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Asphyxia is generally accompanied by ‘dyspnoea’ i.e. the sensation of laboured breathing described by patients as ‘air hunger’
Prolonged asphyxia results in hypoxia, i.e. a lack of oxygen in the tissues, which mainly affects the tissues and organs most sensitive to oxygen deficiency, such as the brain.
If hypoxia is prolonged, the tissues stop functioning and a series of sequential events quickly occur: loss of consciousness, irreversible brain damage, coma and death of the patient.
Interestingly, the need to breathe is induced by increasing levels of carbon dioxide in the blood rather than by too low levels of oxygen.
Sometimes the level of carbon dioxide is not sufficient to induce ‘air hunger’ and the subject becomes hypoxic without realising it.
Causes of asphyxia
There are three main causes of asphyxia:
- the presence of intrinsic or extrinsic airway obstruction;
- the absence of adequate oxygen concentration in the environment;
- the presence of chemical or psychological interference.
There are various causes that can prevent gases from passing through the airways, creating mechanical barriers in them.
These obstructions can be intrinsic (the obstruction is internal to the airway) or extrinsic (the obstruction is external to the airway but comes to strongly compress it).
The most common causes of mechanical obstruction are:
- compression of the chest or abdomen (compressive or compression asphyxia, see appropriate section);
- obstruction of the external airways;
- presence of food or foreign objects in the trachea;
- strangulation (sometimes performed to increase sexual arousal);
- narrowing of the airways due to bronchial asthma or anaphylactic shock;
- aspiration of vomit (typical in children and drug users).
Outside air alteration
Asphyxia can result from prolonged exposure to an atmosphere containing too low a concentration of oxygen, which occurs in various situations, such as
- loss of pressurisation in the cabin of an aircraft. The pressure inside commercial aircraft is maintained at that equivalent to 6000 ft (1800 m), but a failure of the pressurisation system can bring the internal pressure back up to that outside.
- when workers descend into a sewer or the hold of a ship containing gases without oxygen and heavier than air, usually methane or carbon dioxide;
- in the case of reckless use of a closed-circuit underwater rebreather where the recirculated breathing air contains insufficient oxygen.
An extreme example of asphyxiation is that caused by exposure to the vacuum of space, as happened in the case of the decompression of the Soyuz 11 spacecraft on 29 June 1971, the day on which human beings died in space for the first and only time.
Chemical or psychological interference with breathing
Various chemical and psychological situations can interfere with the body’s ability to absorb and use oxygen or regulate oxygen levels in the blood:
- inhalation of carbon monoxide, e.g. from the exhaust of a car, carbon monoxide has a high oxygen-like affinity for haemoglobin in red blood cells, so it binds strongly with haemoglobin, replacing the oxygen it should normally carry within the body;
- contact with chemicals, including pulmonary agents (such as phosgene) and blood agents (such as hydrogen cyanide);
- self-induced hypocapnia through hyperventilation, such as in shallow or very deep water, and asphyxiation;
- a respiratory crisis that stops normal breathing;
- obstructive apnoea during sleep;
- overdose resulting from drug intake;
- central alveolar hyperventilation syndromes;
- acute respiratory distress syndrome.
Compression asphyxia (also called chest compression) refers to the limitation of lung expansion by compression of the torso, which interferes with breathing.
Compression asphyxia occurs when the chest or abdomen is compressed.
In accidents, the term ‘traumatic asphyxia’ or ‘crush asphyxia’ is commonly used to describe the compression asphyxia of a person who is crushed or pinned under a great weight or force.
An example of traumatic asphyxia is when a subject, while using a mechanical lever to repair a car, is crushed by the weight of the vehicle when the lever slips.
In fatal crowd-related disasters, such as the Heysel Stadium disaster, traumatic asphyxia is called ‘crowd compression’.
Contrary to popular belief, it is not blunt trauma that causes the vast majority of deaths in many cases, but rather compression asphyxia caused by trampling by the crowd: people at the bottom are literally trampled by other individuals, preventing the former from expanding their chests necessary for proper breathing.
Asphyxia, how quickly does one die?
If asphyxia, and hence hypoxia, is prolonged over time, tissues stop functioning one after the other, starting with the brain (whose tissue is particularly avid for oxygen) and a series of events quickly occur in sequence: loss of consciousness, irreversible brain damage, coma and death of the patient.
The time at which death occurs is extremely variable by virtue of various factors such as age, state of health, state of fitness and mode of asphyxia.
An elderly individual, suffering from diabetes, hypertension and pulmonary emphysema, if subjected to a compressive force (e.g. strangulation) resulting in mechanical asphyxia, can lose consciousness and die in less than a minute, as can a child suffering from bronchial asthma.
An adult, fit individual, accustomed to prolonged exertion (think of a professional athlete or diver), subjected to chemical asphyxia, such as that from carbon monoxide inhalation, may, on the other hand, take several minutes to lose consciousness and die.