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

Abstract

Background: 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.

Methods: 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.

Results: 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.

Conclusion: 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.