Vagus Nerve Dysfunction Types

Within the intricate network of our nervous system, the vagus nerve emerges as an essential player, bridging the brainstem to vital organs like the heart, lungs, and digestive tract. As the longest cranial nerve, its influence extends over a myriad physiological functions. However, its function isn’t always consistent; its activity can manifest as low or high vagal tone, with each presenting its unique set of implications. Additionally, there’s the phenomenon of excessive vagal tone, which can have significant repercussions on health. In this chapter, we will navigate the complexities of these vagal tone variations, exploring their causes, characteristics, and the broader effects on the body’s symphony of functions.

Vagus nerve pathway and innervations

Low Vagal Tone

A lowered functioning or decreased vagal tone can lead to a range of physiological, emotional, and psychological changes. Here is an exhaustive list of potential presentations of a patient with diminished vagus nerve function:

Physiological Symptoms and Signs

• Tachycardia: An increased resting heart rate due to reduced

parasympathetic (vagal) control.

• Reduced Heart Rate Variability (HRV): HRV refers to the

variation in the time interval between heartbeats. Lower HRV

is often seen in conditions with diminished vagal tone and is

associated with increased cardiovascular risk

• Dyspepsia: Problems in digestion due to reduced gut motility.

• Gastroesophageal Reflux Disease (GERD): Reduced vagal tone can

impair the lower oesophageal sphincter’s function, leading to reflux.

• Constipation: Due to decreased gut motility.

• Reduced Gut Secretions: Diminished production of digestive

enzymes and gastric juices.

• Shallow Breathing: Less diaphragmatic and deep breathing,

potentially leading to lower oxygen saturation.

• Elevated Respiration: Higher respiratory rate may indicate low vagal tone or high sympathetic tone.

Emotional and Psychological Symptoms:

• Depression: Reduced vagal tone has been associated with depressive symptoms.

• Anxiety: Reduced parasympathetic activity can lead to heightened

arousal states and anxiety.

• Difficulty in Emotional Regulation: Individuals may have challenges processing and regulating their emotions.

• Reduced Social Bonding: The vagus nerve is believed to play a role in creating feelings of connection and social bonding. Reduced

function can lead to feelings of social disconnection.

• Decreased Resilience to Stress: Reduced capacity to cope with and

recover from stressors.

Cognitive Symptoms:

• Attentional Problems: Difficulties in maintaining attention and

being easily distracted.

• Memory Issues: Potential challenges in memory retrieval and

formation.

Other Potential Symptoms:

• Fatigue: General feelings of tiredness and lack of energy.

• Weakened Immune System: Leading to an increased susceptibility

to infections.

• Difficulty in Swallowing: Due to reduced muscular control in the

oesophagus.

• Voice Changes: Potential hoarseness or changes in voice quality

because the vagus nerve also innervates the larynx.

Potential Behavioural Symptoms:

• Reduced Gag Reflex: The gag reflex can be diminished or absent.

• Difficulty Reading Facial Expressions: Challenges in recognizing

and interpreting others’ emotional facial cues.

Excessive Vagal Tone

Excessive vagal tone, or hyperactivity of the vagus nerve, can manifest with a variety of symptoms. Here’s an exhaustive list and description of potential presentations in a patient with increased vagal function:

Physiological Symptoms and Signs

• Bradycardia: A slower-than-normal heart rate.

• Hypotension: Reduced blood pressure, particularly upon standing

(orthostatic hypotension).

• Syncope: Fainting or sudden, temporary loss of consciousness often due to a drop in blood flow to the brain. This can be triggered by a variety of stimuli, like sudden emotional distress.

• Hyperactive Bowel Sounds: Increased gut motility can lead to more noticeable bowel sounds.

• Diarrhoea: Increased peristalsis and gut motility can lead to frequent bowel movements.

• Stomach Cramping: Due to hyperactivity of the digestive tract

muscles.

• Bradypnea: Abnormally slow breathing rate.

• Dyspnoea: Difficulty breathing.

Emotional and Psychological Symptoms:

• Calmness or Excessive Relaxation: While a balanced vagal tone is

associated with a calm demeanour, excessive vagal tone might make an individual overly calm or relaxed, potentially to the point of apathy.

• Reduced Stress Response: While decreased stress response might

seem beneficial, it could be detrimental in situations that require

prompt and alert reactions.

Cognitive Symptoms:

• Potential Cognitive Lethargy: Overly calm states might make

individuals less reactive or slow to process information.

Other Potential Symptoms:

• Excessive Salivation: The vagus nerve influences salivary gland

secretion.

• Difficulty Swallowing: Dysphagia might occur due to altered

muscular coordination.

Potential Behavioural Symptoms:

• Enhanced Gag Reflex: Increased sensitivity can lead to easy triggering of the gag reflex.

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