Asphyctic Deaths

Introduction

The term asphyxia, as used in the traditional forensic pathology context, is not well defined and is often used to include conditions which are not truly as-phyxial in nature. In most instances, asphyxiation refers to mechanical interference with oxygenation of the tissues but there are other conditions, including cyanide and carbon monoxide poisoning, where the interference with oxygenation occurs at a cellular level. The issues relating to the definitions ofasphyxia and its effect on the human organism are comprehensively discussed in the literature. There are a number of natural diseases, including anemia and circulatory failure, for whatever cause, which can interfere with tissue oxygenation and produce cellular asphyxiation; however, it is not the purpose of this chapter to discuss these conditions. Similarly, many cases of drowning are associated with mechanical interference with tissue oxygenation but this topic will not be included in this chapter.
The physiological definition of asphyxia is complex and often means more than hypoxia. The forms of asphyxiation to be considered in this article are: exposure to gases in the atmosphere; mechanical obstruction by closure of external orifices; mechanical obstruction by interference with respiratory movements; mechanical obstruction by neck compression and sexual asphyxias.

General Autopsy Findings in Asphyxial Deaths

Because hypoxia is associated with an increase in pulmonary blood pressure and right heart failure,many of the findings in asphyxial deaths are characteristic of right heart failure but are not of themselves diagnostic of asphyxiation. The significance of these features will vary with individual cases and may be completely absent or masked by other postmortem findings. Some of the most common findings are:
1. pulmonary edema with associated froth in the trachea and bronchi;
2. bulky, crepitant and overdistended lungs;
3. right ventricular dilatation;
4. petechial hemorrhages on the conjunctiva and facial skin, usually above the level of airway obstruction in cases of neck compression.
Petechial hemorrhages are usually pinhead size he-morrhagic spots caused by the rupture of tiny venules although sometimes described, probably incorrectly, as ruptured capillaries. They may be very few and difficult to detect but they may also be so numerous as to give the area of skin affected an apparent cyanotic appearance. They usually occur in the skin of the face, eyelids and conjunctiva in cases of mechanical asphyxiation involving obstruction to the tissues of the neck. They are also seen on the skin of the upper abdomen, chest and neck in cases of crush asphyxiation. Petechial hemorrhages beneath the visceral pleura and visceral pericardium are often referred to as ‘Tardieu spots’ and were regarded by Tardieu as pathognomonic of death by mechanical asphyxiation. It is now widely accepted that they can found on the surface of the viscera in a variety of deaths.
It appears that petechial hemorrhages are produced by two primary mechanisms. There is increased vascular permeability due to hypoxia as a direct consequence of the asphyxial process. Increased per-meablity is also an important element of petechial hemorrhages developing after death in areas of livid-ity. Increased capillary and venous pressure associated with the mechanical obstruction to venous return is probably the most important mechanism determining the characteristic distribution of petechiae in cases of neck obstruction.
Petechiae are found in a variety of nonasphyxial deaths. In one series of 100 consecutive autopsies apparent petechiae were present in 33 cases, mostly unrelated to mechanical asphyxiation. The opinion has been expressed that the time has come to disregard these hemorrhages as diagnostic of mechanical asphyxia.
Petechial hemorrhages also occur as a postmortem phenomenon associated with the development of lividity. Petechial hemorrhages may be prominent within areas of lividity and often around the edges of lividity staining. These are almost certainly as a result of vascular decomposition with gravity-produced pressure inducing vascular leakage and hemorrhage.
It is not unusual during microscopic examination of tissues in cases of hypoxic deaths, to find tiny interstitial petechial hemorrhages. These are often observed within the brain in the perivascular areas and at best these microscopic features indicate terminal hypoxia. They should not be considered as evidence of mechanical obstruction to respiration.


Deaths Associated with Exposure to Gases in the Atmosphere

Although suffocation is not a specific term, it usually refers to deaths associated with a reduction of available oxygen in respired air. Oxygen may be reduced or absent from respired air or may be displaced by the presence of other gases, which are more readily absorbed by hemoglobin. Reduced atmospheric pressure, as may occur in aircraft cabin failure, or at high altitude environments may reduce the ability of oxygen to pass through the pulmonary alveolar walls. Diving accidents are often associated with exhaustion of the oxygen component of the usual nitrogen/oxygen mixture with death resulting from hypoxia. Breathing only nitrogen, which essentially functions as in inert gas, will cause rapid syncope and death.

