Correlation of Auditory Evoked Brainstem Response Characteristics and Salivary Cortisone Concentration in Noise-exposed Workers

The research is cross-sectional. The expected duration of the survey is at least 18 months. Assuming that the characteristics of the auditory evoked brainstem potentials are correlated with salivary cortisone concentration with a correlation coefficient of 0.4, a test power of 80% and a significance level of α = 0.05, at least 46 subjects should be included in the study. Test power analysis was performed using MedCalc Statistical Software, version 19.1 (MedCalc Software bv, Ostend, Belgium; https://www.medcalc.org; 2019). According to the data distribution (Kolmogorov-Smirnov test), appropriate parametric and / or non-parametric statistical tests will be applied in accordance with the obtained results. The data will be presented in tables and graphs. Numerical variables will be represented using the range, arithmetic mean and standard deviation, respectively, the median and the interquartile range, in cases of distribution that does not follow the normal distribution. The categorical variables will be presented using absolute frequencies and their respective proportions. Differences in the values of the numerical variables between the test groups with a defined hearing threshold will be analyzed by parametric Student's t-test for independent samples, and non-parametric Mann-Whitney U test for independent samples. Differences in categorical variables between the examined groups will be analyzed by chi-square test or Fisher's exact test in cases where the number of subjects in each group is less than 5. The corresponding correlation coefficients (Pearson's or Spearman's) between individual clinical variables will be calculated. An appropriate regression model for the prediction of belonging to a group with a defined hearing threshold shift will be made, which will include those that have a significance level of P≤0.20 in the previous statistical analyzes. In the above tests, significant P values will be considered to be less than 0.05. The statistical analysis of data will use IBM SPSS Statistics licensed software version 25.0.

Material:

1. Audiometer Audiometer AC40
2. DD45 audiometric headphones
3. Interacoustics AZ26 tympanometer
4. Equipment for testing auditory evoked brainstem potentials: ABR Interacoustics Eclipse, EPA Preamplifier, 3M E-A-RTONE Insert Earphone ABR
5. Cortisol-Salivette Cotton Salad Carrier
6. High Performance Liquid Chromatography (HPLC)
7. validated questionnaire in the Croatian language - assessment of psychosocial risk factors in the HSE workplace 8th validated questionnaire in Croatian - The scale of stress experienced

Research plan:

An employer finds workers who meet points 1-5 of study inclusion criteria. A head of the research checks their medical history and includes them in the study if they do not meet any of first six exclusion criteria. A head of the research orally informs these workers at the meeting and helps them to understand and sign a written informed consent for participation in the research. Each of them receive an information about the date of arrival at the place of research and also a unique password that encodes saliva samples, completed questionnaires and electronic and printed findings derived from the assessment of hearing health. The research leader, research mentors, and occupational safety manager, who is responsible for supervising the sampling and storage of saliva samples in the refrigerator at +4 ℃ in the workplace, know the password and associated name.