Stephen A. Fausti

Auditory and vestibular dysfunction associated with blast-related traumatic brain injury

The dramatic escalation of blast exposure in military deployments has created an unprecedented amount of traumatic brain injury (TBI) and associated auditory impairment. Auditory dysfunction has become the most prevalent individual service-connected disability, with compensation totaling more than 1 billion dollars annually. Impairment due to blast can include peripheral hearing loss, central auditory processing deficits, vestibular impairment, and tinnitus. These deficits are particularly challenging in the TBI population, as symptoms can be mistaken for posttraumatic stress disorder, mental-health issues, and cognitive deficits. In addition, comorbid factors such as attention, cognition, neuronal loss, noise toxicity, etc., can confound assessment, causing misdiagnosis. Furthermore, some auditory impairments, such as sensorineural hearing loss, will continue to progress with age, unlike many other injuries. In the TBI population, significant clinical challenges are the accurate differentiation of auditory and vestibular impairments from multiple, many times overlapping, symptoms and the development of multidisciplinary rehabilitation strategies to improve treatment outcomes and quality of life for these patients.

An individualized, sensitive frequency range for early detection of ototoxicity

OBJECTIVE The aim of this study was to identify auditory frequencies at which serial threshold testing would provide the greatest sensitivity for early detection of ototoxicity. The overall objective is to develop a more time-efficient ototoxicity monitoring protocol. DESIGN Threshold data were analyzed from 370 hospitalized patients treated with aminoglycoside antibiotics (AMGs) or cisplatin (CDDP) who received serial auditory monitoring before, during, and after treatment at conventional (0.25 to 8 kHz) and high (9 to 20 kHz) frequencies. RESULTS For patients showing hearing changes due to ototoxicity, a frequency range was identified for its apparent high sensitivity to initial ototoxicity. This sensitive range is identified according to an individuals hearing threshold configuration, and is, therefore, unique for each patient. The range consists of five frequencies, generally separated by 1/6 octave, e.g., 8, 9, 10, 11.2, and 12.5 kHz. To determine frequencies and combinations of frequencies that were most often involved in ototoxicity detection, threshold data in the sensitive range were analyzed in detail. This analysis suggests that patients receiving treatment with AMG or CDDP can be monitored for hearing thresholds at only five frequencies, resulting in an 84% detection rate for AMG and 94% for CDDP compared with monitoring at all conventional and high frequencies. CONCLUSIONS This comprehensive analysis supports earlier observations that a sensitive, limited frequency range exists in which serial threshold monitoring will provide early warning of ototoxicity before effects in the speech frequency range. This finding is now being evaluated in a prospective investigation.

A system for evaluating auditory function from 8000–20 000 Hz

A system for the measurement of auditory function from 8000--20 000 Hz is described. This system introduces advances in: (a) maximum power output, (b) signal fidelity, and (c) transducer characteristics. Two case studies are presented to illustrate the clinical information gained from the measurement of high-frequency auditory sensitivity, which is not readily apparent in conventional threshold assessment.

High-frequency audiometric monitoring strategies for early detection of ototoxicity

Therapeutic drugs such as the aminoglycoside antibiotics (AMG) and the chemotherapy agent cisplatin (CDDP) are known to cause irreversible hearing loss, typically affecting highest frequency hearing first with progression of loss to the lower frequency regions. Conventional (0.25-8 kHz) and high-frequency (9-20 kHz) serial hearing threshold monitoring was done in 123 hospitalized patients (222 ears) administered AMG or CDDP. Of ears showing a decrease in sensitivity corresponding with treatment, 62.5% demonstrated initial hearing loss solely in the high-frequency range, 13.5% first showed loss only in the conventional-frequency range, and 24.0% showed loss in both frequency ranges concurrently. Thus, if only high frequencies had been monitored, early change in auditory sensitivity would have been detected in 86.5% of these patients. Further analysis revealed a range of five frequencies, specific to each individuals hearing threshold configuration, in which initial ototoxicity appeared most likely to be detected. Testing only these five frequencies would have identified 89.2% of ears that showed change. The results of this study confirm the need to serially monitor auditory thresholds, especially in the high-frequency range, of patients receiving ototoxic drugs. A shortened five-frequency monitoring protocol is presented and suggested for use with patients unable to tolerate lengthy audiometric testing procedures.

The effects of noise upon human hearing sensitivity from 8000 to 20 000 Hz

High-frequency (8 to 20 kHz) hearing sensitivity was compared in thirty-six, 20 to 29-year-old military veterans with histories of steady-state or impulsive noise exposure. Threshold shifts were prominent for the steady-state noise subjects from 13 to 20 kHz. Mean thresholds from 8 through 12 kHz were maximally 20 dB poorer than a sample of young adult normals. Audiometric configurations for this group were generally smooth and symmetrical above 8000 Hz. For the impulsive noise group, substantial shifts in sensitivity were seen from 2 to 20 kHz and the high-frequency audiometric configurations were often jagged and/or asymmetrical. The variability of subjects in this group was greater than that seen in the steady-state noise exposed sample. Several case studies are presented to illustrate these characteristics. Measurement of auditory sensitivity from 8 to 20 kHz extends the mapping of basal cochlear function, providing information which often is not predictable from conventional audiometric measurement. This additional information provides for more comprehensive inter- and intra-subject comparison of the degree and extent of threshold changes present.

Hearing health and care: the need for improved hearing loss prevention and hearing conservation practices.