Inert gases

Carbon dioxide, which although not of itself poisonous, may accumulate in the atmosphere at the expense of respirable oxygen and can cause hypoxia. Other gases, which may be biologically inert, may also displace atmospheric oxygen. Under such circumstances, the victims may initially suffer from headache or drowsiness and it is widely recognized that placing an individual in an oxygen-depleted atmosphere may be associated with very rapid systemic collapse and death.

Carbon monoxide

Carbon monoxide is one of the most frequently encountered toxic agents encountered in forensic practice. It has an affinity for hemoglobin that is between 200 and 300 times greater than oxygen. Therefore, very low concentrations of carbon monoxide in inspired air will rapidly displace oxygen from the red cells and lower the oxygen-carrying capacity of blood. Although there may be some direct toxic effects from the presence of carbon monoxide on tissue chemistry, the principal effect is undoubtedly the reduction in oxygen transport capacity.
Carbon monoxide combines with hemoglobin to produce the pink pigment, carboxyhemoglobin,which can readily be identified at postmortem. The classic ‘cherry pink’ discoloration of the skin and tissues is usually evident when the carboxyhemoglo-bin saturation of the blood exceeds about 30%. Under most conditions following death, deoxygena-tion of hemoglobin occurs but in carbon monoxide poisoning the carboxyhemoglobin bond is stable and the body will retain its characteristic pinkish so-called flesh tone and discoloration for many hours after death even until decomposition commences.
Fatal concentrations of carboxy hemoglobin saturation will vary but a normal healthy adult will rarely die with saturations under 50% and concentrations as high as 80% are not infrequently recorded. In elderly people, the concentrations may be relatively low, often as low as 30% and in infants under one year of age, the concentrations are also similarly low and have been reported as low as 20-25% saturation.
In relatively low atmospheric concentrations of carbon monoxide, the symptoms and signs of poisoning may develop relatively slowly. Concentrations of 20-30% may be associated with nausea, headache and vomiting and as the concentration levels rise towards 40%, there may be seizure activity.
The majority of carbon monoxide poisoning cases encountered in forensic practice relate to fire deaths and accidental deaths where there has been incomplete combustion in heating systems with the slow accumulation of toxic levels of carbon monoxide in the atmosphere. Suicide cases, where vehicle exhaust fumes are used to induce fatal concentrations of carbon monoxide in inspired air, are also relatively common.

Cyanide poisoning

Historically, atmospheric cyanide poisoning has been relatively rare except in cases of judicial execution. However, cyanide is produced by the combustion of plastics and significant levels of atmospheric cyanide may accumulate in fires. Cyanide acts by linking with the ferric iron atom of cytochrome oxidase preventing the uptake of oxygen for cellular respiration and causes death by cellular asphyxiation.
Toxicological analysis of cyanide and interpretation of cyanide concentrations in blood and other tissues is fraught with difficulty. Not only are small concentrations of cyanide present in normal blood but cyanide can accumulate in stored samples of blood. However, even in ideal storage situations, cyanide may be lost from the sample within days of sample collection. Cyanide has also been found to diffuse through the tissues and from body cavities opened to cyanide perhaps as a result of trauma or fire. As a result, tissue concentrations derived from toxicological analysis of samples of blood and other tissues for cyanide have to be interpreted with caution and there is no generally accepted minimal or fatal level.

