Transient evoked otoacoustic emissions in the elderly

The purpose of this study was to analyse the changes in transient evoked otoacoustic emissions (TEOAEs) with age. We studied 232 subjects above 60 years of age with a battery of audiological tests, including TEOAEs Our criterion for the presence of TEOAEs was based on a cut-off at overall wave reproducibility 55% or overall response level 4 dB SPL. The prevalence of TEOAEs in left ears was 55.6%. No TEOAEs were found in subjects with a pure-tone average (PTA) above 40 dB HL. In the subgroup with TEOAEs, a significant decrease in overall wave reproducibility with age was found. We compared 45 normal-hearing elderly subjects with TEOAEs with a control group of 20 normal-hearing young adults The elderly had significantly lower mean overall response levels and mean overall wave reproducibility. Average hearing level was significantly higher in the elderly than in controls We conclude that the prevalence of TEOAEs decreases with age, and that the overall response level and overall reproducibility decrease with age. This decrease may not be seen in isolation from the increase in hearing threshold level.     

Frequency specificity of the auditory brainstem responses. A derived-band study

Auditory brainstem responses evoked by both clicks and 0.5 kHz tone-bursts were recorded using the derived-band paradigm in 10 normal-hearing subjects. The derived-band analyses showed a similar distribution of activity with both stimuli, the largest contributions coming from the 2-4 and 4-8 kHz bands. Neither the click nor the 0.5 kHz tone-burst is a frequency-specific stimulus, and both would appear to be unsuitable for brainstem response audiometric evaluation of the apical cochlea.     

Brain-stem responses of the cat and interaural attenuation

Summary The early auditory evoked responses have been studied in bilaterally hearing cats, and in animals with hereditary unilateral anacusis. Cross-over stimulation of the hearing ear occurs at an interaural attenuation of 50-50 dB, and all six waves of the responsare present at supra-threshold stimulus levels.This investigation has been supported by the Norwegian Research Council for Science and the Humanities through grant C.37.59-1.     

Frequency-following responses in the cat

The frequency-following response was studied in five cats aged 1 week to 3 years. Animals studied had either monaural or binaural hearing. Responses were recorded differentially from vertex and circumaural electrodes to tonebursts at octave intervals from 0.5 to 4 kHz. Thresholds and dynamics of the responses with and without white-noise masking were investigated. Evidence was found to support the view that the cochlear microphonic makes a major contribution to the frequency-following response, while the double frequency-following response to the 0.5 kHz stimulus is neural.     

Objective assessment of hearing aid use

Hearing aid use was assessed using both objective (time recorded in the memory of the hearing aid) and subjective methods (interview and patient diary) in a clinical series of consecutive adult female and male Finnish and Norwegian hearing aid candidates (n = 84). The median study time was 34 days (minimum 21, maximum 73). Over a third of the subjects used their hearing aid for less than 4 hours a day according to an objective assessment. Both of the subjective methods tended to overestimate the use. This preliminary study shows that an objective assessment of hearing aid use is needed and the subjective methods must be validated.     

Sleeve gastrectomy,but not duodenojejunostomy,preserves total beta-cell mass in Goto-Kakizaki rats evaluated by three-dimensional optical projection tomography

Background

In type 2 diabetes mellitus, there is a progressive loss of beta-cell mass. Bariatric surgery has in recent investigations showed promising results in terms of diabetes remission, but little is established regarding the effect of surgery on the survival or regeneration of pancreatic beta-cells. In this study, we aim to explore how bariatric surgery with its subsequent hormonal alterations affects the islets of Langerhans.

Methods

Twenty-four Goto-Kakizaki rats were operated with duodenojejunostomy (DJ), sleeve gastrectomy (SG) or sham operation. From the 38th week after surgery, body weight, fasting blood glucose, glycosylated hemoglobin, mixed meal tolerance with repeated measures of insulin, glucagon-like peptide 1, gastrin and total ghrelin were evaluated. Forty-six weeks after surgery, the animals were euthanized and the total beta-cell mass in all animals was examined by three-dimensional volume quantification by optical projection tomography based on the signal from insulin-specific antibody staining.

Results

Body weight did not differ between groups (P _g = 0.37). SG showed lower fasting blood glucose compared to DJ and sham (P _g = 0.037); HbA1c levels in SG were lower compared to DJ only (p < 0.05). GLP-1 levels were elevated for DJ compared to SG and sham (P _g = 0.001), whereas gastrin levels were higher in SG compared to the two other groups (P _g = 0.002). Beta-cell mass was significantly greater in animals operated with SG compared to both DJ and sham (p = 0.036).

Conclusion

Sleeve gastrectomy is superior to duodenojejunostomy and sham operation when comparing the preservation of beta-cell mass 46 weeks after surgery in Goto-Kakizaki rats. This could be related to both the increased gastrin levels and the long-term improvement in glycemic parameters observed after this procedure.