STUDIES ON THE INFLUENCE OF MIDDLE-EAR PR ESSURE CHANGES ON THE INNER-EAR OF GUINEA-PIGS (CAVIA-PORCELLUS) WITH RUPTURES OF THE ROUND WINDOW MEMBRANE

The electrical activity of the inner ear before and after rupture of t he round window membrane was monitored in guinea pigs under different pressure conditions with the aid of electrocochleography. Following st udies were conducted weekly over a period of 4 weeks. Findings showed that overpressure below the pressure needed to open the Eustachian tub e caused strong temporary functional disturbance of the cochlea, espec ially at high frequencies. Irreversible changes that were pressure-dep endent were observed and occurred mainly at high frequencies. Applicat ion of low pressure to the round window membrane caused a functional l oss comparable to changes after over-pressure. Animals with a predamag ed cochlea reacted to over pressure that was below opening pressure of the tube and to corresponding low pressure with a longer lasting func tional loss than did animals with an undamaged cochlea.