Mechanical Obstruction by Closure of External Orifices

Smothering

Smothering is usually defined as the blockage of the external air passages usually by a hand or soft fabric and a particular variety of suffocation called gagging may occur when fabric or adhesive tape obstructs the mouth and nose. In some text topics, the term suffocation is often used to include conditions such as smothering. However, for the purposes of this article, the term suffocation is used as defined above and will be restricted to circumstances where there is a reduction to the amount of respirable oxygen. Smothering can be homicidal, suicidal or accidental. In homicidal suffocation, there is usually considerable disparity between the assailant and the victim or the victim is debilitated by disease, drugs or injury. Evidence of such disease or injury may be identified at the time of postmortem examination. Examination of the scene of death may not be helpful. Some cases of infant death previously attributed to sudden infant death syndrome (SIDS) have now been blamed on deliberate smothering by a caregiver and if the victim is incapacitated or unable to defend themselves then there may be little evidence of injury or struggle at the scene.
Smothering can occur as a result of mechanical occlusion to the mouth and nose during collapse of a work trench, in landslides such as the 1966 Welsh Aberfan disaster involving over 140 victims, in mine collapses and even in crowd crush situations.
Probably one of the commonest causes of suffocation seen in forensic practice is suicidal suffocation using a plastic bag. A plastic bag pulled over the head to cover the mouth and nose may or may not be fastened around the neck with a loosely tied ligature. This is one of the recommended methods in the ‘suicide guide’. Accidental deaths by plastic bag suffocation are described in children playing with plastic containers.
The autopsy signs of smothering may be minimal. If pressure has been applied to the face around the mouth and nose there may be evidence of bruising and it may require full facial dissection to reveal such injuries. If the pressure has been maintained after death, then there may be pressure pallor within areas of lividity around the mouth and nose. When injuries are present around the mouth and nose in cases of suspected smothering, they should be view as highly suspicious and the possibility that the smothering has been deliberate and homicidal considered. There may be no other findings. Petechial hemorrhages are more frequently absent than present. If present, petechiae may be found on the visceral surfaces of the thoracic organs or in the region of the larynx and pharynx.

Overlaying

This entity has been described as having an ancient pedigree. Reference is made in the Old Testament in the First topic of Kings when Solomon had to adjucate between two women both claiming motherhood of a child allegedly ‘overlain’. In the twentieth century, cases of (SIDS) were attributed to overlaying, however this seems an unlikely mechanism of SIDS. It seems likely that overlaying is a relatively rare mechanism of death unless evidence of crush type injuries is found. In the absence of such injuries it is difficult to support a diagnosis of death from overlaying.

Postural asphyxia

Postural asphyxia is a form of smothering that may occur accidentally when an individual is incapacitated often as a result of alcohol or drug intoxication, coma from natural disease, injury or epilepsy. Such individuals are frequently overweight and the pressure of the weight of the head against a soft fabric may be sufficient to compress the nostrils and obstruct the mouth. Under such circumstances, cyanosis may be relatively prominent. However, because of postmortem de-oxygenation of blood, diagnosis of cyanosis at postmortem must be made with caution.

Choking

This is the term that usually refers to obstruction to the upper internal airways usually between the pharynx and main bronchi. A foreign body such as a large bolus of food, and small toys and other hard objects in cases of children, may completely or partially obstruct the air passages and can cause apparent very sudden death without producing any classical signs of asphyxiation. Benign and malignant tumors of the pharynx, larynx and main bronchi may also induce choking and although such lesions may be apparently relatively slow-growing obstructions, death is often relatively rapid with a very short history of respiratory difficulty. Such methods of relatively slow airway obstruction and choking are also seen occasionally with neck tumors and in cases of neck trauma where there may be large interstitial hematomas and even collapse of the laryngeal structures as a result of major trauma.
Pharyngeal and laryngeal injuries identified in such choking cases must be interpreted with caution since the obstructing object itself may cause injury. More frequently, attempts at resuscitation, intubation and removal of the foreign body often result in injuries to the pharynx piriform fossa and larynx.
In some cases of choking, death may be so rapid that the manifestations of hypoxia and asphyxia have had little time to take effect. It seems likely that these deaths may be caused by neurogenic cardiac arrest or have been accelerated by excess catecholamine release from the adrenaline response. Such cases are often attributed to vagal inhibition since it is well recognized that the larynx is a well innervated area structure. Deaths from vagal inhibition are discussed later in the section on Strangulation.
The vast majority of choking deaths are accidental. Suicides and homicides occur very rarely. The most common situation is the so-called ‘cafe coronary’. Victims are usually intoxicated or have pre-existing neurological debilitation. Choking occurs while eating. However, the inhalation or aspiration of gastric contents of partly digested food as a primary event in an otherwise healthy adult is relatively unusual. Many of these cases may in fact be ‘cafe coronaries’ occurring as a direct consequence of a cardiac dysrythmic event. An important cause of fatal choking is the inhalation of blood associated with facial injuries, particularly fractures involving the facial bones. Accidental and homicidal injuries to the head and face associated with bleeding into the back of the pharynx and larynx may result in fatal choking as a result of the aspiration and inhalation of large amounts of blood.
In some cases of choking, resuscitation has resulted in removal of the causative obstruction and it may be require detailed dissection and examination to reveal any evidence of the primary cause for death.

