EFFECTS OF EFFUSION IN THE MIDDLE-EAR AND PERFORATION OF THE TYMPANICMEMBRANE ON OTOACOUSTIC EMISSIONS IN GUINEA-PIGS

The influence of fluid in the middle ear and of perforation and closur e of the tympanic membrane (TM) on otoacoustic emissions (OAEs) was ev aluated in guinea pigs. Click-evoked otoacoustic emissions (CEOAEs) an d distortion product otoacoustic emissions (DPOAEs) were measured afte r the auditory bulla was opened. Neither OAE level changed significant ly when fluid filled only half the space in the bulla, but both OAE le vels disappeared when fluid completely filled the bulla. These changes were reversible. Thus, the presence of fluid in the bulla influenced CEOAE and DPOAE levels only when its volume filled more than half the space of the bulla. Changes in both CEOAE and DPOAE levels were affect ed by the size of the perforation of the tympanic membrane. For the sm allest perforation, the reduction in both CEOAE and DPOAE levels was r estricted to the lower frequencies. However, as the size of the perfor ation increased, a decrease in high-frequency function occurred. Thus, the results indicate that the magnitude of both OAEs was proportional to the size of the perforation. Both OAE levels improved after the pe rforation was closed. Because CEOAEs were mole sensitive than DPOAEs t o perforation and closure of the TM, DPOAEs may be better suited for O AE measurement in ears with perforated TMs. (C) 1998 Elsevier Science B.V. All rights reserved.