Abstract
AbstractThe mechanisms by which blast pressure waves cause mild to moderate traumatic brain injury (mTBI) are an open question. Possibilities include acceleration of the head, direct passage of the blast wave via the cranium, and propagation of the blast wave to the brain via a thoracic mechanism. The hypothesis that the blast pressure wave reaches the brain via a thoracic mechanism is considered in light of ballistic and blast pressure wave research. Ballistic pressure waves, caused by penetrating ballistic projectiles or ballistic impacts to body armor, can only reach the brain via an internal mechanism and have been shown to cause cerebral effects. Similar effects have been documented when a blast pressure wave has been applied to the whole body or focused on the thorax in animal models. While vagotomy reduces apnea and bradycardia due to ballistic or blast pressure waves, it does not eliminate neural damage in the brain, suggesting that the pressure wave directly affects the brain cells via a thoracic mechanism. An experiment is proposed which isolates the thoracic mechanism from cranial mechanisms of mTBI due to blast wave exposure. Results have implications for evaluating risk of mTBI due to blast exposure and for developing effective protection.
Highlights
Though the concept of traumatic brain injury (TBI) due to blast wave exposure is not new [1,2], mildto-moderate traumatic brain injury resulting from blast pressure waves has garnered attention as the signature injury of recent military conflicts in the Middle East [3,4].Pressure waves can injure neural cells [5,6]
In light of ballistic as well as blast pressure wave research, we considered the hypothesis that blast pressure waves may be transmitted to the brain via the thorax with enough magnitude to cause moderate traumatic brain injury (mTBI)
Characterizing experimental conditions in terms of the mechanical work done by the ballistic projectile permits comparisons across studies
Summary
Though the concept of traumatic brain injury (TBI) due to blast wave exposure is not new [1,2], mildto-moderate traumatic brain injury (mTBI) resulting from blast pressure waves has garnered attention as the signature injury of recent military conflicts in the Middle East [3,4]. Cernak et al published epidemiologic studies of mTBI due to blast injury [7,8] as well as results of several experiments in animal models investigating how blast waves may be transmitted to neural tissue and what cellular alterations result [9,10,11,12] This body of work led to a hypothesis that a thoracic mechanism may underlie mTBI due to blast exposure [13,14]. In addition to the possibility of passing directly through the cranium, the blast wave may be entering the cranial cavity through orbital and/or aural openings This is theoretically possible, and blast overpressure has been shown to cause direct damage to ocular neurons as deep as the midbrain in rats [21]. While ear protection reduces maximum pressure in the ear canal [29,30], it is unclear what role, if any, hearing protection plays in preventing mTBI due to blast
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