dr. Busacker is recipient of the American Academy of Allergy, Asthma, and Immunology Strategic Training in Allergy Research (ST*AR) Award.

Dr. Busacker is recipient of the American Academy of Allergy, Asthma, and Immunology Strategic Training in Allergy Research (ST*AR) Award.

Grant support was provided by National Institutes of Health HL69149, HL64368, HL69349, HL69170, HL-69155, HL69174, HL69130, HL69167, HL69116, and HL69174–05.

Grant support was provided by National Institutes of Health HL69149, HL64368, HL69349, HL69170, HL-69155, HL69174, HL69130, HL69167, HL69116, and HL69174–05.

The authors have no conflicts of interest to disclose.

The authors have no conflicts of interest to disclose.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).


Chest. 2009;135(1):48-56. doi:10.1378/chest.08-0049
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Background:  Patients with severe asthma have increased physiologically measured air trapping; however, a study using CT measures of air trapping has not been performed. This study was designed to address two hypotheses: (1) air trapping measured by multidetector CT (MDCT) quantitative methodology would be a predictor of a more severe asthma phenotype; and (2) historical, clinical, allergic, or inflammatory risk factors could be identified via multivariate analysis.

Methods:  MDCT scanning of a subset of Severe Asthma Research Program subjects was performed at functional residual capacity. Air trapping was defined as ≥ 9.66% of the lung tissue < − 850 Hounsfield units (HU). Subjects classified as having air trapping were then compared to subjects without air trapping on clinical and demographic factors using both univariate and multivariate statistical analyses.

Results:  Subjects with air trapping were significantly more likely to have a history of asthma-related hospitalizations, ICU visits, and/or mechanical ventilation. Duration of asthma (odds ratio [OR], 1.42; 95% confidence interval [CI], 1.08 to 1.87), history of pneumonia (OR, 8.55; 95% CI, 2.07 to 35.26), high levels of airway neutrophils (OR, 8.67; 95% CI, 2.05 to 36.57), airflow obstruction (FEV1/FVC) [OR, 1.61; 95% CI, 1.21 to 2.14], and atopy (OR, 11.54; 95% CI, 1.97 to 67.70) were identified as independent risk factors associated with the air-trapping phenotype.

Conclusions:  Quantitative CT-determined air trapping in asthmatic subjects identifies a group of individuals at high risk for severe disease. Several independent risk factors for the presence of this phenotype were identified: perhaps most interestingly, history of pneumonia, neutrophilic inflammation, and atopy.

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