Patients with long Covid might have suffered lung damage that doesn't show up in routine testing, scientists have revealed.
Using cutting-edge MRI imaging, the University of Sheffield managed to detect lung abnormalities in patients living with long Covid.
And they believe it is this damage that can cause breathlessness months after contracting the virus.
The hyperpolarised xenon technology was pioneered by the university and unlike normal MRI scans, this one only takes a few minutes, and as it doesn't require radiation exposure, it has been repeated time after time to track changes to the lungs.
The government-funded study, EXPLAIN, is one of 19 studies that received nearly £40 million in investment from the National Institute for Health Research (NIHR) to improve understanding of long Covid, from diagnosis and treatment, through to rehab and recovery.
Using teams from Sheffield, Oxford, Cardiff, and Manchester, researchers used these specialised scans to investigate how the lungs of long Covid patients are faring.
A hyperpolarised xenon MRI requires the patient to lie in the scanner and breathe in one litre of inert gas xenon - that has been hyperpolarised so that it can be seen using MRI.
As xenon behaves in a very similar way to oxygen, radiologists can then observe how the gas moves from the lungs into the bloodstream.
While a future study will recruit about 400 participants, 36 people took part in the initial pilot study.
Those who took part were then split into three groups, which were: patients diagnosed with long Covid, who had been seen in long Covid clinics and who had normal CT scans, people who’ve been in hospital with Covid-19 and discharged more than three months previously, who had normal or nearly normal CT scans and who are not experiencing long Covid.
The researchers also included a control group of people who didn't have any symptoms of long Covid and who had not been hospitalised from Covid.
After scanning every patient, the researchers discovered that there was "significantly impaired gas transfer" from the lungs to the bloodstream in the long Covid patients when their other tests were normal.
Professor Jim Wild, Head of Imaging and NIHR Research Professor of Magnetic Resonance at the University of Sheffield, said: “Xenon MRI is uniquely placed to help understand why breathlessness persists in some patients post Covid."
Professor Wild who pioneered the diagnostic scanning technique in UK clinical trials added: “Xenon follows the pathway of oxygen when it is taken up by the lungs and can tell us where the abnormality lies between the airways, gas exchange membranes, and capillaries in the lungs.
"This multicentre study is very exciting, and I really look forward to it helping translate lung MRI methods that we have developed further towards clinical use in the UK.”
The study’s Chief Investigator, Fergus Gleeson, a professor of radiology at the University of Oxford, said: “We knew from our post-hospital COVID study that xenon could detect abnormalities when the CT scan and other lung function tests are normal.
"What we’ve found now is that, even though their CT scans are normal, the xenon MRI scans have detected similar abnormalities in patients with long Covid.
“These patients have never been in hospital and did not have an acute severe illness when they had their COVID-19 infection. Some of them have been experiencing their symptoms for a year after contracting COVID-19."
Professor Gleeson, who is also a consultant radiologist at Oxford University Hospitals NHS Foundation Trust, added: “There are now important questions to answer.
"Such as, how many patients with long Covid will have abnormal scans, the significance of the abnormality we’ve detected, the cause of the abnormality, and its longer-term consequences.
"Once we understand the mechanisms driving these symptoms, we will be better placed to develop more effective treatments.”
Dr Emily Fraser, a respiratory consultant who leads the Oxford Post-COVID Assessment Clinic, commented on the study.
She said: “These are interesting results and may indicate that the changes observed within the lungs of some patients with long Covid contribute to breathlessness.
"However, these are early findings, and further work to understand the clinical significance is key.
“Extending this study to larger numbers of patients and looking at control groups who have recovered from COVID should help us to answer this question and further our understanding of the mechanisms that drive long Covid.”
The full EXPLAIN study will recruit 200 long Covid patients with breathlessness, along with 50 patients who have had COVID-19 but now have no symptoms at all.
It also hopes to bring on board 50 patients who have no breathlessness, but do have other long Covid symptoms, such as ‘brain fog’; and 50 people who have never had long Covid who will act as controls for comparison.
Professor Nick Lemoine, Chair of NIHR’s Long Covid funding committee and Medical Director of the NIHR Clinical Research Network, said: “More than a million people in the UK continue to experience symptoms months after having COVID-19, with breathlessness one of the most commonly reported symptoms.
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