Hearing Damage Induced by Blast Overpressure at Mild TBI Level in a Chinchilla Model.

INTRODUCTION: The peripheral auditory system and various structures within the central auditory system are vulnerable to blast injuries, and even blast overpressure is at relatively mild traumatic brain injury (TBI) level. However, the extent of hearing loss in relation to blast number and time course of post-blast is not well understood. This study reports the progressive hearing damage measured in chinchillas after multiple blast exposures at mild TBI levels (103-138 kPa or 15-20 psi). MATERIALS AND METHODS: Sixteen animals (two controls) were exposed to two blasts and three blasts, respectively, in two groups with both ears plugged with foam earplugs to prevent the eardrum from rupturing. Auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) were measured in pre- and post-blasts. Immunohistochemical study of chinchilla brains were performed at the end of experiment. RESULTS: Results show that the ABR threshold and DPOAE level shifts in 2-blast animals were recovered after 7 days. In 3-blast animals, the ABR and DPOAE shifts remained at 26 and 23 dB, respectively after 14 days. Variation of auditory cortex damage between 2-blast and 3-blast was also observed in immunofluorescence images. CONCLUSIONS: This study demonstrates that the number of blasts causing mild TBI critically affects hearing damage.

Surgical management of multiple metatarsal fractures in a chinchilla (Chinchilla lanigera).

CASE DESCRIPTION A 3-month-old sexually intact female chinchilla (Chinchilla lanigera) was examined for sudden onset of non-weight-bearing lameness of the right hind limb. CLINICAL FINDINGS On physical examination, the right pes was swollen. An open wound on the medial aspect of the metatarsal region exposed the second metatarsal bone, and the pes was displaced laterally. Radiographs of the right pes revealed oblique displaced fractures of the 4 metatarsal bones. TREATMENT AND OUTCOME Surgical treatment was elected, and enrofloxacin was administered prior to surgery. The protruding fragment of the second metatarsal bone was excised, and the third and fourth metatarsal bones were repaired with intramedullary pins and external skeletal fixation. The chinchilla was bearing weight on the affected limb 9 days after surgery with only mild lameness. The implants were removed 35 days after surgery when radiographs showed bony union of the third and fourth metatarsal bones and continued reduction of the fractures of the second and fifth metatarsal bones. Fifty-six days after surgery, the chinchilla was bearing full weight on the limb, and radiographs showed bony union of the third, fourth, and fifth metatarsal bones. CLINICAL RELEVANCE Findings suggested that intramedullary pinning combined with an epoxy resin external fixator may be an effective technique for metatarsal fracture repair in chinchillas. This method allowed physiologic positioning of the limb and functional hind limb use during fracture healing. Prospective studies of fracture healing in exotic small mammals are indicated.

Impulse Noise Injury Model.

OBJECTIVES: The new Auditory 4.0 model has been developed for the assessment of auditory outcomes, expressed as temporary threshold shift (TTS) and permanent threshold shift (PTS), from exposures to impulse noise for unprotected ears, including the prediction of TTS recovery. METHODS: Auditory 4.0 is an empirical model, constructed from test data collected from chinchillas exposed to impulse noise in the laboratory. Injury outcomes are defined as TTS and PTS, and Auditory 4.0 provides the full range of TTS and PTS dose-response curves with the risk factor constructed from A-weighted sound exposure level. Human data from large weapons noise exposure was also used to guide the development of the recovery model. RESULTS: Guided by data, a 28-dBA shift was applied to the dose-response curves to account for the scaling from chinchillas to humans. Historical data from rifle noise tests were used to validate the dose-response curves. New chinchilla tests were performed to collect recovery data to construct the TTS recovery model. CONCLUSIONS: Auditory 4.0 is the only model known to date that provides the full TTS and PTS dose-response curves, including a TTS recovery model. The model shows good agreement with historical data.