Background: Climate change will increase the average temperature and frequency of heat waves. Many studies have showed that ambient temperature is significantly related to mortality and morbidity. Children have less effective heat adaptation capacity than adults, because of their differences in physiology and baseline metabolism. The prevalence of asthma among children in Australia is the leading cause of burden of disease in children aged 0–14 years in Australia, accounting for 17.9% of the total burden in boys and 18.6% in girls. However, no study has examined the impact of ambient temperature on lung function and respiratory symptoms in children with asthma in Australia.
Aims: This thesis aims to assess the effect of ambient temperature/temperature variability on lung function and respiratory symptoms in children with asthma in Australia. In addition, this thesis aims to discover whether the effects of ambient temperature on lung function in children are different in Australia and China.
Methods and Results: A comprehensive literature review examined the associations between air pollutants and lung function and respiratory symptoms in children. The review found that a panel study with mixed models is a good choice for examining the short-term effects of ambient temperature on lung function and respiratory symptoms, since many studies have used this method to examine the short-term impacts of air pollutants on lung function and respiratory symptoms in children while controlling for the effect of ambient temperature. So, in the thesis, I used a panel study with mixed models to assess the association between temperature and lung function and respiratory symptoms.
In this thesis, a panel of 270 children (7‒12 years) with asthma living in six Australian cities was recruited. They were asked to perform three successive forced expiratory manoeuvres using a portable electronic peak flow meter twice daily for four weeks. The highest values for peak expiratory flow (PEF) and forced expiratory volume in one second (FEV1) were stored for each session. At the same time, they were asked to record their respiratory symptoms (e.g., “cough/phlegm” and “wheeze/chest tightness”) every morning (for night-time symptoms) and evening (for daytime symptoms). Mixed models were used to examine the effects of temperature on lung function, controlling for individual characteristics and environmental factors. I found that ambient temperature was negatively related to both morning and evening PEF and FEV1. In general, the effects of temperature were stronger for boys than for girls for PEF, while the effects for evening FEV1 were stronger for girls. Children with asthma living in southern cities were more sensitive to high temperature than those in the north.
A mixed logistic regression model was used to examine the effects of ambient temperature on respiratory symptoms. I found that the relationships between ambient temperature and respiratory symptoms were linear. Higher temperatures increased the risks of children’s asthmatic symptoms, especially for “wheeze/chest tightness” and to a lesser extent for “cough/phlegm”. With increasing ambient temperature, boys were more at risk than girls.
Mixed models, adjusting for children’s individual characteristics and air pollution, were used to examine the effects of diurnal temperature range (DTR) on lung function and respiratory symptoms. I found that DTR had linear effects on PEF and respiratory symptoms. An increase in DTR induced a reduction in lung function and increased the occurrence of respiratory symptoms.
I also examined the impact of ambient temperature on children’s lung function in spring in Baotou, China, to compare the results with the Australian’s. I found that low temperature was significantly associated with a decrease in lung function in Baotou, China.
Conclusion: The thesis gives a new insight into the association between ambient temperature and lung function and respiratory symptoms in children. The results show that high temperature is a risk factor for children with asthma in Australia. The effect estimates varied by gender and city. Low temperature is negatively associated with children’s lung function in Baotou, China, when data was used only in the spring. The findings can be used to help plan and implement interventions to reduce respiratory problems related to ambient temperature for children.