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Hyper Smash

Tuesday, October 21, 2008

Cochlear Microphonics & CNAP recording in Neuromonitoring??

Anatomy of the ear
Organ of CortiAnatomy of Ear (pic fromHearing and Hair Cells John S. Oghalai, M.D.Baylor College of Medicine ) (human ear pic: Muni's_neuromonitoring1)Jorge Bohorquez et al describes a system in their recent publication listed below, according to their study one can test both outer hair cell and inner hair cell electrical activity during surgical procedures. Though this work is evaluated in aniamal study, it is pretty interesting if this can be moved to the OR in our neuromonitoring procedures. I am not sure if this is already practiced in the OR by any neuromonitoring companies. It is a very common procedure to do auditory brain stem evoked potentials in tumor resection or craniotomy procedure that might put the 8th nerve in risk, nevertheless, this CM, CAP and CNAP will be a very important approach in certain cases where injury to both IHC and OHCs can be avoided?. 

Journal of Neural EngineeringNeuromonitoring of cochlea and auditory nerve with multiple extracted parameters during induced hypoxia and nerve manipulation

Jorge Bohórquez et al 2005 J. Neural Eng. 2 1-10   doi: 10.1088/1741-2560/2/2/001

Abstract.  A system capable of comprehensive and detailed monitoring of the cochlea and the auditory nerve during intraoperative surgery was developed. Jorge Bohórquez et al 2005 J. Neural Eng. 2 1-10 E-mail: jbohorquez@miami.edu

The cochlear blood flow (CBF) and the
electrocochleogram (ECochGm) were recorded at the round window (RW) niche using a specially designed otic probe.
The ECochGm was further processed to obtain cochlear microphonics (CM) and compound action potentials (CAP). The amplitude and phase of the CM were used to quantify the activity of outer hair cells (OHC); CAP amplitude and latency were used to describe the auditory nerve and the synaptic activity of the inner hair cells (IHC). In addition, concurrent monitoring with
a second electrophysiological channel was achieved by recording compound nerve action potential (CNAP)
obtained directly from the auditory nerve. Stimulation paradigms, instrumentation and signal processing methods were developed to extract and differentiate the activity of the OHC and the IHC in response to three different frequencies. Narrow band acoustical stimuli elicited CM signals indicating mainly nonlinear operation of the mechano-electrical transduction of the OHCs. Special envelope detectors were developed and applied to the ECochGm to extract the CM fundamental component and its harmonics in real time. The system was extensively validated in experimental animal surgeries by performing nerve compressions and manipulations.

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