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Magnetic Resonance Augmented Cardiopulmonary Exercise Testing

Barber, Nathaniel; (2019) Magnetic Resonance Augmented Cardiopulmonary Exercise Testing. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

The clinical quantitative assessment of exercise capacity is usually achieved through measurement of peak oxygen consumption (VO2) during cardio-pulmonary exercise testing (CPET). In most patients with cardiovascular disease reduced peak VO2 is primarily the result of a limited capacity to augment cardiac output (CO). An important secondary cause is reduced peripheral oxygen extraction. As conventional CPET does not measure CO or tissue oxygen extraction it cannot comprehensively determine the causes of exercise limitation. Invasive CPET combining conventional exercise testing with pulmonary and systemic arterial catheterisation can differentiate the causes of exercise impairment however it is practically challenging, suitable only for limited groups of patients and precluded in children. We developed an alternative non-invasive approach to exercise testing combining real-time magnetic resonance imaging (MRI) flow measurement with respiratory gas analysis, using a system modified for safe use in the MRI environment. Using the Fick equation it is possible to determine the arterio-venous oxygen concentration difference (a-vO2) in addition to CO and VO2 throughout exercise. The first part of this work describes the development of MR-augmented CPET (MR-CPET) and validation in 17 healthy adults. MR-CPET was well tolerated and demonstrated strong correlations with conventional CPET metrics. MR-CPET allowed differentiation of the contributions of a-vO2 and CO to peak VO2. The second part of this work describes the application of MR-CPET in 10 healthy children, 10 with repaired Tetralogy of Fallot (ToF) and 10 children with Pulmonary Arterial Hypertension (PAH). MR-CPET was found to be safe and feasible in all three groups and demonstrated different patterns of abnormal response to exercise in the two disease groups with a significantly lower peak a-vO2 in the PAH group and a greater rest to peak difference in CO but lower peak CO in the ToF group. The final part of this work describes the application of MR-CPET in 13 young adults with the Fontan circulation and 13 matched controls. Adults with the Fontan circulation demonstrated chronotropic incompetence with an inability to augment CO. Although a-vO2 was lower in patients than controls this was not significant.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Magnetic Resonance Augmented Cardiopulmonary Exercise Testing
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
URI: https://discovery.ucl.ac.uk/id/eprint/10071717
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