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Evaluation of long-term sequelae by cardiopulmonary exercise testing 12 months after hospitalization for critical COVID-19

Background: Cardiopulmonary exercise testing (CPET) is an important clinical tool that provides a global assessment of the respiratory, circulatory and metabolic responses to exercise which are not adequately reflected through the measurement of individual organ system function at rest. In the context of critical COVID-19, CPET is an ideal approach for assessing long term sequalae. Methods: In this prospective single-center study, we performed CPET in 60 patients, 12 months after a critical COVID-19 infection that required intensive care unit (ICU) treatment. Lung function at rest and chest computed tomography (CT) scan were also performed. Results: Twelve months after severe COVID-19 pneumonia, the majority of the patients had a peak O2 uptake (VO2) considered within normal limits. However, length of ICU stay remained an independent predictor of VO2. Surprisingly, more than half of the patients with a normal peak predicted VO2 showed ventilatory inefficiency during exercise (high VE/VCO2 ratio and high VE/VCO2 slope) with increased physiological dead space (VD/Vt) and low end-tidal CO2 partial pressure (PETCO2) values. This impairment was even more pronounced in patients with persistent dyspnea. Notably, peak VD/Vt values were positively correlated with peak D-Dimer plasma concentrations from blood samples collected during ICU stay. Conclusions: Even if reduced exercise capacity was rare 12 months after critical COVID-19, more than half of the patients with normal exercise capacity showed ventilatory inefficiency.