The Cortisol Awakening Response: A Feasibility Study Investigating the Use of the Area Under the Curve With Respect to Increase as an Effective Objective Measure of Tinnitus Distress

Vulnerability to chronic stress and the phenotypic heterogeneity of presbycusis with subjective tinnitus

Age-related functional reserve decline and vulnerability of multiple physiological systems and organs, as well as at the cellular and molecular levels, result in different frailty phenotypes, such as physical, cognitive, and psychosocial frailty, and multiple comorbidities, including age-related hearing loss (ARHL) and/or tinnitus due to the decline in auditory reserve. However, the contributions of chronic non-audiogenic cumulative exposure, and chronic audiogenic stress to phenotypic heterogeneity of presbycusis and/or tinnitus remain elusive. Because of the cumulative environmental stressors throughout life, allostasis systems, the hypothalamus-pituitary-adrenal (HPA) and the sympathetic adrenal-medullary (SAM) axes become dysregulated and less able to maintain homeostasis, which leads to allostatic load and maladaptation. Brain-body communication via the neuroendocrine system promotes systemic chronic inflammation, overmobilization of energetic substances (glucose and lipids), and neuroplastic changes via the non-genomic and genomic actions of glucocorticoids, catecholamines, and their receptors. These systemic maladaptive alterations might lead to different frailty phenotypes and physical, cognitive, and psychological comorbidities, which, in turn, cause and exacerbate ARHL and/or tinnitus with phenotypic heterogeneity. Chronic audiogenic stressors, including aging accompanying ontological diseases, cumulative noise exposure, and ototoxic drugs as well as tinnitus, activate the HPA axis and SAM directly and indirectly by the amygdala, promoting allostatic load and maladaptive neuroplasticity in the auditory system and other vulnerable brain regions, such as the hippocampus, amygdala, and medial prefrontal cortex (mPFC). In the auditory system, peripheral deafferentation, central disinhibition, and tonotopic map reorganization may trigger tinnitus. Cross-modal maladaptive neuroplasticity between the auditory and other sensory systems is involved in tinnitus modulation. Persistent dendritic growth and formation, reduction in GABAergic inhibitory synaptic inputs induced by chronic audiogenic stresses in the amygdala, and increased dendritic atrophy in the hippocampus and mPFC, might involve the enhancement of attentional processing and long-term memory storage of chronic subjective tinnitus, accompanied by cognitive impairments and emotional comorbidities. Therefore, presbycusis and tinnitus are multisystem disorders with phenotypic heterogeneity. Stressors play a critical role in the phenotypic heterogeneity of presbycusis. Differential diagnosis based on biomarkers of metabonomics study, and interventions tailored to different ARHL phenotypes and/or tinnitus will contribute to healthy aging and improvement in the quality of life.

Hair-cortisol and hair-BDNF as biomarkers of tinnitus loudness and distress in chronic tinnitus

The role of stress and its neuroendocrine mediators in tinnitus is unclear. In this study, we measure cortisol as an indicator of hypothalamus–pituitary–adrenal (HPA) axis alterations and brain-derived neurotrophic factor (BDNF) as a marker of adaptive neuroplasticity in hair of chronic tinnitus patients to investigate relationships with tinnitus-related and psychological factors. Cross-sectional data from chronic tinnitus inpatients were analyzed. Data collection included hair sampling, pure tone audiometry, tinnitus pitch and loudness matching, and psychometric questionnaires. Elastic net regressions with n-fold cross-validation were performed for cortisol (N = 91) and BDNF (N = 87). For hair-cortisol (R² = 0.10), the strongest effects were sampling in autumn and body-mass index (BMI) (positive), followed by tinnitus loudness (positive) and smoking (negative). For hair-BDNF (R² = 0.28), the strongest effects were hearing aid use, shift work (positive), and tinnitus loudness (negative), followed by smoking, tinnitus-related distress (Tinnitus Questionnaire), number of experienced traumatic events (negative), and physical health-related quality of life (Short Form-12 Health Survey) (positive). These findings suggest that in chronic tinnitus patients, higher perceived tinnitus loudness is associated with higher hair-cortisol and lower hair-BDNF, and higher tinnitus-related distress with lower hair-BDNF. Regarding hair-BDNF, traumatic experiences appear to have additional stress-related effects, whereas hearing aid use and high physical health-related quality of life appear beneficial. Implications include the potential use of hair-cortisol and hair-BDNF as biomarkers of tinnitus loudness or distress and the need for intensive future research into chronic stress-related HPA axis and neuroplasticity alterations in chronic tinnitus.

