Abstract

Breathlessness is common in patients after coronavirus disease 2019 (COVID-19) [1]. Patients may have an isolated impairment of gas transfer (diffusing capacity of the lung for carbon monoxide (D_LCO)) at lung function testing, often without obvious interstitial lung disease or classical pulmonary emboli on imaging. Iodine maps from post-COVID-19 patients undergoing dual-energy computed tomography (DECT) demonstrate hypoenhancement in areas of normal lung parenchyma [2] (figure 1). We hypothesised that in breathless patients recovering from COVID-19, low D_LCO would correlate with a computed tomography (CT) marker of lung perfusion, measured using DECT-derived iodine enhancement, including in patients where parenchymal disease was absent. As an even more specific indicator for the pulmonary vascular compartment, we hypothesised that the transfer coefficient of the lung for carbon monoxide (K_CO) (i.e. D_LCO corrected for alveolar volume) would even better correlate with DECT perfusion, and more so than forced vital capacity (FVC) and CT measures of interstitial lung involvement.