RESUMEN
INTRODUCTION: Pharmacological protection of cochlear function is one of the most exciting goals of inner ear medicine. The selective glutamate antagonist MK 801 may be neuro-protective to the cochlea.1 This study aims to investigate whether round window administration of MK 801 protects cochlear function against a combination of noise and atmostpheric hypoxia. METHODS: Eight guinea-pigs were studied. Round Window E. Catheters (Durect Inc., USA) were implanted through a trans-bulla approach and EcoG thresholds determined at 8, 16, 24 and 30 kHz. Artificial perilymph (n = 4) or 10 mM MK 801 (n = 4) was then perfused onto the round window membrane. After 15 min the anaesthetized animals were exposed to 100 dB white noise in 11.5-12. 5% atmospheric oxygen. Thresholds were determined before and 15 min after exposure. RESULTS: The mean threshold shifts from pre-perfusion at 8, 16, 24 and 30 kHz were 40, 33, 35 and 17 dB, respectively (in control animals) and 29, 28, 33 and 41 dB, respectively (in treated animals). A marginal protective effect was demonstrated at 8 kHz (P = 0.06). The 30-kHz thresholds in the treated group fell by 61 dB before noise exposure compared to < 1 dB in the controls (P = 0.0007), suggesting that at high frequencies, 10 mM MK 801 may itself be ototoxic. CONCLUSIONS: These results partially support existing data suggesting that pharmacological protection against noise/hypoxia is possible. Administration of round window NMDA antagonists may affect normal auditory threshold making detailed evaluation of the toxicity of potential inner ear therapies essential before clinical use is contemplated.
RESUMEN
INTRODUCTION: Procedures within the external meatus and tympanum constitute a large part of otological surgery. Successful healing after procedures on the tympanic membrane will in large part be dependent on the integrity of local blood flow. However, there appear to have been relatively few studies investigating blood flow in the external auditory meatus and tympanum in normal subjects and those with conditions requiring surgery, e.g. tympanoplasty. The aim of this study is to obtain such data using Laser Doppler Blood Flowmetry. METHOD: Control volunteers (n = 30) and patients requiring tympanoplasty (n = 20) were recruited for the study. Laser Doppler Blood Flowmetry was performed in all patients using a commercially available system (Periflux 5000, Perimed AB, Sweden) at four sites: (1) preauricular skin; (2) cartilaginous ear canal; (3) bony ear canal; and (4) tympanic membrane. Mesotympanic temperature was also measured using a Braun Infrared thermometer. Blood flow (flux) was measured as RBC density 'speed following internal calibration. RESULTS: Analysis revealed that in both the control subjects and pretympanoplasty patients, the ranking of blood flow at the sites was 3, 2, 1 and 4 (highest to lowest). Comparing matched sites, there were no significant differences between the two groups. The amplitude of flow was not found to be correlated with mesotympanic temperature. CONCLUSION: Grafts applied to repair perforations of the tympanic membrane are likely to obtain the majority of their blood supply from the bony external auditory meatus rather than that tympanic membrane. Further studies are ongoing to define local blood flow patterns in order to optimize the results of tympanoplasty.
RESUMEN
A truncated transmission line probe (TLP) has been utilized to excite and detect time domain responses after pulsed excitation in electron paramagnetic resonance (EPR) spectroscopic experiments in the frequency range 200-400 MHz. The TLP device is a modified short-circuited coaxial line, which allows the irradiation of the sample by the traveling wave B1 fields in the frequency range of kilohertz to 30 GHz. In EPR studies at 300 MHz carrier frequency, with 10 W incident power, a 45 degrees pulse is 45 ns in duration. This corresponds to a 0.9-G B1 field. Using the TLP, time-domain responses from the solid N-methyl pyridinium tetra-cyanoquinodimethane (TCNQ) were collected at 200, 250, 300, and 350 MHz, with the range limited by the amplifiers. In addition two tubes containing TCNQ placed side-by-side vertically along the axis of the probe were used to collect time domain responses in the presence of magnetic field gradients to test the feasibility of two-dimensional imaging using a TLP. The magnetic field gradient was steered in the xz plane and 36 projections were collected at 5 degrees intervals. Using filtered back-projection image reconstruction, the two-dimensional spatial image in the xz plane was obtained at good resolution. Copyright 1998 Academic Press.
