A ligature such as a belt or rope around the neck, or hands or arm pressure on the neck compresses the internal carotid artery
. Apart from the direct restriction of blood to the brain there are two other significant responses produced by pressing on the neck:
- Pressing on the carotid arteries also presses on baroreceptors. These bodies then cause vasodilatation (dilation (widening) of the blood vessels) in the brain leading to insufficient blood to perfuse the brain with oxygen and maintain consciousness.
- A message is also sent via the vagus nerve to the main pacemaker of the heart to decrease the rate and volume of the heartbeat, typically by up to a third. In some cases there is evidence that this may escalate into asystole, a form of cardiac arrest that is difficult to treat. There is a dissenting view on the full extent how and when a person reaches a stage of permanent injury, but it is agreed that pressure on the vagus nerve causes changes to pulse rate and blood pressure and is dangerous in cases of carotid sinus hypersensitivity.
This method is responsible for most, but not all, of the reported fatalities. The method is especially dangerous when practiced alone and can be mistaken for suicide where the motivation is not known.