Combined effect of lung function level and decline increases morbidity and mortality risks

Lung function level and decline are each predictive of morbidity and mortality. Evaluation of the combined effect of these measurements may help further identify high-risk groups. Using Copenhagen City Heart Study longitudinal spirometry data (n = 10,457), 16–21 year risks of chronic obstructive pulmonary disease (COPD) morbidity, COPD or coronary heart disease mortality, and all-cause mortality were estimated from combined effects of level and decline in forced expiratory volume in one second (FEV₁). Risks were evaluated using Cox proportional hazards models for individuals grouped by combinations of baseline predicted FEV₁ and quartiles of slope. Hazard ratios (HR) and 95 % confidence intervals (CI) were estimated using stratified analysis by gender, smoking status, and baseline age (≤45 and >45). For COPD morbidity, quartiles of increasing FEV₁ decline increased HRs (95 % CI) for individuals with FEV₁ at or above the lower limit of normal (LLN) but below 100 % predicted, reaching 5.11 (2.58–10.13) for males, 11.63 (4.75–28.46) for females, and 3.09 (0.88–10.86) for never smokers in the quartile of steepest decline. Significant increasing trends were also observed for mortality and in individuals with a baseline age ≤45. Groups with ‘normal’ lung function (FEV₁ at or above the LLN) but excessive declines (fourth quartile of FEV₁ slope) had significantly increased mortality risks, including never smokers and individuals with a baseline age ≤45.