Neuromonitoring of cochlea and auditory nerve with multiple extracted parameters during induced hypoxia and nerve manipulation

Non-invasive intraoperative monitoring of cochlear function by cochlear microphonics during cerebellopontine-angle surgery

In vestibular-schwannoma (VS) surgery, hearing-preservation rate remains low. Besides damage to the cochlear nerve, intraoperative cochlear ischemia is a potential cause of hearing loss. Here, we used non-invasive cochlear microphonic (CM) recordings to detect the cochlear vascular events of VS surgery. Continuous intraoperative CM monitoring, in response to 80-95 dB SPL, 1-kHz tone-bursts, was performed in two samples of patients undergoing retrosigmoid cerebellopontine-angle surgery: one for VS (n = 31) and one for vestibular neurectomy or vasculo-neural conflict causing intractable trigeminal neuralgia, harmless to hearing (n = 19, control group). Preoperative and postoperative hearings were compared as a function of intraoperative CM changes and their chronology. Monitoring was possible throughout except for a few tens of seconds when drilling or suction noises occurred. Four patterns of CM time course were identified, eventless, fluctuating, abrupt or progressive decrease. Only the VS group displayed the last two patterns, mainly during internal-auditory-canal drilling and the ensuing tumor dissection, always with postoperative loss of hearing as an end result. Conversely, eventless and fluctuating CM patterns could be associated with postoperative hearing loss when the cochlear nerve had been reportedly damaged, an event that CM is not meant to detect. Cochlear ischemia is a frequent event in VS surgery that leads to deafness. The findings that CM decrease raised no false alarm, and that CM fluctuations, insignificant in control cases, were easily spotted, suggest that CM intraoperative monitoring is a sensitive tool that could profitably guide VS surgery.

Cochlear blood flow and speech perception ability in cochlear implant users

OBJECTIVE

The effect of cochlear blood flow (CBF) on speech perception ability in cochlear implant (CI) users has not been reported. We investigated various factors influencing speech perception including CBF in CI users.

PATIENTS

Eighty-two patients who received CI surgery at an academic hospital.

METHODS

CBF was measured during CI surgery using laser Doppler flowmetry. The speech perception level was measured after a sufficient interval after CI surgery. Multivariate analysis was used to evaluate the influences of age, duration of deafness, sex, cause of deafness, and CBF on the speech perception level.

RESULTS

CBF decreased significantly with age but was not related to the speech perception level. In patients with congenital hearing loss, the speech perception level was significantly worse in children who received a CI at 3 years of age than in those who received a CI at 2 years of age or younger. Duration of deafness before CI surgery had deteriorative effects on the speech perception level.

CONCLUSION

CBF may be associated with progression of hearing loss. However, measuring CBF during CI surgery is not useful for predicting postoperative speech perception.

A comparison of three brain-computer interfaces based on event-related desynchronization, steady state visual evoked potentials, or a hybrid approach using both signals

Brain-computer interface (BCI) systems rely on the direct measurement of brain signals, such as event-related desynchronization (ERD), steady state visual evoked potentials (SSVEPs), P300s, or slow cortical potentials. Unfortunately, none of these BCI approaches work for all users. This study compares two conventional BCI approaches (ERD and SSVEP) within subjects, and also evaluates a novel hybrid BCI based on a combination of these signals. We recorded EEG data from 12 subjects across three conditions. In the first condition, subjects imagined moving both hands or both feet (ERD). In the second condition, subjects focused on one of the two oscillating visual stimuli (SSVEP). In the third condition, subjects simultaneously performed both tasks. We used logarithmic band power features at sites and frequencies consistent with ERD and SSVEP activity, and subjects received real-time feedback based on their performance. Subjects also completed brief questionnaires. All subjects could simultaneously perform the movement and visual task in the hybrid condition even though most subjects had little or no training. All subjects showed both SSVEP and ERD activity during the hybrid task, consistent with the activity in both single tasks. Subjects generally considered the hybrid condition moderately more difficult, but all of them were able to complete the hybrid task. Results support the hypothesis that subjects who do not have strong ERD activity might be more effective with an SSVEP BCI, and suggest that SSVEP BCIs work for more subjects. A simultaneous hybrid BCI is feasible, although the current hybrid approach, which involves combining ERD and SSVEP in a two-choice task to improve accuracy, is not significantly better than a comparable SSVEP BCI. Switching to an SSVEP BCI could increase reliability in subjects who have trouble producing the EEG activity necessary to use an ERD BCI. Subjects who are proficient in both BCI approaches might be able to combine these approaches in different ways and for different goals.

