Friday, October 3, 2014

Latest Wellness N'At Blog Post: The Neurobiology of Keeping Your Cool, Explained

Originally published here.

Getting Along With Your Vagus Nerve: The Neurobiology of Keeping Your Cool, Explained

brain heartKeeping your cool. Grace under pressure. These familiar idioms describe states that most of us hope to achieve when faced with a stressful situation. So why do some people seem to possess the ability to stay calm and in control, no matter what is happening around them?
Part of the answer may lie in yourvagus nerve. The vagus nerve is one of the twelve cranial nerves (number 10), and the largest. It exits your brain via the medulla oblongata, runs down your neck, and into your chest and abdomen. Along the way, branches of the vagus nerve innervate your heart, lungs, digestive tract, and other abdominal organs.
                Among its many jobs, the vagus nerve helps control your heart rate, breathing, and digestion. When you're resting, it maintains a state of homeostasis. When you're stressed, it helps turn off your body's alarm system, signaling to your brain that it's ok to return to a normal heart rate and breathing pattern. How well your vagus nerve modulates these important functions is often referred to as your level of "vagal tone".
It may seem obvious, then, that we should care about how well our vagus nerves are functioning, given their role in keeping our hearts and lungs running smoothly. However, thanks to a growing body of research on stress and cardiovascular function, we now know that the importance of vagal tone to your overall health and well-being extends even further. People with higher resting vagal tone have been shown to have increased resilience to a variety of stressors and score higher on measures of positive emotions and psychosocial well-being – essentially, a healthy vagus nerve may "buffer" you against social and psychological stressors (1,2,3).
On the other hand, low vagal tone is associated with a prolonged stress response at the basic physiological level – when your body goes into "fight or flight" mode, it takes longer for your vagus nerve to counteract that stress-induced stimulus that shot your heart rate up in the first place – leaving you predisposed to cardiovascular problems both immediately (arrhythmias) and in the future (low vagal tone predicts mortality after heart attacks as well as heart failure) (4,5,6). On the psychological side, chronic stress, anxiety, and low mood are among the factors that have been associated with lower vagal tone (7,8,9).
The good and bad news? Vagal tone is not static – it fluctuates with your physical and mental stress levels. When we push ourselves too hard – an overload of 80 hour work weeks, the overtrained athlete, an onslaught of emotional stressors – vagal tone drops. On the flip side, there's well-researched evidence that you can do things to increase your vagal tone:
Breathe Deeply
Yes, it may be that simple. Deep, slow breathing from your abdomen stimulates the vagus nerve, putting you back into a state of "rest, relax and digest" rather than "fight or flight". An emphasis on deep breathing may be the reason why practices such as meditation and yoga are associated with better vagal tone. This is a technique that can be used in times of acute stress – you've just had a bad meeting at work, so you stop and take a few slow, deep breaths to calm down that stress response—and has carryovers to long-term nervous system health as well.
Exercise
Physical activity (with programs ranging from moderate aerobic exercise (10) to high intensity interval training (11)) has been shown to improve cardiac vagal tone. A good way of indexing this is with heart rate variability– a practical measure of autonomic nervous system function, as greater heart rate variability (HRV - a good thing!) is related to better vagal tone. Regular physical exercise improves HRV in healthy adults as well as individuals with cardiovascular disease. While we haven't figured out precisely how exercise increases HRV and enhances vagal tone, by creating this shift, the amount of work your heart has to do decreases – your resting heart rate and the amount of oxygen consumed by your heart muscle drop. As with the other health benefits of exercise, this is a "use it or lose it" phenomenon – vagal tone can decrease with exercise detraining.
The bottom line? Take a few deep breaths and take it out at the gym the next time your mental and physical alarm bells go off. Your body, your brain, and your heart will thank you for it!
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$4.        Sabbah H. N., Ilsar I., Zaretsky A., Rastogi S., Wang M., Gupta R. C. (2011).Vagus nerve stimulation in experimental heart failure.Heart Fail. Rev.16, 171–178
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$6.        Volders P. G. (2010).Novel insights into the role of the sympathetic nervous system in cardiac arrhythmogenesis.Heart Rhythm7, 1900–1906
$7.        Rozanski A., Blumenthal J. A., Kaplan J. (1999).Impact of psychological factors on the pathogenesis of cardiovascular disease and implications for therapy.Circulation99, 2192–2217
$8.        Lucini D., Di Fede G., Parati G., Pagani M. (2005).Impact of chronic psychosocial stress on autonomic cardiovascular regulation in otherwise healthy subjects.Hypertension46, 1201–1206
$9.        Gorman J. M., Sloan R. P. (2000).Heart rate variability in depressive and anxiety disorders.Am. Heart J.140, 77–83
$10.     Sugawara, J. et al. (2001) Change in post-exercise vagal reactivation with exercise training and detraining in young men. European Journal of Applied Physiology  85 (3-4): 259-263.
$11.     Guirdaud T. et al. (2013) High-intensity interval exercise imrpoves vagal tone and decreases arrhythmias in chronic heart failure. Med Sci Sports Exercise 45(10): 1861-1867
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