Strenuous Dynamic Vagus Nerve Testing at Caring Medical Florida

The most important nerve in the body is the vagus nerve and we have two of them - one on each side of the neck. The vagus nerve provides 75% of the total input for the parasympathetic nervous system. The vagus nerves are the longest in the body and go from the brainstem to the innermost depths of the abdomen. They affect every tissue and organ in the body.

A healthy nervous system is one in which both the parasympathetic nervous system (PSNS) and the sympathetic nervous system (SNS) are strong. When sympathetic nervous system (SNS) activity exceeds that of the parasympathetic nervous system, the overall state of the autonomic nervous system is said to be one of sympathetic dominance or overload.

The parasympathetic nervous system (PNS) is the surveyor, conductor, captain, and boss of the body’s internal machinery. The health of the body is determined by the ability of these two vagus nerves to accurately, quickly, and effectively assess everything going on from moment to moment. The vagus nerves assess everything we eat, say, hear, think, and do and help the body make the proper adjustments for vigorous optimal health. With healthy vagus nerves, the overall nervous system is stronger, faster, calmer, and better equipped to handle stress. Strong vagus nerves are correlated with energy, mental alertness, intelligence, and vibrant functioning of the human body.

Poor vagus functioning, called vagopathy or vagal tone, precedes illness. It also perpetuates illness and makes recovery from diseases difficult. Low vagus nerve function has four main manifestations in the human body that increase the risk for almost all human diseases: chronic inflammation, elevated oxidative stress, sympathetic dominance, and coagulopathy.

For this reason, Caring Medical Florida initiated a strenuous dynamic vagus nerve testing protocol to help patients assess the current status of their vagus tone and optimize recovery of it. The state of the nervous system is determined by its status at rest, its response to stress, and then recovery from that stress.  The process of increasing one’s vagus nerve function is vital for life.



Using high-resolution ultrasound, the diameters of the right and left vagus nerves in the neck are obtained. When the vagus nerves are degenerating, meaning neurons within the vagus nerves are dying, the diameter and the cross-sectional area diminish (much like a muscle that is atrophying). With proper treatment, the size of the vagus nerves improves.


The vagus nerves primarily receive blood flow through branches of the external carotid artery but can involve the internal carotid and subclavian arteries. This blood flow is examined by carotid duplex ultrasound scanning. The blood flow is visualized with the person supine and if abnormalities are found, then also while the person is upright and moving their neck in various positions.



The status of the nervous system is first tested at rest. In a comfortable chair, the patient’s vagus and sympathetic vigor is assessed non-invasively by measuring:

  • Pulse
  • Temperature
  • Breathing rate
  • Surface electromyography (EMG)
  • Skin conductance (sweat response)
  • Heart rate variability (HRV)

A healthy person has both a strong PSNS and SNS but at rest, the PSNS should dominate as evidenced by a low pulse, breathing rate, surface EMG activity, and fingertip sweat but high body temperature and HRV. In 95% of the patients that come to Caring Medical, a state of sympathetic dominance (low vagal tone) is found with baseline measurements showing: low HRV and temperature along with a high pulse, breathing rate, and sweat output.


A patient’s vagus nerve response to stress is a direct measure of their health status. Depending on their clinical presentation, the above parameters are monitored while the patient undergoes some of the following stressors:

  • Neck and head position
  • Exercises (i.e. squats)
  • Breath-holding
  • Modified valsalva (inhalation and exhalation against resistance)
  • Breathing rate
  • Noise
  • Music
  • Hauser’s jokes
  • Mathematical or other analytical computations
  • Emotional challenges

A person in vibrant health can respond to challenges, no matter how difficult with a coordinated response from both the PNS and SNS. Once the stressor finishes, the baseline PNS dominance is restored quickly. A sympathetic dominant person exhibits an exaggerated and prolonged sympathetic response to stressors because the stressor causes their system to become even more sympathetic dominant!

Strenuous dynamic nervous system testing helps determine how much of a person’s vagopathy is due to structural issues, such as cervical instability, versus systemic issues such as emotional and other stressors.  It also helps guide other analyses in the office. Blood flow and cervical instability studies (digital motion x-ray) can be done in the neck and head position that produced the most amount of vagus nerve stress, thereby providing an overall picture of the true cause of the patients’ symptoms.

Vagus nerve testing can also be used to teach patients what to do to optimize vagus nerve regeneration. As the patient sits comfortably, the variables that are tested, including pulse, temperature, breathing rate, surface EMG, sweat, and/or HRV, are viewed on a computer screen and a printout is later created. Scenarios are chosen to optimize HRV parameters that correlate best with vagus nerve function and PSNS/SNS balance. A specific breathing rate, type of music, positive affirmations, and/or even neck position are some of the stimuli that will be decided upon to stimulate HRV values to increase!  A take-home HRV finger probe monitor is provided and used at home to optimize health and vitality.


Our hands typically sweat and cool during stressful situations. The sympathetic (galvanic) skin response is through the SNS. It measures the change of skin epidermal resistance due to sweat gland activity. The sweating hands cause the skin conductance to rise and as the sympathetic nerves cause blood vessel vasoconstriction our hands get cold. Someone with low vagal tone and sympathetic dominance has exaggerated responses to stressors, manifested by excessive sweating and skin conductance and low fingertip temperature. As health is restored to the body by enhanced vagal tone, the skin conductance decreases and skin temperature increases.


Heart Rate Variability (HRV) has significant clinical importance! Low HRV is a predictor of both physical and emotional diseases. It also is an indicator of psychological resiliency and behavioral flexibility, reflecting an individual’s capacity to adapt effectively to changing social and environmental demands and stressors. We encourage everyone to get to know their HRV, as well as what improves it and what diminishes it!


Want to learn more about the vagus nerve and cervical instability? Dr. Hauser presented a 3-part webinar series on the vagus nerve, each 2 hours long.

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