CT Total vessel count and vessel count percentages: associations with exercise capacity, symptoms, and rapid FEV ₁ decline in COPD

Introduction Existing computed tomography (CT) vascular pruning measures rely on volumes, such as the proportion of blood volume in vessels with cross-sectional area (CSA)<5 mm 2 or <10 mm 2 /total blood volume (BV5/TBV, BV10/TBV, respectively), but may underestimate vascular pruning due to blood redistribution to larger vessels in individuals with milder chronic obstructive pulmonary disease (COPD). We aim to develop a novel CT vessel measure, the total vessel count (TVC), quantify small and combined small/intermediate vessel count percentages, and compare these measures with BV5/TBV and BV10/TBV in terms of associations with lung function and its decline. As a secondary aim, associations with exercise capacity and COPD symptoms will be investigated. Methods CanCOLD participants underwent CT imaging. BV5/TBV and BV10/TBV were generated using vessel segmentation. TVC, and small (CSA<5 mm 2 , VC ≤5 /TVC) and combined small/intermediate (CSA<10 mm 2 , VC ≤10 /TVC) vessel count percentages were calculated. Fully adjusted regression models assessed associations with forced expiratory volume in 1 s (FEV 1 ), FEV 1 /forced vital capacity (FEV 1 /FVC), carbon monoxide diffusing capacity (DL CO ), accelerated FEV 1 decline over 3-years, maximal oxygen consumption (VO 2peak ), 6-minute walk distance (6MWD) and Medical Research Council (MRC). Results 1254 CanCOLD participants were investigated. TVC, VC ≤5 /TVC and VC ≤10 /TVC were associated with FEV 1 /FVC (p<0.05), DL CO (p<0.05) and FEV 1 decline (p<0.05); VC ≤10 /TVC was associated with VO 2peak (p<0.05) and both VC ≤5 /TVC and VC ≤10 /TVC were associated with MRC (p<0.05). BV5/TBV and BV10/TBV were only associated with 6MWD (p<0.05) and MRC (p<0.05). Conclusion Pulmonary vessel count percent, a measure of vasculature narrowing/loss, is associated with lung function and its decline, reduced exercise capacity and increased symptoms in COPD.