People with shortness of breath from long COVID who had not been hospitalized with COVID-19 may have impaired gas transfer not evident on standard imaging such as computed tomography (CT) that is detectable via hyperpolarized 129Xenon MRI (Hp-129XeMRI), according to results of new research recently published in Radiology.
The research also indicated that individuals with long COVID who had not been hospitalized with COVID-19 had significantly lower total lung diffusion capacity for carbon monoxide percent predicted for age and sex (DLCO%) than patients who had been previously hospitalized with COVID-19.
A common characteristic of a syndrome informally known as long COVID or post-COVID-19 condition is the persistence of dyspnea and lung abnormalities for weeks or months after acute COVID-19 has subsided. In such cases, CT and lung function tests may be normal, said researchers for the current study, who noted that a recent study found Hp-129XeMRI was able to detect gas exchange abnormalities not found on CT in patients who were 3 months post hospitalization for COVID-19. The researchers therefore sought to determine whether Hp-129XeMRI could be an effective tool for detecting lung function abnormalities in patients with long COVID who had not been hospitalized for acute COVID-19.
From June, 2020 to August 2021, researchers at the Universities of Oxford and Sheffield in the United Kingdom recruited 3 types of participants for the prospective study: patients who had not been hospitalized for COVID-19 but subsequently showed symptoms of long COVID (non-hospitalized long COVID [NHLC], N=11), patients who had been previously hospitalized with COVID-19 (post-hospitalization COVID [PHC], N=12), and healthy volunteers (N=13) who served as controls.
Participants in the 2 groups diagnosed with COVID-19 underwent low-dose inspiratory chest CT, Hp-129XeMRI, pulmonary function testing, and the 1-Minute Sit-to-Stand Test. These 2 groups of participants also completed a breathlessness questionnaire. Healthy participants had the Hp-129XeMRI only. The investigators evaluated the CT for lung disorder severity.
The Hg-129XeMRI revealed significant differences between healthy controls and both PHC and NHLC participants in mean red blood cell: tissue plasma (RBC:TP; controls, 0.45 ± 0.07 vs PHC, 0.31 ± 0.10 [P =.02]), vs NHLC, 0.37 ± 0.10 [P =.03]) but not between NHLC and PHC patients (P =.26), the investigators reported. The similarity of the findings for the PHC and NHLC groups was also notable for several reasons, said the researchers. The abnormality on Hp-XeMRI was only marginally less in the group of patients who had not been hospitalized and were experiencing long COVID vs patients in the group admitted to hospital for COVID-19, despite the fact that those who had been hospitalized presumably had clinically more severe acute infections. Moreover, “The NHLC participants were also on average further from their initial infection than the PHC group (287 v 149 days),” said the researchers.
The investigators added that “All the NHLC participants in this study with abnormal Hp-XeMRI were imaged more than 6 months after their initial infection, indicating that these abnormalities were not a transient phenomenon following acute infection.”
The researchers also found a difference in gas transfer measured as DLCO% between the NHLC (76 ± 8%) vs PHC participants (86 ± 8%; P =.04). Shortness of breath was evident in NHLC and PHC participants, with a respective average Dyspnea-12 score of 9 ± 5 and 10 ± 5 (P =.67) and Modified Borg Dyspnea Scale pre- and post-Sit to Stand Test of 2 ± 2 and 7 ± 1 and 2 ± 2 and 5 ± 1 (P >.05 in all cases). No significant variances were observed in mean percent forced expiratory volume or forced vital capacity, and no other differences in lung function were perceived, said the investigators.
Study limitations included the small cohort size and a lack of sufficient older participants. The researchers also noted that caution was necessary in interpreting the Hp-129XeMRI findings “as it is unknown whether participants with other respiratory tract infections such as flu have abnormal Hp-XeMRI gas transfer months after infection even when non-hospitalised and with a normal CT.”
Overall, Hp-129XeMRI may be a useful tool in the diagnosis, quantification and follow-up for long COVID, the researchers concluded. “Hp-XeMRI has identified objective impairment in gas transfer in the lungs of non-hospitalised dyspneic Post-Covid-19 condition participants with normal CT scans, providing preliminary evidence that lung abnormalities exist that cannot be detected with conventional imaging,” the authors stated. “The significance and underlying pathophysiology of this abnormality is currently unknown and highlights the need for further research in this field,” they added.
Grist JT, Collier GJ, Walters H, et al. Lung abnormalities depicted with hyperpolarized xenon MRI in patients with long COVID. Radiology. Published online May 24, 2022. doi:10.1148/radiol.220069