5Mechanisms of death 1. Air way obstruction 2. Arteries and veins obstruction3. Heart failure due to RSCD (Remotely Stimulated Cardiac Dysfunction)Mixture of above.Air ways, veins or arteries obstruction alone cannot cause death in manual strangulation. Though the victim looses consciousness in 10 sec of hypoxia, it needs 4 minutes of continuous obstruction for the brain to die, which is not practical at all.
6HF due to RSCD-if constriction of carotids on or above the carotid bodies, it takes it as raised blood pressure and hence decrease the heart rate.If constriction is below the carotids, it takes it as decreased BP and hence increase the heart rate. So in both mechanisms heart goes into heart failure due to arrhythmias. Heart failure can cause increase of venous pressure. When it lasts more than about 15 seconds it gives rise to Asphyxial features.
7Some times, when the obstruction is on or above the carotids, heart can go into sudden asystole by vagal stimulation (called vagal inhibition). In such cases Asphyxial signs are absent. This is the mechanism which supposed to be operated in accidental manual strangulation.
8Manner of death 1. Usually homicidal. Usually victims are females. Usually following rape or sexual abuse.2. Accidental- very rare.Eg. During hugging. Mechanism is supposed to be vagal inhibition.3. Suicidal- only one case is reported.Can be due to vagal inhibition or HF due to RSCD. Other methods cannot be operated, as when the person loses consciousness, the pressure on neck is released and the person recovers.
9Post Mortem Investigation 1. Authority- magistrate order2. History-history of the incident- when, where, why, what, who did that.History after the incidentHistory before the incident (PMH/PSH/ SH)
103. Visit to the scene-commonly rape murder incidents. So collecton of trace evidences, volitional activities, weapons, ect must be collected.4. Identification of the body-by relatives or friends.5. Autopsy- preliminary investigations-photographs of injuriestrace evidence collection- hair, nails, fibres, swabs from anus, vagina and mouth.X-ray- neck – AP and lateral.
116. Clothing examination- 7. External examination-General –identification features.Post mortem changes to asses time since death.Specific features-Features due to mechanism of death (asphyxial features present or not)Features due to the agent (finger nail abrasions and finger pulp contusions)Features due to circumstances (sexual abuse features)
12Specific external features 1. Due to mechanism of death-A.) Asphyxial features due to HF or mixture of all mechanisms. – important feature is they are above a tide level in neck.Petechiae- on eyes, conjunctivae, forehead, behind ears, cheeks.Congestion and oedema of face.Bluish discoloration of face.Confluent haemorrhages- large sub-conjunctival haemorrhages, ear bleeding, nasal bleeding, patchy SAHs.B. no asphyxial features – eg. Accidental strangulation by vagal inhibition
142. Due to the agent- A) finger nail abrasions- Three types-Impact nail abrasions-Cresentic,Triangular,Batons shape,ExclamationOvalRectangular,Scratch nail abrasions-Claw nail abrasions-Do not comment on the direction of assault by using the concavity of the nail abrasions. (Bernard Knight)
16Defense scratches-vertical, multiple, almost parallel, superficial nail abrasions on neck. They are inflicted by the victim himself while struggling to survive.
17B. Finger pulp contusions- 1-2 cm diameter, (5 penny contusions).Round, oval or irregular shapes.Four methods of causation,One hand x from frontBoth hands x from frontBoth hands x from behindPalmNot received by victims hands. All are causes by assailant.
183. Circumstantial features- Due to sexual abuse- Genital injuries with hymenal tares.
19Internal examinationDissection by using Prinsloo-Gordon technique to remove contusion artifacts which could be formed by infiltration of blood in to neck tissues after death or during dissection.Release the congestion in neck by removing blood from cranial end by removing the brain first. Then dissect the neck by using a V dissector, layer by layer, insitu, in a bloodless field. Do a facial dissection also by elevating the skin upto nose.Internal injuries are more than external injuries in manual strangulation.
20Three types of internal features Due to mechanism of death (asphyxial features)Due to agent (finger pulp contusions)Due to circumstances (sexual assault features)
211. Internal features due to mechanism of death. Asphyxial features -above a tide level in neckPetechiae – on thyroid glands, epiglottis, larynx.Congestion and oedema,bluish discoloration,confluent haemorrhages – patchy SAHs, epiglottis haemorrhages.
222.Internal features due to agent- finger pulp contusions- more extensive haemorrhages are seen in internal structures than on external. Round, oval or irregular contusions on strap muscles, thyroid glands, etc. Contusions on front and sides of larynx are significant. Contusion behind the larynx could be Prinsloo - Gordon artifact, which is commonly seen in postmortems. Contusions also can occur in oesophagus..
23Fractures- hyoid bone horns, thyroid horns, cricoid, tracheal rings Fractures- hyoid bone horns, thyroid horns, cricoid, tracheal rings. Some times thyroid plate fracture can occur if palm pressure is uses. To say a laryngeal fracture as AM, must see macroscopic evidence of bleeding at the site of the fracture.Carotid intimal tears-Usually no injuries to the vertebral column or spinal cord.