Burking

This is a rare form of smothering death. The term is used to describe a procedure apparently invented by the Scottish murderers, Burke and Hare, during the 1820s. Their victim was plied with alcohol and one of the murderers knelt or sat on the chest and the other closed the mouth and nose with his hands. External injury was absent and but for the evidence of Hare, this mechanism of asphyxiation might never have been discovered.

Mechanical Obstruction by Interference with Respiratory Movements

Traumatic (crush) asphyxia

Interference with the movement of the primary muscles of respiration, namely the intercostal muscles and diaphragm, will result in fatal hypoxia. In most occasions, this is the result of accident in which the body of the victim is subject to direct compression by a heavy weight as may occur in a rock fall in a mining accident. Traumatic or crush asphyxia is characterized by intense discoloration of the skin of the head, neck and upper chest with multiple pe-techial hemorrhages within this area of congestion. Such incidents are also associated with external and internal evidence of direct trauma to the chest and upper abdomen. The intense congestion of the skin and cutaneous petechiae characteristic of this mechanism of death may in part be due to obstruction to the superior vena cava, the subclavian veins and the veins of the head and neck.
In some instances, for example accidental burial in grain silos or sand/gravel pit collapses, the restriction to respiratory movement characteristic of traumatic asphyxiation may be superimposed on a smothering mechanism of death.
Traumatic asphyxia also occurs in mass disaster situations involving crushing in crowds. Such tragedies have occurred at sporting events throughout the world and other instances have been associated with crowd panic.

Hog-tying

A number of cases have been described where an individual, often a person requiring restraint during arrest, has been tied up, usually with the wrists and ankles tied together behind the back. If such an individual is left lying face down on a hard surface then the restricted movements induced by the ligatures together with possible reduced chest movement caused by an apparent splinting effect produced by contact with the floor, may result in hypoxia and sudden death. This method of restraint is known as hog-tying. Variations of this form of death may be associated with sexual asphyxiation described below.
In North America, hog-tying is a not infrequent method of restraining prisoners during the process of arrest. Sudden death has been reported in some of these individuals. In some instances, however, the victims have been intoxicated with alcohol and or using cocaine. It may be that chemical suppression of respiration is a factor in such deaths. These cases often show evidence of injury associated with the ligatures but no other evidence of asphyxiation.

Pickwickian syndrome

A form of chronic asphyxiation associated with respiratory failure is the Pickwickian syndrome. This condition, named after the Pickwickian fat boy who kept falling asleep, is associated with extreme obesity where, as a result of obesity and excess body weight, diaphragmatic and intercostal movement is significantly reduced. The victims become chronically hypoxic, and develop high carbon dioxide levels with associated narcosis.

Death by crucifixion

This form of punishment was apparently introduced to the Romans by the Phoenicians. The victim was suspended from a cross in such a fashion that in order to breathe, he was required to raise his body by pressing down on his feet which were either nailed or supported by part of the mechanism. The victim rapidly became exhausted and death occurred when the muscles of respiration failed and right heart failure occurred. In the case of inverted crucifixion as in the death of St Peter, respiratory paralysis would be induced by the weight of the abdominal viscera.
Cases of accidental inverted suspension causing death have been documented and in all of these cases, death is as a result of respiratory exhaustion. With the exception of the circumstances of death, these cases are indistinguishable from those of postural asphyxia.

