The process of death may be initiated by failure of any of the three vital systems of the body-
1. Failure of the nervous system – Coma
2. Failure of the circulatory system – Syncope
3. Failure of the respiratory system – Asphyxia.
In coma, there is loss of consciousness which may be partial or complete, depending on the degree of involvement of the central nervous system. When unconsciousness is complete without any response to any sort of stimulus, we term it deep coma. When the patient is partially conscious and responds to deep and painful stimuli, it is partial coma. In case of deep coma, the reflexes are lost. In case of partial coma, the reflexes may be sluggish, normal or even brisk.
A man may go to coma due to —
1. Cerebral compression resulting from head injury. In head injury cases, cerebral compression may be caused due to intra-cranial haemorrhages, cerebral oedema, depressed com-minuted fracture.
2. Cerebral injuries or injuries to the brain matter at different levels.
3. Infective states like, encephalitis, meningitis, abscess.
4. Compression caused by a new growth.
5. Metabolic disorders like diabetes, uraemia.
6. Lack of circulation in brain as in case of embolism or occlusion of carotid and vertebral arteries.
7. The effects of certain drugs and poisons like, opium, barbiturate, alcohol, chloroform, CO, CO2 etc.
8. Miscellaneous causes like, epilepsy, heat stroke.
Post mortem findings —
The general external and internal findings are insignificant. The specific cause in the form of injury, brain oedema, abscess or new growth may be obvious during postmortem examination. Poisoning may give typical physical signs and may also be detected by chemical analysis of the viscera/organs and blood, preserved from the dead body.
In syncope, there is failure of function of the heart and the circulatory system.
With circulatory collapse, there is rapid, weak or slow pulse, fall of blood pressure; there may be air hunger and feeling of oppression in the chest with ringing in the ear and dimness of vision. Lately, there is cyanosis, cold skin and sweating. Vital centres at the base of the brain fails due to lack of oxygen, due to circulatory failure.
Causes of Syncope —
1. Pathology of the heart — This may be in the myocardium, pericardium, the heart valves, the conduction system of the heart and the heart circulation.
2. Vagal inhibition of the heart.
3. Anaemia, particularly, sudden loss of excessive amount of blood. If the quantity of sudden loss of blood due to injury or some disease is l/3rd or more of the total volume of the body blood, then chance of death is very high.
4. Anoxia – In severe hypoxia, the otherwise healthy heart may fail to function normally and may stop functioning before the failure of the respiratory centre and before respiration stops.
5. Cardiac poisons – They may cause heart failure though the heart may otherwise be healthy.
6. Even when none of the above factors is present, simple over-exercise or exhaustion may cause syncope.
Postmortem findings — The cause, or the pathology due to the cause, is more obvious than the direct effects of syncope. In case of diseased condition of the heart, the pathology may be detectable macroscopically or microscopically. In case of vagal inhibition, no specific signs are expected. In case of severe blood loss, the body and the organs will look pale. In case of anoxic condition, some or many of the signs of asphyxia will be there and that may create problem as to, whether the heart failed early or respiration ceased early. In case of poisoning, the postmortem examination may reveal some macro-findings due to the effects of poison and chemical examination will reveal the poison. In case of syncope due to exhaustion, no specific findings may be expected. In such a case rigor mortis appears early and passes off early.
Death is said to have occurred due to asphyxia when, respiratory function ceases first and initiates the process of failure of the other two vital systems. In asphyxia, there is prevention of exchange of air between the atmosphere and to the lungs alveoli and there is lack of oxygen supply to the tissues.
Asphyxia may be mechanical, toxic, traumatic or pathological. The causes thus are as follows—
1. Constriction around or pressure over the neck, as in cases of hanging, strangulations including throttling.
2. Closure of the external respiratory orifices, as in case of smothering.
3. Occlusion of the respiratory passage from inside, as in cases of drowning, choking and gagging.
4. Restriction of the respiratory movement caused due to compression over the chest, as in cases of traumatic asphyxia and overlying.
1. Poisons which depress the respiratory centres, like – Opium, barbiturate, CO2, H2S, chloroform, bromides etc.
2. Respiratory tract irritants, like, irritant volatile poisons or irritant vapours, e.g., chlorine gas, SO2, vapours of HNO3, HCl, ammonia gas etc.
