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Learning unit 4 Asphyxia Associated deaths
Medicina Forensis (University of the Free State)
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Department of Forensic Medicine
University of the Free State
MEDICINA FORENSIS: LMDF4824
Forensic Medicine and Pathology Lecture Notes
This document serves as a guideline to 3rd and 4th-year law students regarding this module. The
purpose of the information in this module is to enable the legal practitioner to apply their gained
knowledge in understanding general concepts in forensic medicine and pathology, solve medical
ethical problems and advise their clients accordingly.
Some of the information, graphics, and/or presentations in this document are not the authors' property.
However, its use is guided by commonly accepted "Fair use" policies for teaching or academic
purposes and remains the intellectual property of its user.
(Updated: Dr Stefan Jv Vuuren_2021)
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CONTENTS
LEARNING UNIT 4: ASPHYXIA ASSOCIATED DEATHS ............................................................. 3
Mechanics of breathing ...................................................................................................................... 3
Asphyxia ............................................................................................................................................ 4
“Cardinal signs” of asphyxia ......................................................................................................... 5
Mechanical asphyxia .......................................................................................................................... 5
Pressure to the chest ........................................................................................................................... 7
Pressure to the neck............................................................................................................................ 7
Manual strangulation ..................................................................................................................... 8
Ligature strangulation .................................................................................................................... 8
Hanging.......................................................................................................................................... 8
Other external pressure to the neck................................................................................................ 8
Drowning ........................................................................................................................................... 9
Signs of drowning .......................................................................................................................... 9
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LEARNING UNIT 4: ASPHYXIA ASSOCIATED
DEATHS
Upon completion of this learning unit you must be able to:
• Understand and discuss the classification of Asphyxia Associated deaths.
• Understand the mechanisms of death involved in Asphyxia Associated deaths.
• Understand and discuss the investigation and forensic outcomes in cases of Asphyxia
Associated deaths and be able to advise your clients accordingly.
Unit specified study material:
• Lecture notes.
Mechanics of breathing
The chest is a ridged structure comprised of the spine, sternum, ribcage, and clavicles. The chest also
contains and protects vital organs including the heart, lungs, and major blood vessels. One of the
functions of the chest is to provide the structure for the mechanics of breathing. It functions as a
negative-pressure suction pump via the actions of the intercostal muscles and diaphragm.
Breathing is a mechanism of actively sucking oxygen-rich air into the lung alveoli through the
airways, and passively expelling carbon monoxide-rich air out through the airways.
It is an involuntary function (but can be voluntarily overridden to a certain extent) controlled by the
respiratory centers in the brainstem. The respiratory center receives information regarding carbon
monoxide concentrations in the blood, adjusting the rate and depth of breathing to compensate for
high carbon monoxide (and low oxygen) levels.
Exhalation is a passive function of stored energy in the expanded chest.
Inhalation is an energy-dependent active process of inhaling air into the lungs. It is accomplished by
muscle contraction to expand the dimensions of the chest and requires energy. States of energy
depletion may thus impair breathing efforts.
The mechanism of breathing thus requires the ridged structure of the chest, expansion of the chest,
energy, and competent airways.
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Asphyxia
Asphyxia is a Latin word which means “absence of pulsation” i.e. cardio-vascular collapse and the
absence of blood flow through the blood vessels.
Asphyxia is defined as an external influence through which the body is deprived of oxygen in one of
three mechanisms:
• Delivery of oxygen to the body,
• Transfer to oxygen from the blood the cells of the body, or
• Utilization of oxygen by these cells.
The fatal consequences of the above mechanisms have all been classified as Asphyxia Associated
deaths. However, any single classification system encompassing all the mechanisms inadvertently
either excludes one or more causes of death considered to be asphyxia related, or includes causes not
considered to be asphyxia related. To confound it even more, these mechanisms may also represent
the pathophysiological processes involved in some natural causes of death e.g. pneumonia where the
mechanism of death involves the failure of oxygen transfer from inhaled air to the blood, or anemia
where the mechanism of death involves the failure of oxygen transportation to the end organs.
It is useful to classify Asphyxia Associated deaths into three categories in terms of the external
circumstances which caused the death of the victim.
1
2
3
Environmental
Asphyxia
Low partial
pressure oxygen in
inspirated air.
Mechanical
Asphyxia
Physical
interference or
impairment of the
mechanics of
breathing.
Histotoxic
Asphyxia
Impaired cellular
uptake or utilization
of oxygen for
metabolic
processes.
