The association of spirometric small airways obstruction with respiratory symptoms, cardiometabolic diseases, and quality of life: Results from the Burden of Obstructive Lung Disease (BOLD) study

Background: Spirometric small airways obstruction (SAO) is common in the general population. Whether spirometric SAO is associated with respiratory symptoms, cardiometabolic diseases, and quality of life (QoL) is unknown. Methods: Using data from the Burden of Obstructive Lung Disease study (N = 21,594), we defined spirometric SAO as the mean forced expiratory flow rate between 25 and 75% of the FVC (FEF25-75) less than the lower limit of normal (LLN) or the forced expiratory volume in 3 s to FVC ratio (FEV3/FVC) less than the LLN. We analysed data on respiratory symptoms, cardiometabolic diseases, and QoL collected using standardised questionnaires. We assessed the associations with spirometric SAO using multivariable regression models, and pooled site estimates using random effects meta-analysis. We conducted identical analyses for isolated spirometric SAO (i.e. with FEV1/FVC ≥ LLN). Results: Almost a fifth of the participants had spirometric SAO (19% for FEF25-75; 17% for FEV3/FVC). Using FEF25-75, spirometric SAO was associated with dyspnoea (OR = 2.16, 95% CI 1.77–2.70), chronic cough (OR = 2.56, 95% CI 2.08–3.15), chronic phlegm (OR = 2.29, 95% CI 1.77–4.05), wheeze (OR = 2.87, 95% CI 2.50–3.40) and cardiovascular disease (OR = 1.30, 95% CI 1.11–1.52), but not hypertension or diabetes. Spirometric SAO was associated with worse physical and mental QoL. These associations were similar for FEV3/FVC. Isolated spirometric SAO (10% for FEF25-75; 6% for FEV3/FVC), was also associated with respiratory symptoms and cardiovascular disease. Conclusion: Spirometric SAO is associated with respiratory symptoms, cardiovascular disease, and QoL. Consideration should be given to the measurement of FEF25-75 and FEV3/FVC, in addition to traditional spirometry parameters

Chronic airflow obstruction attributable to poverty in the multinational Burden of Obstructive Lung Disease study

Poverty is strongly associated with all-cause and chronic obstructive pulmonary disease (COPD) mortality. Less is known about the contribution of poverty to spirometrically defined chronic airflow obstruction (CAO) – a key characteristic of COPD. Using cross-sectional data from an asset-based questionnaire to define poverty in 21 sites of the Burden of Obstructive Lung Disease study, we estimated the risk of CAO attributable to poverty. Up to 6% of the population over 40 years had CAO attributable to poverty. Understanding the relationship between poverty and CAO might suggest ways to improve lung health, especially in low- and middle-income countries

Prevalence of small airways obstruction and its risk factors in the multinational Burden of Obstructive Lung Disease (BOLD) study

Background: Small Airways Obstruction (SAO) is a common feature of obstructive lung diseases. There is limited research on SAO, its global prevalence and risk factors. Methods: Using data from 41 sites in the cross-sectional Burden of Obstructive Lung Disease study (N=26,448), we defined SAO as either: 1) mean forced expiratory flow rate between 25% and 75% of the forced vital capacity (FEF25-75) less than lower limit of normal (LLN), or 2) forced expiratory volume in three seconds to forced vital capacity ratio (FEV3/FVC) less than the LLN. We estimated the prevalence of pre- and post-bronchodilator SAO for each site. To identify risk factors for SAO, we performed multivariable regression analyses within each site, and pooled estimates using random effects meta-analysis. Findings: Prevalence of pre-bronchodilator SAO ranged from 5% (34/624) in Tartu (Estonia) to 34% (189/555) in Mysore (India) for FEF25-75, while for FEV3/FVC it ranged from 5% (31/667) in Riyadh (Saudi Arabia) to 31% (287/981) in Salzburg (Austria). Prevalence of post-bronchodilator SAO was universally lower. Risk factors associated with FEV3/FVC included increasing age, low body mass index, active and passive smoking, low level of education, working in a dusty job for more than 10 years, and previous tuberculosis. Results were similar for FEF25-75, except for increasing age, which was associated with reduced odds of SAO. Interpretation: Despite the wide geographical variation, SAO is common and more prevalent than chronic airflow obstruction worldwide. SAO shows the same risk factors as chronic airflow obstruction. However, further research is required to investigate whether it also associates with respiratory symptoms and lung function decline. Funding: National Heart and Lung Institute; Wellcome Trust (085790/Z/08/Z)