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Chapter 4 Mechanical Asphyxia

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1 Chapter 4 Mechanical Asphyxia

2 Section 1 An Introduction to Asphyxia
1. Definition Asphyxia has been defined as primarily a state or series of states, induced by an oxygen supply short of tissue needs. 2. General aspects of asphyxia (1) Classification of asphyxia i. Mechanical asphyxia: smothering, throttling, strangulation by ligature (hanging), occlusion of the air-passages by foreign bodies and drowning etc. ii. Toxic asphyxia: intoxication with poisons such as cyanide and organic phosphate fertilizers, and by inhalation of irrespirable gases, such as carbon monoxide.

3 iii. Electrical asphyxia: muscular spasm or paralysis from malfunction of the central nervous system due to lightning, or electrocute. iv. Asphyxia due to low atmospheric oxygen content, for example, in closed lift or poorly-ventilated pit-cave. v. Pathological asphyxia: the occlusion of the airway by the effects of scalding or corrosives, angioneurogenic edema and acute inflammation etc. vi. Neonatal asphyxia: hypoxic hypoxia due to distorted umbilical cord or uterus spasm.

4 (2) General pathological changes
i. The external appearances (a) Lividity appears early and is well formed. The colors of lividity vary in intensity from duskiness to a dark-blue tint. The time of its appearance is accelerated (b) The face is congested and livid in colour, but in some cases it may be pale or slightly dusky, e.g., in cases of hanging.

5 ii. The internal appearances
(a) Visceral congestion Visceral congestion can be found as a general pathological change, and is usually well marked in deaths from mechanical interference with respiration. The larynx and trachea may contain a varying amount of slightly froth mucus. The lungs show highly congested and edematous. (b) Petechial hemorrhage Petechial hemorrhages in the visceral pleurae and visceral pericardium are often referred to (known) as “Tardieu’s spots” because they were originally described by A. A. Tardieu, a French Pathologist.

6 (c) Dark fluid blood When the postmortem autopsy is performed shortly after death, the blood is usually fluid, and its colour is often dark-blue. The fluid blood may result from the release of fibrinolysin shortly after death. The dark-blue blood is due to the large amount of reduced hemoglobin. (d) Cardiac dilatation Cardiac dilatation can usually be found at autopsy shortly after death from asphyxia, but it is not characteristic sign of asphyxia because distention of the atria and ventricles is a common postmortem phenomenon and may result from secondary muscular flaccidity.

7 Section 2 Suffocation 1. Definition
Suffocation is an obstruction to the passage of air into the respiratory tract caused by a closing of the external respiratory orifices. Suffocation includes deaths by smothering or overlaying, those due to foreign bodies in the larynx, trachea, and bronchi, and those due to inhalation of irrespirable gases. Suffocation may, therefore, result from natural diseases, accident, suicide or homicide.

8 Accidental cases of suffocation seem mostly observed in infants who has turned into a prone position, and apparently buried its face in a pillow or blankets during sleep, or accidental suffocation of an infant may occur in cases where the infants has to share the bed of its parent or parents. Suicidal suffocation is uncommon. Homicidal suffocation is relatively common in cases where the victim is too weak to resist against the assailant because of old age or illness or when the victim is sleeping or poisoned. However suffocation is one of the commonest methods used to kill the infants, because the criminal may smother the baby with a pillow, bedclothes or the palm of a hand without using much force.

9 (1) Special pathological changes
2. Mechanism of death Death is usually due to hypoxic hypoxia or anoxic anoxia due to interference with the oxygen supply. 3. Autopsy findings (1) Special pathological changes i. Postmortem lividity As we have learnt, the distribution of postmortem lividity depends upon the position of the body in the cases of suffocation. Lividity is usually deep purplish-blue.

