Publication Date

2010

Document Type

Honors Thesis

Department

Engineering

Keywords

Intracranial pressure-Measurement, Otoacoustic emissions, Audiometry, DPOAE, Posture

Abstract

Intracranial pressure (ICP) monitoring is essential to the treatment of several severe brain conditions, such as hydrocephalus and brain injury. Auditory measurements have been shown to have an increased potential as a non-invasive alternative to current invasive ICP monitoring devices. Posture-induced ICP changes were previously shown to generate systematic changes in distortion product otoacoustic emissions (DPOAEs). This work focuses on the development of a novel system for the collection and analysis of DPOAE mea- surements associated with posture-induced ICP changes. Currently, the average level and angle components of DPOAEs are analyzed separately. The study described here develops, implements and analyzes a new approach to DPOAEs combining level and angle data in one representation. Additionally, the study intro- duces an extended analysis of all DPOAE points collected at each frequency instead of the average value, presents a novel method for the elimination of noisy DPOAE points, and an assesment of the time required for DPOAEs to reach steady-state values after postural changes. Data were collected from four ears of three normal-hearing subjects (ages 20 to 22 years) over three sessions. 68 bu er points and the corresponding averages were collected at 13 frequencies (0.5 to 4 kHz range) at two postural positions (90 and -45 degrees with the horizontal). Repeated measurements were made while transitioning from upright to tilted and vice versa at three frequencies over two and ten minutes, respectively. Separate level and angle representations showed signi cant separation between data at the two position in both level and angle at the lower fre- quencies (< 2kHz). The combined representation yielded \cloud-like" clusters of data at each position and frequency. Centroids computed for groups of data at di erent positions showed greatest separation at middle frequencies (1 to 2 kHz), thus suggesting that the development of DPOAEs into an ICP monitoring tool should be focused on the mid-frequency range. A case study analysis of the combined representation for one ear showed that no systematic variations occur within bu ers for each measurement. The new representation of noise within the combined approach was shown to allow better understanding of noise and elimination of individual noisy bu er points rather than of the entire average. Slopes computed at each frequency for the rst two minutes of measurements made while transitioning from tilted to upright were larger that those for the last seven minutes of the same measurements, indicating that DPOAEs reach steady-state value within the rst few minutes after postural changes. A comparison of DPOAE data in the upright position before and after tilting showed that DPOAEs recovered fully to their initial values 10 minutes after tilting.

Language

English

Comments

121 p. : ill. (some col.) Honors Project-Smith College, Northampton, Mass., 2010. Includes bibliographical references (p. 119-121)

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