Airflow limitation classified with the fixed ratio or the lower limit of normal and cause-specific mortality - A prospective study.

BACKGROUND

There is controversy as to whether airflow limitation should be defined as forced expiratory volume in 1 s (FEV)/vital capacity (VC) < 0.7 or as FEV/VC< the lower limit of normal (LLN). The aim was to examine whether different definitions of airflow limitation differ in predicting mortality.

METHODS

Longitudinal prospective study of a national cohort of Swedish workers (199,408 men; 7988 women), aged 20-64 years with spirometry without bronchodilation at baseline followed from 1979 until death, or censorship at 2010. Airflow limitation (AL) by Global Obstructive Lung Disease criteria, AL, was defined as FEV/VC < 0.7; AL as FEV/VC < LLN. All all-cause, COPD and cardiovascular disease mortality was analyzed among men and women in relation to AL and AL, adjusted for age and smoking.

RESULTS

Among men, all-cause mortality risks were similar by airflow limitation criteria: AL RR = 1.32, 95% CI 1.26-1.38; AL, RR = 1.37, 95% CI 1.31-1.44. The risk estimates were also similar by airflow limitation definition for cardiovascular mortality and for COPD mortality. Among women, all-cause mortality was also similar by airflow limitation criteria, but significantly higher as compared to men: AL RR = 2.10, 95% CI 1.66-2.66; AL, RR = 2.09, 95% CI 1.66-2.62. Also cardiovascular and COPD mortality by airflow limitation criteria was significantly higher among women as compared to men.

CONCLUSIONS

Defined either as FEV/VC < 0.7 or as FEV/VC < LLN, airflow limitation predicted excess mortality risk of similar magnitude. Mortality in relation to airflow limitation was higher among women compared to men.