Fractal analysis of pulmonary vasculature in COPD: Association with pulmonary function, functional capacity and symptoms

<bold>Background:</bold> The pulmonary vasculature undergoes remodeling and pruning in chronic obstructive pulmonary disease (COPD). While existing computed tomography (CT) imaging measures quantify vascular pruning, advanced methods can capture greater complexity of the structural changes. <bold>Aim:</bold> Investigate the association of CT vascular fractal dimension (VFD) measurements with pulmonary function, functional capacity and symptoms, independent of existing CT vessel pruning measures, in COPD. <bold>Methods:</bold> CanCOLD participants underwent CT imaging and analysis (VIDA Diagnostics). The relative volume of the vessels <5mm in cross-sectional area to the total blood volume (BV5/TBV) was generated. Segmented vasculature complexity was measured by VFD using Minkowski-Bouligand box-counting dimension. Fully adjusted linear regression models for pulmonary function, exercise limitation (6-minute walk test, 6MWT) and symptom burden (Medical Research Council Dyspnoea Scale, MRC) with VFD and BV5/TBV were performed in both separate and the same models. <bold>Results:</bold> 1325 CanCOLD participants were analyzed: n=279 never-smokers, n=405 at risk, n=366 GOLD I, and n=275 GOLD II+ COPD. In separate multivariable regression models, VFD measurements were associated with reduced FEV₁ (p<0.05) and 6MWD (p<0.05), and increased MRC scores (p<0.05). In the same model as BV5/TBV, only VFD was associated with reduced 6MWD (p<0.05) and increased MRC scores (p<0.05). <bold>Conclusion:</bold> CT vascular fractal dimension measure captures greater complexity of vessel remodeling and is independently associated with respiratory morbidity in COPD, providing complementary information to existing vascular pruning measures.