Mechanical Obstruction by Neck Compression

Strangulation

Strangulation, sometimes referred to as throttling, is divided into two main types: manual and ligature. Not infrequently however, in the homicidal situation, strangulation may be as a result of the combination of manual and ligature compression of the neck. Strangulation is usually defined as the application of a compressing force to the neck where the force acting on the neck is other than that of the weight of the body. This distinguishes it from deaths by hanging described below.
Strangulation, both manual and ligature, probably represents the most common cause of homicidal asphyxiation. Manual and ligature strangulation are both associated with external and internal neck injuries, which in some cases may be minimal, but in most cases are easily seen. Petechial hemorrhages are also a characteristic, although not diagnostic, finding in such deaths. When such petechiae occur in cases of strangulation, they are almost always distributed above the level of neck obstruction and distal to the heart. Although such petechiae are characteristically seen in strangulation, and their distribution should be noted in detail, it is most important to recognize that petechiae are a relatively common nonspecific autopsy finding. They occur in a wide variety of non-asphyxial states and may even be a postmortem phenomenon associated with the postmortem posture of the body. In strangulation, there may be partial or complete obstruction and compression of all of the principal anatomical structures in the neck, including the veins, arteries, airway and nerves.
Occlusion of the neck veins is almost solely responsible for the classic signs of congestion, cyanosis and petechiae above the level of neck constriction. Pressures as low as 2 kg will compress the jugular veins and obstruct venous return to the heart. This can cause a rapid rise in venous pressure in the head with the associated rupture of small venules.
Airway obstruction Strangulation may be associated with either partial or complete obstruction to the airway by direct compression of either the larynx or trachea. Obstruction at the level of the pharynx may be produced by manual elevation of the larynx so that air entry is blocked by the root of the tongue being pressed against the palate. Compression of the larynx may fracture the pharyngeal cartilages and hyoid bone, although the number distribution and nature of these fractures will depend on the age of the victim and degree of calcification and fusion of these structures. Collapse of the larynx associated with these fractures may, of itself, cause airflow obstruction. Various experiments have shown that forces of approximately 15 kg will close the trachea. This is substantially more than is required to occlude the blood vessels.
Arterial compression Compression of the arteries in the neck is less common than venous occlusion since the carotid arteries are largely obscured by the sterno-mastoid muscles. Bilateral occlusion of the carotids may cause rapid loss of consciousness as the arterial blood supply to the brain is reduced and it appears that vertebral artery circulation alone is insufficient to maintain cortical function. It seems unlikely, therefore, that occlusion of the carotid arteries alone would be sufficient to cause death. Occlusion of the vertebral arteries by neck compression appears to be almost impossible because of the anatomical location of these vessels. The general opinion is that permanent brain damage is very unlikely if arterial occlusion persists for less than 4-5 min and it has been reported that even in normothermic conditions total recovery has occurred after 9-14 min of vascular occlusion.
Neurological effects (vagal inhibition) Direct pressure or manipulation of the baroreceptors situated in the carotid sinuses (carotid bodies) can result in reflex bradycardia or total cardiac arrest. This mechanism acts through a vagal nerve reflex arc arising in the complex nerve endings of the carotid sinus and returning via the brainstem and the vagus nerve to exert its slowing effect on the heart.
Susceptibility to vagal cardiac arrest appears to be variable and it has been suggested that fear, apprehension and possibly struggling may heighten sensitivity to this vagal mechanism by the release of catecholamines. The amount of force that must be applied to the carotid sinuses and the duration of the application of such force is variable and unpredictable. There are many well-documented examples of sudden impacts to the neck causing cardiac arrest and other cases where the application of simple neck massage has induced death.
If cardiac arrest occurs quickly during compression of the neck, then petechial hemorrhages which are often associated with relatively long periods of neck compression lasting more than 2 min, may be minimal. It seems likely that a vagal cardiac arrest component of death in strangulation cases is much more likely in manual strangulation than ligature strangulation because of the ability of the fingers to compress and massage the carotid sinus area of the carotid arteries. Most forensic pathologists will have experienced cases where this mechanism of apparently sudden death in neck compression cases has occurred, and it is the opinion of this writer that vagal inhibition is an important component of death or incapacitation in many cases of manual strangulation.
A frequently asked question of forensic pathologists is how long must neck compression be applied before an individual is rendered unconscious or dies. Because of the complexity of the mechanisms of in-capacitation, loss of consciousness and death in strangulation, there is no simple answer to this question. It would appear that for petechial hemorrhages to occur, the compression must last for at least 30 s. However, although it is probably correct, in most cases, to suggest that the development of petechial hemorrhages is an indication of a sufficiently longtime compression to induce unconsciousness, it is not possible to determine this period of time with any degree of accuracy.

