Lidocaine Diffusion and the Round Window Membrane
Transactions of the Pacific Coast Oto-Ophthalmological Society annual meeting 02/1977; 58:97-104.
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ABSTRACT: The distribution patterns of horseradish peroxidase (HRP) reaction products in the inner ears of guinea pigs were studied after injections into the middle ear cavities and perilymphatic and subarachnoid spaces. The normal round window membrane resisted HRP penetration from the middle ear side, but when it became pathological after repeated applications, its permeability increased. HRP deposits were found in the cochlear and vestibular sensory cells and in the lumen of the endolymphatic sac. HRP reaction products were minimal at the cochlear apex even after long survival times, suggesting that perilymph flow, if it exists, is rather weak toward this direction. Whereas the stria vascularis is impermeable to HRP, the vestibular dark cells were accessible; thus, the metabolic activity of the dark cells can be more readily controlled by drug applications through the middle ear cavity. The finding of HRP deposits on the scala vestibuli surface of Reissner's membrane and the absence of HRP in the upper portion of the spiral ligament at the basal turn suggests that the oval window is a secondary route of passage for these particles from the middle ear cavity to the inner ear. In order to determine the route of HRP into the endolymphatic sac from the middle ear cavity or scala tympani, the cochlear and/or vestibular aqueducts were obliterated singly or together. The route of HRP was determined to be the vestibular aqueduct. HRP is believed to enter the sac lumen through Reissner's and saccular membranes and the sac epithelium. Drugs and other large molecular substances instilled in or gaining access to the middle ear cavity may reach the endolymphatic sac causing its functional alteration.
Article: Review of Round Window Permeability[Show abstract] [Hide abstract]
ABSTRACT: The round window membrane (RWM) is permeable to certain biological substances. Those substances that can pass through the RWM have the potential to cause inner ear damage, leading to functional disturbances. The RWM is permeable to water, and the existence of osmotically active substances in the middle ear cavity can induce an alteration of inner ear fluid osmolality, leading to membrane displacement. However, several limiting factors exist that prevent free passage of substances from the middle ear to the inner ear. These include the morphological barrier of the three-layered RWM, the molecular weight of the substances, and the nature and concentration of substances in the middle ear cavity. The degree and duration of the inflammation in the middle ear cavity, as well as the morphological integrity of the RWM, also play an important role in controlling the passage of noxious substances into the inner ear. Further characterization of the factors involved in RWM permeability, and clarification of the mechanisms of the inner ear damages caused by substances passing into the inner ear through the RWM, are necessary for an understanding of the inner ear dysfunction caused by middle ear inflammation.
Article: Lidocaine in the middle ear[Show abstract] [Hide abstract]
ABSTRACT: Anesthesia of the ear canal is produced by injection of lidocaine hydrochloride into the skin of the lateral external ear canal. Ear canal, tympanic membrane, and middle ear surgeries are performed with this injection. The fluid found in the middle ear during tympanotomy was collected and analyzed. The percentage of lidocaine in the fluid was calculated by an enzyme immunoassay technique. Fifteen surgical cases were undertaken in which perilymphatic fluid in the middle ear would not be suspected, such as tympanotomy for otosclerosis. Lidocaine was found in all middle ears in which there was sufficient fluid to collect. The authors question the validity of using the presence of clear fluid in the middle ear, even with reaccumulation, as the sole criterion for identifying perilymph and cerebrospinal fluid.
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