10 ii. External wounds in the region of the mouth and nostrils
In homicidal suffocation, abrasions and bruises are generally found in the region of the mouth and nostrils. These injuries are usually produced during struggling, but they may be absent in cases where the victim is unable to resist. (2) Non-specific general pathological changes In cases of suffocation, visceral congestion is marked, and numerous petechial haemorrhages are usually found in the pleurae and pericardium.



13 1. Definition 2. Occurrence Section 3 Manual strangulation
Manual strangulation or throttling is the application of force to the neck of a person by pressure from the hands or forearms of another person. 2. Occurrence This is almost invariably homicidal. Throttling may occur in the course of assaults, and in cases of robbery and rape. Occasionally person may die from reflex cardiac arrest due to firm pressure on the side of the neck during an embrace.

14 3. Mechanism of death (1) Pressure on the sides of the neck may constrict the larynx and prevent the free passage of air down to the respiratory tract. This results in hypoxic hypoxia which can lead to rapid death. (2) Compression of one or both of the carotid sinuses can result in reflex cardiac arrest and sudden death. (3) Obstruction of the carotid arteries and internal jugular veins can result in cerebral hypoxia. Death may result if the cerebral hypoxia is maintained for a sufficient period of time.

15 (1) Special pathological changes
4. Autopsy findings (1) Special pathological changes i. External findings of the neck (a) The crescent abrasions and superficial bruise caused by fingernail may be observed on the neck. The position or distribution of the abrasions depends upon the attack on the victim. (b) When the assailant uses one hand and the attack comes from the front of the victim. The bruises and abrasions may be more numerous on one side of the neck than on the other side.

16 (c) When an assailant uses one hand and changes his grip, or when using both his hands, many bruises and abrasions may be found over the front and sides of the neck. (d) When the assailant uses his forearm in throttling, the attack usually comes from behind the victim. In such cases external injuries are usually absent.

17 ii. Internal findings of the neck
(a) Bruises may be found in the deeper tissues such as the deeper layers of the skin, the superficial fascia, the deep fascia, the sheaths of muscles, the cervical muscles and the substance of the thyroid gland. (b) Injuries to the hyoid bone and the laryngeal cartilages. Fractures of the hyoid bone are common phenomena in cases of throttling. This fracture is usually an irregular break in the continuity of the bone and is often accompanied by bleeding at the site of fracture. Not all fractures of hyoid bones are found in the case of throttling. However, when fractures of the hyoid bones are found, it is highly suggestive of throttling.

18 iii. Other injuries Generally, bruises and abrasions may be found on the other parts of the body because there are always struggling or fighting in cases of throttling. iv. Obstruction to the venous return from the head and neck Signs of mechanical obstruction to the venous return from head and neck include: lividity of the face and lips, engorgement and petechial hemorrhages in the conjunctiva, and petechial hemorrhage in the skin of the face and neck. (2) Non-specific general pathological changes The visceral congestion and numerous petechial bleeding are found in the pleurae and pericardium in the most cases of throttling.




22 Section 4 Ligature strangulation
1. Definition Ligature strangulation is a constriction of the neck by ligature, the constricting force being applied directly to the ligature. 2. Occurrence Accidental and suicidal cases of strangulation are uncommon. Homicidal strangulation is relatively common. 3. Mechanism of death Generally death is caused by anoxic hypoxia due to obstruction of the airway and jugular veins and/or carotid arteries, but in some cases it may be due to a reflex cardiac arrest which is produced by compression of the carotid sinus.

23 4. Autopsy findings (1) Special pathological changes i. On external examination, a single external ligature mark or more than one marks may be found surrounding the neck , which appear brown and dry. ii. The ligature marks are usually found over the lower part of larynx and the upper part of the trachea and transverse across the neck. Ligature marks sometimes are accompanied by abrasions and bruises. iv. The thin and hard ligature may cause a deep and narrow ligature furrow. iii. Fractures of the hyoid bone and the laryngeal cartilages are not common. (2) Non-specific general pathological changes Visceral congestion usually is found at autopsy.







