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PubMed2001

The importance of human cochlear anatomy for the results of modiolus-hugging multichannel cochlear implants.

HYPOTHESIS: The fact that the anatomy of the basal turn of the human cochlea, especially, is essentially different from that of other species is likely to influence the outcome of cochlear implantation. BACKGROUND: Multichannel cochlear implants give better speech understanding than single-channel devices. They are intended to make use of the tonotopic organization of the cochlea by selectively stimulating subpopulations of the auditory nerve. At higher stimulus levels and with monopolar stimulation, excitation of nerve fibers from other turns may interfere with this concept, especially with modiolus-hugging electrodes. METHODS: A three-dimensional spiraling computer model of the human cochlea, based on histologic data, was used to test the spatial selectivity and the dynamic range before cross-turn stimulation takes place for the Clarion HiFocus implant with and without a positioner. The results were compared with a similar model of the guinea pig cochlea. RESULTS: In humans (in contrast to the guinea pig), a well-designed modiolus-hugging electrode yielded reduced current thresholds and high spatial selectivity without reduction of the useful dynamic range. The apical turn of the human cochlea, however, is largely comparable in this respect with the guinea pig cochlea, where cross-turn stimulation reduces the dynamic range substantially. CONCLUSION: The clinical success of cochlear implantation in humans and the favorable results with modiolus-hugging devices depend on the anatomy of the human cochlea.

Acoustic Stimulation↗
PubMed2004

Ultrasonic tissue characterization of the mouse myocardium: successful in vivo cyclic variation measurements.

BACKGROUND: Measurements of the systematic variation of backscattered ultrasonic energy from myocardium during the heart cycle (cyclic variation) have been successfully used to characterize a wide spectrum of cardiac pathologies in large animal models and human subjects. The purpose of this study was to evaluate the feasibility of extending cyclic variation measurements to the study of genetically manipulated mouse models of cardiac diseases as a method for developing further insights into the disease-altered properties of the myocardium and its characterization with ultrasound. METHODS: Parasternal long-axis images of the heart were obtained in 9 wild-type mice under light anesthesia using a commercial imaging system with a 15-MHz nominal center frequency linear array. Images of a tissue-mimicking phantom and the mouse hearts were obtained for a series of specific receiver gains for each of a series of specific dynamic range settings. Analyses of these data formed the basis for gray-scale image calibration. Cyclic variation measurements were obtained by determining the average gray-scale value for a region of interest placed in the midmyocardium of the posterior wall for each frame acquired during 4 cardiac cycles and converting these mean gray-scale values to backscatter values expressed in decibels using the determined calibration. Results are expressed in terms of the magnitude and time delay of cyclic variation. To evaluate repeatability of these measurements the same group of mice underwent the identical imaging protocol 2 weeks after the first study. RESULTS: The mean magnitude of cyclic variation was found to be 4.6 +/- 0.2 dB with a corresponding normalized time delay of 1.02 +/- 0.03 for data averaged over all dynamic range settings. There was no significant difference among results obtained with each of the dynamic range settings. A comparison of these results with those from data acquired 2 weeks after the initial study showed no significant difference. CONCLUSION: This study represents the first reported measurement of cyclic variation in mice and demonstrates that reliable cyclic variation measurements can be obtained among individual animals and over different time points and, hence, forms the basis for subsequent investigations addressing specific cardiac pathologies and effects arising from myocardial anisotropy.

Algorithms↗
PubMed1992

A comparison of round-window and transtympanic promontory electric stimulation in cochlear implant candidates.

We compared within-subjects electrical thresholds and dynamic ranges obtained with direct round-window and transtympanic promontory stimulation carried out preoperatively in 12 patients who were candidates for a cochlear implant. Square waves with frequencies of 50, 100, 200, and 400 Hz were delivered in a 50% duty cycle to both sites in each patient. With the exception of threshold at 50 Hz (promontory thresholds were lower than round-window thresholds), there were no statistically significant differences for either thresholds or dynamic ranges between the two sites of stimulation. There was a general trend for round-window thresholds to be lower and dynamic ranges larger, especially for the higher frequencies of stimulation. Mean threshold slopes for the two sites of stimulation were nearly identical.

Adult↗
PubMed1994

Response properties of nociceptive and low-threshold neurons in rat trigeminal pars caudalis.

