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Lung function is a strong predictor of overall mortality in asthma and chronic obstructive pulmonary disease (COPD). FEV1 is considered to be the "gold standard," whereas peak expiratory flow (PEF) is mostly used in absence of FEV1 measurements. We compared the predictive power of PEF and FEV1, measured after maximal bronchodilation, which included a short course of oral corticosteroids. The study population comprised 491 asthmatics and 1,095 subjects with COPD. Pulmonary function tests were performed between 1983 and 1988, and survival data were obtained by September 1997, when 127 asthmatics and 723 subjects with COPD had died. Predictors of survival were examined by Cox proportional hazards analyses. After controlling for age, smoking, sex, and body mass index, we found best PEF to be at least equal to best FEV1 as predictor of overall mortality in subjects with COPD. The predictive power of best PEF was in part maintained after controlling for best FEV1. In asthma, best FEV1 seemed to be a better predictor of mortality than best PEF. Despite close correlation to FEV1, PEF apparently provides independent prognostic information in patients with COPD. This may be due to PEF and FEV1 reflecting different components of COPD, i.e., chronic bronchitis, small airways disease, and emphysema. Furthermore, extrapulmonary components such as muscle mass and general "vigour" probably affect PEF to a greater extent than they affect FEV1.

The importance of reversible airflow obstruction to the prognosis of asthma and chronic obstructive pulmonary disease (COPD) is not clear. We tested the hypothesis that reversibility to corticosteroid and bronchodilator is not an independent predictor of prognosis, but merely reflects a component of the maximal attainable lung function, which is the best spirometric predictor of survival. During a 6-yr period (1983-1988), 1,586 subjects with asthma or COPD underwent standardized bronchodilator and corticosteroid reversibility tests at a chest clinic in Copenhagen. The vital status was obtained by September 1997. The relationship between mortality and age, gender, smoking, FEV1, and reversibilities was examined by Cox proportional hazards analyses. Of 1,586 subjects, 850 had died before September 1997. Age, smoking, and FEV1 were significant predictors of mortality. After controlling for baseline FEV1, bronchodilator and corticosteroid reversibility were significantly associated with better survival. However, after controlling for best FEV1 all reversibilities became nonsignificant and nonpredictive. The combined use of corticosteroid and bronchodilator reversibility in survival analyses is a novel approach, and we have shown that both contribute to survival prediction to the extent that they modify FEV1. However, reversibility per se does not influence survival in subjects with moderate to severe asthma or COPD.