Chest
Clinical InvestigationsAsthma COPDQuantitative Computed Tomography Detects Air Trapping due to Asthma
Section snippets
Study Population
We studied 18 adult asthmatic patients of whom 8 were men and 10 were women, none of whom ever smoked. Their ages ranged from 24 to 76 years (average age, 53.5 years). We defined asthma as (1) the presence of intermittent symptoms of wheezing, coughing, or chest tightness, plus (2) significant bronchial hyperresponsiveness. Bronchial hyperresponsiveness was considered significant if the patient's forced expiratory volume in 1 s (FEV1) rose at least 20 percent following the administration of a
Results
The results of the pulmonary function tests and the pixel indices for both groups are summarized in Table 1. As expected, asthmatic subjects had significantly more airflow limitation and hyperinflation compared with normal subjects. We observed a significant elevation in the mean pixel indices for asthmatic subjects on HRCT with both superior and inferior level expiratory scans, and on the conventional CT expiratory inferior level scan. Figure 1 demonstrates the pixel indices for the normal and
Discussion
The results of the current investigation indicate that expiratory CT scans through the lower lung zone can distinguish asthmatics with air trapping from normal subjects. Furthermore, the CT findings using the density mask techniques correlate well with the pulmonary physiologic abnormalities found in asthmatics.19,20 Both HRCT (1.5 mm) and conventional CT (10-mm collimation) scans proved useful in detection of these abnormalities in asthmatics.
To our knowledge, this is the first study to
Conclusion
In conclusion, by quantitating areas of low attenuation on CT and HRCT scans, it is possible to objectively differentiate asthmatics with air trapping from normal control subjects. The discrimination is optimized by obtaining a single expiratory HRCT scan above the level of the diaphragm. The CT findings are indicative of air trapping and airflow limitation. Future research should examine the value of this tool in assessing air trapping in other lung diseases and longitudinally in asthma.
ACKNOWLEDGMENTS
The writers thank Rick Orton, R.N., for his assistance in enrolling and testing volunteers, and Kristen Moore for secretarial assistance.
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Supported in part by Physician Scientist Award ES-00173 from the US Public Health Service, grant ES-04843, and SCOR grant HL-27353.
Manuscript revision accepted October 28.