Persistence of fatigue in the absence of pathophysiological mechanisms in some patients more than 2 years after the original SARS-CoV-2 infection.

Following an acute infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a substantial percentage of patients report the persistence of debilitating symptoms, often grouped in a syndrome termed 'long COVID'. We sought to identify potential pathophysiological mechanisms responsible for the persistence, in some long COVID patients, of symptoms related to fatigue/exercise intolerance (excessive or early fatigue, excessive or early dyspnoea, muscle weakness, and myalgias) more than 2 years after the original infection. Twelve patients who reported persistent symptoms (Long COVID group; 57 ± 6 years, mean ± SD), and 14 patients without the symptoms (Control group; 57 ± 8 years) were evaluated. An extensive series of measurements were performed to identify pathophysiological mechanisms potentially responsible for the symptoms. In long COVID patients, all items evaluating quality of life (SF-36 questionnaire) had lower scores (P < 0.01) compared to control. The habitual level of physical activity, muscle size and strength, maximal aerobic power and the ventilatory thresholds, peak cardiac function, the mechanical efficiency of cycling, pulmonary ${\dot{V}}_{O_2}$ kinetics, microvascular/endothelial function (hyperemic response in the common femoral artery during passive leg movements), skeletal muscle oxidative metabolism (peak fractional O₂ extraction and muscle ${\dot{V}}_{O_2}$ recovery kinetics by the repeated occlusions test, by near-infrared spectroscopy) were not different in the two groups. Evidence of ventilatory inefficiency was described in a subgroup of long COVID patients. More than 2 years after the original SARS-CoV-2 infection, a discrepancy was observed between the persistence of debilitating symptoms of fatigue/exercise intolerance and the absence of several investigated pathophysiological mechanisms. The discrepancy may be due to factors that remain to be elucidated.