30 Section 5 Hanging 1. Definition
Hanging is a constriction of the neck by a ligature, the constricting force being applied indirectly to the ligature through the weight of the body. In cases of hanging, the body is usually wholly suspended, but partial suspension or in a sitting posture can be seen occasionally. 2. Occurrence Statistically, death by hanging is a common form of suicide, accidental and homicidal hanging are rarely found in the forensic practice.



33 3. Mechanism of death (1) Death is due to the obstruction of the airway by the upward displacement of the base of the tongue against the palate and the posterior pharyngeal wall. (2) Death may be caused by the cerebral hypoxia due to obstruction of the carotid arteries and/or jugular veins or vertebral arteries by compression of the neck through ligature. (3) Death may be due to a reflex cardiac arrest which is caused by compression of the carotid sinus. (4) Death may be due to fracture-dislocation of the cervical vertebrae which is caused by jumping from a height and the falling arrested by a sudden jerk of the ligature.

34 4. Autopsy findings (1) Special pathological changes
i. Postmortem lividity When the body is suspended completely, lividity is usually seen in the dependent lower limbs and hands; in cases of partial hanging or suspension, lividity is found in the dependent lower parts of the body. ii. The external ligature mark (a) General appearances A single ligature mark is usually present on the neck, but in some cases, more than one mark may be found on the neck, because the ligature is composed of a double strands or several strands.

35 (b) Situation The mark is usually situated over the upper part of the larynx, but it may be lower in cases of partial suspension. (c) Direction Usually ligatures are tied in fixed loops with only one knot, but more than one knots may be found. In some cases of hanging, a running noose ligature is used. ① When a fixed loop is used with a single knot in the midline either under the chin or at the back of the head, the mark is seen on both sides of the neck and is directed obliquely upwards the position of the knot over the front or back of the neck.

36 ② When a fixed loop is used with the knot in the region of one ear, the mark differs on each side of the neck. On the side where the knot is situated, the mark is directed obliquely upwards towards the knot, whereas it is directed transversely on the other side. (d) Injuries to the tissues of the neck Bruises of the connective tissues and muscular tissues at the site of ligature mark may be found in cases of hanging.

37 (e) Injuries to the hyoid bone
Fracture of hyoid bone can occur in hanging. Especially, the greater born of the hyoid is often found fractured in aged persons in hanging. (f) Rupture of endothelium of the carotid artery Rupture of endothelium of the carotid artery may occur with subendothelial hemorrhage. This phenomenon is more common in aged persons. (2) Non-specific general pathological changes The visceral congestion may be found at autopsy in cases of hanging.
















53 Section 6 Drowning 1. Definition
Drowning is a form of death in which there is defective oxygenation of the blood in the lungs, due to the presence of fluid in the respiratory tract, the fluid entering the air passage through the nose and the mouth. 2. General aspect of drowning Usually, a person is completely immersed in drowning, but in some cases, if the persons are poisoned or unconscious, they may drown in a fluid medium which only covers their nostrils and mouth.

54 (1) When the first sudden intake of water occurs the larynx goes into spasm and a minimal amount of fluid enters the lungs. As the result the tissues become anoxia, and the death is due to the obstructive asphyxia. This type of death is usually called dry drowning. It is estimated that about 20 percent of cases of drowning dies from this mechanism. (2) In the most parts of cases of drowning, the person submerges, sucks in water, rises to the surface, expires, and submerges again drowning in more water. This process continues until the lungs become steadily heavier and finally full of water and then the body sinks to the bottom. At the same time, some fluid is swallowed.

55 Accidental drowning is the commonest form of death.
3. Occurrence Accidental drowning is the commonest form of death. Suicidal cases of drowning are also very common, but what is emphasized is that person who has determined suicide before hand may tie his hands and legs together or attach weight to his body before immersion. However, if the deceased could not tie himself up in the manner, he might be killed homicidally. But homicidal form of drowning is rarely seen.

