Channel interactions with high-rate biphasic electrical stimulation in cochlear implant subjects.

Channel interactions were assessed using high-rate stimulation in cochlear implant subjects using the Ineraid electrode array. Stimulation currents were applied on one intracochlear electrode and their effects on psychophysical detection thresholds on an adjacent electrode were measured. Stimuli were trains of brief, biphasic, 50-micros/phase pulses presented at a rate of 2000 pulses per second per channel. In experiment I, we studied how the detection of a probe signal was influenced by a sub-threshold perturbation signal presented either simultaneously or non-simultaneously (with no overlap) on an adjacent electrode. Results showed that simultaneous activation led to strong channel interactions, producing threshold changes consistent with instantaneous electric field summation. Non-simultaneous activation revealed much weaker interactions, producing threshold changes of opposite sign. In experiment II, we studied how the temporal delay between perturbation and probe pulses, as well as how the level of the perturbation signal influenced non-simultaneous channel interactions. First, threshold changes when reversing the polarity of the perturbation did progressively vanish when increasing the delay between pulses. This suggested that non-overlapping stimulation of adjacent electrodes produced channel interactions that were in part due to residual polarization of the nerve membrane. Second, increasing the perturbation to supra-threshold levels produced threshold elevations that were independent of the interpulse interval. This suggested channel interactions due to neural masking. These results provide insights into the different concurrently active mechanisms of channel interactions in cochlear implant systems using this type of stimuli.

Effects of the acoustical dynamic range on speech recognition with cochlear implants.

The amplitude compression function in a speech processor for cochlear implants maps the wide acoustical dynamic range of sounds into the smaller electrical dynamic range available on the implanted electrodes. In this study, we examined the effects of systematic variations of the acoustical dynamic range of the compression function on speech recognition with cochlear implants. Statistical measures of the amplitude distribution of speech sounds were made in each channel of a research speech processor providing more than 50 dB of input signal-to-noise ratio. Several systematic variations of the dynamic range of the compression function were implemented on this basis, and speech recognition was determined using vowel and consonant identification tests in three experienced cochlear implant users. Results demonstrated that the acoustical dynamic range of the compression function does have a significant effect on speech recognition with cochlear implants. They suggest that a dynamic range of about 45 dB is necessary for optimal speech recognition.

Frey syndrome treatment with botulinum toxin.

The goal of this work is to present our results of the intradermic infiltration with botulinum toxin in patients with Frey syndrome. Sixteen hemifaces in 15 patients were studied. Gustatory stimulation was evoked by sucking on a slice of lemon while measurements were done on both hemifaces, with the normal side being used as a control. Skin temperature and color (erythema) were measured with a digital surface thermometer and a skin chromameter, respectively. Sweat quantity and surface were measured by using the previously described blotting paper and iodine-sublimated paper histogram methods, respectively. Testing was repeated 2 weeks after skin infiltration with botulinum toxin (dilution of 50 U/mL). The interinjection distances were 1 cm, and 0.1 mL (5 U) was infiltrated at each injection site. Frey syndrome complaints disappeared in all patients. Small residual amounts of sweat were measurable. The difference in sweat quantity before and after botulinum toxin infiltration was significant in every patient (P < 0.001). Skin temperature and color measurement gave inconclusive results. In conclusion, Frey syndrome treatment with botulinum toxin is an efficient and well-tolerated technique. Further work should address the optimal injection parameters.

New objective and quantitative tests for gustatory sweating.

Two newly developed tests for gustatory sweating, providing both quantitative and topographic information, are presented. In both tests a paper stencil shaped to fit the complex anatomy of the parotid region is used. The blotting paper technique uses the difference in weight before and after gustatory stimulation to measure the amount of sweating. The iodine-sublimated paper histogram (ISPH) uses iodine sublimated office paper that changes colour when wet. The paper stencil is than digitized and a histogram algorithm applied to measure the area of sweating. A calibration of these tests with known and appropriate quantities of saline is presented.

Prevention of Frey syndrome during parotidectomy.

OBJECTIVE: To evaluate the incidence of Frey syndrome (auriculotemporal nerve syndrome) after parotidectomy with and without placement of a subcutaneous implant and to examine the relationship between different implants and postoperative wound complications (hematoma, seroma, salivary fistula). DESIGN: A prospective nonrandomized controlled trial. SETTING: A primary care and referral university hospital center. PATIENTS: All patients scheduled for parotidectomy from April 1994 through August 1998 were eligible. Seventy patients were enrolled (2 refused). All 70 patients were evaluated for wound complications. Sixty patients with a follow-up of more than 1 year were evaluated for Frey syndrome. INTERVENTION: The choice of implant was left to the individual surgeon: 24 patients had no implant; 7, lyophilized dura implant; 7, polyglactin 910-polydioxanone (Ethisorb) implant; and 32, expanded polytetrafluoroethylene (e-PTFE) implant. OUTCOME MEASURES: The incidence of Frey syndrome was evaluated (1) subjectively by history (clinical Frey syndrome) and (2) objectively by using 2 newly developed tests. Both hemifaces were tested, with the normal side being used as a control. RESULTS: Clinical Frey syndrome was present in 12 patients: 11 without implants (11/24 [53%]) and 1 with an implant (1/46 [2%]) (P<.001). Objective tests were positive in 24 patients: 16 (76%) of 21 without implants and 8 (20%) of 39 with implants (P<.001). In the implanted patients, the objective tests were positive in 71% (5/7) of those with lyophilized dura, 14% (1/7) of those with Ethisorb, and 8% (2/29) of those with e-PTFE implants (P<.001). Wound complications included hematoma in 5 patients (7%), seroma in 4 patients (6%), and salivary fistula in 15 (21%). Salivary fistula occurred more frequently with Ethisorb (57%) and e-PTFE (25%) implants (P = .04). CONCLUSIONS: In patients without an implant, the incidence of Frey syndrome is 50% for subjective and 80% for objective evaluation. In patients with an implant, these incidences are 3% and 10%, respectively. Some implants are associated with a higher incidence of salivary fistula.

Within-patient longitudinal speech reception measures with continuous interleaved sampling processors for ineraid implanted subjects.

OBJECTIVE: To assess within-subject changes in speech reception over time in a group of Ineraid subjects fitted with continuous interleaved sampling (CIS) wearable processors fabricated in Geneva. To compare asymptotic performance between CIS and Ineraid processors for the same subjects. DESIGN: Twelve patients, all users of the 4-channel Ineraid cochlear implant system for several years and with no previous experience of CIS processors in daily life, were equipped with Geneva Wearable Processors programmed to implement a high-rate CIS sound processing strategy using four to six channels. Their speech reception performance with CIS processors was monitored over a period of 1 yr with consonant and vowel identification tests. For comparison, speech reception performance also was measured with Ineraid processors before switching to CIS and after 6 mo of non-use of Ineraid processors. RESULTS: At fitting, CIS processors produced significantly better consonant identification but no better vowel identification. Subsequently, consonant and vowel scores with CIS processors improved progressively to asymptote after 6 mo of daily use. At 6 mo and beyond, performance with CIS processors was significantly superior to that obtained with Ineraid processors on both consonant and vowel identification tests. Control tests made with Ineraid processors after 6 mo of non-use of the device yielded results that were indistinguishable from those obtained before the study. CONCLUSIONS: The full potential of the CIS strategy is not revealed at fitting. Accumulation of daily experience provides significant improvements, asymptotic performance being reached after about 4 to 6 mo of use. All Ineraid users might greatly benefit from CIS processors.