There are two basic types of NR: those that apply pressure to the front of the neck and those that apply pressure to both sides of the neck. The former targets the airway and the latter target the vascular structures of the neck. The former are referred to as respiratory neck restraints and the latter as vascular neck restraints. I will refer to them as respiratory neck techniques (RNT) and vascular neck techniques (VNT) respectively.
What is the mechanism of injury with NR? I'm referring to a Queensland Crime and Misconduct Commission report into the use of a VNT by Queensland police officers which resulted in a suspect experiencing serious brain injury, i.e. a vegetative state. The independent medical opinion (Dr Hoskins) annexed to the report considers the mechanisms of injury associated with a NR.
There are four basic mechanism of injury associated with a NR:
1. Occlusion of the airway.
2. Occlusion of the carotid arteries.
3. Occlusion of the jugular veins.
4. Stimulation of the carotid sinuses.
There is no suggestion that the VNT turned into a RNT in the struggle with the mentally disturbed suspect when attempting to restrain him. So the pressure was applied to the sides of the neck and not the front of the neck. It is disturbing that the occlusion of the airway was ruled out as being responsible for the injury for reasons other than an understanding that a VNT does not apply pressure to the front of the neck.
It is a common explanation that a VNT is designed to occlude the carotid arteries and thereby stop the supply of oxygenated blood to the brain causing unconsciousness. The vertebral arteries which transfer blood to the brain along the cervical spine vertebrae continue to feed the brain with enough oxygen to stave off brain damage but not enough to maintain consciousness.
Dr John Pi (who is also an FBI Special Agent) organised and led a panel of medical personnel to research the carotid restraint (VNT) and, among other things, create a better understanding of the medical explanation for its effectiveness. The results of the study were also published in Advanced Concepts in Defensive Tactics: A Survival Guide for Law Enforcement. The panel considered the effectiveness of the technique was due to occlusion of the jugular veins and stimulation of the carotid sinus rather than occlusion of the carotid arteries. The reasoning includes the relative amounts of pressure that needs to be applied to occlude the veins and arteries. Two to three times more pressure is required to be applied to occlude the carotid arteries than the jugular veins.
Occluding the jugular veins has the effect of stopping the deoxygenated blood from returning to the heart. Dr Hoskins explains that it is an over-pressure phenomenon where blood is being pumped to the head while its exit is blocked by pressure on the veins. He suggests that it is thought, but lacks experimental corroboration for obvious reasons, that it takes 20 to 30 seconds for this phenomenon to develop. The obvious evidence of occlusion of the jugular veins is a blood engorged face.
Is it an either/or proposition? Is either the occlusion of the carotid arteries or the jugular veins the cause of injury? Dr Hoskins refers to blood bleeding from the nose and ears, and pinpoint bleeds over the eyelids and the whites of the eyes when the jugular veins are occluded. But what if the carotid arteries are occluded at the same time? The only blood trapped in the head is the blood that was in the head at the time the carotid arteries were occluded.
Research has demonstrated that unconsciousness from a VNT results from a lack of oxygen to the brain. Dr Pi's panel suggest that occluding the jugular veins has the effect of stopping the forward flow of blood into the brain. Studies have shown that VNTs result in unconsciousness in approximately 10 seconds. Does occluding the jugular veins result in unconsciousness slower or faster than occluding the carotid arteries? Were the aforementioned studies also occluding the jugular veins?
These questions have not be considered let alone studied.
Now lets turn to the carotid sinus mechanism. Dr Pi's panel suggest stimulation of the carotid sinus is also responsible for unconsciousness when applying a VNT. Dr Hoskins eventual determination as to cause of injury was the stimulation of the carotid sinus (after a process of elimination). Stimulating the carotid sinus causes a reduction in heart rate. This has been referred to as an 'interesting theory' by noted forensic pathologists when it's referred to in connection with deaths from strangulation (including NR).
I've tried it. Yes! I've tried to stimulate my carotid sinus in order to render myself unconscious. I've used manual and mechanical means to stimulate my carotid sinus. I've had my GP who is trained in carotid sinus massage, massage my carotid sinus in order to reduce my heart rate (and hopefully render me unconscious). Nothing!
When included in the force options available to police officers, these techniques have been described as providing 'more protection to the officer than any other known method of control, and it concludes physical resistance without injury to the subject faster than any other restraint means known.' They are techniques that are capable of being 'used effectively regardless of the size of either the person to be controlled or the size of the police officer,' and being the only safe way to subdue very violent offenders or those who are not responsive to pain compliance techniques, such as those under the influence of drugs, emotionally disturbed or mentally ill persons, and those experiencing an adrenalin rush.(taken from the draft of my chapter)
The Canadian Police Research Centre (CPRC) has produced a number of reports on the use of NRs by law enforcement. They love them. However, deaths have been associated with the use of NR. This association is a matter worthy of its own post, however, the CPRC and many other authorities tend to lay the blame for any fatalities on RNT while favouring VNT. They favour VNT because they are so effective.
There is a serious flaw in the logic. VNT are capable of stimulating the carotid sinus. You do not need to stimulate both carotid sinus like you do with occlusion of the carotid arteries. It takes less pressure to stimulate the carotid sinus than it does to occlude the carotid arteries or jugular veins. And once the carotid sinus has been stimulated it cannot be unstimulated. If stimulating the carotid artery results in a slowing of the heart rate, sometimes too much and death, then VNT are inherently more dangerous than RNT. I am staggered that this logic has not been considered by any who have considered the use of NR by law enforcement.
The stimulation of the carotid sinus mechanism exists. A senior student of Jan de Jong shared an experience with me where he was nearly rendered unconscious when Maggie de Jong performed a technique on him during a demonstration. It was a defence with a jo (4ft staff) that applied force with the forearm and jo to the neck to cause the attacker to fall to the ground. The technique was held on for the barest of seconds and therefore his experience could not be attributed to occlusion of the arteries and/or veins. As it turns out, he has a slight heart condition, which some authorities suggest puts him at in a high risk category of injury with VNT. I have since advised this student that he is not to have any VNT or similar neck techniques applied to him because of his underlying heart condition.
What is the conclusion from this study of NR. They are very effective, but the exact mechanism for their effectiveness and their inherent risk to life is not known.
There is a duty of care issue here (a part of another chapter in my book). If you don't know the mechanism of injury, how can you prevent or control injury if teaching these techniques? Ignorance is no defence.
When I've discussed my work with other martial artists, many have expressed scepticism and suggested that people are only interested in the 'how' and not the 'why.' The same instructors are then often seen supporting their how instruction with a why explanation. Any instructor who explains the how of NR are doing so on flawed information.
If any instructor attempts to explain the why behind the how, they had better do the leg work to understand the why. Based on experience, the why is not easy to come by within the literature associated with activities associated with preparing a person to survive a violent encounter.