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EXSTRACT F.

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Part C: The nature of the "whiplash mechanism". Continues

Chapter C.2 How the mechanics may affect vital parts of the body.

1. Affecting the spine.

A mechanism as the "whiplash-mechanism" caused by accelerating forces between the back of seat and the seated body, has to affect not only the neck region, but also the hole spine from the lumbar section and into the brain structures through the medulla. The extension of the affected areas is dependent of both how the person is seated and the level of the energies involved, it means the level of velocity in which the collision occurs. The higher the energy involved, the longer will the acting forces be acting.

This means larger deformations of affected parts and larger impulses introducing shock waves into other structures increasing both the amplitude of waves and the depth the affected section before being absorbed by the structure.

The lumbar region.

The acceleration of the body will start by the acceleration of that part of the body with the closest contact with the seat. Normally this will be found to be the lumbar regions towards a seat being shaped to give good support to that region.

The acceleration of this region makes a difference in the velocities of different parts of the body giving stretching forces along the spine. The difference in velocities and then the probability of a significant strength of the forces will depend on the energy involved, increasing the loads affecting the region as the strength of collision increase.

At this stage, when the acceleration a/g of the car exceeds the coefficient of friction between the seat and the person, this movements will set up shear stresses and torsion stresses combined with bending stresses affecting the "joints" between the spine and the pelvis together with longitudinal forces F along the spine. See Fig. C.2.

Affection of the spine all the way up to the neck region.

As the car is moving forward, more elements of the body are picked up by the back of seat and accelerated forward, moving the accelerated parts upwards just as when handling a whip.

2. The neck region.

The head moving, free swinging as a heavy body at the end of the "whip", causes high longitudinal stretching forces and transverse shear forces combined with extreme deflections either forward, backward or aside. If the accelerating force do not go through the centre of gravity of head, as it will be if it is an initial turning of head, or the impact is not acting in line with the car, the structures are affected by torsion stresses as well.

In a motion like the "whiplash mechanism" with a free swinging head in a curved path, there will be a stretching force through the neck, during the hole movement called the centripetal force. This force, tensioning the neck region, is an additional force to the accelerating force trough the neck region, acting in the same direction..

The centripetal force, shown as Sf in Fig. C.4, affecting as a force tensioning the neck region all through the head's forward motion, change with the radius of that curved path. These two forces, acting in the same direction are to be added giving varying stretching loads affecting the neckregion, the spine and the spinal cord all through foreward movement of the head as well as during the acceleations during phase A and phase B

5. Affection towards the brain and other structures inside the scull.

In many ways much of the different organs within a body could be described as elements elastic supported, giving a degree of free movement when the body is exposed to changes in the velocities. This ability of internal flexibility gives the body the ability to sustain normal activities without making any harm to vulnerable "instruments".

On the other hand this flexibility does an acceleration of the body as in the "Whiplash-mechanism" not to be only a series of external impacts, but even inside the body the organs will achieve a difference in velocity and the accelerations.Within the scull, there are objects to be given special attention in cases where both an extreme acceleration and rotation may occur.

6. Loads towards the brain and the spinal cord.

The brain is surrounded by membranes making thin layers filled with liquid. This liquid surrounds the brain, fills the ventricles, the void spaces within the brain structures, and surrounds the spinal cord. In any acceleration of head, this body, connected to the spinal cord by the medulla, will behave like a separate body within the scull. If the head is exposed to any kind of impacts, the brain will be shifted relatively to the scull, as the acceleration of brain will be delayed and not start until sufficient acceleration force has been reached.

This pressure from the scull will displace the liquid as the scull is pressed towards the brain. In a rapid shifting, as it might be when the head is exposed to violence and other high external loads, or when a person is falling, this rapid shifting of brain may cause counter effects at the opposite side as the pressure reach almost vacuum and the boiling effects caused by vacuum most like cavitation on ship propellers, may occur. See Fig. C.10. An acceleration of head will give a compression of the brain structures, with the highest degree of compression in the outer structures reduced as the distance from the outer surface increase.

As soon as the head is exposed to an acceleration not only giving a longitudinal change of velocity but an additional rotation as it will be in some extent in Phase 1 and 3 of the "Whiplash-mechanism", and to the greatest extent where there is no proper "head support", and during the slow down in the forward position in Phase 2, there will probably be an additional radial shift of the brain structure. The displacement of the liquid will probably increase the friction between the brain itself and the scull, as the pressure towards brain increase. Such an effect to the brain structure will result in radial stretching of the structure. As the pressure is decreasing at increasing distance from the outer surface, this effect decreases as well. The areas affected of such loads combining a compression and radial stretches of the brain structures will increase both in with and depth as the energy involved increase.

During the forward movement in the curved path, the brain will be pressed towards the scull as shown in Fig. C.12. As the brain and the scull will move at almost the same velocity there will be no shifting of the brain relative to the scull in the period where no acceleration takes place. I will assume that pressure between the upper section of brain and the scull to be of minor interest when considering the effects of this mechanism.

What has to be taken into consideration is the stretching force acting towards the spinal cord through the medulla or the brain stem. Like the neck region, these structures will be affected by stretching loads all through the movements. These stretch loads will cause act as stretching forces acting towards the brain by all structures able to lead these loads into neighbouring structures. As I have learned from my discussion with medical experts these loads will rise stretching forces through the medulla and into central parts of brain as the pons and along the inner surface of the central ventricles called the tent.

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