“Classical” signs of asphyxia
These signs are non-specific and are not only often absent in typical hypoxic deaths, but may also sometimes be present in non-hypoxic deaths. The matter is complicated further by the fact that some asphyxic deaths may occur without hypoxia, for instance neurogenic cardiac arrest. Bernard Knight, a well-known forensic pathologist, believes that the non-specific nature of these signs are so obvious, that it forms part of forensic mythology. However, as it is sometimes dogmatically advocated by some authors, it is discussed in this study guide to give some perspective on this matter.
Petechial, punctate or pinpoint haemorrhages originate from small venules which are less than 2 mm in diameter. It may occur on the skin, eyes (sclera and conjunctiva), as well as the thoracic organs and the membranes covering the body cavities (pleura and pericardium). The petechial haemorrhages of the pleural surface was first described by Tardieu, and are also noted in cases of sudden infant death syndrome (SIDS or cot death). There is often also some degree of swelling of the tissue. Possible causes include increased venous pressure, decreased intrapleural pressure and/or hypoxic damage to the walls of the blood vessels. The pressure in the thoracic cavity is usually negative, and this assists in keeping the lung in an inflated position. With airway obstruction the individual will struggle to inhale air. The muscles of respiration will contract more powerfully, and the negative pressure in the thoracic cavity will increase even further. The blood will be ``sucked'' from the small blood vessels in the pleural tissue. Petechial haemorrhages can also occur in the post-mortem period, as discussed in the study unit on post-mortem hypostasis (study unit 3).
When there is obstruction of venous blood flow, blood will accumulate above the level of obstruction. In the beginning there is congestion of blood in the vessels, but later fluid from the vessels leak into the surrounding tissue, causing swelling. In the lungs this oedema will produce a foamy fluid, as air and fluid will be mixed during breathing. This is often pronounced in cases of drowning.
Cyanosis is a colour change which occurs when the haemoglobin concentra-tion, saturated with oxygen, drops below 85%. The skin, lips and other mucosal surfaces assume a blue hue or appearance. Post-mortem cyanosis is controversial, because death is generally associated with lack of circulation, and therefore insufficient oxygenation of the haemoglobin. The degree of cyanosis is therefore not an indication of the type of death.
This alleged characteristic of asphyxic death is often discussed in Asiatic literature. It is however a non-specific phenomenon.
To summarise: There is no single sign which is indicative of asphyxic death. The diagnosis therefore depends on circumstantial evidence, as well as other external changes, such as scratch marks on the neck or fractures of the hyoid bone.
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