For this prospective study, researchers set out to determine whether previously described lung abnormalities on Hp-XeMRI in post-hospitalized COVID-19 participants are also present in non-hospitalized participants with long COVID.

Eleven non-hospitalized long COVID (NHLC) participants and 12 post-hospitalized COVID-19 (PHC) participants were enrolled from June 2020 to August 2021. All participants had symptoms of breathlessness. NHLC participants were 240-334 days from infection, and PHC participants were 105-190 days from infection. As a control group, healthy volunteers with no evidence of prior COVID-19 infection were recruited from staff at the University of Sheffield and the University of Oxford.


Participants were given chest CT, Hp-XeMRI, pulmonary function tests, one-minute sit-to-stand tests and breathlessness questionnaires. Control subjects underwent HP-XeMRI only. CT scans were analyzed for post-COVID lung disease severity using a previously published scoring system, and Full-scale Airway Network (FAN) modelling. Analysis used group and pair-wise comparisons between participants and controls, and correlations between participant clinical and imaging data. NHLC and PHC participants had normal or near normal CT scans.

"We saw that the ability of gas to transfer from the lungs into the blood stream was less in non-hospitalized patients in comparison to those hospitalized with COVID," Dr. Gleeson said. "Furthermore, both groups of participants had lower dissolved phase Hp-XeMRI values than healthy participants, pointing to potential defects in either the lining of the lung or the surrounding blood vessels."

The results showed that there were significant differences in mean red blood cell to tissue plasma ratio between healthy controls and PHC/NHLC participants, indicating potential differences in lung function.

Although participants had normal or near normal CT scores, total lung diffusion capacity for carbon monoxide percentage was significantly lower between NHLC and PHC participants, potentially indicating a decrease in lung function but not structure.

The researchers said their next step is to expand their study to look at larger numbers of participants seen in dedicated post-COVID clinics at four U.K. centers.

"We will assess different groups of participants who have had COVID and correlate the findings with physiological data, symptom-based questionnaires and cardiac MRI to better understand the clinical significance of our findings," Dr. Gleeson said. "Further work to delineate the nature of the abnormality will also be undertaken which will then enable us to determine whether specific treatments may be beneficial."

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