A healthy vagal tone is indicated by a slight increase of heart rate during inhalation, and a decrease of heart rate during exhalation. Deep diaphragmatic breathing—with a long, slow exhale—is vital to stimulating the vagus nerve and slowing heart rate and blood pressure, especially in times of stress or anxiety. A higher vagal tone index is linked to physical and psychological well-being.
The vagus nerve is continuously sending information about the condition of the body's organs to the brain. To close the feedback loop, messages also travel from the brain, through the vagus nerve, to the organs, allowing for an inner-calm necessary for resting and digestion during times of safety or to prepare your body for “fight-or-flight” in dangerous situations.
The sympathetic nervous system thrives on adrenaline and cortisol and is part of the fight-or-flight response, the mechanism by which the body reacts to and deals with stressful or life-threatening conditions and situations. The parasympathetic nervous system, on the other hand, is the polar opposite. The vagus nerve is command central for the function of your parasympathetic nervous system. It acts by slowing body functions: it lowers heart rate, blood pressure, and helps your heart and organs slow down.
To our body’s dismay, the vagus nerve’s reflexive responses can backfire and become an inconvenience. Anytime the psyche is under stress (important event, feeling intimidated, angry or insecure), the vagus nerve interprets it as an actually dangerous situation which exacerbates these negative responses.
All of the physical symptoms of anxiety—racing heart, sweaty palms, dry mouth, upset stomach, nausea &/or vomiting, tremors—are the result of your vagus nerve disengaging. By taking deep abdominal breaths, though, you can minimize these occurrences.