A clinical comparison of DPOAE fine structure reduction methods.

OBJECTIVE: To evaluate two real-time methods for reducing distortion product otoacoustic emission (DPOAE) fine structure in terms of DPOAE amplitude and fine structure depth. DESIGN: A prospective, repeated-measures design was used to assess DPOAE characteristics in response to a conventional stimulation method (Conv.), as well as for methods implementing either a generic suppressor tone (Supp.) or frequency modulation of the f2 primary tone (FM). STUDY SAMPLE: Eighty-three young adults (58 females) between the ages of 20 and 34 years with normal hearing completed testing for this study. RESULTS: Use of the Conv. and FM methods resulted in consistently higher DPOAE levels relative to the Supp. method, with average advantages of 6 and 5 dB, respectively. For all methods, increased fine structure depth was observed for stimulation with lower level (25-45 dB SPL) and lower frequency (1000-3000 Hz) primary tones. Finally, use of the Supp. and FM methods resulted in significantly decreased fine structure depth relative to the Conv. method. CONCLUSION: Through frequency modulation of the f2 primary tone, it was possible to reduce the depth of fine structure across a clinically meaningful range of stimulation levels and frequencies without concomitant reduction in DPOAE amplitude.

Subclinical conductive hearing loss significantly reduces otoacoustic emission amplitude: Implications for test performance.

OBJECTIVES: Distortion product otoacoustic emissions (DPOAEs) are a time-efficient, non-invasive means of assessing the integrity of active inner ear mechanics. Unfortunately, the presence of even relatively minor conductive hearing loss (CHL) has been suggested to reduce the clinical utility of DPOAEs significantly. The primary aims of this study were to systematically evaluate the impact of CHL on DPOAE amplitude and to determine if ear-specific primary tone level manipulations can be used to mitigate CHL impact and recover DPOAE measurability. METHODS: For 30 young adults (57 ears) with normal hearing, DPOAEs were obtained for f2 = 1-6 kHz. Observed DPOAE amplitudes were used to generate ear- and frequency-specific models with the primary tone levels, L1 and L2, as inputs and predicted DPOAE amplitude, LDP, as output. These models were then used to simulate the effect of CHL (0-15 dB), as well as L1 manipulations (0-15 dB), on DPOAE measurability. RESULTS: Mean LDP for every CHL condition was significantly different from that for all other conditions (p = <.001), with a mean LDP attenuation of 8.7 dB for every 5 dB increase in CHL. Mean DPOAE measurability in response to a standard clinical stimulation paradigm of L1/L2 = 65/55 (dB SPL) was determined to be 99%, 84%, 37%, and 9% in the presence of 0, 5, 10, and 15 dB CHL, respectively. In the presence of 10 dB CHL, altering L1 resulted in an approximately 25% increase in DPOAE responses. CONCLUSION: Subclinical CHL loss is sufficient to significantly impair DPOAE measurability in a meaningful proportion of otherwise healthy ears. However, through strategic alteration of primary tone levels, the clinician can mitigate CHL impact and at least partially recover DPOAE measurability.

Feedback reduction system influence on additional gain before feedback and maximum stable gain in open-fitted hearing aids.

OBJECTIVE: The primary purpose of this study was to update existing data on additional gain before feedback and maximum stable gain in commercially available, open-fit hearing instruments. A secondary purpose was to evaluate ratings of sound quality with feedback reduction systems active. DESIGN: Additional gain before feedback, maximum stable gain and subjective sound quality ratings were obtained for six commercially available hearing instruments utilising modern feedback reduction systems. STUDY SAMPLE: Twenty adults (22-46 years) with normal hearing participated in gain measurement testing. Thirty adults (22-39 years) with normal hearing provided ratings of sound quality. RESULTS: Mean additional gain before feedback for 2000-4000 Hz ranged from 5 to 16 dB across manufacturers. Mean maximum stable gain in the same frequency region ranged from 25 to 35 dB across manufacturers. However, meaningful performance differences between participants within each given manufacturer were also identified. Sound quality ratings were not related to the type of feedback reduction algorithm. CONCLUSIONS: AGBF and MSG continue to vary significantly both across manufacturers as well as individual ears within a given manufacturer. User satisfaction and performance with hearing aids might be improved by identifying the feedback reduction system optimal for the individual patient.

