Chest
Volume 114, Issue 2, August 1998, Pages 416-425
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Clinical Investigations: COPD
Identification of Smokers Susceptible to Development of Chronic Airflow Limitation: A 13-Year Follow-up

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Background

Cigarette smoking is the cardinal cause of COPD, but only a relatively small percentage of smokers have development of clinically overt disease.

Objectives

To identify high-risk subjects and to assess the prognostic significance of “small airways” tests.

Setting

University teaching hospital.

Subjects

Fifty-six smokers and ex-smokers of mean age 62.5 years (SD, 2.7) with a smoking history of 40.6 (18.9) pack-years were studied at the end of a 13-year follow-up period.

Measurements

Questionnaire and lung function tests, including static and dynamic lung volumes, airway resistance, maximal expiratory flow rates, and small airways tests, such as nitrogen slope of the alveolar plateau (N2 slope) and closing volume.

Results

Eighty-two percent of subjects with a normal FEV1/vital capacity (VC) ratio at the start of the study (half of them with abnormal results of small airways tests) still had a normal FEV1/VC ratio 13 years later. In the remainder, all but one had final FEV1/VC values >60%. About 80% of subjects with a decreased FEV1/VC at the start (subjects with airflow obstruction) reached at the end of study lower than predicted FEV1/VC values. Only about 10% of these subjects showed an accelerated loss of FEV1, reaching end FEV1/VC values of <45%. Initial N2 slope predicted about 80% of end FEV1 values.

Conclusion

Middle-aged smokers are at no evident risk of functional deterioration if their FEV1/VC ratio is normal. This is so even if results of small airways tests are abnormal. A decreased FEV1/VC ratio has no serious implications in itself. Only an associated high N2 slope adds the necessary information to predict a low FEV1. Present data suggest that a subgroup of smokers in their 50s, characterized by a low FEV1/VC ratio and a high N2 slope, are probably the susceptible smokers at high risk for development of COPD.

Section snippets

Materials and Methods

We have examined 56 former steelworkers, now retired, all men, aged 62.5±2.7 years (mean±SD), at the end of a 13-year follow-up study. Briefly, at the start of the study, we investigated a homogeneous group of 104 “blue collar” active workers from a steel plant near Brussels (Belgium), 50 years old on the average. All of them were long-term smokers (31.7± 14.3 pack-years). Selection criteria included an age between 45 and 55 years and at least 10 years of service in the same company. Workers

Results

Table 1 (right) presents the anthropometric and the functional data, as well as the smoking history (expressed as pack-years) for the whole group of 56 subjects studied after 13 years. At the end of follow-up, there were 21 former smokers (35±13 pack-years) and 35 current smokers (45±20 pack-years). There was no change in either average height or weight over time. FEV1/VC ratio was 63.1 ±11.3% in current smokers and 66.8± 11.3% in former smokers (p>0.05). The corresponding FEV1 values were

Discussion

Cigarette smoking is recognized as the cardinal cause of COPD, but only a relatively small percentage of smokers are developing clinically overt disease.23 How to identify these high-risk smokers is still considered an elusive task. Present results show that a subset of smokers characterized by a low FEV1/VC ratio (or low FEV1 and a high N2 slope are probably the high-risk subjects. Indeed, after 13 years, they reached a functional profile observed in the advanced stages of COPD.

At the end of

Acknowledgments

The authors thank Constant Pahulycz, MA, for technical assistance with the manuscript, and Professors B. Nemery and K.P. Van de Woestijne for critical reading of the manuscript and fruitful suggestions.

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    This study was supported by grant 7280-03-020 of the European Coal and Steel Community.

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