The relationships between tracheal index and lung volumeparameters in mild-to-moderate COPD

Background: Although elongated morphological changes in the trachea are known to be related to lungfunction in chronic obstructive pulmonary disease (COPD), whether the tracheal morphological changesare associated with airflow limitations or overinflation of the lung in the early stages of COPD has notyet been determined. Thus, our aim was to investigate the association of tracheal index (TI) with lungfunction parameters, including lung volume parameters, in COPD patients with mild-to-moderate airflowlimitations.Materials and methods: A retrospective study was conducted in 193 COPD patients with GOLD grades 1-2(post-bronchodilator forced expiratory volume in 1 s [FEV1] ? 50% predicted with FEV1/forced vital capac-ity ratio ? 70%; age range, 40-81) and 193 age- and gender-matched subjects with normal lung functionas a control group (age range, 40-82). Two independent observers measured TI at three anatomical levelson chest radiographs and CT scans.Results: Compared with the control group, TI was reduced significantly and "saber-sheath trachea" wasobserved more frequently in COPD patients. Patients with GOLD grade 2 disease had a lower TI than thosewith GOLD grade 1. TI had apparent inverse correlations with total lung capacity, functional residualcapacity, and residual volume, regardless of the anatomical level of the trachea. Even after adjustmentsfor covariates, this association persisted.Conclusions: TI is reduced even in mild-to-moderate COPD patients, and TI measured on chest CT showssignificant inverse relationships with all lung volume parameters assessed, suggesting that trachealmorphology may change during the early stages of COPD.