Avoiding disconnection: An evaluation of telephone options for cochlear implant users.

OBJECTIVE: The primary aim of this study was to evaluate the effect of coupling method on telephone-based speech recognition and perceived listening difficulty in noise for cochlear implant (CI) users. A secondary aim was to evaluate potential impacts of additional processing modifications within coupling conditions, such as activating noise reducing algorithms or muting environmental microphones. DESIGN: Hochmair-Schulz-Moser sentences were bandpass-filtered (300-3400 Hz) and presented unilaterally either via telephone handset or advanced wireless streaming device in a background of cafeteria babble (signal-to-noise ratio =15 dB). Sentence recognition was scored at the word level and perceived listening difficulty was assessed via visual-analogue scale for each of five test conditions. STUDY SAMPLE: Twenty native German-speaking CI users participated. RESULTS: Repeated measures analysis of variance revealed coupling via advanced streaming significantly improved sentence recognition and reduced listening difficulty, when compared to either telecoil or acoustic coupling configurations. In addition, program modifications further increased benefit within a coupling condition. CI users who exhibited the most difficulty during basic acoustic coupling were most likely to benefit from advanced wireless streaming. CONCLUSION: CI users have several options for improving speech recognition and decreasing listening difficulty over the telephone when listening in noisy environments.

Paired associative stimulation of the auditory system: a proof-of-principle study.

BACKGROUND: Paired associative stimulation (PAS) consisting of repeated application of transcranial magnetic stimulation (TMS) pulses and contingent exteroceptive stimuli has been shown to induce neuroplastic effects in the motor and somatosensory system. The objective was to investigate whether the auditory system can be modulated by PAS. METHODS: Acoustic stimuli (4 kHz) were paired with TMS of the auditory cortex with intervals of either 45 ms (PAS(45 ms)) or 10 ms (PAS(10 ms)). Two-hundred paired stimuli were applied at 0.1 Hz and effects were compared with low frequency repetitive TMS (rTMS) at 0.1 Hz (200 stimuli) and 1 Hz (1000 stimuli) in eleven healthy students. Auditory cortex excitability was measured before and after the interventions by long latency auditory evoked potentials (AEPs) for the tone (4 kHz) used in the pairing, and a control tone (1 kHz) in a within subjects design. RESULTS: Amplitudes of the N1-P2 complex were reduced for the 4 kHz tone after both PAS(45 ms) and PAS(10 ms), but not after the 0.1 Hz and 1 Hz rTMS protocols with more pronounced effects for PAS(45 ms). Similar, but less pronounced effects were observed for the 1 kHz control tone. CONCLUSION: These findings indicate that paired associative stimulation may induce tonotopically specific and also tone unspecific human auditory cortex plasticity.

Clinical evaluation of cochlear implant sound coding taking into account conjectural masking functions, MP3000™.

Efficacy of the SPEAK and ACE coding strategies was compared with that of a new strategy, MP3000™, by 37 European implant centers including 221 subjects. The SPEAK and ACE strategies are based on selection of 8-10 spectral components with the highest levels, while MP3000 is based on the selection of only 4-6 components, with the highest levels relative to an estimate of the spread of masking. The pulse rate per component was fixed. No significant difference was found for the speech scores and for coding preference between the SPEAK/ACE and MP3000 strategies. Battery life was 24% longer for the MP3000 strategy. With MP3000 the best results were found for a selection of six components. In addition, the best results were found for a masking function with a low-frequency slope of 50 dB/Bark and a high-frequency slope of 37 dB/Bark (50/37) as compared to the other combinations examined of 40/30 and 20/15 dB/Bark. The best results found for the steepest slopes do not seem to agree with current estimates of the spread of masking in electrical stimulation. Future research might reveal if performance with respect to SPEAK/ACE can be enhanced by increasing the number of channels in MP3000 beyond 4-6 and it should shed more light on the optimum steepness of the slopes of the masking functions applied in MP3000.

