Surgery – Diagnostic testing – Structure of body-contacting electrode or electrode inserted...
Reexamination Certificate
2000-08-10
2003-10-28
Cohen, Lee (Department: 3739)
Surgery
Diagnostic testing
Structure of body-contacting electrode or electrode inserted...
C600S478000, C600S504000, C600S559000
Reexamination Certificate
active
06640121
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a microprobe useful for assessing auditory function by enabling clinical and intraoperative measurements of blood flow, particularly cochlear blood flow and neural compound action potentials, particularly of the cochlea and auditory (vestibulocochlear) nerve, also known as cranial nerve VIII.
2. Description of Related Art
Interruption of cochlear blood flow and damage to the auditory nerve have been implicated as the primary causes of sensory hearing loss that may occur during acoustic neuroma tumor removal. Neurosensory monitoring involving electrophysiological signals and continuous blood flow measurements have been proposed to save the hearing of patients undergoing such procedures. The most commonly monitored electrophysiological signals are the auditory brainstem response (ABR) and the compound action potential (CAP) of cranial nerve VIII. Each of these traditionally targeted signal sources have drawbacks, making theses sources less than optimal for mitigating hearing loss.
Auditory brainstem response is the most easily applied procedure and is noninvasive, yet suffers from low signal to noise ratios (SNR). As a result, extensive averaging must be performed to generate usable data.
Measurement of compound action potentials provides better signal to noise ratios than may be obtained with auditory brainstem response. However, compound action potential monitoring requires invasive techniques for optimal recording conditions, and requires at least some averaging to obtain recognizable responses. Although both auditory brainstem response and compound action potentials provide critical information about the transfer of auditory information from the cochlea to the auditory nerve, they are not the best methods for monitoring cochlear ischemia due to delays in changes in the measures after alterations in cochlear blood flow. For example, due to metabolic reserve, changes in electrophysiological activity after an interruption of blood flow in the internal auditory artery take about 20-60 seconds.
Monitoring cochlear blood flow with laser-Doppler measurements has the potential to overcome some of the drawbacks of electrophysiological monitoring. Since it directly monitors blood flow to the cochlea, laser-Doppler does not succumb to metabolic reserve or prolonged signal averaging problems, and has been shown in animal models to follow changes in cochlear blood flow in near real time. The rapid feedback from laser-Doppler can provide surgeons with timely information regarding the effect of surgical maneuvers and vasospasm on cochlear blood flow, with the potential to reverse both cochlear ischemia and adverse hearing outcome.
Electrocochleography (EcochG) is a measure of the most peripheral of the neuroelectric auditory-evoked responses. The compound action potential component of the EcochG response represents the same activity as Wave I of the auditory brainstem response, and is the most useful for intraoperative monitoring. The EcochG has the advantage of being a near-field recording and as such requires fewer averages and less time to obtain a response. Detailed descriptions of stimulus and recording parameters are known in the art. The EcochG can be recorded from the external auditory canal or within the middle ear (transtympanic). Previous investigators have compared the time and number of sweeps required to obtain a response using both techniques. EcochGs recorded within the middle ear showed improved signal to noise ratios resulting in waveforms obtained with fewer sweeps over a shorter period of time. Positioning of the recording electrode at the round window provides the most robust response. The surface or subdermal reference electrode is placed in the midline between the vertex and forehead. Ground electrodes can be located near the recording electrodes at a convenient spot (e.g. ipsilateral shoulder or contralateral forehead).
The stimulus should be a broad band rarefaction click of high intensity (85 to 95 dBnHL) with a rate of 21.1 sec. An impedance of as high as 100 k&OHgr; may be acceptable in a transtympanic (middle ear round window) montage as compared to the need for extremely low impedance of less than 5K&OHgr; required for ear canal electrodes.
Adequate preoperative baseline responses must be obtained against which to judge changes observed during the procedure. Significant changes in compound action potentials indicate, and can be used to differentiate between, cochlear and neural injury. Twenty seconds or more must elapse before changes in the EcochG response can be detected. This delay presumably occurs as a result of metabolic reserves which sustain cochlear function until their depletion from prolonged ischemia causes failure of electrophysiologic activity.
When a parallel laser beam is incident on a medium containing randomly distributed particles, a fraction of the incident power is absorbed by the particles and a fraction is scattered, in theory at all angles. The angular intensity distribution of the scattered laser radiation depends mostly on the wavelength and geometry of the incident beam and on the distribution and size of the scattering particles. When the scattering particles are stationary, the scattering angle for each scattering event, and thus the spatial distribution of intensity, is stationary as well.
When the scattering particles move at any given velocity, the scattering angle varies with the particle velocity and with the angle between the direction of incidence and the direction of movement of the particle. As a result, the scattered light intensity measured in any direction is no longer stationary. The scattered signal contains a broad spectrum of frequencies which is a function, among others, of the particle velocity distribution and of the direction of the particles. A frequency analysis of the scattered intensity signal in a given direction provides information on the velocities of the particles. Because the frequency shifts when the speed or direction of the particles varies, this optical technique for flow measurement is called laser Doppler velocimetry.
Several optical configurations have been used for laser Doppler velocimetry. Laser Doppler velocimetry has been used in biology and medicine mostly as a noninvasive diagnostic tool to characterize blood flow in vitro and in vivo in the eye or percutaneous tissue.
The feasibility of using laser-Doppler velocimetry for in situ in vivo measurement of blood flow was demonstrated by several investigators by using an optical fiber design. In fiber optic laser Doppler velocimeters, the incident light signal is delivered to the measured tissue volume through a single multimode optical fiber (excitation fiber) with a diameter of 50 to 100 microns. The light scattered back by the tissue is collected either with the same optical fiber, or with one or two separate optical fibers (collecting fibers) located next to the excitation fiber. The light transmitted through the collecting fibers is sent to separate photodetectors connected to the signal processing unit. The main advantage of fiber optic laser Doppler velocimetry is that the excitation and collecting fibers can be integrated into a miniature hand held probe for minimally invasive in situ measurements of blood flow. The design of the probe can be adapted for different types of measurement conditions, including endoscopic measurements or measurements at 90 degrees.
The blood supply to the cochlea in humans and animals is provided by an end-artery branch of the internal auditory artery. Abolition of this blood supply results in a complete loss of auditory function in animals. Measurement of cochlear blood flow has been of experimental interest because cochlear ischemia is assumed to be one of the principal causes of certain types of presbycusis and for the many cases of sudden idiopathic sensorineural hearing loss (SNHL). Vascular compromise of the cochlea is commonly thought to cause some forms of sound-induced acoustic trauma. Additionally, some of the hearing
Manns Fabrice
Ozdamar Ozcan
Parel Jean-Marie
Telischi Fred
Cohen Lee
Nixon & Vanderhye P.C.
The University of Miami
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