Abstract Increasing numbers of COVID-19 patients, continue to experience symptoms months after recovering from mild cases of COVID-19. Amongst these symptoms, several are related to neurological manifestations, including fatigue, anosmia, hypogeusia, headaches and hypoxia. However, the involvement of the autonomic nervous system, expressed by a dysautonomia, which can aggregate all these neurological symptoms has not been prominently reported. Here, we hypothesize that dysautonomia, could occur in secondary COVID-19 infection, also referred to as “long COVID” infection. 39 participants were included from December 2020 to January 2021 for assessment by the Department of physical medicine to enhance their physical capabilities: 12 participants with COVID-19 diagnosis and fatigue, 15 participants with COVID-19 diagnosis without fatigue and 12 control participants without COVID-19 diagnosis and without fatigue. Heart rate variability (HRV) during a change in position is commonly measured to diagnose autonomic dysregulation. In this cohort, to reflect HRV, parasympathetic/sympathetic balance was estimated using the NOL index, a multiparameter artificial intelligence-driven index calculated from extracted physiological signals by the PMD-200 pain monitoring system. Repeated-measures mixed-models testing group effect were performed to analyze NOL index changes over time between groups. A significant NOL index dissociation over time between long COVID-19 participants with fatigue and control participants was observed (p = 0.046). A trend towards significant NOL index dissociation over time was observed between long COVID-19 participants without fatigue and control participants (p = 0.109). No difference over time was observed between the two groups of long COVID-19 participants (p = 0.904). Long COVID-19 participants with fatigue may exhibit a dysautonomia characterized by dysregulation of the HRV, that is reflected by the NOL index measurements, compared to control participants. Dysautonomia may explain the persistent symptoms observed in long COVID-19 patients, such as fatigue and hypoxia. Open access, https://www.nature.com/articles/s41598-021-93546-5
I think this is interesting. All authors from Suresnes, France. The authors seem to acknowledge a biological cause, and yet they still want to treat Long Covid with exercise. So, they had three cohorts - controls, Long Covid with fatigue, and Long Covid without fatigue. They used the NOL Index, which appears to be an objective measure of nociception ("Nociception, in contrast to pain, is not a subjective feeling, but the physiological encoding and processing of nociceptive stimuli" - So, I guess it's a proxy for pain). Note that the NOL index is more than HRV, despite the authors talking mostly about HRV. Also note that the index ranges from 0–100: a NOL of 0 suggests a very low sympathetic activation equal to a nociception free state, while a NOL of 100 suggests high sympathetic activation, representing high nociception levels. Here's the results: So, the people with Long Covid (red and blue) appear to be experiencing less nociception(!) than the controls (or perhaps not reacting normally to the stress of standing?). It's a bit hard to know what was going on without knowing what was going on with the individual components of the NOL Index. Maybe the people with Long Covid have lower blood pressure, or perhaps their peripheral tissues are colder, so there is less sweating? Also the sample sizes of this study were quite small. I think looking at these physiology biomarkers while going through a range of activities from lying down to doing some exercises is a really interesting thing to do. I hope there are more studies on this sort of thing.
A note on Dr Barizien -- he heads the physical medicine and rehabilitation department of the Foch Hospital, on the outskirts of Paris, which has been operating a long Covid clinic named "Rehab-Covid" since June of last year. He is a strong proponent of exercise therapy for long Covid and has recently co-authored a book entitled "Long Covid, how to make it out of it in 8 weeks". It is holistic program he proposes is centered around diet, physical activity, wellness and olfactory rehabilitation.
