Experimental production of serous effusion in the middle ear of animals has been achieved by other investigators by direct attack upon the Eustachian tube with cautery or ligation.l-" It would appear that the bullar effusion which results may be caused by one of three processes: 1) trauma to the tubal lumen may induce infection which could extend to the bulla and cause an outpouring of inflammatory exudate; 2) tubal edema or fibrosis could result in tubal obstruction followed by effusion ex vacuo; or 3) peritubal lymphatic compromise, may lead to extravasation of fluid from the bullar lymphatic vessels.In the present experiment an attempt was made to separate these factors. Accordingly, an aseptic external approach via the base of the skull without violation of the tubal lumen was carried out, followed by ligation of the Eustachian tube in order to ensure definitive obstruction without infection. The variable of lymphatic obstruction remained, and it was hoped that it might be controlled by providing middle ear ventilation through myringotomy. If bullar effusion is indeed due to diminished pressure and not to lymphatic compromise or infection, it should not occur if middle ear pressure is kept equal with that of the outside world. METHODThe tympanic membranes of healthy cats were examined under intravenous pentobarbital sodium anesthesia using a Zeiss surgical microscope for illumination and magnification. Twenty-three cats with normal-appearing drum membranes and clean ear canals were retained in the experiments.
Previous experiments have shown that Eustachian tube ligation via an external aseptic approach, inevitably incited tympanic bullar effusion in the cat unless permanent myringotomy was accomplished.' Experimental palate splitting and pterygoid hamulotomy also resulted in such effusion, but not with the same predictable regularity.f These results favor the "hydrops ex vacuo" theory over the lymphatic compromise or inflammation concepts of the genesis of this condition as it occurs in man. In a further attempt to test this premise it seemed advisable to design experiments which would determine whether or not spontaneous bullar pressure changes actually occur in the face of auditory tube obstruction. Should such alterations prove to be demonstrable, it was hoped that an estimation of their magnitude and time course might be achieved. METHODFive cats were anesthetized with intraperitoneal pentobarbital of sodium, and the tympanic membranes were examined through a surgical otoscope. Animals with diseased ears were rejected. The cats were rendered insensate by bilateral ablation of the mesencephalic reticular formation by suction through trephine openings in the parietal bones. This technique made it possible to keep the cats unconscious for as long as seven days. The Eustachian tube was made nonfunctional by external, aseptic ligation through a submandibular route or by pterygoid hamulotomy, To make pressure measurements the middle ear was connected to a water manometer by one of two methods. In some animals myringotomy was performed, and a metal cannula was secured in the ear canal by circumferential subcutaneous, auricular ligation to provide an airtight seal. In others no myringotomy was done, but an airtight Foley catheter was introduced through an opening drilled in the posterior bullar wall. A fine polyethylene tube connected the bullar cannula to a water manometer graduated for pressure readings. In each animal the control consisted of manometric recordings from an airtight cannula ligated in the canal of the opposite ear upon which no myringotomy was performed. This control served to rule out variations due to changes in ambient temperature and atmospheric pressure. All reported pressure data were derived by deducting the pressure changes of the control ear from those of the experimental side. The middle ear pressure, control pressure, barometric pressure, temperature, and time were recorded by visual observation and by photography through a Nizo Super-S camera equipped with a timer and a Hash attachment. One exposure per minute was made round-the-clock throughout the experimental period.Each animal was run for at least five hours after reaching a stable level of pressure diminution. Three cats were run for three days to determine whether further reduction in pressure would occur. The animals were sacrificed at the termination of the experiment, and their bullae were opened and inspected for fluid accumulation and mucosal abnormality, RESULTSAll five animals evinced a steady fall of middle ear pressure until a ...
The reported failures of Jacobson-nerve resection to eliminate parotid secretion in clinical cases suggest that alternative secretory routes to the parotid gland exist. By stimulating the inferior salivatory nucleus and successively transecting suspected pathways, it was found that only the facial nerve trunk carries accessory efferent fibers to the gland in the cat. No efferent fibers were found in the chorda tympani, but afferent fibers of the salivary reflex arc are provided by this nerve.
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