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Appraisal of Extended Bilateral Cooling of the Ears in Healthy Subjects for Future Otoprotective Applications
Shaumiya Sellathurai1, Andreas Radeloff2, Dominik Péus3
1Department of Neurology, University Hospital Basel, Basel, Switzerland.
Objective:
To investigate the feasibility and acceptability of bilateral ear cooling as a potential method for future therapeutic otoprotection and to assess its impact on otoacoustic emissions.
Study Design:
Pilot study.
Setting:
Neurotologic outpatient clinic.
Subjects:
Ten subjects with normal hearing.
Interventions:
In the first experiment, the subjective experience of dizziness was evaluated during unilateral ear canal cooling with 30 °C water delivered through the external ear canal (EEC), using a questionnaire and a vertigo Visual Analog Scale (VAS). The second experiment evaluated the acceptability and cochlear reach of bilateral ear cooling with water at 30 °C and 24 °C for 20 minutes. Objective measures included changes in tympanic membrane temperature and transient evoked otoacoustic emissions (TEOAE). Subjective dizziness was again assessed using the questionnaire and VAS. The third experiment focused on the influence of head position relative to the Earth's gravity vector on the perception of vertigo during simultaneous bilateral stimulation.
Results:
Unilateral cooling was significantly more uncomfortable than bilateral cooling. Simultaneous cooling at 30 °C was well tolerated and led to a significant tympanic temperature reduction of 2.31 ± 1.2 K. Cooling at 24 °C resulted in a stronger sensation of vertigo and a greater temperature reduction of 5.01 ± 3.04 K. Bilateral ear cooling at 24 °C significantly reduced total-TEOAE response levels by 2.12 ± 4.01 dB SPL, whereas 30 °C cooling had no significant effect on total-TEOAE levels. Analysis of TEOAE response across frequency bands showed varying results. The TEOAE signal-to-noise ratio (SNR) significantly decreased across all frequency bands after both 30 °C and 24 °C cooling. Head position relative to gravity appeared to have a lesser effect on the perception of vertigo compared with the influence of symmetrical, simultaneous bilateral ear cooling, which effectively mitigated discomfort.
Conclusion:
Bilateral ear cooling is a feasible and well-tolerated in human subjects, effectively lowering tympanic membrane temperature. However, the relevance of TEOAE measurements for detecting cochlear temperature changes remains uncertain. Further research is necessary to validate these results and to evaluate the utility of TEOAE as a reliable measure in this context.
