Newswise — Loudness Discomfort Levels (LDL) measurements have been considered an important component of the hearing aid evaluation and fitting process. Historically, the measurements have been applied only to patients with hearing loss; today, some have recommended the LDL for evaluation and follow-up of tinnitus and hyperacusis patients who might present either normal-hearing or hearing loss.
Others are not so sure. Although LDL is one of the most important tests used to investigate hypersensitivity to sound, there is no consensus about the best procedure to evaluate the sound tolerance on hyperacusic subjects. It has been suggested that the procedures used to determine the maximum output for hearing aids should be modified to minimize the discomfort of hypersensitive to sound patients during testing.
As LDL depends on the patient's collaboration, some authors suggested that a direct correlation between the acoustic reflex threshold (ART, the contraction of the stapedius muscle in response to intense sound, increasing impedance of the middle ear and thereby protecting the inner ear from the sound) and the LDL might permit the use of the former to predict LDL measurements. Some experts in hearing believe the correlation would be especially useful for adapting hearing aids on children or handicapped subjects although this remains controversial.
The new role of the LDL led a team of Brazilian researchers set out to systematically study the LDL on normal subjects. A secondary purpose of their research was to examine the possible correlation between the values of LDL and acoustic reflex. This study is the first to investigate LDL on normal hearing patients with the objective of finding results that could be used as a normal reference values on the evaluation of patients with tinnitus and intolerance to sound (hyperacusis, misophonia and phonophobia). The method used to test the LDL was the same used on the most important centers specialized on evaluation and treatment of tinnitus and hyperacusis.
Apart from determining the median for all frequencies of LDL (86 to 98 dB HL), their results indicated a rather large standard deviation. Thus, the history of hypersensitivity to sound should strongly support the suspicion of hyperacusis, instead of only trusting the LDL values during a routine audiological evaluation. On the other hand, good reliability suggests that this test might be adequate for a patient follow-up.
The authors of "Loudness Discomfort Level for Normal Hearing Subjects: Is It a Reliable Test?" are Keila Alessandra Baraldi Knobel and Tanit Ganz Sanchez MD, PhD, both from the University of São Paulo, School of Medicine, São Paulo, Brazil. Their findings will be presented at the American Academy of Otolaryngology—Head and Neck Surgery Foundation http://www.entnet.org Annual Meeting & OTO EXPO, Orlando, FL, being held September 21-24, 2003.
Methodology: Sixty-four normal-hearing subjects with negative otological history and ages ranging from 18 to 25 years were tested in this investigation. Thirty-four were female (53.1 percent) and thirty were male (46.9 percent), with mean age of 21.8 years. Their air-conduction threshold levels were no poorer than 25 dB at the octave frequencies from 250 to 8000 Hz. Tympanograms were normal with peaks within +/-50 mm H2O and with presence of contralateral acoustic reflexes in at least three frequencies between 500 and 4000 Hz. Written informed consent was obtained from all subjects.
Pure-tone air conduction thresholds and LDL were measured. The stimuli were presented for two seconds, with one-second interval. The initial stimulus intensity was 50 dB HL followed by an ascending presentation. Each subject was instructed that this was a test of tolerance for sound intensity and was asked to respond "when the sound gets to the point which you would rather not hear it for very long". All testing was performed binaurally and immediately repeated (test and retest situation). The choice of the beginning ear was alternated. After that, tympanometry and contralateral acoustic reflexes (ART) were measured.
ResultsLDL and ART values were best fitted using a lognormal distribution function. Censured data (no response to LDL at maximum audiometer output) was considered to determine best fit the parameters of the lognormal distribution, which reduced the risk of underestimating the LDL value.
As Chi-square test showed no statistic significant difference on LDL results between ears, nor on test/retest situation, the researchers considered only the lower response of each individual. This choice was based on the inherent purpose of this test, which should give as a result the level at which one would first be annoyed by loudness. The assumption was made that with real life situation (binaural hearing) it would happen when loudness of sound reaches LDL of the more sensitive ear.
A key finding was that LDL medians are quite stable across frequencies, except for 8000 Hz. Despite the reliability of the test, a rather large standard deviation (ranging from 13.19 dB HL on 500 Hz to 17.93 dB HL on 6000 Hz) is observed. This fact may indicate that the LDL alone is not a sufficient instrument for the diagnosis of a hyperacusic patient,. Thus, the history of hypersensitivity to sound should strongly support the suspicion of hyperacusis, instead of only trusting the LDL values during a routine audiological evaluation.
Conclusion: No correlation was found between LDL and ART. The median for all frequencies of LDL varied between 86 and 98 dB HL, with no differences for right and left ears nor on test and retest situation. Inter-subject differences indicate that LDL measurements alone should be cautiously interpreted. Good reliability suggests that this test might be adequate for a patient follow-up.
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