The epidemiology of pulmonary function and COPD mortality in the multiple risk factor intervention trial.

The potential determinants of the changes in chronic obstructive pulmonary disease (COPD) mortality were evaluated using both the Multiple Risk Factor Intervention Trial (MRFIT) screenees, the longitudinal analysis of the participants, and the differences in special intervention (SI) and usual care (UC) groups. COPD was the underlying cause for only one third of all death certificates listing COPD. Small changes in classification will have a major impact on reported COPD death rates. Cigarette smoking is clearly the primary determinant of COPD mortality. Decreased pulmonary function is an independent risk factor for coronary heart disease (CHD) mortality. Smoking cessation results in a slower rate of decline in pulmonary function over time, especially among heavy smokers. Careful evaluation of smoking cessation, including repeat chemical measures, suggest that the percentage of long-term quitters, especially among heavy smokers has been overestimated. The low percentage of quitters substantially reduced the power to detect an intervention effect. The increased cigarette smoking among recent older cohorts, and failure to substantially reduce smoking, especially among heavy smokers, may be an important factor accounting for the failure to note a decline in COPD mortality among older persons.