John A. Ferraro

ECoG Results in Perilymphatic Fistula: Clinical and Experimental Studies

Patients with perilymphatic fistula have been described as having symptoms similar to Menieres disease and endolymphatic hydrops. Direct clinical or experimental evidence linking the two inner ear disorders has been lacking. An enhancement of the summating potential observed with electrocochleography suggests a diagnosis of ELH in both of these inner ear disorders. In this study, ECoG results of 27 patients with surgically confirmed PLF are reported. Fourteen patients with surgically confirmed spontaneous PLF had abnormal ECoG. Six of these 14 patients had normal hearing. The ECoG changes in patients with Menieres disease and those with surgically confirmed PLF are identical, indicating the underlying pathologic change in both is hydrops. But there is no specific diagnostic abnormality on ECoG that differentiates these two inner ear disorders. Also, an experimental model of PLF was developed and studied in guinea pigs. “Inactive” PLF is defined as “an opening was made into the cochlea, but if no perilymph moved out through the fistula, it was defined as inactive” An “active” PLF occurs when perilymph actually moves from the inner ear out to the middle ear. ECoGs were recorded before and after creation of an “active” PLF. ECoG abnormalities were seen in “active” PLF and correlated with histologic data demonstrating ELH. An abnormally enhanced summating potential was demonstrated after active removal of perilymph through the experimentally created fistula. Cochlear duct histology showed hydropic distention of Reissners membrane in the experimental ears and no changes in the membranous labyrinths of the unoperated, control ears. Experimental PLF, with histologically confirmed secondary ELH, produced changes similar to those observed in guinea pigs with ELH experimentally produced on a primary basis. Preliminary experimental data suggest ECoG may be helpful in differentiating (acute) PLF and (secondary) ELH. ECoG obtained in intensity series showed greatest intensity effect at 40 dB and no effect at 60 dB. Further studies using similar intensity series information will be elucidated to better determine the significance of these observations. The underlying common denominator for the two disorders of inner ear fluid dynamics is ELH. ELH, either primary or secondary, is indicated by the same ECoG changes of enhancement of the summating potential. Since the abnormal ECoG can occur in patients with vertigo but no clinical hearing loss, it is presumed ELH can occur in the vestibular labyrinth as well as in the cochlear duct.

Tympanic Ecochg and Conventional Abr: A Combined Approach for the Identification of Wave I and the I-v Interwave Interval

Identification of wave I and measurement of the I-V interwave interval (IWI) are important parameters of the auditory brain stem response (ABR). However, at low stimulus sensation levels, wave I may be absent in the presence of wave V when the ABR is recorded conventionally with scalp electrodes. Several studies have shown that the amplitude and detectability of wave I (or N1) can be enhanced via extratympanic electrocochleography (ECochG), and even more so with tympanic ECochG. In the present study, tympanic ECochG was combined with conventional ABR to compare the amplitude and sensitivity of N1, wave I, and wave V in normally hearing subjects, and to identify the N1-V IWI in hearing impaired subjects whose conventional ABRs did not contain a reliable wave I. For the normally hearing subjects, the amplitude of the N1 was considerably larger than the amplitudes of waves I and V of the conventional ABR and there was no significant difference between N1 and wave V thresholds. For the hearing impaired group, the combined ECochG-ABR approach allowed for the identification of N1 and measurement of the N1-V IWI in all subjects. Our results support the use of tympanic ECochG in combination with conventional ABR for certain audiological and neurological applications.

Improved sensitivity of electrocochleography in the diagnosis of Meniere's disease

