Association between frailty index, lung function, and major clinical determinants in chronic obstructive pulmonary disease

Background: Airflow limitation alone is unable to capture the complexity of chronic obstructive pulmonary disease (COPD), better explained by comprehensive disease-specific indexes. Frailty is a clinical condition characterized by high vulnerability to internal and external stressors and represents a strong predictor of adverse outcomes. Aims: Primary objective was to test the association between indexes of lung function and COPD severity with frailty index (FI), and secondary to evaluate the association between FI and comorbidities, cognitive and physical function, BODE index, and mortality. Methods: 150 stable COPD outpatients were enrolled and followed up to 4 years. At baseline, participants performed a geriatric multidimensional assessment, pulmonary function tests, arterial blood gas analysis, 6-min walking test, and bioimpedance analysis. BODE and FI were calculated. Spearman’s ρ was used to assess correlations. Mortality was assessed using Kaplan–Meier curves. Results: Participants were followed up for a median of 39 months. Mean age was 73 years and median frailty index 0.15 (IQR 0.11–0.19). FI was higher in frequent exacerbators (≥ 2/year) (mean 0.18 vs 0.15, p 0.01) and dyspnoeic patients (mMRC ≥ 2) (mean 0.21 vs 0.14, p < 0.01) and correlated with lung volumes, expiratory flows, and pressure of arterial oxygen. FI was positively correlated with the number of comorbidities, depressive symptoms, cognitive decline, and BODE index. Mortality was higher in patients with BODE higher than 3 (HR 3.6, 95% CI 1.2–10.9), and not associated with FI. Discussion: FI positively correlates with all clinical drivers orienting the choice of treatment in COPD. Conclusions: FI associates with lung function and COPD severity, but does not associate with mortality.