Localization and Quantification of Regional and Segmental Air Trapping in Asthma

Objective: To assess the feasibility of volumetric and densitometric software to localize and quantify signs of regional air trapping after methacholine bronchoprovocations in asthma.

Methods: Eight atopic subjects with mild-to-moderate asthma using short-acting beta(2)-agonists only, with hyperresponsiveness to methacholine, were evaluated. Low-dose baseline expiratory 16-slice multidetector computed tomography scans before and after a methacholine bronchoprovocation were acquired. MeVisPULMO3D software (Bremen, Germany) was applied to the scans, providing quantitative information on volume and density measures of the total lung and each lobe.

Results: After methacholine, the expiratory scan showed a median (interquartile range) increase in volume of 534 mL (357-1279 mL), a decrease in lung density (mean and 15th percentile) of 52 Hounsfield Units (HU) (116-39 HU) and 34 HU (78-25 HU), respectively, and an increase in percentage low attenuation areas of 3% (2%-6%) for the total lung, with similar patterns in individual lung lobes. The rig it and left lower lung lobes showed the largest increases in air trapping, 211 mL (117-363 mL) and 229 mL (15.5-315 mL), respectively, versus a volume increase of 70 mL (20-249 mL) 26 mL (-16-92 mL), and 91 mL (-28-241 mL) for the right upper, middle, and left upper lobes, respectively. Volume chances in the lower lobes were associated with baseline forced expiratory flow between 25% and 75% of forced vital capacity, whereas low attenuation areas changes in the lower lobes were not.

Conclusions: This study suggests that multidetector computed tomography scans are able to localize and quantify regional air trapping in asthma after methacholine bronchoprovocations. Volumetric measurements of the lobes as compared to densitometric measurements are superior in detecting local air trapping in gravity-dependent areas of the lung.