# Long COVID Patients with Orthostatic Intolerance Have Reduced Heart Rate Variability and Preserved Physiological Response to Active Standing

## TL;DR

Long COVID patients with orthostatic intolerance have lower heart rate variability at rest but similar responses to standing as healthy people, suggesting possible recovery over time.

## Contribution

The study shows that long COVID patients with orthostatic intolerance have preserved autonomic response to standing despite reduced resting heart rate variability.

## Key findings

- Long COVID patients had lower resting heart rate variability compared to healthy controls.
- Both groups showed similar physiological changes in heart rate variability during active standing.
- The results suggest possible recovery of cardiac autonomic modulation over time post-infection.

## Abstract

A substantial number of patients recovering from COVID-19 develop symptoms three months after infection, lasting at least two months and not explained by other diagnoses, a condition known as long COVID. They include symptoms of autonomic nervous system dysfunction: orthostatic intolerance (dizziness, fainting), fatigue, brain fog, headache, sleep problems, and palpitations. The present study assessed the autonomic nervous system modulation of the heart by performing an analysis of heart rate variability at rest and during standing in patients with long COVID and orthostatic intolerance compared to asymptomatic healthy people. The time from SARS-CoV-2 infection to testing in the COVID-19 group was 573 ± 289 days. Long COVID patients had lower heart variability at rest compared to healthy participants. In response to standing, both groups had similar physiological changes in heart rate variability. This indicates that patients with long COVID and orthostatic intolerance, despite having reduced heart rate variability at rest, do not show immediate autonomic dysregulation upon standing. These results warrant further studies to prove if the cardiac autonomic modulation may recover after the long elapsing time post-infection.

The aim of this study was to assess the heart rate variability (HRV) at rest and during active orthostatic challenge in long COVID patients with orthostatic intolerance symptoms (dizziness, pre-syncope, and syncope). We performed a cross-sectional, observational, comparative study of 60 subjects of both sexes, aged 18 to 60 years (31 met the criteria of long COVID, 15 were infected individuals without symptoms, and 14 who had neither infection nor symptoms formed the age-matched control group). HRV was obtained from continuous electrocardiograms in a supine position and active standing with spontaneous breathing. The time from SARS-CoV-2 infection to testing in the COVID-19 group was 573 ± 289 days. The resting (supine position) values of SDNN, RMSSD, SD1, and SD2 were lower in long COVID patients than in control participants, while all other HRV indexes were similar between groups. In response to active standing, both groups had similar changes in all HRV indices. In conclusion, an active orthostatic test was not able to exhibit an autonomic dysregulation in these patients with long COVID, suggesting that cardiac autonomic modulation may have recovered due to the long time that elapsed after SARS-CoV-2 infection.