Tolerance of deformation varies with the type of tissue: bone is the strongest, and neural and vascular elements are the most vulnerable (Graham et al., 2002). Tensile strain and shear strain are the two types that most commonly cause damage to the vasculature and brain (Graham et al., 2002).


Dynamic loading is categorized as either impulsive or impact loading. Impulsive loading occurs when the head is stopped or set into motion by an indirect impact, such as a blow to the thorax. Head injury results from the inertia produced by the movement of the head. Impact loading, the more common form of dynamic loading, results when a blunt object strikes the head. Inertia and contact occur in combination. An example would be deceleration of the head when a moving automobile strikes a tree and then the driver’s head strikes the steering wheel.

FIGURE 2.2 Classification of TBI based on primary insult.

FIGURE 2.2 Classification of TBI based on primary insult.

Penetrating and Perforating Injuries

Missile injuries, such as gunshot wounds, are a common cause of TBI. These injuries are classified as either penetrating or perforating depending on how the missile traverses the head (Graham et al., 2002). In penetrating injuries, the object enters and lodges within the cranial cavity. Perforating injuries occur when the object traverses the cranial cavity and leaves through an exit wound. The extent of damage is governed by features of the missile (shape and mass) and by its direction and velocity (Morales et al., 2005). Damage is also related to the amount of energy that is released in passage through the brain (Graham et al., 2002). Although brain damage is often severe, there are instances when the bullet bypasses critical centers and the person maintains consciousness (Graham et al., 2002).

THERAPEUTICS AND TRAUMATIC BRAIN INJURY

A number of recent reviews have addressed pharmacologic strategies of treatment for TBI (Faden, 2002; Morales et al., 2005; Thompson et al., 2005; Marklund et al., 2006; Schouten, 2007). The strategies have targeted secondary injury cascades, including those related to excitotoxicity, calcium channels, oxidative stress, inflammation, cell-death pathways, calpains, endocrine-related abnormalities, altered neurotransmission, and growth factors (Marklund et al., 2006). Pharmacologic blockade targeting those pathways has improved the outcome in animal



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