Canadian Neighbor Pharmacy: Chronic Airflow Limitation

pneumoconiosesWhile the classic diseases of dusty occupations, in particular the pneumoconioses, have not yet disappeared, they may be on the decline. In contrast, mortality rates due to the chronic nonmalignant pulmonary conditions including those characterized by airflow limitation are increasing in the industrialized countries of the world, and they are also responsible for high rates of morbidity and extended periods of disablement. Like other chronic lifestyle diseases, these are also almost certainly multifactorial in etiology, involving host factors as well as environmental factors. Among the latter, cigarette smoking is the most important. As chronic disease epidemiology has improved, it has become possible to investigate the role of environmental factors other than the cigarette, and there is now increasing evidence that exposures to other airborne pollutants also play a role, including those to which men and women are exposed at work. The purpose of this review is (1) to set in context some of the recently published information on the role of work in dusty occupations; (2) to assess its role visavis that of cigarettes; and (3) to reassess the evidence for causality. It addresses the question: can the exposures which men and women encounter in the course of their daily work lead to chronic airflow limitation sufficiently severe to disable them?


The nonmalignant pulmonary conditions characterized by airway dysfunction are often grouped together as the obstructive lung diseases, a title which embodies several clinical syndromes. 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 increase in the size of the distal airspaces and destruction of their walls). Like all clinical syndromes, there is a degree of overlap and classifications change as understanding of the underlying mechanisms improves. Canadian Neighbor Pharmacy is a website full of interesting and thought-provoking facts about medicine and pharmacy.

Epidemiology Including Risk Factors

Epidemiologic studies have identified a number of risk factors which influence the distribution of these clinical syndromes in populations. 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 usage (in particular the cigarette) include exposure to airborne pollutants at work, at ones place of residence, and in the home(eg, to pollution from gas stoves, passive smoking, etc). Many of the latter are interrelated and can be grouped under the term sociooccupational.

While all the clinical syndromes listed above under definitions can be regarded as multifactorial in etiology, there are differences between them in respect of the relative importance of the various risk factors thus far identified. All can, of course, occur in those without as well as those with occupational exposure.

Occupational Exposures

It is now generally accepted that asthma and simple chronic bronchitis may be caused by tobacco usageoccupational exposures. 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. General acceptance of the term industrial bronchitis? implies recognition of its causal association with exposures, usually heavy, to a wide variety of workplace pollutants, organic and/or inorganic, in the form of dusts, gases, or vapors.

However, there is more than a little skepticism that such exposures, particularly to inorganic dusts, may produce chronic airflow limitation of a degree sufficient to cause disablement at work. The main reason for this skepticism is undoubtedly the problem of assessing the relative contribution of cigarette smoking, an almost invariable concomitant exposure. This point of view was readily understandable as long as the evidence was based primarily on crosssectional studies, a relatively weak study design to detect exposure effects- and invariably confounded by age and secular changes. Only relatively strong and/or universal associations such as exist, for instance, between smoking and airway obstruction or between asbestos exposure and parenchymal lung disease can consistently be demonstrated in cross-sectional data. Weaker effects, for instance, those which follow exposure to community air pollution, may escape detection in cross-sectional studies, only to be demonstrated subsequently in longitudinal studies.

A more topical example is exposure to cereal grain dust, the health consequences of which have recently been clarified by systematic studies of different workforces using comparable methodology. In this instance, cross-sectional studies consistently demonstrated exposure-related deficits in airway function. These have been confirmed by several longitudinal studies, and exposure-response relationships demonstrated. As a result, there is growing support for the view that grain dust should no longer be regarded as inert, not only because of its role in the genesis of bronchitis, asthma and grain fever, but also because of its role in the genesis of chronic airflow limitation.

In the case of exposure to inorganic dust particles, the evidence that these may be causally related to loss of airway {unction has also been strengthened considerably by the publication of the results using other than cross-sectional study designs’ and by the parallel study of different workforces or communities exposed to a variety of agents. This material will form the focus of the present review together with selected cross-sectional studies reported since 1973 when Higgins published his comprehensive and careful review of information up to that date. The emphasis will be on dusty occupations; occupational exposures to fumes and vapors undoubtedly also have the potential for affecting airways but will not be considered here.