A cohort study of forced vital capacity, airway obstruction, and survival in the multinational Burden of Obstructive Lung Disease study

Background: In the USA, higher forced vital capacity (FVC) is linked with longer survival, and FVC is associated with survival independently of ethnicity. The implications for the low FVC values in parts of Asia and Africa are unknown. Methods: We used data from 16 sites of the multinational Burden of Obstructive Lung Disease (BOLD) study that completed follow-up of participants between 2019 and 2021 and reported at least five deaths between baseline and follow-up. We assessed the association of mortality with FVC and Forced Expiratory Volume in 1 second (FEV₁)/FVC ratio within each site using Cox proportional hazards models. These models were adjusted for age, smoking, height, and weight. Effect estimates from all sites were combined using meta-analysis. Systematic regional differences were investigated. Results: Of 9927 study participants with follow-up data, 1120 (11.3%) had died [mean follow-up = 8.7 years, standard deviation (SD) = 3.3 years]. Baseline post-bronchodilator FVC and FEV₁/FVC were inversely associated with mortality. When both FVC and FEV₁/FVC were mutually adjusted for each other, the decreased mortality rates were more pronounced for each SD higher FVC at baseline [44% (95% confidence interval (CI): 25%, 58%) for men and 28% (95% CI: 11%, 41%) for women] than for FEV₁/FVC at baseline [14% (95% CI: 8%, 20%) for men and 7% (95% CI: −10%, 21%) for women]. The probability of true regional differences was low. Conclusions: People with a higher FVC adjusted for age, sex, and height have a longer survival. Regional adjustments to lung function standards are inappropriate when assessing prognosis.