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Influence of middle ear effusion on perilymph.

To investigate the influence of middle ear effusion (MEE) on perilymph (PL), an experimental otitis media with effusion (OME) was provoked in chinchillas by injecting the tympanic cavity with immune complexes. MEE remained for up to 9 days after the injection of immune complexes. PL was aspirated on the 4th, 10th, and 21st day after the inoculation. The mean concentrations of albumin, IgG, and prostaglandin E2 (PGE2) were significantly greater in PL from OME induced ears than in that form normal control ears. 3H-PGE2 placed on the round window membrane of pathologically affected ears passed into PL in significantly greater amounts than in normal controls. The findings of the present study indicate that MEE affects the biochemical environment of PL. However, this influence was transient and reversible.

Albumins↗

Effects of round window membrane rupture on cochlear blood flow and inner ear pressures.

Effects of round window membrane rupture on cochlear blood flow and inner ear pressures were investigated using non-radioactive microspheres and a servo-micropipet system in guinea pigs. When perilymphatic pressure was raised through a glass capillary tube inserted into the perilymphatic space, both endolymph pressure and perilymph pressure rose. When these inner ear pressures were raised to relatively high levels, cochlear blood vessels could be compressed and endocochlear potential decreased to a negative value due to the interruption of cochlear blood flow. However, in the case when the round window membrane was ruptured by further increase in perilymph pressure, the inner ear pressures decreased and restoration of cochlear blood flow and endocochlear potential was observed. When the round window membrane was ruptured with a fine needle under ordinary inner ear pressures, cochlear blood flow did not change significantly.

Animals↗

Alterations in oxygenation of cochlear endolymph during loud sound exposure.

The oxygen tension (pO2) of endolymph of the guinea pig cochlea was measured during exposure to loud sound (12 kHz or high-pass noise; 110 dB SPL up to 1 h duration). A small, but significant, steady decline in mean pO2 was observed after both pure tone and high-pass noise exposure. The extent of the change in pO2 varied from 0-50% in individual animals, compared with unexposed control animals. All exposed animals had an extensive loss of compound action potential (CAP) thresholds at frequencies of 8-30 kHz. However, there was no relationship between the extent of the change in pO2 of endolymph and CAP threshold loss.

Animals↗

The perilymph fistula syndrome defined in mild head trauma.

Neurological and neuro-otological studies were carried out on 102 adults with mild cranio-cervical trauma productive of positional vertigo and perilymph fistula as confirmed by laboratory tests, and by the finding of perilymph fistula at tympanotomy in the surgically managed group. In this patient group, all other neurological and neuro-otological diagnoses were excluded, e.g. epilepsy, cerebral palsy, multiple sclerosis, retardation; and for the neuro-otological group those with a history of ototoxicity, labyrinthitis, Meniere's disease, chronic ear infections, or developmental or familial disorders. Emphasis in this study was on mild trauma: fewer than half of the sample had been rendered unconscious in the injury of record, and a third of the cases were of whiplash type, with no loss of consciousness (LOC) and no remembered headstrike. These concomitant lesions comprise the perilymph fistula syndrome (PLFS) with a unique profile of neurological, perceptual, and cognitive deficits resembling a post-concussion injury. A complete description of the clinical picture is given, including psychological, cognitive and diagnostic tests, and the outcome of bedrest vs. surgical management. PLFS can arise from minor trauma, fistula are frequently bilateral (71/102), a mild sensorineural hearing loss is of variable occurrence (53%), secondary hydrops is not uncommon, and women appear more vulnerable than men for developing the syndrome. As based upon combined laboratory techniques and clinical symptomology, fistula were correctly predicted in 61 of 65 laser-operated ears. The positional vertigo component of PLFS was in all cases managed according to a special physical therapy program utilizing exercises for vestibular symptom habituation. Even when diagnosed late, a good-to-excellent outcome was achieved in 70% of treated patients.

