On the Pressure Response in the Brain due to Short Duration Blunt Impacts

Abstract

When the head is subject to non-penetrating (blunt) impact, contusion-type injuries are commonly identified beneath the impact site (the coup) and, in some instances, at the opposite pole (the contre-coup). This pattern of injury has long eluded satisfactory explanation and blunt head injury mechanisms in general remain poorly understood. There are only a small number of studies in the open literature investigating the head's response to short duration impacts, which can occur in collisions with light projectiles. As such, the head impact literature to date has focussed almost exclusively on impact scenarios which lead to a quasi-static pressure response in the brain. In order to investigate the response of the head to a wide range of impact durations, parametric numerical studies were performed on a highly bio-fidelic finite element model of the human head created from in vivo magnetic resonance imaging (MRI) scan data with non-linear tissue material properties. We demonstrate that short duration head impacts can lead to potentially deleterious transients of positive and negative intra-cranial pressure over an order of magnitude larger than those observed in the quasi-static regime despite reduced impact force and energy. The onset of this phenomenon is shown to be effectively predicted by the ratio of impact duration to the period of oscillation of the first ovalling mode of the system. These findings point to dramatically different pressure distributions in the brain and hence different patterns of injury depending on projectile mass, and provide a potential explanation for dual coup/contre-coup injuries observed clinically.

Anatomical head model to measure impact force transfer through the head layers and their displacement

“…The results of Pearce and Young 15 highlighted the importance of repetitive short duration high impacts, which were also observed in our study, suggesting the head to be susceptible to critical intercranial pressure transients upon impact. In our study, the base of the brain still received 78.41 N (7.08% of the initial impact force), which indicates that the brain is still subject to inertial forces and highlights the potential danger of repetitive impact forces to the head.…”

Intracranial pressure–based validation and analysis of traumatic brain injury using a new three-dimensional finite element human head model

“…The shape of the cerebrum is approximated to a sphere, without clear representation of gyri and sulci structures on the brain surface. 1,3,5,[10][11][12][13][14] One of the earliest models 15 used a spherical liquid mass model to represent head where simple boundary conditions with homogeneous material properties were assumed, and coup and contrecoup pressures were observed. Subsequently, a number of intricate three-dimensional (3D) models were reported, resulting in an improved understanding of TBI mechanics.…”

Do blast induced skull flexures result in axonal deformation?

“…Nevertheless, the loading time is short, and tissue strains are small. Therefore, previous studies have used pressure or stress response in the brain to quantify the injury [ 12 , 13 ]. However, the mechanical response (stress/pressure), obtained at a tissue level, might not be fully representative of the pathological changes (such as axonal swellings along the axonal tracts) in the brain.…”