Cochlear Microphonic Waveforms Research Articles

Comparison of Cochlear Microphonics Magnitude with Broad and Narrow Band Stimuli in Healthy Adult Wistar Rats.

Cochlear microphonic (CM) is a cochlear AC electric field, recorded within, around, and remote from its sources. Nowadays it can contribute to the differential diagnosis of different auditory pathologies such as auditory neuropathy spectrum disorder (ANSD). This study compared CM waveforms (CMWs) and amplitudes with broad and narrow band stimuli in 25 healthy male young adults Wistar rats. This experimental study was accomplished in the School of Rehabilitation Sciences of Iran University of Medical Sciences, Tehran, Iran (April, 2016). Using an extratympanic technique in ECochG (Electrocochleography) recording, CMWs in response to click and tonal stimuli with different octave frequencies were recorded at a high intensity level in subjects. The CMW amplitudes were calculated by a graphical user interface (GUI) designed in MATLAB. The CMW magnitude increased upon an increase in bandwidth stimulation. CM amplitude with click stimulation was larger than tonal stimuli. Across tonal stimuli, the CMW amplitudes at lower frequency tones were larger than those at higher frequency tones. Those findings were statistically significant (P<0.001). CMW amplitude with click as broadband stimulus was larger than those with tone bursts as narrowband stimulation. Click stimulation due to the width of spectral involves greater regions of cochlear partition. Therefore, CMW most likely is a reflection of spatial summation of voltage drops generated by hair cell groups in response to acoustic stimulation. In order to production nature of CM potentials as well as their very small magnitudes especially with tonal stimuli, thus, we recommend using click stimulation for CM potential recording.

Effects of Stimulus Intensity on Low-Frequency Toneburst Cochlear Microphonic Waveforms.

This study investigates changes in amplitude and delays in low-frequency toneburst cochlear microphonic (CM) waveforms recorded at the ear canal in response to different stimulus intensities. Ten volunteers aged 20-30 were recruited. Low-frequency CM waveforms at 500 Hz in response to a 14-ms toneburst were recorded from an ear canal electrode using electrocochleography techniques. The data was statistically analyzed in order to confirm whether the differences were significant in the effects of stimulus intensity on the amplitudes and delays of the low-frequency CM waveforms. Electromagnetic interference artifacts can jeopardize CM measurements but such artifacts can be avoided. The CM waveforms can be recorded at the ear canal in response to a toneburst which is longer than that used in ABR measurements. The CM waveforms thus recorded are robust, and the amplitude of CM waveforms is intensity-dependent. In contrast, the delay of CM waveforms is intensity-independent, which is different from neural responses as their delay or latency is intensity-dependent. These findings may be useful for development of the application of CM measurement as a supplementary approach to otoacoustic emission (OAE) measurement in the clinic which is severely affected by background acoustic noise. The development of the application in the assessment of low-frequency cochlear function may become possible if a further series of studies can verify the feasibility, but it is not meant to be a substitute for audiometry or OAE measurements. The measurement of detection threshold of CM waveform responses using growth function approach may become possible in the clinic. The intensity-independent nature of CMs with regards to delay measurements may also become an impacting factor for differential diagnoses and for designing new research studies.

High-frequency hearing impairment assessed with cochlear microphonics

Conclusion: Cochlear microphonic (CM) measurements may potentially become a supplementary approach to otoacoustic emission (OAE) measurements for assessing low-frequency cochlear functions in the clinic. Objective: The objective of this study was to investigate the measurement of CMs in subjects with high-frequency hearing loss. Currently, CMs can be measured using electrocochleography (ECochG or ECoG) techniques. Both CMs and OAEs are cochlear responses, while auditory brainstem responses (ABRs) are not. However, there are inherent limitations associated with OAE measurements such as acoustic noise, which can conceal low-frequency OAEs measured in the clinic. However, CM measurements may not have these limitations. Methods: CMs were measured in human subjects using an ear canal electrode. The CMs were compared between the high-frequency hearing loss group and the normal-hearing control group. Distortion product OAEs (DPOAEs) and audiogram were also measured. Results: The DPOAE and audiogram measurements indicate that the subjects were correctly selected for the two groups. Low-frequency CM waveforms (CMWs) can be measured using ear canal electrodes in high-frequency hearing loss subjects. The difference in amplitudes of CMWs between the high-frequency hearing loss group and the normal-hearing group is insignificant at low frequencies but significant at high frequencies.

