Forensic Pathology Chapter 2 - Pathophysiology of Death

Vegetative state

the person irreversibly loses its sentient personality, being unconscious, unable to be are of its environment, and unable to appreciate any sensory stimuli or to initiate any voluntary movements

reflex nervous activity may persist, and circulatory and respiratory functions continue so that the tissues and cells of the body are alive and functioning

Cellular death

the tissues and their constituent cells are dead, they no longer function or have metabolic activity (the final stage of death)

Somatic death

virtually equated with brain death

the survival of the brainstem which ensures that spontaneous breathing will discontinue and therefore cardiac function is compromised (victim can remain in deep coma almost indefinitely)

occurs when life support is withdrawn and the heart stops beating

Brain death

when the brainstem suffers neuronal damage, the loss of the "vital centers" that control respiration, and of the ascending reticular activating system that sustains consciousness

causes the victim not only to be irreversibly comatose, but also to be incapable of spontaneous breathing (need artificial respiration)

without medical intervention, hypoxic cardiac arrest inevitably follows within minutes and then the usual progressssion of cellular death ensues

Brainstem

the structure that connects the cerebrum of the brain to the spinal cord and cerebellum

Parts of the brainstem

midbrain, pons, and medulla oblongata

Reticular activating systems (RAS)

a network of neurons in the brainstem responsible for regulating wakefulness, consciousness, and selective attention by filtering sensory information and activating the cerebral cortex

Cerebral cortex

thin layer of gray matter on the outermost layer of the brain (6mm thick)

responsible for higher functions like thinking, learning, and memory

Above and below tentorium

above - supratentorial (cerebrum)

below - infratentorial (cerebellum)

Corpus collosum

connection between the 2 hemispheres of the brain

Physiological window after brain death

after brain death, the organs aren't in cellular death for a short period of time, so this is the time for organ harvesting and transplants

3 essential findings in brain death

coma, absence of brainstem reflexes, and apnoea

Glasgow coma scale (GCS)

used to assess the level of consciousness

6 brainstem reflexes

pupillary light reflex

corneal reflex

oculo-vestibular reflex

pain stimulus

gag reflex

cough reflex

Eye signs of brainstem death

loss of corneal and light reflexes leading to insensitive corneas and fixed, unreactive pupils

the pupils usually assume a mid-dilated position, which is the relaxed neutral position of the pupillary muscle, though they may later alter as a result of rigor

there may be a marked difference in the degree of dilation of each pupil, but this has no significance as a diagnostic sign either of a brain lesion or of drug intoxication

post-mortem changes of forensic importance

to the forensic pathologist a number of post-mortem changes are of interest and potential usefulness, mainly in relation to the estimation of time of death, possible interference with the body, and an indication of the cause of death

Hypostasis - livor mortis

occurs when the circulation ceases, as arterial propulsion and venous return then fail to keep blood moving through the capillary bed, and the associated small afferent and efferent vessels

gravity then acts upon the now stagnant blood and pulls it down to the lowest accessible areas

Hypostasis appearance

blotchy post-mortem hypostasis forming in the early hours after death, the patchy disposition has no significance, and this usually sinks down and becomes confluent in the most dependent areas within a few more hours

commonly seen between 2 and 4 hours postmortem, its onset may been in the "early period," as little as 30 mins postmortem

the usual hue is a bluish red, but variation is wide

The color of hypostasis

carboxyhemoglobin - "cherry-pink" (CO poisoning)

cyanide poisoning - bright or brick red

hypothermia - pink over joints

hydrogen sulfide - blue green

opium - black

phosphorus or potassium chlorate - chocolate brown

nitrites, nitrobenzene, aniline - chocolate brown

clostridium perfringes - bronze

methanol poisoning - purple

Main cause of cyanide poisoning

smoke inhalation, suicidal ingestion, and industrial exposures are the most frequent sources of cyanide poisoning

treatment with sodium nitroprusside or long-term consumption of cyanide-containing foods is a possible source

Rigor mortis

the stiffening of the muscles after death

Range of time for rigor mortis

the flaccid period immediately after death is variable, but commonly extends between 3 and 6 hours before stiffening is first detected

rigor is first apparent in the smaller muscle groups, (such as the jaw and face muscles)

the body becomes flexed - flexor muscles are larger

reach a maximum within 6-12 hours, this state remains constant until the muscle mass begins to undergo autolysis, which releases rigor gradually at a stage before overt postmortem changes are visible externally

the duration of full rigor may be 18-36 hours, until it begins to fade in roughly the same order of muscle groups as it appeared

Factors affecting the timing of rigor mortis

modified by temperature - the colder the environment the slower the process and vice versa

in near freezing conditions, rigor will be suspended almost indefinitely

Decomposition - What causes decomposition 

a mixed process ranging from autolysis of individual cells by internal chemical breakdown to tissue autolysis from liberated enzymes

and external processes introduced by bacteria and fungi from the intestine and outer environment

animal predators, from maggots to mammals, can be included in the range of destruction

Decomposition - how does it differ from body to body 

decomposition may differ from body to body, from environment, and even from one part of the same corpse to another

sometimes one portion of a corspe may show leathery, mummified preservation while the rest is in a state of liquefying putrefaction

Decomposition - different types of decomposition 

most unembalmed bodies undergo putrefaction, in which the tissues become moist and gas-ridden, and eventually liquefy down to the skeleton

alternatives are dry decomposition, termed mummification, or a conversion to waxy substances, called adipocere

in some stillbirths as aseptic autolysis of a fetus dead in utero is known as maceration

