MECHANICAL ASPHYXIA : Forensic Medical Examination

In mechanical asphyxia the air-passages are blocked mechanically.

In intravital development of Mechanical Asphyxia there are 2 periods lasting 5-7

minutes and known as pre-asphyxial period and asphyxial period. The preasphixyal

period is a delay of breath. It is not asphyxia. A person without any harm to his/her

health can delay breath during 10-15 seconds, but if the obstacle is not removed the next period develops.

The asphyxial period has 5 stages:

  1. Stage of inspiratory dyspnea;

  2. Stage of expiratory dyspnea;

  3. Stage of relative rest (terminal pause);

  4. Stage of terminal breath;

  5. Terminal Stage.

  • The duration of each stage can be from 1 to 3-5 minutes. In the beginning dyspnea has inspiratory character. In the clinical aspect, it is expressed by enhanced deep inspiration at which the organism tries to compensate lack of oxygen. Thus, the thorax sharply extends, which complicates transition of blood in arteries. Blood overfills the right half of heart and passes in venous system.

  • Then the expiratory dyspnoea develops featured by expiration movements, increase of muscular weakness, cyanosis and swelling of the face; complete loss of consciousness, convulsions, involuntary discharge of faeces, urine and seminal fluid develop.

  • In Stage III a short respiratory standstill due to depression of functions of the respiratory centre.

  • Stage IV appears at the 4th or 5th minute when deep breath and pauses develop. Terminal breath is caused by depression of functions of the respiratory centre and weak stimulation of the spinal cord centres.

  • Stage V (terminal) is complete respiratory standstill. Heart can function within 5- 30 minutes.

Classification of Mechanical Asphyxia

I. Asphyxia by compression:

a.) Strangulation Asphyxia:

  • Hanging;

  • Ligature Strangulation;

  • Strangulation by hands (extremities).

b) Compressive Asphyxia

  • External compression of the chest and abdomen interfering with respiratory movements.

  • External compression of the chest

  • External compression of the abdomen

II. Asphyxia by closure:

a) Obstructive Asphyxia:

  • Closure of the external respiratory orifices, as in Smothering.

  • Closure of the airways by the impaction of foreign bodies in the larynx or pharynx, as in Choking.

b) Aspirative Asphyxia:

  • By loose substances, by fluid, by blood, by vomitive masses, etc.

  • Drowning

III. Insufficiency of oxygen in the inspired air (in enclosed places, trapping in a

disused refrigerator or trunk. It can happen at a placement of child or only his head in a

plastic bag.

Common (general) Asphyxial Signs

External:

  1. Livores mortis is well developed.

  2. The face is often cyanosed and purple, and sometimes swollen and oedematous.

  3. The eyes are prominent, the conjunctivae are congested and the pupils are dilated.

  4. Petechial haemorrhages in the conjunctiva. They are most marked where for mechanical reasons, capillary congestion is most prominent. Their distribution lies above the level of obstruction. They appear commonly as a rash-like shower in the scalp, eyebrows and face in hanging and strangulation, and in the zone above the level of compression in traumatic asphyxia. They are produced by simple mechanical obstruction to the venous return of blood from the paits, resulting in acute rise in venous pressure and over-distension and rupture of thin-walled peripheral venules and capillaries, especially in lax unsupported tissues, such as the eyelids, forehead, and skin behind the ears, circumoral skin, conjunctivae and sclerae.

  5. Involuntary defecation, urination, discharge of seminal fluid, pushing mucus plug from the cervix — valuable but non-permanent signs.

Internal:

  1. Dark liquid blood in the heart and large venous vessels.

  2. Venous congestion of inner organs. The large veins are full of blood. The postmortem fluidity of the blood is due to presence of fibrinolysins. Under certain conditions, the fibrinolysin may be so active that fibrin is destroyed as rapidly as it is produced, and post-mortem clots never develop in the vessels. In other cases, thrombi are formed, but they undergo lysis.

