A quasi-free-field transducer system for high-frequency audiometry

Aging and high-frequency hearing sensitivity

As part of a large population-based study of hearing and aging, ultra high-frequency (9-20 kHz) threshold measures are reported for 3396 participants grouped by age (48-59 years, n = 1233; 60-69 years, n = 1031; 70-79 years, n = 851; 80-92 years, n = 281). Ultra high-frequency (UHF) thresholds were higher for older age groups. The percentage of unmeasurable responses also was significantly higher for older age groups and for higher frequencies in the UHF range. The observed age effects remained significant after adjusting for gender. In general, UHF thresholds were significantly higher for men compared to those for women at lower UHF frequencies (9-14 kHz), but were not significantly different by gender for the highest UHF frequencies (16, 18, and 20 kHz). After accounting for hearing loss at traditional audiometric frequencies (250-8000 Hz), the age effect still remained; even for comparable degrees of sensorineural hearing loss, participants in older age groups evidenced higher UHF thresholds.

Extended high frequency audiometry in pre-school children

Since adequate and reliable earphones are now available and standards have been established, clinical audiometry can be performed at extended high frequencies (EHFs). In the present study, 47 preschool children (aged 4-7 years) were examined with EHFs (8-16 kHz) using the new Sennheiser HDA 200 earphone. The hearing thresholds correspond to those of other studies; the median thresholds and range increase with increasing frequency. The medians and quartiles were: 10 kHz: 25 (5-35) dB(SPL), 11.2 kHz: 35 (20-40) dB(SPL), 14 kHz 40 (30-50) dB(SPL) and 16 kHz: 50 (40-60) dB(SPL). The hearing thresholds could be more reliably determined in the older children (> 5 years) and were 5 dB better than in the younger ones (< 5 years). Thresholds in the 10-12.5 kHz range correspond to those of adults but are more sensitive by 5-12 dB in the 14-16 kHz range.

Effects of adverse perinatal events on hearing

The hearing sensitivity for frequencies 8 kHz through to 18 kHz was compared between children with adverse perinatal factors (study group) and children without adverse perinatal factors (control group). Children in both groups had hearing at levels of 20 dB HL or better in the frequency range between 250 Hz to 8 kHz with normal middle ear pressure. High frequency hearing tests showed that the mean high frequency hearing threshold levels were worse in the study group. Statistical analysis showed significant differences in hearing levels at and above 12 kHz frequencies between the study and control groups. The hearing levels were found to be more significantly affected in females as compared to males, indicating that the high frequency hearing of females was more vulnerable to damage. The results indicate that adverse perinatal events are associated with raised high frequency thresholds in both sexes, especially in females.

High-frequency air conduction audiometry. Testing of a new low impedance circumaural transducer system in normal young persons

A new circumaural transducer was tested in the frequency range 125 Hz to 20 kHz. The new transducer has a low acoustic impedance and loads the ear closely to free-field conditions, thus ensuring that sensitivity to different positions of the transducer around the ear is reduced compared to conventional audiometric headphones. The transducer was tested on 57 individuals (114 ears) in the age range 10 to 20 (median age 17.0 years). The results, showing a fairly good accordance with the ISO standard free-field thresholds values, seem to confirm that the new transducer system loads the ears similarly to free-field conditions. The results were also compared with the threshold values from other high-frequency investigations using different transducer systems. In order to verify the reliability of the system, a test-retest was carried out on 12 inexperienced normal individuals (24 ears) (median age 26.5 years; range values from 22 to 44 years). The standard deviations of the test-retest ranged from 2.8dB to 6.6dB. A comparison of these values with the results from other high-frequency test-retests is of dubious value, as such retests have often been performed and estimated in different ways. International standards for high-frequency audiometry threshold and international standards for test-retest procedure are needed. The increasing administration of cytotoxic drugs in the treatment of malignant diseases will increase the need for reliable high-frequency audiometry equipment.

The effects of occupational exposure to styrene on high-frequency hearing thresholds

Subchronic exposure to styrene has been reported to produce high-frequency hearing loss in rats. In humans, hearing thresholds for higher frequencies (greater than 8 kHz) are also more vulnerable to ototoxic drugs than those at lower frequencies. Since hearing loss at frequencies above 8 kHz does not seem to play a role in speech processing, hearing loss at frequencies above 8 kHz in workers exposed to styrene or other solvents might easily escape detection. Therefore, hearing thresholds were evaluated at frequencies up to 16 kHz in workers exposed to styrene and compared to those of a control group of unexposed workers. The airborne concentrations of styrene typically did not exceed 150 mg/m3 although individual exposures did, at times, reach higher values (up to 700 mg/m3). In accordance with the literature, an age-dependent increase in hearing thresholds at high frequencies was found. Compared to controls, workers exposed to styrene did not appear to demonstrate an aggravated age-dependent decrease in hearing high frequencies. A comparison, however, within the experimental group between the least exposed and the most exposed workers revealed a statistically significant difference on hearing thresholds at high frequencies.

