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Estimation of post mortem interval

Post Mortem interval – The interval between death, and the time of examination of a body is known as post mortem interval. This is important

(1) to know when the crime was committed,

(2) it gives the police a starting point for their inquiries, and allows them to deal more efficiently with the information available,

(3) it might enable to exclude some suspects and the search for the likely culprits started earlier,

(4) to confirm or disprove an alibi,

(5) to check on a suspect’s statements.

In civil cases, it might determine who inherits property or whether an insurance policy was in force.

The exact time of death cannot be fixed by any method, but only an approximate range of time of death can be given, because there are considerable biological variations in individual cases.

One should never give a single estimate of the time since death, but use a range of times, between which the death was presumed to have taken place. The longer the post mortem interval, the wider is the range of estimate, i.e. the less accurate the estimate of the post mortem interval.

In determining time of death, the doctor should not over-interpret what he sees and should not make dogmatic, unsupportable and potentiallyinaccurate statement.

First, all available history should be taken, and then local physical or environmental factors at the scene of crime, such as presence of fires and domestic heating, open windows, atmospheric temperature, etc. The range of time provided is at best an educated guess, based on knowledge and experience and subject to error.

The points to be noted to estimate the post mortem interval are:

(1) Cooling of the body

(2) Postmortem lividity

(3) Rigor mortis

(4) Progress of decomposition, adipocere and mummification

(5) Entomology of the Cadaver in post mortem interval: Entomology is the study of the form and behaviour of insects. Myiasis is a condition caused by infestation of the body by fly maggots. Flies (Musca domestica and M.vicinia) may deposit their eggs (pearly-white, one mm, long; about 120 to 150 eggs at one sitting) on the fresh corpse in any natural or traumatically created shaded orifices. These include between the lips or the eyelids, in the nostrils, genitalia, or in the margins of a fresh wound, ears, mouth, hair and the ground-body interface, within a few minutes after death, and in some cases even before death during the agonal period.

When skin decomposition begins, the eggs can be deposited anywhere. In 8 to 24 hours in summer, larvae or maggots (white, segmented, 1 to 2 mm. in length at birth; 12 mm. when full grown) are produced from the eggs, which crawl into the interior of the body and produce powerful proteolytic enzymes, and destroy the soft tissues.

The maggots burrow under the skin and make tunnels and sinuses which hasten putrefaction by allowing air and bacteria. The maggots become pupae (dark-brown, barrel-shaped, 6 mm. length) in 3 to 6 days, and the pupae become adult flies in three to six days. The complete life cycle from egg to adult may take 5 to 6 days in summer and 8 to 20 days in winter. Body lice usually remain alive for three to six days, after death of a person.

(6) Gastrointestinal Tract in post mortem interval: The amount of stomach contents and the extent of their digestion may be helpful to estimate the time of death, if the hour at which the deceased took his last meal is known. The gastric emptying of either liquids or solids is subject to relatively wide differences in the same and different individuals even if the same meal is ingested.

The state of digestion and transportation rate of food from the stomach into the duodenum depends on several factors, such as anatomical, physiological, pathological, psychological, agonal, kind of food, etc., which contribute to great ultra- and interindividual variability of gastric emptying. The quantity and digestive state of gastric contents is modified by the following factors:

  • The total quantity of food taken at a meal.
  • Additional snacks taken between a meal.
  • The ratio of solid to liquid in the meal.
  • The carbohydrate/fat content.
  • Marked variation between individuals.
  • Variation in the same individual from day to day.
  • Dramatic variations due to psychogenic and endocrine factors.

The stomach contents do not enter the duodenum after death. Digestion of the stomach contents may continue for some time after death. This may create further difficulties. It seems that there are no significant differences in solid food emptying rates between young and old persons.

The emptying rate increases directly with meal weight. The stomach empties gradually. The stomach usually starts to empty within ten minutes after the first mouthful has entered. The bulk of the meal leaves the stomach within two hours.

A light meal (small volume) usually leaves the stomach within 1 to 2 hours after being eaten, a medium-sized meal requires 3 to 4 hours and a heavy meal 5 to 8 hours. A carbohydrate meal leaves the stomach more rapidly than a protein meal, because carbohydrates are reduced to a semi-fluid state rapidly and a protein meal leaves the stomach more rapidly than fatty meal. Fluids and semi-fluids leave the stomach very rapidly (within two hours), after being swallowed.

If water is ingested with a solid meal, the water is emptied rapidly and separately and is not influenced by either the weight or total calories of the accompanying solid meal. Milk leaves rapidly, whereas meat and pulses are retained longer. Meat, green vegetables and roots cannot he recognised after four hours.

A head injury, physical or mental shock or stress, may completely inhibit the secretion of gastric juice, the motility of the stomach and the opening of the pylorus, and undigested food may be seen after more than 24 hours. Any illness or emotional stress, may prolong the emptying time for many hours.

Digestion is delayed during sleep and is probably suspended during coma. Strong alcohols irritate the mucosa and tend to delay emptying. Hypermotility caused by emotional disturbance can result in rapid passage of food through the intestines causing diarrhoea. The head of the meal reaches the hepatic flexure in about six hours, splenic flexure in 9 to 12 hours, and pelvic colon in 12 to 18 hours.

The actual recognition of stomach contents may be useful as it may indicate what the last meal consisted of and narrow the time of death to the interval between two meals, provided the type of meal is definitely known. Unless death was sudden and unexpected, reliance cannot be placed upon the state of digestion or the volume of stomach contents. If the stomach is full containing undigested food, it can be said that death occurred within two to four hours of the eating of the last meal.

Any estimate of a post mortem interval is only an opinion based upon probabilities and is subject to limitations. The presence of food in the small intestine or of faecal matter in large intestine is not of much value in determining the time of death.

