Ventilatory efficiency in long-term dyspnoeic patients following COVID-19 pneumonia

Background: Long COVID is defined as persistency of symptoms, such as exertional dyspnea, twelve weeks after recovery from SARS-CoV-2 infection. Objectives: To investigate ventilatory efficiency by the use of cardiopulmonary exercise testing (CPET) in patients with exertional dyspnea despite normal basal spirometry after 18 (T18) and 36 months (T36) from COVID-19 pneumonia. Methods: One hundred patients with moderate-critical COVID-19 were prospectively enrolled in our Long COVID program. Medical history, physical examination and lung high-resolution computed tomography (HRCT) were obtained at hospitalization (T0), 3 (T3) and 15 months (T15). All HRCTs were revised using a semi-quantitative CT severity score (CSS). Pulmonary function tests were obtained at T3 and T15. CPET was performed in a subset of patients with residual dyspnea (mMRC >= 1), at T18 and at T36. Results: Remarkably, at CPET, ventilatory efficiency was reduced both at T18 (V'E/V'CO2 slope = 31.4 +/- 3.9 SD) and T36 (V'E/V'CO2 slope = 31.28 +/- 3.70 SD). Furthermore, we identified positive correlations between V'E/ V'CO2 slope at T18 and T36 and both percentage of involvement and CSS at HRCT at T0, T3 and T15. Also, negative linear correlations were found between V'E/V'CO2 slope at T18 and T36 and DLCO at T3 and T15. Conclusions: At eighteen months from COVID-19 pneumonia, 20 % of subjects still complains of exertional dyspnea. At CPET this may be explained by persistently reduced ventilatory efficiency, possibly related to the degree of lung parenchymal involvement in the acute phase of infection, likely reflecting a damage in the pulmonary circulation.