Physiological and pathological responses to head rotations in toddler piglets.

Closed head injury is the leading cause of death in children less than 4 years of age, and is thought to be caused in part by rotational inertial motion of the brain. Injury patterns associated with inertial rotations are not well understood in the pediatric population. To characterize the physiological and pathological responses of the immature brain to inertial forces and their relationship to neurological development, toddler-age (4-week-old) piglets were subjected to a single non-impact head rotation at either low (31.6 +/- 4.7 rad/sec(2), n = 4) or moderate (61.0 +/- 7.5 rad/sec(2), n = 6) angular acceleration in the axial direction. Graded outcomes were observed for both physiological and histopathological responses such that increasing angular acceleration and velocity produced more severe responses. Unlike low-acceleration rotations, moderate-acceleration rotations produced marked EEG amplitude suppression immediately post-injury, which remained suppressed for the 6-h survival period. In addition, significantly more severe subarachnoid hemorrhage, ischemia, and axonal injury by beta-amyloid precursor protein (beta-APP) were observed in moderate-acceleration animals than low-acceleration animals. When compared to infant-age (5-day-old) animals subjected to similar (54.1 +/- 9.6 rad/sec(2)) acceleration rotations, 4-week-old moderate-acceleration animals sustained similar severities of subarachnoid hemorrhage and axonal injury at 6 h post-injury, despite the larger, softer brain in the older piglets. We conclude that the traditional mechanical engineering approach of scaling by brain mass and stiffness cannot explain the vulnerability of the infant brain to acceleration-deceleration movements, compared with the toddler.