Chest
Volume 88, Issue 4, October 1985, Pages 608-617
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Occupational and Environmental Lung Disease
Chronic Airflow Limitation: Its Relationship to Work in Dusty Occupations

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The classic diseases of dusty occupations may be on the decline, but this is not the case for chronic nonmalignant lung disease characterized by airflow limitation. This group of diseases, almost certainly multifactorial in etiology, occurs in those engaged in dusty occupations as well as in those who are not. Among the environmental factors concerned, cigarette smoking is clearly one of the most important, but occupational exposures are increasingly implicated. It is also clear that not all with similar exposures are affected, pointing to the importance of host or personal factors. Evidence is now accumulating in support of what has been called the Dutch hypothesis. This explanation of the natural history of chronic airflow limitation suggests that an “asthmatic tendency” is a necessary factor whether the putative exposure is to cigarettes or to other airborne pollutants. Further research should therefore be directed towards clarifying the relationships of acute and chronic airway dysfunction in response to airborne pollutants of all types.

Section snippets

Definitions

The nonmalignant pulmonary conditions characterized by airway dysfunction are often grouped together as the obstructive lung diseases,3 a title which embodies several clinical syndromes.3, 6 These include: asthma (acute recurrent episodic reversible airflow limitation), simple chronic bronchitis (mucus hypersecretion), chronic obstructive bronchitis (characterized by mucus hypersecretion and chronic airflow limitation, largely irreversible), and emphysema (defined in anatomical terms as an

Epidemiology Including Risk Factors

Epidemiologic studies have identified a number of risk factors which influence the distribution of these clinical syndromes in populations.3, 4 Host factors implicated include age and sex, past and present health experience particularly in relation to respiratory illnesses, and genetic characteristics such as the ability to produce effective protease inhibitors, ABO and secretor status and the liability to immunoglobulin E mediated allergic reactions. Environmental factors other than tobacco

Occupational Exposures

It is now generally accepted that asthma and simple chronic bronchitis may be caused by occupational exposures.7, 8 This is implicit in the general acceptance of the term occupational asthma, used to describe asthma, associated with exposures to various organic and inorganic workplace pollutants; however, problems of definition remain.7 General acceptance of the term industrial bronchitis9 implies recognition of its causal association with exposures, usually heavy, to a wide variety of

Association vs Causality

Associations between occupational exposure(s) and chronic processes such as those resulting in mucus hypersecretion and in airflow limitation can often be demonstrated.4,5,11 Not all such associations are causal, and there are several classic examples in epidemiology to illustrate this point. How then do we distinguish between association and causality, given the chronic nature of these disease processes, their background level in the general population without occupational exposure and the

Cross-Sectional Surveys and Matched Pair Studies of Men in Dusty Occupations

In 1973, Higgins11 reviewed the published studies of chronic pulmonary disease of men engaged in dusty occupations. Almost all were cross-sectional in design, comparing dust-exposed and non-exposed workers. In almost all, there were higher prevalences of bronchitis and lower ventilatory function in the former compared to the latter. The differences remained after standardization for smoking. However, exposure response relationships were not consistent, and Higgins was reluctant to ascribe the

Longitudinal Studies of Men in Dusty Occupations

In unraveling the role not only of environmental exposures but also of host factors in the causation of a disease process as slow to develop as chronic airflow limitation, longitudinal studies have on occasions proved more powerful than cross-sectional studies. This is not surprising when the agent(s) (eg, exposure to community air pollution) are weak and the effects small relative to those of smoking. Even the effect of smoking has in certain populations only been identified by longitudinal as

Studies Based on Pathologic Material

If emphysema is defined in pathologic terms as an increase in the size of the distal airspaces and destruction of their walls,3 its relationship, potential or real, to occupational exposure can only be conclusively determined from examination of pathologic material. The development of quantitative methods of analysis of emphysema in whole lung sections has provided the impetus for this type of study.56, 57, 58

Table 3 summarizes the results of selected studies on coal miners;59, 60, 61, 62 other

Natural History of Chronic Airflow Limitation

It is not easy to write the natural history of a chronic disease process particularly when, as Speizer and Tager4 point out, “There is no one point in time when patient, physician, and epidemiologist will agree that chronic obstructive airways disease has begun.” Two distinct schools of thought have emerged based on two major prospective epidemiologic studies.64, 65 In what came to be known as the British hypothesis,3, 4 chronic bronchitis (mucus hypersecretion) and chronic airflow limitation

Underlying Mechanisms

Whether or not inorganic dust particles will induce reaction in airways and/or lung parenchyma depends, in addition to dose, on their physical, chemical, and perhaps their biological properties. Size, shape, and density are likely to determine where in the airway they will be deposited, and hence, the mechanism(s) of clearance to which they will be subjected. Chemical properties including solubility will affect retention. Both chemical and biological properties influence the nature of the

Unanswered Questions, Future Research and Clinical Implications

In the light of this evidence, it is impossible to escape the conclusion that exposure in certain dusty occupations may cause chronic airflow limitation. The criteria called for by Hill to distinguish association from causality (namely consistency, strength, coherence and dose-response relationships) have all been fulfilled for coal mining63 and for certain industrial exposures,17 including for the latter decreased risk following withdrawal. The answer to the first part of the question posed in

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