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Otoacoustic emission (OAE) screening is perhaps one of the most common diagnostic tools used on both adults and children alike to clinically asses hearing health. However small to moderate middle ear pressures (both positive and negative), which are quite prevalent among the general population, are known to significantly reduce the OAE response specifically among frequencies below 2 kHz. This study focuses on the design and development of a software controlled syringe pump which will be used for the automatic compensation of middle ear pressure. This study reports validating test results which confirm the feasibility of using this system for future clinical trials.

An automated Auditory Brainstem Response (ABR) peak identification and labelling system is developed and evaluated. The system uses a set of matched filters and a rule base for on-line peak labelling. The matched filters are designed to reflect the spectral and biphasic characteristics of the ABR peaks. The rules are designed to identify ABR peaks based on the latencies and amplitudes of the peaks found in the matched filter output buffers. The system is capable of automatic generation of latency-intensity functions. The algorithm was tested using 168 ABRs from four adults, yielding only 2 incorrectly labelled recordings.

In this study, Auditory Steady State Responses (ASSR) to 100 /spl mu/sec clicks and 4 msec cochlear chirps are recorded in adult subjects at repetition rates of 20 to 100 Hz in 10 Hz increments. Response characteristics of ASSRs are compared in the frequency domain. Results show that response amplitudes to both stimuli peak in the proximity of 40 Hz and 80 Hz, but chirps generate responses with larger amplitudes at all repetition rates. The responses at 40 Hz repetition rates for both clicks and chirps are larger than the corresponding responses at 80 Hz stimuli in awake adults. The 40 Hz responses, however, show greater variability than the 80 Hz responses depending on the subject's state of consciousness. The predictions of the ASSR waveforms at each repetition rate were then synthesized by superimposing the suitably shifted Middle Latency Response (MLR) waveforms that were recorded during the same session with a stimulus repetition rate of 10 Hz for both click and chirp recordings. This part of the study was undertaken to Investigate the validity of the hypothesis which states that the steady state responses are simply the linear additions of transient MLRs. The results showed that the synthesized waveforms resembled the real recordings to some extent, but consistently had larger amplitudes. This difference is assumed to be a result of the adaptation effects of higher stimulus rates.

A neuromonitoring system using compound action potential (CAP) and cochlear blood flow (CBF) is developed to assess the functional status of the cochlea during hypoxia. The system uses a specially designed optic probe capable of acquiring CAP and CBF signals and modules to process and display these signals. The system is tested in rabbits by creating cochlear hypoxia by manual compression of the auditory nerve and acoustic artery. Results show that CAP and CBF measurements can provide almost real time information on the status of the cochlea under compromising situations.