Lung function and respiratory symptoms in association with mortality: The HUNT Study

Whether respiratory symptoms are associated with mortality independent of lung function is unclear. The authors explored the association of the exposures i) lung function, ii) respiratory symptoms, and iii) lung function and respiratory symptoms combined, with the outcomes all-cause and cardiovascular mortality. The study included 10,491 adults who participated in the Nord-Trøndelag Health Study (HUNT) Lung Study in 1995-1997 and were followed through 2009. Cox regression was used to calculate adjusted hazard ratios (HRs) with 95% confidence intervals for all-cause and cardiovascular mortality associated with pre-bronchodilator% predicted forced expiratory volume in 1 second (ppFEV1), chronic obstructive pulmonary disease (COPD) grades, and respiratory symptoms (chronic bronchitis, wheeze, and levels of dyspnoea). Lung function was inversely associated with all-cause mortality. Compared to ppFEV1 ≥100, ppFEV1 <50 increased the HR to 6.85 (4.46-10.52) in women and 3.88 (2.60-5.79) in men. Correspondingly, compared to normal airflow, COPD grade 3 or 4 increased the HR to 6.50 (4.33-9.75) in women and 3.57 (2.60-4.91) in men. Of the respiratory symptoms, only dyspnoea when walking remained associated with all-cause mortality after controlling for lung function (HR 1.73 [1.04-2.89] in women and 1.57 [1.04-2.36] in men). Analyses of lung function and dyspnoea when walking as a combined exposure further supported this finding. Overall, associations between lung function and cardiovascular mortality were weaker, and respiratory symptoms were not associated with cardiovascular mortality. In conclusion, lung function was inversely associated with all-cause and cardiovascular mortality, and dyspnoea when walking was associated with all-cause mortality independent of lung function.