Change of Guinea Pig Inner Ear Pressure by Square Wave Middle Ear Cavity Pressure Variation

Abstract

The inner ear fluid pressure of guinea pigs was measured during square wave middle ear cavity pressure variation. Time constants were derived for the slopes of the inner ear pressure recovery curves after middle ear pressure change. A "single exponential" function did not fit well and therefore more complicated functions were used for this purpose. For middle ear pressure increasing from zero to a few centimetres of water, returning to zero again, decreasing from zero to minus a few centimetres of water and then returning to zero again, time constants for the inner ear pressure recovery curves were on average 15.0, 8.6, 2.5 and 2.5 s, respectively. The results could not be described using a linear model with constant window membrane compliance and cochlear aqueduct flow resistance. A possible explanation for the large difference in time constants for positive or negative middle ear pressure changes is a dependence on aqueduct flow resistance or round window membrane position.

Cochlear Aqueduct Flow Resistance Depends on Round Window Membrane Position in Guinea Pigs

“…3a), expressed in percentage of its diameter. (Ghiz et al 2001), and that the contribution of the round window displacement to the inner ear volume change is 5 times that of the oval window (Ivarsson and Pedersen 1977).…”

“…The experimental design was basically the same as described before (Feijen et al 2002). The head of the guinea pig was fixated and a flexible tube, glued airtight in the external meatus, was connected to a pressure generator [modified WPI 900A micropressure system (World Precision Instruments Inc.)] controlled by a synthesized function generator (DS345; Stanford Research Systems).…”

“…This makes it difficult to derive the relation between the resulting inner ear pressure changes and the middle ear pressure changes produced by experiments in which the Meniett is the pressure generator. Therefore, we studied inner ear pressure changes in the guinea pig induced by middle ear pressure changes with a simple rectangular profile (Feijen et al 2002). One of the outcomes of this study was that the resistance for fluid flow through the cochlear aqueduct, which connects scala tympani with the cerebrospinal fluid space, is not constant but depends on both inner ear volume and pressure.…”

The Estimation of the Time Constant of the Human Inner Ear Pressure Change by Noninvasive Technique

“…The intralabyrinthine pressure ILP in the inner ear is considered as the output signal (Figures 2(a) and 2(b)), this output signal is represented by P i . Our objective was to find the relationship between ILP, ICP, and R A C. Based on the physical model described by Feijen et al [20], the differential equation…”

“…The second response "τ 2 " was a direct reaction to the cessation of the pressure stimulus. Later, Wit et al repeated a similar experiment on the guinea pig and calculated a new time constant called (R A C) [19][20][21]. R A C was mainly determined by the flow resistance of the aqueduct, combined with the compliance of the cochlear windows.…”