This is prompted by this answer and the description of blood chokes included. It states that

Cerebral blood flow (CBF) chokes involve restricting the flow of blood to the brain, thereby denying it of oxygen

As far as I have learned, the blood choke rather effects the veins, because arteria are under the muscles or within them and often quite well protected by them, while the veins are prominently positioned right under the skin, e.g. vena jugularis externa.

Therefore, the effect is that no blood can go out of the head or at least much more goes in than out, resulting in

  1. red head because of blood coming in, but not out
  2. higher pressure until no new blood may enter the head
  3. the oxygen within the blood getting used without proper replenishment
  4. unconsciousness due to lack of oxygen.

Therefore, aneurysm being the main danger because of higher pressure, but no problem for healthy people if the hold is not maintained more than ~1 minute thereafter, like backed up by the excellent answer of @DaveLiepmann there. I always found this to be very convincing compared to the "we primarily attack arteria", which lay under the muscular structures or are embedded.

Is that what blood chokes really work like? What is the actual mechanism going on?

EDIT to flesh this out a bit more:

I stumbled over this resource searching Wikipedia (full text and pdf available for free).

The findings are

  1. That any effect of baroreceptors (receptors for the blood pressure) being irritated could not be shown. This quite popular theory seems to be simply wrong.

  2. They claim it is due to compression of the carotid arteries.

My objection against this is that the method of pressure measurement (kind of a tube-collar with tubes in two different heights, depicted in the pdf file) and the data that are measured could - in my understanding, which is limited as I'm no physicist - equally like be explained by the theory presented earlier. Some phenomenon like the face getting read and the veins swollen even better.

Therefore, every (not necessarily that technical and medical) answer addressing this would be welcome.

up vote 7 down vote accepted
+100

According to forensic science it is pressure applied to the carotids and not the veins that causes loss of consciousness, although pressure on the veins leaves specific signs of strangulation when they bust, but are not a cause of death or unconsciousness. (pg. 297, 14.2 Strangulation, see section #2 re: carotid compression).

Although the deeper carotid that feeds the brain is under the neck muscles and more "protected" it's also important to realize the neck muscles are relatively thin, and aimed at keeping the head upright - they do not have a lot of force to resist direct perpendicular pressure. This is amplified more by the fact that carotid chokes involve pinning the person's head or neck in such a way they can't pull away from it - you compress the carotid against the spinal column itself.

  • First, thanks for the answer. Second, perhaps my perceptions regarding the uselessness of neck muscles are quite different because I am a judoka and "trained" in being choked (plus, neck muscle training is regularly part of our warmup), but I take your point. And last but not least, I will wait till friday with my acceptance, but this seems a good, sourced candidate for it, therefore +1. – Philip Klöcking Jan 17 '16 at 21:14

What I've picked up over the years about how blood chokes actually work - and I could be wrong - is this: There's a nerve in the neck called the Vagus nerve. One of its many functions is to sense blood pressure of the arteries in the neck. When you compress those arteries, it will cause blood pressure to increase rapidly. The Vagus nerve senses it and reports it to the brain. The brain sees the rapid increase in blood pressure and, as a defense mechanism, orders blood pressure to be reduced. The sudden drop in blood pressure accidentally causes you to faint.

The same thing can be achieved by striking at that part of the neck where the Vagus nerve sits. You might do it with a karate knife-hand strike, for example. And there are videos on youtube demonstrating exactly this. The sudden strike to the nerve itself will cause the nerve to freak out and tell the brain that the blood pressure is too high. And that causes the person to pass out.

You can sometimes see a rear-naked choke work instantly, within the first one or two seconds of it being applied. That's a good indication that it's working because of this nerve feedback mechanism which drops blood pressure and therefore causes you to faint. It works more quickly if you put the choke on very hard and very sharply, almost like striking that vagus nerve. [But please don't do that! It can break someone's neck or cause them to have a stroke! Be gentle with people in class. Save that stuff for when your life depends on it.]

The primary health problem with these chokes, I believe, isn't the risk of aneurysm. At least that's not something I typically hear being warned by instructors. Instead, the warning is not to do these chokes to people over the age of about 40, because of the possibility of causing a stroke.

Strokes might happen if you dislodge arterial plaque inside of the arteries in the neck. The plaque travels to the brain, where it gets stuck somewhere as the blood vessels narrow. And that causes that part of the brain to lose its blood supply, which triggers the stroke. People die from strokes. I think this is more of a concern for older people, and it should be a higher risk as you increase the amount of force and the speed by which the choke is applied.

I think strokes are going to be pretty rare when applying blood chokes, even in competition when you do it more quickly and more forcefully. Striking the neck with a knife-hand chop would probably be more of a risk. But I have no idea. I'm not sure if we have any statistics collected and available on this subject.

Anyway, those are my thoughts.

  • This article seems to proof that the mechanism ongoing has actually few to nothing to do with baroreceptors, but does not even consider what I said, although, especially considering the measurement installment, the data may also be interpreted the way I described it. Or that's what I can make out of it. – Philip Klöcking Jan 14 '16 at 8:56
  • Blood pressure may not have been affected by the choke, that is correct. It doesn't have to be. What matters is that the Vagus nerve triggers a signal to the brain saying that the blood pressure has spiked too high. The Vagus nerve can be tricked into doing this by simply compressing it, stretching it, or striking it. The actual blood pressure is not necessarily increasing for it to send a "high blood pressure" signal to the brain. At least this is how I think it works in many cases. It might not explain all cases. – Steve Weigand Jan 14 '16 at 18:40
  • This is exactly what they looked for and they falsified this theory. – Philip Klöcking Jan 14 '16 at 19:21
  • 1
    No, they didn't look at the Vagus nerve firing. They merely took blood pressure measurements. But what they did show was one way the blood choke can work, which is by restriction of blood flow. That doesn't explain all of the cases where someone faints due to blood choke. It explains the chokes that take 5, 10, 15 seconds to work. It doesn't explain the ones that work instantaneously. And we know that strikes to the Vagus nerve causes people to faint also. There appear to be two mechanisms. – Steve Weigand Jan 14 '16 at 19:52

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