An observational study in COVID-19, sponsored by University College, London. Completed at 1 site in United Kingdom. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2023-05-16.
Sponsored by University College, London · Observational
The MEXICO study is an observational study that aims to identify underlying mechanisms contributing to exercise intolerance in the presence of persistent COVID-19 symptoms (Long COVID).
Persistent symptoms of fatigue and severe exercise intolerance have been observed in some patients following infection with CoV-2. Termed 'Long COVID', these symptoms may persist for months after the acute infection has resolved. The mechanisms underlying exercise intolerance in Long COVID are not fully understood and could be the result of dysfunction at any point along the transfer pathway of oxygen from atmosphere to skeletal muscle (uptake in the lungs, heart and blood vessel function and metabolism within skeletal muscle).
The primary objective of the MEXICO study was to identify underlying mechanisms that contributed to exercise intolerance in the presence of persistent covid-19 symptoms (long COVID). Initially it was planned that this would involve a comparison of people with long COVID with and without exercise intolerance. It became clear that recruitment to these two groups was unlikely to complete as while most people with long COVID had some degree of exercise intolerance, severe exercise intolerance was infrequent. Consequently the study was revised to include a reference group of healthy individuals with the primary analysis focusing on a comparison of people with and without long COVID. A comparison of people with long COVID with or without severe exercise intolerance was retained as a secondary exploratory analysis. Ethical approval for the measurements conducted in healthy control subjects was granted by the UCL research ethics Committee.
Revised sample size calculations for study were based on a two-sample t-test (equal variance for simplicity - although the planned analysis would be using a doubly robust potential outcomes method accounting for potential confounders). Sample size estimates were performed using GPower 3.1.9.7 (alpha = 0.05 (two-tailed) and 80% power) assuming that the minimum clinically important difference for the primary outcomes corresponded to a standardized effect size of 0.88 based on previous studies (typically this represents a 10-20% difference in outcome measure). The study was designed to recruit cases and controls in an approximate proportion of 2:1 to enhance the power of the planned substudy analysis. On this basis 32 and 16 participants were required in the long COVID case and healthy group respectively (48 in total).
7,774 studies on the registry are indexed under COVID-19; 482 are open to participants now.
This study's enrollment of 51 is below the median of 260 across 3,188 observational studies indexed under COVID-19.
Browse COVID-19 studies →University College, London is the lead sponsor of 647 studies on the registry; 145 are open to participants now.
Of its 6 completed or terminated interventional studies of FDA-regulated products, 2 (33%) have results posted.
Counted across the registry records on this site, refreshed daily.
Study population (n=51) are either patients with symptoms of Long COVID who have been referred for clinical investigation (with or without severe exercise impairment) or healthy controls.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Patients with prior serological or clinical diagnosis of CoV-2 infection and a referred to the UCLH Long-COVID clinic for persistent fatigue or exercise intolerance.
Healthy sex-matched and age-matched to within 5 years of Long Covid participants were recruited from UCL staff and students.
Patients with prior serological or clinical diagnosis of CoV-2 infection and a referred to the UCLH Long-COVID clinic for persistent fatigue or exercise intolerance and an abnormal walk test criteria included: peripheral oxygen desaturation, \<85% predicted walk distance, a lactate rise\> 1.0 from baseline or a Borg score \> 5 for breathlessness or fatigue at end of test.
Pulmonary function (spirometry)
Pulmonary function (ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) (FEV1/FVC)), measured using spirometry, is a co-primary outcome. Compare pulmonary function between long COVID patients with and without severe exercise impairment.
Time frame: Baseline
Cardiac function (echocardiography)
Cardiac function (ejection fraction), measured by echocardiography, is a co-primary outcome. Characterise and compare cardiac function between long COVID patients with and without severe exercise impairment.
Time frame: Baseline
Microvascular function (microvascular reactivity)
Microvascular reactivity, measured by near-infrared Spectroscopy (NIRS), is a co-primary outcome. Characterise and compare microvascular function between long COVID patients with and without severe exercise impairment.
Time frame: Baseline
Macrovascular function (central BP)
Central blood pressure, measured by pulse wave analysis, is a co-primary outcome. Characterise and compare macrovascular function between long COVID patients with and without severe exercise impairment.
Time frame: Baseline
Skeletal muscle oxidative capacity
Skeletal muscle oxidative capacity (assessed as the rate of oxygen consumption recovery post-exercise), measured using NIRS, is a co-primary outcome. Characterise and compare skeletal muscle oxidative capacity between long COVID patients with and without severe exercise impairment.
Time frame: Baseline
Change in cardiorespiratory fitness (VO2max)
Compare changes in VO2max, measured on cardiopulmonary exercise testing, to changes in key markers of the oxygen transport pathway (the primary outcomes).
Time frame: Baseline and 9 months
Plan to share: Undecided
Ran from May 2021 to primary completion in Jun 2022, 13 months.
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This study is completed, as verified in May 2023. You cannot join it, but the record below documents what was studied.
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