Spatial Intracranial Pressure Fields Driven by Blast Overpressure in Rats

Abstract

Free-field blast exposure imparts a complex, dynamic response within brain tissue that can trigger a cascade of lasting neurological deficits. Full body mechanical and physiological factors are known to influence the body's adaptation to this seemingly instantaneous insult, making it difficult to accurately pinpoint the brain injury mechanisms. This study examined the intracranial pressure (ICP) profile characteristics in a rat model as a function of blast overpressure magnitude and brain location. Metrics such as peak rate of change of pressure, peak pressure, rise time, and ICP frequency response were found to vary spatially throughout the brain, independent of blast magnitude, emphasizing unique spatial pressure fields as a primary biomechanical component to blast injury. This work discusses the ICP characteristics and considerations for finite element models, in vitro models, and translational in vivo models to improve understanding of biomechanics during primary blast exposure.

Keywords: Biomechanics; Blast-induced traumatic brain injury; In vivo; Injury characterization; Intracranial pressure.

Fig. 1

Overview of experimental procedures. a Sensors were surgically inserted through the occiput where sensor location was varied between subjects. Subjects were then placed in a taut mesh sling inside the 1 ft x 1 ft test section of the ABS and exposed head-on to 12 blast waves where the overpressure magnitude was varied. b Following the blast procedures, location of sensor placement was confirmed using biplanar X-rays and c H&E staining, as indicated by the red arrows

Fig. 2

SOP and ICP profiles. a Representative ICP response compared to the associated SOP where an initial frequency response and peak pressure amplification in the ICP is evident. b Overlaid SOP profiles and c ICP profiles from all animals. The peak ICP was greater than the corresponding peak SOP and a distinct frequency response following the peak ICP was visible in all cases

Fig. 3

Representative pressure fields by sensor location. a Sensor location of each subject mapped onto the rat brain atlas and stratified by color into superior (green), midbrain (blue), and inferior (purple) brain regions. b Pressure fields displaying the ICP (colored according to stratified region) and corresponding SOP (gray) within the ventricle, superior colliculus, thalamus, and hypothalamus regions. The shaded sections zoom in on the first 0.15 ms and the gray arrow indicates a plateau region in the ICP

Fig. 4

Peak ICP as a function of a SOP magnitude and b sensor location (normalized by peak SOP). Peak ICP increased with SOP magnitude for each subject (p < 0.0001). Average peak ICP was lower in the inferior hypothalamus region compared to the superior and midbrain thalamus regions (p = 0.08)

Fig. 5

ICP rise time as a function of a SOP magnitude and b sensor location (normalized by the respective SOP rise time). ICP rise time did not significantly change with SOP magnitude and was significantly higher in the superior regions (green) compared to the thalamus and hypothalamus regions (p < 0.01)

Fig. 6

ICP peak dP/dt as a function of a SOP magnitude and b sensor location (normalized by the respective SOP peak dP/dt). ICP peak dP/dt increased with SOP magnitude (p < 0.0001) and was significantly higher in the midbrain thalamus region (blue) compared to the superior and inferior regions (p < 0.01)

Fig. 7

a ICP positive duration and b ICP positive impulse as a function of SOP magnitude. ICP positive duration significantly increased and ICP positive impulse significantly decreased with increasing SOP magnitude (p < 0.0001). Statistical analysis of c ICP positive duration and d ICP positive impulse as a function of sensor location (normalized by the respective SOP duration or impulse). Sensor location did not significantly influence metrics for ICP positive duration (p = 0.3) or impulse (p = 0.2)

Fig. 8

ICP frequency as a function of a SOP magnitude and b sensor location. ICP frequency significantly decreased with increasing SOP magnitude between 28 and 172 kPa (p < 0.0001). ICP frequency was significantly lower in the superior regions (green) where it was lowest in the ventricle compared to the thalamus and hypothalamus (p < 0.01)