Cause and Mechanism of Death

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Cause and Mechanism of Death

• 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
• Mechanism of death- a biochemical or physiologic
  abnormality produced by the cause of death that
  is incompatible with life

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Manner of Death

• defined as the fashion in which the cause of
  death came to be
• Four manners of death
• Natural
• Accidental
• Suicidal
• Homicidal

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Time of Death

• Three methods used to estimate time of death
• Rigor Mortis
• Livor Mortis
• Algor Mortis

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Time of Death

• Rigor Mortis- stiffening of muscles which occurs
  following death
• Results from a chemical reaction with glycogen
• ATP is used up and not reformed
• 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

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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

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Time of Death

• Algor Mortis- cooling of the body after death,
  and assumes ambient temperature is lower than
  body temperature
• General rule of thumb- a nearly nude body exposed
  to 18-20 degrees Centigrade loses 1.5 degrees
  first 8 hours

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Classification of Traumatic Deaths

• Traumatic deaths are classified as
• Mechanical- sharp and blunt trauma
• Chemical- poisoning
• Thermal- exposure to excessive heat or cold
• Electrical- electrocution

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Mechanical Trauma

• Mechanical trauma occurs when applied physical
  force exceeds the tensile 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

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Mechanical Trauma

• Exsanguination- death after a significant loss of
  blood - a major artery or the heart is damaged
  and blood loss occurs, and can occur in either
  sharp or blunt force trauma

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Firearm Injuries

• Firearm projectiles cause blunt trauma
• Firearm projectiles are classified by their
  propellants
• Gunpowder
• Smokeless gunpowder- nitrocellulose
• Most common suicidal and homicidal wounds are
  results of firearm blunt trauma

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Firearm Injuries

• Firearm injuries are distinct due to type of
  weapon
• Rifled weapons- rifles, handguns
• Smooth bored weapons shotguns and antique
  weapons
• Injuries produced are result of velocity of
  projectile
• The extent of injury increases as the square of
  the velocity increases times the mass of the
  projectile

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Firearm Injuries

• Gunshot wounds can be classified in two manners
• Penetrating- creates an entrance wound but not
  exit wound- projectile must be recovered from
  body to confirm this
• Perforating creates both an entrance and exit
  wound- no projectile recovered from body

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Firearm Injuries

• Distance each component of reaction travels is
  the basis for determining the distance of the
  barrel from the victim of the shooting
• Gas is projected from barrel only a few inches
  and creates a near-contact wounds which creates
  blackening of skin if victim is close to
  discharge of weapon
• Skin will also show lacerations from force of gas

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Firearm Injuries

• Carbon monoxide from discharge mixes with
  hemoglobin and myoglobin in wound to produce
  carboxyhemoglobin and carboxymyoglobin, which are
  both bright red in color, compared to normal dull
  red color of hemoglobin and myoglobin

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Firearm Injuries

• As the distance of the barrel away from the skin
  increases, gas diminishes and only unburned
  powder and bullet can penetrate skin
• Stippling- created by unburned powder on skin
  around defect produced by bullet
• Handguns create stippling when held .5
  centimeters to 1 meter away from skin

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Firearm Injuries

• Distant gunshot wounds
• Lack smoke and powder effects
• Range is normally indeterminate
• Comprised of a circular skin defect and rim of
  abraded skin around edges
• Diameter of skin defect is some indication of
  diameter of bullet, but not always reliable due
  to differences in diameters of common bullets

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Firearm Injuries

• Directionality- direction from which bullet
  enters and traverses the body.
• Emergency room physicians without forensic
  training who assess directionality of entrance
  wounds to the body have error rate of almost 100
  in assessing direction of wound when an exit
  wound is present

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Firearm Injuries

• Estimating velocity of exiting bullet
• Assess exit wound
• Small, slit shaped wounds with few side
  lacerations are generally from bullets traveling
  at slow speeds
• Exit wounds with many side lacerations generally
  have traveled at high speeds- military or hunting
  long arm rifles

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Firearm Injuries

• Exit wounds are supported or shored if victims
  wears tight clothing such as a heavy leather
  coat, or is against a material such as dry wall
  which will support the skin and allow penetration
  of the bullet
• Shored exit wounds appear to be remarkably like
  entrance wounds- one must closely note the rim of
  abrasion of the wound, as it is larger

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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

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Firearm Injuries

• Normally, bullets that exit body waste kinetic
  energy
• However, with handguns, alterations made to a
  bullet affect the probability of exiting.
  Designed to enlarge during passage through
  tissue, they are called
• Hollow points
• Jacketed hollow points

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Blunt Force Trauma

• Blunt force trauma can result from motor vehicle
  accidents
• Generally, with exception of gunshot wounds,
  homicidal blunt force trauma in an adult requires
  lethal head injury injuries to other areas
  rarely produce death
• In children, head injuries are most common,
  however, but chest and abdominal trauma with
  lacerations to spleen, liver and heart are seen

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Blunt Force Trauma

• Most common mechanism of death from blunt force
  trauma is drowning in blood that has aspirated
  into lungs
• Contusion- accumulation of blood in tissue
  outside the blood vessels- most commonly caused
  by blunt force trauma
• Pattern of blunt object may be transferred to
  person who is struck

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Chemical Trauma

• Ethyl alcohol, (ethanol) active ingredient in
  beer, wine and liquor is a contributory factor in
  50 of traumatic deaths
• Alcohol is a depressant it slows reactions and
  communications from the brain and spinal cord
  neurons
• Person under influence of alcohol breathes slower
  and slower until lack of oxygen causes death
• Around a .30 gram percent of blood alcohol,
  person goes into coma

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Chemical Trauma

• Barbituates, diazepams, and opiates produce
  deaths in same manner as death from alcohol
• Cocaine is a stimulant and high doses can cause
  seizures, extremely high body temperatures and
  uncontrolled quivering of heart
• Marijuana is exception- never known to have
  produced an overdose death

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Stomach full of bags of cocaine
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Chemical Trauma

• Carbon Monoxide (CO) is an odorless, colorless,
  explosive gas
• Deaths due to CO may be accidental, suicidal or
  homicidal
• CO kills by asphyxiation binds to hemoglobin 300
  times more than oxygen and cuts off oxygen to
  brain

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Chemical Trauma

• Cyanide is generally available as sodium or
  potassium salt
• Has a distinct odor like almonds
• Up to 50 of the population cant smell cyanide
• Forensic Pathologists should be able to smell
  cyanide, especially in cases of suspected of
  suicide by cyanide.

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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

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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 hyperthermia-
  temperatures 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

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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

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Struck by lightning
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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

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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

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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

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Asphyxias

• Asphyxia may be caused by
• Manual strangulation using hands
• Strangulation by ligature

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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

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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

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Asphyxias

• Ligature strangulation, whether by hanging or
  garroting, generally results in findings of a
  furrow in the neck