The presence of urine in the bladder may indicate that death could have occurred late in the night.

(7) Cerebrospinal fluid: Cisternal fluid is examined. The amount of potassium increases at a constant rate in relation to the temperature of the body during the first 20 hours. The concentrations of sodium, calcium and magnesium have no obvious relationship to time since death.

(8) Blood: There is a progressive increase of lactic acid. The values increase by 50 to 75 fold in 12 to 24 hours, the steepest increase occurring in first 6 to 8 hours. Aminoacid nitrogen is less than 14 mg/dl up to 10 hours, but rises to 30 mg/dl by48 hours. Acid phosphatase levels increase 20 times by 48 hours. Amylase levels increase 3 to 4 times on second day. Glutamate-oxalate transaminase (AST4) and lactate dehydrogenase (LDH) increase linearly over the first 60 hours. Sodium levels fall by 0.9m Eq/l per hour. Organic phosphorus level in serum reach 20 mEq/l at 18 hours after death.

(9) Pericardial Fluid: 10 to 15 ml can be obtained, as opposed to 1 to 2 ml of vitreous humour and 5 ml of CSF. Constituents are not helpful in estimating time since death.

(10) Synovial Fluid: There is linear rise of potassium, which increases more than double within the first two days.

(11) Vitreous Humour: The potassium concentration at the time of death is 5 to 8 mmo1/1 The rise of potassium concentration per hour is0.17 to 0.238 mmo1 per hour. The reason for varying range may be due to electrolyte imbalances at the time of death.

The variation between the two eyes may be up to 10% The relationship between potassium concentration and time after death is not completely linear, as it depends on the degree and rapidity of decomposition. The slope is 0.2 mmo1/1 per hour. Madea and Henssge proposed the following formula.

PMI = 5.26 x K conc — 30.9

There is a linear relationship between vitreous potassium concentration and time elapsed after death up to 120 hours. The 95% limits of confidence are ±20 hours up to 100 hours. The rise is mainly due to diffusion from the retina into the centre of the globe. Temperature, chillness and urea retention affect the range.

There is a linear rise of hypoxanthine(Hx) up to 120 hours. The rise begins immediately after death. There is a correlation between vitreous hypoxanthine and vitreous potassium values. The 95% confidence limits are ± 32 hours.

Chlorides decrease at less than 1 mmo1/1/h and sodium by about 0.9 mmo 1/1/h. Urea exceeding 150 mmo1/1 indicates uraemia. The vitreous glucose usually falls after death and can reach zero within a few hours. A vitreous glucose of more than 11.1 mmo1/1 indictes diabetes, and less than 1.4 mmo1/1 of hypoglycaemia.

(12) Muscle Enzymes: Myofibrillar protease activity increases linearly and creatinine phosphokinase decreases linearly after death. A strong positive correlation is found between the ratio of non-protein nitrogen and total soluble protein and also creatinine concentration and time since death.

All the biochemical changes are temperature dependent. The above findings apply to cold and temperate climates. Chemical methods are of limited practical value. They are widely considered as the least reliable and the least practicable of all other methods.

(13) Hair: Hair does not grow after death; the contraction of the skin towards the hair roots gives the illusion of growth. A sample of hair is shaved from the chin and its length measured. From this, a rough estimation of the time since the last shave can be made, for beard hair grows at the rate of 0.4 mm. per day and nails at 0.1 mm per day.

(14) The Scene of Death: The dates on mail or newspapers, sales receipts or dated slips of paper in the deceased’s pockets, when the neighbours last saw the person, degree of coagulation of milk, state of food on a table, etc. may be valuable. The state of dress should be noted as regards whether the person is fully dressed or in the night dress.

If the watch has stopped, the hour at which it has stopped should be noted. If it is still going, the time it takes to run down should be observed. In drowning, the watch commonly stops shortly after immersion. If a corpse lies undisturbed on growing grass, or plant- bearing soil, underlying grass or vegetation soon dries, turns yellow or brown and dies.

Radioactive Carbon

C14 accumulates in living organic matter. The 14 content of the organism is steadily maintained as long as it lives. After death, the radioactivity gradually weakens taking about 5,600 years to reach half its initial activity.

A simple carbon compound, such as CO2 or acetylene, or even carbon itself is prepared from the bones, and the radioactivity is estimated. For medico-legal purposes, radiocarbon dating is not useful as the technique cannot date bones less than a century old.

Effects of keeping Cadavers in Refrigerating Chamber: If the body is refrigerated soon after death, the onset of rigor mortis is delayed. Reddish patches appear on the surface, especially in the hypostatic region and sometimes in internal organs. The blood is bright-red and injuries like abrasions and contusions have an intensified appearance. The tissues become hard.

Tower of silence is used by Parsees to dispose off dead bodies.

PRESUMPTION OF DEATH

This condition has only legal importance, and medical evidence is rarely necessary. This question arises in cases of inheritance of property or in obtaining insurance money, when a person is alleged to have been dead and the body is not found.

Under the Indian Evidence Act (S 107), a person is presumed to be alive, if there is nothing to suggest the probability of death within 30 years. But if proof is produced that the same person has not been heard of for seven years by his friends and relatives, death is presumed (S. 108, I.E.A.).

PRESUMPTION OF SURVIVORSHIP

The question of presumption of survivorship may arise in connection with inheritance of property, when two or more persons die in a common disaster, e.g., earthquake, shipwreck, plane-crash accident, etc.

The question may arise as to who survived longest, and if no direct evidence on this is available, the question becomes one of presumption. The case is decided by the facts and evidence available. In the absence of such evidence, age, sex, constitution, nature and severity of injuries and the mode of death should be taken into consideration.

Commorientes: Persons who die together on the same occasion, where it cannot be ascertained who died first.

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