  3. Spleen anaemia.

  4. Overflow by blood of the right part of the heart and at the system of superior vena cava.

  5. Petechial sub-epicardial and subpleural haemorrhages. These are often referred to as Tardieu spots, after the French Police Surgeon who described them in 1866.

  6. Acute alveolar emphysema.

SEPARATE KINDS OF A MECHANICAL ASPHYXIA

Hanging

Hanging is the form of asphyxia which is caused by suspension of the body by a

ligature, which encircles the neck, the constricting force being the weight of the body.

Ligature Mark

The most important and specific sign of death from hanging is the Ligature Mark in the neck. It is imprint of a loop on the skin of the neck. The ligature produces a

groove in the tissues, which is pale in colour, but it later becomes yellowish or yellow-

brown, hard and parchment-like due to the drying of the slightly abraded skin. It is

oblique, does not completely encircle the neck; usually seen at high up of the neck

between the chin and larynx.

In the typical case of a fixed loop, the mark is seen on both sides of the neck, and is

directed obliquely upwards towards the position of the knot over the back of the neck.

In partial hanging when the body leans forward, a horizontal ligature mark may be seen.

The ligature mark usually encircles the entire neck, except for the place where the

knot was located. The mark is situated above the level of thyroid cartilage. The width of

the groove is about, or slightly less than width of the ligature.


Ligature Strangulation

Ligature Strangulation is that form of mechanical asphyxia, which is caused from

constriction of the neck by a ligature or a part of other flexible object by their tension, a

force of extraneous or own human arms or any mechanisms.

At ligature strangulation on a corps we found the general (common) asphyxial

signs and ligature mark. The ligature mark is situated at the level of thyroid cartilage or

below, is almost horizontal, and encircles the neck completely. The mark may be absent

on the any area due to the presence of clothing or long hair between the ligature and the

skin.

The character of the mark depends upon the nature of ligature but is also affected

by the number of turns round the neck and length of time it remains applied. The

pattern of the ligature may be imprinted on neck as a pressure abrasion (mirror image

phenomenon) or bruise. If the ligature has gone round the skin more than once,

corresponding number of marks, one above the other and close to each other are seen.

In such cases, there may be evidence of skin bruising if it is caught between the rounds

of ligature. There is always some damage to skin underneath the ligature. A careful

search of the neck may reveal minute fibres or any other material from the ligature. The

ligature should be examined for presence of blood, hair, or suspicious substances.


Strangulation by Hand (Hands, Extremities)

Asphyxia produced by compression of the neck by human hands is called

Strangulation by hands, or extremities (syn.: Throttling, Manual Strangulation).

The bruises are produced by the tips or the pads of the fingers. Their shape may be

oval or round and of the size of the digits, but continued bleeding into the contused area

usually increases the size.

A grip from right hand from the front produces a thumb impression on the right

side of the victim's neck, which is usually under the lower jaw over the cornu of thyroid.

Several finger-marks are seen on the left side of the neck obliquely downwards and

outwards, and one below the other, but sometimes are grouped together and cannot be

distinguished separately. In a grip from behind the victim, the pressure is applied all

round the neck, but some areas of bruising are more prominent due to the pressure of

the fingertips.

When both hands are used to compress the throat, the thumb-mark of one hand and

the finger-marks of other hand are usually found on either side of the throat.

Sometimes, both thumb-marks are found on one side and several finger-marks on the

opposite side. A grip from both hands, one being applied to the front and the other to

the back, produces bruises on the front and back of the neck. Due to the shifting of the

grip, and sometimes the frank struggle of victim, bruises may be seen in a completely

haphazard manner. If the fingertips are pressed deeply, the pressure of the nails produce

crescentic marks on the skin. If a soft material is kept between the hand and throat,

bruising may not be seen. Marks of struggle are similar to those found in strangulation.


External Compression of the Chest and/or Abdominal Walls

External compression of the chest and/or abdominal walls (Compressive Asphyxia)

is a form of asphyxia resulting from external pressure on the chest, abdomen, or back,

which prevents normal respiratory movements.


