Evaluation of cochlear function in an acute endolymphatic hydrops model in the guinea pig by measuring low-level DPOAEs.
During and after microinjection of artificial endolymph into scala media of the guinea pig, the 2f1- f2 -DPOAE at 4.5 kHz generated by low-level primaries was recorded. Reproducible changes were measured when 1.1 microl of artificial endolymph was injected at a rate of 1.65 nl/s (1.53-1.83). This volume corresponds with an acute endolymphatic hydrops of 23%. After the onset of injection the inner ear pressure immediately increased to a mean higher level of 22 Pa, whereas the 2f1- f2 -amplitude and -phase did not change for about 1 min. Thereafter, the amplitude decreased 2.6 dB (+/- 0.7) on average and slowly regained almost its initial value, with recovery frequently starting within the period of injection. In an attempt to explain the observed changes in 2f1- f2 -amplitude the basilar membrane displacement towards scala tympani at the 2f1- f2 generation site is estimated to be 19 nm for a 1.1 microl increase of endolymph volume. A small deflection of the outer hair cell stereocilia and as a consequence a change in cell conductance may explain the 2f1- f2 -amplitude changes. However, the precise mechanism of cochlear function change caused by endolymph volume increase (hydrops) remains to be elucidated.
Valk
Willem L
WL
Department of Otorhinolaryngology, University Hospital Groningen, P.O. Box 30.001, 9700 RB Groningen, The Netherlands. w.l.valk@kno.azg.nl
Wit
Hero P
HP
Albers
Frans W J
FW
D000208:Acute Disease; D000818:Animals; D001489:Basilar Membrane / Q000503:physiopathology; D001696:Biomechanical Phenomena; D002908:Chronic Disease; D003051:Cochlea / Q000503:physiopathology*; D004195:Disease Models, Animal; D004710:Endolymph / Q000502:physiology; D018159:Endolymphatic Hydrops / Q000209:etiology / Q000503:physiopathology*; D005260:Female; D006168:Guinea Pigs; D006801:Humans; D008575:Meniere Disease / Q000209:etiology / Q000503:physiopathology; D008845:Microinjections; D017084:Otoacoustic Emissions, Spontaneous