Eur J Appl Physiol (1992) 65:403-408

Applied Physiology Journal of

and Occupational Physiology © Springer-Verlag1992

Age variation in the upper limit of hearing Shintaro Takeda, Ikuharu Morioka, Kazuhisa Miyashita, Akeharu Okumura, Yoshiaki Yoshida, and Kenji Matsumoto* Department of Hygiene, Wakayama Medical College, 27 Kyubancho, Wakayama, 640, Japan Accepted May 26, 1992

Summary. The upper limit of hearing was measured in 6105 otologically normal ears of subjects ranging in age from 5 to 89 years. The results are as follows: in each age group from 5 to 59 years in both sexes, the upper limit of hearing showed an approximately normal distribution if a logarithmic scale was used for the upper limit of hearing axis. The mode of the distribution shifted to a lower frequency with increasing age. Over age 60 years, the distribution became much wider. Standard upper limit age curves were established by calculating 10th, 25th, 50th, 75th and 90th percentiles for each age group. From early childhood where no age variation was recognized in conventional audiometry, deterioration of the upper limit of hearing was already in progress. This deterioration was slight between ages 25 and 39 but at ages over 40 it was accelerated and led to socalled presbycousis. The upper limit of hearing was found to be one of the best parameters for showing the quantitative age-related changes in hearing.

Among physiological functions, acoustic acuity has been found to decrease progressively with age; hearing impairment begins somewhere during the fourth decade of life, affects initially the highest frequencies, and accelerates with age [Corso 1963; Robinson and Sutton 1979; International Organization for Standardization (ISO) 1982]. Recent advances in acoustic instrumentation now permit the assessment of hearing levels in the high frequency range from 8 to 20 kHz (Harris and Myers 1971; Fausti et al. 1979; Gauz and Allen 1983). High frequency audiometry has been primarily studied in presbycousis (Robinson and Sutton 1979; Rosen et al. 1964; Rosen and Rosen 1971), noise induced permanent threshold shift (Corliss et al. 1970; Erickson et al. 1980; Fausti et al. 1981), ototoxicity (Jacobson et al. 1969; Dreschler et al. 1985), and miscellaneous clinical applications (Osterhammel 1980; Gauz et al. 1986; Dieroff

Key words: Upper limit of hearing - Ageing - Auditory acuity

Table 1. Age and sex distribution of the subjects Age (years)

Males subjects (n)

Introduction Physiological functions of various organs have been studied with some parameters showing age-related changes. The rate of change with age varies among individuals so much that biological age, as distinct from chronological age, has been widely studied by multivariate analysis using various age-related parameters (Furukawa et al. 1975; Webster et al. 1976; Borkan and Norris 1980; Dubina et al. 1984). Choosing the correct agerelated parameters is very important in these studies when predicting biological age. * Present address: Department of School Health, Faculty of Education, Tottori University, Tottori, 680, Japan Correspondence to: I. Morioka

Females ears (n)

subjects (n)

ears (n)

5- 9 10-14 15-19 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-89

179 201 120 133 91 82 74 100 98 69 51 67 104 86 97 62

341 380 224 246 166 147 129 170 160 108 75 92 130 95 90 44

154 202 194 187 94 65 88 148 140 146 111 120 215 140 123 95

295 384 366 348 173 118 155 255 232 232 168 169 275 157 115 66

Total

1614

2597

2222

3508

404

and to set standard ageing curves as one of the best parameters for the purpose of evaluating the age-related changes in hearing.

and Schuhmann 1986). However, a number of differences may be discerned such as test methods, reference values of hearing, signal characteristics and equipment, and so forth, hindering comparisons of the results of such studies. Moreover, the appropriate parameter which can be easily measured has never been established, making it difficult to analyse statistically factors effective to age-related changes in hearing. Recent research in our laboratory, in which we have measured the upper limit of hearing with fixed intensity and changing frequency, has led us to conclude that the test procedure for measuring the upper limit of hearing with the equipment used yielded precise and reliable data, and was hardly affected by background noise (Takeda et al. 1992). The present research was designed to clarify the age variation in the upper limit of hearing

Frequency Counter I FeUnnC~nr

Methods Subjects. The subjects were healthy individuals ranging in age from 5 to 89 years from Wakayama, Nara and Hyogo prefectures of Japan. A preliminarily check of each subject's history was made and a conventional audiometry test was done. If subjects had been exposed to drugs or to noise levels harmful to hearing, or their audiogram showed deafness of unknown origin, they were excluded. One ear of a subject was excluded if it showed evidence of otitis media, low frequency impairment, or apparent diseases of the tympanic membrane. The subjects finally accepted comprised 6105 otologically normal ears. Table 1 presents the age and sex distribution of the subjects.

Test procedure. New equipment was designed for measuring the upper limit of hearing (Fig. 1). The test stimuli were generated continuously with a function generator set to produce stimuli from 0.5 to 50 kHz. The stimulus output was monitored by a frequency counter. The stimuli were passed through an attenuator to an amplifier, the output of which was fed into a headphone. The headphone was constructed of an ear-cap, an adapter and a 0.5 inch condenser microphone (Bruel and Kjaer, 4134), fitted tightly in the centre of the cavity. It was coupled to the subject's head in a conventional manner. Its output sound pressure level was steady at 7 5 + 10 dB within the frequency range from 0.5 to 25 kHz. Figure 1 also gives a diagram of the headphone.

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Fig. 1. Block diagram of the measuring equipment of the upper limit of hearing and diagram of the headphone. The output level was 10.0 V (root mean square) at 80 dB. The polar potential was set at 150 V DC

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The headphone was fitted to the test ear so that the subject could hear comfortably and an earmuff of the same shape was put on the opposite ear. Output frequency was gradually and continuously changed from high frequency, which the subjects were unable to perceive as a tone, to low frequency. The upper limit of hearing was the frequency which the subjects first perceived as a tone and it was shown on the frequency counter of the equipment. After three to five trials, if the results showed little variation, the upper limit of hearing was the median value of the five measurements. These measurements were taken in a quiet room where the background noise level was below 60 dB [32-56 dB(A)].

Results

Figure 2 shows the variation with age of the hearing threshold levels of each frequency. Levels began to increase clearly after the mid-forties. In particular, the threshold levels at 4 kHz and 8 kHz increased progressively. Over age 50 years, the threshold level of males at 4 kHz was significantly greater than that of females (P