The effect of ambient air pollution on airway function and respiratory symptoms in asthmatics and chronic bronchitics.
A study was performed in the North West of England investigating the effects of air
pollution on various measures of respiratory health in subjects with asthma and chronic
bronchitis. The study consisted of three distinct phases: the collection of peak flow and
symptom diary data during two summers and one winter period; analysis of the data to
investigate any interaction between aero-allergen levels and pollution; and repeated
measurements of asthmatic bronchial hyperreactivity (BHR) on days of differing pollution
levels. The pollutants investigated were ozone, sulphur dioxide, nitrogen dioxide and
black smoke (second summer only) and levels of pollens and spores were also recorded.
A total of 199 peak flow rate/symptom diaries were collected, representing over 4700
person days of data. Seventy five subjects returned adequate peak flow diaries during the
first summer compared with 50 subjects in winter and 63 subjects in the second summer.
Pollution and allergen interaction analysis was performed using data from 35 subjects
found to be methacholine reactors. Thirty eight subjects participated in the repeat
bronchial reactivity testing phase of the study (a total of 109 tests were performed). Daily
mean pollution levels were below World Health Organisation (WHO) guidelines
throughout the study.
Phase 1: Summertime pollution (summer 1991) was found to be associated with small but
significant adverse effects on respiratory health, despite levels of pollution being below
WHO guidelines. The associations were strongest for ozone. These adverse effects could
not be demonstrated during the winter or second summer. Levels of ozone were
considerably lower during the latter two periods of data collection, suggesting that there
may be a "no effect" level of ozone exposure.
Phase 2: Adverse changes in peak flow in association with increases in allergen level
(spore count) were found to be larger the higher the subjects' ozone exposure on the
previous day, suggesting that ozone exposure may have potentiated the effect of the
allergen. However, the magnitude of the enhanced response was small.
Phase 3: Methacholine bronchial hyperreactivity was found to increase with rising levels
of sulphur dioxide and nitrogen dioxide and these changes were not related to variations in
pre-challenge spirometry. Associations were strongest for nitrogen dioxide, accounting for
10% of the variation in within-subject BHR.
In conclusion, this study was able to demonstrate adverse health effects of ambient air
pollution. Although the magnitude of the changes detected was small, they occurred at
levels of pollution below WHO guidelines. Adverse effects of pollution on peak flow and
symptom reporting were only found for the first summer of data collection, during which a
high peak of ozone exposure occurred. An interaction between pollution and allergen
was also found during this first summer. Changes in bronchial reactivity with pollution
were detected despite the low levels pollution that occurred during the second summer.