Third-Window Vibroplasty With an Active Middle Ear Implant

Mechanical stimulation through a cochlear third window into the scala tympani in a chinchilla model with normal and fixed stapes can generate cochlear responses equivalent to acoustic stimuli. Cochlear stimulation via the round window (RW) using active middle ear implants (AMEIs) can produce physiologic responses similar to acoustic stimulation including in a model of stapes fixation. However, pathologic conditions, such as advanced otosclerosis, can preclude delivery of sound energy to the cochlea through the oval window and/or the RW. Cochlear microphonic (CM) and laser Doppler vibrometer measurements of stapes and RW velocities were performed in 6 ears of 4 chinchillas. Baseline measurements to acoustic sinusoidal stimuli (0.25-8 kHz) were made. Measurements were repeated with an AMEI driving the RW or a third window to the scala tympani before and after stapes fixation. AMEI stimulation of the third window produced CM waveforms with morphologies similar to acoustic stimuli. CM thresholds with RW and third-window stimulation were frequency dependent but ranged from 0.25 to 10 and 0.5 to 40 mV, respectively. Stapes fixation, confirmed by laser Doppler vibrometer measurements, resulted in a significant frequency dependent impairment in CM thresholds up to 13 dB (at <3 kHz) for RW stimulation and a nonsignificant frequency-dependent improvement of up to 10 dB (at >3 kHz) via third-window stimulation. AMEI mechanical stimulation through a third window into the scala tympani produces physiologic responses nearly identical to acoustic stimulation including in a model of stapes fixation with decreased efficiency.

Application of force to the cochlear wall: Effect on auditory thresholds, outer hair cell transduction, and distortion‐product otoacoustic emissions

Described are the changes in cochlear sensitivity and mechanoelectrical transduction during a novel cochlear perturbation: the application of force to the cochlear wall. While numerous methods exist to create transient shifts in the operating point of the outer hair cell (OHC) transducer, including low‐frequency acoustic bias [G. Frank and M. Kössl, Hear. Res. 113, 57–68 (1997)] and hydrostatic bias [A. N. Salt and J. E. DeMott, Hear. Res. 123, 137–147 (1998)], attempts to create prolonged operating point shifts are largely thwarted by the numerous sources of ac coupling in the auditory system which prevent transmission of dc stimuli to the hair cells. The application of force sufficient to deform the otic capsule produced a consistent drop in neural thresholds and a sustained bias of the OHC operating point that did not rapidly adapt back to normal. Near‐simultaneous measurements of compound action potential thresholds, distortion‐product otoacoustic emissions, the OHC transfer curves derived from low‐frequency cochlear microphonic waveforms, and the endocochlear potential were performed. The data provide ample evidence of the resistance of the cochlea to dc mechanical stimuli, particularly those which do not cause a large pressure differential across the basilar membrane. [The authors gratefully acknowledge the surgical assistance of Dr. Peter Sellick.]

The influence of transducer operating point on distortion generation in the cochlea.

Distortion generated by the cochlea can provide a valuable indicator of its functional state. In the present study, the dependence of distortion on the operating point of the cochlear transducer and its relevance to endolymph volume disturbances has been investigated. Calculations have suggested that as the operating point moves away from zero, second harmonic distortion would increase. Cochlear microphonic waveforms were analyzed to derive the cochlear transducer operating point and to quantify harmonic distortions. Changes in operating point and distortion were measured during endolymph manipulations that included 200-Hz tone exposures at 115-dB SPL, injections of artificial endolymph into scala media at 80, 200, or 400 nl/min, and treatment with furosemide given intravenously or locally into the cochlea. Results were compared with other functional changes that included action potential thresholds at 2.8 or 8 kHz, summating potential, endocochlear potential, and the 2 f1-f2 and f2-f1 acoustic emissions. The results demonstrated that volume disturbances caused changes in the operating point that resulted in predictable changes in distortion. Understanding the factors influencing operating point is important in the interpretation of distortion measurements and may lead to tests that can detect abnormal endolymph volume states.

