Many of the symptoms associated with post-COVID syndrome or persistent COVID could be related to the effects of SARS-CoV-2 on the vagus nerve, one of the most important nerves with many functions in the body. This is what is suggested by new research carried out by Dr. Gemma Lladós and Dr. Lourdes Mateu, from the Germans Trias i Pujol University Hospital in Badalona (Barcelona, Spain), and colleagues and which will be presented at the European Congress of Clinical Microbiology and Infectious Diseases this year (ECCMID 2022), which will be held in Lisbon from April 23 to 26.
The vagus nerve is responsible for a wide range of bodily functions, including some as important as control of heart rate, speech, the gag reflex -an involuntary defense mechanism that protects the pharynx and throat from foreign bodies-, the transfer of food from the mouth to the stomach, the movement of food through the intestines, or sweating, among others. This nerve extends from the brain to the torso, heart, lungs, and intestines, and to various muscles, including those involved in swallowing.
The researchers hypothesize that vagus nerve dysfunction (VND) due to the impact of coronavirus infection could explain some symptoms of prolonged COVID-19, such as dysphonia (persistent voice problems), dysphagia ( difficulty swallowing), dizziness, tachycardia (abnormally high heart rate), orthostatic hypotension (low blood pressure that occurs when standing up from a sitting or lying position) and diarrhoea.
Vagus Nerve Dysfunction Linked to Prolonged COVID
The authors conducted an extensive pilot morphologic and functional evaluation of the vagus nerve, employing imaging and functional testing in a prospective observational cohort of individuals with prolonged COVID with symptoms suggestive of vagus nerve dysfunction. In their total cohort of 348 patients, 228 (66%) had at least one symptom suggestive of VND. The current evaluation was carried out in the first 22 people with symptoms of VND (10% of the total) treated at the Long COVID Clinic of the Germans Trias i Pujol University Hospital between March and June 2021. The study is still ongoing and continues to recruit patients.
The most frequent symptoms related to VND were: diarrhea (73%), tachycardia (59%), dizziness, dysphagia and dysphonia (45% each) and orthostatic hypotension (14%).
Of the 22 individuals studied, 20 (91%) were women with a median age of 44 years. The most frequent symptoms related to VND were: diarrhea (73%), tachycardia (59%), dizziness, dysphagia and dysphonia (45% each) and orthostatic hypotension (14%). Almost all (19 subjects, 86%) had at least three VND-related symptoms. The median prior duration of symptoms was 14 months. Six of the 22 patients (27%) showed abnormality of the vagus nerve in the neck seen on ultrasound, including thickening of the nerve and increased “echogenicity,” signaling mild reactive inflammatory changes.
A chest ultrasound showed flattened “diaphragmatic curves” in 10 of 22 (46%) subjects (corresponding to reduced diaphragmatic mobility during respiration, or simply abnormal respiration). A total of 10 of 16 (63%) individuals analyzed presented reduced maximum inspiratory pressures, showing weakness of the respiratory muscles.
Some patients also experienced disturbances in feeding and digestive function, with 13 of 18 evaluated (72%) having a positive test for self-perceived oropharyngeal dysphagia (difficulty swallowing). An assessment of gastric and intestinal function in 19 patients revealed that eight (42%) had impaired ability to bring food into the stomach (via the esophagus), and two of these eight (25%) reported difficulty swallowing.
Gastroesophageal reflux was found in nine of 19 (47%) individuals; four of these nine (44%) also had difficulty getting food into the stomach and three of these nine (33%) had a hiatal hernia, which occurs when the upper part of the stomach protrudes through the diaphragm into the chest cavity.
A Voice Handicap Index 30 test (a standard way of measuring voice function) was abnormal in 8/17 (47%) of the cases, and seven of these eight cases (88%) suffered from dysphonia.
The authors have concluded: “In this pilot evaluation, the majority of long-COVID subjects with symptoms of vagus nerve dysfunction had a variety of significant, clinically relevant, structural, or functional alterations in their vagus nerve, including nerve thickening, difficulty swallowing and symptoms of difficulty breathing. Our findings so far point to vagus nerve dysfunction as a core pathophysiologic feature of prolonged COVID.”