Understanding Postmortem Changes and Time of Death

Postmortem Changes and Time of Death 12.1.14

Postmortem = after death Necessary interdependent systems for life: Respiratory system Circulatory system Central nervous system Clinical death: All three of the above systems must be non-functioning Legal death: Can be determined based on absence of neurological function despite lack of clinical death

Determination of Clinical Death Observation for breathing Auscultation for heart beat Palpation for a pulse Instrumentation Electroencephalogram measures brain activity Can be misleading in cases of hypothermia due to depressed body functions Electrocardiogram

Immediate Postmortem Changes

Immediate Postmortem Changes Cessation of respiration Cessation of circulation Muscular relaxation Loss of reflexes Skin pallor (paleness loss of natural color) Dilated pupils

Early Postmortem Changes (not immediate) Apparent after one or two hours:

Early Postmortem Changes (not immediate) Apparent after one or two hours: Algor mortis Livor mortis Rigor mortis

Early Postmortem Changes (not immediate) Apparent after one or two hours: Algor mortis body cooling Livor mortis discoloration due to blood settling Rigor mortis stiffening of muscles

Algor Mortis Normal body temperature varies Body cooling does not occur at a uniform rate Under average conditions, the body cools at the rate of about 2.0-2.5oF per hour for the first few hours, then slower afterwards. Skin cools more rapidly than the inside of the body that is why the inner body core temperature should be taken at the scene.

Modes of Heat Loss Conduction Radiation Convection -

Modes of Heat Loss Conduction Heat transfer by items in contact Radiation Infrared heat transfer Convection Heat transfer by air movement

Factors Affecting Algor Mortis

Factors Affecting Algor Mortis Time Environmental temperature Location of body In water the temperature of a body would drop more rapidly, on the ground more slowly due to insulating effect of soil, etc. Body type and clothing obesity or heavy clothing slows cooling due to insulation Humidity and air currents body exposed to wind will cool more rapidly

Livor Mortis Discoloration of the skin in lower regions of the body Usual color of lividity is red-purple Begins immediately at death due to lack of circulation Blood settles due to gravity Small vessels and capillaries become congested with blood

Livor Mortis Not generally apparent for 1-2 hours Fixed (or permanent) after 6-12 hours Blood will not flow to a new region if the body is moved after livor is fixed, thus inappropriate lividity (livor mortis in an unexpected location) is an indication that the body has been moved at least 6-12 hours after death

Livor Mortis Pressure can effect appearance of livor mortis, as pressure can displace blood in regions that should otherwise be darkened

Livor discoloration Red-purple Normal Pink Cyanide or cold Cherry-red CO or fluoro-acetate Brown Nitrites or methemoglobin Note: Livor can be confused with bruises livor can be drained, but blood from bruises cannot since the blood has infiltrated the surrounding tissues and is no longer in the capillaries

Livor Mortis While livor mortis is a poor indicator of time of death, it is excellent for determining the place/position of death

Rigor Mortis A post-mortem stiffening of the muscles due to lactic acid causing a cross-linkage between actin and myosin (the proteins involved in muscle contraction)

Rigor Mortis ATP generally breaks this cross-linkage, but ATP is depleted shortly after death Rigor persists until decomposition begins to break down the protein complex, thus relaxing the muscles

Factors Affecting Rigor Rigor is generally noticeable at ~3 hours, but can be accelerated by: Environmental heat Fever in victim prior to death Some drugs Exercise prior to death Can be slowed by: Cold environment Emaciation

Rigor/Algor at Average Temperatures Body warm and flaccid: <3 hours Warm and rigid: 3-8 hours Cold and rigid: 8-36 hours Cold and flaccid: >36 hours

Other time of death indicators?

Other time of death indicators? Insects various insects deposit eggs and those eggs develop and known rates Stomach contents -

Other time of death indicators? Insects various insects deposit eggs and those eggs develop and known rates Stomach contents food takes approximately two hours to digest and then be emptied from the stomach under normal conditions

Late changes in Death Decomposition Adipocere Mummification Skeletonization

Decomposition Two processes drive decomposition: Autolysis Putrefaction

Decomposition Two processes drive decomposition: Autolysis Body s own digestive enzymes begin to break down cellular proteins and other molecules. Begins immediately after death. Putrefaction

Decomposition Two processes drive decomposition: Autolysis Body s own digestive enzymes begin to break down cellular proteins and other molecules. Begins immediately after death. Putrefaction Decomposition driven by bacterial activity. This is the primary factor causing decomposition.

Putrefaction process Green discoloration of abdomen begins at 24-36 hours after death Marbled appearance often noticeable due to intravascular hydrogen sulfide producing bacteria Gas formation and bloating noticeable at 60-70 hours causes blisters and skin slippage, loss of hair and nails

Putrefaction Liver filled with holes why??

Putrefaction Liver filled with holes due to invasion and proliferation of gas-producing bacteria during decomposition

Factors affecting decomposition

Factors affecting decomposition Temperature Humidity Body location: Decomposition rates on land are generally twice as fast as in water, and eight times as fast as those when a body is buried due to lack of oxygen and lower temperatures

Alterations to normal decomposition Adipocere Grave Wax Conversion of fats to oleic, palmitic, or stearic acids (these are waxes, not fats) Occurs in damp, warm, anaerobic (no oxygen present) environments Due to lack of oxygen, other decomposition changes do not occur

Adipocere

Mummification The process of desiccation of a body Occurs in exceedingly dry conditions Normal decomposition processes prevented due to lack of water necessary for bacterial growth