Alf Axelsson

Hypersensitivity to sound: Questionnaire data, audiometry and classification

This study included consecutive case histories and audiometry of 100 patients with hypersensitivity to sounds. There are several different conditions with the symptom of hypersensitivity to sounds. Hyperacusis is one of those and is seldom described in the literature. The term hyperacusis is often used synonymously with hypersensitivity to sound. We propose that there is a specific condition that could be termed hyperacusis. Hyperacusis is often elicited by loud sounds or by a number of other traumata or diseases. It is not typical of occupational noise exposure (with the exception of exposure to music). The typical patient is relatively young, the mean age being approximately 10 years less than for a population of patients with tinnitus or noise-induced hearing loss. In addition to hypersensitivity to sound, the patients often suffer from tinnitus (86%). Sounds are frequently painful and exposure to loud sounds worsens the condition for some time. The patients often have headaches. Pure tone audiograms show normal hearing or a slight high tone loss. The uncomfortable loudness level is markedly decreased, mostly less than 90 dB HL. Patients with hyperacusis may also be divided into those hypersensitive to the loudness of sounds with a decreased pure tone uncomfortable loudness level and those hypersensitive to certain specific sounds irrespective of loudness showing relatively high pure tone uncomfortable loudness levels and decreased uncomfortable loudness levels to specific sounds. With a careful history other conditions with the symptom of hypersensitivity to sound can be excluded.

Tinnitus in noise-induced hearing loss.

Tinnitus was analysed in 94 patients with noise-induced hearing loss. Tinnitus of a pure tone character was most common followed by narrow-band noises, and a combination of these. A broad-band noise type of tinnitus was the least common finding. Tinnitus was most common at high frequencies. The suggested mean tinnitus level (in dBHL) corresponded well with the mean audiometric threshold for these patients. Most patients characterized their tinnitus as moderate to severe. Subjective tinnitus grading showed poor correlation to the audiometric threshold or to sensation level e.g. patients with a suggested tinnitus threshold corresponding to the hearing threshold could consider their tinnitus severe. The most common subjective discomforts were concentration difficulties, insomnia and decreased speech discrimination. In most cases residual inhibition was limited to 60 seconds.

Hearing in Classical Musicians

(1981). Hearing in Classical Musicians. Acta Oto-Laryngologica: Vol. 91, No. sup377, pp. 1-100.

The Laser Doppler: A Non-invasive Measure of Cochlear Blood Flow

The present investigation demonstrates the utility of the laser Doppler flowmeter to provide a measure of cochlear blood flow dynamics. Cochlear and cutaneous blood flow were compared with arterial blood pressure during and following exposure to Angiotensin II, 5% carbon monoxide, 100% oxygen, mannitol, and saline. The observations indicate that: 1) cochlear blood flow generally parallels cutaneous blood flow; however, 2) when cutaneous beds vasoconstrict (e.g., AII, alpha-agonists), cochlear blood flow parallels blood pressure; and, 3) under the influence of agents that affect peripheral and central circulation (5% CO, 100% O2), cochlear blood flow may dissociate from cutaneous blood flow and blood pressure. The implications of these findings are discussed in terms of local control mechanisms that may be involved in the inner ear vasculature.

Immediate Noise Effects on Cochlear Vasculature in the Guinea Pig

Nine guinea pigs were exposed to a 4 kHz narrow band noise at 120 dB for 30 minutes. The animals were killed immediately following exposure and the cochlear tissues prepared using a soft-surface preparation technique. Experimental and control animals were mixed and randomly assessed without prior knowledge of the groups of which the specimens belonged. The results were analysed by computer. Statistically significant differences in the vasculature between noise-exposed and control animals of a general nature included: more changes in spiral lamina than external wall vessels, more changes in vessels facing perilymph than endolymph, and more changes apically than basally. Results indicate slight intracochlear compensations in blood flow, that could potentially maintain a more constant circulation in regions of the cochlea corresponding to the 4 kHz narrow band exposure noise. Methodological aspects of our inner ear vascular technique as well as some hypothetical explanations regarding the observed changes in the blood supply are discussed.

Is There a Relationship Between Hypercholesterolaemia and Noise-induced Hearing Loss?

