The Cortisol Awakening Response (CAR): a feasibility study investigating the use of the Area Under the Curve with Respect to Increase (AUCi) as an effective objective measure of tinnitus distress.

Purpose: Tinnitus is a chronic medical condition which can result in distress, concentration difficulties, and clinical depression. An effective, objective measure of tinnitus distress does not currently exist. Endocrinal studies into the condition have been few, with those investigating the Cortisol Awakening Response (CAR) limited in scope. It was hypothesised that distressed individuals with tinnitus would awaken, and be unable to effectively prepare for the day ahead due to a blunted cortisol response.

Method: Twenty individuals with varying tinnitus distress were compared with a control group (n=10) in a pilot study which measured salivary cortisol concentrations on awakening. Multiple exclusion variables were applied.

Results: In line with previous studies, total cortisol volume (as measured by Area Under the Curve) was not found to be significantly different in the most distressed individuals with tinnitus [F (2, 26) = 0.254; p = 0.777ns.]. However, a separate measure of changing cortisol levels – the Area Under the Curve with Respect to Increase (or AUCi) – was found to be significantly less robust in those individuals reporting the most severe tinnitus distress [F (2, 26) = 7.671; p = 0.002]. This indicates that that fewer resources would be available to cope with the demands of the day ahead. Additionally, the AUCi correlated negatively with tinnitus distress later the same day.

Conclusions: Relationships between proposed objective and self-reported components of self-reported tinnitus distress are considered, with some aspects of tinnitus distress more closely related to physiological mechanisms than others. It is suggested that with further research, the CAR (AUCI) may be put forward as a credible objective biomarker of tinnitus distress.