arteries of the neck for oxygenation of the brain. At the brain’s cellular level, blood exchanges oxygen for CO2 gas, which is then transported down the neck’s jugular veins to the lungs for exhalation. Other liquid and solid waste products travel through the circulatory system and are excreted by the kidneys and gastrointestinal track.
Figure 1. Vital neck structures. (Illustration courtesy Yesenia Aceves and the Training Institute on Strangulation Prevention.)
Figure 2-a and b. Carotid and vertebral arteries.
Cessation of oxygenated blood flow to the brain cells leads to anoxia. Hypoxia (eg, decreased oxygen levels) results from strangulation when pressure to the neck compromises air flow. Anoxia and hypoxia from compressive force on the arteries and air passages of the neck is the most common cause of death in strangulation. Based on videotapes of hanging death, the last breath occurs between 62 and 157 seconds.6,23 Injuries to neck structures may also lead to compromised air and blood flow. Pressure to the neck can result in hyoid bone or laryngeal fractures, carotid or vertebral artery dissections, intrinsic neck muscle bleeding, cervical spine ligament tears, nerve injury, and cervical spine fractures. Injury-associated bleeding, swelling, and/or functional disability in maintaining a patent airway interferes with oxygenation leading to hypoxia. The following is a more detailed explanation of underlying neck structures, including their location, function, and susceptibility to compressive forces of strangulation.
CAROTID ARTERIES
The carotid arteries originate from the aortic arch at the top of the heart and are located on the left and right side of the neck. Protected by neck muscles, the carotid arteries lie slightly deeper and medial to the jugular veins. The carotid arteries carry approximately 80% of the oxygenated, nutrient-rich blood from the heart to the head and brain. Pressure inside the carotid arteries exerts the force required not only to deliver oxygenated blood but to diffuse oxygen throughout the brain tissues.
It takes approximately 11 pounds of pressure to occlude the carotid arteries and compromise oxygenated blood flow to the brain. Sustained pressure causes unconsciousness within 10 seconds as a result of immediate cessation of oxygenated blood flow. Immediate relief of pressure allows consciousness to return in approximately 10 seconds. Death occurs within 1 to 2.5 minutes of constant pressure on the arteries.23 A tear, called a dissection, can occur to the internal lining of the carotid arteries. The body’s response to a dissection is to form a blood clot around the tear and begin the hemostasis phase of healing. Blood clots can completely occlude the artery or can break off, travel to the brain, and compromise blood flow and oxygenation, resulting in neurologic compromise and stroke. The clot may not break off until days, weeks, or months after injury, and the strangulation victim remains asymptomatic until the moment of the stroke.24 A screening CTA is required to rule out the presence of a carotid artery dissection (Appendix 7).
VERTEBRAL ARTERIES
The vertebral arteries originate from the subclavian arteries and are the primary blood supply to the upper spinal cord, brainstem, cerebellum, and the posterior circulation of the brain. They carry 15% to 20% of the brain’s blood supply. When the carotid arteries are occluded but the vertebral arteries remain patent, the vertebral arterial blood flow is primarily responsible for the development of petechial hemorrhages on the integument skin and mucous membrane surfaces of the face and the oto-oral-pharyngeal areas. There are 2 mechanisms for occluded vertebral arteries. First, if pressure is applied just above the collarbone to occlude the subclavian arteries4,25 or second, if lateral neck pressure is applied from a thin ligature or with hands in a choke hold, 100% of arterial blood flow to the brain can be blocked.26 Compression of both the carotid and vertebral arteries will result in a “pale strangulation” or a “pale hanging” because petechiae will not develop. A screening CTA is required to rule out the presence of a vertebral artery dissection (Appendix 7).
CAROTID ARTERY GANGLION
The carotid artery ganglion, also called the carotid body, is a cluster of cells located at the bifurcation of the carotid artery. An important neurologic sensor, the carotid body is primarily stimulated by oxygen and is highly sensitive to carbon dioxide. The carotid body’s main function is to trigger nerve impulses, relaying important information to the central nervous system. Although it requires a specific area of compression with strangulation, sustained stimulation of the carotid body for 3 to 4 minutes could activate the carotid sinus reflex, resulting in bradycardia and hypotension. However, death does not occur from carotid sinus stimulation.21,22
HYOID BONE
The hyoid bone is a horseshoe-shaped bone located at the base of the mandible and above the larynx (Figure 3). It is free-floating (ie, not connected to any other bone in the body). The hyoid bone’s main function is to support a wide range of tongue, pharyngeal, and laryngeal movements, including swallowing. A fracture of the hyoid bone may lead to difficulty swallowing (ie, dysphagia), painful swallowing (ie, odynophagia), and pain on neck rotation. Effective swallowing is important to maintain uncompromised air flow during respiration. Therefore, the impact of a hyoid bone fracture on swallowing, as well as the potential for associated bleeding and/or swelling, may compromise airway patency. Hyoid bone fracture is reported with a frequency of 17% to 71% in fatal strangulation27 and occurs during manual strangulation, ligature strangulation, and in hangings. Hyoid bone fracture is infrequently recognized in nonfatal strangulation.28
Figure 3. The hyoid bone. The greater horns (cornu) are the most common location for fractures.
JUGULAR VEINS
The jugular veins are vessels located on the left and right side of the anterior neck and are more external and lateral to the carotid arteries. The jugular veins return the majority of CO2 gases in deoxygenated blood from the brain and head back to the heart and lungs where the CO2 gases are exhaled as waste.
It takes approximately 4.4 pounds of pressure to occlude the jugular veins. This occlusion causes venous outflow obstruction, resulting in deoxygenated blood backing up into vessels of the head and brain. This build-up of deoxygenated blood is known as stagnant hypoxia. If venous outflow is obstructed without carotid artery occlusion, the veins above the level of constriction begin to dilate in order to accommodate the incoming blood that cannot exit the neck. This obstructive process causes the veins to engorge, resulting in increased internal venous pressure. When pressure is sustained for approximately 20 to 30 seconds without complete arterial (carotid and vertebral) occlusion, the dilated vessels rupture, causing pinpoint hemorrhages known as petechiae. Petechiae may occur anywhere above the level of constriction, including the brain, scalp, skin, conjunctiva of the eyes, soft palate of the mouth, and the external ear canal.
LARYNX
The larynx (ie, voice box) is a tubular structure of cartilage between the superior hyoid bone and inferior trachea. The larynx serves 2 important functions: first, it is part of the respiratory tract,
