Assessment of the muscular metaboreflex in volunteers with exercise intolerance in long COVID: an observational case-control study.
Acute post-COVID-19 syndrome, exercise tolerance, cardiovascular physiological, autonomic nervous system disease, and muscular metaboreflex.
Background: A significant number of COVID-19 patients who have recovered exhibit persistent symptoms, such as fatigue and exercise intolerance, known as Long COVID. Despite numerous studies exploring the correlation between fatigue, exercise intolerance, and autonomic and endothelial dysfunction, the impact of the muscular metaboreflex remains unexplored. Objective: This study aims to investigate the response of the muscular metaboreflex (MRM) in patients experiencing exercise intolerance due to Long COVID. Materials and Methods: This observational case-control, crossover study includes volunteers with long COVID who present exercise intolerance, as determined by the cardiopulmonary exercise test (CPET), from the Federal District and surrounding areas, compared to participants without post-COVID sequelae. Initial assessments will span 4 days: Day (D), moment 1 (D1): clinical assessment, questionnaire administration, and CPET; D2: familiarization with handgrip (HG), assessment of maximum voluntary contraction (MVC), and analysis of endothelial function via flow-mediated dilation (DFM); D3: evaluation of cardiac function using transthoracic echocardiogram and resting electrocardiogram. On D4, following initial assessments and protocol familiarization, the MRM will be assessed using HG with 30% of MVC combined with post-exercise circulatory occlusion (PECO). On that day, volunteers will be randomized into two groups: OCPE- (no PECO after HG exercise) and OCPE+ (undergoing PECO). During the MRM protocol, autonomic function will be assessed using heart rate variability; blood pressure and heart rate will be monitored using an automatic oscillometric monitor; blood flow and peripheral vascular resistance will be evaluated using ultrasound; and peripheral muscle oxygen extraction will be analyzed using near-infrared spectroscopy. Expected Results: The potential outcomes of this study may reveal a blunted MRM response, autonomic dysfunction, compromised endothelial function, impaired cardiac function, and decreased oxygen extraction from skeletal muscles in patients with Long COVID and exercise intolerance. Such data will enhance comprehension of the MRM's role in this population and elucidate the mechanisms underpinning exercise intolerance. These findings hold clinical significance for the advancement of future assessment and therapeutic approaches for this condition, fostering enhanced prognosis and quality of life