vertebral venous capacity limits

A forum to discuss Chronic Cerebrospinal Venous Insufficiency and its relationship to Multiple Sclerosis.

vertebral venous capacity limits

Postby Cece » Wed Aug 03, 2011 1:13 pm

http://jap.physiology.org/content/94/5/1802.full
In contrast, nonjugular drainage patterns insubject 6 seem mainly to follow the VVs as fewer deep cervical veins could be visualized. Combined with a deeper location of the cervical veins, predominantly surrounding the splenius capiti muscles, circular neck compression probably did not result in any significant flow obstruction, explaining the absent VV flow rise. Overall, the additional cervical vein obstruction led to a further VV flow increase of 58 ± 53 ml/min (range: −10 to 140 ml/min), yielding VV flow values compensating 19% (one-fifth) of the jugular drainage capacity. A similar VV capacity of 26% (one-fourth of jugular venous flow) was seen within the upright body position (23).

If you compress the jugular veins when lying down, the vertebral veins will take on 19% of the jugular drainage capacity. Similarly, when upright, without any compressing, they take on 26% of the jugular drainage capacity.

Maybe the vertebral venous drainage system is only capable of taking on a percentage of the jugular drainage, around 26% as seen here. So combined stenoses of up to 26% in the jugulars might be what the body can compensate for. As soon as our stenoses get beyond 26%, the body cannot compensate as well, although it tries. If the jugular stenoses get up to 80 to 100%, as mine did, it would seem that the vertebral venous system, however valiant, cannot compensate.

What do you think? I found this possibly informative.

The article does discuss the role of deep cervical veins and the intraspinal epidural system which the authors assume must be responsible for taking the remaining jugular flow (a rather large 50%) that has been dispersed.
The only moderate further VV flow increase during circular neck compression (8% of total jugular flow) is probably due to a limited compression effect on deep cervical veins caused by their anatomic location (Fig. 2).

While I agree that these veins would play a role as well, how would we know if a percentage of this flow is not dispersed to different veins but instead the flow slows down due to the outflow obstruction? That they did not find anywhere near the total dispersed flow from the jugulars in the vertebral veins or the deep cervical veins could lend support to the outflow obstruction slows down the inflow theory, which would lend support to the idea of hypoxia playing a role in CCSVI.

Dr. Doepp of Germany happens to be an author on this study, from 2002.
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Postby Cece » Wed Aug 03, 2011 3:54 pm

Cerebral venous drainage in humans is thought to be ensured mainly via the internal jugular veins (IJVs). However, anatomic, angiographic, and ultrasound studies suggest that the vertebral venous system serves as an important alternative drainage route. We assessed venous blood volume flow in vertebral veins (VVs) and IJVs of 12 healthy volunteers using duplex ultrasound. Measurements were performed at rest and during a transient bilateral IJV and a circular neck compression. Total venous blood volume flow at rest was 766 ± 226 ml/min (IJVs: 720 ± 232, VVs: 47 ± 33 ml/min). During bilateral IJV compression, VV flow increased to 128 ± 64 ml/min. Circular neck compression, causing an additional deep cervical vein obstruction, led to a further rise in VV volume flow (186 ± 70 ml/min). As the observed flow increase did not compensate for IJV flow cessation, other parts of the vertebral venous system, like the intraspinal epidural veins and the deep cervical veins, have to be considered as additional alternative drainage pathways.

Where did the missing IJV flow go. The VVs were the most prominent alternative pathway, the deep cervical veins the next most prominent. Together they did not come anywhere close to equaling the original figure for flow through the IJV. IJVs were at 720 ml/min, VVs were at 47 ml/min; when the IJVs were compressed, the VVs went up to 128 ml/min. That leaves about 639 ml/min unaccounted for. Their explanation is that, despite the VVs taking so little, all the littler veins must be taking up the slack. I am not sure if this is physiologically possible. Should it not have shown up on the imaging if this were true? A possible alternative explanation for some of the missing flow is that cerebral outflow has slowed due to the outflow obstruction.