Adult↗

Effect of glycerol on pressure difference between perilymph and endolymph.

The pressure difference between the perilymph and the endolymph following administration of 50% glycerol (12 ml/kg) was studied in guinea pigs. The perilymphatic and endolymphatic pressures were measured simultaneously with two sets of a servo-nulling system. Glycerol was administered for about one minute via a gastrocatheter. Both the perilymphatic and endolymphatic pressures began to decrease about 5 min after the administration of glycerol, and thereafter the decrease continued for about one hour with no significant difference between the two pressures. We concluded from the results that the glycerol-induced pressure difference between the perilymph and the endolymph, if present, is only a very small one, although a collapse of the scala media after glycerol intake was reported in guinea pigs and chinchillas.

Animals↗

Bacteriological characterization of the effusion material in an animal model for serous and purulent otitis media.

By means of cleaving the soft palate and blocking the Eustachian tube, two otomicroscopically well defined types of otitis media, serous and purulent, were created in an animal model (rat). The microbiological pattern of these conditions were characterized at 1, 2, 3, 4 and 6 weeks after the onset. Samples were collected from the middle ear cavity via the bulla tympanica and cultured for aerobic as well as anaerobic bacteria. The serous effusion was culture-negative. The purulent effusion material was culture positive, and mixed with Gram-positive (S. aureus, S. epidermidis, Strept. faecalis) and Gram-negative (E. coli, Proteus mirabilis) bacteria of which the latter dominated. No anaerobic species were detected. The study shows that the two otomicroscopically different types of otitis media also differ with regard to the microbiological pattern. The rat thus provides the opportunity to study these two different inflammatory middle ear responses--infectious and noninfectious--during standardized conditions.

Animals↗

Urea and hearing in patients with menière's disease.

Transient hearing improvement was recorded in around 60% of patients with Menière's disease 2 hours after the ingestion of 20 g of urea perorally. Urea slightly increased the serum osmolality, which is thought to cause a transient reduction of the endolymphatic hydrops. Urea has no inconvenient side effects and is recommended primarily as a test substance for the verification of endolymphatic hydrops, in conformity with glycerol.

Administration, Oral↗

Quantifying psychoacoustic tuning curves for clinical use.

Psychoacoustic tuning curves (PTCs) were obtained in a number of normal-hearing and hearing-impaired subjects using a simultaneous tone-on-tone masking technique. PTCs at three different centre frequencies (500, 1,000 and 2,000 Hz) were studied. In order to estimate the degree of frequency selectivity of the inner ear, an algorithm for quantification of PTCs was constructed. The method of linear regression was used to calculate the slopes of the linearized curves. Three different parameters of the curve, the low and high frequency slope and the height of the curve, were calculated using computer programs which allowed automatic evaluation of the data. The values of these parameters concerning normal and hearing-impaired subjects are presented in terms of scores and percentages of normal values. The algorithm for quantification of PTCs presented in this paper may in clinical work serve as a method of evaluating auditory frequency selectivity, particularly for very abnormal PTCs.

Audiometry, Pure-Tone↗

Analysis of the phamacokinetics of ribostamycin in serum and perilymph of guinea pigs after single and multiple doses.

The pharmacokinetics of ribostamycin in serum and perilymph of guinea pigs was studied after a single s.c. injection of 400 mg/kg or 14 daily injections of the same dose. The repetitive administration of ribostamycin did not produce functional impairment of the kidney and ototoxicity was slight. The pharmacokinetic data were analysed by non-linear least mean squares regression. Ribostamycin did not accumulate in either serum or perilymph after multiple dosing. The half-life of the drug in perilymph was 15.8 h after a single injection, but 7.6 h after the last of 14 injections. The area under the ribostamycin concentration in perilymph against time curve was also reduced after multiple dosing. These changes were found to be due to a marked increase in the rate of transfer of the drug from perilymph to serum after multiple dosing.

Animals↗