Download Cause and Mechanism of Death

Cause and Mechanism of Death
1. Cause of death- a disease or injury that
initiated the lethal chain of events ,
however prolonged or brief, that led to
death of the person
2. Mechanism of death- a biochemical or
physiologic abnormality produced by the
cause of death that is incompatible with
life
Manner of Death
• defined as the fashion in which the
cause of death came to be
– Four manners of death:
a. Natural
b. Accidental
c. Suicidal
d. Homicidal
Time of Death
– Three methods used to estimate time
of death
• Rigor Mortis
• Livor Mortis
• Algor Mortis
Time of Death
– Rigor Mortis- stiffening of muscles which occurs
following death:
• Results from a chemical reaction with glycogen
• Normally sets in about 4 hours after death
• Exceptions include instant rigor mortis and
death from electric shock- both create shorter
onset of rigor mortis from time of death
• Generally disappears 24-48 hours after death
Time of Death
• Livor Mortis- discoloration of body from
settling of red blood cells after blood stops
circulating (aka lividity)
– In light skinned individuals, lividity may be seen
within an hour after death
– In dark skinned individuals, lividity may not be
able to be seen
– Substantial blood loss may result in little lividity
– Lividity becomes fixed about 12 hours after death,
and slowly disappears with decomposition after
36 hours
Time of Death
• Algor Mortis- cooling of the
body after death, and assumes
ambient temperature is lower
than body temperature
Classification of Traumatic
Deaths
– Traumatic deaths are classified as
a. Mechanical- sharp and blunt trauma
b. Chemical- poisoning
c. Thermal- exposure to excessive heat or
cold
d. Electrical- electrocution
Mechanical Trauma
1. Mechanical trauma occurs when applied
physical force exceeds the strength of the
tissue to which the force is applied
– Sharp objects produce incised and stab wounds
• Example- a stab wound by an object, such as a knife,
which has more depth than its other dimensions
– Blunt objects produce lacerations
• Example- a wound caused by an item such as a brick or
stone, which creates significant damage
2. Firearm Injuries
A. Firearm projectiles cause
blunt trauma
B. Most common suicidal and
homicidal wounds are results
of firearm blunt trauma
Forensic Firearm Analysis
Firearm Injuries
C. Gunshot wounds can be classified in
two manners
1. Penetrating: creates an entrance wound
but not exit wound- projectile must be
recovered from body to confirm this
2. Perforating: creates both an entrance and
exit wound- no projectile recovered from
body
More on Firearm Injuries
• Entrance wounds are generally round
due to being fired from a rifled barrel
• Rotation of bullet during flight causes
wound to be round or elliptical
• Yawing- when a bullet enters a body
sideways
• Yawing does not normally occur, but
can when bullet passes through a
medium thicker than air
• Another Video on Ballistics
D. Blunt Force Trauma
1. Blunt force trauma can result from motor
vehicle accidents
2. Generally, with exception of gunshot
wounds, homicidal blunt force trauma in an
adult requires lethal head injury – injuries to
other areas rarely produce death
3. In children, head injuries are most common,
but chest and abdominal trauma with cuts to
spleen, liver and heart are seen
Blunt Force Trauma
4. Most common mechanism of death
from blunt force trauma is drowning in
blood that has aspirated into lungs
5. Contusion- accumulation of blood in
tissue outside the blood vessels- most
commonly caused by blunt force trauma
6. Pattern of blunt object may be
transferred to person who is struck
Chemical Trauma
1. Ethyl alcohol, (ethanol) active
ingredient in beer, wine and liquor is
a contributory factor in 50% of
traumatic deaths
2. Alcohol is a depressant: it slows
reactions and communications from
the brain and spinal cord neurons
3. Person under influence of alcohol
breathes slower and slower until
lack of oxygen causes death
Chemical Trauma
4. Barbituates, diazepams, and opiates
produce deaths in same manner as death
from alcohol
5. Cocaine is a stimulant and high doses
can cause seizures, extremely high body
temperatures and uncontrolled quivering
of heart
Chemical Trauma
6. Carbon Monoxide (CO) is an odorless,
colorless, explosive gas
7. Deaths due to CO may be accidental,
suicidal or homicidal
8. CO kills by asphyxiation
9. Lungs show bright cherry red color
when carbon monoxide poisoning is
present- this can determine if someone
died in a fire or was placed into the fire
after death
Chemical Trauma
• Cyanide is generally available as
sodium or potassium salt
• Has a distinct odor like almonds
• Up to 50% of the population can’t smell
cyanide
• Forensic Pathologists should be able to
smell cyanide, especially in cases of
suspected of suicide by cyanide.
Thermal Trauma
• Exposure to excessive heat or cold may
produce death
• Exposure to either cause breakdown of body
mechanisms that maintain body temperature
around 37 degrees Celsius
• Hypothermia death common in individuals
who are intoxicated by alcohol- alcohol
increases loss of body heat and reduces
appreciation of the cold
Thermal Trauma
• Hyperthermia – heat related illness which can cause
death
• The ability to maintain homeostasis declines as
people age
• Thermal burns are wounds caused by hyperthermiatemperatures above 65 degrees C (140 F) will
produce burns upon direct contact
• People who die at fires most commonly die from
inhalation of Carbon monoxide
• People who die with only a 1-2% CO level in a burned
structure is presumptive evidence they were dead or
not breathing when fire started
Electrical Trauma
• Passage of electricity through a person may
cause death by a number of different
mechanisms
– Low voltage AC current ( under 1000 volts)
crosses the heart and ventricular fibrillation is
experienced (nonpropulsive quivering of heart)
that leads to nonresucitability within minutes
– Heart normally produces 300 quivers per minute
– AC produces 3600 quivers per minute
Struck by lightning
Electrical Trauma
• In high voltage exposures:
– Poration occurs: result of flow of current
through tissues which creates holes in
membrane of cells. This creates a
devastating loss of limbs in person
exposed to high voltage
– Electrical current burns person in a
fraction of a second
Asphyxias
• Asphyxia- interruption of oxygenation to
brain
• Drowning- death from asphyxiation due to
immersion in water or other liquid
• Water enters stomach, then coughing and
reflex inhalation cause water to enter smaller
air passages of lungs
• Loss of consciousness occurs within 1-2
minutes, unless additional air can be
obtained
Asphyxias
• Diatoms assist in providing clues to
determine time and place of drowning
– Diatoms are small unicellular one celled
organisms found in salt or fresh water
– Contain silica, and resist degradation
– During late stages of drowning, diatoms in
aspirated water are circulated by heart to organs,
including bone marrow
– Not normally found in bone marrow, diatoms can
assist especially if body is severely decomposed
or skeletonized
Asphyxias
• Asphyxia may be caused by:
– Manual strangulation using hands
– Strangulation by ligature
Asphyxias
• Results of manual strangulation using
hands
• Typically, manual strangulation
fractures the cornu of the thyroid
cartilage
• Even more common in manual
strangulation is hemorrhage of muscles
in neck
Asphyxias
• In manual strangulation, fracture of
hyoid bone in neck is infrequent, and
seen in elderly women who have
osteoporosis, which makes fracturing
the bone easier
Asphyxias
• Ligature strangulation, whether by
hanging or garroting, generally
results in findings of a groove in
the neck