High-frequency audiometry in children

On the grounds of recent literature and of their own previous studies, the authors have examined a group of 25 normal-hearing children, ranging from 7 to 10 years of age, with high-frequency audiometry. The results were compared with those obtained in a group of young adults. On the basis of these findings, average threshold values were derived for this age group; such data have not yet been published for this simple headset technique. Furthermore, the comparison between the two age groups enabled the authors to determine a deterioration of the high-frequency hearing threshold which takes place at a fairly early age. Reliability of the equipment, in which headphones were used as transducers, was checked and the reproducibility for this test was shown to be adequate, as seen from the low test-retest variability.

Cumulative and acute toxicity of repeated high-dose tobramycin treatment in cystic fibrosis

Forty-six patients with cystic fibrosis and chronic bronchopulmonary Pseudomonas aeruginosa infection entered a study of tobramycin-related chronic and acute nephro- and acousticovestibular toxicity. The patients (mean age, 15.7 years) had previously received 2-week courses of tobramycin therapy, for a mean cumulative total of 279 days each. The cumulative tobramycin dose ranged from 632 to 7,644 mg/kg. The patients were studied before and at the end of a 2-week course of treatment with tobramycin (10 to 20 mg/kg per day) to discriminate between acute and chronic toxicity. In patients studied at the beginning of the present course of treatment, the glomerular filtration rate, measured as 24-h creatinine clearance, did not correlate with the cumulative dose of tobramycin received during previous courses. Eighteen patients (39%) had a reduced glomerular filtration rate compared with normal values (mean, 12.5% reduction) but normal serum creatinine values. Two patients (5%) had a high-frequency hearing deficit (above 8 kHz), but only one deficit was possibly related to tobramycin. No chronic vestibular toxicity was observed. During the course of treatment, no patients developed acute nephrotoxicity. After 2 weeks of treatment 32% had a slightly reduced hearing threshold (15 to 30 dB) in two or more high frequencies, and 28% had a fall in vestibular response greater than 25% of the initial value but remained within normal limits. Thus, the acute and chronic toxicity of repeated high-dose tobramycin treatment in cystic fibrosis patients seems to be very mild.

Influence of different kinds of noise on the ear and some physiological and psychological parameters

The reactions of the human organism to noise are complicated and difficult to separate from other stressors, with the exception of hearing damage. After thorough experimental planning and a rigorous selection of sample persons, the reaction to noise of varying structures was studied by reactions of heart rate, blood pressure, reaction time, the temporary threshold shift (TTS) of hearing and the psychological parameters "Mood" (in German "Befinden"). We found a special kind of TTS dependent on the structure o noise and no effect of physiological parameters. The psychological parameter tended to have a significant influence on individual factors.

High-frequency audiometry using precision earphones: reliability under laboratory and field conditions

New circumaural earphones were tested in the frequency range from 100 Hz to 20 kHz and compared to commonly used supra-aural earphones. The circumaural earphone HD 230 (Sennheiser) generates test stimuli at up to 20 kHz with almost constant sound pressure levels when its pos ed on an artificial ear. The reproducibility of hearing threshold mea ed with a new microprocessor-controlled Békésy audiometer using the ne was nearly as good as under free-field conditions. The practicabil diagnostic value of high-frequency audiometry have been demonstrated er field conditions. For this application, the good sound attenuation these earphones (30 dB above 1 kHz) are important. High-frequency he ds of healthy pupils and of pupils with a history of otitis media are kHz, the hearing threshold level difference between both groups reached 20 dB.

High-frequency audiometry above 8 kHz. Comparative results of normative thresholds obtained with a headphone system and a quasi-free-field system

Since a standard method for high-frequency audiometry does not yet exist, the authors, using 20 young subjects, compare the results obtained with a quasi-free-field system devised by Osterhammel et al. [Scand. Audiol. 6:91-95, 1977] and those obtained by a headphone system. The headphone system is considered to be better, because it offers many practical advantages.

