Effect of middle ear effusion on distortion product otoacoustic emissions

Otitis media with effusion is a very common childhood disease which has negative effects on the feasibility of recording of otoacoustic emissions. The aim of the present study was to determine the influence of different types of effusion on distortion product otoacoustic emissions [DPOAE]. Preoperative and first postoperative day DPOAE signal to noise ratio were compared in 50 children [100 ears] undergoing myringotomy and/ or tympanostomy tube insertion for secretary otitis media. The results were analyzed by paired samples test and ANOVA. In the preoperative evaluation, glue effusion caused a significant reduction in DPOAE at 2, 4 and 8 kHz [p<0.05] compared to serous or mucous effusion. Comparison between preoperative and first postoperative day DPOAE signal to noise ratios showed significant differences at 1, 1.5, 2 and 4 kHz [p< 0.05]. On the first postoperative day, the maximum increase in emission was observed at 2 kHz in ears which previously showed glue effusion. Glue effusion causes a reduction in DPOAEs at 2, 4 and 8 kHz more than other types of effusion

Effect of hypotensive anaesthesia on cochlear function

During surgery of the small structures of the middle ear, even minor bleeding can impair the surgeon's ability to operate under an optical microscope. Hypotensive anaesthesia is effective in keeping bleeding to a minimum. However, preliminary results showed that cochlear function was worsened by systemic hypotension which could play a role in the pathogenesis of sudden hearing loss. By recording transient evoked otoacoustic emissions [TEOAEs] in the external auditory canal, the present study was designed to: a- Evaluate the possible auditory functional consequences of cochlear blood flow changes during hypotensive anaesthesia. b- Determine the safe mean arterial blood pressure [MAP] below which cochlear function is deleteriously affected. 20 patients scheduled for middle ear surgery received general anaesthesia with isoflurane. After 15min. of haemodynamic stability, controlled hypotension was induced by an i.v. infusion of glyceryl trinitrate. TEOAEs were recorded in the contralateral ear on the day of surgery prior to admission to the theatre [control value], and then intraoperatively during controlled hypotension at MAP of 65, 60, and 55mmHg, respectively, as well as on the first postoperative day. Statistical analysis included the arithmetic mean, standard deviation, standard error, hypothesis Student's "t", and Pearson's correlation tests. During controlled hypotensive anaesthesia, the intraoperative TEOAE amplitude decreased significantly [p<0.01] and was completely abolished at a MAP