A growing list of studies are demonstrating that patients with persistent concussion symptoms have suboptimal delivery of oxygen delivery to the brain. A recent study has specifically tied impairment in working memory with low oxygenation of the dorsolateral prefrontal cortex (DLPRC).
The brain uses approximately 20% of the body’s available glucose and oxygen but only has approximately a 1-second of reserve oxygen, the precise regulation of cerebral blood flow (CBF) is critical for brain function and survival.
From Helmich et al, J Neuropsychiatry Clin Neurosci 2015.
In the diagram above, the thick solid red line above shows increased delivery of oxygen to the DLPFC in healthy controls during a mental challenge. The thin red line that represents individuals with severe concussions showed a decrease in the ability to deliver oxygen to the brain when given the same mental challenge. As a consequence of the impaired oxygen delivery, these subjects performed poorly on testing of their working memory.
The inability to meet the oxygen demands of brain as demonstrated above is primarily responsible for a large proportion of cognitive impairments individuals experience after experiencing a traumatic brain injury.
Blood flow within the brain is regulated by carbon dioxide levels, metabolic demands for glucose and oxygen by the brain as well as the autonomic nervous system. Alteration of these will cause a disruption in the delivery of oxygen and other nutrients to the brain.
Although any portion of the brain can be damaged by a traumatic brain injury, the autonomic nervous system seems to be quite sensitive to physical trauma. The autonomic nervous system is divided into 2 branches, the sympathetic and parasympathetic, and controls blood pressure regulation, all organ function and directly controls a large portion of both the hormone and immune systems.
Damage to the sympathetic branch of the autonomic nervous system commonly leads to poor blood pressure regulation within both the peripheral and central vascular systems. Peripheral dysregulation results in orthostasis, headaches, neck tightness and wide swings in blood pressure. Damage to the central or cerebral regulations results in suboptimal brain oxygen levels with poor memory and concentration as well as increased levels of anxiety.
Traumatic brain injury can prevent the normal increase in sympathetic modulation or decrease in parasympathetic response to the gravitation stress when sitting or standing upright. This translates into a decrease of brain perfusion pressure with resulting inadequate oxygen delivery. Alleviate of the gravitation stress when laying down allows normalization of brain oxygen levels and is why symptoms such as headaches, altered balance and anxiety resolve when supine.
Fortunately, spectral analysis testing of the autonomic nervous system is capable of accurately and quickly detecting autonomic damage. Spectral analysis testing is relatively simple, portable (all equipment fits into a small suitcase), and does not required specialized training to perform. The following example of sympathetic damage after traumatic brain injury illustrates how simple interpretation of spectral analysis reports can be.
This is a portion of the spectral analysis report demonstrating sympathetic damage after sustaining a traumatic brain injury. The red bar indicates the strength of the sympathetic signal from the brain during a 5-minute stand test, and should extend into the grey zone which demotes normal function.
Unfortunately, her brain injury left this athlete with very weak (low) sympathetic function that leads to the low brain oxygen delivery subsequent memory and cognition problems.
Fortunately, the athlete was enrolled in the Autonomic Advantage™ Brain Recovery Program, and their sympathetic function completely recovered (see below) with resolution of their symptoms.
It is important to re-emphasize certain points about autonomics and brain injury:
- Many of the symptoms from traumatic brain injuries are due to the inadequate delivery of oxygen to the brain.
- Damage to the sympathetic branch of the autonomic nervous system is responsible for the impaired delivery.
- Detection of autonomic damage via spectral analysis is inexpensive, fast and portable.
- Autonomic damage is reversible even if the damage has persisted for decades.
Too many athletes are being allowed to return to play in spite of having underlying brain injury because subjective screening assessments are insensitive to detect such damage.
Spectral analysis of the autonomic nervous system is a sensitive, scientifically valid method of detecting the underlying damage commonly associated with many symptoms from brain injury, and needs to be utilized more aggressively to detect and monitor recovery in athletes suffering from traumatic brain injuries.