PMC

(A) The reflected and static pressures were measured to describe the blast wave profile. The stagnation pressure was measured with the pressure sensor as shown in (facing the oncoming blast wave). The static pressure was measured with the pressure sensor turned 90°, so that the sensing surface was facing vertically (side-on to the blast wave). Note the rapid onset of the blast wave at 0 ms, the blast wind peak about 2–3 ms later, and then the under-pressure from ∼6–20 ms. These waveforms are characteristic of that seen with an explosive detonation. The arrows highlight reflected waves that occurred outside of the blast chamber. The inset is an average power spectral density analysis of the stagnation pressure from five blast waves. (B) Varying the pressure in the reservoir chamber changed the blast wave profile. (C) There was a linear relationship between the reservoir chamber (tank) pressure and the peak blast pressure. (D) Larger magnitude blasts produced slightly longer blast durations, consistent with a longer blast wind.

1A shows average number (± standard error of the mean, SEM) of β-APP immunoreactive zones in the gray matter of blast and sham swine sections. The number of β-APP immunoreactive zones in the gray matter of high blast overpressure sections were significantly high (‡) compared to those in sham and medium blast overpressure (p<0.05; LSD; One-way ANOVA). 1B shows average number (± standard error of the mean, SEM) of β-APP immunoreactive zones in the white matter of blast and sham swine sections. The number of β-APP immunoreactive zones in the white matter of high blast overpressure sections (‡) were significantly high compared to those in sham and medium blast overpressure (p<0.05; LSD; One-way ANOVA). Furthermore, the extent of white matter immunoreactive zones was also significantly high in the medium blast overpressure sections (§) compared to sham (p<0.05; LSD; One-way ANOVA). 1C shows a control section stained without the primary antibody showing no apparent immunoreaction. 1D shows a sham section showing a less intense gray matter β-APP immunoreactive region. 1E and 1F shows an intensely stained gray matter immunoreactive zone from a representative high and medium blast overpressure swine sections. 1G and 1H show representative β-APP reactive retraction balls in the cortical white matter tracts. 1I shows an immunoreactive zone with stellate-like profiles in the white matter tracts of a swine subjected to high blast overpressure.

The blast peak pressure is given in the lower right of each plot. (A,B) The lowest blast pressure cohort had a nearly complete recovery of ABR thresholds and a partial recovery of DPOAE thresholds within two weeks. However there were still statistically significant differences between the ABR and DPOAE thresholds before the blast compared to 14 days after blast (two-way ANOVA, p<0.001 for both sets of curves). (C,D) By 14 days, the middle blast pressure cohort had less recovery of ABR thresholds and almost no recovery of DPOAE thresholds (two-way ANOVA, p<0.001). (E,F) The highest blast pressure cohort had ABR and DPOAE thresholds that were even larger, and by 14 days remained higher than the thresholds before the blast (two-way ANOVA, p<0.001). (G,H) The average of the ABR and DPOAE thresholds at 16, 23, and 32 kHz (the most sensitive frequencies) two weeks after the blast. Higher peak blast pressures led to higher thresholds for both ABR and DPOAE averages (one-way ANOVA, p<0.001).

6A shows extent of the microglial counts in the blast and sham groups. Microglial counts in sections from the high and medium blast overpressure blast groups were significantly high compared to those from sham group. 6B-D show representative images from sham, medium and high blast overpressure exposed sections highlighting variations in microglial proliferation. Microglia in blast sections appeared to be enlarged in size.