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Auditory perception or hearing can be defined as the interpretation of sensory evidence, produced by the ears in response to sound, in terms of the events that caused the sound. We do not hear a window but we may hear a window closing. We do not hear a dog but we may hear a dog barking. And we do not hear a person but we may hear a person talking. Hearing impairment can result in anxiety or stress in everyday life. Pure-tone hearing loss (or threshold shift) is a measure of hearing impairment. Aging and excessive noise are the main causes of hearing impairment. Speech perception is another concept. The difference with the former is best illustrated by the disabled individual declaring "I can hear that someone is talking to me, but I don't understand what she says". Being unable to understand easily and clearly significant others, especially in understanding speech in a noisy environment, can give rise to considerable psychosocial and professional consequences (disability). Presbycusis is the decline in hearing sensitivity caused by the aging process at different levels of the auditory system. However, it is difficult to isolate age effects from other contributors to age-related hearing loss such as noise damage, genetic susceptibility, inflammatory otologic disorders, and ototoxic agents. Therefore, presbycusis and age-related hearing loss are often used synonymously. In this report pathophysiology is mostly described with regard to presbycusis, and the main peripheral types of presbycusis (sensory or Corti organ-related, strial, and neural) are summarized. An original experimental model of strial presbycusis, based on chronic application of furosemide at the round window, is further described. Central presbycusis is mainly determined by degeneration secondary to peripheral impairment (concept of deafferentation). Central auditory changes typically affect speed of processing and result in poorer speech understanding in noise or with rapid or degraded speech. Last, age-related cognitive factors can be associated to peripheral hearing impairment and increase disability in speech understanding in noise.

The relationships between tinnitus and hearing loss are studied from a clinical prospect. Five critical points are discussed. 1. Some degree of hearing loss is found in the vast majority of tinnitus patients; but an individual may well have a sensorineural hearing loss and no tinnitus at all. 2. A minor adjunction to the neurophysiological model of Jastreboff is proposed to take account of the association between tinnitus and hearing loss. 3. Tinnitus appears to cause more distress when hearing loss is marked. 4. Self-reported hearing loss should be considered when implementing habituation sound therapy. 5. According to McKinney, the rate of success on tinnitus that can be expected with habituation sound therapy is not significantly affected by hearing level.

We present today our preliminary results of the TEFLAG test performed on 58 patients suffering from Meniere's disease. This test completed in 1993 has already led to a 4-stage classification of noise induced hearing losses. On the one hand, it is based on the morphological study of susceptance B curves, and on the other hand, on the study of the resonant frequency (RF) of the annular ligament of the stapes, provided by a multifrequential impedancemeter. The endolymphatic hydrops coming with the Meniere's disease practically always cohabits in the intercritical period with the decrease of the perilymphatic pressure of the scala vestibuli, which is shown in the morphology of Stage IV curves especially, and the decrease of the annular ligament rigidity. Inversely, during the vertigo or around, we mainly have stage I curves, and an increase of the stapes annular ligament resonant frequency (RF), testifying the labyrinthic hydrops, which is the physiopathological essence of the Meniere's disease.

Objectives: To establish that susceptance-conductance tympanograms at a probe-tone frequency of 2 kHz reflects the status of the annular ligament (AL) and through it of the cochlea., Methods: Experimental study in 5 chinchillas and 22 guinea pigs. Six validating experiments were used: blockages of the stapes and of the round window membrane (RWM), fistula of the RWM, fluid removal from the cochlea, injection of saline in the scala tympani (ST) and acoustic trauma (AT). Quantitative data (mean values of Y226, FR, Y2000, G2000 and B2000) and shape of the curves were analyzed before and immediately after lesions were done., Results: Guinea pig was the most convenient provided bulla was vented and the same tip was used along the experiments. Only the shape of the curves are discriminant: 1/a supplementary sharp peak, centered around negative pressures, is observed in Y/G tympanograms in every case of RWM fistulas and in some case of AT. 2/injection of saline into ST induces immediate and reproducible Y2000, G2000, et B2000 curves modifications. 3/RWM and stapes blockages provoke foreseeable stiffening and sharpening of the tympanograms at 2 kHz. 4/on the contrary, fluid removal from the cochlea induces multiple peaks curves., Conclusions: Experimentally-induced modifications at the AL either direct (stapes blockage) or indirect by AT or decrease/increase of pressure load at the cochlear interface at the footplate result in noticeable, constant, reproducible changes of curves registered at 2 kHz. The stapes behaves both as the plotter of the curves and the interpreter of the inner ear pressure.

