Abstract:The flow of viscous fluid in the cochlea induces shear forces, which could provide benefit in clinical practice, for example to guide cochlear implant insertion or produce static pressure to the cochlear partition or wall. From a research standpoint, studying the effects of a viscous fluid in the cochlea provides data for better understanding cochlear fluid mechanics. However, cochlear perfusion with a viscous fluid may damage the cochlea. In this work we studied the physiological and anatomical effects of per… Show more
“…These simulations are analogous to a recent experiment by Wang and Olson ( 54 ). In the experiment, they perfused viscous fluids into the scala tympani through the open round window.…”
Section: Resultssupporting
confidence: 83%
“… Figure 4 Effect of fluid viscosity. Different levels of fluid viscosity were simulated, and results were compared with experimental data (Wang and Olson, ( 54 ), their Fig. 3, C and D ).…”
Section: Resultsmentioning
confidence: 99%
“…Existing experiments are consistent with our conclusion that the extra-OCC fluids are not the medium through which most cochlear acoustic energy is dissipated. Wang and Olson ( 54 ) replaced the perilymph of the cochlea with fluids with higher viscosity. They showed that the cochlear sensitivity was compromised when the fluid viscosity level was increased by more than 50 times the physiological value.…”
The cochlear cavity is filled with viscous fluids, and it is partitioned by a viscoelastic structure called the organ of Corti complex. Acoustic energy propagates toward the apex of the cochlea through vibrations of the organ of Corti complex. The dimensions of the vibrating structures range from a few hundred (e.g., the basilar membrane) to a few micrometers (e.g., the stereocilia bundle). Vibrations of microstructures in viscous fluid are subjected to energy dissipation. Because the viscous dissipation is considered to be detrimental to the function of hearing-sound amplification and frequency tuning-the cochlea uses cellular actuators to overcome the dissipation. Compared to extensive investigations on the cellular actuators, the dissipating mechanisms have not been given appropriate attention, and there is little consensus on damping models. For example, many theoretical studies use an inviscid fluid approximation and lump the viscous effect to viscous damping components. Others neglect viscous dissipation in the organ of Corti but consider fluid viscosity. We have developed a computational model of the cochlea that incorporates viscous fluid dynamics, organ of Corti microstructural mechanics, and electrophysiology of the outer hair cells. The model is validated by comparing with existing measurements, such as the viscoelastic response of the tectorial membrane, and the cochlear input impedance. Using the model, we investigated how dissipation components in the cochlea affect its function. We found that the majority of acoustic energy dissipation of the cochlea occurs within the organ of Corti complex, not in the scalar fluids. Our model suggests that an appropriate dissipation can enhance the tuning quality by reducing the spread of energy provided by the outer hair cells' somatic motility.
“…These simulations are analogous to a recent experiment by Wang and Olson ( 54 ). In the experiment, they perfused viscous fluids into the scala tympani through the open round window.…”
Section: Resultssupporting
confidence: 83%
“… Figure 4 Effect of fluid viscosity. Different levels of fluid viscosity were simulated, and results were compared with experimental data (Wang and Olson, ( 54 ), their Fig. 3, C and D ).…”
Section: Resultsmentioning
confidence: 99%
“…Existing experiments are consistent with our conclusion that the extra-OCC fluids are not the medium through which most cochlear acoustic energy is dissipated. Wang and Olson ( 54 ) replaced the perilymph of the cochlea with fluids with higher viscosity. They showed that the cochlear sensitivity was compromised when the fluid viscosity level was increased by more than 50 times the physiological value.…”
The cochlear cavity is filled with viscous fluids, and it is partitioned by a viscoelastic structure called the organ of Corti complex. Acoustic energy propagates toward the apex of the cochlea through vibrations of the organ of Corti complex. The dimensions of the vibrating structures range from a few hundred (e.g., the basilar membrane) to a few micrometers (e.g., the stereocilia bundle). Vibrations of microstructures in viscous fluid are subjected to energy dissipation. Because the viscous dissipation is considered to be detrimental to the function of hearing-sound amplification and frequency tuning-the cochlea uses cellular actuators to overcome the dissipation. Compared to extensive investigations on the cellular actuators, the dissipating mechanisms have not been given appropriate attention, and there is little consensus on damping models. For example, many theoretical studies use an inviscid fluid approximation and lump the viscous effect to viscous damping components. Others neglect viscous dissipation in the organ of Corti but consider fluid viscosity. We have developed a computational model of the cochlea that incorporates viscous fluid dynamics, organ of Corti microstructural mechanics, and electrophysiology of the outer hair cells. The model is validated by comparing with existing measurements, such as the viscoelastic response of the tectorial membrane, and the cochlear input impedance. Using the model, we investigated how dissipation components in the cochlea affect its function. We found that the majority of acoustic energy dissipation of the cochlea occurs within the organ of Corti complex, not in the scalar fluids. Our model suggests that an appropriate dissipation can enhance the tuning quality by reducing the spread of energy provided by the outer hair cells' somatic motility.
