Abstract:
One defining characteristic of asthma is the clusters of extremely under-ventilated airways that occur in the lungs during an asthma attack, referred to as ventilation defects (VDs or VDefs for short). There have been extensive studies of open and closed states exhibited by individual airways as well as qualitative analysis of the branching airways of the human lung, but it is still not fully understood how the ventilation defects manifest together in localised regions or under which conditions these VDs arise. An existing model addresses this question for the terminal bronchioles of the lungs, and it is found that by varying the airway smooth muscle pressure, ventilation defects do occur when the total flow conducted through these bronchioles is conserved. However, it leaves the problem as to how VDs occur in the remaining branching airways. The work presented in this thesis attempts to address this problem by developing an original model to describe the dynamic behaviour of the airways that make up the remaining branching tree structure of the lung. Using numerical computation to investigate branching airway behaviour, it is found that varying the airway smooth muscle pressure does not achieve open and closed states in this new model, so the pre-existing model mentioned above is incorporated to include the behaviour of the terminal airways. By combining the two models to simulate the dynamics of the entire lung, it is found that the airway behaviour is similiar to that obtained from the investigation of just the new model of the bronchial tree. However, the addition of the existing model to this new one presents the possibility that varying other parameters associated with the physical properties of the system may also cause ventilation defects to occur.