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The effect of indoor pollutants on exhaled nitric oxide in healthy children

Franklin, Peter James (2000) The effect of indoor pollutants on exhaled nitric oxide in healthy children. PhD thesis, Murdoch University.

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Air pollution in the home has been associated with asthma and asthma-like symptoms in children. To understand how they contribute to the initiation and/or exacerbation of asthma, the toxic effects of these pollutants on the human respiratory system have been studied under controlled laboratory conditions. In these clinical studies exposure is short and concentrations are generally higher than those encountered on a daily basis. Domestic levels of air pollutants are quite low and little is known about how chronic exposure to these low level pollutants can affect asthma prevalence and severity. Inflammatory changes in the airways are important for both the development of asthma and triggering of symptoms. The main aim of this thesis was to investigate the effects of selected indoor pollutants on exhaled nitric oxide, a marker of asthmatic airway inflammation, in healthy children. The primary objective was to improve our knowledge regarding a possible mechanism by which these pollutants can contribute to asthma in children.

The research was divided into two parts. In the first part methodological and physiological factors that can affect measurements of exhaled nitric oxide in a healthy paediatric population were investigated. One hundred and fifty seven children aged between 6 and 13 years were recruited for this study. Children were recruited from local primary schools via a respiratory health questionnaire and only those children without current respiratory disease or a history of respiratory illness were included. The children underwent a respiratory assessment at the Respiratory Medicine Department of Princess Margaret Hospital for Children (Perth, Western Australia). This included spirometry, a skin prick test and measurement of exhaled nitric oxide. Methodological issues that were investigated included a suitable expiratory flow for children for eNO measurements and the repeatability of eNO measurements. Physiological factors studied included skin prick reactivity (atopy), age, height and spirometric variables (forced vital capacity (FVC) and forced expiratory volume in one second (FEV 1)).

Exhaled NO levels are flow dependent and if the flow is too high differences in eNO levels between subjects is reduced. Three expiratory flows were used (50, 75 and 100 mis'1) for measuring eNO levels in this study. A flow of 75ml.s'1 seemed to be the most comfortable for the children, while, at this flow, there remained good discrimination of eNO levels between subjects. The twenty-four hour repeatability of eNO levels for each expiratory flow was measured in 10 children. The coefficient of repeatability of measurements were 8.3 ppb, 5.2 ppb and 6.3 ppb, respectively, which represents 9.9%, 6.9% and 10.0% of the range of eNO levels at each flow. Two physiological factors were positively associated with eNO levels in healthy children. These were age (p < 0.05) and atopy (p < 0.001). These findings had not been reported previously and the mechanisms require further investigation.

A possible mechanism for the relationship between atopy and raised eNO levels is subclinical inflammation caused by exposure to allergens. To investigate this house dust mite allergen levels were collected from the mattress of those children who had a positive skin prick reaction to house dust mite. Exhaled NO measurements were repeated in these children during the period allergen levels were collected. There was no association between current allergen exposure, as determined by mattress levels, and eNO in these children.

The main part of this thesis was a cross sectional study to investigate the effect of indoor air pollution on eNO levels in healthy children. This study involved 224 children (6 to 13 years old) who were free of respiratory disease. The homes of the children were monitored for formaldehyde and nitrogen dioxide using passive sampling techniques, while their exposure to environmental tobacco smoke was determined by questionnaire. These three pollutants - formaldehyde, nitrogen dioxide and environmental tobacco smoke - were chosen for the study due to reported associations with asthma and evidence that they can induce inflammatory responses in human airways. During the week their homes where monitored the children underwent a respiratory assessment (as above). Neither measured N02 concentrations nor reported smoking in the home were associated with changes in eNO levels in the children. However, children living in homes with formaldehyde levels that were greater than or equal to 50 parts per billion had significantly higher levels of eNO than children exposed to levels less than 50 ppb in the home (15.5 ppb v 8.7 ppb, p < 0.002).

The results of this study suggest that exposure to low levels of air pollution in the home can be associated with inflammatory changes in the airways. These results need to be confirmed and extended in future research. Future studies should include an investigation of how these indoor pollutants affect the developing lungs and immune system in infants, thereby improving our understanding of their role in the initiation of asthma.

Item Type: Thesis (PhD)
Murdoch Affiliation: Division of Science and Engineering
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Dingle, Peter and Stick, Steve
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