Pathophysiology of Facial Nerve Stimulation and Its Implications for Electrical Stimulation in Cochlear Implants.

OBJECTIVES: A small number of cochlear implant (CI) users experience facial nerve stimulation (FNS), which can manifest as facial twitching. In some patients, this can be resolved by adjusting the electrical stimulation parameters. However, for others, facial stimulation can significantly impair CI outcomes or even prevent its use. The exact mechanisms underlying FNS are unclear and may vary among patients. DESIGN: Transimpedance measurements were used to assess lateral and longitudinal spread of current within 15 cochlea of nucleus CI recipients with FNS (13 unilateral recipients and 1 bilateral recipient). We compared the transimpedance measurements with programming parameters from clinical visits and pre- and postoperative temporal bone computed tomography (CT) scans to identify factors that may contribute to FNS in each CI ear. RESULTS: In nine ears, transimpedance curves showed inflection, which suggests a localized current sink within the cochlea. This indicates a low-impedance pathway through which current exits the cochlea and stimulates the labyrinthine segment of the facial nerve canal. Electrodes near this current sink were disabled or underfit to minimize facial stimulation. In the other seven ears, current flow peaked toward the basal end of the cochlea, suggesting that current exits through the round window or other structures near the basal end of the cochlea, stimulating the tympanic segment of the facial nerve. CONCLUSIONS: Objective transimpedance measurements can be used to elucidate the mechanisms of FNS and to develop strategies for optimizing electrical stimulation parameters and speech coding to minimize or eliminate FNS in a small subset of CI users.

Subcutaneous Air Around Receiver-Stimulator Causing Open-Circuit Failures: An Uncommon But Readily Treatable Condition Related to CPAP Use After Cochlear Implant Surgery.

OBJECTIVE: To raise awareness of a unique complication associated with continuous positive airway pressure (CPAP) use after cochlear implantation to improve early detection, prevent unnecessary testing, and facilitate treatment. STUDY DESIGN: Case series. SETTING: Tertiary referral center. SUBJECTS: Patients who developed subcutaneous air around the receiver-stimulator device and the associated ground electrode in the setting of CPAP usage, which resulted in open-circuit electrode failures. MAIN OUTCOME MEASURES: Clinical course and intervention. RESULTS: Two patients were identified that fit this criterion. Both patients were noted to have poor implant performance secondary to high or open impedances and concomitant emphysema surrounding the cochlear implant receiver-stimulator. Manual massage offered transient improvement, but programming changes ultimately led to improved sound quality and resolution of impedance anomalies in both cases. CONCLUSIONS: Subcutaneous air collection surrounding the cochlear implant receiver-stimulator in the setting of CPAP use is an uncommon but clinically relevant complication that can be recognized by characteristic physical examination findings and impedance changes. Early and accurate recognition of this event can prevent unnecessary testing and facilitate early effective treatment.

Do Modern Hearing Aids Meet ANSI Standards?

BACKGROUND: The American National Standards Institute (ANSI) provides standards used to govern standardization of all hearing aids. If hearing aids do not meet specifications, there are potential negative implications for hearing aid users, professionals, and the industry. Recent literature has not investigated the proportion of new hearing aids in compliance with the ANSI specifications for quality control standards when they arrive in the clinic before dispensing. PURPOSE: The aims of this study were to determine the percentage of new hearing aids compliant with the relevant ANSI standard and to report trends in electroacoustic analysis data. RESEARCH DESIGN: New hearing aids were evaluated for quality control via the ANSI S3.22-2009 standard. In addition, quality control of directional processing was also assessed. STUDY SAMPLE: Seventy-three behind-the-ear hearing aids from four major manufacturers, that were purchased for clinical patients were evaluated before dispensing. DATA COLLECTION AND ANALYSIS: Audioscan Verifit (version 3.1) hearing instrument fitting system was used to complete electroacoustic analysis and directional processing evaluation of the hearing aids. Frye's Fonix 8000 test box system (Fonix 8000) was also used to cross-check equivalent input noise (EIN) measurements. These measurements were then analyzed for trends across brands and specifications. RESULTS: All of the hearing aids evaluated were found to be out of specification for at least one measure. EIN and attack and release times were the measures most frequently out of specification. EIN was found to be affected by test box isolation for two of the four brands tested. Systematic discrepancies accounted for ∼93% of the noncompliance issues, while unsystematic quality control issues accounted for the remaining 7%. CONCLUSIONS: The high number of systematic discrepancies between the data collected and the specifications published by the manufacturers suggests there are clear issues related to the specific protocols used for quality control testing. These issues present a significant barrier for hearing aid dispensers when attempting to accurately determine if a hearing aid is functioning appropriately. The significant number of unsystematic discrepancies supports the continued importance of quality control measures of new and repaired hearing aids to ensure that the device is functioning properly before it is dispensed and to avoid future negative implications of fitting a faulty device.

Predictive properties of the video head impulse test: measures of caloric symmetry and self-report dizziness handicap.

OBJECTIVES: The purpose of this investigation was to determine whether a predictable relationship existed between self-reported dizziness handicap and video Head Impulse Test (vHIT) results in a large sample of patients reporting to a dizziness clinic. Secondary objectives included describing the characteristics of the vHIT ipsilesional and contralesional vestibulo-ocular reflex slow-phase velocity in patients with varying levels of canal paresis. Finally, the authors calculated the sensitivity and specificity of the vHIT for detecting horizontal semicircular canal impairment using the caloric test as the "gold standard." DESIGN: Participants were 115 adults presenting to a tertiary medical care center with symptoms of dizziness. Participants were administered a measure of self-report dizziness handicap (i.e., Dizziness Handicap Inventory) and underwent caloric testing and vHIT at the same appointment. RESULTS: Results showed that (1) there were no significant group differences (i.e., vHIT normal versus vHIT abnormal) in the Dizziness Handicap Inventory total score, (2) both ipsilesional and contralateral velocity gain decreased with increases in caloric paresis, and (3) a caloric asymmetry of 39.5% was determined to be the cutoff that maximized discrimination of vHIT outcome. CONCLUSIONS: The level of self-reported dizziness handicap is not predicted by the outcome of the vHIT, which is consistent with the majority of published reports describing the poor relationship between quantitative tests of vestibular function and dizziness handicap. Further, the study findings have demonstrated that vHIT and caloric data are not redundant, and each test provides unique information regarding the functional integrity of the horizontal semicircular canal at different points on the frequency spectrum. The vHIT does offer some advantages over caloric testing, but at the expense of sensitivity. The vHIT can be completed in less time, is not noxious to the patient, and requires very little laboratory space. However, the study data show that a caloric asymmetry of 39.5% is required to optimize discrimination between an abnormal and normal vHIT. It is the authors' contention that the vHIT is a complementary test to the balance function examination and should viewed as such rather than as a replacement for caloric testing.

The predominant forms of vertigo in children and their associated findings on balance function testing.

This article reports vestibular laboratory findings from the most common disorders known to cause dizziness and vertigo in children. Specific information regarding migraine, trauma, benign paroxysmal vertigo of childhood, vestibular neuritis, and otitis media is reviewed, along with indications for balance function testing in children.