An interesting article was published this month in Frontiers of Neuroscience exploring the possible connection between the delayed (and progressive) symptoms of CTE and micro trauma from the normal beating of the heart.
There is ample evidence that CTE is caused by repeated brain trauma from external forces (think repeated hits in combat or contact sports). But the symptoms of CTE often don’t show for many years after the hits. And from there the symptoms get progressively worse? Why? The athors of the recent article “The brain’s weakness in the face of trauma: How head trauma causes the destruction of the brain” suggest that each beat of the heart puts a tiny strain on the blood vessels of the brain and over time the beats become the straw which breaks the camels back.
They suggest the initial trauma from repeated hits plays a role. Then theorize that since many cases of Alzheimer’s can be explained by “small vessels (in the brain)…subjected to the pulse and to the shear forces of blood flow (leading to) pulse-induced and age-linked breakdown of these small blood vessels” the same mechanism can explain delayed CTE symptoms with brain structures being initially injured by external trauma and then further degraded over the decades due to this natural relentless internal force.
The authors summarize their theory as follows:
• Dementia pugilistica, CTE, TBI, and Alzheimer’s dementia are the result of trauma to the brain, affecting the capillaries of the brain.
• Alzheimer’s dementia results, potentially in everyone, because the brain is subject to the internal trauma of the pulse, which causes capillary damage, accumulating with age (Stone et al., 2015). Each capillary hemorrhage is clinically silent, but in the later decades of life, the cumulative damage done by the bleeds overwhelms any compensatory mechanisms the brain may have, and clinical symptoms appear, of loss of cognition–Alzheimer’s dementia.
• External trauma, from sports or accident or combat, adds to the internally caused damage, bringing forward the appearance of clinical symptoms. So, external trauma sums with internal trauma.
• The dementias are progressive because the pulse continues, indeed becomes more damaging with age, as the great distributing arteries of the body harden and pulse pressure rises (Stone et al., 2015).
Whether this theory is right or wrong the paper concludes with the following sensibel observation on the “value of life long protection of the brain“
In the mid-20th Century we learnt, the hard way, that our lungs need lifelong protection from inhaled carcinogens, that seemed harmless in our youthful enjoyment of smoking but in later life exacted a death rate of ∼50%. In recent decades we are learning, the hard way, that our brains need lifelong protection from head-knocks that seem harmless in our youthful enjoyment of sports but bring on dementia in later life. It remains then briefly to state the obvious: The level of protection that our brains need cannot be provided in the context of several hugely popular sports. For players, the price of participation is the risk of the destruction of their minds in a healthy body. For carers and society as a whole, the price includes the burden of long pre-mortem care for the afflicted, and the grief of their early death.