Fluid dynamics of the cochlea

Structure of the cochlea

The figure below shows the structure of the human ear. The cochlea is part of the inner ear which is indicated in blue.

As can be seen in the following figure, the cochlea is a coiled system of three ducts: scala vestibuli, scala tympani, and scala media (or cochlear duct). All of them are filled by lymphatic fluid - the scalae vestibuli and tympani by perilymph and the scala media by endolymph.
Furthermore, the cochlea contains a partition which is often called, for simplification, the "basilar membrane". It comprises, amongst others, the scala media, the organ of Corti, the tectorial membrane, and the basilar membrane. This partition is essential for our sense of hearing.
The uncoiled cochlea shows a length of about 35 mm and a diameter of 1.5 mm.

Transmission of sounds

Sound waves reaching the ear lead to oscillatory motions of the middle ear ossicles. This stimulation is transmitted through the oval window into the cochlea. Here, the fluid in the outer ducts, scalae vestibuli and tympani, is set in motion, as well as the basilar membrane.
The latter is moved by a travelling wave. The location of the maximal amplitude of this wave depends on the frequency of the incoming sound signal: a frequency analysis takes place.
The motion of the basilar membrane leads to a stimulation of nerve cells which are located in the organ of Corti. They send electrical signals to the brain, the sound is perceived. Furthermore, the movement of the basilar membrane is amplified by the so-called outer hair cells situated in the organ of Corti. This process is called active amplification. It takes place in a nonlinear way: relative to the ossicular displacement, low input signals evoke larger basilar membrane displacements than high sound levels. In addition, the travelling wave of the active basilar membrane is tuned much more sharply than that of the passive basilar membrane. So active amplification enables the perception of softer sounds and smaller frequency differences.

Our studies of cochlear fluid flow

In our studies we focus on the transient dynamics of fluid flow in the cochlea. This signifies that, e.g., we solve for the response to non-harmonic stimulation of the cochlea, such as clicks and changing frequencies.
The aspects listed below of fluid flow in the cochlea and of basilar membrane motion are being investigated:

• The effects of pulsating inflow conditions in cochlear-like geometries are studied using a full Navier-Stokes solver.
• Active amplification of the basilar membrane motion is investigated by coupling a Hopf bifurcation to an inviscid, one-dimensional model of cochlear fluid flow.
• By means of an inviscid, two-dimensional, and passive model of the cochlea which is formulated in the time domain we study transient fluid flow and basilar membrane motion.
• We examine the the cochlear dynamics on the basis of wave packet pseudomodes. The theory of wave packet pseudomodes is used for predicting resonance phenomena in the cochlea.

Cooperation with the Department of Otorhinolaryngology of the University Hospital Zurich

In our studies of cochlear fluid flow we cooperate with a group of the Department of Otorhinolaryngology of the University Hospital Zurich. See COCHLEAwiki for further information.

Refereed Journal Articles and Conference Papers related to the Current Projects

• Edom E., Obrist D., Kleiser L., Viscous and nonlinear flow phenomena in the cochlea
  Proceedings of the EUROMECH COLLOQUIUM 521 Biomedical Flows at Low Reynolds Numbers, 29–31 August 2011, ETH Zurich, Zurich, Switzerland, 61-62, 2011.
• Edom E., Obrist D., Kleiser L., Simulation of fluid flow and basilar membrane motion in a two-dimensional box model of the cochlea
  Proceedings of the 11th International Mechanics of Hearing Workshop, Williamstown (MA), 16-22 July 2011, 608-610, 2011.
• Edom E., Sim J.H., Huber A.M., Kleiser L., Obrist D., Numerical simulation of the fluid flow due to rocking stapes motion
  Biomedizinische Technik 55, 209-211, doi: 10.1515/BMT.2010.647, 2010.
• Obrist, D., Schmid, P.J.
  Resonance in the cochlea with wave packet pseudomodes
  22nd International Congress of Theoretical and Applied Mechanics (ICTAM2008), August 24-30 2008, Adelaide, 2008.
• Obrist, D.
  Transient inviscid flow in a passive linear model of the cochlea
  Proc. Appl. Math. Mech. 9, 2009.

Abstracts & Posters (conferences without proceedings)

• Edom E., Sim J.H., Huber A.M., Kleiser L., Obrist D., Numerical simulation of the fluid flow due to rocking stapes motion
  BMT 2010, 6-8 October 2010, Rostock-Warnemünde, 2010.
• Edom E., Obrist D., Kleiser L., Fluid flow in the cochlea due to rocking stapes motion
  8th European Fluid Mechanics Conference EFMC-8, 13-16 September 2010, Bad Reichenhall, 2010.
• Chatzimichalis M., Sim J.H., Edom E., Obrist D., Eiber A., Lauxmann M., Huber A.M., Effects of Stapes Rocking Motions on Cochlea Response: Experimental results and Numerical Simulation of Cochlea Fluid Flow
  97. Frühjahrsversammlung der Schweizerischen Gesellschaft für Oto-Rhino-Laryngologie, Hals- und Gesichtschirurgie, 17.&18. Juni 2010, Zürich, 2010.
• Edom, E., Obrist, D., Kleiser, L.
  Coupling a Hopf Bifurcation to a Cochlear Fluid Flow Model
  SSBE Annual Meeting, 27.& 28. August 2009, Bern.

Student Projects

• Hartmann, J.
  Fine-Tuning eines aktiven Modells der menschlichen Cochlea.
  Bachelorarbeit FS 2012.
• Benner, C.-F.
  Numerische Simulation von Distorsionsprodukten otoakustischer Emissionen in der Cochlea.
  Bachelorarbeit FS 2011.
• Schwärzler, S. R.
  Numerische Simulation der Fluidströmung in der Cochlea und der Basilarmembranbewegung infolge von Klick-Stimulierung.
  Bachelorarbeit FS 2011.
• Grossmann, M.
  Numerische Simulation der Fluidströmung in der Cochlea und der Basilarmembranbewegung infolge von Stimulierung mit Frequenzpaaren.
  Bachelorarbeit FS 2011.
• Müller, A.
  Fluid flow in the cochlea: Modeling the active basilar membrane by means of a Hopf-bifurcation.
  Semesterarbeit HS 2010.
• Gorji, H.
  Time domain response of the cochlea in a two dimensional passive inviscid model.
  Semester project, HS 2008.
• Piehl, H.
  Transiente Dynamik der Cochlea.
  Semesterarbeit HS 2007.
• ... click here to find for your own student project!