A new technique for diagnosing pulmonary embolism based on respiratory exchange

• Main Author: Magor-Elliott, Snapper
• Format: Dissertation
• Language: English
• Published: University of Oxford 2022
• Subjects: Cardiovascular system; COVID-19 (Disease); Physiology; Pulmonary circulation; Pulmonary gas exchange

This thesis was primarily concerned with whether it would be possible to develop a technique for diagnosing pulmonary embolism without employing ionising radiation. Unfortunately, the COVID-19 pandemic halted experimental work in this area, and so a second aim of this thesis became to determine whether any residual physiological abnormalities in cardiopulmonary function could be detected in patients who had recovered from acute COVID-19 infection. Chapter 1 provides a brief introduction to the hypotheses and goals of the research contained within the thesis. Chapter 2 outlines the key concepts explored by this thesis and reviews relevant literature relating to cardiopulmonary physiology, gas exchange, pulmonary embolism and COVID-19. Chapter 3 describes a pre-existing molecular flow sensing technology and model of the lungs that form the basis of the work in the following chapters. Chapter 4 covers development of a novel model of the circulation and body gas stores which gives estimates of blood gas states across the circulation (and allows recirculation when connected to a model of the lung). This model is validated in Chapter 5, with good reproduction of measured changes demonstrated using a number of experiments that perturb the storage of body gases. Chapter 6 presents a small study collecting gas exchange measurements from hospital patients with suspected pulmonary embolism. Significant differences are observed between pulmonary embolism positive and negative patients when circulatory model estimates of blood gas state are compared with measurements of blood gases from a venous cannula. Chapter 7 extracts data from a cohort of pulmonary embolism negative patients to further investigate the ability of the proposed method to correctly estimate blood gas states in health. In Chapter 8, data were collected from participants who had recovered from COVID-19 infection and several pathological changes to model lung parameters are shown to scale with the severity of initial COVID-19 infection. Chapter 9 presents validation work using enhanced gravity to induce changes in the distribution of lung compliance but not deadspace. The pre-existing lung model successfully disentangled these two sources of expired gas profile smearing. Finally, Chapter 10 concludes this thesis with a summary of my findings, their implications and potential future avenues of research.