Neurovascular lesions and mechanisms in suicidal hanging: an anatomical, physiological and pathological study
Warning!! Contains forensic photos (Full pdf attached, 545 pages)
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The common carotid arteries are covered by skin, platysma muscle, deep cervical fascia, sternocleidomastoid muscle and carotid sheath from the level of the cricoid cartilage until their bifurcation at the upper border of the thyroid cartilage. During this part of their course, they rest on the unyielding surfaces of the transverse processes of the fourth, fifth and sixth cervical vertebrae. This anatomical configuration renders the patency of the vessels vulnerable to forces which can compress them against the subjacent vertebral transverse processes and cartilaginous larynx with any force greater than 3.5 to 5 kg causing carotid occlusion with consequent cerebral ischaemia, anoxia and loss of consciousness.The vertebral arteries, on the other hand, are protected from this type of compressive pressure because they ascend through the transverse foramina in the cervical vertebrae, requiring a force of 16.6 kg for occlusion. However, they do not do so through the seventh cervical vertebra, creating a potentially vulnerable locus to compressive force. This site, however, lies below the usual point of suspension in suicidal hangings, tending to negate this vulnerable locus for compression. It is only with the drop in judicial hangings that injuries to the vertebral artery are commonly expected. A point of neurological, rather than anatomical, importance is that the vertebral arteries carry an insufficient supply of blood to the brain (2% of cerebral blood flow) to maintain neuronal viability and integrity in the face of complete bilateral carotid occlusion.
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Compression of the carotid arteries, on the other hand, results, as has been shown, not only in major damage to these vessels and their accompanying veins, but, in addition, must produce a dramatic element of cerebral ischaemia. This would account for the rapid onset of unconsciousness, i.e. within 11 to 12 seconds. Moreover, the unremitting, unrelieved constrictive force of the ligature on these vessels, if perpetuated and left unchecked, would, it is suggested, lead inevitably to brain death in the ensuing 3 to 4 minutes. (This, of course, does not imply death of the individual as a whole, i.e. somatic death, as different organs die at different rates. Death, therefore, occurs by degrees). Unconsciousness, thus, appears to be the critical factor for it is the state when the victim is unable to save himself or herself. Without unconsciousness survival may occur, but with it, death becomes inevitable. The question then arises – what is the cause of unconsciousness? In physiological terms, carotid artery occlusion induces rapid unconsciousness, i.e. within 11 seconds, resulting in ultimate death. In other words, the sudden and unremitting pressure of the ligature must inevitably result in death. On the other hand, the sudden application of a ligature with consequent vagal nerve compression may produce instantaneous cardiac arrest with cessation of blood flow to the brain and resultant loss of consciousness. This event would produce unconsciousness in less than the time period of 11 seconds of carotid artery occlusion (although the brain continues to survive for several minutes thereafter despite cessation of heart beat).
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An interesting clinical point made by Polson is that severe obstruction of the carotid arteries, requiring only a tension of about 3 kg (6.6 lb, i.e. slightly more than the weight of the head), will rapidly induce cerebral anoxia and unconsciousness. A simple but interesting calculation follows: 3 ÷ 13.6 = 0.220 mm Hg; 1 kg = 1000 mg. This would therefore be equivalent to a pressure of 220 mm Hg in a narrow tube, i.e. equivalent to severe hypertension.Consciousness is lost within about 10-12 seconds, thus accounting for the failure of suicides to save themselves should they change their minds. It appears that once launched upon suicide by hanging there is no retreat. Of course, in the intervening 10-12 second interval between initiation of pressure and resulting unconsciousness, the self-induced victim of hanging does have sufficient time to make abortive attempts at loosening the ligature.
