Which spirometric indices best predict subsequent death from chronic obstructive pulmonary disease?

Background-Previous epidemiological studies have related mortality from chr onic obstructive pulmonary disease (COPD) to forced expiratory volumes (FEV 1 or FEV0.75) and it is unknown whether other spirometric indices might hav e greater predictive power. Methods-A case-control study of fatal COPD was conducted within a cohort of London civil servants who performed forced expiratory spirograms in 1967-9 and were followed up for mortality over 20 years. The spirograms of 143 me n who died of COPD (ICD8 491, 492 or 519.8) were compared with those of 143 controls individually matched for age, height, and smoking habit who survi ved longer than their matched case. Flow rates in different parts of the sp irogram were compared within case-control pairs and analysed as predictors of fatal COPD by conditional logistic regression. Results-Within pair case:control ratios of FEV1, mid expiratory flow rates (e.g. FEF50-75) and FEF75-85 were highly intercorrelated (r>0.7) but correl ations with FEF85-95 were weaker (r<0.5). All indices except the FEV1/FVC r atio were stronger predictors of death from COPD within the first 10 years than of later deaths (15-19 years). After adjustment for FEV1, mid expirato ry flow rates independently predicted fatal COPD but end expiratory flow ra tes did not. The FEV1 adjusted mortality ratios associated with a 10% decre ment in each index were 2.24 (95% CI 1.54 to 3.76) for FEF50-75, 1.20 (95% CI 1.00 to 1.42) for FEF75-85, and 1.10 (95% CI 0.96 to 1.26) for FEF85-95. Conclusion-This study confirms FEV1 and mid expiratory flow rates as powerf ul predictors of mortality from COPD, and suggests that measurement of end expiratory flow rates would add little extra predictive information.