Kjell K. Karlsson

The Hearing of Symphony Orchestra Musicians

The question has recently been raised as to whether the performance of symphony orchestra music involves a risk of sustaining hearing impairment. The following investigation presents a population study of 417 musicians, of whom 123 were investigated twice, at an interval of 6 years. Median values of screened tone thresholds were compared with a reference material, according to Spoor & Passchier-Vermeer (1969). The tone thresholds measured did not differ from the reference values although the actual sound exposure in some situations exceeded the permitted sound levels applied to industrial noise. We suggest that the sound exposure criteria for industrial noise are not valid when discussing such sounds as are produced by acoustic instruments in a symphonic environment.

Quinine causes isolated outer hair cells to change length.

The outer hair cells have been shown to exhibit motile properties which are likely to participate in the cochlear performance. Quinine is known to induce hearing loss as well as contraction of skeletal muscle. Isolated outer hair cells were exposed to quinine and tetracaine. This resulted in a biphasic elongation-shortening response, quantitatively as well as qualitatively altered by tetracaine. These findings are in good agreement with similar studies on muscle.

Audiometry as a possible indicator of quinine plasma concentration during treatment of malaria

The spread of chloroquine-resistant malaria has led to a resurgence of quinine in clinical use. One of the well-known side effects of quinine, reversible hearing loss, is closely related to the plasma concentration. We suggest that this hearing effect could be used as an aid in therapy control when quinine drug assay is not available.

The effects of quinine on the cochlear mechanics in the isolated temporal bone preparation

Quinine is known to induce a reversible hearing loss and to evoke motile responses of isolated outer hair cells. To study the effect of quinine, mechanical tuning curves of the Hensens cells were measured in the isolated cochlea preparation in response to acoustical stimuli applied to the ear before and after application of the drug. It was shown that 0.5-4 mM quinine increased the vibration amplitude at the peak of the mechanical resonance curves and increased the sharpness of tuning. The time course of the event depended on whether the scala media was opened or not. The results show that quinine alters the micromechanical tuning of the organ of Corti.

The Effect of Quinine on Psychoacoustic Tuning Curves, Stapedius Reflexes and Evoked Otoacoustic Emissions in Healthy Volunteers

Quinine causes reversible hearing loss, closely related to the quinine plasma concentration. The effects of quinine on psychoacoustic tuning curves, stapedius reflex thresholds and evoked otoacoustic emissions were studied in healthy volunteers. The tuning curves became shallower, whereas reflex thresholds were unaffected. The shift in the emission thresholds paralleled that of the pure-tone thresholds. There were also qualitative changes in the emissions: 1) the exponent of the stimulus-response function changed from 0.34 to 0.56; 2) decay time shortened; 3) the power spectrum shifted towards lower frequencies. The results are discussed in relation to various aspects of cochlear performance and are suggested to depend on an outer hair cell dysfunction.

Reversible hearing impairment related to quinine blood concentrations in guinea pigs

The hearing ability was measured in anaesthetised guinea pigs by recording cochlear evoked potentials induced by standardised sound stimulation. The animals were given quinine intravenously and blood samples were withdrawn for assay of quinine. The shift in hearing threshold was closely related to the quinine blood concentration. The effect-concentration relationships were analysed according to the equation L = 10 (log k+a.log (s-b] which can be viewed as a special case of the Hill equation assuming that the stimulation (s) is of very low intensity compared to the stimulus at which half of the maximum response would be obtained and introducing an absolute limit for a stimulus at which no response is obtained.

