Type of Resources
The brainstem auditory evoked response (BAER) test is a commonly used objective tool for estimating hearing sensitivity in newborn humans and could be a useful diagnostic test for humans who are unable or unwilling to participate in behavioral audiometric testing. The BAER test is currently the gold standard for testing domestic canine hearing and could similarly be used either as a screening tool or diagnostically. The test procedure is minimally invasive and could provide ear-specific estimates of hearing sensitivity. While the general morphology of the waveform resulting from a BAER test is generally agreed upon, questions remain regarding the expected latency values of the response. Latency values might be used to guide waveform detection that then determines a pass or refer result on a screening test or to evaluate the presence of a pathology on a diagnostic test. Thus, determining expected latency values for this species is needed given the importance placed on the BAER testing procedure. Domestic canines exhibit a variety of body sizes and head shapes that might affect this electrophysiologic measure. Previous research has been equivocal on the effect of head size on BAER waveforms. The purpose of this doctoral scholarly project was to examine the effect of head size on three components of the BAER result: the absolute latency of Wave I, the absolute latency of Wave V, and the Wave I-V interpeak latency. Thirty-four dogs between the ages of one and eight years with suspected normal hearing were divided into three groups based on measured head size (small, medium, and large). Brainstem auditory evoked response waveforms were collected and analyzed from the right ear of each subject. A correlational analysis was performed examining the relationship between head size and the absolute latencies of Waves I and V and the Wave I-V interpeak latency. A limited relationship was observed with head size explaining up to 29.84%, 25.26%, and 22.68% of the variation in these latencies, respectively. Notably, the strength of the relationship between these variables diminished when using an alternative measure of head size (head width) or when measuring the latency of Wave V by the peak alone and ignoring the presence of a shoulder on that wave. These differences might account for the equivocal findings in the literature on the effect of head size on the BAER test in canines. It is recommended that future researchers standardize the measurements used for both head size and wave latency as well as account for differences in latencies observed due to head size when determining normative values for adult canines.