Dysautonomia and Concussion

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What is dysautonomia?

The function and control of the nerves of the body are divided into to multiple systems. The voluntary nervous system includes any action we have active control over, such as commanding the muscles in the arms or legs to move.  The autonomic nervous system consists of commands from our brain to another part of the body, which we do not have to consciously think about, in other words, automatic control of our bodies other systems and function.  Examples of actions controlled by the autonomic nervous system include dilation and contraction of the pupils of the eyes, movement of food through the digestive system, regulation of blood pressure, sweating, or how fast the heart is beating in response to stress or exercise.

The autonomic nervous system is further divided into the sympathetic and parasympathetic nervous systems.  These two systems influence the function of almost every organ in our body. Some of the actions of the sympathetic nervous system have been referred to as the “fight or flight response” while the parasympathetic nervous system has more control over the bodies “rest and digest” functions.  Our brain controls the delicate balance between the sympathetic and parasympathetic nervous systems to ensure all organs function properly.  Any deregulation of this balance is called dysautonomia and can results in problems with stress response, exercise tolerance, or other basic organ functions that we normally take for granted.

How is dysautonomia associated with concussions?

When someone experiences a concussion, connections between the nerves in the brain are damaged and the communication of nerves is disrupted.  Control of the autonomic nervous system is not immune to these disruptions.  Those who experience dysautonomia after a concussion may experience overactive sympathetic nervous system activity.  These individuals may have increased heart rates while resting.  When they attempt to exercise the heart rate may also increase at a faster rate than normal causing symptoms such as headache, dizziness, or nausea. The brain may not regulate blood pressures appropriately in response to changes in body position, such as laying down to standing up, which can cause dizziness or light-headedness.  Poorly regulated blood flow to the brain can also contribute to headaches, attention, or cognitive difficulties.  Dysautonomia may also contribute to increased sensitivity to light, due to the pupils not constricting normally in response to bright lights.

How can dysautonomia be diagnosed?

The symptoms caused by dysautonomia in concussion patients may not always be easy to see. In these instances, dysautonomia symptoms may be more prominent when the patient participates in exercise and then evaluating changes in the function of the autonomic nervous system. This can be done using a number of different exercise tolerance stress tests such as the Buffalo exertion test.  During these tests patients typically start with light exercise on a stationary bike or treadmill and intensity may be gradually increased as tolerated.  As the workload increases the patient is frequently asked to rate the severity of symptoms, such as headache, dizziness, and/or nausea. The addition of heart rate monitors, electrocardiograms and blood pressures cuffs can be used to measure the responses of the autonomic nervous system to exercise.  When dysautonomia is present abnormal heart rate and blood pressure responses to exercise can tip off providers even when athletes don’t endorse any symptoms.

Several other tests are also used to assess dysautomonia including the Valsalva Maneuver Ratio and orthostatic testing.

The Valsalva Ratio is a simple test that can be used to assess dysautonomia.  The patient is asked to bear down by exhaling with their mouth closed to ensure no air escapes and the heart rate is monitored.  Normally the heart rate increases while holding ones breath and then rapidly decrease to below normal before returning to normal.  If the heart rate does not increase and decrease as expected it suggests autonomic dysfunction.

By checking the blood pressure of a patient who is laying flat and comparing it to their blood pressure after they stand you are able to determine if orthostatic hypotension or tachycardia is present. Under optimal autonomic control the blood pressure will normally experience a temporary drop due to the affect of gravity on the blood.  The brain then is able to sense that the blood pressure is low and will return it to normal quickly.  If the blood pressure drops, but then does not return to normal quickly dysautonomia may be present.  During this time the heart rate is also monitored to check for an increased heart rate, or postural tachycardia syndrome, which may occur when the patient moves from a laying to standing position.

Tilt table testing is similar to orthostatic testing, but instead of laying down then standing up, the patient lays on a table that can be moved to different angles, which is moved from a horizontal to a vertical position while heart rate and blood pressure are monitored.

Sweating is also controlled by the autonomic nervous system, and it can be used for testing also. One method involves administering a medication into the skin, which stimulates sweating. Sensors are then used to measure the sweating response in different areas of the body.  An alternative test is done by covering the patient in a powder that changes color when it comes in contact with sweat.  The patient’s body temperature is then increased to cause them to sweat and a special camera is used to see and track the areas that change colors.

How is concussion associated dysautonomia treated?

Active rehab is a treatment option for dysautonomia and prolonged symptoms after a concussion.  It consists of gradual increases in exercise amounts typically over a time period of weeks.  Active rehab is most often started 2-3 weeks after a concussion injury if symptoms are still present, however recent research has suggested it may be beneficial to start as early as 48 hours in some patients.  Exercise testing performed in the doctor’s office will be used to determine what level of exertion is tolerable by the patient.  The patient then exercises within the same parameters each day at home, without exceeding the established tolerable limit. After 1-2 weeks of exercise the patient returns and testing is repeated to establish a new exercise threshold, which is typically a 10-20% increase in duration and intensity.  This continues until the patient is able to return to maximal exertion. This gradual increase in exercise helps to restore autonomic nervous system balance, along with the other benefits exercise offers.


By Dallin Erickson and Mo Mortazavi, MD



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