There is little doubt that trigeminal nociceptive neurons play a critical role in signaling the presence of harmful, or potentially harmful, orofacial stimuli. Unfortunately, there is only a limited understanding of how these neurons code such stimuli and whether this code is maintained in those structures responsible for generating overt reactions. The present series of experiments were designed to quantitatively document the response properties of nociceptive neurons in the rat trigeminal pars caudalis using the same electrical and innocuous and/or noxious mechanical and thermal stimuli employed in the characterization of nociceptive neurons with orofacial receptive fields in the rat superior colliculus. Neurons were classified as either low-threshold mechanoreceptive, wide-dynamic-range, or nociceptive-specific (type I, II) depending on their responsiveness to these stimuli. Nociceptive pars caudalis neurons (92/135, 68%) had receptive field organizations and input fibers (as indicated by latencies to electrical stimuli) quite different from those of low-threshold neurons (43/135, 32%). Nociceptive stimulus-response relationships for the population of wide-dynamic-range and nociceptive-specific type I neurons to contact heat stimuli were positively accelerating power functions with exponents of 3.9 and 4.4, respectively. This contrasted sharply with the low-threshold component of wide-dynamic-range neurons which was a negatively accelerating power function with an exponent of 0.7. All categories of nociceptive neurons also responded vigorously to cold stimuli. The thresholds of both hot and cold stimuli were often below psychophysical estimates of thermal pain, suggesting that "nociceptive" neurons process far more information than that required to signal potentially harmful stimuli. The fundamental similarities in nociceptive properties in pars caudalis and other structures of the central nervous system suggest that there is little transformation of the information encoded at successive levels of the neuraxis. This is consistent with the idea that the functional role of nociceptive neurons is reflected more in which circuits they are integrated and less in differences in their physiological properties.

Animals↗
PubMed1981

Dynamics of acoustic reflex growth.

Acoustic reflex growth was measured as a function of activator bandwidth in 10 subjects with normal hearing and in 5 subjects with different configurations of sensorineural hearing loss. The activators consisted of tones with frequencies of 500, 1 000 and 4 000 Hz, fractions and multiples of octave bands centered at these frequencies, and broadband noise. Growth functions for the normal-hearing subjects measured with a 660-Hz probe tone had smaller peak magnitudes and shallower slopes than the growth functions measured with a 220-Hz probe tone. The slope of the growth function and the peak magnitude of acoustic impedance were not affected in any consistent manner by activator bandwidth or activator center frequency. The dynamic range of the growth function increased with an increase in activator bandwidth beyond 1 octave. The resistive component of acoustic impedance did not exhibit a consistent pattern of change with increasing activator intensity level. The reflex growth functions for normal-hearing subjects separated into two groups, those with steep slopes and large peak magnitudes and those with shallow slopes and small peak magnitudes. 3 out of the 5 cases with sensorineural hearing loss presented growth functions with shallower slopes, smaller dynamic ranges and smaller peak magnitudes than normal. The other 2 cases had steeper slopes and larger peak magnitudes than normal. The dynamic range did not increase with an increase in activator bandwidth beyond 1 octave. The differences in reflex growth functions with probe-tone frequency observed for the normal group were diminished or absent in 4 of the 5 cases of sensorineural hearing loss. The frequency of 4 000 Hz appeared to be the most sensitive to reflex manifestations of hearing loss.

Acoustic Impedance Tests↗
PubMed2002

Otoacoustic emissions for monitoring aminoglycoside-induced ototoxicity in children with cystic fibrosis.

