SCANNING ELECTRON MICROSCOPIC STUDIES ON INNER EAR BAROTRAUMA MAINLY ON THE DAMAGE OF COCHLEAR SENSORY HAIRS

Abstract

In order to investigate the influence of high pressure on the inner ear sudden atmospheric pressure changes were given to the guinea pigs in a chamber.
They were sacrificed immediatele, 1 week, 2 weeks, 1 month and 2 months after the conditional loading.
The morphological changes of cochlear sensory hairs were observed by means of a scanning electron microscope. The time required to increase or decrease atmospheric pressure was changed from 8, 4 to 2 minutes. As the result, the followings were clarified.
1) The sensory hairs were damaged less than 4 minutes by both increasing and decreasing pressures, showing barotrauma in the inner ear.
2) The main morphological changes of sensory hairs were swelling, bleb formation, derangement, fusion, break-off and/or disappearance.
3) The damage of sensory hairs was noted immediately after the conditional loading in all cochlear turns, and there was hardly any difference in the degree of damage in each turn. Outer hairs were more easily damaged than inner ones.
4) The damage of sensory hairs became severe by rapid change and decreasing rather than by gradual change and increasing of pressure.
5) Round window membrane rupture was noted in about one third of animals in the group of decreasing pressure for 2 minutes, and the damage was severer than that without membrane rupture.
6) The damage of sensory hairs was not noted, when the tympanic membrane had been perforated previously.
7) Strong pressure itself, starting with pressure differences between the middle and outer as well as inner ear, and reaching the inner ear via the inner ear window, is the direct cause of the inner ear barotrauma, and it is not caused temporarily as a result of round window membrane rupture.