Combined motor imagery and SSVEP based BCI control of a 2 DoF artificial upper limb

A Brain-Computer Interface (BCI) is a device that transforms brain signals, which are intentionally modulated by a user, into control commands. BCIs based on motor imagery (MI) and steady-state visual evoked potentials (SSVEP) can partially restore motor control in spinal cord injured patients. To determine whether these BCIs can be combined for grasp and elbow function control independently, we investigated a control method where the beta rebound after brisk feet MI is used to control the grasp function, and a two-class SSVEP-BCI the elbow function of a 2 degrees-of-freedom artificial upper limb. Subjective preferences for the BCI control were assessed with a questionnaire. The results of the initial evaluation of the system suggests that this is feasible.

Asynchronous steady-state visual evoked potential based BCI control of a 2-DoF artificial upper limb

A brain-computer interface (BCI) provides a direct connection between the human brain and a computer. One type of BCI can be realized using steady-state visual evoked potentials (SSVEPs), resulting from repetitive stimulation. The aim of this study was the realization of an asynchronous SSVEP-BCI, based on canonical correlation analysis, suitable for the control of a 2-degrees of freedom (DoF) hand and elbow neuroprosthesis. To determine whether this BCI is suitable for the control of 2-DoF neuroprosthetic devices, online experiments with a virtual and a robotic limb feedback were conducted with eight healthy subjects and one tetraplegic patient. All participants were able to control the artificial limbs with the BCI. In the online experiments, the positive predictive value (PPV) varied between 69% and 83% and the false negative rate (FNR) varied between 1% and 17%. The spinal cord injured patient achieved PPV and FNR values within one standard deviation of the mean for all healthy subjects.

Preventing hearing damage using topical dexamethasone during reversible cochlear ischemia: an animal model

HYPOTHESIS

Local application of dexamethasone to the round window (RW) niche prevents cochlear damage caused by local reversible ischemia.

BACKGROUND

Cochlear ischemia induced by internal auditory artery (IAA) compression/stretching is thought to cause postoperative sensory hearing loss after attempted hearing preservation removal of acoustic neuroma tumors. Dexamethasone administered to the RW niche traveling through the membrane to the cochlear fluids may prevent ischemic damage.

MATERIALS AND METHODS

Ten young albino rabbits were used for this study. Ischemic episodes were induced by compressing the IAA. Laser Doppler cochlear blood flow was measured using a probe positioned at the RW niche. Transtympanic electrocochleography was measured at 4, 8, and 12 kHz. In 5 test ears, dexamethasone was administered topically at the RW for approximately 50 minutes before the IAA compressions, whereas in 5 control ears, saline was applied in the same way. Each ear underwent one 10-minute IAA compression with a 60-minute postischemic period of transtympanic electrocochleography monitoring.

RESULTS

In both control- and dexamethasone-treated ears, ischemic episodes measured by Laser Doppler cochlear blood flow were comparable. Fifty minutes after IAA decompression, in dexamethasone-pretreated ears, cochlear microphonic and compound action potential amplitudes at all test frequencies were 10 to 15% less reduced than those in control ears. Compound action potential latencies in dexamethasone-pretreated ears resulted in shorter latency delay than in control ears.

CONCLUSION

The RW seems to be an efficacious route for the administration of dexamethasone into the inner ear. Dexamethasone showed a protective effect on cochlear function after local ischemia. Transtympanic electrocochleography was found to be a sufficient and effective tool in monitoring hearing.

