Author

Participants

Factors

Results

Conclusion

Nam et al. (2021) [11]

15 patients (24 ears)

Noise

Exposure

Pure tone audiometry from 250 Hz to 8 kHz:

No significant threshold differences were observed between the control group and noise-exposed group.

ABR at 90 dB SPL:

Amplitude of Wave I, Wave V, and interpeak interval between Wave I and Wave V did not show a significant change between the noise exposure and the control groups.

Noise Exposure

No significant differences were observed between the control and noise exposed group

Salvi et al. (2018) [4]

10 young patients (mean age of 20.09 years)

6 elderly patients (mean age of 62.66 years)

Age

Subjects were then tested in a noisy environment by using BBN at 20 dBHL and then at 30 dBHL

20 dBHL:

· Young subjects threshold stayed almost identical.

· Elderly subject’s thresholds were above the mean threshold of normal subjects and outside normal range.

· 30 dBHL:

· Young subjects experienced an increase in threshold

· Elderly patients also experienced a greater shift in responses especially at high frequencies above mean threshold of younger subjects.

Significant threshold shift was observed when presenting broadband background noise at 30 dBHL in both groups.

Elderly patients were more affected especially at higher frequencies which explains poorer speech intelligibility compared to the control group.

Ishikawa et al. (2019) [9]

45 guinea pig models

Aminoglycoside (AG)

induced ototoxicity

Five aminoglycoside medications were tested for dose dependent ototoxicity. Namely, neomycin, gentamicin, paromomycin, apramycin, gentamicin C1a.

At three different dosages: 60 mg/mL, 210 mg/mL, and 420 mg/mL.

Threshold differences were noticed for all three concentrations of all five drugs at different times ranging from minutes to days.

A direct correlation was observed between the different aminoglycosides dosages and threshold shifts especially at high frequencies.

There is a deterioration in the integrity of the cochlear amplifiers, also known as the outer hair cells (OHCs) which could also explain poorer speech intelligibility.

Mellado et al. (2014) [10]

Pathogen-free mice from both

Genders [12]

Schwann cells

ablation

When mice were injected with a tamoxifen from P21 to P23, an ABR was performed at 1, 4, 8, and 16 weeks from injection time.

Three differences were noted at all periods when stimulus was presented at 70 dB SPL:

1) Reduction in the Wave I amplitude

2) Increase in wave I latency

3) Increase in widths

A reduction in the AP of ABR Peak 1 in DTA and increase in the SP/AP ratio was noted.

Schwann cells ablation resulted in an impairment of the auditory system.