Jamieson, Alexandra Clare; (2024) An investigation into the mechanisms underlying exercise intolerance in long COVID: insights from clinical and remote measurements. Doctoral thesis (Ph.D), UCL (University College London).

Text Alexandra_Jamieson_PhD_Thesis_Final.pdf - Accepted Version Access restricted to UCL open access staff until 1 March 2025. Download (6MB)

Abstract

The pathogenesis of exercise intolerance and persistent fatigue which can follow a SARS-CoV-2 infection (‘Long COVID’) is not fully understood. The aim of this thesis is to investigate the mechanisms underlying exercise intolerance in long COVID through the application of novel clinical and remote measurements. Near-infrared spectroscopy (NIRS) measures changes in oxygenated and deoxygenated haemoglobin to estimate skeletal muscle oxidative capacity. Development of this method occurred through an exercise protocol comparison and reproducibility study in non-athletic adults. Good agreement between exercise protocols and good reproducibility of oxidative capacity using NIRS was observed. NIRS was applied to adults recruited from a post COVID-19 clinic at University College London Hospital reporting symptoms of exercise intolerance and fatigue. A comparison of the integrated response to exercise, oxidative capacity and microvascular function, between long COVID cases and healthy individuals was performed. Cases exhibited reduced exercise performance on cardiopulmonary exercise testing (CPET) and lower oxidative capacity on NIRS. Autonomic nervous system measures fell below normal limits in a considerable proportion. These multi-system factors might contribute to impaired exercise tolerance in long COVID sufferers. Smartwatches estimate cardiorespiratory fitness and exercise capacity parameters using proprietary algorithms, but their accuracy remains undetermined. Smartwatch parameters were assessed for accuracy, precision and reproducibility during three sub-maximal tests of exercise capacity: 6-minute walk test (6MWT), 3-minute step test (3MST) and 10-chair rise test (10CRT). Smartwatch estimates of cardiorespiratory fitness (V̇O2peak) and remote 6MWT parameters were compared to CPET in two population-based cohort studies which included long COVID cases. Similar exercise performance on CPET but altered HR parameters during remote 6MWT were observed. Step count was more accurate and precise than GPS-measured distance. HR assessment was accurate and reproducible during rest and recovery, but precision and reproducibility declined during exercise. Smartwatches overestimated V̇O2peak. Remote 6MWT parameters were weakly associated with CPET outcomes.

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