56 4. Mechanism of death Death is usually due to hypoxic hypoxia, or anoxic anoxia or reflex neurogenic cardiovascular failure. 5. Autopsy findings (1) External appearances i. The face is usually pale but may sometimes appear pink and life-like due to oxygenation of the blood in the surface capillaries. ii. The most important external sign is the presence of fine foam and froth at the mouth and nostrils. The froth is composed of fine bubbles and results from the mixing together of air, mucus and water. This is almost a precise diagnostic sign of drowning. At the early time of death, when froth is clear of, it may continue to be forced out of the mouth and nostril.

57 iii. Cutis anserina or ‘goose skin’ occurs when immersion took place before molecular death and is caused by the contraction of involuntary muscular fibers. iv. If the deceased has been immersed in the fluid for a long time, the skin may become puckering or wrinkled. When this occurs on the hands it is known as washerwoman’s hand. This is caused by the action of the water or thickened epidermis.

58 v. Because the body often changes its position in the fluid, the lividity is difficult to establish. Sometimes, lividity may distribute over the forehead and chest, and is pink in colour. vi. In certain cases of drowning, grass or weeds or other objects in the fluid are grasped firmly by the deceased. This condition is cadaveric spasm which occurs antemortem or at the time of death, which is a diagnostic sign of drowning.




62 (2) Internal appearances
i. On opening the thoracic cavity, the larynx, trachea and bronchi are filled with froth which is the same as those found at the mouth and nostrils. ii. The lungs bulge outwards in a state of ballooning. It is due to the presence of fluid and air in the bronchi. As the result of increased volume, the lungs often show impressions of ribs upon their surfaces. Usually the lungs appear to be only moderately congested, and sometimes are very pale, due to air and water which forces the blood from the lungs and compressing the vessels in the inter-alveolar septa. iii. Fluid may be observed in the stomach and intestine, which has been swallowed during drowning.


64 i. Chloride content in the right and left ventricles.
(3) Other findings i. Chloride content in the right and left ventricles. In normal conditions, the chloride content of the blood is the same in both sides of the heart. When the water enters the lung alveoli in large amounts, the chloride may diffuse between the inhaled fluid and the blood in the pulmonary capillaries. If the drowning has taken place in fresh water, the percentage of chlorides in the pulmonary capillaries is lowered, where as the percentage is raised when drowning occurs in salt water. Chloride determinations have greater diagnostic value in cases of suspected drowning in sea water. In most of these cases the chloride level is higher in the left side of the heart.

65 ii. Diatoms in organs Diatom is a kind of very small planktons which is present in the fluid such as river and sea. It is now generally accepted that, during drowning, in water containing diatoms, the inhaled diatoms may penetrate in small quantity into the pulmonary capillaries, reach the left heart and are thus distributed throughout the body by the arterial circulation. On microscopic examination they may be found in the tissues of many organs, such as the lungs, the kidneys and bone marrow etc. Isolation of these viscera is also useful for the diagnosis of drowning by chemical digestion.




69 Section 7 Choking by foreign-body impaction
Death from choking may result from the impaction of foreign bodies in the pharynx, larynx, trachea or bronchi. 1. Occurrence Most of cases of death from choking occur in children, because they often place small objects such as marbles, coins or buttons in their mouth or they happen to be choked by food during dinner. Homicidal cases of choking are not common.

70 2. Mechanism of death The mechanism of death from choking may be described as follows: (1) Large foreign bodies may obstruct the airway completely and is due to hypoxic or anoxic anoxia. (2) Smaller foreign bodies may not be large enough to obstruct the airway, but they may cause a laryngeal spasm which interferes with the respiration. (3) Sudden reflex neurogenic cardiovascular failure may account for part of the death.

71 3. Autopsy findings (1) Foreign bodies may be found in the pharynx, larynx, trachea or bronchi during autopsy. (2) Other external and internal appearances are the same as those of asphyxia as mentioned before, such as dark-blue lividity, congestive viscera and petechial hemorrhage.


73 END

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