Last month, we introduced ourselves to the vagus nerve. We learned that it has quite an expansive work area, as it innervates most of our major organs. As part of the parasympathetic nervous system, it regulates our unstressed, rest and digest state. The vagus nerve actually serves to dampen the stress response.
Vagal tone is referring to the function, the activity of the vagus nerve. Strengthening it is referred to as enhancing vagal tone. This is considered by many to be an excellent therapeutic strategy to improve the function and health of the various systems it innervates—such as stimulating the muscles of the digestive tract, decreasing heart rate, and regulating response to stress, fear, and trauma. States of depression and anxiety are related to under-activation of the vagus nerve (low vagal tone).
Having good vagal tone is indexed by something called heart rate variability (HRV). This is not the same as our heart rate, which quantifies how many times the heart beats in a minute. Our heart rate lets us know how strong our heart is, since a well-conditioned heart typically beats less times per minute than a heart that is not.
Heart rate variability, on the other hand, gives us a look into how well the nervous system is operating. It’s the variation of time between heart beats. For example, if a heart beats 60 times per minute, we might think that’s one beat every second, on the second. Not so. There is such a thing as milliseconds, and time measured in milliseconds may vary quite a bit between beats.
A healthy HRV is not like a metronome or a ticking clock, with its precise cadence. Instead, a healthy HRV is one that micro-adapts, has guided, nuanced ebb and flow, senses the needs of any given situation and environment, and adapts immediately. We want variability, not rigidity. It is believed that greater variability between heartbeats—an indicator of adaptability and the ability to manage stress—is associated with better vagal tone.
The value of HRV can be seen when we are under stress. Our heart rate increases. We can feel our pounding heart or faster pulse; but because the source of stress was a false alarm, our nervous system can settle our heart back down. The ability to calmly deal with a situation when under physiological and psychological pressure involves the vagus nerve—and since this nerve regulates our HRV, assessing our HRV can be a window into our vagal tone.
To sum things up, vagal tone has a lot to do with our heart’s ability to respond to stress and how well our body recovers from exercise, or any other kind of stress. Higher HRV means better vagal tone, and lower HRV means weaker vagal tone. Electrocardiograms and HRV monitors are tools that people are using to have a glimpse into vagal tone.
Next month, we will continue looking into this topic, which I hope is becoming increasingly interesting to you.