Low atmospheric oxygen
e.g. a child locked in an abandoned fridge suffocates due to depleted
oxygen
Oxygen being displaced by other gasses
e.g. a person suffocates due to displacement of oxygen by paint fumes
Obstruction of the airways
e.g. a victim is smothered by closing their nose and mouth with a plastic bag
e.g. a child chokes to death after aspirating a small toy
Impairment of the mechanics of breathing
e.g. a miner dies of traumatic asphyxia after heavy rocks pins down on his
chest to prevent him breathing
Poisons and drugs
e.g. a person dies from carbon monoxide poisoning
In some instances a combination of these categories may occur e.g. a person in a house fire may suffer
environmental and toxic asphyxia due to the combustion processes involved which deplete
atmospheric oxygen and produce gasses which may replace oxygen in the blood cells.
It is very important to acknowledge that asphyxia as an “isolated” mechanism of death does not exist.
The cardio-respiratory systems work in synergy and are interdependent. Any adverse
pathophysiological process of the respiratory system will inadvertently lead to pathophysiological
responses from the cardiac system!
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The Manner of death in Asphyxia Associated deaths may include suicide, homicide, and accidental
deaths. Most cases of homicidal death due to asphyxia involves Mechanical Asphyxia.
“Cardinal signs” of asphyxia
Most often, the most important information indicating Asphyxia Associated death comes from the
scene of death where the body is found hanging, immersed, pinned down by a weight, etc. The
diagnosis of an asphyxia death is one of exclusion of other more plausible causes of death.
Several signs may be noted during autopsy which may support a diagnosis of an Asphyxia Associated
death. Cyanosis, petechial hemorrhage, visceral congestion, and fluidity of the blood are often
described as the “cardinal” or “classical” signs of asphyxia. However, these signs are all, individually
or in combination, present in other causes and mechanisms of death not associated with asphyxia.
These cardinal signs are most pronounced in causes of death associated with impaired blood return of
the neck veins, as one would see in some asphyxia scenarios. The cardinal signs of asphyxia are thus
singly or in combination merely “consistent with” and not “diagnostic of” a death due to asphyxia.
Diagnosis of death due to asphyxia is often a diagnosis of exclusion and is usually made by1:
1. History or circumstantial information of environmental, mechanical, or histotoxic
asphyxia e.g. the deceased was found inside a locked fridge.
2. Signs of any of the three mechanisms or categories of asphyxia e.g. aspirated toy in the
airway of a child.
3. The classical signs of asphyxia.
4. Exclusion of another more plausible cause of death.
Mechanical asphyxia
Mechanical asphyxia is the mechanical- or physical interference of breathing of a person by either
preventing airflow through the airways or impairment of the mechanics of breathing.
•
Obstruction of the airways
The airway may be obstructed at various anatomical points, from the orifices (lips and nose),
pharynx, larynx, trachea, and bronchi.
•
Impaired mechanics of breathing
The expansion of the chest can be impaired by either external compression or prevention of
expansion or splinting of the diaphragm to prevent movement e.g. positional or traumatic
asphyxia.
Examples of mechanical asphyxia associated deaths:
Smothering
External obstruction of the mouth and nose via a physical barrier e.g. a pillow, hands, duct-tape, etc.
It is often associated with homicidal deaths but may also be present in accidental and suicidal deaths.
In homicides, smothering may sometimes be consistent with the intent to kill the victim. It may also
represent an effort of the perpetrator to silence the victim that has “gone wrong”.
1
Not all 4 indicators need be present, but the 1st and 4th are most important.
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In accidental deaths, smothering may be encountered in scenarios of severe alcohol intoxication.
Often scenarios of Sudden Unexplained Deaths of the Infant (SUDI and/or SIDS2) also presents as
smothering.
The amount of pressure needed to occlude the airway opening is minimal but usually depends on the
ability of the victim to prevent occlusion e.g. as an intoxicated person may not be capable to turn their
head away from the occlusion.
Choking
Choking refers to the internal occlusion of the larynx, trachea, or bronchi with a foreign body or
substance.
Choking is most often encountered as an accidental inhalation of a foreign object by children, or
intoxicated persons while eating.
Gagging
Gagging is the internal obstruction of the oropharynx by e.g. forcing a wet cloth into the mouth of a
victim Gagging is a form of choking associated with homicides, as with smothering.
Throttling
Throttling is a term used for manual strangulation via external pressure to the neck by the
perpetrator’s hands.
Hanging
One of the mechanisms of death in hangings is the occlusion of the airway via the application of an
external ligature, where the pressure to the neck from the ligature is due to the complete or partial
weight of the body (see Pressure to the neck).
