Influence of inspiration level on bronchial lumen measurements with computed tomography

Abstract

Bronchial dimensions measured in CT images generally do not take inspiration level into consideration. However, some studies showed that the bronchial membrane is distensible with airway inflation. Therefore, re-examination of the elasticity of bronchi is needed. To assess the influence of respiration on bronchial lumen area (defined as distensibility) in different segmental bronchi and to explore the correlations between distensibility and both lung function and emphysema severity. In 44 subjects with COPD related to alpha-1-antitrypsin deficiency (AATD), bronchial lumen area was measured in CT images, acquired at different inspiration levels. Measurements were done at matched locations in one apical and two basal segmental airways (RB1, RB10 and LB10). Airway distensibility was calculated as lumen area difference divided by lung volume difference. Bronchial lumen area in the lower lobes (RB10 and LB10) correlated positively with FEV(1)%predicted (p=0.027 for RB10; and p=0.037 for LB10, respectively). Lumen area is influenced by respiration (p=0.006, p=0.045, and, p=0.005 for RB1, RB10 and LB10, respectively). Airway distensibility was different between upper and lower bronchi (p<0.001), but it was not correlated with lung function. Lumen area of third generation bronchi is dependent on inspiration level and this distensibility is different between bronchi in the upper and lower lobes. Therefore, changes in lumen area over time should be studied whilst accounting for the lung volume changes, in order to estimate the progression of bronchial disease while excluding the effects of hyperinflation.