![]() ![]() The aforementioned studies suggested a link between mild head injury and poor cognitive, psychosocial, and neurologic outcomes in some patients, but they raised even more questions regarding mechanism of injury (impact versus nonimpact, linear versus rotational), associated neurophysiology, and individual vulnerability. Although its focus was on the neuropathologic impact that resulted from linear forces on the brain, the research of Gennarelli et al 5 was instrumental in documenting cerebral injury from an apparently mild nonimpact head injury. Shear strain injury is observed as the tearing or stretching of axons, which is frequently not detected in patients with mild head injuries using gross neuroimaging techniques, such as magnetic resonance imaging or computed tomographic scans. Microscopic examination of brain tissue from primates exposed to this experimental model revealed axonal shear strain on autopsy. In their model, a mild cerebral injury could be administered to an animal without direct impact to the skull using acceleration-deceleration forces. Gennarelli et al 5 developed and used an animal model of injury analogous to the whiplash-type injury experienced by patients with mild head injuries involved in automobile crashes. 3, 4 Their research revealed that some of these mild injuries resulted in impaired neurocognitive functioning that persisted for 1 to 3 months after trauma and caused slower-than-expected return to work.Ĭoncurrent with early findings of poor outcome after mild head injury, other investigators designed animal studies to detect the presence of gross neuropathologic and histologic indications of disrupted brain functioning. This limited understanding of the mechanism and sequelae of mild head injury was challenged in the late 1970s and early 1980s by Rimel et al, 1 Barth et al, 2 and Gronwall and Wrightson. Poor outcomes from mild head injury were attributed to conversion disorders (wherein physical symptoms or deficits that imply a neurologic or medical problem have psychological factors as a basis), depression, or other psychological overreactions to an apparently minor, transient injury. ![]() ![]() 1 Before that time, mild head trauma was considered little more than an inconvenience or nuisance to the health care community. Since elapsed time is\boldsymbol.It has been more than 20 years since the epidemic of mild head injury and the associated medical, social, psychological, and economic consequences were first documented in the scientific literature. Taking the initial time to be zero, as if time is measured with a stopwatch, is a great simplification. Notation: t, x, v, aįirst, let us make some simplifications in notation. In this section, we develop some convenient equations for kinematic relationships, starting from the definitions of displacement, velocity, and acceleration already covered. But we have not developed a specific equation that relates acceleration and displacement. We might know that the greater the acceleration of, say, a car moving away from a stop sign, the greater the displacement in a given time. Kinematic equations can help us describe and predict the motion of moving objects such as these kayaks racing in Newbury, England. Calculate displacement and final position of an accelerating object, given initial position, initial velocity, time, and acceleration.įigure 1.Calculate final velocity of an accelerating object, given initial velocity, acceleration, and time.Calculate displacement of an object that is not acceleration, given initial position and velocity. ![]()
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