Objective and Measurable Biomarkers in Chronic Subjective Tinnitus

Tinnitus is associated with increased social costs and reduced quality of life through sleep disorders or psychological distress. The pathophysiology of chronic subjective tinnitus, which accounts for most tinnitus, has not been clearly elucidated. This is because chronic subjective tinnitus is difficult to evaluate objectively, and there are no objective markers that represent the diagnosis or therapeutic effect of tinnitus. Based on the results of studies on patients with chronic subjective tinnitus, objective and measurable biomarkers that help to identify the pathophysiology of tinnitus have been summarized. A total of 271 studies in PubMed, 303 in EMBASE, and 45 in Cochrane Library were found on biomarkers related to chronic subjective tinnitus published until April 2021. Duplicate articles, articles not written in English, review articles, case reports, and articles that did not match our topic were excluded. A total of 49 studies were included. Three specimens, including blood, saliva, and urine, and a total of 58 biomarkers were used as indicators for diagnosis, evaluation, prognosis, and therapeutic effectiveness of tinnitus. Biomarkers were classified into eight categories comprising metabolic, hemostatic, inflammatory, endocrine, immunological, neurologic, and oxidative parameters. Biomarkers can help in the diagnosis, measure the severity, predict prognosis, and treatment outcome of tinnitus.

Tinnitus and stress in adults: a scoping review

OBJECTIVE

Tinnitus and stress are recurrently reported together. The strength and direction of this relationship is not clear. The aim of this review is to catalogue the evidence of this relationship, how it has been described in adults and which instruments were used.

DESIGN

Five-stage framework was followed. An online search of databases and published journals were conducted. The main inclusion criteria were original studies published in English and conducted in an adult human population, in which both tinnitus and stress were measured using different instruments.

STUDY SAMPLES

5699 records were identified in the searching stage and 50 studies were eligible for data extraction.

RESULTS

Measurements of perceived stress were most frequently used. Tinnitus patients tend to report louder and more bothersome tinnitus when they are stressed, but not all tinnitus patients associated stress with the onset or the severity of their tinnitus. Any positive correlation reported between stress and tinnitus levels varied in strength according to the used instrument. Post-intervention changes in stress and tinnitus levels showed inconsistency.

CONCLUSION

There is considerable room for further research to study the relationship between stress and tinnitus. We highlight principal issues that should be considered in future studies.

Effects of Cardiovascular Health Factors and Personal Listening Behaviors on Hearing Sensitivity in College-Aged students

OBJECTIVES

This study examined the association between pure tone hearing sensitivity and music listening behaviors among traditional college-aged students and sought to determine factors that mediate hearing sensitivity, including health and fitness levels, gender, and personal listening device (PLD) use.

METHODS

A convenience sample of college students (N = 182; 133 females, 49 males, mean age = 19.8 ± 1.4 year, average PLD use = 1.52 ± 7.1 hours•day^-1) completed hearing assessments, music listening behavior questionnaires, and health and fitness tests.

RESULTS

Most students listened to music at safe intensity levels (<80 dBA), though 18% had higher hearing levels (≥25 dB HL at one of the measured frequencies). Longer listening duration behavior approached but did not reach a statistical association with compromised hearing sensitivity. Of all variables measured, including cardiovascular health, fitness, and music listening, two variables: total cholesterol: triglycerides (TC:TG) and total cholesterol: high-density lipoproteins (TC:HDL) significantly associated with hearing sensitivity at 2 kHz. The odds hearing loss occurring at 4 kHz was 59% lower in females compared with males.

CONCLUSION

The majority of college students had healthy music listening behavior and fitness, contributing to normal hearing sensitivity in most. In cases where greater hearing threshold levels at one or more frequencies was detected, TC:HDL and TC:TG were statistically related and at 2 kHz, males were more likely to demonstrate higher listening levels compared with females of similar health and fitness level.