BUFFALO, NY--Pulmonary function, as measured by forced expiratory volume in one second (FEV1), is an independent predictor of mortality from all causes, as well as from specific causes, such as ischemic heart disease. What is more, FEV1 can predict mortality risk in both genders over several decades.

Those are the findings of a 29-year study of 554 men and 641 women who were part of the Buffalo Health Study cohort.[1] "Subjects in the bottom 20% of pulmonary function had about a twofold increase in mortality risk, compared with those in the top 20%," reported lead author Holger J. Schünemann, MD, PhD. "This risk increase was fairly constant over time."

A RANDOM SAMPLE

The subjects were a randomly selected sample of the general population in Buffalo, New York. They were participants in the Buffalo BP/Erie County Air Pollution-Pulmonary Function Study, which enrolled 2,273 men and women ages 15 to 96 years between June 1960 and December 1961.

One of that study's goals was to assess the effect of tobacco use and air pollution on pulmonary function. Therefore, spirometry was performed at enrollment to obtain baseline FEV1 values for each subject.

About half the original enrollees were included in the study by Schünemann et al. Among the reasons for patient exclusion were incomplete baseline data, unsatisfactory tracings of spirometry curves, the inability to confirm vital status, and age less than 20 years at baseline. (Pulmonary function may vary in people under age 20 years because many are still growing, the authors explained.) Unfortunately, the authors also had to exclude 369 patients who were African American or members of other minority groups, largely because too few such patients were available at follow-up to permit the creation of reference equations for pulmonary function.

Thus, the remaining 1,195 patients were white adults who had been between the ages of 20 and 89 at baseline.

FEV1 AND MORTALITY

Of these subjects, about 55% of the men and 43% of the women died during follow-up, which ended on December 31, 1989. Cardiovascular disease, especially ischemic heart disease, was the leading cause of death in both sexes.

On average, FEV1 was found to be higher in men than in women. However, when FEV1 was expressed as a percentage of predicted (FEV1%pred), it was lower in men.

Even after adjustment for patient age, body mass index, systolic blood pressure, smoking status, and education, FEV1%pred had a statistically significant inverse relationship with all-cause mortality in both sexes during the overall follow-up period. For each 1% increase in FEV1%pred, the risk of death from all causes fell by 1% in women and by 1.5% in men.

For the follow-up period as a whole, subjects in the lowest quintile of pulmonary function had a significantly greater all-cause mortality risk than did those in the highest quintile (relative hazard ratio, 2.24 for men and 1.81 for women). A risk increase was also found among subjects in the second lowest quintile (relative hazard ratio, 1.61 for men and 1.43 for women).

However, the inverse association between FEV1%pred and the all-cause mortality risk appeared to be somewhat dependent on the duration of follow-up. Among men, it lost statistical significance after more than 25 years' follow-up. A more unusual pattern emerged among women: The association was not significant after more than 20 years' follow-up, but it regained significance after more than 25 years' follow-up. Thus, the clinical relevance of this finding is unclear.

An inverse relationship was also found between the FEV1%pred and mortality from ischemic heart disease during the overall follow-up period. This relationship only reached borderline statistical significance, however. Compared with the top quintile of pulmonary function, the lowest quintile had relative hazard ratios for death from ischemic heart disease of 2.11 in men and 1.96 in women. The likelihood of death from ischemic heart disease was also elevated among men in the second lowest quintile (relative hazard ratio, 2.62) but not in the women in that quintile.

The study findings confirm those of previous, smaller investigations. Given the value of FEV1 for independently predicting overall mortality, it is surprising that this simple measure has not gained more importance as a general health assessment tool, commented Dr. Schünemann, a Research Assistant Professor of Medicine and of Social and Preventive Medicine at the State University of New York at Buffalo.

FEV1 is also an important tool that can be used when counseling patients with reduced pulmonary function due to asthma or other causes. "When advising these patients about how to maximize their health, you want to be able to show them exactly what their risk of dying will be over the next 20 or 30 years," Dr. Schünemann stressed.

--Timothy Begany

Reference
1. Schünemann HJ, Dorn J, Grant BJ, et al. Pulmonary function is a long-term predictor of mortality in the general population: 29-year follow-up of the Buffalo Health Study. Chest. 2000;118:656-664.

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