The lognormal lung: quantifying inhomogeneity of ventilation

Thesis

Chronic obstructive pulmonary disease is a significant cause of morbidity and mortality worldwide. Despite this, the most common lung function testing techniques are not sensitive enough to detect the disease in its early stages, limiting opportunities for secondary prevention. It has been shown that measures of inhomogeneity detect signs of the disease earlier than spirometry, the most common form of lung function test. There is however, currently no "gold standard" method for assessing the inhomogeneity of the lungs.

A common technique for investigating inhomogeneity of ventilation is the multi-breath nitrogen washout. During this procedure a patient is switched from breathing room air to pure oxygen, and the concentration of nitrogen in the expired gas is measured as it washes out of the lungs. In this thesis we propose a novel method of assessing the inhomogeneity of the lungs from high quality nitrogen washout data.

This method involves the estimation of parameters from a mathematical model of the lungs which may then be reported as measures of inhomogeneity. The mathematical model we develop aims to represent the underlying physiology well; while having a small parameter set, and governing equations that may be solved quickly and accurately.

Careful attention is also paid to the parameter estimation procedure. We develop a practical approach which uses the available data, and considers computational constraints. We test our method on synthetic data to investigate the uncertainty of the parameters we estimate.

Finally, we present results from a small experimental trial designed to test our method in fifteen volunteers. The results appear promising, with our method distinguishing between the young, the old, and those with respiratory disease. However, there are some inconsistencies in our results. We highlight these, and suggest some areas for future investigation that might improve the work presented in this thesis.

Authors: Mountain, J

• DOI: 10.5287/ora-v05kodqwp
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford