After the death, some natural changes occurs in human body. To understand some common post mortem changes and the conditions that affect them to allow the forensic pathologist to estimate the post mortem interval.

It also provide a time frame during which the death occurred. Post mortem refers to the process that occur in a body after death producing different changes in the body. The events can be predicted, many changes in the body can influence the rate and extent of alterations in the body.

The changes in ambient temperature tend to alter the rate but do not change the biological mechanism of post mortem changes. The putrefaction may cause interpretational problems. The purging of putrefaction fluid from the mouth and the nostrils is confused with blood.

Introduction

After death, a sequence of changes naturally occur in the human body. To understand common post mortem changes and the other affects that allow the forensic pathologist to more accurately estimate the postmortem interval and to provide a time frame during which death occurred. As with other biological phenomena, there are many variables influencing postmortem changes. Post mortem examination, also known as autopsy, is the examination of the body after death. The aim of post mortem is to determine the cause of death. Post mortem provides various information about when, how and why someone died.

A post mortem will be carried out if it is been requested by:

1. A hospital doctor- to find about more about his illness or the cause of death
2. A coroner- because the cause of the death is unknown or following a sudden ,violent or unexpected

A post mortem will be carried within 2 to 3 working days of a person's death. In some cases it may be possible to only take 24 hours. The post mortem takes place in a room that looks like a operation theater. During the procedure, the deceased person's body is opened and the organs are removed for the examination. When the post mortem is done, the organs are returned and the body is stiched and the body is returned.
After post mortem is done, the pathologist writes the report of the findings. If the post mortem was requested by the coroner, the coroneris given the report by the pathologist. If the post mortem was suggested by the hospital doctor, then the hospital is given the report.

The human tissue authority ensures that human tissue is used safely, ethically and with proper consent. The authority regulates organizations that remove, store and use of tissue for research, medical treatment, post mortem examination. In all premises where the post mortem is carried out must be licensed by the human tissue authority.

Types of post mortem

1. Coroner's post mortem examination:

   A coroner is a judicial officer responsible for the investigation of death in certain death. They are usually lawyers or doctors with the experience of minimum 5 years. In some cases, a doctor or the police refer a death to the coroner. A death will be referred to the coroner if:
   # It is unexpected, such a sudden death
   # It's violent, unnatural or suspicious, such as suicide
   # The result of accident or injury
   # It occurred during or after the hospital procedure
   
   The main aim of post mortem requested by the coroneris to find out how someone died and decided whether an inquest is needed. A coroner may decide to hold an inquest after a post mortem has been completed. Sample of organs may need to be retained until after the inquest has finished.
    

2. Hospital post mortem examination:

   Post mortems are sometime requested by hospital doctors to provide more information about illness or the cause of death. Sometimes the relative of the deceased request the hospital for post mortem to find more details about the death. Hospital post mortem may limit to particular areas of the body.

Factors affecting post mortem changes

The rate of post mortem changes varies on intrinsic and extrinsic factors. Intrinsic factors involving the subject that affect postmortem changes primary include a body mass and the surface area of the body. Extrinsic factors that affect post mortem changes primary include the clothing and insulation, the environment of the death scene and storage of body after death. Some of the factors that increase the rate of post mortem changes include freezing temperature, scantily dressed or naked storage of the body in a cold chamber shortly after death.

Classification of post mortem changes

Immediate post mortem changes

It is also known as rapid changes after death. It relate to the cessation of bodily functions including the respiratory, circulatory and nervous system. These changes are specifically the signs of death. Respiration completely stops after death resulting in loss of respiratory movements and breathing sounds. Circulatory stoppage results in a loss of pulse which can also be confirmed by a flat electrocardiogram (ECG Machine) in a hospital setting. The absence of cardiac and respiratory sounds on auscultation over a period of 5 minutes indicates a sign of death. The break-up of the columns of blood in the retinal blood vessels on ophthalmoscopy confirms stoppage of circulation. It is the one of the earliest indications of death. Cessation of nervous system functions results in the loss of sensory and motor functions and reflexes. The muscles also begin to become flaccid with lose of tone.

Early post mortem changes

The changes in eye occur during the early post mortem period include corneal turbidity and tache noire formation. The intraocular tension falls to nil in about 2 hours after death. Algor mortis is the post mortem cooling of body temperature until it equalizes the temperature of the surrounding environment. The rate of cooling becomes linear before slowing down again as it approaches the ambient. The ambient temperature is a critical factor that affects the rate of post mortem cooling of the body. A prudent forensic pathologist will not estimate the time since death based on the single criterion of algor mortis as the rate of post mortem cooling of the body is affected by multiple variables.

Livor mortis is also known as post mortem hypostasis or post mortem lividity. It is a passive process of blood accumulating within the blood vessels in the parts of the body as a result of gravity that causes a discoloration of the skin that varies from pink to dark purple. It begins to be apparent about an hour after death. It is well formed in 4 hours after death and gets fixed about 8 hours of the death. It is worth noting that timing of livor mortis is highly variable. Hemolysis leads to fixation of lividity, which may be absent in anemic or in those who died of severe hemorrphage.

Rigor mortis is the stiffening of the muscles of the corpus due to depletion of adenosine triphosphate after death with build-up of lactate in muscle tissue which results in an inability to release the actin-myosin bond. The process of rigor mortis involves all muscles of the body. Rigor mortis occurs in both voluntary and involuntary muscles including the cardiac muscle. It is the first evident in the facial muscles after 4 hours of the death. The rate at which rigor mortis passes off will be rapid in a hot environment as the onset of the putrefaction is hastened in environment. Cold temperature lengthen the duration of rigor.

Late post mortem changes

The late post mortem is divided into decomposition, mummification and adipocere formation. There are two mechanism involved in decomposition i.e. autolysis and putrefaction. Decomposition begins soon after death in the form of autolysis. Autolysis is a process that occurs due to leakage of hydrolytic cellular enzymes from cells after death. The changes that occur in this process are on a microscopic rather than a macroscopic level. Autolytic changes are most prominent in the pancreas and other organ with high concentration of cellular enzymes.

Mummification results from tissue desiccation. It is a phenomenon that occurs when corpse is in an environment that is hot and dry. The skin of corpse becomes dark, dry and leathery in appearance. The body appears parched.

Audipocere is yellowish to gray, waxy substance that can preserve the corpse as a whole or some parts of it. It is buccad pad of fat that retain outline of cheeks. The process occurs in corpses in environment that are high in moisture. The formation is recorded to have occurred about 3 weeks after death. In many caases, it becomes apparent only months after death.

Post mortem stages of death

Death is one of the main fact of the life. It is inevitable. Once a person dies, the body undergoes a series of changes in different manners. These stages are also affected by the factors of corpse. To determine the stage and state of decomposition of the body, the pathologist can estimate a time frame in which the death occurred. It is essential in medicolgal investigation. It is impossible to determine the exact time of death unless there is a witness or any other verifiable source of this information.

There are 4 stages of death in post mortem:

• Pallor mortis
  It is the first change that occur in a corpse, that is the paleness in the face and other parts of the body. It is due to cessation of the capillary circulation. The first sign is shown within 15 to 30 minutes of the death. It is usually insignificant to determine the time of death, unless the death has occurred shortly before finding of the body.
   
• Algor mortis
  This process ceases the function after death. A corpse eventually starts from cooling or heating to match the outside temperature. The rate at which the temperature of the body is adjust to the outside temperature gives indication of the post mortem interval. It can be affected by the number of factors that adjust the temperature.
   
• Rigor mortis
  After death, all muscles of the body becomes weak. After that the whole body will stiff. This stiffenes in the body is called rigor mortis. It helps in many ways and is used to determine the time of death. Muscles need energy to function, and that energy is provided by the adenosine triphosphate molecules. Muscles are composed of 2 bands, those are myosin and actin. These bands move towards each other and contract. Then the energy is required to break this bond. Therefore after death, respiration stops and no more adenosine triphosphate is released. So, the muscles freezes in there last position. The process of rigor mortis starts within 2 hours of the death and takes around 8 hours to complete.
   
• Livor mortis
  It is the final stage of death. When the heart stops beating, the blood is at the mercy of gravity. When the skin is pressed the colour of the skin turns white and then return to the bluish colour, which depends on the removal of the pressure. The bluish colour on the skin is livor mortis or lividity. Livor mortis can give insight at the time of death. It also helps the investigators to determine that the body has been moved from one place to the other.
  
  Changes in skin at the time of post mortem
• Livor mortis
  It is the discoloration of skin, which results from blood pooling into the interstitial tissues under the force of gravity. The intensity of color depends on the amount of hemoglobin in the blood. The skin will turn white when the pressure will be applied within first 12 hours. The lividity can be altered till 6 hours after onset of death.
   
• Vibices
  These are the pale marks on a dead body that are caused by dermal pressure. Like from the rope in case of hanging death.
   
• Tardieu spots
  These are the dark pinpoint spots on the dead body which are developed in dependent areas. Like in the case of hanging death, the lags of the hanged person due to increased gravitational pressure.
   
• Venous pattering
  These are the prominent purple discoloration of sub dermal vessels.
   
• Degloving
  They are the thermal exposure, immersions or advanced decomposition of skin and tissues that result in degloving of skin. It is common in hands and feet of the dead body.

Embalming artifacts

It is a funeral home procedure that prepares and preserves a body for an open funeral. It attempts to reduce the effects of various post mortem changes. It leads to drying and hardening of soft tissues. After clothes are removed, the hair is shampooed and a man's face is shaved, then the body is cleaned. An incision allows blood to be drained from the venous system and embaling fluid is perfused under pressure into an arterty. Fluid is a mixture of formaldehyde, anticoagulants, perfumes, surfactants to reduce surface tension and increase permeation of fluid, coloring agents, modifying agents and solvents carrying various embalming chemicals.

Clinical significance

Early and late post mortem changes are definite signs of death. The immediate post mortem changes are clinically significant in diagnosing death. Suspended animation is a condition where the person appears to be dead due to the vital condition at a low pitch as to be minimum compatible with life. The early and late post mortem changes are significant from a forensic perspective, estimating the time since death or post mortem interval.

Forensic significance

Post mortem interval is the time between the death of a person and the time he is found for post mortem. It is an essential tool in forensic investigation providing an estimate time of death. It is pivotal in judicial cases and can even either incriminate or acquit a suspect. Earlier a corpse is found, the more accurate the post mortem interval estimation is to be. Once a corpse undergoes putrefication, post mortem interval can only be provided as a rough range as many variables affect the rate of these changes.

Conclusion The two main reasons for post mortem examination are:

• To estimate the time of death of the person through post mortem examination
• To recognize the reason of changes in the body that occurs after death, to avoid misinterpretation of post mortem changes for sign of violence.

References:

1. Forensic science in criminal investigation and trials - B.R.Sharma
2. Post mortem changes- StatPearls- NCBI