Biomedical subjects

M P Widick

Publications and source records attributed to M P Widick.

3 recordsLinked to original sources

PubMed1998

Distortion-product otoacoustic emission monitoring of cochlear blood flow.

Distortion-product otoacoustic emissions (DPOAEs) have been shown to be ideally sensitive to interruptions of the cochlear blood flow. However, a 15- to 30-second latency typically occurs between cessation of circulation and measurable DPOAE level changes. DPOAEs can also be characterized by phase measures. The aim of the present study was to determine in 10 rabbits the effects on DPOAE phase of repetitively compressing the internal auditory artery. In contrast to the delays measured by DPOAE level, phase changes were detected 1 to 5 seconds after internal auditory artery compression. These data suggest that the essentially "real time" monitoring of cochlear function with DPOAE phase can be used to ensure hearing preservation during surgery involving the porus acousticus and skull base.

Acoustic Stimulation↗

PubMed1995

Monitoring cochlear function intraoperatively using distortion product otoacoustic emissions.

Distortion product otoacoustic emissions (DPOAEs) elicited by a bitonal stimulus complex are low-level sounds that are generated within the cochlea, and are easily measured by a miniature microphone system placed in the external auditory canal. Under conditions of rapid measurement, DPOAEs have been shown in an animal model to be exquisitely sensitive to interruption of the blood supply to the inner ear. Currently, there is no real-time procedure available for monitoring hearing function intraoperatively during neurotologic surgery. The goal of the present study was to determine the utility of DPOAEs in monitoring cochlear status intraoperatively, particularly during procedures commonly used to remove acoustic neuromas. Distortion product otoacoustic emissions were measured pre- and intraoperatively in 11 patients, who were under general anesthesia for a variety of otolaryngologic procedures, including acoustic neuroma resection. High frequency emissions (i.e., > or = 4 kHz) were less affected by the elevated levels of acoustic noise present in the operating-room environment, thus permitting emitted responses to be updated as quickly as every 2 seconds. However, a number of technical problems were encountered and addressed during development of the emission monitoring technique. Despite these difficulties, overall, DPOAEs appear to be a promising adjunct to the intraoperative monitoring of auditory function.

Acoustic Impedance Tests↗

PubMed1994

Early effects of cerebellopontine angle compression on rabbit distortion-product otoacoustic emissions: a model for monitoring cochlear function during acoustic neuroma surgery.

A rabbit model was developed to simulate the effects of ischemia that may occur during surgical removal of tumors involving the cerebellopontine angle or internal auditory canal. Specifically, the internal auditory artery was visualized through a posterior craniotomy and mechanically compressed for repetitive 1-minute intervals with a micromanipulator-controlled glass pipet terminating in a smooth bead. The 2f1-f2 distortion-product otoacoustic emissions were used to monitor the susceptibility of cochlear function to compressive effects. Distortion-product otoacoustic emissions were measured during discrete preblock, block, and postblock periods to determine the time course of distortion-product otoacoustic emission reduction and its return to baseline levels after rapid obstruction and resumption, respectively, of the cochlear vascular supply. Comparisons during these times indicated that preblock distortion-product otoacoustic emission levels were very stable, often varying by less than 1 dB. Additionally, distortion-product otoacoustic emissions were very sensitive to brief vascular occlusions in that, within approximately 25 seconds of blockage onset, emission levels at all frequencies decreased at rates of about -1.5 dB/second. On alleviation of the occlusion, distortion-product otoacoustic emissions rapidly and completely returned to preblock levels with a delay of about 4 seconds and recovery slopes of about 10.5 dB/second. A notable finding in some animals was that early and reproducible variations in distortion-product otoacoustic emission levels occurred within 5 to 8 seconds of internal auditory artery compression. When present, these transitory changes in distortion-product otoacoustic emission levels acted as early warning signs for vascular compromise of cochlear function.

Animals↗