Embalmed

artificial preservation of bodies in formaldehyde (used for funerals)

Environment of mummification

during the process of mummification, the body becomes progressively dehydrated and the normal putrefactive decomposition is inhibited

it occurs most readily in a current of dry, warm air

although dryness is clearly necessary, exactly how warm the atmosphere needs to be is less certain

Environment of adipocere

adipocere ("grave wax") is a waxy or greasy decomposition product formed by hydrolysis and hydrogenation of tissue fats

once formed, it appears stable for extended periods

adipocere has generally been considered to result from bacterial action, commonly in warm, damp, anaerobic environments

Putrefaction

the usual process of corruption of the dead body begins at a variable time after death, but in an average temperature climate may be expected to begin at about 3 days in the unrefrigerated corpse

Sequence of putrefactive changes - first sign of decomposition

usually the first external naked-eye sign is discoloration of the lower abdominal wall, most often in the right iliac fossa where the bacteria-laden caecum lies fairly superficially (where the large intestine and small intestine meet)

direct spread of organisms from the bowel into the tissues of the abdominal wall breaks down hemoglobin into sulphemoglobin and other pigmented substances

this discoloration spreads progressively over the abdomen, which in the later phase begins to become distended with gas (bloat)

Sequence of putrefactive changes - spread of bacteria

the putrefactive bacteria, which largely originate in the intestines and lungs, spread mostly easily in fluid so they tend to colonize the venous system, hemolyzing the blood that stains the vessel walls and adjacent tissues

this gives rise to "marbling," a branching outline of aborsent red, then greenish pattern in the skin, seen most clearly on the thighs, sides of the abdomen, and chest and shoulders

this stage may be seen about one week in the "baseline" timetable, where the corpse is in air at 18-20 degrees C

Sequence of putrefactive changes - swelling of the body

the scrotum and penis may swell up to a remarkable size and the neck and face will become grotesquely bloated, making visual identification difficult or impossible

the press may cause the eye globes and tongue to protrude

Sequence of putrefactive changes - skin slippage

at or even before the stage of marbling, skin blisters may appear, at first on the lower surfaces of trunk and thighs where hypostatic edema has located the tissues with fluid

the upper epidermis becomes loosened, the so-called "skin slippage" giving rise to large, fragile sacs of clear, pink or red serous fluid

these may become so large that they are pendulous and soon burst, leaving areas of slimy, pink epidermis

Sequence of putrefactive changes - maggot infestation and organ putrefaction 

purging of urine and feces may occur due to the intra-abdominal pressure

heavy maggot infestation will almost have supervened except in winter conditions, and the destruction of skin by innumerable maggot holes and sinuses gives better access to other bacteria that may invade from the environment (the maggots secrete a proteolytic enzyme that speeds up the destruction of the tissues)

organs putrefy at markedly different rates - the lining of the intestines, the adrenal medulla, and the pancreas autolyze within hours of death, yet the prostate and uterus may still be recognizable in a partially skeletonized body a year later

Decomposition in immersed bodies

water, slows down putrefaction, mainly because of the lower ambient temperature, and protection from insect and small mammal predators

temperature is the major determinant of the rate of putrefaction

Decomposition in buried bodies

the rate of decay of bodies buried earth is much slower than of those in either air or water - the process of putrefaction may be arrested to a remarkable degree in certain conditions, allowing exhumations several years later to be of considerable value

in this respect the prospect of an exhumation should never be dismissed on the grounds that because of the lapse of time, it is bound to be worthless

although most bacteria originate in the intestine, there is less access for secondary invaders and the restriction of oxygen inhibits aerobic organisms

deep burial, as in the usual cemetery interment, preserves the corpse better than the shallow grave seen in some concealed homicides

the deep burial is colder, it excludes air better, and unless waterlogged, is not directly affected by rain

Formation of adipocere

an important and relatively common post-mortem change is the formation of adipocere, a waxy substance derived from the body fat

after months or years have passed adipocere becomes brittle and chalky, the color can vary from dead white, through pinkish, to gray or greenish-gray

the chemistry of adipocere has been studied extensively - it contains palmitic, oleic, and stearic fatty acids together with some glycerol

Mummification

the third type of long-term change after death is mummification - a drying of the tissues in place of liquefying putrefaction

Post-mortem damage by predators

such injuries are not naturally often regarded with suspicion by the police

the complete absence of bleeding or reddening of the wound margins, as well as the unlikely shape and situation of the injury, make its postmortem origin obvious

Post-mortem cooling - rate of cooling 

except where the environmental temperature remains at or even above 37 degrees C, the human body will cool after death

a uniform homogenous laboratory "body" will cool according to Newton's Law of Cooling - which states that the rate of cooling is proportional to the difference in temperature between the body surface and its surroundings

Post-mortem cooling - taking body temperature after death

though conditions vary enormously, a body indoors will feel cold on exposed areas in 2-4 hours and in protected areas after some 6-8 hours

the traditional method of taking the postmortem temperature is by placing a mercury thermometer in the rectum - the tip must be inserted to at least 10cm above the anus, it should be left in place for several minutes for the reading to stabilize before being recorded

The use of vitreous humor chemistry in timing death

the most common chemical estimation performed on the vitreous fluid in the context of the postmortem interval is that of potassium

there is a marked and progressive rise in the potassium concentrations after death