Low-attenuation areas of the lungs on high-resolution computed tomography in asthma

To investigate the low-attenuation areas of the lungs (LAA) in asthma, we c ompared the mean lung density (MLD) and the LAA in 22 asthmatics (12 ex-smo kers and 10 nonsmokers) and 13 patients with chronic obstructive pulmonary disease (COPD) by high-resolution computed tomography. The MLD and the rela tive area of the lung with attenuation values lower than -950 Hounsfield Un its at full inspiration (inspiratory RA(950)) were significantly different in nonsmoking asthmatics compared to patients with COPD and asthmatics with a smoking history. The MLD and the RA(950) correlated significantly with t he FEV1 in all groups and with the DLCO in patients with COPD and asthmatic s with a smoking history but not in nonsmoking asthmatics. We concluded tha t the LAA in asthmatics with a smoking history indicates the presence of em physema, but in nonsmoking asthmatics it reflects hyperinflation and nonemp hysematous expiratory airflow limitation rather than emphysematous lesions.