One mechanism of sudden sensorineural hearing loss after sildenafil and sexual activity.

Objectives: A case of sudden sensorineural hearing loss following use of sildenafil was examined in detail over a period of three days from first report to recovery.

Design: Case study. The subject presented with sudden sensorineural hearing loss and diplacusis a day after onset.

A meta-analysis comparing the performance of narrowband CE-Chirp and 500 Hz tone burst stimuli in recording cervical vestibular evoked myogenic potential (cVEMP).

Due to contradictory outcomes in the literature, the aim of this meta-analysis is to verify whether the narrowband (NB) CE-Chirp stimulus (centred at 500 Hz) would produce more robust cervical vestibular evoked myogenic potential (cVEMP) responses relative to the conventional 500 Hz tone burst. The literature search was conducted using PubMed, Scopus, and Web of Science databases and the terms used were "vestibular evoked myogenic potential" and "chirp". The cVEMP parameters to be analysed were P1 latency, N1 latency, and P1-N1 amplitude.

The Narrowband CE-Chirp Stimulus Does Not Necessarily Produce More Robust Cervical Vestibular Evoked Myogenic Potential.

Objective: Various studies have been conducted to search for the most optimal stimulus for eliciting cervical vestibular evoked myogenic potential (cVEMP). More recently, there is a growing interest to study the usefulness of chirp stimuli in cVEMP recording. Nevertheless, contradictory outcomes have been reported across the studies, and further research with larger samples would be beneficial to provide better insight into this matter.

Acoustic impedance rhinometry (AIR): a technique for monitoring dynamic changes in nasal congestion.

We describe a simple and inexpensive method for monitoring nasal air flow resistance using measurement of the small-signal acoustic input impedance of the nasal passage, similar to the audiological measurement of ear drum compliance with acoustic tympanometry. The method requires generation of a fixed sinusoidal volume-velocity stimulus using ear-bud speakers, and an electret microphone to monitor the resultant pressure fluctuation in the nasal passage. Both are coupled to the nose via high impedance silastic tubing and a small plastic nose insert.

Rotation of the eyes (not the head) potentiates the postauricular muscle response.

Objective: The authors investigated how eye and head rotation modulate the human postauricular muscle response (PAMR), to determine the optimal strategy for potentiating the PAMR, or minimizing it to reduce contamination of small neurogenic responses.

Design: The authors recorded the PAMR evoked by binaural bipolar clicks (50 dB SL, 360 µsec per phase with 53-msec interval) from behind the right ear of 12 normally hearing adults, and attempted to enhance it with (a) voluntary ear contraction alone, (b) head rotation alone (with the eyes forward-directed and tracking a target attached to the head), or (c) by lateral eye movement alone (toward the right measurement side, with the head facing forward).

Results: When the head alone was rotated with eyes fixed relative to the head, the PAMR increased only slightly in some subjects, as did the ongoing electromyography (EMG) (probably due to EMG activity from nearby neck muscles).

Ion flow in cochlear hair cells and the regulation of hearing sensitivity.

This paper discusses how ion transport proteins in the hair cells of the mammalian cochlea work to produce a sensitive but stable hearing organ. The transport proteins in the inner and outer hair cells are summarized (including their current voltage characteristics), and the roles of these proteins in determining intracellular Ca(2+), membrane potential, and ultimately cochlear sensitivity are discussed. The paper also discusses the role of the Ca(2+) sequestration sacs in outer hair cells in the autoregulation of hair cell membrane potential and cochlear gain, and how the underdamped control of Ca(2+) within these sacs may produce the observed slow oscillations in cochlear sensitivity and otoacoustic emissions after cochlear perturbations, including perilymphatic perfusions and prolonged low-frequency tones.

Ion flow in stria vascularis and the production and regulation of cochlear endolymph and the endolymphatic potential.

This paper reviews some of what is known about ion transport through the cells of the mammalian stria vascularis, and discusses how the endolymph and endocochlear potential in scala media are produced by the stria's main cell types. It discusses the role of each cells' ion transport proteins from an engineering perspective, and the advantages and disadvantages in using the different transport proteins in the different cells to perform their different roles. To aid this discussion, the use of spreadsheet analysis in the modelling of ion transport in single cells and homogenous epithelia is outlined, including the current-voltage (IV) characteristics of the three main categories of transport proteins (pores, ports and pumps), and the constraint equations that apply under various conditions (the voltage or ionic steady states in the open- and closed-circuit conditions).

Evidence that the compound action potential (CAP) from the auditory nerve is a stationary potential generated across dura mater.

We have investigated the generation of the compound action potential (CAP) from the auditory nerve of guinea pigs. Responses to acoustic tone-bursts were recorded from the round window (RW), throughout the cochlear fluids, from the surface of the cochlear nucleus, from the central end of the auditory nerve after removal of the cochlear nucleus, from the scalp vertex, and from the contralateral ear. Responses were compared before, during and after experimental manipulations including pharmacological blockade of the auditory nerve, section of the auditory nerve, section of the efferent nerves, removal of the cochlear nucleus, and focal cooling of the cochlear nerve and/or cochlear nucleus.

Frequency-specific electrocochleography indicates that presynaptic and postsynaptic mechanisms of auditory neuropathy exist.

