Longitudinal studies of air pollution effects on lung function.

Abstract

Longitudinal evaluation implies comparisons of lung func­ tion of same individual over time. The effects of air pollu­ tion on humans are frequently measured as changes in lung func­ tion. In this paper we consider study designs and methods employed to assess relationship between air pollution ex­ posures and temporal changes in lung function over time. Temporal changes in lung function may occur over long periods of time, for example, over decades, and represent chronic loss of lung function. The American Thoracic Society defined such chronic changes as explicit markers of adverse health ef­ fects of air pollution indicated by increased rate of decline of pulmonary function with aging in adults and failure to main­ tain their predicted lung function growth-curve in children (I). On other hand, temporal changes in lung function may oc­ cur over short periods of time, for example, a few hours, and represent acute, possibly reversible changes. Acute, largely re­ versible changes in lung function were not defined by Amer­ ican Thoracic Society as adverse, since the percentage change that indicates an adverse effect can vary from group to group and situation to situation. On other hand, US Environ­ mental Protection Agency (2) and World Health Organiza­ tion (3) have both accepted acute changes in lung function as indicators of adverse effects of exposure to ozone pollution (4). While longitudinal studies usually bring to mind long-term multiyear studies of change in lung function, a substantial body of air pollution literature is based on studies of longitudinal change of lung function over much shorter time scales. EXAMPLES OF LONGITUDINAL AIR POLLUTION STUDIES This discussion of air pollution studies is structured around time scales that have been considered in evaluating air pollution effects. We start with most acute changes of response over minutes, progressing to hours, days, weeks, months, and years. In each case we will present examples of air pollution study de­ signs, factors affecting change in pulmonary function of same time scale, rriethodologic problems, and major findings. We re­ strict out attention to human studies, but consider both controlled exposure (clinical) studies and natural exposure (epidemiologic) studies. Weargue that effects of air pollution on lung function have been easier to demonstrate over short time periods (minutes to weeks) than over long time periods (years to decades). This is not a comprehensive review of effects of air pollu