| Resumo: | <p>Current techniques of assessing respiratory health and cardiovascular function have inherent limitations. Commonly used methods of assessing lung function are generally insensitive to early stage respiratory disease, while techniques for evaluating cardiac output are highly invasive. The aim of this thesis is to demonstrate new techniques for assessing respiratory function and cardiac output that exploit the information encoded within breathing profiles, and which can address these shortcomings.</p>
<p>A molecular flow sensor (MFS) has been developed that utilises laser absorption spectroscopy to measure the number densities of O2, CO2, and H2O every 10 ms in the main airway. Respiratory flow is measured using a custom pneumotachograph. The highly-accurate respiratory profiles recorded by this device during a nitrogen washout procedure are fit to a computational model of lung to provide estimates of lung inhomogeneity. This thesis presents the first applications of this technique in clinical settings, describing a series of studies that evaluated lung inhomogeneity in patients with asthma, chronic obstructive pulmonary disease, and pneumothorax.</p>
<p>A compact Herriott cell was integrated into the MFS, facilitating the measurement of CH4 and C2H2 in addition to the pre-existing spectroscopic systems. C2H2 is soluble in blood, whereas CH4 is relatively insoluble. Thus, analysis of the relative uptake rates of these gases by the body, when small amounts are included in the inspiratory gas, can provide insight into an individual’s cardiac output. This strategy was utilised, with cardiac output assessed by fitting a model of CH4 and C2H2 uptake to MFS recorded data. This method was validated in a study that evaluated healthy volunteers at rest and during moderate exercise on five consecutive days.</p>
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