Many investigators who have analysed the possible correlation between hearing loss and high serum cholesterol levels have found that hearing appears to be influenced by high blood lipids. Noise, as is well known, also influences hearing, particularly at high frequencies. It increases serum cholesterol levels during short-term experiments. The present investigation addresses the question of a possibly increased ototraumatic influence by the combination of high serum cholesterol levels and occupational noise exposure. Seventy-eight 50-year-old men with high serum cholesterol levels from a WHO study were compared with 75 50-year-old men who were randomly selected from the same WHO material. Group mean audiograms showed that hearing was similar in both groups, with a moderate high frequency hearing loss having a configuration suggestive of a noise-induced hearing loss. Analysis of the individual histories and the pure-tone audiograms showed that noise was the most predominant factor influencing hearing at any specific frequency or combination of frequencies. There was a statistically significant tendency for the high-cholesterol group that had suffered the most noise exposure, to have a high-frequency hearing loss. There was also a tendency for the low-cholesterol group to have a high-frequency loss if they had been excessively exposed to occupational noise. No further correlations were found. The present results indicate a slightly increased risk of acquiring a high-frequency sensorineural hearing loss for people who work in noisy environments and have high serum cholesterol levels.

Effect of low level acoustic stimulation on temporary threshold shift in young humans

To assess the effect of a low level acoustic stimulation on the susceptibility to noise, young human subjects were exposed to music at 70 dBA for 6 h per day during 9 days (training period). Noise sensitivity was assessed by measuring temporary threshold shift (TTS) induced by 105 dBSPL, 1/3 octave band noise at 2 kHz for 10 min. On the fifth day of the training period, a significant decrease of TTS was observed in the frequency range 3-3.5 kHz, in comparison with the baseline TTS obtained before being trained. As the training continued, the frequency range which showed a significant reduction of TTS expanded to 2-5 kHz.

Protection from noise-induced hearing loss by prior exposure to a nontraumatic stimulus: role of the middle ear muscles.

Recent evidence suggests that prior exposure to a moderate-level acoustic stimulus can reduce damage due to later exposure to the same stimulus at high intensity [Canlon et al., Hear. Res. 34, 197-200 (1988)]. To test the role of the middle ear muscles (MEMs) in this phenomenon, Mongolian gerbils were conditioned by exposure to a two-octave band of noise (1414-5656 Hz) at 81 dB SPL for 3 weeks. Either immediately afterward, or following a one week rest period, they were exposed to the same stimulus at 110 dB SPL for one hour. The ABR thresholds of these animals were compared to those seen in animals exposed at 110 dB SPL without conditioning. The MEMs of one ear in each subject were cut, to determine their role in any noise trauma protection effects. In the unoperated ears, conditioning without a recovery period did not alter the effects of the 110 dB stimulus. Conditioning followed by a one week recovery period reduced both temporary (TTS) and permanent (PTS) threshold shift. MEM section had no effect on either TTS or PTS in unconditioned subjects, and did not alter the reduction in TTS or PTS seen with conditioning. It is concluded that the noise trauma resistance provided by acoustic conditioning is not mediated by the MEMs.

The effects of noise on histological measures of the cochlear vasculature and red blood cells: A review

This paper compiles the results from seven experiments which have investigated noise exposure effects on histological measures of the cochlear vasculature and red blood cells. Two of these studies included at least two experimental conditions and all evaluated numerous histological parameters in several cochlear vessels. The combined results suggest that noise has a consistent general effect of reducing apparent cochlear blood flow as indicated by decreased RBC density, increased aggregation of RBCs, increased variability in RBC density, decreased number of RBC columns, increased vessel lumen irregularity and encroachment of perivascular cells upon the lumen wall. When considered at the level of the individual vessels, however, inconsistent results were observed. Fewer effects were noted in experiments which permitted animals to survive after the noise exposure than in those which sacrificed the animals immediately. Impulse noise resulted in more frequent vascular sequelae than did continuous noise. Further, impulse noise more frequently influenced vessels of the external wall than did continuous noise.

Hearing in Pop/rock Musicians: A Follow-up Study

In 1976, the threshold hearing levels (HLs) of 83 Swedish and British pop/rock musicians were examined with pure tone audiometry. At that time we found 13% of the musicians with a hearing loss >20 dB HL at a high frequency pure tone average (3,4,6, and 8 Wz). The aim of the present investigation was to conduct an audiometric follow-up study of these musicians 16 years after the first examination. Fifty-three of the 83 pop/rock musicians were retested in 1991 to 1992. They also filled in a questionnaire concerning occupational noise activities, leisure noise activities, general health problems and subjective symptoms related to loud music exposure. The median pure tone audiogram was within 20 dB HL at all test frequencies. On an individual basis, 63% had normal high frequency pure tone average scores and another 15% had a very limited high frequency hearing loss (≥25 dB HL). It seems surprising that pophock musicians after performing for 26 years have such well-preserved hearing. There might be a protective effect by the generally positive attitude from the musicians toward their performance and their audience. Regarding the loud and more or less continuous sound levels over 86 dBA there might also be a protective effect from a continuous contraction of the stapedius muscle.