Study On Auditory Safety And Prevention Of Middle Ear Barotrauma In Fast Buoyant Ascent Escape From Large Depth

【Objective】To study the middle ear barotrauma caused by fast buoyant ascent escape and its influence on hearing,to initially explore the inflammatory mechanism of middle ear barotrauma,and to study the prevention of middle ear barotrauma by tympanocentesis.【Methods】1.Divers,who experienced fast buoyant ascent escape from different depth,underwent tests of ear endoscope,acoustic immittance,acoustic reflex and pure tone audiometry,to evaluate auditory safety during fast buoyant ascent escape.2.SD rats were used to simulate fast buoyant ascent escape from the depth of 200 meters.The barotrauma of middle ear and its effect on hearing were evaluated by ear endoscopy,tympanometry,acoustic reflex test,auditory brainstem response(ABR)threshold and histopathological observation.3.Before simulating fast buoyant ascent escape from the depth of 200 meters,SD rats suffered tympanocentesis.Ear endoscopy and ABR was used to evaluate the middle ear injury and hearing.The preventive effect of tympanocentesis on middle ear barotrauma was evaluated by comparing the results before and after modeling.Changes in the expression levels of inflammatory factors in middle ear were detected after buoyant ascent escape from the depth of 200 meters with or without tympanic membrane puncture.4.The parameters of human ear were determined by searching the literature.Finite element analysis was used to establish ear model with eardrum perforation.The perforation diameter ranged from 0.1mm to 1.0mm,and the diameter gradient was 0.1mm.By means of hydrodynamics analogue simulation,the process of rapid pressurization in fast buoyant ascent escape from the depth of 200 meters was simulated.The pressure change curves on both sides of tympanic membrane were compared to study the preventive effect of tympanic membrane perforation with different diameters on barotrauma of human middle ear.5.Eardrums were perforated when the depth was deeper than 150 meters,to confirm the prevention of perforation on middle ear barotrauma and its security.【Results】1.One subject suffered bilateral middle ear barotrauma in fast buoyant ascent escape from the depth of 100 meters,resulting in congestion of tympanic membrane and effusion in the tympanic chamber in the left ear,and resulting in perforation of tympanic membrane in the right ear.Besides,the air conduction hearing threshold of both ears was increased and the bone conduction hearing threshold did not change significantly.Other three subjects had no middle ear barotrauma,and there was no significant difference in the examination results after the test compared with that before the test.2.After the rats simulating fast buoyant ascent escape from the depth of 200 meters,the incidence of middle ear barometric injury was 100%,among which O’Neill Ⅱ was 85.7% and tympanic membrane perforation occurred in 2 ears.Tympanograms were A type before modeling,and it changed to B type after modeling.The acoustic reflex thresholds of different frequencies(2 k Hz,3 k Hz,4 k Hz)showed no significant difference between before and after modeling.After modeling,ABR threshold of each frequency(4 k Hz,8 k Hz,16 k Hz,24 k Hz,32 k Hz)was significantly increased comparing to that before modeling.3.There was no obvious middle ear barotrauma was observed after fast buoyant ascent escape from the depth of 200 meters with eardrum punctured before modeling.ABR threshold of each frequency was significantly increased at post-puncture compared to pre-puncture,but showed no significant difference compared to post-modeling.After modeling,the expression of inflammatory factors in middle ear was changed significantly.The expression levels of proinflammatory factors IL-1β,Mc P-1,MIP-1α,IL-1α,IL-6 and GRO/KC were significantly increased.The expression levels of pro-inflammatory factors IFN-γ,TNF-α,IL-18,GM-CSF and anti-inflammatory factors IL-4 and IL-13 were significantly decreased.Prophylactic tympanipuncture could attenuate the increased or decreased expression of inflammatory factors in the above models.4.When the diameter of tympanic membrane perforation ranged between 0.5mm and1.0mm,the pressure curves of both sides of the tympanic membrane can completely coincide.When the diameter ranged from 0.1mm to 0.4mm,the pressure in the tympanic cavity rose slower than in the external acoustic meatus,and the delay is more significant with the diameter shrinking.5.After tympanic membrane puncture,there was no significant increase in the hearing threshold of both air conduction and bone conduction.Experiencing fast buoyant ascent escape from the depth of more than 150 meters with membrane puncture,no obvious middle ear barotrauma was observed,and no significant influence in the hearing of both air conduction and bone conduction.【Conclusion】1.For divers,middle ear barotrauma might occur in fast buoyant ascent escape,which did not injure inner ear.Middle ear barotrauma could be avoided by continuous opening of eustachian tube.2.For rats,middle ear barotrauma was caused by fast buoyant ascent escape from the depth of 200 meters,which resulting in conductive hearing loss.3.Tympanic membrane puncture can cause hearing loss in rats,but it has obvious preventive effect on middle ear barotrauma.4.The expression of inflammatory factors in the middle ear cavity changed significantly when the middle ear barotrauma occurred after modeling.Prophylactic tympanic membrane puncture could attenuate the changes of inflammatory factors expression.5.The results of fluid mechanics computer analogue simulation indicate that the perforation of eardrum can effectively balance the internal and external pressure of the middle ear to prevent barotrauma.The minimum diameter of the perforation meeting the requirements of safe compression is 0.5mm.6.Security and feasibility of tympanic membrane puncture to prevent middle ear barotrauma caused by fast buoyant ascent escape from the depth of more than 150 meters were confirmed.