Manual strangulation

The autopsy findings in manual strangulation include the signs of injury to the neck, both external and internal, and the signs of the mechanism of death.
Manual strangulation is often associated with external bruising of the neck which may be more prominent on one side than the other. These bruises are usually caused by compression by the pads of the fingers or thumb. They tend to be at the level of the thyroid cartilages and are on either side of the front of the neck. Internal examination of the neck structures requires layer-by-layer dissection of the neck tissues in situ. Only after such careful dissection is it possible to identify bruising at various levels within the neck tissues. In some cases, the evidence of external bruising may be minimal but careful dissection of all the anterior and posterior neck structures will reveal evidence of deep bruising.
Abrasions may be found on the skin usually at the front of the neck. These abrasions may be characteristically linear or semilunar in form and are usually caused by fingernails. In many instances it is the fingernails of the victim trying to release the compressing hand which produce the injuries. It is probably more frequent to have fingernail marks produced by the victim than by the fingernails of the assailant.
Prominence of bruising on one side of the neck may suggest that the pressure has been caused by a thumb, rather than a group of fingers, but this is not necessarily correct. As a general rule it is wrong to use asymmetrical grouping of bruising in the neck as evidence of right or left handedness. Such grouping of bruises may be entirely fortuitous and may be determined as much by the relative positions of victim and assailant, as the position of the hand of the assailant. In some cases, patterned injuries may be present on the front of the neck when a textured garment lies between the compressing hand and the skin.
In cases of bodies undergoing early decomposition, particularly if the bodies have been lying in a prone position, there may be hemorrhage into the tissues of the neck and between the layers of neck muscle. These bruises are purely artifactual associated with vascular decomposition and gravity-dependent postmortem bleeding. In manual strangulation, the greater cornuae (lateral horns of the hyoid bone) may be fractured. However, in children and young adults, incomplete ossification and union of the components of the hyoid bone may make it almost impossible for fractures to occur. Because of the significance of such fractures, it is most important that removal of the hyoid bone and pharyngeal cartilages at the time of postmortem should be carried out with the utmost care.
Radiological examination may fail to reveal any fractures. Careful dissection of the cartilaginous structures is usually required to identify the fractures. The presence of bruising and hemorrhage associated with fractures to the larynx and hyoid bone may be considered evidence of the antemortem nature of the injuries. In the absence of such bruising and hemorrhage the possibility that the fractures are post mortem must be considered.
Fractures of the hyoid bone and laryngeal cartilages can occur as a result of direct blows to the neck and, therefore, in the absence of other evidence of strangulation, are not necessarily diagnostic of strangulation.
Because of the importance of identifying evidence of vagal inhibition as a possible factor in death, dissection and microscopic examination of the region of the carotid artery bifurcation including the carotid sinus is important and should be a routine part of the examination in alleged strangulation cases.

Ligature strangulation

Pressure on the neck by a constricting ligature, sometimes called ‘garroting’, frequently leaves a prominent grooved and abraded ligature mark around the neck. Such ligature marks, however, are not necessarily circumferential. The ligature mark although invariably horizontal may be interrupted by the positioning of clothing or long hair. Cords, wires, ropes and belts can be used as ligatures. Occasionally soft fabrics such as scarves and towels may leave little evidence of a ligature mark. In many cases, the ligature mark is not a simple linear mark but may be complex with evidence of criss-crossing of the ligature. The complexity of the mark may in part be caused by this overlapping of the ligature but may also be caused by either movement of the ligature on the neck or a double or repeated application of the ligature.
Although the majority of cases of ligature strangulation are homicidal in nature, suicidal ligature strangulation can occur. However, because, in the process of strangulation, the victim will become unconscious, self-strangulation requires a ligature which is either elastic and tightens itself around the neck, or some form of twisting device, such as a Spanish windlass which will prevent the ligature loosening.
Injuries to the neck musculature tend to be less marked in ligature strangulation than manual strangulation and may be entirely confined to the area immediately beneath the ligature.
Fractures of the hyoid bone and laryngeal cartilages are much less frequently seen in ligature strangulation than in manual strangulation. However, dissection and microscopic examination of the larynx may reveal evidence of internal hemorrhage.
Ligature strangulation is more often associated with the classic signs of asphyxia than manual strangulation unless reflex vagal inhibition with a cardiac arrest occurs and thus limits the development of these signs. Congestion and cyanosis above the level of the ligature may be prominent. The veins are completely obstructed in ligature strangulation but complete occlusion of the arterial system is relatively rare.

