**3. Baseline test procedure**

This testing was accomplished under the University of Cincinnati IACUC protocol #07-12-19-01 and USAMRMC proposal number 18263008, award number A2-7467. This protocol was approved after annual review on July 18, 2021. The hearing evaluation was considered normal clinical testing. Moreover, advantage was taken of these multipurpose canines undergoing normal flight (helicopter) training. We simply conducted pre- and posthearing evaluations to obtain auditory data for this research. Given the limitations placed on us to have access to these dogs, we were only able to conduct limited further threshold BAER testing at later times postflight to observe changes in the postflight threshold shifts.

Seven [7] military working dogs (MWDs) ranging from 2 to 5 years of age were baseline tested at a military base veterinary clinic using the following procedure: a BAER threshold estimation test was run using a 100-microsecond click stimulus on an Intelligent Hearing Systems (IHS) unit. This test was conducted using the following parameters:

Polarity: rarefaction.

*Canine Hearing Management DOI: http://dx.doi.org/10.5772/intechopen.105515*

Rate: 31.1. Sweeps: 500.

Stimulus intensities: 110 dB peSPL (74 dB nHL), 100 dB peSPL (64 dB nHL), 90 dB peSPL (54 dB nHL), 80 dB peSPL (44 dB nHL), 70 dB peSPL (34 dB nHL),

60 dB peSPL (24 dB nHL), 50 dB peSPL (14 dB nHL).

\*There is a 34-dB conversation/calibration factor from dB peal sound pressure level (peSPL) to dB normal hearing level (nHL) on the particular IHS system used for this project.

Amplification: 100,000.

Low-pass filter: 1500 Hz.

High-pass filter: 100 Hz.

Stimulus: 100 microsecond click.

Based on the results of the baseline BAER, a Wave I–V latency intensity function was developed for each ear.

The BAER test analysis consisted of observing similar wave 1, III, and V latencies in two separate runs.

All the dogs were taken directly from their kennel and then pretested in the veterinary clinic in the kennel complex. Prior to testing, an otoscopic examination was conducted to ensure that no occlusion or the possibility that conductive issues were present. The tympanic membrane was viewed in all the dogs. The dogs then proceeded directly to their flight training where they were flown for 30 minutes in an H60 helicopter as usual. The handlers normally used their own means of protection for the dog such as simply folding the ears over, cotton, or nothing at all. In this case, the handlers elected not to use any form of hearing protection with the exception of one handler by choice. This flight time was shorter than normal although, depending on the mission, helicopter transit times vary greatly. At the end of flight, they were immediately brought back to the veterinary clinic and retested (postflight). Threshold estimations were noted. Dogs were sedated during BAER testing procedures with dexmedetomidine based off weight to minimize muscle artifact.

The procedure began with BAER testing each dog at an intensity of 76 dB hearing loss (HL) and increasing the stimulus intensity by 10 dB HL until all the waves were present and a second set of similar waveforms existed. Then, the intensity was lowered by 5 dB HL until similarity was no longer present. This, then, constituted the dog's threshold for that test sequence. The same protocol was followed postflight, 30 and 60 minutes later.
