(University of Western Ontario) – Many who experience what is now called “long COVID” report feeling brain fog, breathless, fatigued and limited in doing everyday things, often lasting weeks or months post-infection. Using functional MRI with inhaled xenon gas, researchers have identified for the first time that these debilitating symptoms are related to microscopic abnormalities that affect how oxygen is exchanged from the lungs to red blood cells.
The LIVECOVIDFREE study, based at five centres across Ontario, and led by Western University professor Grace Parraga, is the largest MRI study of patients with long COVID. The research, published in Radiology, is the first to show a potential cause of these long COVID symptoms. By better understanding the cause, team members responsible for patient care are able to target treatment for these patients.
“I think it is always a conundrum when someone has symptoms, but you can’t identify the problem. Because if you can’t identify the problem, you can’t identify solutions,” said Parraga, Tier 1 Canada Research Chair in Lung Imaging to Transform Outcomes at Western’s Schulich School of Medicine & Dentistry.
By having study participants inhale polarized xenon gas while inside the MRI, the researchers see in real time the function of the 300-500 million alveolar sacs that are responsible for delivering oxygen to the blood.
“With our MRI technique, we can watch in real time the air moving through the alveolar membrane and through to the blood cells – and we can actually see the function of the tiny alveolar sacs in the lungs,” said Parraga. “What we saw on the MRI was that the transition of the oxygen into the red blood cells was depressed in these symptomatic patients who had had COVID-19, compared to healthy volunteers.”
Further CT scans pointed to “abnormal trimming” of the vascular tree, indicating an impact on the tiny blood vessels that deliver red blood cells to the alveoli to be oxygenated.
There does not appear to be any difference in severity of this abnormality between patients who had been hospitalized with COVID-19, and those who recovered without hospitalization, the study found. This is an important finding as the latest wave of COVID-19 infection has affected large numbers of people who did not need hospital-based care.
“For those who are symptomatic post-COVID, even if they hadn’t had a severe enough infection to be hospitalized, we are seeing this abnormality in the exchange of oxygen across the alveolar membrane into the red blood cells,” said Parraga.
The researchers recruited patients with suspected long COVID from two hospitals in London, Ontario: London Health Sciences Centre’s (LHSC) Urgent COVID-19 Care Clinic (LUC3), and St. Joseph’s Health Care London’s post-acute COVID-19 program. Participants were those with persistent shortness of breath more than six weeks post-infection. Some study participants were still symptomatic after 35 weeks.
Study co-author Dr. Michael Nicholson, a respirologist with St. Joseph’s post-acute COVID-19 program, said patients who were describing these symptoms were showing normal results on clinical breathing tests.
“We were looking for further modalities to look at their lung function that were not found through traditional clinical testing,” said Nicholson. “The findings allowed us to show that there was a physiological impact on their lungs that correlated with their symptoms.”
A one-year follow-up is under way to better understand these results longitudinally. The study was done in collaboration with researchers at LHSC, St. Joseph’s, Lakehead University, McMaster University, Toronto Metropolitan University, and Sick Kids Hospital in Toronto.