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CT pulmonary vessel volume in ex-smokers with normal FEV1

Introduction: The clinical relevance of abnormal DL­CO in ex-smokers with normal spirometry is not well-understood. We previously observed abnormally elevated MRI apparent diffusion coefficients (ADC) consistent with airspace enlargement due to emphysema or alveolar distention in ex-smokers with low DLCO but normal CT and spirometry (Kirby et al, Thorax 2013). These ex-smokers were longitudinally followed as part of the TINCan cohort study and we hypothesised that pulmonary vascular function and total number of airways would also be abnormal. Objective: In the same participants with elevated ADC and no CT evidence of emphysema, we measured pulmonary vessel tree volume and airway count from non-contrast-enhanced CT. Methods: We evaluated 38 ex-smokers with normal FEV1 and no vascular disease. Abnormal DLCO was defined as Results: TBV and TAC trended lower in ex-smokers with abnormal DLCO (n=19, Figure 1). CT TBV weakly correlated with DLCO (r=.28, p=.04) but not FEV1 (r=.18, p=.2) or TAC (r=.32, p=.06). In a multivariable model, TBV and ADC significantly contributed to DLCO (R=.69, p=.001) while TAC did not. Conclusion: In ex-smokers without airflow limitation, CT pulmonary vessel volume and MRI ADC explained DLCO which was abnormal in half of participants.