Exercise Intolerance in Post-COVID Patients (EXILE)

Physiological Characterization of Functional Limitations and Exercise Intolerance in Post-COVID Patients

The post-COVID syndrome poses an unprecedented challenge to modern society, affecting millions of people worldwide. Persistent fatigue and exercise intolerance are among the most common complaints of these subjects. The mechanisms of exercise intolerance in post-COVID subjects are remained yet unknown, which make the rehabilitation efforts complex and challenging. The overall goals of this project are to: 1) improve physiological understanding of symptoms in this clinical condition, 2) elucidate plausible mechanisms to explain exercise intolerance/symptom exacerbation, and finally 3) provide knowledge that can be directly applied in the clinical setting to improve diagnosis, care, and individualized rehabilitation of subjects with post-COVID syndrome. Post-COVID subjects and age/sex matched healthy controls will undertake a comprehensive set of physiological and functional assessments, followed by 3 experimental visits (in a randomized order), where acute exercise responses will be assessed in either continuous moderate intensity aerobic exercise, high intensity interval exercise, or strength training. The same set of physiological assessments will also be performed after 1 year in both post-COVID subjects and healthy-matched controls to better understand the time course of the syndrome. It is hypothesized that the mechanism responsible for exercise intolerance is linked to specific symptoms and will vary across subjects. However, it is expected that most post-COVID subjects will respond well to at least one type of exercise.

Exercise intolerance, Acute exercise, Skeletal muscle, Cardiorespiratory fitness, Post-COVID syndrome

Upon collection, data will be pseudonymized (both group and intervention) to facilitate unbiased analysis.

Subjects will perform high-intensity-interval exercise, where the acute exercise responses will be closely monitored, including measurements of O2 saturation, blood pressure, ventilatory response, oxygen uptake, and blood lactate. In addition, blood samples will be collected before, immediately after, and 2 hours after each exercise session to describe leukocyte and cytokine release as well as systemic metabolism. After a 48-hour rest period subjects will return to the laboratory for symptom assessment, submaximal exercise response (CPET), and blood sampling.

Subjects will perform moderate intensity continuous exercise, where the acute exercise responses will be closely monitored, including measurements of O2 saturation, blood pressure, ventilatory response, oxygen uptake, and blood lactate. In addition, blood samples will be collected before, immediately after, and 2 hours after each exercise session to describe leukocyte and cytokine release as well as systemic metabolism. After a 48-hour rest period subjects will return to the laboratory for symptom assessment, submaximal exercise response (CPET), and blood sampling.

Subjects will perform a series of a whole-body resistance exercises, where the acute exercise responses will be closely monitored, including measurements of O2 saturation, blood pressure, ventilatory response, oxygen uptake, and blood lactate. In addition, blood samples will be collected before, immediately after, and 2 hours after each exercise session to describe leukocyte and cytokine release as well as systemic metabolism. After a 48-hour rest period subjects will return to the laboratory for symptom assessment, submaximal exercise response (CPET), and blood sampling.

Subjects will perform a series of baseline assessment including neurophysiological function, circulatory and vascular function, respiratory/ventilatory function, maximal oxygen uptake, strength, physical function and fitness, blood status, muscle biopsies, cytokine profiling, and T-cell metabolism.

Subjects will perform the same series of baseline assessment in 1-year time, including neurophysiological function, circulatory and vascular function, respiratory/ventilatory function, maximal oxygen uptake, strength, physical function and fitness, blood status, muscle biopsies, cytokine profiling, and T-cell metabolism.

Post-exercise malaise symptoms of post-COVID subjects and age/sex matched controls in response to different exercise trials.

The score in DePaul Symptom Questionnaire-Post-Exertional Malaise (DSQ-PEM) will be used to assess exercise intolerance (immediately after, 2 hours and 48 hours post) in response to different exercise trials (high intensity interval training, moderate intensity continuous exercise and strength exercise) across the post-COVID subjects and age/sex matched controls.

Absolute immune cell count in blood samples of post-COVID subjects and age/sex matched controls in response to different exercise trials.

Absolute immune count will be assessed via BD TruCount in collected blood samples (before, immediately after, 2 hours and 48 hours post) in response to different exercise trials (high intensity interval training, moderate intensity continuous exercise and strength exercise) across the post-COVID subjects and age/sex matched controls. PBMCs will be analysed for distribution of B cells, NK cells, monocytes, CD4+ T cells, CD8+ T cells, with additional panels to capture plasma, effector and memory cells.