Audiometric threshold screening method using envelope detection filters of intensity ramping click auditory steady-state responses

The Auditory Steady-state Responses (ASSR) elicited by click stimuli can be utilized for hearing screening as is traditionally done with click-evoked Auditory Brainstem Responses (ABR). In a typical ASSR or ABR hearing screening, several recordings at different intensities are required to find the response threshold. In this study the use of binaural click stimulus with time ramping intensity produces dual-ear evoked potentials in only one recording session, decreasing significantly the recording time. To achieve this performance a one second sweep consisting of repetitive click stimuli, with logarithmically ramping up intensity, is presented to one or both ears simultaneously. Unique repetition frequencies for each ear are used in order to differentiate the responses coming from each ear. The stimuli sweep is repeated and the EEG data corresponding to each sweep is averaged until a pre-specified residual noise level is achieved. Hilbert-transform-based envelope detection filters in the time domain are used to estimate the signal and noise energy around the main stimulation rate. Because the stimulus time-intensity functions are known, thresholds can be estimated from the response onset time position by estimating the significance of the signal to noise ratio. Preliminary results indicate a strong agreement of the obtained thresholds with behavioral thresholds.

Intraoperative monitoring of hearing during cerebellopontine angle tumor surgery using transtympanic electrocochleography

OBJECTIVE

To investigate the use of transtympanic electrocochleography (TT-ECochG) analyzed on-line by a detector strategy software that made possible automatic extraction of TT-ECochG components intraoperatively in real-time domain.

PATIENTS

Fifteen patients with cerebellopontine angle tumor among 50 patients were included in this study.

INTERVENTION

All subjects were operated on via middle fossa or retrosigmoid approach. Pure-tone average (PTA) was measured at 0.5, 1.0, and 2.0 kHz, and calculations were performed before and after surgery. Auditory function was monitored intraoperatively via TT-ECochG, and analyzed data were displayed on-line.

MAIN OUTCOME MEASURES

TT-ECochG changes in morphology were described. Postoperative PTA elevation level correlated with TT-ECochG morphology changes occurring intraoperatively.

RESULTS

Analyzed on-line, TT-ECochG data were displayed as first negative peak of compound action potential amplitude and latency in time domain every 3 to 5 seconds. A good correlation between postoperative PTA elevation and TT-ECochG morphology changes was showed (Spearman rank test, R = +0.93; t(N-2) = 9.00; p < 0.0001).

CONCLUSION

TT-EcochG seemed to effectively mirror even minimal changes in auditory function during intraoperative monitoring in real-time domain. Developed strategy of on-line analysis makes the intraoperative hearing status assessment faster and easier.

Expression of adhesion molecular proteins in the cochlear lateral wall of normal and PARP-1 mutant mice

Sound can damage peripheral cochlear function through a number of mechanisms, and emerging evidence suggests that inflammation may be one of them. Using immunohistochemistry and poly (ADP-ribose) polymerase-1 (PARP-1) mutant mice, we tested whether PARP-1 contributes to loud-sound induced cochlear lateral wall damage by triggering inflammatory effects, including upregulating intercellular adhesion molecule-1 (ICAM-1), P-selectin and platelet-endothelial cell-adhesion molecule-1 (PECAM-1). In control conditions, we found that there was no detectable poly-ADP-ribose (PAR) in the marginal cells and microvessels. ICAM-1 was expressed only at low levels in the vessels of the stria vascularis and the spiral ligament. P-selectin and PECAM-1 were barely detected and only in the vessels of the spiral ligament. Following loud-sound exposure, PAR was detected in numbers of marginal cells and some vessels of the spiral ligament. Also, an elevated expression of ICAM-1 was demonstrated in some vessels of the stria vascularis and spiral ligament. Increased expression of P-selectin and PECAM-1 were mainly located in the vessels of the spiral ligament, while increased populations of non-migrated and migrated leukocytes were observed in the area of the spiral ligament. However, neither increased expression of adhesion proteins nor increased population of leukocytes, were observed in the PARP-1 knockout mouse. We thus conclude that loud-sound stress activates the expression of adhesion molecular proteins in the lateral wall and that PARP-1 modulates inflammation-linked protein expression and leukocyte migration.