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The purpose of this study was to describe the prevalence of hearing loss and tinnitus in a cohort of Iraq and Afghanistan Veterans (IAV) with common post-deployment conditions, including traumatic brain injury (TBI), post-traumatic stress disorder (PTSD), and other typical post-concussive conditions such as headaches and vertigo/dizziness. This retrospective observational study used data from the national Veterans Health Administration (VA) data repository from fiscal years 2001-2014. Veteran data was included if there were at least three years of VA care, with one or more years of care in 2007 or after. We identified comorbidities that may be associated with post-deployment hearing loss or tinnitus including TBI, PTSD, depression, and common post-concussive symptoms using International Classification of Diseases, 9th Revision, Clinical Modification codes. A multinomial logistic regression analysis was used to examine conditions associated with hearing loss or tinnitus. Among IAV, 570,332 were included in the final analysis. Of these, 7.78% of these were diagnosed with hearing loss alone, 6.54% with tinnitus alone, and 6.24% with both hearing loss and tinnitus. Comorbid TBI, PTSD, and depression were significantly associated with increased rates of hearing loss, tinnitus, or both conditions together. Older individuals, males, and those with TBI, PTSD, or vertigo/dizziness were significantly more likely to have hearing loss, tinnitus, or both. In order to provide more holistic post-deployment support, this myriad of conditions should be carefully considered in the planning of clinical care and beyond.

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Objective: To describe the prevalence and impact of vestibular dysfunction and nonspecific dizziness diagnoses and explore their associations with traumatic brain injury (TBI) severity, mechanism, and postconcussive comorbidities among post-9/11 veterans. Setting: Administrative medical record data from the US Departments of Defense and Veterans Affairs (VA). Participants: Post-9/11 veterans with at least 3 years of VA care. Design: Cross-sectional, retrospective, observational study. Main Measures: International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes for TBI, vestibular dysfunction, dizziness, and other commonly associated postconcussive conditions; Neurobehavioral Symptom Inventory. Results: Of the 570 248 post-9/11 veterans in this sample, 0.45% had a diagnosis of vestibular dysfunction and 2.57% had nonspecific dizziness. Those with either condition were more likely to have evidence of TBI (57.11% vs 28.51%) and reported more disruption from neurobehavioral symptoms. Blast and nonblast injuries were associated with greater symptom disruption, particularly in combination. Conclusions: There was a consistent, significant association between TBI and vestibular dysfunction or nonspecific dizziness, after controlling for sociodemographic factors, injury mechanism, and comorbid conditions. Given that most deployed post-9/11 veterans report blast and/or nonblast injuries, the need for prompt identification and management of these conditions and symptoms is clear.

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Measurements of perilymph hydrodynamics in the human cochlea are scarce, being mostly limited to the fluid pressure at the basal or apical turn of the scalae vestibuli and tympani. Indeed, measurements of fluid pressure or volumetric flow rate have only been reported in animal models. In this study we imaged the human ear at 6.7 and 3-μm resolution using μCT scanning to produce highly accurate 3D models of the entire ear and particularly the cochlea scalae. We used a contrast agent to better distinguish soft from hard tissues, including the auditory canal, tympanic membrane, malleus, incus, stapes, ligaments, oval and round window, scalae vestibule and tympani. Using a Computational Fluid Dynamics (CFD) approach and this anatomically correct 3D model of the human cochlea, we examined the pressure and perilymph flow velocity as a function of location, time and frequency within the auditory range. Perimeter, surface, hydraulic diameter, Womersley and Reynolds numbers were computed every 45 degrees of rotation around the central axis of the cochlear spiral. CFD results showed both spatial and temporal pressure gradients along the cochlea. Small Reynolds number and large Womersley values indicate that the perilymph fluid flow at auditory frequencies is laminar and its velocity profile is plug-like. The pressure was found 102–106° out of phase with the fluid flow velocity at the scalae vestibule and tympani, respectively. The average flow velocity was found in the sub-μm/s to nm/s range at 20–100 Hz, and below the nm/s range at 1–20 kHz.

Hearing is an extremely complex phenomenon, involving a large number of interrelated variables that are difficult to measure in vivo. In order to investigate such process under simplified and well-controlled conditions, models of sound transmission have been developed through many decades of research. The value of modeling the hearing system is not only to explain the normal function of the hearing system and account for experimental and clinical observations, but to simulate a variety of pathological conditions that lead to hearing damage and hearing loss, as well as for development of auditory implants, effective ear protections and auditory hazard countermeasures. In this paper, we provide a review of the strategies used to model the auditory function of the external, middle, inner ear, and the micromechanics of the organ of Corti, along with some of the key results obtained from such modeling efforts. Recent analytical and numerical approaches have incorporated the nonlinear behavior of some parameters and structures into their models. Few models of the integrated hearing system exist; in particular, we describe the evolution of the Auditory Hazard Assessment Algorithm for Human (AHAAH) model, used for prediction of hearing damage due to high intensity sound pressure. Unlike the AHAAH model, 3D finite element models of the entire hearing system are not able yet to predict auditory risk and threshold shifts. It is expected that both AHAAH and FE models will evolve towards a more accurate assessment of threshold shifts and hearing loss under a variety of stimuli conditions and pathologies.