Neck holds and arm locks

Neck holds are taught by law enforcement agencies as a means of subduing suspects resisting arrest or to control prisoners who are combative and unmanageable. There are two basic types of neck holds. The ‘carotid sleeper hold’ often portrayed in professional wrestling competitions, and the ‘bar arm hold’ or ‘choke hold’.
Generally speaking, the choke hold, which involves pressure by the forearm of the assailant against the front of the neck of the victim, may cause collapse of the airway and serious injury to the structures of the neck. The carotid sleeper hold preserves the airway and is designed to compress the common carotid arteries producing transient cerebral ischemia and unconsciousness. The dangers associated with these holds have been researched and well documented. It is well recognized that deaths may occur during the application of these holds and during an arrest or controlling situation, where the victim is struggling, it may be almost impossible to apply a sleeper hold correctly. There is also some evidence that victims intoxicated with cocaine may be at increased risk of cardiac arrest and sudden death in such restraint situations.

Hanging

Hanging is a form of ligature strangulation in which the force applied to the neck is derived from the gravitational weight of the body or part of the body. In hanging, suspension of the body does not have to be complete. The forces required to compress the various neck structures and the clinical effects of experimental hanging have been fully documented.
Hangings may be accidental, suicidal, or homicidal. Accidental hanging is relatively uncommon but there are many cases recorded where adults and children have been accidentally hanged by being suspended after becoming entangled in ropes or clothing.
The commonest from of hanging is suicidal hanging. The degree of suspension is very variable and the victim’s feet are often resting on the ground and in some cases, the victim may be sitting on the ground with the force applied to the ligature being only that of the upper part of the body.
Homicidal hanging, with the relatively rare exception of lynching, is very rare and is usually associated with other injuries indicating a struggle prior to the hanging process. In homicidal hanging there are often other detectable reasons for incapacitation such as intoxication or head injury. In a few cases of homicidal strangulation, the body is suspended after death to make the case appear to be one of suicidal hanging.
The mark on the neck in hanging can almost always be distinguished from ligature strangulation. Because the force applied to the ligature is that of the weight or part of the weight of the body, the ligature is rarely horizontally positioned around the neck. It is usually directed upwards indicating the point of suspension and producing a ligature mark at the point of suspension, which may resemble an inverted V. A hanging mark often does not completely encircle the neck. Depending on the type of knot used and the tightness of the ligature, it is possible for relatively complex marks to be produced on the neck as the ligature slips, stretches or tightens around the neck structures.
In hanging cases, the surface texture of the ligature mark is frequently reproduced as a parchmented, grooved patterned abrasion characteristic of the particular ligature. The spiral weave or woven surface of a rope or cord may be accurately reproduced on the skin.
The autopsy findings in hanging frequently involve only the ligature mark on the outside of the neck. There may be no internal bruising detected, even after careful dissection and petechial hemorrhages in cases of complete suspensions are relatively rare. In hanging cases, with petechial hemorrhages distributed above the level of the ligature, the suspension has usually been incomplete. Similar effects can also be produced if the ligature breaks and the tension of the ligature is relieved. Dissection of the carotid arteries may show occasional linear traction (stretch tears) of the intima and fractures of the vertebrae do not occur unless there is a significant drop such as in judicial hanging. Even in judicial hanging fractures are relatively rare although bruising and tearing of the inter-vertebral ligaments may be seen.

Sexual Asphyxias

Auto-erotic or masochistic practices may involve compression of the neck inducing partial asphyxiation, alleged to heighten sexual pleasure and induce orgasm. Sexual asphyxias occur almost exclusively in men with only a few reports in the literature involving women. In the majority of deaths associated with sexual asphyxiation, there has been complete or partial suspension of the body with complex systems of ligature application, usually involving at least compression of the neck and obstruction of respiration. These deaths are usually accidental because the fail-safe mechanisms built into the routine of the practitioner have failed.
Characteristic findings in sexual asphyxias may include padding of the ligatures to prevent permanent injury, the presence of erotic or pornographic materials at the scene of death or evidence of prior ligature-related activities including grooves or damage to suspension points. The victims often arrange mirrors or cameras so that they can either witness or record their activities. Many of these activities are associated with a variety of fetish activities, transvestitism, cross-dressing and other evidence of sexual activity including binding or piercing of the genitalia and breasts.

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