Couldn't cerebral perfusion be measured, with bilateral jugular compression and without it, in healthy subjects?
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Postby NZer1 » Wed Aug 03, 2011 10:33 pm

This is good and interesting Cece.
Dr Flanagan has in his book described the flood dynamics quite well.
I think that the answers are going to come from very expensive testing such as a MRI quantum flow study to give more answers.
I have the belief that when blood flow is impeded in one vein all other veins will help with the additional outflow needs. The opposite side jugular for instance also helps when there is flow depletion in its opposite. An example is when there is no opposite vein or when there is a totally occluded vein. There will therefore be parts of the brain that have slow flow because they are distant or positionally at a disadvantage.
Many regions of our brains depend on flow from a set outlet and yes there is a back up or several back ups. The challenge is to provide equal flow and volume with the alternative routes.
Often it is found as we see impeded flow through the jugulars and which areas of the brain will benefit from the improvement is a lottery. There may be other reasons that the flow has been redirected within the brain system as well as the common CCSVI issues.
Most of us have more than one issue and CCSVI requires two plus for a CCSVI dx. So what is the upstream effect? What has to suffer low flow and the ongoing problems, the oxygen depleted blood, the lack of a toxin flushing effect, the lack of glucose and other vital nutrients the brain requires, a sap.
This whole flow issue is a major. It needs lots of effort by researchers to achieve understanding in many diseases that currently have no know cause.
I'll go back to cooking tea now.
Regards, thanks Cece,
Nigel
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Postby NZer1 » Sun Aug 07, 2011 2:25 am

http://uprightdoctor.wordpress.com/2010 ... n-cooling/
"CCSVI, Brain Cooling and Blood Flow
Posted on September 3, 2010 by uprightdoctor

The upper cervical spine plays an important role in the venous drainage system of the brain, brain blood flow and brain cooling. Back pressure against the vertebral venous outlets in the upper cervical spine can thus be a cause of CCSVI, decreased blood flow and decreased cooling capacity of the brain. An overview of the cranial veins will make the connection clear.

The cranial veins include the veins of the face and scalp, the diploic veins, the emmisary veins and the dural sinues. The diploic veins, seen in the picture above, and mentioned in the previous post, sit between the inner and outer plates of the membranous bones of the skull that cover the cranial vault.

The dural sinuses seen in the pictures below are the main drainage routes of the brain inside the cranial vault. They are called dural sinues because they are not true veins. Instead they are tunnels formed by the outer coat of the brain itself, the dura mater. The inside walls of the dural sinuses are lined with the inner walls of veins. The dura mater, which means tough mother or material, makes the dural sinus drainage system much stronger than typical veins. As a result, they are better able to withstand stress and resist deformation from the pressure and movement of the brain, which sits on top of and presses down against them.

The cranial veins of the face and scalp, diploe and dural sinuses are all interconnected by the emissary veins. In contrast to the rest of the body, none of the cranial veins have valves to check or prevent reverse flows. That’s an important fact when it comes to discussing MS lesions, which I won’t go into here.

If you click on the picture to the left and look closely, you will see that the dural sinuses are depicted by stripes inside the skull. You will also see little black semicircles on the top and the bottom of the skull. The semicircles represent emissary veins, which link the face and scalp veins to the diploic veins and to the dural sinues.

The emissary veins play an important role in draining the head and brain. The ones located toward the back and bottom of the skull seen behind the outline of the ear, drain into the vertebral veins of the spine. In addition to drainage, the emissary veins also play a critical role in cooling the brain. They do so by delivering blood, that has been cooled by conduction and sweat evaporation at the surface of the face and scalp, to the diploe and to the dural sinues.

Besides cooling the diploe and dural sinuses, the brain also uses two counter current heat exchanger tunnel systems in the dural sinuses to cool incoming arterial blood before it enters the brain. The two cavernous (dural) sinuses are located inside the cranial vault. If you click on the picture to the right you will see the internal carotid depicted passing through the cavernous sinus before it enters the brain.

The other tunnel is called the suboccipital cavernous sinus, which is also known as the atlantooccipital membrane as depicted in the picture below. The suboccipital cavernous sinus is located just outside the skull between the first cervical vertebra and the occipital bone at base of the skull.


Even though it is outside the skull, studies have shown that the suboccipital cavernous sinus is constructed of nearly identical materials, in the same way and serves the same function as the cavernous sinus. For this reason, some scientists now consider it to be part of the dural sinuses of the brain. The suboccipital cavernous sinus contains and cools the two vertebral arteries before they enter the brain.

Thus, the brain is surrounded by cooled venous blood in the cranium and incoming arterial blood keeping the brain about two to three degrees cooler than the rest of the body. Some physical anthropologists attribute the extra large size of the human brain more to its exceptional cooling capacity than to the increase in arterial blood flow that comes with upright posture. Anthroplogists refer to human encephalization due to enhanced cooling capacity as the “radiator theory.”