Objectives: The physiological mechanisms underlying auditory neuropathy (AN) remain unclear and it is likely that the multiple disruptions are classified under the broadly defined term. Cochlear implantation is being more widely used in this population to bypass the suspected site-of-lesion although a number of cases have been identified within the Sydney Cochlear Implant Centre where this management strategy has been unsuccessful. It is likely that this relates to the different physiological mechanisms underlying AN.

Changes in cochlear responses in guinea pig with changes in perilymphatic K+. Part I: summating potentials, compound action potentials and DPOAEs.

We have measured the effects of changing perilymphatic K+ by perfusing scala tympani in guinea pigs with salt solutions high or low in K+, while monitoring the distortion product otoacoustic emissions (DPOAEs) in the ear canal (a measure of mechanical vibration of the organ of Corti), the summating potential (SP) evoked by high-frequency tone-bursts (taken to be a measure of pre-synaptic electrical activity of the inner hair cells) and the compound action potential (CAP) of the auditory nerve (taken to be a measure of post-synaptic neural activity). We have attempted to investigate the osmotic effects of our perfusates by comparison with simple hyperosmotic sucrose perfusates and iso-osmotic versions of perfusates, and for the effects of changes in other ions (e.g.

Mathematical model of outer hair cell regulation including ion transport and cell motility.

To understand the regulatory processes within the cochlea, and outer hair cells (OHCs) in particular, we have developed a mathematical model of OHC regulation that takes into account their known electrical properties, and includes fast and slow somatic motility. We model how cytosolic Ca(2+) is involved in regulation of (i) the OHC membrane potential, (ii) the operating point of OHC mechano-electrical transduction (MET) channels via slow motility; (iii) basolateral wall K(+) permeability via Ca(2+)-sensitive K(+) channels; and (iv) cytosolic concentrations of Ca(2+) itself, via Ca(2+)-ATPase-mediated sequestration within the OHCs and Ca(2+)-induced Ca(2+)-release (CICR) from the same intracellular Ca(2+) storage organelles. To account for some aspects of the cochlea's transient response to experimental perturbations, we have included a putative intracellular second-messenger cascade based on cytosolic Ca(2+).

Rising-frequency chirps and earphones with an extended high-frequency response enhance the post-auricular muscle response.

The purpose of this study was to determine whether rising-frequency chirps presented via earphones with an extended high-frequency response would optimize the post-auricular muscle response (PAMR). The PAMR was recorded in adults using three different stimuli (a click, a rising-frequency chirp, and a truncated speech stimulus, /t/). Conventional ER-3A insert earphones were compared to ER-2 insert earphones to determine whether the PAMR is enhanced by the ER-2's extended highfrequency response.

The post-auricular muscle response: an objective electrophysiological method for evaluating hearing sensitivity.

Post-auricular muscle responses (PAMRs) were recorded in sixteen adults with normal hearing and twenty adults with sensorineural hearing loss. Click stimuli were presented at 20 to 80 dB nHL via insert earphones. Only one ear was tested in hearing-impaired subjects, but normal-hearing subjects were tested monaurally and binaurally.

Primary afferent and cochlear nucleus contributions to extracellular potentials during tone-bursts.

Gross electrical responses to tone bursts were measured in the guinea pig with electrodes located in scala tympani (ST) and scala vestibuli (SV) of the cochlea, on the central portion of the VIIIth nerve fibres in the internal auditory meatus, and on the surface of the cochlear nuclear complex (CN). Intracochlear perfusion of pharmacological blockers of neural and postsynaptic activity as well as aspiration of parts or all of the CN were used to dissect the origin of the many components of the gross responses. It was shown that single-ended recordings from either ST or SV or those derived from the sum of the ST and SV responses not only contain mixed responses from the auditory nerve fibres and cochlear hair cells, but are contaminated or modified by neural activity central to the internal auditory meatus, probably in various parts of the CN.

The origin of the 900 Hz spectral peak in spontaneous and sound-evoked round-window electrical activity.

We have monitored the spectrum of the (spontaneous) neural noise at the round window (RW) and on the surface of the antero-ventral cochlear nucleus (CN) and the dorsal CN (DCN) of anaesthetised guinea pigs. We have also obtained the average gross extracellular waveform evoked by 20 kHz tone-bursts (0.25 ms and 25 ms) at each of these recording sites, and calculated the spectrum of the average waveforms (SAW).

Non-linear aspects of outer hair cell transduction and the temporary threshold shifts after acoustic trauma.

The 200-Hz cochlear microphonic potential (CM) and the compound action potential (CAP) of the auditory nerve evoked by tone-bursts were recorded in the basal turn of the cochlea of anaesthetised guinea pigs, before and after exposure to traumatic high-frequency tones that produce a temporary threshold shift (TTS) in this cochlear region. The drop in CM and the TTS were highly correlated, suggesting that it is the disruption of the outer hair cells generating the CM that causes the TTS. The previously measured rise in endocochlear potential and drop in organ of Corti K+ levels suggest that the TTS is due to a temporary closure of outer hair cell mechanoelectrical transduction (MET) channels, which produces a drop in the mechanical sensitivity of the organ of Corti, due to disruption of the active process provided by outer hair cells.