Does repeated hyperbaric exposure to 4 atmosphere absolute cause hearing impairment? Study in Guinea pigs and clinical incidences.
OBJECTIVE
Direct pressure applied on the inner ear cannot induce hearing loss.


BACKGROUND
Three possible causes have been described in the literature for inner ear permanent lesions during scuba diving: pressure imbalance between the middle ear and the external ear, appearance of microbubbles in the internal ear, and direct effect of pressure on the inner ear. We seek to determine whether this last factor can be involved.


METHODS
We submitted two groups of guinea pigs previously implanted with an electrode in the round window to a protocol of air diving in a hyperbaric chamber. Eardrums of animals in one of the two groups had been perforated beforehand. Twenty dives were practiced over 4 weeks. We chose dive parameters consistent with common sport diving: maximal pressure of 4 atmosphere absolute and duration of 30 minutes. Auditory threshold and cochlear spontaneous activity were recorded at regular intervals. Furthermore, we recorded spontaneous cochlear activity in Heliox 400-m and 600-m dives to determine whether our conclusions hold for "extreme" diving.


RESULTS
In the group with perforated eardrums, no variation of those parameters were recorded, even in extreme diving. Important variations were noticed in the other group.


CONCLUSIONS
Pressure applied directly on the inner ear during diving does not disturb cochlear activity.
D000818:Animals; D001265:Athletic Injuries / Q000473:pathology / Q000503:physiopathology*; D001274:Atmospheric Pressure; D001309:Auditory Threshold / Q000502:physiology; D003051:Cochlea / Q000293:injuries* / Q000503:physiopathology; D003055:Cochlear Microphonic Potentials / Q000502:physiology; D003638:Deafness / Q000503:physiopathology*; D003665:Decompression Sickness / Q000503:physiopathology*; D004242:Diving / Q000009:adverse effects* / Q000502:physiology; D006168:Guinea Pigs; D006317:Hearing Loss, Noise-Induced / Q000503:physiopathology*; D006371:Helium; D008876:Middle Ear Ventilation; D010100:Oxygen; D010898:Pitch Perception / Q000502:physiology; D018058:Tympanic Membrane Perforation / Q000503:physiopathology
D006371:Helium; C038949:heliox; D010100:Oxygen