Background: Cigarette smoking is the cardinal cause of COPD if it be not that only a relatively small percentage of smoker have increase of clinically overt disease.

Objectives: To identify high-risk exposes and to assess the prognostic significance of "small airways" tests

Setting: University teaching hospital.

Subjects: Fifty-six smoker and ex-smoker of mean age 625 years (SD 27) with a smoking history of 406 (189) pack-years were studied at the extreme point of a 13-year follow-up period.

Measurements: Questionnaire and lung function trials including static and dynamic lung bulks airway resistance, maximal expiratory follow rates, and small airways examples such as nitrogen slope of the alveolar plateau ([Nsub2] slope) and closing volume

Results: Eighty-two percent of enslaves with a normal [FEV.sub.1]/vital capacity (VC) ratio at the start of the reflection (half of them with abnormal follows of small airways tests) still had a normal [FEVsub1]/VC ratio 13 years later. In the remainder, all further one had final [FEV.sub.1]/VC values [is greater than] 60% About 80% of make subordinates with a decreased [FEV.sub.1]/VC at the start (subject with airflow obstruction) reached at the [i]finale[/i] of study lower than predicted [FEVsub1]/VC values. solely about 10% of these enthralls showed an accelerated loss of [FEVsub1] reaching close [FEV.sub.1]/VC values of [is les than] 45% Initial [Nsub2] inclination predicted about 80% of fall of the curtain [FEV.sub.1] values.

Conclusion: Middle-aged smoker are at no evident risk of functional deterioration if their [FEVsub1]/VC ratio is normal. This is in like manner even if results of small airways examples are abnormal. A decreased [FEVsub1]/VC ratio has no serious implications in itself. no other than an associated high [N.sub.2] oblique direction adds the necessary information to predict a soft [FEV.sub.1]. Present data suggest that a subgroup of smoker in their 50 characterized by the agency of a low [FEV.sub.1]/VC ratio and a high [Nsub2] oblique direction are probably the susceptible smoker at high risk for increase of COPD.

(CHEST 1998; 114:416-425)

Key words: chronic obstructive pulmonary disease; lung function tests; small airways tests; smoking

Abbreviations: [Nsub2] slope=nitrogen incline of the alveolar plateau; RV=residual volume; SAD=small airway disease; SGaw=specific airway conductance; TLC=total lung capacity,; VC=vital capacity'; Vmax=maximal expiratory proceed rate

greatest in quantity information on COPD and its natural history was provided pair to three decades ago on cross-sectional studies of smokers or disabled patients. Longitudinal studies were limited to the efficiencys of smoking on pulmonary symptoms and spirographic experiment results. A detailed insight into the functional aspects of COPD was obtained and nothing else relatively recently. Pathologic and physiologic investigations of the early 1970 have shown that COPD affects in its earlier stages the small, peripheral airways, considered to contribute relatively little to the total airway resistance to flow[12] However, since the narrowing of the peripheral airways is unevenly distributed, it would impair distribution of ventilation and of gas exchange. Several proofs such as frequency dependence of compliance,[3] nitrogen acclivity [i]or[/i] declivity of the alveolar plateau ([Nsub2] slope)[4] or closing volume[5] were consideration to reflect the small airways narrowing. Indeed, inflammation and fibrosis of small airways were shown to be related to the impairment of small airways tests[6-8] Small airways disease (SAD) was considered to be not and nothing else early "disease," but also a first stage in a protracted proces leading eventually to chronic airflow obstruction. Since early disease cannot be finded by measuring airway resistance or [FEVsub1] meditation to be insensible, some authors have propos to use instead "small airways" exhibitions Cross-sectional studies have shown that small airways trials were able to detect a functional blemish despite a normal [FEV.sub.1], thus suggesting that [FEVsub1] is not sensitive enough to find not at home subtle functional changes.[9-14] However, the progres of the disease is mirrored by the decrease of [FEVsub1] leading a minority of smoker to the clinical stages of COPD[15] most numerous longitudinal studies[16-19] have found any link between impairment of small airways touchstone results and subsequent loss of [FEVsub1] However, solitary part of the decline in [FEVsub1] was explained from the initial impairment of small airways touchstone results, which also failed to identify susceptible smoker ie, those at high risk to become disabled through disease.

To assess the prognostic significance of small airways experiment results and to identify high-risk smoker we investigated 56 former steelworkers, rife and former smokers, at the close of 13 years of follow-up

MATERIALS AND METHODS

We have examined 56 former steelworkers, now retired, all men aged 625 [+ or -] 27 years (mean [+ or -] SD) at the cessation of a 13-year follow-up consideration Briefly, at the start of the inquiry we investigated a homogeneous cluster of 104 "blue collar" active workers from a hanger plant near Brussels (Belgium), 50 years advanced in years on the average. All of them were long-term smoker (317 [+ or -] 143 pack-years). Selection criteria included an age between 45 and 55 years and at least 10 years of service in the same company. Workers with bronchial asthma and those with a previous occupational prospect to dust were rejected. Details of the selection of make subordinates were given previously.[20] Reference lung function values (one-sided 95% limits) were established from data of 54 asymptomatic nonsmokers from the same plant. At the start of the application of mind subjects were divided into three collections The first group (n=37), thereafter called "subject with airflow obstruction," had an [FEV.sub.1]/vital capacity (VC) ratio (597 [+ or -] 64%) les than our cut-off limit of 666% The remaining bring under rules with a normal [FEV.sub.1]/VC ratio were divided into sum of two units groups according to the carriage of an abnormal [N.sub.2] obliquity or closing capacity. In single in kind group, subjects had either an abnormal closing capacity or an abnormal [Nsub2] incline (n=32) and were therefore called "the cluster with SAD." Their [FEV.sub.1]/VC ratio was 717 [+ or -] 38% In the third assign places to called "resistant" (n=35), both [Nsub2] direction downward and closing capacity, as well as the other lung function criterion results, were within normal limits ([FEVsub1]/VC was 748 [+ or -] 42%) Age and height were similar in the three assign places tos Eighty-five of the original 104 exposes were studied 6 years later[21] and 56 subdues were studied 13 years later. (In our first article,[20] originates of 105 smokers were reported. However, undivided of these subjects declared later that he was, in fact, a nonsmoker.) The latter deductions are reported in this article: 18 subdues came from the group with airflow obstruction and 19 make liables came from the SAD and the resistant clusters Thirteen subjects died between start and period of study (7 of cancer, 3 of myocardial infarction, 2 of cerebrovascular accident, and 1 of hepatic cirrhosis) and 35 others either emigrated or refused to be studied again. controls unavailable for follow up (those who died, emigrated, or refused to be examined again) were not statistically different from those evaluated again 13 years later. Indeed, at the start of the close attention physical and lung function data, as well as smoking history, were comparable in the pair groups (Table 1).

...