Boltzmann analysis of CM waveforms using virtual instrument software

We describe a modification to our technique for the rapid analysis of low-frequency cochlear microphonic (CM) waveforms in the basal turn of the guinea pig cochlea (Patuzzi and Moleirinho, 1998). The transfer curve relating instantaneous sound pressure in the ear canal to instantaneous receptor current through the outer hair cells (OHCs) is determined from the distorted microphonic waveform generated in the extracellular fluid near the hair cells, assuming a first-order Boltzmann activation curve. Previously, the analysis was done in real time using custom-built electronic circuitry. Here, the same task is performed numerically using virtual instrument software (National Instruments LabVIEW 4.1) running on a personal computer. The assumed theoretical function describing the CM waveform is V cm= V off+ V sat/{1+exp[( E o+ Z. P o.sin(2π f+φ tot))/ kT]}, where the six parameters are (i) a DC offset voltage ( V off); (ii) the frequency of the sinusoidal stimulus ( f); (iii) the phase of the sinusoidal stimulus (φ tot); (iv) the maximal amplitude of the distorted microphonic signal ( V sat); (v) the sensitivity of the transduction process ( Z); and (vi) the operating point on the sigmoidal transfer curve ( E o). The software obtains the least-squares fit to the CM waveforms by continuously deriving the six parameters at a speed of about one determination per second. The independent fitting of the frequency and phase allows the data to be analysed off-line from data previously recorded to tape (i.e. the frequency and phase of the microphonic response need not be known accurately beforehand). We present here an outline of the software we have used, and give an example of the changes which can be monitored using the technique (transient asphyxia). The method’s advantages and limitations have been discussed in our previous paper. The virtual instrument described here is available from the authors on request.

Electrophysiological responses in guinea pig cochlea to low frequency sound stimuli: distortion of cochlear microphonic (CM) wave form.

The present experiment investigated whether or not auditory responses of the middle and/or inner ear in guinea pigs to low frequency sound stimuli [ 60 Hz-2 kHz at 90-120 dB(SPL) ] exhibited the harmonic distortion phenomenon resulting from cochlear microphonics (CM). Measurement of CM leading in turn I by the differential electrode recording method involved measurement of 50 microV isopotential responses, output voltages and CM wave form distortion at each constant sound pressure. The results obtained were as follows: (1) On the 50 microV isopotential response curve and the output voltage curves, the changes at 60-90 Hz were different from those at higher frequencies. (2) At stimuli of 90 or 100 dB(SPL), CM wave form distortion appeared frequently at frequencies below 120 Hz, but were less pronounced above approximately 200 Hz. (3) When raised to 110 and 120 dB(SPL), almost all CM wave forms were distorted at all test frequencies between 60 and 500 Hz. (4) The patterns of CM wave form distortion at frequencies below approximately 120 Hz showed peak clipping and triangular wave distortions, while those at frequencies above approximately 200 Hz showed little of these distortions.

Acoustic biasing of CM and N1 responses to high‐frequency tone pips

The effect of basilar membrane (BM) displacement and associated endocochlear potential (EP) change produced by a 50‐Hz, 80–110‐dB SPL tone (modulator) upon the cochlear microphonic (CM) and whole nerve (N1) responses to high frequency tone pips was studied in the guinea pig. CM responses to low level 3.1 kHz tone pips and the EP variation produced by the modulator were recorded with a scala media electrode in the first turn. A round window electrode recorded N1 responses. CM and N1 amplitudes were measured as a function of the timing of the tone pip during the cycle of the modulator. The CM amplitude, which was proportional to EP change for modulator levels below 95 dB SPL and reduced except near the zero crossings of EP change for higher levels, is consistant with a model having a saturating nonlinearity in the transfer curve between the CM and acoustic waveforms. In contrast, the N1 amplitude was reduced everywhere and at all modulation levels, reduction being least near both zero crossing. [Work suppor...