Pressure and Shear Stress in MS Lesions

Image by Reigh LeBlanc via Flickr

According to Schelling one of the likely causes of MS lesions is venous back jets into the brain. He proposes that one of the possible sources arises from normal cardiorespiratory waves. The other is from trauma. In either case venous blood flows backwards and into the brain.

One route of venous back jets into the brain is through the jugular veins. Schelling proposes that certain people are born with or acquire incompetent valves in the jugulars that fail to check the reverse flows. The other route is through the vertebral veins which have no valves to prevent reverse flows. In the picture above, the jugular veins are the large veins in the front of the neck. The vertebral veins are the smaller veins in the back of the neck. The large veins inside the skull are called dural sinuses.

Typically most, but not all veins have valves to check and prevent back flow. Technically speaking none of the dural sinuses have valves. The alignment of some of the cerebral veins however serves to prevent reverse flows to a limited degree, which I won’t go into here. Disregarding that little piece of not so trivial information, the large veins of the brain basically have no valves.

If you click on the image and enlarge it you will find little boxes with the names of the veins as you mouse over them. Following the veins backwards, upstream and counter current to normal flow, the jugular and vertebral veins next connect to the sigmoid sinus, the S shaped sinus directly above them. The transverse sinus is the short flat sinus that runs from the sigmoid sinus to the back of the skull. At that small circular junction at the back of the skull is another sinus that runs forty-five degrees upward and toward the middle of the brain. It’s called the straight sinus. Going straight up, beyond the junction of the transverse and straight sinus is the largest sinus of the brain that runs up to the top of the brain. It’s called the superior sagittal sinus. The superior cerebral veins attach to it. As an aside, these are the veins mentioned above that attach to the superior sagittal sinus at angles counter current to blood flow. It has been suggested that their angle of attachment may serve as a semi valve-like mechanism.

Now if you follow the straight sinus inward you will see it connects to the Great Vein of Galen, the Basal Vein of Rosenthal and the internal cerebral veins. These veins all drain the core of the brain.  More importantly, regarding this discussion they go to the periventricular areas of the brain. If you click on the picture and enlarge it once more, you will see a large shadow in the middle of the brain. The shadow you see is the lateral ventricle. The ventricles of the brain produce and are filled with cerebrospinal fluid (CSF) which is made mostly of water. CSF cushions, protects and supports the brain. If you look down by the vertebral veins you will see another shadow. That shadow is the spinal cord. Among other things it contains the subarachnoid space surrounding the cord, which is likewise filled with CSF. The subarachnoid space is part of the protective covering of the brain and cord called meninges. The ventricles, subarachnoid space and CSF pathways likewise have no valves. In contrast to being inside the cord, the vertebral veins surround the cord inside the spinal canal.

I would like to put aside cardiorespiratory waves, which I disagree with as a source of injury to the brain, and focus on trauma. In contrast to relatively mild normal cardiorespiratory waves, trauma produces massive uncontrolled forces that can reflux into the brain under significant pressure. In this regard, the vertebral veins contain a large volume of unchecked blood. The subarachnoid spaces at the lumbar cistern of the cord also contain a significant volume of unchecked CSF. Lastly, the valves of the jugular veins have physical limitations which may be easily overwhelmed by massive forces.

According to Schelling venous back jets and massive refluxes from trauma simply follow the course of the dural sinuses. It makes sense then that the lesions in MS tend to show up around the largest veins in the brain and get progressively smaller as you follow the veins upstream counter-current to flow. MS lesions also tend to show up in the periventricular areas, which, as mentioned above, drain into the straight sinus system.  The ventricles are depicted in red in the sketch to the left.

In other words venous blood back jets into the brain and stretches the largest veins of the brain that take the brunt of the crushing force, causing them to balloon out and strain nearby surrounding myelinated nerves. Researchers studying normal pressure hydrocephalus surmized many years ago that stretching from something as simple as edema alone was enough to break myelin. Basically speaking, myelin, is simply no match for the massive forces generated by whiplash and other similar severe type traumas. Trauma can generate significant pressure in the veins of the entire body never mind the brain. What’s more, pressure associated with trauma often causes rapid, acute rises in surrounding tissue pressures.

In contrast to trauma, normal inversion and Valsalva maneuvers cause reverse flows into the brain. Hanging upside down or standing on your head causes inversion flows. A Valsalva maneuver is performed by blowing real hard against maximum resistance. Pilots and scuba divers use Valsalva maneuvers to control pressure in the brain and ears respectively. The famous trumpet player “Satchmo” Louis Armstrong performed Valsalva maneuvers when he played long powerful high sustained notes. His neck and facial veins would buldge and his eyes would literally pop out. Technically speaking, he should have blown his cork before middle age if inversion flows were a problem. Instead he lived a good and long life. Additionally, Olympic style competition weight lifters do Valsalva maneuvers when they lift heavy weights. In this regard, Valsalva maneuvers are beneficial in that they help shore up, stabilize and strengthen the spine.

In light of inversion flows and Valsalva maneuvers, I decided decades ago to study bats, whales and giraffes because of the extreme inversion flows they face during head inversion and deep dives. It turned out to be a great idea. As I expected, these mammals appear to have developed compensatory mechanisms. Based on my studies, it is my opinion that giraffes use the extra large spaces inside their skull called diploe as a drip pan to catch blood that has been rerouted during head inversion. I discussed the diploe in humans and their role in brain cooling in previous posts.

This extra large rather handsome looking giraffe with the beautiful bedroom eyes and full sensous lips, also has a particularly distguished prominent bump over the paranasal bones of the nose. I believe that large giraffes use these extra special, strategically located bumps, called accessory horns, to further increase the capacity of the accessory drainage system of the diploe during head inversion. The challenge for humans is just the opposite. Humans developed compensatory mechanisms to contend with upright posture. Interestingly, the valveless veins of the skull and spine appear to play similar roles in all the mammals mentioned above. What is even more fascinating is that humans and whales use the vertebral veins to stabilize intracranial pressure (ICP) and fluid mechanics in the brain but in completely opposite ways. In brief, moderate inversion flows don’t appear to be the problem. On the other hand, acute venous back jets are an entirely different story.

Unfortunately, back jets don’t explain the full story behind the lesions you find in the cord. Again, that’s where Schelling’s theory makes the most sense. I will discuss cord lesions in MS in my next post. In contrast to massive pressure from venous back jets that stretch nearby myelin in the brain, according to Schelling the myelin in the cord simply snaps due to shear forces acting on attachment points inside the cord itself. Those shear forces are amplified by a Tsunami of CSF waves flowing backwards through the subarchnoid space of the cord.

For additional information on this and related topics visit my website at http://www.upright-health.com.