How do blood chokes actually work?

Question

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 arteries 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 face 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

And so aneurysms are the main danger due to the higher pressure, but this is not a problem for most healthy people if the hold is not maintained more than ~1 minute (see DaveLiepmann's answer). I always found this to be very convincing compared to the "we primarily attack arteries", which lay under the muscular structures or are embedded.

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

Any answer (not necessarily that technical and medical) addressing this is welcome.

Answer 1

The following study (on hadaka-jime and nami-juji-jime) supports the claim that compression of the carotid (and vertebral) arteries is associated with loss of consciousness in judo-style chokes:

By means of continuous wave doppler the effect of two choke holds (Carotid sleeper, Nami-juji-jime) on the carotid and vertebral arteries was investigated. For both choke holds, which are characterized by pressure on lateral parts of the neck, we found an obstruction up to a complete stop of flow. The degree of obstruction depended on the direction of force. The vertebral artery can be compressed between the subclavian artery and the foramina transversaria, therefore it was most effective to press on the lower neck. Tensing the neck muscles can reduce the effect of choking.

• Carotid and vertebral artery circulation in forearm choke holds in Doppler sonography (1990)

16 of the 24 officers lost consciousness in 7-10 seconds with only 84% compression of the carotids. Four tapped out before unconsciousness and four managed to maintain consciousness - but had significantly less carotid compression.

• Mechanism of loss of consciousness during vascular neck restraint, Journal of Applied Physiology (2012)

While venous compression is normally also present in these chokes (and is noted to be responsible for the initial flushed face etc), reduced venous flow alone does not normally cause unconsciousness, and it is not until considerable pressure is applied to the arteries that this generally occurs:

Reduced venous return sharply lowers SV and blood pressure during Phase II of a Valsalva maneuver (5). Although most normal subjects do not lose consciousness during a Valsalva maneuver, decreased blood pressure could contribute to a loss of consciousness.

• Ibid.

You lock the choke, compressing venous outflow. The face gets flushed. The choke tightens down, the opponent’s carotids narrow, blood flow falls below a critical level, the vision closes in, and consciousness is lost.

• The Physiology Of A Rear Naked Choke, Or: What Happens When You Get Choked Out (Interview with Dr. Charlie Moore, emergency medicine/trauma doctor)

However it is noted that investigation of the mechanism underlying this phenomenon is understudied and that it may be more complex than mere arterial constriction:

Vascular neck restraint (VNR), an effective technique practiced within police and military combatives and in mixed martial arts and grappling sports, is of both interest and controversy. In any context the goal of VNR (referred to as a choke within combat sports) is to restrict brain blood flow enough to threaten or result in unconsciousness. The physiologic basis for the resultant unconsciousness has been depicted as being solely because of restriction of carotid blood flow due to direct external compression. This view is likely simpler than what is actually going on, but it's an area not well explored in the medical literature...

Most studies have looked at this essentially to the exclusion of two other contributing entities: jugular compression resulting in increased [inter-cranial pressure] from reduction of outflow, and reduction of actual whole body MAP due to reduced cardiac output from vagal stimulation coming from a pressure affected carotid body. This article fleshes out some of these physiologic variables and discusses the related available literature.

• There is more to the mechanism of unconsciousness from vascular neck restraint than simply carotid compression. (2019)

Answer 2

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.

Answer 3

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.