No adequate treatment exists for individuals who remain disabled by bilateral loss of vestibular (inner ear inertial) sensation despite rehabilitation. We have restored vestibular reflexes using lab-built multichannel vestibular prostheses (MVPs) in animals, but translation to clinical practice may be best accomplished by modification of a commercially available cochlear implant (CI).
We developed software and circuitry to sense head rotation and drive a CI's implanted stimulator (IS) to deliver up to 1Kpulses/s via 9 electrodes implanted near vestibular nerve branches. Studies in two rhesus monkeys using the modified CI (MCI) revealed in vivo performance similar to our existing dedicated MVPs.
Like commercially available CIs, our design uses an external head-worn unit (HWU) that is magnetically coupled across the scalp to the IS. The HWU must remain securely fixed to the skull to faithfully sense head motion with gyroscopes and maintain continuous stimulation. We measured normal and shear force thresholds at which HWU-IS decoupling occurred as a function of scalp thickness and calculated pressure exerted on the scalp. The HWU remained attached across the human scalp thicknesses from 3mm to 7.8mm for forces experienced during routine daily activities, with magnets exerting pressure on the scalp that remains below capillary perfusion pressure.
Impaired neural conductivity shown by delayed latency and reduced amplitude of characteristic peaks in somatosensory evoked potentials (SSEPs), has been used to monitor hypoxic-ischemic brain injury after Cardiac Arrest (CA). However, rather than characteristic peak deferral and suppression, the time jitter of the peak in SSEP related with time-variant neurological abnormalities is diminished by the commonly used ensemble average method. This paper utilizes the second order blind identification (SOBI) technique to extract characteristic peak information from one trial of SSEPs. Sixteen male Wistar rats were subjected to 7 or 9 minutes of asphyxial CA (n=8 per group). The SSEPs from median nerve stimulation were recorded for 4 hours after CA and then for 15 minute periods at 24, 48 and 72 h. Neurological outcomes were evaluated by Neurologic Deficit Score (NDS) at 72h post-CA. The SSEP signal was analyzed offline with SOBI processing in Matlab. The N10 feature of SSEP was compared between good (NDS≥50) and bad (NDS<50) outcomes. After processed by SOBI, the N10 detection rate was significantly increased (p<0.001) from 90 min post-CA. Statistical difference of the latency variance of the N10 between good and bad outcome groups existed at 24, 48 and 72 h post-CA (p<=0.001). Our study is the first application using SOBI detecting variance in neural signals like SSEP. N10 latency variance, related with neurophysiological dysfunction, increased after hypoxic-ischemic injury. The SOBI technique is an efficient method in the identification of peak detection and offers a favorable alternative to reveal the neural transmission variation.
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