The Nashville air pollution study

The role of air pollution in asthma

Laboratory studies have clearly shown that inhalation of SO2 by asthmatics can cause a significant degree of wheezing at concentrations considerably lower than those which affect non-asthmatics. Concentrations as low as 0.2 p.p.m. have a significant effect, especially in subjects who are mouth breathing or undergoing heavy exercise. The effects of SO2 appear to be short-lived and not increased by more prolonged exposure (10 min versus 1 hr). WHO air quality guidelines on levels of SO2 have been based to a large extent on these studies and are set at or just below the reported threshold for effects on at risk groups. Thus the 1 hr recommended maximum is 0.16 p.p.m. (350 micrograms/m3). These guidelines have been exceeded in the U.K. on many occasions in the recent past [2] suggesting that asthmatics are at risk in high pollution areas from SO2 induced exacerbations of their asthma. This is particularly true considering that virtually all the laboratory studies have been performed on mild asthmatics. The effects on moderate and severe asthmatics, or those with marked lability of their asthma, could conceivably be seen at much lower concentrations of SO2. Similarly O3 can cause impairment in lung function at concentrations frequently detected in ambient air in the U.K. in both asthmatics and non-asthmatics with no evidence of an increased effect on asthmatics. This appears to be a restrictive rather than an obstructive defect. Ozone can also cause an increase in airways responsiveness to both non-specific bronchoconstrictors such as histamine and specific allergen. Both these effects are likely to be due to the pro-inflammatory effects of ozone and as such could be implicated both in exacerbating asthma through increased airway responsiveness and causing asthma through triggering an inflammatory reaction in the airways. No study has addressed the important question as to whether the incidence of bronchial hyperresponsiveness is increased in areas of high ozone pollution. The results with NO2 in the laboratory are equivocal. On balance the evidence suggests that any effect on asthmatics is likely to be small. Similarly while inhalation studies with acid aerosols have demonstrated some impairment in lung function in asthmatics the changes have been small and of brief duration. Laboratory studies while raising the level of suspicion and allowing dose response curves to be calculated cannot accurately mimic the effects of real air pollution with its combination of interacting circumstances and effects of prolonged exposure.(ABSTRACT TRUNCATED AT 400 WORDS)

The changing prevalence of respiratory symptoms in atopic children in response to air pollution

Following the promotion of anti-air pollution measures in steam power stations using crude oil, atmospheric concentrations of sulphur dioxide, nitrogen dioxide and suspended particulates have declined. These changes in atmospheric concentrations were accompanied by a decline in the prevalence of respiratory symptoms among schoolchildren living near the power stations. In analysing the correlation between air pollutant concentrations and the prevalence of respiratory symptoms, those with positive skin reactions to house dust extract (the positive group) showed a more significant correlation coefficient compared to those who had never had a positive skin reaction (the negative group). In addition, schoolchildren more heavily exposed to air pollutants showed the higher prevalence of respiratory symptoms than the others. With regard to the kind of air pollutants, both sulphur dioxide and nitrogen dioxide were more closely associated with the prevalence of respiratory symptoms than suspended particulates. This study has therefore demonstrated that the positive group is a useful population for monitoring the health effects associated with low-degree air pollution of gaseous agents.

Asthma and air pollution in the Los Angeles area

Daily asthma attack diaries of 16 panels of asthmatics residing in the Los Angeles area were collected by the Environmental Protection Agency for 34-week periods during the years 1972-1975. There data are examined here for the relationship between daily attack occurrence and daily levels of photochemical oxidant, total suspended particulates, minimum temperature, relative humidity, and average wind speed. A separate multiple logistic regression is used for each panelist's attack data. Variables representing the presence or absence of attack on the preceding day, as well as day of week and time since the start of the study, are included in the regressions. The most significant predictor of attacks was the presence of an attack on the preceding day. On the average, the panelists tended to have increased attacks on days with high oxidant and particulate pollution, on cool days, and during the first two months of the study. Panelists' attack propensity also differed by day of week; in particular they had more attacks on Saturdays (the last day of the weekly reporting period) than on Sundays. Each panelist's regression coefficients are classified according to age, sex, hay fever status, and self-assessed attack precursors; this classification is used to examine subgroups among the panelists with high coefficients corresponding to the above factors.