Controversy: Does repetitive transcranial magnetic stimulation/ transcranial direct current stimulation show efficacy in treating tinnitus patients?

BACKGROUND: Tinnitus affects 10% of the population, its pathophysiology remains incompletely understood, and treatment is elusive. Functional imaging has demonstrated a relationship between the intensity of tinnitus and the degree of reorganization in the auditory cortex. Experimental studies have further shown that tinnitus is associated with synchronized hyperactivity in the auditory cortex. Therefore, targeted modulation of auditory cortex has been proposed as a new therapeutic approach for chronic tinnitus. METHODS: Repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are noninvasive methods that can modulate cortical activity. These techniques have been applied in different ways in patients with chronic tinnitus. Single sessions of high-frequency rTMS over the temporal cortex have been successful in reducing the intensity of tinnitus during the time of stimulation and could be predictive for treatment outcome of chronic epidural stimulation using implanted electrodes. RESULTS: Another approach that uses rTMS as a treatment for tinnitus is application of low-frequency rTMS in repeated sessions, to induce a lasting change of neuronal activity in the auditory cortex beyond the duration of stimulation. Beneficial effects of this treatment have been consistently demonstrated in several small controlled studies. However, results are characterized by high interindividual variability and only a moderate decrease of the tinnitus. The role of patient-related (for example, hearing loss, tinnitus duration, age) and stimulation-related (for example, stimulation site, stimulation protocols) factors still remains to be elucidated. CONCLUSIONS: Even in this early stage of investigation, there is a convincing body of evidence that rTMS represents a promising tool for pathophysiological assessment and therapeutic management of tinnitus. Further development of this technique will depend on a more detailed understanding of the neurobiological effects mediating the benefit of TMS on tinnitus perception. Moreover clinical studies with larger sample sizes and longer follow-up periods are needed.

Effects of modified ultrafiltration on coagulation as measured by the thromboelastograph.

Hemodilution during cardiopulmonary bypass (CPB) continues to be a cause of morbidity associated with coagulation dysfunction, bleeding, and allogeneic blood transfusion. Clot formation and strength have been shown to impact bleeding and transfusions. Strategies to reduce hemodilution may be negated based on the course of the cardiac procedure itself. Modified ultrafiltration (MUF) is commonly used in pediatric cardiac surgery; however, it is not well accepted in adult surgery. This study aimed to evaluate clot formation and strength, bleeding, and transfusions in adult subjects undergoing MUF. Nineteen subjects having primary coronary artery bypass, aortic, or mitral valve surgeries were recruited and randomized to having MUF (n = 10) or no-MUF (n = 9) performed after the termination of CPB. Five time points for data collection were designated: T1, baseline/induction; T2, termination CPB; T3, post-MUF; T4, post-protamine; T5, 24 hours postoperative. Subjects randomized to MUF had 1505 +/- 15.8 mL of effluent removed, and no-MUF subjects had the CPB remnants processed with a cell salvage device. There was no statistical difference seen in 24-hour chest tube output, thromboelastograph values, or allogeneic transfusions at any time point between MUF and no-MUF subjects. There was a significant difference between MUF and no-MUF in the number of autologous cell salvage units processed (1.3 +/- .48 vs. 2.9 +/- .78, p = .0013) and end of procedure net fluid balance (+2003 +/- 1211 vs. +4194 +/- 1276 mL, p = .001), respectively. Estimated plasma loss from the cell salvage device was 477.6 mL greater in the no-MUF group. In primary adult cardiac procedures, MUF did not change coagulation values as measured by thromboelastography, number of allogeneic unit transfusions, or chest tube output at 24 hours postoperatively. There was a significant difference in autologous cell salvage units processed and end of procedure net fluid balance that benefited MUF subjects.