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Background: There is a considerable overlap between the clinical presentation of post-COVID-19 condition (PCC) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Many of their common symptoms can be linked to dysregulation of the autonomic nervous system (dysautonomia). This study aimed to objectively assess autonomic function in a general group of patients with PCC and in a group of patients with ME/CFS whose disease was not related to COVID-19. We hypothesize that the similarity in the chronic symptoms of patients with PCC and ME/CFS extends to objective autonomic nervous system abnormalities., Methods: Synchronous recordings of an electrocardiogram and continuous dynamics of blood pressure in the digital artery using the Penaz method were obtained using the spiroarteriocardiorhythmography method in 34 patients diagnosed with ME/CFS, in whom the onset of the disease was not associated with COVID-19, 29 patients meeting the PCC definition and 32 healthy controls. Heart rate variability (HRV) and systolic and diastolic blood pressure variability (BPV) were assessed at rest and in tests with fixed respiratory rates. Indicators of baroreflex regulation (baroreflex effectiveness index and baroreflex sensitivity) were additionally determined at rest., Results: The total power and power of low-frequency and high-frequency of RR interval variability at rest as well as baroreflex sensitivity were significantly lower both in PCC and ME/CFS patients compared to healthy controls. Several diagnostic prediction models for ME/CFS were developed based on HRV parameters. During slow breathing, the HRV parameters returned to normal in PCC but not in ME/CFS patients. The correlation analysis revealed a close relationship of HRV, BPV parameters and baroreflex sensitivity with fatigue, but not with HADS depressive/anxiety symptoms in the ME/CFS and PCC patients., Conclusions: A similar pattern of HRV and baroreflex failure with signs of a pathological acceleration of age-dependent dysautonomia was identified in the ME/CFS and PCC patients. The clinical, diagnostic and therapeutic implications of these findings are discussed, in light of previously described relationships between inflammation, vascular pathology, atherosclerotic cardiovascular disease and autonomic dysfunction.

Background: Chronic fatigue syndrome (CFS) is a complex multisystem disease that affects around 1 million of the Indian population every year and is characterized by persistent fatigue. CFS is related to cardiovascular illness, and cardiovascular autonomic nervous system dysfunction is often seen. We investigated the state of cardiac autonomic function in CFS and associated it with their level of inflammatory markers and disease severity since there is not much research on the subject. Aims and Objectives: The objective of this study is to evaluate cardiac autonomic functions by using heart rate variability (HRV) in patients with CFS and in healthy controls. The study aimed to evaluate the correlation between HRV and inflammatory markers in patients with CFS and in healthy controls. Materials and Methods: Thirty controls and 30 diagnosed cases of CFS were used in the research. The short-term variability of heart rate was used to measure autonomic function. We measured tumor necrosis factor-alpha (TNF-α) and interleukin (IL-10) in 3 mL of overnight fasting serum. TNF-α and IL-10 were used to evaluate the severity of CFS. Results: Patients with CFS showed a substantial reduction in low frequency (LF) (P=0.00*), high frequency (HF) (P=0.00*), LF/HF ratio (P=0.00*), and time domain parameters of HRV, namely RMSSD (P=0.03*), SDNN (P=0.00*), NN50 (P=0.00*) and total power (P=0.00*). Patients with CFS had considerably higher levels of TNF-α. TNF-α and LF/HF ratio and RMSSD, NN50, and HF were shown to have a substantially favorable correlation. Conclusions: Our research indicates a substantial correlation between autonomic dysfunction and inflammatory activity, as well as the severity of CFS. Therefore, we suggest that HRV might be a useful technique for accurately screening CFS patients for autonomic disruption symptoms early on, which can significantly lower morbidity and death in the future. [ABSTRACT FROM AUTHOR]