Erratum to: Specific stressors in endonasal skull base surgery with and without navigation

European Archives of Oto-Rhino-Laryngology -     

Complex level alterations of the 2<Emphasis Type="Italic">f</Emphasis><Subscript>1</Subscript>−<Emphasis Type="Italic">f</Emphasis><Subscript>2</Subscript> distortion product due to hypoxia in the guinea pig

It is controversially discussed inasmuch acute hearing disorders might originate from impaired cochlear circulation. Hypoxia-specific alterations of inner ear parameters measurable in patients with acute sensorineural hearing loss would therefore be of great interest. Aim of this study was to characterize hypoxia-related alterations of the 2f ₁−f ₂ distortion product. Nine guinea pigs were anaesthetized by i.m. administration of Midazolam, Medetomidin and Fentanyl. For introduction of hypoxia, the spontaneously breathing animals were offered a gas mixture of N₂O and O₂ containing either 21 or 12–13% O₂. Distortion product otoacoustic emissions (DPOAEs) were continuously monitored at f ₂ = 16 kHz; f ₂/f ₁ = 1, 2; DP-definition = 2f ₁−f ₂; L ₁ = 65 dB and L ₂ = 55 dB, while inhaled oxygen was switched from 21 to 12–13% and back. Oxygen saturation (SaO₂) was continuously monitored. Data from an hypoxic interval were only used for further data processing if DPOAE levels were stable before and after hypoxia. Six hypoxic intervals in five animals fulfilled the stability criterion. During the hypoxic interval with the highest measured SaO₂ (75%), no alterations of DPOAE levels were observed. During the remaining five hypoxic intervals, when SaO₂ ranged between 57 and 70%, DPOAE levels were on average lower with an increased standard deviation compared to mean pre-hypoxic levels. Mean decrease correlated with the decrease of SaO₂ (r = 0.90, P = 0.014). Alterations followed a characteristic time course—when hypoxia was started, DPOAE levels exhibited a short increase before they decreased and remarkably destabilized. After re-oxygenation DPOAE levels showed a pronounced level decrease, while SaO₂ already had recovered to pre-hypoxic values. After reaching a minimum, DPOAE levels slowly recovered to pre-hypoxic values. The decrease of DPOAE levels during hypoxia and the post-hypoxic level alterations have similarly been described by other authors before, while the distinct destabilization and transiently increased DPOAE levels have not been explicitly mentioned. A micromechanical mechanism that might explain a transient level increase and the post-hypoxic DPOAE level changes is discussed.     

Level alterations of the 2f 1–f 2 distortion product due to hypoxia in the guinea pig depend on the stimulus frequency

Increased intracranial pressure (ICP) is known to affect the levels of distortion product otoacoustic emissions (DPOAEs) in a frequency-specific manner. DPOAEs might, therefore, be used for monitoring the ICP non-invasively. Hypoxia can also cause alterations of DPOAE levels, which can be distinguished from ICP-related changes only, when their characteristics, in particular frequency specificity, are known in detail. DPOAEs at f ₂ = 2, 4, 8, 12 and 16 kHz and oxygen saturation (SaO₂) were continuously monitored in nine spontaneously breathing guinea pigs, anaesthetized by i.m. administration of midazolam, medetomidin and fentanyl, during the respiration of a gas mixture of N₂O and O₂ containing either 30% O₂ or 13% O₂. Fourteen hypoxic intervals in eight animals were included into final data analysis. Characteristic hypoxic level alterations with a level decrease and a remarkable level destabilization during hypoxia, and a pronounced reversible level decrease after reoxygenation were observed at the frequencies of 4, 8 and 16 kHz. At 2 and 12 kHz, the only reproducible effect of hypoxia was an increased fluctuation of the DPOAE level, which was significantly less pronounced compared with the other frequencies (P < 0.05 for 12 vs. 16 and 8 kHz and for 2 vs. 16 kHz). DPOAE level alterations due to hypoxia depend on the frequency in guinea pigs. Studies in human are warranted to improve non-invasive ICP monitoring with DPOAE by the detection of hypoxia-related changes.     

