Any mechanical interference with the respiratory process, causing lack of oxygen and death of an individual is called violent asphyxial death.
Effective respiration depends on the combination of three critical elements:
- An open and patent airway
- A functional muscular pump or bellows system to achieve airflow in and out of lungs
- An adequate gas exchange between the alveoli of the lungs and the pulmonary vascular system
1. Mechanical Asphyxia
Smothering is a form of asphyxia caused by mechanical occlusion of external air passages, which include the nose or mouth by hand, cloth, plastic bag or any other material.
Choking is a form of asphyxia caused by mechanical occlusion of the lumina of the air passages by a solid object. (Café coronary)
Throttling is the manual strangulation
- By hands (throttling)
- By ligature
- By hanging
General Causes of Hypoxia
- Absence/reduction of oxygen in general atmosphere (suffocation) e.g. plastic bags, well, gutter, tank, etc.
- Closure of external respiratory orifices i.e. mouth and nose (smothering, gagging)
- Obstruction of internal respiratory passages at:
- Pharynx –choking due to foreign body, laryngeal edema, food bolus, hemorrhages, dentures
- Trachea –throttling, strangulation, mugging
- Bronchi –aspiration, drowning
- Restriction of respiratory movements
- Diseases of lungs
- Cardiac failure
- Blood disorders –anemia
- Carbon monoxide poisoning
- Cyanide poisoning
Classical Signs of Asphyxia
1. Petechial hemorrhages on the face and neck, due to rupture of small venules on application of pressure. Pressure may be severe enough in strangulation to rupture larger plexus of venules producing larger echymoses.
Second most common place for petechial hemorrhages is chest especially visceral and parietal pleura, due to negative pressure developed in an increased effort to inspire.
2. In manual strangulation, arterial supply is not hampered while venous drainage of head and neck is obstructed, leading to more leakage of fluid from veins. This results in bulging of eyes, protrusion of tongue, edema and congestion
3. Cyanosis is most commonly seen on the face, i.e. bluish discoloration of face due to reduced oxygenated hemoglobin.
4. Increased fluidity of blood and enlargement and engorgement of right heart is also found, but these findings are not included in the classical signs of asphyxia.
Petechial hemorrhages are seldom seen in hanging and not seen at all in drowning. They might be seen in some bleeding disorders as well.
Petechial Hemorrhages (Tardieu’s Spots)
Petechial hemorrhages are the pinpoint (1-2 mm) collections of blood in serosal and skin surfaces due to rupture of small venules under pressure.
- Most often seen on face and conjunctiva
- Bleeding from nasal mucosa and external auditory meatus
- Most often seen on serosal membranes of thorax. Mostly on visceral pleura and rarely on parietal pleura
- Commonly seen on the heart surfaces
- Also may be found on the thymus in infants
- Never seen on peritoneal serosa
Significance of Petechial Hemorrhages
- Generally petechial hemorrhages are highly unreliable signs of asphyxia
- Only the facial and ocular petechiae may have significance as indicator of asphyxia
- Normally they are present in areas of hypostasis
- Post mortem petechiae can appear especially in dependent parts
- In drowning and suffocation, petechiae are seldom visible
2. Positional Asphyxia
Positional asphyxia occurs when the position of a person’s body interferes with respiration, resulting in death from asphyxia or suffocation.
At death, the victim must be found in a position that interferes with pulmonary gas exchange (breathing). Such a position may range from one that causes obstruction of the mouth and nares, to one that causes restriction of the chest and diaphragm.
In inability of the victim to escape this position must be explained. In positional asphyxia death unrelated to restraints, unconsciousness due to acute alcohol intoxication is the most frequent explanation of the victim’s inability to escape from asphyxiating posture.
All other causes of death –natural or unnatural, medical or traumatic, must be explored by autopsy and excluded to a reasonable degree of medical certainty.
3. Restraint Asphyxia
- Arm lock
Mugging/’Arm lock’ (Carotid sleeper or Bar arm)
When strangulation is affected by compressing victim’s neck against the forearm, it is known as mugging (choke-hold). It may leave no external or internal mark of injury.
4. Sexual Asphyxia or autoerotic asphyxia
5. Traumatic asphyxia
- Homicidal traumatic
- Penetrating trauma
- Pressure on chest
- Accidental trauma