Wearable Heart Rate Variability Monitoring, Autonomic Dysfunction and Post-exertional Malaise in Long COVID: An Observational Study.
OBJECTIVES Patients with long coronavirus disease (COVID) experience disabling fatigue, autonomic dysfunction, reduced exercise capacity and post-exertional malaise (PEM). Heart rate variability (HRV) can evaluate autonomic function and monitor overexertion, potentially helping to mitigate PEM. This study aimed to use continuous multi-day HRV recordings to monitor overexertion and study autonomic function in long COVID. METHOD Heart rate and HRV were continuously measured in 121 patients with long COVID (43 ± 11 years, 32% male) and 21 healthy controls (42 ± 13 years, 48% male), with daily life activities tracked in a logbook. Participants underwent a (sub)maximal cardiopulmonary exercise test to determine heart rate at the first ventilatory threshold (VT1) to study HRV responses to exercise at different intensities. RESULTS AND DISCUSSION HRV was lower in patients with long COVID compared with healthy controls during various daily activities and sleep (p = 0.027). Across all exercise intensities surrounding the VT1, HRV remained lower for 24 h in patients compared with controls (p = 0.010). Nighttime HRV decreased with intense exercise and longer durations in patients with long COVID (p = 0.018), indicative of exercise-induced diurnal disturbances of the autonomic nervous system in long COVID. CONCLUSION Heart rate variability, assessed by wearables, suggests autonomic dysfunction in patients with long COVID. The delayed recovery of the sympathovagal balance after exercise close to and above VT1, suggests that the risk of PEM rises above VT1. APPLICATION These results confirm the applicability of wearables to assess autonomic function and manage overexertion in patients with long COVID.