Abstract ECochG has long been shown to complement the diagnosis of MD, primarily through measurement of the SP/AP amplitude ratio. While reported in the literature to be highly specific to this disorder, ECochGs sensitivity in the general MD population remains relatively low (ranging from 20–65%). The current study assessed the sensitivity and specificity of the ECochG protocol we employ for suspected MD patients, which includes measuring both the amplitudes and areas of the SP and AP to clicks (to derive the SP/AP amplitude and area ratios), and the SP amplitudes to 1000 and 2000 Hz tone bursts. A retrospective chart review was conducted to compare ECochG results from 178 suspected MD patients with their eventual diagnoses. Measurements of highest sensitivity and specificity (determined using a logistic regression analysis) included: SP amplitude, SP area, SP/AP area ratio, and total SP-AP area. Sensitivity and specificity values associated with these measures were 92% and 84%, respectively. The sensitivity value is considerably higher than previously reported, and is attributable to the inclusion of area measurements in our protocol. Sumario La ECochG ha demostrado ser complementaria en el diagnóstico de la enfermedad de Meniere (MD) principalmente medi-ante la medición de la amplitud del ratio SP/AP. Mientras que se ha reportado en la literatura la alta especificidad de la ECochG, su sensibilidad en la población general con MD permanece relativamente baja (en un rango del 20 al 65%). Este estudio evalúa la sensibilidad y la especificidad del protocolo de ECochG que empleamos en pacientes con sospecha de MD, el cual incluye la medición tanto de la amplitud y las áreas de SP y AP con clics (para derivar los ratios de área y amplitud SP/AP), y las amplitudes de SP con burst tonales de 1000 y 2000Hz. Se construyó una tabla retrospectiva para comparar los resultados de ECochG de 178 pacientes con sospecha de MD, con sus diagnósticos eventuales. Las mediciones de la más alta sensibilidad y especificidad (determinadas mediante un análisis de regresión logística) incluyeron: amplitud SP, área SP, ratio de área SP/AP y área total SP-AP. La sensibilidad y la especificidad asociadas con estas mediciones fueron 92% y 84% respectivamente. El valor de sensibilidad es considerable-mente mayor que el previamente reportado y se atribuye a la inclusión de la medición del área en nuestro protocolo.

Cochlear potentials in clinical audiology

The recording of cochlear and auditory nerve potentials in humans via Electrocochleography (ECochG) has emerged as a valuable tool for a variety of clinical applications. This review consolidates current research on the use of cochlear potentials and ECochG in the clinical setting and identifies several areas in need of additional study. Methodological topics discussed include a review of ECochG recording approaches (i.e. transtympanic versus extratympanic) and issues related to choice of stimuli (clicks versus tonebursts). The review of current applications for cochlear potentials focuses primarily on the use of ECochG in the identification and treatment of Ménières disease/endolymphatic hydrops (MD/ELH). Other uses for ECochG also are presented (e.g. intraoperative monitoring, enhancement of ABR wave I, estimation of hearing sensitivity). Several suggestions are offered to maximize the predictive value of ECochG in the diagnosis of MD/ELH.

The human lateral lemniscus and its nuclei. The human auditory pathways: a quantitative study.

Abstract Quantification of the human lateral lemniscus and its nuclei in 15 brains of patients without hearing impairment revealed these average values: Cross-sectional surface area of the bundle at the level of the nucleus of cranial nerve IV of 2.5 mm 2 , fiber density of 77,000/mm 2 ; 194,000 total fibers on each side; grouping of the nerve cells in three nuclei (olive remnant, ventral, and dorsal) the largest of which is the ventral; cell density in the olive remnant of 5009/mm 3 , in the ventral nucleus of 15,184/mm 3 , and 13,169 cells per mm 3 in the dorsal nucleus; total cell populations in all nuclei of 20,063 on the left and 26,137 on the right; glial-neuronal index of 9.2; cell dimensions of 23.6 × 15.4 microns in the olive remnant and 21.2 × 12.2 in the other nuclei; combined nuclear volume of 1.91 mm 3 . Loss of neurons was not apparent in the aged brains but a significant reduction in counts of axons and in lemniscal bulk appeared in two of the older brains of the series (77 and 91 years).

Comparison between AER and behavioral thresholds in normally and abnormally hearing chinchillas.

The present study compared the auditory evoked response (AER) and behavioral thresholds from the chinchilla before and after acoustic overstimulation. Bipolar electrodes were chronically implanted in the inferior colliculus of seven monauralized behaviorally conditioned animals (shock-avoidance). AER to 20-msec and behavioral thresholds to 20- and 500-msec tone bursts were determined for a range of frequencies before and after a 4-hour exposure to a 2000 Hz, 120dB SPL pure tone for six of the animals. One animal served as control and received no exposure. Results revealed a relatively close correspondence between AER and behavioral thresholds both before and after noise exposure in the same animal. Postexposure AER and behavioral thresholds displayed mild to moderate losses in sensitivity in the 1 to 4 kHz range. These findings justify further development of this particular AER as an indicator of hearing sensitivity in the chinchilla.

ABR recordings in newborns using an ear canal electrode.

