Functional significance of air trapping detected in moderate asthma

The aim of this study was to evaluate bronchial and lung abnormalities in p atients suffering from moderate asthma as defined by international guidelin es, with special attention to air trapping on CT in comparison with that de tected in smoking and non-smoking normal subjects. Twenty-two patients clas sified as moderate asthma and control subjects including healthy volunteers , smokers (n = 10) or non-smokers (II = 12) were prospectively explored by :h-resolution CT (HRCT) performed at suspended full inspiration and expirat ion. The same expiratory protocol was performed 15 min after inhalation of 200 mu g of salbutamol. Patients underwent pulmonary function tests within the same week and bronchodilator response was assessed following inhalation of salbutamol. Abnormalities of bronchi and lung parenchyma on inspiratory CT and air trapping on expiratory CT, in dependent and non-dependent areas . were assessed and scored semi-quantitatively by two independent observers . Comparison of score mean values between the different groups was performe d using Mann-Whitney test and Spearman correlation between CT findings and pulmonary function tests were calculated. Mosaic perfusion was observed in 23% of asthmatics. Air-trapping scores were significantly higher in asthmat ic patients than in non-smoking control subjects (p = 0.003), but not than in smokers. This difference was ascribed to non-dependent zones of the lung fur which air-trapping scores were also higher in asthmatic patients (p = 0.003) and in smoking subjects (p = 0.004) than in normal controls. In the asthmatic group, a significant positive correlation was found between airwa ys resistance and bronchial dilatation score (p = 0.01), and between small airways obstruction index and mosaic perfusion score (p = 0.05). In additio n, both FEV1 and reversibility of small airways obstruction values correlat ed with air-trapping score (p = 0.03 and p = 0.007, respectively). No chang e could be detected in air-trapping score following salbutamol inhalation. Patients suffering from I moderate asthma present mosaic perfusion and larg er areas or air trapping man normal subjects, particularly in non-dependent areas of the lung. These lung abnormalities are related to small airways o bstruction.