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

Long COVID is defined as persistency of symptoms, such as exertional dyspnea, twelve weeks after recovery from SARS-CoV-2 infection.

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.

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.

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 DL_CO at T₃ and T₁₅.

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.