Evaluation of the microgrinding procedure for the microscopic analysis of temporal bones.

INTRODUCTION: The microgrinding technique is used to study cochlear implant electrode positioning and cochlear trauma. It may be argued that this technique might cause damage to inner cochlear structures even without a cochlear implant insertion and thus it should not be recommended. Most papers do not explain how microgrinding is performed, referring to older papers for its description. Properly describing the technique and re-evaluating its safety may reassure researchers of their findings when studying trauma after cochlear implant insertion. OBJECTIVE: To accurately describe the microgrinding technique and re-evaluate its safety to assess intracochlear trauma by studying non-implanted temporal bones. METHODS: Four fresh temporal bones were removed before 24 hours postmortem and frozen at -20°C. Two were prepared for microgrinding before 24 hours of freezing and the others after 6 months. A descriptive analysis of the microscopic anatomy was performed, as well as a comparison between the bones processed within 24 hours of freezing and the bones frozen for 6 months. RESULTS: A total of 80 surfaces was evaluated. Preservation of even the most delicate intracochlear and vestibular structures was observed, such as the crista ampullaris, Reissner's and basilar membranes, permitting an adequate micro-anatomical study. Artifacts were rare and did not interfere with the analysis. Bones studied before 24 hours postmortem exhibited better quality than those frozen for 6 months. CONCLUSIONS: The microgrinding technique accurately preserves the inner ear's membranous microscopic anatomy and thus it is useful to study cochlear implant electrode positioning and trauma inside the cochlea. Studies that aim to evaluate inner ear microanatomy should be performed with fresh bones or bones frozen for less than 24 hours since they exhibit a better micro-anatomical quality.

Reliability of the Heart Rate Variability Threshold using Visual Inspection and Dmax Methods.

The purpose of this study was to compare heart rate variability threshold (HRVT) in 6 incremental tests and test its reproducibility using visual inspection and Dmax methods for root mean square of successive differences between the adjacent normal R-R intervals (RMSSD), standard deviation of the normal RR interval (SDNN) and standard deviation of instantaneous beat-to-beat variability (SD1). 12 adult males performed an incremental test to volitional fatigue on a cycle simulator during 6 visits to the laboratory. The initial test load was 25 W, and the intensity was increased by 25 W every 3 min until volitional fatigue set in. The HRV during the incremental test was analyzed using the RMSSD, SDNN and SD1 indices and the determination of HRVT was performed using 2 methods: visual inspection and Dmax. The results demonstrated that the SD1 and RMSSD indices, determined by the visual inspection method, presented the highest reproducibility of HRVT when compared with the other indices and methods. We concluded that the best method for determining HRVT was the technique using the point of stabilization by visual inspection in the SD1 and RMSSD indices during the incremental test, due to its high reproducibility, lower coefficient of variation and increment size.