Aspiration
Aspiration is a similar term as choking, used in scenarios of accidental inhalation of fluids from the
stomach, airways, or mouth into the small airways (bronchioles and alveoli).
Positional asphyxia
Prevention of the expansion of the chest due to impaired contraction of the diaphragm muscle either
due to states of depleted energy or splinting of the diaphragm.
It is also referred to as postural asphyxia as certain body postures can splint the diaphragm to impair
its function. One of the mechanisms of death associated with historic crucifixion is postulated to be
positional asphyxiation.
In homicidal scenarios, it is sometimes associated with deaths in custody where detainees are
“hogtied” or where they are left on their stomachs, hands tied behind their back. It is also closely
related to scenarios of “excited delirium”.
Traumatic asphyxia
Prevention of the expansion of the chest via external pressure, constriction, or closed spaces. It is also
called crush asphyxia or mechanical asphyxia (a Forensic misnomer). A good example of accidental
traumatic asphyxia is the constriction of an anaconda around the chest of its prey. Traumatic asphyxia
2
Sudden Infant Death Syndrome
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is commonly encountered in other accidental settings like mining accidents or motor vehicle
accidents.
Pressure to the chest
Pressure on the chest may prevent the expansion of the chest and impair the active inhaling of
oxygen-rich air into the lungs. If death ensues, this is called Traumatic asphyxia.
Traumatic asphyxia is most often associated with accidental or homicidal scenarios of death.
Accidental traumatic asphyxiation may be found in occupational accidents (e.g. in mining accidents
where a person is trapped by the weight of fallen rocks), motor vehicle accidents (e.g. the occupant is
trapped by bent/deformed vehicle parts which prevent the expansion of the chest), crowd stampedes
(e.g. where continuous weight from people prevents expansion of the chest), or SUDI (e.g. overlying
of the baby by the mother in situations of co-sleeping).
Homicidal traumatic asphyxia is most often associated with situations of restraint procedures during
arrests made by the police.3 It is then also often found in association with Positional asphyxia and
Excited Delirium Syndrome.
Pressure to the neck
Pressure to the neck may be so severe that it occludes the airways and cause asphyxia. It is associated
with scenarios of hanging, ligature strangulation, manual strangulation, and external pressure to the
neck. All these scenarios have one of, or a combination of, 4 mechanisms of death in common, caused
by the pressure to the neck (in order of least to the most amount of pressure needed for effect):
3
•
Venous occlusion
Minimal pressure is needed to completely (or partially) occlude the veins of the neck. This
leads to impaired venous blood return from the head and neck, and subsequent congestion,
edema, and increased pressure in the brain. These pathophysiological mechanisms will, if not
alleviated, lead to loss of consciousness and death within minutes.
•
Carotid sinus excitation
Minimal pressure on the carotid sinuses, situated in the bifurcation of the carotid arteries high
up in the neck, may lead to cardiac arrhythmias via the cardiac control center in the midbrain.
If prolonged or severe, or if the victim has underlying cardiovascular pathology, it may lead
to acute cardiac failure and subsequent death.
•
Arterial occlusion
Some pressure is needed to occlude the arteries of the neck. This leads to acute hypoxia of the
brain and subsequent death if not alleviated. The brain is extremely sensitive to ischemia and
hypoxia. With complete occlusion of the arteries to the brain, loss of consciousness will ensue
within seconds, and death soon thereafter.
•
Airway occlusion
Much pressure is needed to occlude the airways of the neck. Airway occlusion (Mechanical
asphyxia) is very seldom associated with deaths due to pressure to the neck.
There have been examples of murder via traumatic asphyxiation.
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Pressure to the neck may theoretically cause injury to the bony tissue of the neck. It is rarely
associated with suicidal hanging or strangulation. Fractures to the cervical spine are associated with
judicial hanging, and is more likely to be due to a rapid jerking action caused by the weight of the
body during the fall in the hanging procedure.
Manual strangulation
Manual strangulation is defined as death due to pressure to the neck where the force of the pressure is
due to tightening pressure of hands applied to the neck. It is also referred to as throttling.
Deaths due to Manual strangulation may indicate intent and it should only be diagnosed as a cause of
death in scenarios where there is a clear indication of manual strangulation i.e. a patterned injury or
injury pattern indicating the use of hands around the neck.
Ligature strangulation
Ligature strangulation is defined as death due to pressure to the neck where the force of the pressure is
due to the tightening of a ligature applied to the neck.
