Chest
Volume 105, Issue 1, January 1994, Pages 175-182
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Clinical Investigations: Miscellaneous
Spirometric Impairments in Long-term Insulators: Relationships to Duration of Exposure, Smoking, and Radiographic Abnormalities

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A study of 2,611 long-term asbestos insulators was well suited to provide information on (1) the prevalence of Spirometric impairments in a large, well-defined population and (2) the effects of cigarette smoking, radiographic abnormalities, and duration from onset of exposure on pulmonary function. Prevalences are reported by a mutually exclusive classification of impairments (normal, restrictive, obstructive, small airways, and combined) as well as by abnormality of specific spirometric tests (FVC, FEV1/FVC, and midexpiratory time). Only 3 percent of nonsmokers (NS) bad obstruction and 6 percent a decreased FEV1/FVC. Frequency of restriction did not vary by smoking history; it was 31 percent in NS and current smokers (CS) and 34 percent in ex-smokers (XS). Obstruction (present in 17 percent) and combined impairment (in 18 percent) were most common in CS. The FEV1/FVC was decreased in 35 percent of CS and 18 percent of XS. The FVC was decreased in 49 percent of CS, 44 percent of XS, and 33 percent of NS. Normal spirometry was most common when the radiograph was normal (almost half the workers with normal radiographs had normal spirometry). Nevertheless, FVC was reduced in 27 percent of those with normal radiographs and a normal radiograph was seen in 11 percent of workers with restriction. Restrictive and combined impairments were most frequent when both parenchyma and pleura were abnormal. Restriction was more frequent in isolated pleural disease (seen in 34 percent such subjects) than in isolated parenchymal disease (22 percent). The contribution of pleural fibrosis to reduced FVC and of asbestos exposure and smoking both to reduced FVC and to reduced FEV1/FVC was confirmed by regression analysis. That reduced FVC and reduced FEV1/FVC are both more frequent in insulators who have smoked (compared with NS insulators or smokers in the general population) suggests an interaction between asbestos and smoking in producing both these physiologic abnormalities.

Section snippets

Population

All surviving active and retired members of the International Brotherhood of Heat, Frost and Asbestos Insulation Workers who had been in the union on January 1, 1967, enrolled in the initial survey5 and now were at least 30 years from onset of occupational exposure were invited to participate. Approximately 55 percent of the surviving cohort were examined in 19 cities in the United States and Canada during the years 1981 to 1983. A sufficient number with lesser duration from onset of exposure

Mean Values

Table 2 shows mean demographic, exposure, and pulmonary function variables by smoking category. Of the 2,611 men, 2,096 (80 percent) had SM. The majority (56 percent) of these or 1,221 men (47 percent of the total population studied) were XS, while 875 (34 percent of the total) continued to smoke. By comparison, in the authors’ random survey of the population of the state of Michigan (from which the spirometric predictive equations were derived), done 4 years earlier, 69 percent of the men had

Discussion

The 2,611 long-term asbestos insulators are a large group, allowing analysis of the effects on spirometric lung function of such independent variables as asbestos exposure (expressed as years from onset), cigarette smoking (expressed as pack years), and presence of radiographic abnormalities. Spirometry is the most easily and universally measured set of lung function tests. The FVC measures “ventilable” lung volume; a decrease therefore reflects (1) restriction secondary to pulmonary or pleural

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