A recent study has revealed that even mild cases of COVID-19 can temporarily reduce heart rate variability (HRV), with stress on the autonomic nervous system lasting up to six months, particularly in older individuals.
Several studies have reported that COVID-19 can lead to changes in HRV, with the severity of symptoms correlating to the extent of these changes. However, it remains unclear whether the duration since infection also influences HRV variables. A new study aimed to determine the impact of mild COVID-19 on HRV.
The cross-sectional study was conducted at two universities in Brazil. Researchers hypothesized that individuals previously infected with SARS-CoV-2 experienced reduced HRV with sympathetic predominance in the early stages of infection. Participants were 18 years or older and had tested positive for COVID-19 via RT-PCR between November 2020 and September 2023.
All participants had mild COVID-19 symptoms, including cough, sore throat, diarrhea, vomiting, loss of taste and smell, muscle pain, fever, malaise, and headache. None required hospitalization. Those with a history of moderate to severe COVID-19, illicit drug use, pregnancy, uncontrolled diabetes, cardiovascular disease, or chronic pulmonary disease were excluded.
The study divided participants into three groups: Group 1 (G1) included individuals assessed within six weeks post-infection; Group 2 (G2) comprised individuals evaluated between two and six months after infection; and Group 3 (G3) included those assessed between seven and twelve months post-infection. A control group (CG) consisted of participants recruited before the pandemic who had no history of respiratory, cardiovascular, metabolic, neurological, or systemic diseases. None of the control participants smoked or reported inflammation or pain.
A total of 130 individuals were included in the study, with 31, 34, 30, and 35 participants in CG, G1, G2, and G3, respectively. All groups had similar age distribution, body mass, and height, and none had cognitive deficiencies. The physical activity levels were comparable across groups, based on questionnaire assessments.
G1 had a higher prevalence of hypertensive (35%) and obese (41%) individuals. G2 had a greater proportion of participants with dyslipidemia (27%). G1 also had the highest proportion of unvaccinated participants and individuals reporting symptoms such as fatigue, loss of taste, cough, headache, and anxiety.
Linear HRV measurements were lower in G1 and G2 compared to CG, suggesting autonomic imbalance and sympathetic predominance. Non-linear analysis also indicated a higher level of regularity or complexity in the HRV signal. A regression model revealed that both age and infection duration were significant predictors of HRV changes.
G1 and G2 showed reduced parasympathetic activity compared to CG, indicating increased stress or sympathetic dominance. In contrast, G3 had higher HRV measures, suggesting parasympathetic recovery. While all groups had reduced parasympathetic activity compared to CG, only G1 demonstrated a significant reduction in absolute HF power, indicating a substantial decline in parasympathetic tone.
Low-frequency (LF) power, which reflects sympathetic dominance, was higher in G1 and G2 compared to CG. G3 exhibited reduced LF and LF/HF ratio, suggesting potential recovery or a protective effect at this stage post-infection.
Age was a significant factor affecting standard deviation of normal-to-normal (SDNN) intervals. Hypertension, BMI, and dyslipidemia were not significant predictors, while stress played an important role as a negative predictor of HRV recovery.
The study findings suggest that individuals recovering from SARS-CoV-2 infection are more likely to experience decreased HRV and increased sympathetic activity compared to healthy controls. Recovery time and age were identified as key factors influencing HRV normalization, implying a transient effect of COVID-19 on the autonomic nervous system.
Future longitudinal clinical trials are needed to confirm these observations and further explore the impact of COVID-19 on HRV recovery over time.