The concentration-effect relationship of quinine-induced hearing impairment

Quinine‐induced reversible hearing impairment at the frequencies of 1000 and 2000 Hz was investigated in healthy volunteers to analyze the plasma concentration‐effect relationship of the drug. Six subjects were given two identical oral doses of quinine and a constant rate infusion of quinine over 6 hours (15 mg · kg−1) on three separate occasions. A simple pharmacodynamic model, E = k · Cγ (in which E is effect, k is a proportionality constant, C is drug concentration, and the exponent γ is a fitting parameter), was found to describe well the relationship between hearing impairment and quinine concentrations in a hypothetical effect compartment. No statistical differences were found in the estimated parameters when the three dosings were compared, indicating that quinine‐induced hearing impairment is independent of route of administration. The first‐order rate constant (keo), linking plasma concentrations to the concentrations in the effect compartment, was (mean ± SD) 0.71 ± 0.19 and 0.99 ± 0.37 hr−1 for 1000 and 2000 Hz, respectively. The corresponding values of k were 0.15 ± 0.10 and 0.12 ± 0.19 and the values of γ were 2.13 ± 0.57 and 3.44 ± 1.04 for 1000 and 2000 Hz, respectively. Effect was also analyzed by semiparametric pharmacodynamic modeling, which gave results comparable to those obtained with the link model. We conclude that a simple power function is a reliable pharmacodynamic model for describing quinine‐induced hearing impairment in healthy subjects.

Clinical study of Widex Senso on first-time hearing aid users

Using psychoacoustic tests and questionnaires, the aim of this study was to clinically test Widex Senso (WS) versus analogue hearing aids on 200 first-time wearers. Half of the participants were selected at random for fitting with the behind-the-ear model (WS C8) or the in-the-canal model (WS CX). On a group basis, WS was found to provide more benefit than a palette of 29 analogue, modern hearing aid models from 10 manufacturers. Only 3 of 100 subjects changed from WS to another hearing aid. On average, the abbreviated profile of hearing aid benefit (APHAB) (Cox & Alexander, 1995) demonstrated superior performance for WS, i.e. no conflict existed between high comfort and high speech recognition. Median aided frequency-modulated tone thresholds in the sound field were better than 25 dB HL at frequencies up to 4 kHz inclusive. A distinct mean aided improvement of speech threshold in competing speech of 2.5 dB was found in both groups.

Ultrastructural Changes in the Outer Hair Cells of the Guinea Pig Cochlea after Exposure to Quinine

The outer hair cells have been shown to have motile properties which are likely to participate in the cochlear performance. Quinine is known to induce hearing loss as well as contraction of skeletal muscles. Isolated outer hair cells and isolated cochleae from guinea pigs have been exposed to quinine, which was also injected into living guinea pigs. When a physiological response was registered, the cells and cochleae were fixed and examined by transmission electron microscopy. In the isolated cells the formation of a central microtubule core occurred and in the cochleae a swelling of the subsurface cisternae in the outer hair cells was observed. The results are discussed in the context of a proposed effect of quinine on the contractile processes of the outer hair cells.

The Role of Genetic Factors for Hearing Deterioration Across 20 Years: A Twin Study

BACKGROUND Hearing deterioration at advanced ages is associated with environmental exposures (eg, to noise and solvents) and genetic influences may also be important. Little is known about the role of genetic influences on hearing when evaluated longitudinally. We sought to investigate longitudinal hearing loss in a cohort of adult male twins to evaluate the importance of genetic and environmental factors for hearing deterioration over time. METHODS Hearing using conventional clinical audiometry was assessed in 583 male twins (128 monozygotic twin pairs and 111 dizygotic twin pairs) aged 34-79 at baseline and again two decades later. The hearing thresholds at two time points were compared at each frequency and in two different frequency regions. Genetic analyses were based on structural equation models. Bivariate Cholesky decomposition was used for longitudinal analysis. RESULTS The prevalence of hearing loss increased over time in better and worse ear. The hearing threshold shift was more pronounced in the high-frequency region, especially at 8000 Hz. Genetic influences were moderate (heritability: 53%-65%) for pure-tone averages at both lower and higher frequencies, and were of equal magnitude at baseline and follow-up. In contrast, environmental influences were of substantial importance (55%-88%) for rate of change of the hearing threshold over the 18-year period. CONCLUSIONS Genetic factors are of considerable importance for level of hearing acuity, but environmental factors are more important for rate of change over an 18-year period.