3. Poisons which affect the pick-up, carriage, and diffusion of oxygen at the tissue level, like, phosgene, CO, cyanides.
4. Lack of oxygen in the inhaled air.
5. Poisons which cause paralysis of the respiratory muscles like, muscle relaxants, curare, cobra snake venom.
1. Injury to both lungs.
2. Pulmonary embolism – Fat and air emboli may be of traumatic origin.
IV. Pathological causes — Infective conditions and new growth of the lungs or in the respiratory tract.
Stages of asphyxia:
The progress of asphyxia manifests in three phases. These are:
1. State of dyspnoea — Initially, increased CO2 level in the blood causes respiratory stimulation and the rate and depth of the respiration is increased. There is breathlessness, feeling of oppression in the chest and headache. There is increased pulse rate and raised blood pressure. Mild degree cyanosis may be noticed.
2. Stage of convulsion – The level of CO2 in the blood is further increased. The pulse rate and the blood pressure are still high. The neck veins are engorged. There is marked cyanosis. Expiratory effort is more prominent. There is convulsion.
3. Stage of respiratory exhaustion — The respiratory centre is depressed. There is gasping respiration, the rate is much diminished. Muscles are relaxed, reflexes are lost or very sluggish, there are deep cyanosis, widely dilated pupils. There is fall of blood pressure, pulse is feeble and slow. Involuntary passage of stool and urine may occur. There is failure of the vital centres and death.
Pathogenesis — In acute cases, the process of asphyxia progresses very rapidly. The increased CO2 tension in the blood causes capillary dilatation and loss of tonicity of the vascular wall. This leads to stasis of blood. On one hand, the organs are congested and on the other, increased permeability of the capillary wall due to asphyxia causes oedema of the organs. The sum effect of capillary dilatation, stasis and congestion is low venous return. This further aggravates the lack of oxygen and increase of CO2 in the blood which in turn exerts its effects as described above. Hence, the progress towards the final stage is very rapid, if the primary cause of the asphyxia continues.
Stasis of blood and distension of capillaries cause their rupture and leakage of blood in the tissue. High CO2 tension also increases the capillary permeability and leakage of whole blood in the tissue. Thus, minute haemorrhagic spots appear in the tissue spaces which are known as petechial haemorrhagic spots or Tardieu’s spots. These are pinhead size or slightly larger haemorrhagic spots, more conspicuous at the under surface of pleura, pericardium and epidermis.
Postmortem features in case of death due to asphyxia –
External features – The postmortem staining is bluish and prominent. Cyanosis is evident at the fingertips, nail-beds, ear lobules and lips. Face may be congested and in some cases of violent asphyxial deaths, there will be presence of Tardieu’s spots over the forehead, eyelids and conjunctiva. In some cases, depending on the mode and process of asphyxiation, there may be protrusion of the eyeballs and the tongue. In some cases there may be involuntary discharge of faeces and urine and in males, in some cases, there is seminal discharge. Externally, evidence of mode of asphyxiation may be present in some cases like, presence of ligature marks in strangulation and hanging dribbling of saliva in hanging, abrasions and bruises around the mouth and nose in case of smothering and on the neck in case of throttling and copious fine white froth in case of drowning.
Internal findings — The organs are in general congested. Congestion is more marked in deaths due to asphyxia of short duration than of long duration. The lungs are congested, oedematous with presence of Tardieu’s spots at the undersurface of pleura, particularly at the interfaces of lobes. Tardieu’s spots are also present at the undersurface of the pericardium and in the brain and meninges. Vessels contain dark fluid blood. In more number of cases, the right side chambers of the heart contain blood and the left side chambers are empty. According to the specific cause of asphyxia, there will be presence of specific signs in different organs like lungs, trachea and larynx as in cases of death due to drowning and strangulations. Similarly, there will be additional findings in the structures of the neck, inside the mouth cavity and the chest wall, in cases of compression of neck, smothering and traumatic asphyxia respectively. For details of those findings see the chapter of violent asphyxial deaths.