Click- and tone-burst-evoked otoacoustic emissions in normally hearing ears and in ears with high-frequency sensorineural hearing loss.

Otoacoustic emissions (OAEs) evoked by clicks and tone bursts (TBs) were measured using a minor modification of the 1987 Bray and Kemp system in normal and hearing-impaired ears with high-frequency sensorineural hearing loss. Sixty ears of 60 subjects were tested. The average behavioral hearing threshold of 20 normally hearing ears was measured for the different "nonlinear" stimulus groups and defined as 0 dBnHL. Emissions were recorded in another 20 normally hearing ears and in 20 ears with steep high-frequency sensorineural hearing loss above 2kHz. An unfiltered click of 80 microseconds duration and TBs at frequencies of 0.5, 1, 2, 3, 4, 5, and 6 kHz served as stimuli. The ears with high-frequency hearing loss were clearly distinguished from the normal ears in that emission energy decreased with higher frequency stimuli above 2 kHz. The mean slopes of the response-growth functions were significantly higher at lower audiometric thresholds. The normal ears showed a slope of 0.21-0.35 dB/dBnHL above 2 kHz while the slope of the pathological ears was 0.04-0.13 dB/dBnHL. These differences in TBOAEs could possibly be used clinically to carry out hearing tests that are more frequency-specific than those measuring solely click-evoked OAEs. Pathological ears had emissions in the lower frequency range, where they had a normal audiometric threshold. However, these emissions had significantly far lower amplitudes at frequencies around 0.5 and 1 kHz when compared to normal ears. This reduced emission energy may indicate a cochlear impairment of the pathological ears in frequency ranges where they still had normal audiometric thresholds.

[Clinical use of click evoked oto-acoustic emissions at the Freiburg ENT clinic]. / Zur klinischen Anwendung Click-Evozierter Otoakustischer Emissionen an der Freiburger HNO-Klinik.

Click-evoked otoacoustic emissions appear to be an efficient way to assess cochlear function in infants and neonates. A new technique developed by Bray and Kemp (1987) enables data to be gathered under clinical conditions. A total of 310 children aged between one day and five years were examined in a realistic clinical situation: 204 of them were admitted to the authors' outpatient department for evaluation of a hearing impairment and 106 were special-care babies or normal newborns. Otoacoustic emissions were successfully tested in 244 of these 310 children at the first attempt after performing behavioural tests. A classification of the emissions by the coefficient of the cross-correlation function and the frequency response spectrum was used. Emissions were observed in 95% (n = 181 ears) of the three- to five-year-old children with a mean behavioural threshold better than 20 dB. In 82% (40/49) of the special-care babies and in 89% (51/57) of the normal newborns a successful emission recording was be obtained. Such findings suggest that this technique for detecting emissions may be useful in early diagnosis of hearing impairments, especially when combined with simple behavioural tests.

Bioavailability of zinc from zinc-histidine complexes. I. Comparison with zinc sulfate in healthy men.

Zinc supplementation is beneficial in some clinical conditions. Histidine has been shown to improve zinc absorption in animals. To test its influence on zinc absorption in humans, we studied the bioavailability of zinc from zinc-histidine complexes as compared to zinc sulfate in 10 healthy volunteers. Ingestion of zinc complexed with histidine at a ratio of 1:2 or 1:12 increased serum-zinc concentration 25% more than ingestion of zinc sulfate. Calculated uptake was 30-40% increased with zinc histidine over zinc sulfate. Urinary excretion was not different with any preparation. Application of 15 mg zinc as zinc histidine 1:2 gave an identical serum-zinc response as 45 mg zinc taken as zinc sulfate. Zinc histidine complexes are better absorbed than zinc sulfate in humans.

Bioavailability of zinc from zinc-histidine complexes. II. Studies on patients with liver cirrhosis and the influence of the time of application.

Supplementation may benefit patients with liver cirrhosis. Zinc uptake from zinc-histidine complex 1:2 was assessed in eight patients with liver cirrhosis. Influence of the time of application was also studied. Compared with healthy controls, patients showed a 40% lower uptake of zinc after 20 mg zinc from zinc histidine. Bioavailability was identical when zinc was taken 6 h or 1 h before a meal but an order of magnitude greater than with or 1 h after a meal. No significant increase of serum zinc was found when zinc was given with a meal or 1 h after. Lower doses of zinc-histidine complexes than of zinc sulfate may be used to supplement patients with liver cirrhosis. Time of application is of great importance if this substitution is to be successful.