All studies with animal subjects were reviewed and approved by the Institutional Animal Care and Use Committee (IACUC). Adult male Long Evans Hooded rats (Charles River Laboratories International, Inc., Wilmington, MA, USA; 250–300 g) were used as subjects. Experimental overpressure exposure was performed using the Walter Reed Army Institute of Research (WRAIR) shock tube simulating effects of air blast exposure under experimental conditions. This shock tube has a 12″ circular diameter, 19.5 ft. long steel tube divided into a 2.5 ft. air compression chamber separated from a 17 ft. expansion chamber by polyethylene Mylar™ sheets (Du Pont Co., Wilmington, DE, USA). The thickness of the Mylar sheets varied depending upon the peak pressure desired (Chavko et al., 2007 (link); Elder et al., 2010 (link)). There were three BOP intensities for the current set of experiments corresponding to 36.6, 74.5, and 116.7 kPa.
The characteristics of the overpressure wave produced by the shock tube used in this study have been described extensively (Long et al., 2009 (link); Chavko et al., 2011 (link)). The overpressure wave produced by the WRAIR shock tube exhibits waveform resembling a Friedlander wave form but with characteristics unique to its construction that do not reflect a strict Friedlander function. Shock tube characteristics differ in important ways that may affect the physiological and functional outcome resulting from exposure. Table 1 provides the defining characteristics of the WRAIR shock tube using the Mylar membranes that approximate the overpressure conditions referred to in this study. The reference “static” pressure inside the shock tube was measured using a piezoelectric sensor (PCB Piezotronics, Buffalo, NY, USA) placed between the rat head and the shock tube walls, approximately 3 cm from the head and 5 cm from the wall in a manner described by Chavko et al. (2011 (link)). The signal was recorded by the NI data acquisition system (National Instrument, Austin, TX, USA) at 500 kHz sampling rate. Other important variables in determining the outcome are also provided in the table. These are measures of overpressure duration and the integral function reflecting the area under the overpressure wave. In general, duration and integral parameters increase as the peak pressure increases.