Exploratory metabolomic and cytokine profiling using blood samples of post-COVID subjects and age/sex matched controls in response to different exercise trials.

Metabolomic and cytokine profiling will be explored in collected blood samples (before, immediately after, and 2 hours post-exercise) in response to different exercise trials (high intensity interval training, moderate intensity continuous exercise and strength exercise) across the post-COVID subjects and age/sex matched controls. Olink PEA platform and GC-MS at the Swedish Metabolomics Centre in Umea will be used and targeted analysis will include IL-6, TNF-a and IFN-g profiling.

Exercise (in)capacity of post-COVID subjects and age/sex matched controls in response to different exercise trials.

O2 saturation, blood pressure, ventilatory/VCO2 response, oxygen uptake, and blood lactate will be thoroughly and continuously monitored during each exercise trial (high intensity interval training, moderate intensity continuous exercise and strength exercise) to be used towards exercise (in)capacity assessment across different exercise types in the post-COVID subjects and age/sex matched controls.

Exercise (in)capacity of post-COVID subjects and age/sex matched controls at 48 hours post different exercise trials.

Submaximal exercise response (CPET), including ventilation and VE/VCO2 ratio, O2 saturation, VO2, heart rate, blood lactate, and rating of perceived exertion (RPE) will be used to assess exercise capacity in all participants at 48 hours following each exercise trial (high intensity interval training, moderate intensity continuous exercise and strength exercise).

The validated 6-minute walk test or the Short Physical Performance Battery (SPPB) test will be used to assess physical fitness of post-COVID subjects and age/sex matched controls at baseline (Day 1) and at 1-year follow-up.

Handgrip dynamometer and isokinetic dynamometry (Biodex) will be used to assess muscle strength of upper and lower body respectively in post-COVID subjects and age/sex matched controls at baseline (Day 1) and at 1-year follow-up.

Postural orthostatic tachycardia syndrome (POTS) in post-COVID subjects and age/sex matched controls.

Head-up TILT test will be used to examine the differences in POTS of post-COVID subjects and age/sex matched controls at baseline (Day 1) and at 1-year follow-up.

VO2max on an electronically braked cycle ergometer using an online gas collection system will be performed to assess the differences in cardiopulmonary function of post-COVID subjects and age/sex matched controls at baseline (Day 1) and at 1-year follow up.

Spirometry will be used to examine the differences in pulmonary function of post-COVID subjects and age/sex matched controls at baseline (Day 1) and at 1-year follow up.

Echocardiography will be used to examine the differences in cardiac function of post-COVID subjects and age/sex matched controls at baseline (Day 1) and at 1-year follow up.

A non-invasive ultrasound test, flow-mediated dilation (FMD) will be used to examine the differences in vascular function of post-COVID subjects and age/sex matched controls at baseline (Day 1) and at 1-year follow up.

To examine the differences in neurophysiological function of post-COVID subjects and age/sex matched controls at baseline (Day 1) and at 1-year follow up, as assessed by electroneurography of motor and sensory nerves in the upper and lower extremities (large nerves), standardized quantitative sensory test including a thermal threshold test in the feet and hands (small nerves), sympathetic skin response (SSR) and heart rate variability (HRV) testing (autonomic nervous system), and needle EMG in proximal and distal muscles (integrity of motor units).

A small muscle biopsy (approximately 200 mg) will be taken from the vastus lateralis muscle at baseline and at 1-year follow-up under local anesthesia using the Bergström needle technique in all participants. Histochemical analyzes of fiber size, fiber type, myonuclear content, and gene/protein expression of markers involved in energy processes, muscle atrophy, endothelial dys(function), angiogenesis and mitochondrial biogenesis will be performed in all participants to investigate for any differences across post-COVID subjects and age/sex matched controls.

Inclusion Criteria: Verified positive covid-19 PCR or antigen test Symptoms persisting for at least 3 months Exclusion Criteria: Subject's complaints may have been present before March 2020 Previous history cardiovascular or respiratory disease History of general anxiety syndrome or somatic symptom disorder

Data will be anonymised and available in public database and/or as supplementary data in peer reviewed publications following the completion of the study.