Characterization of the Jet-Flow Overpressure Model of Traumatic Brain Injury in Mice

Abstract

The jet-flow overpressure chamber (OPC) has been previously reported as a model of blast-mediated traumatic brain injury (bTBI). However, rigorous characterization of the features of this injury apparatus shows that it fails to recapitulate exposure to an isolated blast wave. Through combined experimental and computational modeling analysis of gas-dynamic flow conditions, we show here that the jet-flow OPC produces a collimated high-speed jet flow with extreme dynamic pressure that delivers a severe compressive impulse. Variable rupture dynamics of the diaphragm through which the jet flow originates also generate a weak and infrequent shock front. In addition, there is a component of acceleration-deceleration injury to the head as it is agitated in the headrest. Although not a faithful model of free-field blast exposure, the jet-flow OPC produces a complex multi-modal model of TBI that can be useful in laboratory investigation of putative TBI therapies and fundamental neurophysiological processes after brain injury.

Keywords: blast; jet flow; multi-modal traumatic brain injury; overpressure chamber.

FIG. 1.

This is a photograph of the principle components of the jet-flow overpressure chamber. On the left is shown the close-ended Test Section into which the animal is placed, and the Pressurize Drive Compartment into which compressed air is delivered in order to burst the membrane. In the middle is shown the diaphragm where the Mylar membrane is placed, between the two chambers. On the right is shown the holder into which the animal is placed.

FIG. 2.

Configuration of the Pitot-static probes installed for analyses of free-field flow conditions generated by the jet-flow overpressure chamber.

FIG. 3.

Illustration of the computational fluid dynamics model of the jet-flow overpressure chamber. Animation of the jet-flow development is presented in Supplemental Figure S1.

FIG. 4.

Representative experimental records from current work.

FIG. 5.

Comparison of experimental records with computational fluid dynamic modeling for the early flow development and peak levels.

FIG. 6.

Frame sequence from high-speed imaging of jet-flow developed at the nominal specimen location. For purposes of referencing time relative to the bursting of the diaphragm, 0.11 ms would be added to each time shown. High-speed video is presented in Supplemental Figure S2.

FIG. 7.

Frame sequence from high-speed imaging of the free-flight motion of a ballasted sphere subjected to the jet-flow impingement. The test sphere attained a velocity of about 15 m/s within 5 ms or an acceleration about 270g.

FIG. 8.

Description of blast-wave profiles for static and dynamic pressure (adapted with permission from Glasstone and Dolan).

FIG. 9.

Description of blast-wave profiles for static and dynamic pressure for the case of 1 lb (0.454 kg) TNT at distances of 5 and 6 ft standoff (1.52, 1.83 m). (reprinted with permission from American National Standards Institute).

FIG. 10.

Frame sequence from high-speed imaging of blast-wave exposure of ‘free-flight’ human-skull replica showing flow patterns; negligible motion was imparted for a blast of 125 kPa and 6 ms duration. (reprinted with permission from Ritzel and colleagues).