| As one of the most susceptible organ, Blast injuries always lead to varying degreesdamages of auditory system and hearing impairment. Accurate evaluation of impairmentand management would be helpful to improve the prognosis of auditory blast injuries.But due to diverse of exploder, complexity of explosive condition and individual differenceof the wounded, damages of auditory organ always be multiple and complicated. Althoughit is most susceptible, injuries of ear often be covered by symptoms of other organs andsystems, and management always focus on the life threaten damages. Furthermore,although there are a few of criterions to evaluate injuries of ear, their accuracy andavailability are unsatisfactory. Therefore, accurate assessment of damages to auditory organis a important role in research of auditory blast injuries. Most previous researches haveattempted to attribute the hearing impairment to mechanical damages, but many researchesprompt that pathological progress is not equal to middle ear and inner ear in many cases. Sobetter understanding of pathological changes of ear would very helpful to knowledge ofauditory injuries induced by blast, improvement the effectiveness of prevent andmanagement.Although the cochlear blood flow is considered as an important support of auditoryfunction and suspected play the important role in many pathological processes such asnoise-induced hearing loss, age-related hearing loss, sudden hearing loss, Meniere’s diseaseand so on, impairment of cochlear blood fow has been considered to be one of the factorsimplicated in the pathophysiology of various kinds of sensorineural hearing loss, it is lackof definite evidence of correlation between impairment of blood flow and hearingdysfunction in blast injuries of auditory system. However, some treatments which aim topromote the blood flow of cochlea have been proved helpful to recovery of hearing function after exposure to intensive noise. It prompts that the disorder of blood flow may play a roleamong the pathologic factors which can affect hearing function in blast injury of cochleatoo. Many researches about the changes of cochlear blood flow in laboratories areconducted in high level of noise or impulse noise. But due to the differences of theexperimental conditions, criteria and research methods, the results are varied, and it hasbeen diffcult to fnd direct evidence of impairment of cochlear blood fow in each case. Abetter understanding of CoBF changes will be helpful for preventing and management ofhearing disorders result form blast damage.In blast injuries of ear Early studies suggested that noise can reduce apparent cochlearblood flow decreased RBC density and increased aggregation of RBCs. But there areopposite results indicate elevation of the CBF after exposure to high-intensity noise andblast wave. Other researches suggested that the changes of cochlear microcirculation areintensity-related. The inconsistent results prompt the diversity of experiment condition andtest methods. Although many types of noise can damage the hearing and influence theblood flow of cochlea, the blast has obvious distinction with noise in nature. The blastproduce the shock wave with high intensity (tens of kPa peak overpressures) and a shortphase (tens to hundreds milliseconds), and blast waves always involve the movement withhigh speed of combustion products and air, under this condition, volume and distribution ofcochlear blood fow would be changed obviously, but these changes must be different fromother pathological processes. Such changes always involved with disorder of CBF andautoregulation of local circulation. But it is difficult to measure CoBF directly in vivo haslimited the investigation of correlation between change of blood flow and hearingdysfunction in auditory blast injuries. Therefore, the role of disorder of CoBF in hearingimpairment induced by blast still remains ambiguous. In autoregulation of the cochlearblood flow, Nitric oxide (NO) has been thought as a plays a key role in the maintenance ofcochlear blood fow in acute focal cochlear microcirculation disorder. The NO/cyclic GMPpathway attenuated ATP-evoked intracellular calcium increase of inner hair cells andsupporting cells in the organ of Corti.To explore a simple and effective method to evaluate the injury performance ofexplosive blast, this study develop a artificial tympanic membrane which is produced byhydroxyl silicon at room temperature, and a supporting device is developed too. Tests proved that this artificial membrane was match the human tympanic membrane in most ofmechanical properties. Application of this device and membrane could effectivelyovercome disadvantages in previous studies, such as complicated methods of measure,great individual difference and high cost etc. To explore the mechanism and pathologicalprogress, we produced a weaker explosion by using a small detonator (160mg RDX),observed changes of pathologic anatomy and assessed impairment of hearing function. Inthis study we focus on the relationship between changes of cochlear blood flow (CBF) andhearing impairment. We detected the association between the changes of CBF and blastenergy. Further study about the regulatory mechanism and impact factors were make too. Inthis study, we use the laser-doppler flowmetry to evaluate the cochlear blood flow. Thefindings indicated the increase of blood flow after exposure to blast wave. Such variationhas obvious relationship with the strength of blast too. The blast wave has more energywhere the distance is more close to epicenter. As the distance prolonging the peak value ofblast wave is dropping and duration of overpressure prolonging. More obvious changes ofCBF were observed in the near distances. Significant changes of CBF were observed wherethe distance is less than60cm, corresponding peak overpressure is more than45.68±6.21kPa and duration is less than0.381±0.018s. In the closest distance(50cm) the peakvalue of baseline reach the227.8%of initial level, and in60cm from the epicenter thepeak value of baseline is142.8%. Different to near distance the baseline of CBF hasn’tobvious change where the distance from the epicenter is more than70cm, correspond to thepeak value of overpressure which is less than35.05±4.11kPa and duration which more than0.411±0.019s.We observed changes of CBF after cochlear window infusion of little dose ofinhibitor of NOS (L-NAME) in blast injury, relationship between changes of hearingfunction and CBF has been discussed too. Results of this study indicated that inhibition ofNOS could reduce CBF and restrain changes of CBF after exposure to blast. Such inhibitionof CBF could induce the aggravation of impairment of hearing function.Immunohistochemical test indicated that NOS distributing widely in cochlea andconcentrated to stria vascularis and spiral ganglion. Corresponding with the increase ofCBF, enhanced expression of NOS has been observed after blast exposure. Correspondentto the inhibition of CBF, TS was more significant than traumatic group merely. Theseprompt that cochlea has strong ability of self regulation to local blood circulation after blast injury and NO played the key role in this regulation. Apoptosis detection found that ratio ofapoptosis cells in cochlea increasing after blast injury, this changes appeared in hair cells,supporting cells (pillar cells, Deiter cells and Hensen cells), stria vascularis edge cells andneurons of spiral ganglion. Furthermore, decrease of CBF by L-NAME induced moreapoptosis in base turn and top turn of cochlea after blast exposure.All these results indicated that changes of CBF involved distinctly in pathologicalprocess of cochlear blast damages. Circulation changes should be taken in count inevaluation of blast damages to auditory system. This imply the additon of the new methodof assessment and new criterion of auditory blast injury. This study also providestheoretical basis and experimental evidence of changes and effects of cochlear circulation inblast injury, the results may lead to the new methods of prevention and management toauditory blast trauma. |
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