Hearing loss affects 31 million Americans, particularly veterans who were exposed to harmful levels of noise during military functions. Many veterans also receive treatment with ototoxic medications, which may exacerbate preexisting hearing loss. Thus, hearing loss is the most common and tinnitus the third most common service-connected disability among veterans. Poor implementation of hearing protection programs and a lack of audiometric testing during medical treatment leave veterans vulnerable to unrecognized and untreated hearing loss until speech communication is impaired. Individualized audiometric testing techniques, including assessment of high frequencies, can be used in clinical and occupational settings to detect early hearing loss. Antioxidants also may alleviate cochlear damage caused by noise and ototoxicity. Ultimately, hearing loss prevention requires education on reducing occupational and recreational noise exposure and counseling on the risks and options available to patients. Technological advances will improve monitoring, allow better noise engineering controls, and lead to more effective hearing protection.

A 5-year prospective study of diabetes and hearing loss in a veteran population.

Hypothesis: Veterans with diabetes will have significantly greater hearing loss than nondiabetic veterans. Background: The association between diabetes and hearing loss remains unclear despite the volume of research that has been devoted to the question. Often, differences in hearing thresholds between diabetic and nondiabetic patients are confounded by age and noise exposure. Methods: In this 5-year prospective study, 342 diabetic veterans and 352 nondiabetic veterans from the Portland VA Medical Center in Oregon were tested on a variety of audiometric measures, including pure-tone thresholds. Results: Age and noise exposure were accounted for in the analyses. There was a trend toward greater hearing loss in diabetic patients 60 years of age and younger across the frequency range. These differences were statistically significant only in the highest frequencies tested (10, 12.5, 14, and 16 kHz). The effects of both diabetes and noise exposure on high-frequency hearing thresholds were dependent on age. For patients older than 60 years, the mean thresholds were not significantly different. Conclusion: These results suggest that diabetic patients 60 years old or younger may show early high-frequency hearing loss similar to early presbycusis. After age 60, difference in hearing loss between diabetic and nondiabetic patients was reduced.

Diabetes-related changes in hearing†

Determine the effects on hearing of diabetes mellitus (DM) severity.

Age-related changes in the auditory brainstem response

PURPOSE This cross-sectional study had two goals: (1) Identify and quantify the effects of aging on the auditory brainstem response (ABR); (2) Describe how click rate and hearing impairment modify effects of aging. RESEARCH DESIGN AND ANALYSIS: ABR measures were obtained from 131 predominately male Veteran participants aged 26 to 71 yr. Metrics analyzed include amplitude and latency for waves I, III, and V, and the I-V interpeak latency interval (IPI) at three repetition rates (11, 51, and 71 clicks/sec) using both polarities. In order to avoid confounding from missing data due to hearing impairment, participants had hearing thresholds <40 dB HL at 2 kHz and 70 dB HL at 4 kHz in at least one ear. Additionally, the median 2, 3, and 4 kHz pure tone threshold average (PTA2,3,4) for the sample, ∼17 dB HL, was used to delineate subgroups of better and worse hearing ears, and only the better hearing sample was modeled statistically. We modeled ABR responses using age, repetition rate, and PTA2,3,4 as covariates. Random effects were used to model correlation between the two ears of a subject and across repetition rates. Inferences regarding effects of aging on ABR measures at each rate were derived from the fitted model. Results were compared to data from subjects with poorer hearing. RESULTS Aging substantially diminished amplitudes of all of the principal ABR peaks, largely independent of any threshold differences within the group. For waves I and III, age-related amplitude decrements were greatest at a low (11/sec) click rate. At the 11/sec rate, the model-based mean wave III amplitude was significantly smaller in older compared with younger subjects even after adjusting for wave I amplitude. Aging also increased ABR peak latencies, with significant shifts limited to early waves. The I-V IPI did not change with age. For both younger and older subjects, increasing click presentation rate significantly decreased amplitudes of early peaks and prolonged latencies of later peaks, resulting in increased IPIs. Advanced age did not enhance effects of rate. Instead, the rate effect on wave I and III amplitudes was attenuated for the older subjects due to reduced peak amplitudes at lower click rates. Compared with model predictions from the sample of better hearing subjects, mean ABR amplitudes were diminished in the group with poorer hearing, and wave V latencies were prolonged. CONCLUSIONS In a sample of veterans, aging substantially reduced amplitudes of all principal ABR peaks, with significant latency shifts limited to waves I and III. Aging did not influence the I-V IPI even at high click rates, suggesting that the observed absolute latency changes associated with aging can be attributed to changes in auditory nerve input. In contrast, ABR amplitude changes with age are not adequately explained by changes in wave I. Results suggest that aging reduces the numbers and/or synchrony of contributing auditory nerve units. Results also support the concept that aging reduces the numbers, though perhaps not the synchrony, of central ABR generators.

Detection of aminoglycoside ototoxicity by high-frequency auditory evaluation: selected case studies.

A practical monitoring procedure utilizing frequencies higher than those tested by conventional audiometry for the detection of ototoxicity has the potential for preventing or minimizing irreversible communication deficits in patients receiving aminoglycoside antibiotic therapy. If ototoxicity produced by these drugs could be detected before it progresses to involve the frequencies essential for communication, it might be possible to lower the dose or to change to another antibiotic to prevent a permanently handicapping hearing impairment. From a total of 77 patients monitored by serial audiograms, three case studies illustrate the various types of auditory sensitivity changes observed with high-frequency audiometry. Ototoxicity was generally detected by high-frequency auditory testing before it could be detected by conventional audiometric procedures. These cases demonstrate the utility of monitoring audition at frequencies higher than those tested conventionally in patients receiving aminoglycoside antibiotics.