Many symptoms of post-COVID syndrome could be caused by lasting damage sustained to one of the most important nerves in the human body during initial infection with coronavirus, new research has suggested.
What is the vagus nerve?
The vagus nerve is the 10th cranial nerve and is the longest and most complex of all of them. It runs from the brain throughout the entirety of the face and chest, reaching the abdomen. The vagus nerve serves as the main connection between the brain and the gastrointestinal tract, sending back information about the state of the inner organs.
As well as being crucial to the gastrointestinal system, as it controls the transfer of food from the mouth to the stomach and moves food through the intestines, the vagus nerve is also responsible for multiple other processes, such as controlling the heart rate, sweat production and the gag reflex, as well as certain muscle movements in the mouth, including those necessary for speech.
New research set to be presented at this year’s European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) investigates the connection between post-COVID syndrome, also known as long COVID, and the vagus nerve.
The pilot study was authored by Dr. Gemma Lladós and Dr. Lourdes Mateu of the Germans Trias i Pujol University Hospital in Badalona, Spain. Its findings will be presented at the congress in Lisbon from April 23-26.
Common symptoms of long COVID
The study suggests that SARS-CoV-2-mediated vagus nerve dysfunction (VND) could be responsible for many of the symptoms of long COVID, including persistent voice problems, difficulty swallowing, dizziness, abnormally high heart rate (tachycardia), low blood pressure and digestive issues.
Long COVID is a condition characterized by persistent and continuous health issues caused by COVID-19 after the patient has recovered from the initial infections. It can affect nearly every organ in the body, as well as cause a range of mental-health and nervous-system disorders. Some of the most common symptoms of long COVID include fatigue, headaches, shortness of breath, loss of smell and taste and muscle weakness.
To further understand the phenomenon, the researchers used imaging and functional tests, as well as a morphological and functional evaluation of the vagus nerve, in an assessment of patients with long COVID who had one or more signs of VND.
Out of the 348 patients taking part in the study, two-thirds (228) had at least one symptom of VND among their long COVID symptoms. After the initial assessments were completed, further evaluations were conducted on a test group of 22 patients, who all had VND symptoms.
Of the 22 subjects analyzed, 20 were women with a median age of 44. The symptoms had been present in the participants for an average of 14 months.
The most frequent VND symptoms presented were diarrhea (73% of subjects), tachycardia (59%) and dizziness, difficulty swallowing and voice problems (45% each). An additional 14% of patients suffered from low blood pressure.
Overall, 86% of the patients assessed had at least three different VND-related symptoms.
Furthermore, in six of the 22 patients, there were visible changes in the vagus nerve in the neck, which could be seen in ultrasounds, including thickening and the indication of mild inflammatory reactive changes.
Ten of the patients in the study showed abnormal breathing patterns and reduced maximum inspiration pressures, indicating weakness in the breathing muscles, which are also connected with the vagus nerve.
Multiple patients also showed changes in digestive function, with 13 of 18 assessed (72%) also having a positive screening for oropharyngeal dysphagia, or trouble swallowing, which can affect the digestive process. Eight patients showed signs of reduced or impaired ability to deliver food to the stomach via the esophagus, with others suffering from acid reflux.
One step closer to treatment
As the exact cause of long COVID and the reason why symptoms present in such a varied way from patient to patient is not currently known, the study’s findings could significantly impact and change the understanding and treatment of the condition going forward.
“In this pilot evaluation, most long COVID subjects with vagus nerve dysfunction symptoms had a range of significant, clinically relevant, structural and/or functional alterations in their vagus nerve, including nerve thickening, trouble swallowing, and symptoms of impaired breathing,” the study’s authors wrote. “Our findings so far thus point at vagus nerve dysfunction as a central pathophysiological feature of long COVID.”