Disclaimer: This is not an exhaustive explanation of blood chokes, but rather an addition to the conversation I have in my classes which discuss blood chokes.
When discussing means of choking someone there are two general categories, air chokes and blood chokes. Air chokes prevent someone from breathing by way of comprising the neck or otherwise compromising air movement and should be avoided. Blood chokes exploit the vulnerability due to compression of the carotid arteries that travel vertically on either side of the trachea (windpipe). The carotids carry 70-80% of the blood to the brain which is very sensitive to drops in blood pressure. Pressure applied to the carotids can cause dizziness and if hard enough and sustained long enough will lead to brief unconsciousness. Practitioners of Judo have learned forms of blood chokes since 1882 and US Law Enforcement has used techniques derived from martial arts intermittently since the 1960s.
Individuals considering experiencing a blood choke should ask their health care provider if they are healthy enough to participate in Judo. There’s a medical procedure called a Carotid Sinus Massage during which a medical provider rubs on one of the carotids. Known reasons not to do that are a past heart attack, a minor stroke (TIA) or major stroke (CVA) within the last three months, an occlusion in the carotid artery, or a history of severe heart arrhythmias (ventricular fibrillation or ventricular tachycardia). In my opinion applying those contraindications to blood chokes in kink is a good practice.
Below are primary sources discussing the risks and relative safety of using these techniques. They are some of the documents from which I have developed my opinions about blood chokes.
Primary Sources:
The Resurgence of Carotid Control (PDF)
How Safe is Choking in Judo? (PDF)