“…One drug delivery technique in particular perfuses solutions throughout the cochlear length by injecting at relatively high rates (2 – 5 uL/min) into the basal turn of scala tympani with an outlet, or fenestration, for flow made at the apex or in the basal turn of scala vestibuli (e.g., Konishi & Kelsey 1968; Kujawa et al 1995; Bobbin & Salt 2005; Wang & Olson 2016). There are several problems that arise from patent fenestrations used with cochlear drug perfusion.…”
Background
Administering pharmaceuticals to the scala tympani of the inner ear is a common approach to study cochlear physiology and mechanics. We present here a novel method for in vivo drug delivery in a controlled manner to sealed ears.
New method
Injections of ototoxic solutions were applied from a pipette sealed into a fenestra in the cochlear apex, progressively driving solutions along the length of scala tympani toward the cochlear aqueduct at the base. Drugs can be delivered rapidly or slowly. In this report we focus on slow delivery in which the injection rate is automatically adjusted to account for varying cross sectional area of the scala tympani, therefore driving a solution front at uniform rate.
Results
Objective measurements originating from finely spaced, low- to high-characteristic cochlear frequency places were sequentially affected. Comparison with existing methods(s): Controlled administration of pharmaceuticals into the cochlear apex overcomes a number of serious limitations of previously established methods such as cochlear perfusions with an injection pipette in the cochlear base: The drug concentration achieved is more precisely controlled, drug concentrations remain in scala tympani and are not rapidly washed out by cerebrospinal fluid flow, and the entire length of the cochlear spiral can be treated quickly or slowly with time.
Conclusions
Controlled administration of solutions into the cochlear apex can be a powerful approach to sequentially effect objective measurements originating from finely spaced cochlear regions and allows, for the first time, the spatial origin of CAPs to be objectively defined.
“…These extraordinary properties of hearing depend on traveling waves of motion that propagate along both the basilar membrane and tectorial membrane (TM), ultimately stimulating mechanosensory receptors. Classical models of cochlear mechanics suggest that the spectral resolution of hearing is limited by viscous damping in the subtectorial fluid, and that cochlear amplification is required to compensate ( 1 , 2 , 3 , 4 , 5 , 6 ). However, several studies have shown that wave motions of the TM may play an important role in determining frequency tuning in a fundamentally different way—by longitudinally coupling many sensory receptor cells ( 7 , 8 , 9 , 10 , 11 , 12 ).…”
Recent studies suggest that wave motions of the tectorial membrane (TM) play a critical role in determining the frequency selectivity of hearing. However, frequency tuning is also thought to be limited by viscous loss in subtectorial fluid. Here, we analyze effects of this loss and other cochlear loads on TM traveling waves. Using a viscoelastic model, we demonstrate that hair bundle stiffness has little effect on TM traveling waves calculated with physiological parameters, that the limbal attachment can cause small (<20%) increases in TM wavelength, and that viscous loss in the subtectorial fluid can cause small (<20%) decreases in TM wave decay constants. However, effects of viscous loss in the subtectorial fluid are significantly increased if TM thickness is decreased. In contrast, increasing TM thickness above its physiological range has little effect on the wave, suggesting that the TM is just thick enough to maximize the spatial extent of the TM traveling wave.
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