Ligature strangulation may be associated with accidental (e.g. the classic scenario of the office
worker’s tie caught in the paper shredder) or homicidal scenarios of death.
In homicidal deaths, ligature strangulation may indicate intent and it should only be diagnosed as a
cause of death with caution.
Hanging
Hanging is defined as death due to pressure to the neck where the force of the pressure is due to the
weight of the partial or complete suspension of the body from a ligature.
Hanging deaths are most often associated with the suicidal manner of death, although this is not
exclusively so. In terms of Forensic Pathology, suicidal hangings should be differentiated from
homicidal hangings and ligature strangulations. This may be attempted by noting specific signs more
consistent with one or the other diagnosis of the manner of death.
Other external pressure to the neck
Choke holds, neck holds, bar arm holds, etc. are often associated with restraint procedures used by
police. It is often associated with Excited Delirium Syndrome where the “victim” is in a state of
uncooperative aggression, excitement, and/or anxiety.
In law enforcement. the intention of such holds is mostly not to be lethal but rather to “calm down” or
restrain. Often, however, the outcome is lethal. This then often presents the court with a dilemma of
intent. “How much pressure was needed?”, “How long must the pressure be applied?”, “Could the
assailant have foreseen…?”, etc. are often questions from the court to expert witnesses. The short
answer to all those questions in most scenarios is that all the mechanisms of death associated in such
circumstances are just too variable to provide the court with a “beyond reasonable doubt” answer.
Any attempt to answer this must be done and interpreted with caution.
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Drowning
From a Forensic Pathology perspective, immersed bodies present a complex circumstance of death
where the cause of death may be related to accidental, suicidal, homicidal, and natural causes.
Immersed bodies often are also in a stage of advanced decomposition, further complicating the death
investigation.
Circumstances of death of bodies retrieved from or near water:
• A person may die while swimming or other activities in the water.
o Natural cause of death: On death investigation signs of drowning and the natural
disease may be noted.
o Unnatural cause of death: On death investigation, clear signs of the unnatural cause of
death will be noted with no signs of drowning.
• A person may die while performing activities near the water, and then the body falls into or
is swept away into the water.
o Natural cause of death: On death investigation, clear signs of the natural disease will
be noted with no signs of drowning.
o Unnatural cause of death: On death investigation, clear signs of the unnatural cause of
death will be noted with no signs of drowning
• A person may die away from the water, and the body is then dumped into or near the water.
o Unnatural cause of death: On death investigation, clear signs of the unnatural cause of
death will be noted with no signs of drowning.
Not all deaths associated with immersions are asphyxial of nature. The mechanisms and causes of
death associated with the immersion of a person include asphyxia, sudden cardiac death, hypothermia,
diverse external causes (e.g. shark attacks), etc.
Signs of drowning
As for deaths due to asphyxia, the most important information indicating death by drowning comes
from the scene of death where the body is found partially or completely immersed in water. The
diagnosis of a drowning death is one of exclusion of other more plausible causes of death.
Drowning is defined as a death due to the partial (airway orifices only) or complete immersion of a
person in a fluid medium. It is per definition due to mechanical asphyxia in that the fluid “obstructs”
the airways either from the outside or if inhaled. This leads to the “wet-drowning-dry-drowning”
hypothesis of signs of drowning.
Most persons, if not incapacitated for some reason, will have a breath-holding response when
submerged into water. While submerged, breath-holding will be maintained until either:
i.
ii.
The victim loses consciousness and death ensues4 i.e. called dry-drowning, or
The victim is overwhelmed by the urge to breathe and inhales water, and death ensues i.e.
wet-drowning.
In victims of dry-drowning, the death investigation often reveals signs of immersion but minimal or
no signs of drowning. The mechanism of death in dry-drowning is as much associated with asphyxia
4
There might still be some gasping efforts with water into the upper airways.
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as with acute cardiac death. In victims of wet-drowning one often finds the “classical signs of
drowning”.
As with the classical signs of asphyxia, the “classical signs of drowning” is a Forensic misnomer.
These signs often are present in non-drowning deaths associated with immersion or not. The classical
signs of drowning are:
• Cutis anserina
• Emphysema aquaosum
• Water in the airways or stomach
• Mastoid air-cell hemorrhages
Diagnosis of death due to drowning is often a diagnosis of exclusion and is made5 by:
1. History or circumstantial information of partial or complete immersion.
2. Signs of immersion.
3. Signs of wet- or dry-drowning.
4. Exclusion of another more plausible cause of death.
5
Not all 4 indicators need be present, but the 1st and 4th are most important.
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