  With the evolution of modern warfare and the increased use of improvised
explosive devices (IEDs), there has been an increase in blast-induced traumatic
brain injuries (bTBI) among military personnel and civilians. The increased
prevalence of bTBI necessitates bTBI models that result in a properly scaled
injury for the model organism being used. The primary laboratory model for bTBI
is the shock tube, wherein a compressed gas ruptures a thin membrane,
generating a shockwave. To generate a shock wave that is properly scaled from
human to rodent subjects the shock wave must have a short duration and high
peak overpressure while fitting a Friedlander waveform, the ideal
representation of a blast wave. A large variety of factors have been
experimentally characterized in attempts to create an ideal waveform, however
we found current research on the gas composition being used to drive shock wave
formation to be lacking. To better understand the effect the driver gas has on
the waveform being produced, we utilized a previously established murine shock
tube bTBI model in conjunction with several distinct driver gasses. In
agreement with previous findings, helium produced a shock wave most closely
fitting the Friedlander waveform in contrast to the plateau-like waveforms
produced by some other gases. The peak pressure at the exit of the shock tube
and 5 cm from the exit have a strong negative correlation with the density of
the gas being used: helium the least dense gas used produces the highest peak
overpressure. Density of the driver gas also exerts a strong positive effect on
the duration of the shock wave, with helium producing the shortest duration
wave. Due to its ability to produce a Friedlander waveform and produce a
waveform following proper injury scaling guidelines, helium is an ideal gas for
use in shock tube models for bTBI.
