“Operating far below the level of our conscious minds, the vagus nerve is vital for keeping our bodies healthy. It is an essential part of the parasympathetic nervous system, which is responsible for calming organs after the stressed ‘fight-or-flight’ adrenaline response to danger. Not all vagus nerves are the same, however: some people have stronger vagus activity, which means their bodies can relax faster after a stress.
The strength of your vagus response is known as your vagal tone and it can be determined by using an electrocardiogram to measure heart rate. Every time you breathe in, your heart beats faster in order to speed the flow of oxygenated blood around your body. Breathe out and your heart rate slows. This variability is one of many things regulated by the vagus nerve, which is active when you breathe out but suppressed when you breathe in, so the bigger your difference in heart rate when breathing in and out, the higher your vagal tone.”