Masters Theses

Date of Award

6-1982

Degree Type

Thesis

Degree Name

Master of Arts

Major

Audiology

Major Professor

Allan O. Diefendorf

Committee Members

Robert Moore, Charles J. Ferrell, Samuel B. Burchfield

Abstract

The purpose of this investigation was to examine acoustic reflex thresholds in neonates under conditions that would optimize elicitation of the reflex. Use of hand held equipment and oscilloscopic display of eliciting stimuli and compliance changes were intended to provide an approach in which obscuring concomitants would be minimized. A secondary purpose was to obtain SPAR results for all infants who exhibited responses to all activating stimuli.

Tympanograms were obtained bilaterally for 10 infants from nine to 55 hours post-birth. Acoustic reflexes were then evaluated unilaterally with stimuli of 500, 1000, and 2000 Hz pure tones and white noise utilizing a probe tone of 220 Hz. Thresholds for acoustic reflexes were recorded from the compliance change meter of an impedance bridge and an oscilloscope. Two observers independently judged reflexes from the instruments while a third judge reported behavioral responses from the infants. Acoustic reflex thresholds were determined according to a pre-determined set of criteria.

Results indicated acoustic reflex thresholds for all stimuli in 60% of all ears tested utilizing visual observation of the compliance change meter of the impedance bridge and 50% of all ears utilizing oscillographic display. Of the remaining infants, two exhibited absent reflexes to all stimuli, and two exhibited absent reflexes only at 2000 Hz. A comparison between the oscilloscope and the impedance results indicated slightly fewer questionable responses for the oscilloscope. However, one infant displayed absent reflexes to all pure tone stimuli when viewed on the oscilloscope but present to those stimuli when recorded from the impedance bridge. SPAR results were obtained for 60% of the infants.

Advantages and disadvantages were noted for use of oscillographic display of reflex responses. The oscillographic display allowed the observer to judge reflex responses in relation to each other as well as to the onset of the activating stimuli. This additional information may increase the accuracy of the measurement. In addition, the oscilloscope can be adjusted so that it is more sensitive to compliance changes in the ear.

There is a disadvantage to added sensitivity, however, in that the oscilloscope is also more sensitive to movements from the infant and/or the investigator holding the equipment. This disadvantage may be alleviated by the use of filters.

The results of this investigation indicate that is is possible to obtain fairly accurate reflex thresholds with neonates. Although the method for eliciting acoustic reflexes with neonates is not complete at present, the procedures utilized in this investigation may aid in the development of a standardized clinical procedure for use with the neonatal population.

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