While there were no fatalities recorded in the use of the holds by that department, neurologists say the dangers of neck compression are indisputable.

Dr. Altaf Saadi, a neurologist at Massachusetts General Hospital, explained that chokeholds and strangleholds could kill or cause brain injuries in two ways. They can compress the trachea, preventing the person from getting air into the lungs. And they can compress the carotid arteries, which are on either side of the neck, adjacent to the trachea. Seventy percent of the blood going to the brain passes through the carotids, Dr. Saadi said. If that blood flow is cut off in a chokehold or a stranglehold, some people can become unconscious in three to four seconds. If the flow continues to be restricted, a person can die within three to four minutes.

If a person loses consciousness, that is an indication of possible injury to the brain, Dr. Saadi said.

Even if the person does not lose consciousness, strokes and permanent brain damage, including cognitive impairment, can result from a chokehold.

People with cardiovascular disease are especially susceptible to brain injury as a result of neck compression.