Covid-19 may cause significant impairment in gas transfer in lungs of long Covid patients who continue to have  breathlessness even when lung function tests and CT scans are normal, according to preliminary results from the EXPLAIN study, which used hyperpolarized xenon MRI scans to detect lung abnormalities in long Covid patients with breathlessness.¹ These findings, which have been published as a preprint and are yet to be peer reviewed suggest that it is these changes in the lungs that cause long Covid patients to experience some shortness of breath long after recovery.

This UK study evaluated 36 participants, which included 11 patients with long Covid (non-hospitalised Long-COVID [NHLC]) with normal or near normal CT scan attending a post-Covid clinic,  12 patients who had been hospitalized with Covid-19 (post-hospitalised COVID [PHC]) with normal or nearly normal CT scans and did not have symptoms of long Covid; 13 healthy adults, with no history of past Covid-19 or any other history of lung or heart disease or smoking were selected to act as controls.

The NHLC patients underwent Hyperpolarized Xenon Magnetic Resonance Imaging (Hp-XeMRI) for evaluation of lungs. These findings were then compared with the PHC patients with normal or near normal CT scans and the healthy controls. They also underwent spirometry and Dyspnoea-12 score and 1 minute sit-to-stand test.

While other parameters in lung function tests like FEV were normal or near normal in the NHLC and PHC patients (100% and 88%), a significant difference was noted in gas transfer capacity (TLco) between the two groups; 76% vs 86%, respectively.

Significant differences in Ratiometric maps (RBC:TP) mean were also noted between the healthy control group (0.45) and the NHLC/PHC groups (0.35/0.31) “indicating a change in lung compartment volumes between groups”. But this difference was nonsignificant between NHLC and PHC groups. “There were significant differences in CT abnormalities between NHLC and PHC patients (0.3/25 [range 0-2] and 7/25 [range 4-8], respectively) despite similarly impaired RBC:TP.”

The Hp-XeMRI results were abnormal in seven out of the 11 NHLC patients.

This study has demonstrated that despite a normal CT scan, the xenon MRI scan could detect impaired gas transfer in the lungs of patients with long Covid even six months after recovering from the illness. These patients had not been hospitalized indicating that they did not have severe Covid-19, yet they continued to experience symptoms of breathlessness.

According to the researchers, the full EXPLAIN study will recruit 200 long COVID patients with breathlessness + 50 patients who have had COVID-19 but do not have any symptoms + 50 patients who do not have breathlessness, but have other long Covid symptom (e.g. brain fog). Fifty persons who have never had long COVID who will act as controls for comparison.

Reference

1. Gris JT, et al. The investigation of pulmonary abnormalities using hyperpolarised xenon magnetic resonance imaging in patients with long-COVID. medRxiv, posted Feb. 2, 2022, doi: https://doi.org/10.1101/2022.02.01.22269999.