Extra-high-frequency auditory thresholds: fine structure, reliability, temporal integration and relation to ear canal resonance

Three trained subjects were repeatedly tested for detection of auditory thresholds at 27 frequencies, from 2 to 18 kHz. A double-blind procedure was used with the method of adjustment, and the quasi-free-field delivery system of Osterhammel et al. [Scand. Audiol. 6:91-95, 1977] was used to monaurally stimulate the ear. A very reliable series of high- and low-threshold changes, termed the fine structure of the extra-high-frequency audiogram, was observed from 8 to 16 kHz. All 6 ears had a major low-threshold region at or near 13.5 kHz, and up to 3 other replicable sensitive frequencies along this one octave range. Thresholds were invariant over 3 conditions of stimulus presentation (constant tone; 500 ms duration, 25 ms rise and decay, 1 s interstimulus interval; and 100 ms duration, 1.5 ms rise and decay, 200 ms interstimulus interval). As the duration of the tone was decreased from 100 to 5 ms, temporal integration (an average of approximately 2.5 dB threshold increase as the duration was halved) was noted. Although temporal integration was slightly less at higher frequencies, the shape of the audiograms remained essentially unchanged as the stimulus duration was decreased to 5 ms. There was no consistent relationship between the maximally sensitive high frequencies and the amount of temporal integration. But there was a general association between the maximally sensitive high frequencies and the resonant frequency characteristics of that particular ear.

High-frequency audiometry. Normative studies and preliminary experiences

A new, commercial high-frequency audiometer, Demlar 20K, for measuring hearing thresholds between 8 and 20 kHz has been used routinely in different patient groups and in a control population over the past 3 years. Test-retest studies have shown that this instrument can be used in the clinic with approximately the same degree of reproducibility as in conventional audiometry. While inter-subject variation is comparatively large, repeated evaluations can be performed in individual cases with an acceptable degree of reliability. This techniques can be helpful in differentiating between noise damage and presbycusis. Pre- and post-operative high-frequency audiometry may prove to be of value in the assessment of middle ear surgical techniques.

Extra-high-frequency noise remotely masks and alters temporal integration at lower frequencies

A quasi-free-field technique was used to assess the effects of extra-high-frequency-band masking on detection threshold of middle and high (1-7 kHz) frequencies. At an SPL of 60 dB, the 10- to 20-kHz masker produced a slight amount of masking. Increasing the masking level by another 5 dB produced a disproportionate increase of the detection thresholds. This increase was greatest in response to 4- and 5-kHz stimuli, and was detected with both constant and pulsed tones. Decreasing the bandwidth of the masker reduced the magnitude of the effect, but not the frequency-specific pattern of the remote masking. Extra-high-frequency masking also increased the amount of temporal integration at middle and high frequencies. The data are discussed in reference to peripheral and central neural changes associated with sensorineural hearing loss.

Ultrahigh-frequency auditory thresholds in young adults: reliable responses up to 24 kHz with a quasi-free-field technique

A quasi-free-field technique was used to assess detection thresholds to pure tones, at frequencies ranging from 2 to 24 kHz. The sound delivery system of Osterhammel et al. [Scand. Audiol. 6:91-95, 1977] was modified in order to deliver constant stimuli at SPLs of at least 117 dB over the entire frequency range. A modified form of the method of adjustment maintained the subjects' interest, and a double-blind procedure minimized experimenter and subject bias. In the first experiment, 78 university subjects from Northern California (18-24 years old) were exposed to tones in 2-kHz increments. All but 12 of these persons could reliably detect the highest frequency, with females being slightly more sensitive. But from 10 to 20 kHz, there were no differences between the sexes. In a second group of 20 students, tested in 1-kHz increments from 8 to 16 kHz, the previously observed 10- to 14-kHz threshold plateau was revealed as a pronounced 13-kHz low-threshold region. The threshold at this frequency was approximately 14 dB lower than the 11-kHz threshold. These data were compared with those obtained in a similar fashion from other cultures.

'Quasi free-field' audiometry: proposal for a modified transducer system

The authors studied a group of 13 young adults by using high-frequency techniques in 'quasi free-field' conditions, as suggested by Osterhammel, and comparing the results with those obtained by means of an original method suggested by the present study group. The data relative to this last-mentioned technique confirmed it as being valid on the grounds of test-retest findings and standard deviation. It is concluded that both methods are equally effective for the study of the physiology of the ear, but that the present method is less practical from the clinical point of view.

An evaluation of high-frequency audiometry suitable for routine clinical use

The evaluation of high-frequency thresholds above 8 kHz has not always been accepted as a reliable, reproducible measure in routine audiological clinics. Using standard equipment we have shown that thresholds at 10 kHz and 12 kHz can be so measured, and that 16 kHz thresholds may be determined with the same degree of reliability with only the minor addition of a signal generator and a set of high performance earphones.

