Spirometry-Defined Restriction Modifies the Association between Forced Vital Capacity and Bronchiectasis Exacerbation

Obstructive ventilatory defect (OVD) is the most common ventilatory pattern in bronchiectasis, with low forced expiratory volume in 1 second (FEV1), which is a well-known risk factor for acute exacerbation (AE). However, the impact of spirometry- defined restrictive components (restrictive ventilatory defects [RVD] or mixed ventilatory defects [MVD]) on AE remains unreported. This study evaluated the association between spirometry-defined restrictive components and AE risk in patients with bronchiectasis.

In this prospective cohort study, patients from 51 referral hospitals in the Republic of Korea were classified into the normal (FEV1/forced vital capacity (FVC) ≥ lower limit of normal [LLN] and FVC≥LLN, n=62), OVD (FEV1/FVC<LLN and FVC≥LLN, n=59), RVD (FEV1/FVC≥LLN and FVC<LLN, n=148), and MVD (FEV1/FVC<LLN and FVC<LLN, n=223) groups. Incidence rate ratios (IRRs) of AE associated with ventilatory defects were compared using the normal group as a reference group.

The MVD group had the highest annual severe AE IRR (3.557; 95% confidence interval [CI], 0.918 to 17.851), followed by the RVD (2.678; 95% CI, 0.704 to 13.422) and OVD groups (1.926; 95% CI, 0.379 to 11.430) (p for trend=0.051) compared to the normal group. Lower FVC and FEV₁ were significantly associated with increased risk of any AE and severe AE in the RVD and MVD groups. The spirometry-defined restrictive component significantly affected the relationships of any AE and severe AE with FVC (p for interaction <0.05), not with FEV1.

The presence of a spirometry-defined restrictive component was associated with higher annual rates for any AE and severe AE, which modified the FVC, not FEV1, effect on the risk for such events.