Effects of the multiple risk factor intervention trial smoking cessation program on pulmonary function. A randomized controlled trial.

To determine whether the decline in pulmonary function in smokers is modified by stop-smoking intervention, a randomized controlled study (the Multiple Risk Factor Intervention Trial) was done comparing participants in a special intervention group that included an intensive smoking cessation program with those assigned to usual care. The subjects were 6,347 middle-aged male smokers who had serial measurements of pulmonary function--principally the forced expiratory volume in 1 second (FEV1)--during 6 to 7 years of follow-up. No overall differences were detected in the rate of loss of FEV1 in the two groups. The use of beta-blockers, which had detrimental effects on FEV1, was significantly more common in the intervention group. Among nonusers of beta-blockers, heavy smokers lost FEV1 at a rate about 11 ml per year slower in the intervention group than in the control group (2P = .09) and ended the trial with an FEV1 about 90 ml higher (2P = .05). These results support the inference from observational studies that smoking cessation has a beneficial effect on pulmonary function in heavy smokers.

The effects of underrecorded forced expirations on spirometric lung function indexes.

A problem with short recorded lengths of expiration, encountered in a large heart attack intervention trial, illustrates the importance of standardization and training in spirometric lung function testing. At baseline, half of the trial's clinical centers had mean FVC values that were between 500 and 1,100 ml below those predicted for these centers. To quantify the effects of underrecorded forced expirations on the FVC, the FEV1/FVC%, the FEF70-80%, the FEF 25-75%, and the FEF45-55%, a study of 80 complete spirograms of good quality was undertaken. The findings were that short lengths of expiration cause underrecording of the FVC, inflating all of the examined FVC-dependent spirometric indexes. The inflation was fairly uniform across all obstructions for the forced expiratory flow rates, but it increased markedly with level of obstruction for the FEV1/FVC%. Virtually no subjects exhibited low values of these spirometric indexes after 3 s of expiration, and the number of subjects with low values was still substantially underestimated after 6 s of expiration. Whereas 18 (23%) of the subjects had FEV1/FVC% greater than or equal to 80% and 21 (26%) had ratios less than or equal to 69% based on complete expiration, 60 (75%) of the subjects had ratios greater than or equal to 80% and only 2 (3%) had ratios less than or equal to 69%, after 3 s of expiration. Even after 6 s, 26 subjects (33%) had ratios greater than or equal to 80%, and only 10 (13%) had ratios less than or equal to 69%. Therefore, completely recorded expirations are essential for accurate measurement of the FVC-dependent spirometric indexes.