The physiological determinants of airway hyperresponsiveness in elderly asthma

Abstract

Asthma in the elderly is associated with worse outcomes when compared with asthma in younger populations. It is often underdiagnosed and undertreated, and as a result, elderly asthmatics suffer worse health outcomes from asthma. The primary aim of this thesis was to determine if asthma in the elderly is physiologically different to asthma in younger subjects. Airway hyperresponsiveness (AHR) was used as a physiological marker of asthma. Firstly, we found that the severity of AHR in older asthmatics is predicted by residual volume and peripheral airway ventilation heterogeneity. These predictors are different to those which predict the severity of AHR in younger asthmatics. Secondly, we found that the predictors of AHR severity are different in age matched asthmatics and COPD subjects, indicating that there is a disease-specific abnormality. Thirdly, we found that excessive airway closure with bronchoconstriction increases with disease duration and is predicted by baseline conducting airway ventilation heterogeneity and gas trapping. Finally, we found that increased peripheral airway ventilation heterogeneity in elderly asthmatics is related to lung volumes and not to increases in lung compliance. Thus, these studies provide strong evidence that asthma in the elderly is physiologically different to asthma in young people. Furthermore, they provide new information about the site and nature of the physiological determinants of AHR in the elderly