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

Abstract

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 (FEV ₁%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). FEV ₁%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

FEV ₁%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.