Bronchial Responsiveness in Children Exposed to Atmospheric Pollution in Hong Kong: Conclusion
Other factors that may have accounted for the differences between districts include the variation in respiratory symptoms in the two groups of children. Our subsets sampled for histamine were comparable, and only one of the 13 symptoms, wheezing, was significantly higher in the KDT sample. A history of asthma and wheezing was associated with increased BR, but the district effect remained when the asthmatic and wheezing patients were excluded.
The mechanism by which atmospheric pollution increases BR is not entirely clear. Several experimental studies have shown that O311,31,32 and NO2 exposure cause an increase in BR in atopic and nonatopic subjects. Ozone levels are much higher in KDT than SDT, but comparable figures for 19891990 were not available. Sulfur dioxide has also been found to cause a decrease in pulmonary function in allergic subjects. Although there are other studies that have not shown any increase in BR after exposure to pollutants, epidemiologic evidence does support a higher prevalence of BHR and higher BR in subjects exposed to atmospheric pollution Moreover, findings of impaired delayed hypersensitivity and a significantly lower helper/suppressor T cell ratio in exposed children suggests an immune-mediated pathogenetic mechanism.
The possible clinical significance of BHR or enhanced BR is important. In studies among population samples, the prevalence of BHR has varied from 4 to 25 percent, a significant proportion of whom do not have clinical asthma. The BHR is associated with a higher prevalence of respiratory symptoms, but the question remaining is whether it is a useful predictor of asthma, impaired lung growth, and perhaps chronic lung disease. Evidence is emerging that BHR also antedates the onset of asthma comments buy antibiotics online. For this reason, therefore, it is important to have longitudinal data to measure the long-term effects of atmospheric pollution. Increased BR may have some predictive value. It may represent a transient and reversible phenomenon as a result of pollutant exposure, but there may be a critical level or duration of exposure which determines the onset of irreversible changes. A follow-up study on our sample of children may contribute additional information.
This study of a response to a histamine challenge has demonstrated raised BR in healthy children living in an area with high levels of air pollutants and confirmed the results of a previous questionnaire-based respiratory health inquiry in the same district. Following our study, legislation requiring the use of low sulfur fuels was implemented and led to an immediate reduction of both SO2 (84 percent) and RSP (23 percent) in KDT Follow-up studies of BR are in progress and may provide evidence of the effectiveness of these measures in controlling specific pollutants and their effects on respiratory health.