ABSTRACT
Introduction: There are a growing number of reports of persistently reduced exercise capacities, dyspnea or cough in a small fraction of Covid-19 survivors, suggesting ongoing impaired lung function long after the acute infection has resolved. The cause of these symptoms is unclear, though they likely originate in subtle damage to alveolar septa or vasculature. Here, we present the case of a patient with persistent post-COVID-19 symptoms who was evaluated with hyperpolarized xenon-129 MRI methods, which are sensitive to both ventilation and exchange in both non-specific tissue-plasma and red-blood-cell bound compartments in the lungs. Case: A 58-year-old never-smoker female patient was diagnosed COVID-19 positive in August 2020. She continued to experience nonspecific symptoms of fatigue, pins-and-needles in the feet, dyspnea, and daily productive cough (green, non-bloody sputum). Chest x-ray showed clear lungs without focal consolidation, pleural effusion, or pneumothorax. The subject underwent xenon-129 MR imaging on December 11, 2020 using a multi-breath scheme, in which sets of 6 ad libitum breaths containing 50mL of hyperpolarized xenon-129 (balance room air) were followed by four breaths of room air, and that 10-breath sequence was repeated until the polarized xenon-129 gas supply was exhausted. As shown in Figure 1, ventilated lung volumes are visually patchy, with heterogeneity corresponding to lobar structures or segmental and subsegmental volumes that are likely fed by airways with varying degrees of blockage. This is consistent with the persistent sputum production experienced by the patient. Further, saturation pulses at the frequency of hemoglobin-bound and tissue-plasma xenon-129 resonances selectively destroy signal in their respective compartments, which is subsequently exchanged to the gas phase. Compared to a healthy volunteer, the fractional depolarization achieved when applying identical saturation pulses is reduced by an average of approximately 40% in the patient. The response to saturation pulses also exhibits significant spatial heterogeneity. Discussion: Although a single case study is unable to determine the origin of alterations seen in a recovered COVID-19 patient, these changes are consistent with an overall reduction in the rate of gas exchange into dissolved compartments, as well as with a somewhat heterogeneous pattern of ventilation characteristic of mild obstructive disease. Further studies will be required to determine if these changes are associated with severe or persistent morbidity, and if correspondence to an age-matched healthy cohort increases as recovery continues.