The autonomic nervous system that controls heart rate, blood pressure, digestion and several other functions has 2 primary divisions, sympathetic and parasympathetic. Generally, we do not control the autonomic system, but rather it simply responds to our environment and circumstances.
The sympathetic system responds to stress, danger and other stimulations increasing heart rate, blood pressure and perspiration while inhibiting digestion. The parasympathetic system slows heart rate, lowers blood pressure and increases digestion. It is activated by relaxation, enjoyable circumstances, meditation, yoga and other similar activities.
Life often “trains” the autonomic nervous system into an imbalanced pattern. This pattern typically involves overactivation of the sympathetic nervous system. Too much stress of any kind begins to teach the system to stay in sympathetic dominance causing ongoing elevation of heart rate, blood pressure and inhibition of digestion. How we shift back and forth from sympathetic to parasympathetic activity will cause the heart rate to constantly increase and decrease. A measure of this, heart rate variability (HRV), is used to demonstrate the balance between the two divisions of autonomic function.
The figure below shows the variation in heart rate from beat to beat measured as the R to R interval. No 2 R to R intervals are exactly the same length.
With healthy balance in the autonomic nervous system, the heart rate speeds and slows down smoothly or in a “coherent” pattern. Overactivity of the sympathetic nervous system generates an “incoherent” heart rate variability pattern. The graphic below shows a training session beginning with an incoherent pattern which is converted to a coherent pattern as the session progresses.
While the autonomic system mostly responds without our direct control, there are body functions that can be voluntarily manipulated to influence autonomic balance. Heart rate variability training uses patterned breathing and imagery during HRV monitoring to help re-train parasympathetic/sympathetic balance lowering blood pressure, relieving stress and improving digestion. We specifically use the HeartMath system which monitors HRV during breath and imagery training.
Observing changes in HRV during these procedures is a form of biofeedback which “teaches” better sympathetic/parasympathetic control. Pre and post session heart rate and blood pressure are also monitored demonstrating the physiologic changes which come from this improved autonomic system balance. The technique is so powerful if done properly that 20-point drops in blood pressure can be seen in about 10 minutes. With time, continued training generates long-term changes in autonomic control.
Some of the change seen with HRV training are thought to involve “learning” in the peripheral autonomic nervous system but also changes in brain activation patterns that control them. This type of training is often combined with neurofeedback which is used to re-train brain activation patterns that have become imbalanced the result of chemical imbalances (food sensitivities, inflammation, etc), mental stress, chronic blood sugar imbalance and other factors.