During a concussion or traumatic brain injury, the soft jelly-like brain tissue is bumped against the inside of the skull causing injury to the nerve tissue of the brain or hemispheres.  What is often overlooked is that the two brain hemispheres receive information via a long tube of nerves called the spinal cord. At the very top, just before this cord blends with the two hemispheres there is a section called the brainstem.
 
The brainstem has integrative functions being involved in cardiovascular system control, respiratory control, pain sensitivity control, alertness and awareness. Thus, brainstem damage is a very serious and often life-threatening problem. It also regulates the central nervous system, and is pivotal in maintaining consciousness and regulating the sleep cycle. So, the brainstem has many basic functions including heart rate, breathing, sleeping, and eating.  Damage of the brainstem can result in abnormalities in the function of cranial nerves that may lead to visual disturbances, pupil abnormalities, changes in sensation, muscle weakness, hearing problems, vertigo, swallowing and speech difficulty, migraine, voice change and co-ordination problems.
 
This brainstem or tail-like structure at the bottom of the rounded brain hemispheres gets stretched and pulled when the head and the brain inside the head gets flicked forwards and backwards during a fall or a blow to the head.  The brainstem is like a cord or rope that is attached to a ball. When the ball gets thrown or kicked that rope or cord gets yanked and pulled where it joins the ball.
 
The difference between a rope and ball versus the brain and the spinal cord is that the spinal cord is made of clusters of soft jelly strings similar in function to telephone wires carrying information to and from the brain to the body.   The brainstem starts level with the bottom of the first neck bone which is 2-3 cm below the bottom of the head. So, the brainstem is not all contained nor protected by the skull. Therefore, the sudden rapid stretching and pulling on the brainstem and spinal cord damages those information pathways. 
 
The brainstem is critical in that most of the bodies automatic activities are controlled from here. Such things as blood pressure, body temperature regulation, breath rate, heart rate, blood flow to and activity of the digestive organs such as the stomach, spleen, liver, kidney, pancreas, the large and small intestines and more. The brainstem even has a direct effect on the hormonal system.
 
A key control system for the organs is the autonomic nervous system which originates in the brainstem. This autonomic system has two parts: the sympathetic part that is like the accelerator in the car which speeds up and readies all the organs, blood flow etc. for action while the other part, the parasympathetic system, is like the brake in a car; it slows everything down and starts the rest and repair phase after a period of high activity. These two parts dance a continuous dance; one responding to the other; one speeding things up the other controlling and slowing things down.
 
When the autonomic system is out of balance, concussion clients can have trouble controlling body temperature so they will be cold and sweating or they might have low energy because one or the other part of that system does not do its complementary part to balance heart rate or blood pressure. This is tiring and makes people feel unwell and unmotivated or they can’t think straight because their brains are trying to make sense of information that it can’t correct or control. Often concussion clients can feel like they are going to black out but never quite do. Other symptoms can be lethargy or in a constant state of high alert or panic. These are just some of the symptoms of autonomic nervous system dysfunction.
 
How does this get assessed?
A simple three-minute test with a plethysmograph gives a pretty good clue if one part of the system is not working nor enough power to bring the system back into balance. 
The plethysmograph is followed up with a treadmill test or the treadmill test can be carried out on its own. This is a test where the client’s heart rate, concussion symptoms and how hard they feel like they are working are closely monitored. If there are sudden changes in any one of those three things; heart rate, effort or symptoms such as headaches increasing, then the test is stopped and a baseline or starting point for treatment using a treadmill or exercycle for a progressive sub-clinical exercise program has been found.   
 
The idea behind the exercise program is to keep the heart working at a set rate forcing the two parts of the autonomic nervous system to work/dance as a complementary inseparable duo again.