Resposta autonômica cardíaca durante e após exercício máximo é preservada em adultos jovens fisicamente ativos com COVID longa

Abstract

Long COVID (LC) is a condition that generally manifests within three months after acute SARS-CoV-2 infection, with symptoms persisting for at least two months and without an alternative diagnostic explanation. Evidence suggests that alterations in the autonomic nervous system (ANS) may contribute to manifestations such as fatigue, palpitations, exercise intolerance, and post-exertional malaise. Heart Rate Variability (HRV) is a widely used non-invasive method for assessing autonomic modulation and its responses to the physical stress imposed by cardiopulmonary exercise testing (CPET). The present study aimed to investigate the autonomic response of individuals with LC during and after CPET using linear and nonlinear HRV analyses, comparing them with a control group (CON) previously infected with SARS-CoV-2 but without persistent symptoms. Thirty-eight physically active young adults aged 18 to 40 years participated in the study: 18 with LC and 20 previously infected controls without persistent symptoms. Analyses were performed at nine time points: rest, peak exercise, immediately after exercise, and at 3, 5, 10, 30, and 60 minutes and 24 hours after the test. This was an observational study with continuous recording of RR intervals using a heart rate monitor, followed by processing in Kubios HRV software. CPET was performed on a treadmill using the Bruce protocol. Analyses were conducted in RStudio (p < 0.05). After filtering the RR intervals (>95% normal beats), linear and nonlinear HRV metrics were extracted at the nine time points. Normality and homogeneity were assessed using the Shapiro-Wilk and Levene tests. Between-group comparisons were performed using Student's t-test or the Mann-Whitney test, according to data distribution. For analyses over time, three-way ANOVA was applied, followed by post hoc comparisons with Tukey adjustment or false discovery rate (FDR) control. Kaplan-Meier curves were used to estimate the time to autonomic recovery, and the log-rank test was used to compare groups. Associations between age and pNN50 were assessed using Pearson's or Spearman's correlation. The discriminative accuracy of the metrics was investigated using ROC curves and AUC comparisons according to the DeLong method. The hypothesis was that the LC group would exhibit greater vagal withdrawal at peak exercise and slower parasympathetic reactivation. No consistent overall differences were observed between the LC and CON groups for most metrics, with only isolated variations across subgroups and sexes. The findings did not support the hypothesis of autonomic impairment associated with LC in this sample, suggesting that potential effects may be subtle, compensated for by physical fitness, or not detectable by the metrics used. These findings provide data for future investigations and rehabilitation strategies.