Fatiga auditiva / Auditory fatigue

Introducción y objetivos: Ante posibles pérdidas de audición a causa de sobrecargas sonoras y la escasa referencia de procedimientos objetivos para su estudio, aportamos una técnica que suministra datos precisos sobre el perfil audiométrico y el factor reclutamiento. El objetivo del estudio es la determinación de la fatiga auditiva temporal a través de la respuesta microfónica coclear ante estímulos de sobrecarga de presión sonora y medida del tiempo de recuperación. Material y método: Instrumentación específica para el estudio de microfónicos cocleares, más un generador que nos proporciona estímulos sonoros de diversa intensidad y componente armónico. Utilizamos ratas Wistar. Medimos la respuesta microfónica normal y después el efecto que sobre ella ha ejercido la aportación de sobrecarga acústica. Resultados: Utilizando un tono puro a 60 dB obtenemos una respuesta microfónica. Fatigando de inmediato con 100 dB en la misma frecuencia, a los 15 min obtenemos una pérdida de 11 dB, a partir de los cuales el deterioro se lentifica y no supera los 15 dB. Mediante sonidos de banda compleja aleatoria o ruido blanco no se produce fatiga ni a niveles de 100 dB durante una hora de sobreestímulo. Conclusiones: No existe fatiga a nivel de los receptores sensoriales. El deterioro de la respuesta mediante intenso sobreestímulo posiblemente se deba a alteraciones bioquímicas de desensibilización por agotamiento. La fatiga auditiva en pruebas clínicas subjetivas afecta a tramos supracocleares. Las pruebas de fatiga auditiva encontradas no coinciden con las obtenidas subjetivamente en clínica ni en psicoacústica (AU)

Introduction and objectives: Given the relevance of possible hearing losses due to sound overloads and the short list of references of objective procedures for their study, we provide a technique that gives precise data about the audiometric profile and recruitment factor. Our objectives were to determine peripheral fatigue, through the cochlear microphonic response to sound pressure overload stimuli, as well as to measure recovery time, establishing parameters for differentiation with regard to current psychoacoustic and clinical studies. Material and method: We used specific instruments for the study of cochlear microphonic response, plus a function generator that provided us with stimuli of different intensities and harmonic components. In Wistar rats, we first measured the normal microphonic response and then the effect of auditory fatigue on it. Results: Using a 60 dB pure tone acoustic stimulation, we obtained a microphonic response at 20 dB. We then caused fatigue with 100 dB of the same frequency, reaching a loss of approximately 11 dB after 15 minutes; after that, the deterioration slowed and did not exceed 15 dB. By means of complex random tone maskers or white noise, no fatigue was caused to the sensory receptors, not even at levels of 100 dB and over an hour of overstimulation. Conclusions: No fatigue was observed in terms of sensory receptors. Deterioration of peripheral perception through intense overstimulation may be due to biochemical changes of desensitisation due to exhaustion. Auditory fatigue in subjective clinical trials presumably affects supracochlear sections. The auditory fatigue tests found are not in line with those obtained subjectively in clinical and psychoacoustic trials (AU)

Evaluating D-methionine dose to attenuate oxidative stress-mediated hearing loss following overexposure to noise.

Noise exposure causes an excessive reactive oxygen species (ROS) generation as an unwanted byproduct of high metabolic activity. Oxidative stress and antioxidative protective mechanisms have been therefore proposed as the most interesting issues in the development of noise-induced hearing loss. The aim of this study was to examine changes in superoxide dismutase (SOD), catalase (CAT) and the auditory brainstem response (ABR) in the cochlea of C57BL/6 mice 1, 7 and 14 days after exposure to 4 kHz octave band noise at the intensity of 110 dB SPL for 8 h. The evaluation of three D-methionine (D-met) doses (100, 200 and 400 mg/kg) has been performed in order to choose an optimal concentration displaying most effectively its antioxidant and thereby otoprotective functions. Administering D-met at the dose of 400 mg/kg resulted in a significant decrease in threshold shift (TS) independently of the evaluation time after exposure to noise. SOD activity was strongly supported by the same concentration (400 mg/kg) of D-met. This effect was seen not shortly, but 7 and 14 days after exposure to noise. CAT activity was induced only by noise and it reached the peak levels 7 days after exposure. D-Met at the doses of 200 and 400 mg/kg significantly decreased noise-induced changes in CAT activity. The findings of this study indicate that the protective effect depends on the concentration of D-met and can be fully expressed only when the drug is administered in the dose 400 mg/kg.