Electrophysiological Monitoring of Cochlear Function as a Non-invasive Method to Assess Intracranial Pressure Variations
The “cochlear” aqueduct is a narrow channel connecting the subarachnoid and intralabyrinthine spaces. Through this communication, cerebrospinal fluid (CSF) pressure variations are transmitted to the intralabyrinthine space and modify the impedance of the
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Abstract The “cochlear” aqueduct is a narrow channel connecting the subarachnoid and intralabyrinthine spaces. Through this communication, cerebrospinal fluid (CSF) pressure variations are transmitted to the intralabyrinthine space and modify the impedance of the ear. Distortion-product otoacoustic emissions (DPOAE) are sounds emitted by cochlear sensory cells in response to sonic stimulation. Cochlear microphonic potentials (CMP) express the electrophysiological activity of cochlear sensory cells. At 1 kHz, the phase of DPOAE and CMP varies according to the impedance of the ear and thus to intracranial pressure (ICP) variations. DPOAE and CMP have been shown to strictly follow ICP variations produced during infusion tests performed in the diagnosis of chronic hydrocephalus. DPOAE and CMP recordings appear to be valuable tools for monitoring ICP non-invasively.
Introduction
catheter misplacement – leading to brain lesions – and infection. Catheter misplacement mainly occurs in the case of brain edema. The probability of infection increases when the duration of monitoring increases [5]. Increased ICP has been reported to alter the results of audiological tests [8]. In addition, ICP variations induced by postural changes lead to acoustic impedance modifications and changes in cochlear responses to sound [1]. The cochlear aqueduct is a narrow channel connecting subarachnoid to intralabyrinthine spaces. Through this communication, ICP and intralabyrinthine pressure (ILP) equalize in static conditions [3]. An ICP increase induces an ILP increase, which, by pushing the stapes footplate outward, increases the stiffness of the ossicular chain and cochlea [2, 3]. The phase of two signals – namely, distortion-product otoacoustic emissions (DPOAE) and cochlear microphonic potentials (CMP) – produced by cochlear sensory cells in response to sonic stimulation vary according to the ear’s impedance. DPOAE and CMP are routinely collected in audiological clinical practice. DPOAE and CMP phase shift have been reported to be proportional to ICP variations at frequencies near 1 kHz. The goal of this work is to evaluate a non-invasive method of ICP monitoring relying on the electrophysiological monitoring of cochlear sensory cells.
At present, the reference measurement of ICP is an intraventricular catheter connected to an external transducer. The main complications of invasive ICP monitoring are: ventricular
Materials and Methods
Keywords Distortion product otoacoustic emission (DPOAE) • Cochlear microphonic potentials (CMP) • Non-invasive monitoring of intracranial pressure
L. Sakka () and J. Chazal Department of Neurosurgery and IGCNC (Image-Guided Clinical Neuroscience and Connectomics), Clermont University, UFR Médecine, 63001, Cedex 1, Clermont-Ferrand, France e-mail: [email protected] A. Thalamy, F. Giraudet, and P. Avan Department of Sensory Biophysics, University School of Medicine, 63001, Cedex 1, Clermont-Ferrand, France T. Hassoun Department of Sensory Biophysics, University School of Medicine, 63001, Cede
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