Post-mortem signs

In addition to signs of asphyxia, and mud or other foreign material on clothing as

the case may be, there are three characteristic features: "ecchymosed mask", pulmonary

carmine-red oedema, and line of demarcation.

The mechanism of Compressive Asphyxia is as follows: The face and neck of the

victim are deeply cyanosed-almost black, the eyes blood-shot, and numerous petechiae

are found over scalp, face, neck, and shoulders ("ecchymosed mask") because

compression of the chest displaces blood from the superior vena cava and subclavian

veins into the veins and capillaries of the head and neck. No valves are present in

superior vena cava because backpressure is normally not present in the venous system

above the level of heart. Valves in subclavian veins prevent spread of the hydrostatic

force set up in the blood column to the veins of upper limbs. The valveless veins and

capillaries of the head and neck are therefore considerably engorged and the hydrostatic

pressure in them rises so rapidly as to burst their walls.

The level of compression is indicated by a well-defined line of demarcation

between the discoloured upper portion of body and the lower normally coloured part.

The tissue of the lungs on section is oedematous, shining, of carmine-red colour. In

mild cases of traumatic asphyxia, injury to the lungs may be in the form of traumatic

emphysema wherein the air in the lungs is forcibly redistributed producing small bullae

along the edges of the lung.

Depending on the mechanism of trauma, other injuries may be found in various

other parts of the body (e.g., fracture of the ribs, which are usually bilateral, multiple).

The cause of death is asphyxia, but not injury in this case.


Obstruction of the Airways

Smothering

Smothering is a form of asphyxia which is caused by closing the external

respiratory orifices either by the hand or by other means, or by blocking up the cavities

of the nose and mouth by the introduction of a foreign substance, such as mud, paper,

cloth, etc.

Choking

Choking is a form of asphyxia caused by an obstruction within the air-passages by

a foreign object.

Drowning

Drowning is a form of asphyxial death in which access of air to the lungs is

prevented by submersion of the body in fluid medium (typically the entire body). The

liquid is most commonly water but drowning can occur in any liquid, e.g., beer, wine,

gasoline, bitumen, dye, paint or some other chemical solution. It is necessary to

distinguish 4 main types of drowning in water: aspirate, spastic (asphyxial),reflex

(syncopal), mixed.


Diagnostic Signs

Foam in the airways: Externally a fine white froth or foam is seen exuding from

the mouth and nostrils (Krushevsky's sign).

The froth is sometimes tinged with blood producing a pinkish colour. If the foam is

wiped away then pressure on the chest wall will cause more to exude from the nostrils

and mouth. It is persistent and resists submersion for several days (up to a week in

winter). The foam is also found in the trachea and main bronchi.

The foam is a mixture of water, air, mucus and surfactant whipped up by

respiratory efforts. Thus it is a vital phenomenon and indicates that the victim was alive

at the time of submersion. Similar foam is found with severe pulmonary oedema from

any cause such as drug overdose, congestive cardiac failure and head injuries.

Emphysema aquosum ("emphyseme hydro-aerique"): The lungs in fresh water

drowning are voluminous, bulky, ballooned, may completely cover the heart, and bulge

out of the chest when the sternum is removed. They retain their shape and often show impressions of ribs upon them. Their surface is pale and they pit on pressure. On

sectioning there is a flow of watery material. The appearances reflect active inspiration

of air and water and cannot be reproduced by the passive flooding of the lungs with

water. However the appearances are not generally distinguishable from pulmonary

oedema.

Contrary to expectations lung weights in fresh water drowning are not statistically

different from lung weights in salt water drowning. The average lung weight is

approximately 700 g with a standard deviation of approximately 200 g so that in a

minority of cases the lungs are "dry".

Larger ecchymoses are sometimes seen in the interlobar surfaces of the lower lobes

(Rasskazov-Lucomsky-Paultauf's haemorrhages). Haemorrhages are the result of tears

in the alveolar walls and this is the explanation for the occasional blood tinging of foam

in the airways. Sub