The multiple treatments of sudden deafness shows how this pathology still remains quite unknown. The authors present a retrospective study of 87 patients treated by normovolemic hemodilution associated to hyperbaric oxygenation. They obtain a total à 60% of significant recovery (ratio between hearing gain and initial hearing loss, above 25%) and in severe hearing loss (threshold between 70 and 90 dB) 60% of good results (ratio above 50%). The importance of the initial form of audiogram and the presence of dizziness as prognostic factors is not confirmed. On the other hand, the evolution of tinnitus is correlated with the deafness and it is a supplementary means to evaluate the therapeutic efficiency. Moreover the persistence of tinnitus represents an important after effect. Sudden deafness still remains a medical emergency and the delay for carrying out any treatment should be as short as possible. On the other hand it is possible to reduce hospital stay by two sessions of hyperbaric oxygenation per day.

Hyperbaric oxygen therapy is one of the numerous therapies which have been proposed in the management of sudden deafness. It is presumptuous to claim the efficiency of any treatment in a pathology where both the origin and the actual rate of spontaneous recovery are unknown. The grounds of therapies are therefore empirical but the need of urgent therapy is dictated by ethics. This study compares the effects of hyperbaric oxygen therapy in two groups of patients; according ot their order in randomization the subjects were treated either at a rate of 1 session or 2 sessions per day. Hyperbaric oxygen therapy was associated with infusion of Naftidrofuryl to counteract the vasoconstrictive effect of increased oxygen pressure in blood. Steroids were also administered simultaneously to avoid, for the same reasons, cerebral oedema. Normovolemic hemodilution (Dauman et al. 1983) was systemically performed in all the patients preliminarily to hyperbaric oxygen therapy, in order to reduce the haematocrit and thus facilitate blood supply. The efficiency and the side effects were similar in the two groups, provided that some principles in the selection and the monitoring of the patients were respected. The rate of 2 sessions of hyperbaric oxygen therapy per day has obvious advantages in view of health policy, but it requires the hospitalization of the patient and should be restricted to the younger subjects.

Tinnitus is often related to a peripheral impairment which seems to trigger an abnormal autonomous functioning of the central auditory system. Moreover peripheral stimulations may diminish, and even suppress their perception, either through masking or through inhibition of an aberrant neuronal activity. Here we present an experimental model of peripheral deafferentation in which a decrease of neurochemical activity is observed in the brainstem auditory nuclei, followed by a progressive recovery after the peripheral destruction. This activity could represent a central morphofunctional correlate of tinnitus. Development of experimental models of tinnitus must be continued. Such models should allow the study of the basic physiological mechanisms behind tinnitus and suggest some therapeutic approaches which could be objectively evaluated.

A simplified method, useful in clinical practice, is described in order to study the frequency selectivity in various conditions. The patient is asked to indicate the levels of pure tones which are necessary to mask completely the perception of an intermittent probe. The resulting psychoacoustic tuning curves are characterized by a more or less narrow bandwidth which reflects the ability to resolve simultaneously presented sounds. Several circumstances where these tuning curves are helpful, are presented: assessment of tinnitus, Menière's disease, unclear impairment of speech intelligibility. Therefore, this technique appears as a valuable tool which can be used in addition to the usual audiometric and electrophysiological tests battery.

The role of electrophysiology (auditory evoked potentials) in children up to 3 years old was studied through the feasibility and results of subjective audiometry. In children over six months old, subjective tests are performed systematically or at least tried before using electrophysiology. Electrophysiology is required when audiometry is impossible, and it is often performed when audiometry is abnormal. When subjective tests were not performed first, either because the child is too young or shows a developmental retardation, and the electrophysiological tests are abnormal, it is absolutely necessary to obtain an exact level of hearing as soon as possible using subjective tests. The results of a study on 244 electrophysiologically tested children between the 0 and 3 years of age are presented briefly. In 73% of the cases, the auditory brainstem responses were sufficient for clarifying or confirming the subjective tests. In 27%, they had to be completed be an electrocochleography (ECochG) under general anesthesia. The information based on the ECochG and the comparison data between the ECochG and subjective thresholds are presented. On one hand, this study highlights the double complementarity between audiometry and electrophysiology on the other, the brainstem potentials and ECochG.