Effect of ipsilateral and contralateral low-frequency narrow-band noise on temporary threshold shift in humans.
OBJECTIVE
To evaluate the effect of ipsilateral and contralateral low-frequency (250 Hz) narrow-band noise (NBN) on the temporary threshold shift (TTS) induced by a 2 kHz tone in young normally hearing subjects with a functioning auditory efferent system.


METHODS
Sixteen young volunteers served as subjects. All the subjects were young (20-30 years), disease-free and had a medical history negative for otological disease, noise exposure and use of ototoxic drugs. They had normal hearing [thresholds of 125-8,000 Hz below 20 dB hearing level (HL)], transient-evoked otoacoustic emissions and contralateral suppression. The subjects were randomly assigned to one of three different groups. Subjects in Group A (n = 5) were exposed to a 90 dB HL 2 kHz pure tone for 10 min. Subjects in Group B (n = 6) were exposed to a 90 dB HL 2 kHz pure tone and an ipsilateral 45 dB HL 250 Hz NBN for 10 min. Subjects in Group C (n = 5) were exposed to a 90 dB HL 2 kHz pure tone and a contralateral 45 dB HL 250 Hz NBN for 10 min. The right ear served as the test ear. The TTS 2 min after the end of the exposure (TTS2) was measured in all subjects at 2, 3 and 4 kHz.


RESULTS
TTS, in Group A was significantly higher at 3 kHz (p = 0.011) and at 4 kHz (p = 0.003) than TTS2 in Group B. At 4 kHz, TTS2 in Group C was significantly higher (p = 0.013) than TTS2 in Group B. Although TTS2 in Group C was lower than TTS2 in Group A, this difference was not significant. The presence of an ipsilateral low-frequency NBN significantly reduced TTS2 induced by a 90 dB HL 2 kHz tone. A contralateral low-frequency NBN reduced TTS2 in this group of subjects; however, the reduction was not significant.


CONCLUSIONS
The results of this study show that an ipsilateral low-intensity, low-frequency (250 Hz) NBN can give protection from a TTS induced by a 2 kHz tone. Contralateral low-frequency NBN did not induce any protective effect.
Quaranta
Antonio
A
Department of Ophthalmology and Otorhinolaryngology, ENT Clinic "G. Lugli", University of Bari, Bari, Italy. otorino1@orl.uniba.it
Scaringi
Angelo
A
Fernandez-Vega
Susana
S
Quaranta
Nicola
N
D000161:Acoustic Stimulation; D000328:Adult; D000704:Analysis of Variance; D001301:Audiometry, Pure-Tone; D001305:Auditory Fatigue; D001309:Auditory Threshold / Q000502:physiology*; D015331:Cohort Studies; D005260:Female; D006317:Hearing Loss, Noise-Induced / Q000503:physiopathology; D006801:Humans; D008297:Male; D009622:Noise / Q000009:adverse effects*; D011336:Probability; D012016:Reference Values; D012680:Sensitivity and Specificity