Both the cavernous and suboccipital cavernous sinuses also play a role in maintaining blood flow and pressure in the brain. Their inner walls contain pressure sensors called baroreceptors that detect pressure in the tunnels. When pressure goes up they send signals that cause the muscles in the incoming arteries to constrict and decrease blood flow. When pressure drops they signal the blood vessels to open up and increase blood flow. Technically it is called the “neurovascular myogenic autoregulatory reflex mechanism.” As an aside, similar important pressure receptors and blood flow regulators are located in the carotid sinuses near the Adams apple of the throat.

The cranial veins drain into two extracranial venous drainage routes. One route is the jugular veins. The other is the vertebral veins. Interestingly, in contrast to the jugular veins, the vertebral veins have no valves making them similar to the cranial veins. Thus, back pressure against the vertebral veins can affect both the drainage and cooling capacity of the brain. This is interesting in light of the fact that in addition to evidence of CCSVI, MS patients often experience symptoms of heat intolerance.

An increase in pressure in the suboccipital cavernous sinus can also decrease blood flow through the vertebral arteries that pass through it before supplying the inner rear and lower most parts of the brain. It can do so by either direct compression of the vertebral arteries, or by stimulating the pressure sensors in the sinus walls thereby causing the arteries to constrict.

Decreased blood flow through the vertebral arteries can cause a wide variety of symptoms such as fatigue, dizziness, loss of balance and coordination to name a few. The complete list of symptoms is too long to discuss here so I will save it for future posts."
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Postby CureOrBust » Sun Aug 07, 2011 5:41 am

lets not forget reflux.
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Postby 1eye » Sun Aug 07, 2011 7:52 am

NZer1 wrote:An increase in pressure in the suboccipital cavernous sinus can also decrease blood flow through the vertebral arteries that pass through it before supplying the inner rear and lower most parts of the brain. It can do so by either direct compression of the vertebral arteries, or by stimulating the pressure sensors in the sinus walls thereby causing the arteries to constrict.


Are we sure that's how the pressure sensors are used? Being Starling Resistors of sorts, increased pressure might cause an unwanted increase in viscosity. Having a pressure sensor would be awfully convenient, because the arteries could react by expanding against the pressure and counteracting it, thus restoring stasis.
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Postby civickiller » Sun Aug 07, 2011 10:15 am

ill ask Dr. Flanagan to stop by and answer questions

*edit* I pmed Dr. Flanagan and asked him to stop by if he could
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Re: vertebral venous capacity limits

Postby uprightdoc » Mon Aug 08, 2011 3:53 am

Cece wrote: ... Maybe the vertebral venous drainage system is only capable of taking on a percentage of the jugular drainage, around 26% as seen here. So combined stenoses of up to 26% in the jugulars might be what the body can compensate for. As soon as our stenoses get beyond 26%, the body cannot compensate as well, although it tries. If the jugular stenoses get up to 80 to 100%, as mine did, it would seem that the vertebral venous system, however valiant, cannot compensate ... The article does discuss the role of deep cervical veins and the intraspinal epidural system which the authors assume must be responsible for taking the remaining jugular flow (a rather large 50%) that has been dispersed ...


Civickiller asked me to answer some questions so I will put in my two cents and then leave you to your discussion.

It should be noted the vertebral venous plexus or VVP is comprised of internal and external vertebral veins. The external veins are alongside the spine. The internal veins are the "intraspinal epidural veins" located inside the spinal canal between the bones and spinal cord. The key routes used by the accessory drainage system during upright posture drain into the intraspinal epidural veins.

That said, I would have to agree with Cece. The vertebral veins cannot begin to take on the full load of the IJVs, nor were they designed to. The accessory drainage system, which includes the occipital marginal sinus and emissary veins that drain into the epidural veins of the VVP, evolved to increase the capacity of the IJV's not to replace them. They also evolved to help drain the lower portion of the posterior fossa.

The transverse, sigmoid sinuses and IJV are relatively much larger than the occiptial marginal sinus and emissary veins. If the IJV's become blocked blood would backup from the larger veins and sinuses into much smaller ones, with much smaller capacity. More than likely, whatever the VVP can't handle when the IJV's are blocked will flow through veins in the middle fossa and face.
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