Subpixel tracking for the analysis of outer hair cell movements

CONCLUSION: Videomicroscopy with subpixel analysis is an excellent system for quantification of outer hair cell (OHC) movements. The resolution of a few nanometers is accurate enough to show induced differences of electromotility. OBJECTIVE: Electromotility of OHCs is a voltage-dependent process resulting from a membrane protein named prestin. Voltage sensitivity is conferred to prestin by intracellular anions. Reduction of these anions reduces electromotility. Videomicroscopy and subpixel tracking combine video-based analysis with a resolution of few nanometers. The aim of this study was to show the feasibility of a system for quantification of OHC movements. MATERIALS AND METHODS: Electromotility was investigated under normal and reduced intracellular chloride conditions. Cells were stimulated by the patch-clamp technique. Voltage steps were 500 ms long, ranging from -170 to +30 mV in 10 mV steps. RESULTS: As in previous studies our results show the following. The direction of OHC movement depends on the polarity of voltage steps, length changes are not equal for symmetrical voltage steps of opposite polarity, average shortening for a depolarizing step (-70 mV to +30 mV) is about 13 nm/mV. Hyperpolarization (-70 mV to -170 mV) on average evokes elongations of about 3 nm/mV. Half maximal chloride concentration reduces motility by 14%; half maximal electromotility is reached by a 94% reduction of chloride.     

Does laryngopharyngeal reflux cause intraoral burning sensations? A preliminary study

Intraoral burning sensations are a common problem in the otolaryngological practice. The aim of this study was to evaluate if laryngopharyngeal reflux can cause intraoral burning sensations by measuring oropharyngeal acid reflux. Patients with recurring intraoral burning sensations underwent oropharyngeal pH monitoring in our outpatient clinic. The pH catheter was placed at the level of the uvula. The catheter contained an externally worn transmitter, which wirelessly sent the data to a monitor. In addition, patients were instructed to indicate meals or the occurrence of burning sensations by pressing provided buttons on the monitor. Corresponding events of burning sensations and a significant decrease in oropharyngeal pH values should be visualized. Twenty two patients suffering from recurring intraoral burning sensations underwent oropharyngeal pH measurement for 21–25 h. We could find oropharyngeal reflux episodes in 11 patients. However, we could not detect any episodes of burning sensations in the mouth corresponding with a decrease in oropharyngeal pH values. Our results suggest that there is no causal connection between LPR episodes and the occurrence of intraoral burning sensations in the examined patients. Although further studies with more patients are necessary in the future, we conclude from our findings that recurring intraoral burning sensations are not an indication for proton pump inhibitor therapy.     

Specific stressors in endonasal skull base surgery with and without navigation

European Archives of Oto-Rhino-Laryngology - The goal of modern organizational psychology is to recognize, anticipate and finally avoid stress situations. The aim of this study was to measure...     

An animal model for the analysis of cochlear blood flood disturbance and hearing threshold in vivo

Impairment of cochlear blood flow (CBF) is considered to be important in inner ear pathology. However, direct measurement of CBF is difficult and has not been investigated in combination with hearing function. Six guinea pigs were used to show feasibility of an animal model for the analysis of cochlear microcirculation by intravital microscopy in combination with investigation of the hearing threshold by brainstem response audiometry (ABR). By the application of sodium nitroprusside (SNP), CBF was increased over 30 min. Reproducibility of measurements was shown by retest measurements. Mean baseline velocity of CBF was 109 ± 19 μm/s. Vessel diameters had a mean value of 9.4 ± 2.7 μm. Mean hearing threshold was 19 ± 6 dB. In response to SNP, CBF velocity increased significantly to 161 ± 26 μm/s. Mean arterial pressure decreased significantly to 36 ± 11 mmHg. After the end of the application, CBF velocity recovered to a minimum of 123 ± 17 μm/s. Within the retest, CBF velocity significantly increased to a maximum of 160 ± 31 μm/s. Second recovery of CBF velocity was 125 ± 14 μm/s. Within the second retest, CBF increased significantly to 157 ± 25 μm/s. ABR thresholds did not change significantly. The increase in blood flow velocity occurred in spite of substantial hypotension as induced by a vasodilator. This may explain the fact that ABR threshold remained unchanged reflecting a maintained blood supply in this part of the brain. This technique can be used to evaluate effects of treatments aimed at cochlear microcirculation in inner ear pathologies.