New Delhi: A new study by researchers from Oxford and Sheffield showed persistent lung damage among recovered Covid-19 patients, even though their CT scans appeared normal. The researchers were able to establish this using a different technology, called a Xenon MRI (Xe MRI) scan.
The study, published in Radiology journal on 25 May, compared the Xe MRI scans of healthy volunteers with the recovered Covid-19 patients, and found that in the latter, there was an “impairment in the transport of gas from the tissue/parenchyma to the red blood cells”.
The participants complained of breathlessness more than three months after recovery, even as their CT scans were “normal or near normal”.
Xenon is a colourless, odourless noble gas that is inhaled by the participant while lying down, just before the MRI scan begins. A Xenon MRI scan is able to traverse all 23 branches of the human lungs and is able to visualise small airways and gas exchange tissues, called the alveolar epithelium. A CT scan, by comparison, visualises the first six branches of the human lungs.
“Many COVID-19 patients are still experiencing breathlessness several months after being discharged from hospital, despite their CT scans indicating that their lungs are functioning normally,” Dr Fergus Gleeson, professor of radiology at Oxford and principal investigator of the study, said in a statement.
“Our follow-up scans using hyperpolarised xenon MRI have found that abnormalities not normally visible on regular scans are indeed present, and these abnormalities are preventing oxygen getting into the bloodstream as it should in all parts of the lungs,” he added.
The study adds to findings about the ongoing effects of ‘Long Covid’ — the condition in which people continue to report symptoms or suffer from bodily damage for weeks or months after testing negative.
Also read: Do I have Long Covid? Here’s what we know about Covid’s lasting effects
What the study says
The study included nine participants aged 51 to 68 years — six men and three women — who had tested positive for Covid-19 through PCR, were hospitalised, and then discharged at least three months before taking part in the study. None had been invasively ventilated during their stay at the hospital.
While the number of participants is very low, which the authors acknowledged as a limitation, they also clarified that the findings are consistent across all individuals.
These participants were compared with five healthy volunteers with negative PCR tests and no history of respiratory disease.
All participants underwent a low-dose CT scan, chest x-ray, and the Xe MRI. The Xe MRI was visualised by calculating the red blood cell to tissue plasma ratio (RBC:TP). While the healthy participants had a RBC:TP ratio of 0.5, the recovered Covid-19 patients had a ratio of 0.3 — termed a “significant decrease”.
This low RBC:TP, the researchers said, is “similar to reports in patients with interstitial lung disease such as idiopathic pulmonary fibrosis”.
Referring to what is now known as Long Covid, the researchers wrote: “Our results are in keeping with the pathogenesis of disease secondary to SARS-CoV-2 virus infection.”
They added: “The abnormalities we have observed specifically reflect the diffusion of xenon across the alveolar epithelium, and therefore the integrity of the alveolar epithelial-capillary structure.”
The researchers also suggested that the damage to the alveolar epithelium, or tissues of the alveoli in the lungs where oxygen passes to the blood, could have happened at the time of initial infection. But they said its persistence as well as possible blood clots in lungs could be contributing to the persistence of symptoms.
The authors also clarified that it is currently unknown when those experiencing such symptoms would eventually recover, and that this is critical to determine future care of recovered Covid patients and the health economic burden.
Also read: What are CT scans, the radiation risk from them & do they cause cancer
XeMRI as a detection tool
Though conducted on a small cohort of people, the results of the study suggest the Xe MRI is a “is potentially a more sensitive technique in detecting pulmonary damage from COVID-19 pneumonia”, and that it is “may be better placed to explain breathlessness in patients with Long COVID, specifically in those with normal or near normal CT scans”.
A statement by the Oxford Biomedical Research Centre said the study is now being extended, and will look at recovered patients who were not hospitalised but going to Long Covid clinics.
Also read: Some Covid long-haulers are baffling doctors with symptoms that go on and on