Asthma COPD Overlap Syndrome on CT Densitometry: A Distinct Phenotype from COPD

Patients with asthma COPD overlap syndrome (ACOS) are an important but poorly characterized group. This study sought to explore the distinct characteristics of ACOS on CT densitometry. The study population was randomly selected from communities via questionnaires. All participants underwent low-dose volumetric chest CT both before and after bronchodilator administration. Each CT scan was performed at full-inspiration and full-expiration for CT densitometry. Emphysema index (EI), air trapping (AT), mean lung density (MLD) and total lung volume (TLV) were measured and compared between the ACOS and COPD groups. The distributions of both EI and AT were compared between patients with ACOS and COPD. The variations between the pre- and post-BD measurements observed in patients with ACOS were compared with those in patients with COPD. A total of 71 patients completed the study, including 32 patients with COPD and 39 patients with ACOS. The patients with ACOS exhibited lower EI and more upper-zone-predominant EI distributions, compared with the patients with COPD. No significant differences were exhibited in AT and its distribution. Following bronchodilator administration, the variations in AT and expiratory MLD were greater in patients with ACOS than in patients with COPD. No differences were observed in the variations of EI and inspiratory MLD. Our results indicate that patients with ACOS have lower extent of emphysema and different emphysema distribution, as well as greater post-BD variations in air trapping, compared with patients with COPD. These findings suggest that CT densitometry characterizes ACOS as a distinct phenotype from COPD.

Lobar analysis of collapsibility indices to assess functional lung volumes in COPD patients

Background

We investigated correlations between lung volume collapsibility indices and pulmonary function test (PFT) results and assessed lobar differences in chronic obstructive pulmonary disease (COPD) patients, using paired inspiratory and expiratory three dimensional (3D) computed tomography (CT) images.

Methods

We retrospectively assessed 28 COPD patients who underwent paired inspiratory and expiratory CT and PFT exams on the same day. A computer-aided diagnostic system calculated total lobar volume and emphysematous lobar volume (ELV). Normal lobar volume (NLV) was determined by subtracting ELV from total lobar volume, both for inspiratory phase (NLV_I) and for expiratory phase (NLV_E). We also determined lobar collapsibility indices: NLV collapsibility ratio (NLV_CR) (%) = (1 − NLV_E/NLV_I) × 100%. Associations between lobar volumes and PFT results, and collapsibility indices and PFT results were determined by Pearson correlation analysis.

Results

NLV_CR values were significantly correlated with PFT results. Forced expiratory volume in 1 second, measured as percent of predicted results (FEV₁%P) was significantly correlated with NLV_CR values for the lower lobes (P<0.01), whereas this correlation was not significant for the upper lobes (P=0.05). FEV₁%P results were also moderately correlated with inspiratory, expiratory ELV (ELV_I,E) for the lower lobes (P<0.05). In contrast, the ratio of the diffusion capacity for carbon monoxide to alveolar gas volume, measured as percent of predicted (DL_CO/V_A%P) results were strongly correlated with ELV_I for the upper lobes (P<0.001), whereas this correlation with NLV_CR values was weaker for upper lobes (P<0.01) and was not significant for the lower lobes (P=0.26).

Conclusion

FEV₁%P results were correlated with NLV collapsibility indices for lower lobes, whereas DL_CO/V_A%P results were correlated with NLV collapsibility indices and ELV for upper lobes. Thus, evaluating lobar NLV collapsibility might be useful for estimating pulmonary function in COPD patients.