The objective of this study was to improve the sensitivity of ABR recordings in newborns via a procedure that utilizes the ear canal as a recording site. Conventional recordings were compared to ear canal recordings of the ABR in 45 normally-hearing newborns who passed their newborn hearing screening. Responses were obtained at stimulus levels of 80, 60, 40, and 20 dBnHL using forehead (+) to ear canal (−), versus forehead (+) to mastoid (−) electrode configurations. ABR parameters evaluated included measurement of component amplitudes of wave I and V, absolute latencies of I and V, the I-V interwave interval, and amplitude ratio. At stimulus levels of 80, 60, and 40 dBnHL, wave I amplitude was significantly larger using the ear canal configuration. This investigation shows that the amplitude of wave I is significantly larger and easier to identify when the ear canal is used as one of the recording sites in comparison to more conventional scalp (mastoid) recordings.

Effects of prolonged noise exposure in chinchillas with severed middle ear muscles

Using the round window-recorded cochlear microphonic as the index of acoustic reflex activity, we noted a decay in the strength of middle ear muscle contraction in the chinchilla following an eight hour exposure to octave band noise (500 Hz. center frequency, 95 dB. sound pressure level). On the basis of this observation it was concluded that the prolonged exposure reduced the effectiveness of the acoustic reflex in protecting the cochlea. This reduction, however, may have been underestimated if the exposure was also sufficient to reduce cochlear output. The present investigation examined this possibility by comparing the effects of a similar exposure in chinchillas with intact (normal) and severed middle ear muscles. Following exposure, the cochlear microphonic magnitude increased slightly in the normal group. Decreases in the cochlear microphonic were observed in the animals with severed muscles even when the overall exposure level was reduced to simulate the effects of middle ear muscle contraction. These findings indicate that although the muscles did afford some degree of protection to the cochlea during the exposure, the protective effects of the acoustic reflex may have been reduced even beyond our original observations.

Acoustic Reflex Decay in Chinchillas during a Long-term Exposure to Noise

Reflex decay to 0.5 kHz octave-band noise at 95 dB SPL was measured in chinchillas during four 2-hr exposure periods separated by 11 -min quiet intervals. Round window electrodes were implanted in six animals. Measures of acoustic reflex decay were inferred from amplitude changes in the cochlear microphonic generated by the octave-band noise. Reflex decay followed essentially the same time course during each exposure period. Vigorous muscular contraction to the signal onset was followed by gradual decay that a symptoted between 30 and 50% of its initial value. The process of decay seemed to be complete sometime between 8 and 30 min. The results suggest that the middle ear muscles in chinchillas provide some protective function during exposures of fairly long duration.

The Effect of Contralateral Pure Tones on the Compound Action Potential in Humans: Efferent Tuning Curves.

BACKGROUND The compound action potential (CAP) has been suggested in the literature as an alternative to otoacoustic emissions for evaluating the efferent auditory system. However, very few studies have examined efferent influence on auditory nerve potentials in humans. PURPOSE This study examines the effects of presenting contralateral pure tones on the ipsilateral CAP onset and offset amplitudes as a potential clinical tool for the assessment of efferent auditory function. RESEARCH DESIGN CAPs for 1- and 4-kHz tone pips (TPs) and clicks were recorded from 9, 9, and 8 participants, respectively. Contralateral tones were presented at levels ranging from 20 to 70 dB HL in 10-dB steps. The frequencies of the contralateral tones were 0.5, 1, 2 kHz for the 1-kHz TP CAP; 2, 4, 8 kHz for the 4-kHz TP CAP; and 0.5, 1, 2, 4, 8 kHz for the click CAP. DATA ANALYSIS The CAP onset and offset amplitudes in all experimental conditions were analyzed and compared to the CAP amplitude without contralateral stimulation (i.e., baseline). RESULTS Maximum suppression of 1-kHz TP CAP onset amplitude was obtained in seven out of nine participants by the 1-kHz contralateral pure tone at 40 dB HL. The 4-kHz TP CAP onset amplitude was maximally suppressed in eight out of nine participants by the 8-kHz contralateral pure tone at 30 dB HL. The click CAP offset amplitude was maximally suppressed in four out of eight participants by the 8-kHz contralateral tone presented at 40 dB HL. The 1- and 4-kHz TP CAP offset and click CAP onset amplitudes were not affected by contralateral stimulation. CONCLUSIONS These results along with the previous studies may suggest that the efferent system is maximally stimulated by moderate signal-level tones (i.e., 30-40 dB HL), and that efferent activity is dependent on frequency cues of both the stimulus and suppressor tones. Other factors that might be affecting efferent influence on the CAP in humans such as sound duration, phase, bandwidth, and periodicity need to be further investigated.