Biomedical subjects
Publications and source records attributed to B Kruger.
The advantages and disadvantages of three types of earphones for audiometric testing are discussed. Supraaural earphones continue to be recommended for this purpose, in preference to circumaural and insert types.
Several recent studies have demonstrated that the ER-3A insert earphone may sometimes be directly substituted, without recalibrating, for a TDH-39/MX-41AR earphone. However, most available data have not been reduced to a form suitable for establishing a revised estimate of the reference threshold levels. This article reports such a data analysis performed on the results of five recent studies. The mean data from the five studies are typically within 1 dB of the provisional reference threshold SPLs given by the ER-3A manufacturer for calibration in a (HA-1) 2-cc coupler. After converting the mean data to equivalent Zwislocki-coupler-type ear simulator SPLs at each of the reported audiometric frequencies (125, 250, 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz), agreement within 1.5 dB was seen with the revised estimate of minimum audible pressures given by Killion [J. Acoust. Soc. Am. 63, 1501-1508 (1978)]. Either the manufacturer's provisional SPLs or the average results from this study may be used with little noticeable difference for most purposes.
The diffuse field to ear canal sound pressure transformations determined for 26 children (34 ears) from birth to 3 years old, confirm the earlier findings [Kruger B. Ruben RJ. Acta Otolaryngol (Stockh) 1987; 103:578-85] that the external ear fundamental resonance frequency is significantly higher at birth (about 6 kHz), and decreases with age to adult values (2.7 kHz) by the second year. The transformations were measured with either single or double probe tubes (coupled to miniature microphones) that were placed in the ear canal of sleeping infants. The accuracy of the magnitude of the transformations is discussed. Previously reported implications for hearing aid selection are supported.
The Welch Allyn AudioScope is a new screening instrument that allows both audiometric testing at 500, 1000, 2000, and 4000 Hz at 25 dB hearing level and otoscopic examination. Sixty-eight patients between 3 and 9 years of age with normal hearing or a variety of hearing losses comprised the study population. Immediately after receiving an audiologic evaluation the subjects were screened with a traditional screening audiometer and two examinations with the AudioScope, performed in a clinic examining room by pediatricians and nurse practitioners unaware of the children's hearing status. The AudioScope was as accurate as traditional hearing screening in identifying children with normal hearing and those with hearing loss. Log-linear modeling demonstrated that the results of AudioScope testing were similar to those of traditional hearing screening. However, the false positive rate was higher at 500 Hz for the first AudioScope examination, suggesting the need for two AudioScope tests. The AudioScope was quick and easy to use, nonthreatening to the subjects, less expensive than a pure-tone screening audiometer, and does not require a sound-treated room.
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In cat, a small tympanic membrane (TM) perforation produces a low-frequency loss--in terms of sound pressure changes (deltaSP) in front of the TM re a 10-micronV round window cochlear microphonic (RW CM)--that varies inversely with frequency at a rate of 12dB/octave with a surgically shortened external auditory meatus (EAM). Losses were determined at the outer opening (deltaSP00) and at the TM (deltaSPTM) of four artificial EAM's of various lengths, volumes, and leakiness. In the low-frequency region, a leaky EAM produced a flat loss. In the midfrequency region, the flatness of losses was attributable to (1) the length of the EAM and (2) the location at which the loss was determined. EAM volume was not related to the configuration of the loss. Losses, under all conditions, were always identical in shape and magnitude for the open and closed systems. Clinically, hearing losses due to TM perforations are essentially frequency independent, especially in the low frequencies. The relation between voltage changes (deltaV) across the transducer and losses with different EAM's suggests that the discrepency between audiometric results and CM losses--at least in the high and midfrequencies--may be due to the use of precalibrated SPL's in clinical audiometry.
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Losses (determined by measuring microphonic responses) were essentially identical, regardless of whether produced by admittance of sound into the middle ear via perforations in the tympanic membrane (TM) or in the bulla. With SPLs monitored directly at the TM, losses increased at 12 dB/oct with inverse frequency for f less than 1 kHz, a pattern determined by the changes in the (calculated) net sound pressure acting from front and back on the TM. Clinically, hearing losses due to TM perforations are frequency-independent. The difference between the two situations has mainly to do with the use of precalibrated SPLs in Clinical Audiometry.
This is a preliminary report about the acoustic characteristics of the external ears of infants. A technique was developed to insert a probe tube that is attached to a miniature microphone into the external auditory canals of sleeping infants. The inlet to the microphone was positioned in the lateral half of the external auditory canal. A diffuse sound field (spectral density of approximately 45 dB SPL) was introduced. The microphone output was recorded, and its Fourier Transform was computed. Diffuse-field-to-ear canal sound pressure level transformations were determined for infants ranging in age from newborn to 37 months. Representative sound pressure level transformations are presented. These are shown to vary systematically with the age of the child. The resonance frequency of the external ear is high in the newborns and declines with age. The asymptotic value (approximately 2,700 Hz) is reached during the second year of life. These findings have potential implications for fitting hearing aids on infants and children.
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