New research suggests that many symptoms of long Covid could be linked to the effect of the virus on the vagus nerve.
Long Covid is a potentially disabling syndrome affecting an estimated 10-15% of subjects who survive COVID-19. Symptoms of long Covid include extreme tiredness, shortness of breath and dizziness.
The vagus nerve extends from the brain down into the torso and into the heart, lungs and intestines, as well as several muscles including those involved in swallowing. This nerve is responsible for a wide variety of bodily functions including controlling heart rate, speech, the gag reflex, transferring food from the mouth to the stomach, moving food through the intestines, sweating, and many others.
The authors propose that SARS-CoV-2-mediated vagus nerve dysfunction (VND) could explain some long COVID symptoms, including dysphonia (persistent voice problems), dysphagia (difficulty in swallowing), dizziness, tachycardia (abnormally high heart rate), orthostatic hypotension (low blood pressure) and diarrhoea.
The new research was presented at this year’s European Congress of Clinical Microbiology and Infectious Diseases.
The relationship between symptoms of long Covid and vagus nerve
The authors performed an extensive morphological and functional evaluation of the vagus nerve, utilising imaging and functional tests in a prospective observational cohort of patients with symptoms of long covid suggestive of VND. In their total cohort of 348 patients, 228 (66%) had at least one symptom suggestive of VND. The current evaluation was performed on the first 22 subjects with VND symptoms (10% of the total) seen in the Long COVID Clinic of University Hospital Germans Trias I Pujol between March and June 2021. The study is ongoing and continues to recruit patients.
Of the 22 subjects analysed, 20 (91%) were women with a median age of 44 years. The most frequent VND-related symptoms were diarrhoea (73%), tachycardia (59%), dizziness, dysphagia and dysphonia (45% each), and orthostatic hypotension (14%). Almost all (19 subjects, 86%) had at least 3 VND-related symptoms. The median prior duration of symptoms was 14 months. Six of 22 patients (27%) displayed alteration of the vagus nerve in the neck shown by ultrasound – including both thickening of the nerve and increased ‘echogenicity’ which indicates mild inflammatory reactive changes.
A thoracic ultrasound showed flattened ‘diaphragmatic curves’ in 10 out of 22 (46%) subjects (which translates to a decrease in diaphragmatic mobility during breathing or more simply abnormal breathing). A total of 10 of 16 (63%) assessed individuals showed reduced maximum inspiration pressures, showing the weakness of breathing muscles.
Eating and digestive functionality
Eating and digestive function were found to be affected in some patients with symptoms of long covid, with 13 of 18 assessed (72%) having a positive screen for self-perceived oropharyngeal dysphagia (trouble swallowing). A further assessment of gastric and bowel function performed in 19 patients revealed eight (42%) had their ability to deliver food to the stomach (via the oesophagus) impaired, with two of these eight (25%) reporting difficulty in swallowing. Additionally, Gastroesophageal reflux (acid reflux) was observed in nine of 19 (47%) individuals; with four of these nine (44%) again having difficulty delivering food to the stomach and three of these nine (33%) with hiatal hernia – which occurs when the upper part of the stomach bulges through the diaphragm into the chest cavity.
A Voice Handicap Index 30 test (a standard way to measure voice function) was abnormal in 8/17 (47%) cases, with 7 of these 8 cases (88%) suffering dysphonia.
The authors commented, “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. Our findings so far thus point at vagus nerve dysfunction as a central pathophysiological feature of long COVID.”