Lobar variation of emphysema impacts lung function

Introduction: The distribution of emphysema in COPD varies considerably between individuals. It is poorly understood how this effects clinical presentation of the disease. This study aims to use quantitative CT imaging to assess the lobar variation of emphysema and describe the relationship with lung function. Methods: AERIS is an epidemiological study where moderate-very severe COPD patients were followed for 2 years. At enrolment each had pulmonary function and HRCT. A sub-cohort of 36 patients were analysed. Image analysis was performed using Apollo software. Emphysema was defined as the % of lung area with attenuation values below -950 HU (%LAA) and was ascertained for each lobe. Results: Lobar %LAA and correlations with lung function is shown in table 1. The right upper lobe most frequently had the greatest amount of %LAA (44% subjects). Mean heterogeneity of LAA (difference between lobes with highest and lowest %LAA) was 17%. 20 subjects had <15% LAA heterogeneity and 16 above this. Subjects with greater heterogeneity had a significantly lower FEV1 (40v49), lower 6MWD (253v321) and higher BODE (5.0v3.1). Conclusion: In COPD the upper lobes are more commonly and more severely affected by emphysema. The quantity of emphysema in the lower lobes has the strongest association with lung function and clinical features. The heterogeneity of emphysema between lobes is variable and subjects with the greatest heterogeneity have worse lung function and functional capacity.