High frequency audiometry and stapedius muscle reflex thresholds in juvenile diabetics

Sixty-one juvenile, insulin-treated diabetics below 50 years of age with a duration of diabetes mellitus longer than 10 years underwent impedance audiometry with determination of stapedius reflex thresholds at 500 Hz, 1, 2, and 4 kHz, conventional pure tone and speech audiometry, and high-frequency audiometry up to 20 kHz. The results were compared with a normative material of non diabetic subjects selected after exactly the same criteria. No significant differences in hearing or stapedius reflex thresholds were found. Among half of the subjects there was a diabetic retinopathy. A comparison between those with and those without retinopathy did not reveal any significant difference in audiological findings. Even subjects with severe diabetic complications and almost life-long diabetes had normal hearing. Recent investigations on plasma-lipoids have discussed the possibility that insulin might prevent a premature ageing of hearing which has been reported by other authors. It is concluded that no statistical data exist that confirm a correlation between hearing impairment and diabetes.

High frequency audiometry. Clinical aspects

For 2 years past a previously described quasi-free-field high frequency audiometer delivering pure tones from 4 to 20 kHz has been incorporated in the audiological test battery. By this technique it is possible to obtain reliable and reproducible thresholds above the age of 8--9 years. In several case histories it is illustrated how high frequency audiometry (HFA) contributes to a better audiological diagnostic and it is predicted that HFA is of value in research studies on presbycusis, ototoxicity, noise vulnerability, and in hereditary studies on deafness. The physiological presbycusis demands normative reference values for each age decade. Many other factors, however, can cause an impaired high frequency hearing which is a severe limitation to the diagnostic value of abnormal findings.

High-frequency audiometry. Age and sex variations

286 normal subject representing both sexes and seven age groups from 10 to greater than or equal to 70 years were tested with both conventional pure tone audiometry and high frequency audiometry (4--20 kHz) using a previously described free field system. The subjects were selected according to very strict criteria. Results from conventional audiometry are similar to other findings in presbycusis studies, though sex difference was seen for the oldest age groups, but only at the frequencies 4 and 5 kHz where the male population showed a significantly poorer hearing. The same sex difference was observed by high frequency audiometry at 4 and 8 kHz. From 10--20 kHz no sex difference was present. At the high frequencies there is an abrupt decrease in hearing sensitivity already from youth. Hitherto, no international standard for zero dB hearing level exists for frequencies above 8 kHz. It is questioned whether a general standard is meaningful at all and that normative data for various age groups should instead be used as a reference level.

High-frequency audiometry and noise-induced hearing loss

A group of noise-exposed male subjects with an audiogram that is characteristic for noise trauma were submitted to high-frequency audiometry (HFA) up to 20 000 HZ. The results were compared with those obtained in a group of normally hearing persons with no history of noise exposure. Conserved high frequency hearing was found. Very strict selection criteria were applied in both groups in order to avoid hereditary diseases and to ensure normal middle ear function. The findings are in good overall agreement with histological findings in noise-exposed animals and also with high-frequency studies in the older literature. Two illustrative case stories from patients with severe 4--6 kHz dips are reported, one with preserved high-frequency hearing in spite of a considerable acoustic trauma and one with extreme sensitivity towards noise and with no hearing at all in the high frequencies. It is concluded that 1) HFA cannot be used as an early indicator of the traumatic effect of high intensity noise; 2) presbycusis and noise damage may be additive elements in the older age groups (above 50 years); 3) persons with abnormal high-frequency hearing are possibly hypersensitive towards excessive noise and HFA might be useful in the routine audiological evaluation of workers before these are exposed to noise.

High-frequency thresholds using a quasi-free-field technique

A free-field transducer system for high-frequency audiometry was applied on two groups of otologically normal, non noise-exposed subjects tested at the frequencies 4--8--10--12--14--16--18--20 kHz. The former group consisted of 46 children 10--12 years old and the second group of 40 adults aged 18--24 years. All participants in the youngest group were able to hear 20 kHz and no difference between right and left ear or between sex could be shown. A similar result was found in the adult group except that 4 males were unable to hear 20 kHz. Hearing thresholds for the two groups were almost identical at 8--14 kHz. Above this frequency range the youngest group showed a statistically significant lower threshold at 18 and 20 kHz. This group might be used for a zero-dB hearing threshold level in further high-frequency studies. The advantage of transferring the SPL value from the entrance to ear canal to absolute ear drum pressure level is discussed.