Review of Department of Defense Test Protocols for Combat Helmets (2014) / Chapter Skim
Currently Skimming:
10 Linking Helmet Protection to Brain Injury
10 Linking Helmet Protection to Brain Injury
Pages 70-90
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 70... ...
blast or a paratrooper hard focus research range from determination of the prevalence landing, are not necessarily attenuated by helmets, but the of reversible declines in hormonal function years after brain injury mechanisms are likely similar to injuries from blunt trauma to acceleration of research in computational modeling head trauma. Blast pressure stress from IEDs and artillery and simulation that can show shear stress fields associated can directly or indirectly transmit pressure fields to the head with the known spectrum of threats and the protective capa that result in shear stresses in the brain (Panzer et al., 2012; bilities of helmets.
|
From page 71... ...
Even when not life threatening, such injuries have the 5 Disruptive and non-disruptive diffuse axonal injury from shear potential for delayed injury, including local brain swelling, stresses as well as long-term consequences with symptoms persisting 6 Tissue stresses and strains produced by motion of the brain many years after the initial brain injury. hemispheres relative to the skull Important and frequently undiagnosed effects include 7 Subdural and epidural hematomas produced by rupture of bridging vessels between the brain and the dura mater alterations in microcirculation that can lead to hypoperfusion 8 Pressure-based rupture of small blood vessels leading to petechial or regional vasospasm with the result of inadequate delivery hemorrhages of vital metabolites to neural tissue.
|
From page 72... ...
FEM Finite element modeling -- a computational system that provides the means to simulate the effects of forces on structures such as the skull and brain tissues. fMRI functional magnetic resonance imaging -- fMRI is similar to MRI, but the image gives information regarding blood flow changes in the brain after some stimulation.
|
From page 73... ...
Some data on injury thresholds exist for low-rate skull fracture, concussion, and diffuse axonal injury. But these have been derived from animal and human studies using experiences from vehicle collisions and laboratory experiments with stresses and rate of change of stress (i.e., strain rate)
|
From page 74... ...
A goal is to determine the injury risk function for the major brain tissue injuries of Over the past 70 years, researchers have attempted to Table 10-1 relevant to militarily relevant injuries such as understand the relationships between head, skull, and brain those associated with BFD and blunt and blast neurotrauma. injury mechanisms and blunt trauma using cadavers, physical models, animals, and computer simulations.
|
From page 75... ...
. In coronal plane rotational acceleration, the critical shear strain associated with the onset of diffuse axonal injury was about 10 percent, and the rotational acceleration threshold for severe diffuse axonal injury was about 16,000 rad/sec2 (Margulies et al., 1990)
|
From page 76... ...
. It is expected that an expansion of these types of study will improve the development of head injury criteria a Strains less than 0.15 can cause diffuse axonal injury.
|
From page 77... ...
it is not directly applicable to military helmet injury criteria. This study developed injury criteria for both test round Skull fracture is a measure of head injury that can be velocity and cadaver peak-impact pressure.
|
From page 78... ...
. FIGURE 10-5 Thresholds for diffuse axonal injury based on nonBrain Shear Stress and Diffuse Axonal Injury human primate rotational acceleration experiments and scaling through computational modeling to human brain masses of 500 g Diffuse brain injury from low-rate traumatic impacts to (thick solid curve)
|
From page 79... ...
Also, currently there is no method to of brain function and perhaps play a role in progressive brain detect if diffuse axonal injury has occurred from head trauma deterioration. They can be detected by high-field MRI if the in the battlefield.
|
From page 80... ...
adrenocorticotropic hormone secretion from the pituitary in TBI patients. Neurobehavioral Effects from Traumatic Brain Injury Most studies found the occurrence of posttraumatic hypopituitarism to be unrelated to injury severity.
|
From page 81... ...
of the computer simulations, realism of the tissue material properties, and the lack of validation. 10.5 COMPUTATIONAL MODELING AND SIMULATION Computational Simulations of Brain Injuries from Blunt Computational modeling and simulation (M&S)
|
From page 82... ...
Several papers (including Moore et al., 2009; Chafi et al., 2010; Panzer et al., 2011; Przekwas et al., 2011; Nyein et al., Simulations of Brain Strains from Ballistic Impacts on 2010; and Sharma and Zhang, 2011) developed human head Helmeted Head models from medical imaging data to study the interaction Finite element simulations to determine expected skull of blast waves with the head, including various anatomical and brain tissue injuries from ballistic BFD trauma were structures resolved to various scales.
|
From page 83... ...
It is unclear, however, what the brain material properties Very-high-resolution anisotropic models have been and detailed network behavior are in this basis, because the developed MRI T1 relaxation weighting and DTI with a underlying experimental work has not been done. three-dimensional, biofidelic finite-element volume mesh FIGURE 10-8 Computational simulations of the protective effect of the Advanced Combat Helmet (center column)
|
From page 84... ...
There is a clear opportunity to extend the existing use of M&S in the area of brain injury biomechanics and protective gear design, as in many other areas of science and engineering. 10.6 MECHANICAL AND CONSTITUTIVE PROPERTIES OF TISSUES FIGURE 10-10 Dependence of shear strain on stress rate shows Characterization of the dynamic mechanical properties the importance offixed Figure 10-10, correct simulation of the shear stress rate in of brain tissue is important for developing a comprehensive simulations.
|
From page 85... ...
For models and simulations of brain trauma not reliable because of the experimental methods employed to be meaningful for injury assessments, they should include to date. The results gathered to date on bovine and porcine constitutive models of brain tissue response that account for tissue properties have been obtained mostly in vitro (Pervin nonlinear and rate-dependent viscoelastic effects.
|
From page 86... ...
2007. Evaluation of head response to ballistic traumatic brain injury as identified using a new experimental model of helmet impacts using the finite element method.
|
From page 87... ...
1995. Biomechanical analysis of experi changes associated with growth hormone insufficiency after com- mental diffuse axonal injury.
|
From page 88... ...
Investigation of traumatic brain injuries using the next generation ics of brain tissue. Acta Biomaterialia 7(1)
|
From page 89... ...
hormone abnormalities after blast-related mild traumatic brain injury.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.