OBJECTIVE: To investigate whether transient-evoked and distortion-product (DP) otoacoustic emissions (OAEs) are more sensitive than pure-tone audiometry (PTA) in revealing gentamicin-induced ototoxicity in children with cystic fibrosis (CF). DESIGN: Prospective case-control study. SETTING: Tertiary referral audiologic center in conjunction with an academic pediatric CF unit. PARTICIPANTS: The study group consisted of a consecutive sample of 12 audiologically normal children with CF and a history of gentamicin exposure (CF-gentamicin group). The control groups consisted of 8 age-matched children with CF and 11 age-matched healthy volunteers. No member of the control groups had a history of aminoglycoside exposure. INTERVENTION: Members of the CF-gentamicin study group received 4 mg/kg of gentamicin per day for a mean of 14.2 days (range, 11-29 days). OUTCOME MEASURES: The PTA thresholds (250-8000 Hz) were the criterion standard. Transient-evoked OAEs' reproducibility at 5 frequency bands (800, 1600, 2400, 3200, and 4000 Hz) and total emission level were measured, as were DP-audiogram (DP-gram) amplitude (1001-6299 Hz), input-output function dynamic range, and detection thresholds at 4004, 6006, and 7996 Hz. Baseline measurements were compared between groups examining the effect of CF and previous gentamicin exposure (2-way analysis of variance). For the CF-gentamicin group, baseline measurements were compared with those at the end of the last gentamicin treatment (paired t test). RESULTS: The PTA findings were normal for all groups at baseline and remained normal in the CF-gentamicin group after treatment. The CF-gentamicin group had significantly lower transient-evoked OAEs total emission level, DP-gram amplitude at 5042 Hz, and input-output dynamic ranges with higher detection thresholds in all frequencies compared with both control groups, which was attributed completely to previous gentamicin exposure (P<.05). After treatment, further decreases in total emission levels, DP-gram amplitudes (>3000 Hz), and dynamic ranges were noted, with increased detection thresholds (P<.05). CONCLUSIONS: Otoacoustic emissions measurement (especially of DP OAEs) proved more sensitive than PTA in revealing minor cochlear dysfunction after gentamicin exposure. They should be used for monitoring patients receiving ototoxic factors such as aminoglycosides.

Adolescent↗
PubMed1994

Improved visualization of stimulated nodules by adaptive enhancement of digital chest radiography.

RATIONALE AND OBJECTIVES: Although digital radiography of the chest has a wide dynamic range, difficulties still remain in visualizing the acquired images faithfully on gray-scale displays (cathode-ray tube [CRT] displays), which have a much lower level of luminance than film view boxes. We propose an adaptive-enhancement algorithm for digital chest radiography that provides faithful visualization of the chest on the CRT. METHODS: We investigated the contrast sensitivity of a CRT monitor and developed an image processing algorithm that compresses the dynamic range and enhances image contrast selectively in the mediastinal area and that transforms the gray scale to visualize the image by use of the full effective dynamic range of the CRT. We performed a receiver-operating characteristic (ROC) study by using simulated nodules to evaluate the clinical value of the proposed algorithm. RESULTS: The processed images provided improved visualization of both mediastinal and lung regions. The area under the ROC curve for retrocardiac or subdiaphragmatic nodule detection increased significantly (from 0.69 to 0.79; P < 0.05). The area under the ROC curve for lung nodule detection also increased (from 0.64 to 0.75; P < 0.1), although not to the level of statistical significance. CONCLUSION: The proposed algorithm allows improved visualization of nodules on digital chest radiographs with the CRT display.

Algorithms↗
PubMed2006

Advances and challenges in liquid chromatography-mass spectrometry-based proteomics profiling for clinical applications.

Recent advances in proteomics technologies provide tremendous opportunities for biomarker-related clinical applications; however, the distinctive characteristics of human biofluids such as the high dynamic range in protein abundances and extreme complexity of the proteomes present tremendous challenges. In this review we summarize recent advances in LC-MS-based proteomics profiling and its applications in clinical proteomics as well as discuss the major challenges associated with implementing these technologies for more effective candidate biomarker discovery. Developments in immunoaffinity depletion and various fractionation approaches in combination with substantial improvements in LC-MS platforms have enabled the plasma proteome to be profiled with considerably greater dynamic range of coverage, allowing many proteins at low ng/ml levels to be confidently identified. Despite these significant advances and efforts, major challenges associated with the dynamic range of measurements and extent of proteome coverage, confidence of peptide/protein identifications, quantitation accuracy, analysis throughput, and the robustness of present instrumentation must be addressed before a proteomics profiling platform suitable for efficient clinical applications can be routinely implemented.

Biomarkers↗
PubMed1992

Phase-scrambled RF excitation for 3D volume-selective multislice NMR imaging.

An RF excitation technique with which one can improve the effective dynamic range of the receiver and reduce the interference between slices for 3D volume-selective multislice MRI is described. The basic idea of the technique is to use phase scrambling in conjunction with slice encoding through the use of RF pulses. The spins in each slice are encoded by RF pulses which have the scrambled as well as slice-encoded phase components along the slice-selection direction. The scrambled, or randomly distributed, phase reduces the peak signal intensity, thereby reducing the dynamic range of the signal. Since the proposed technique utilizes RF slice encoding together with phase scrambling, interslice image interference is greatly reduced and the dynamic range is improved. In addition, the method has several advantages such as a reduction in the power requirement for the RF pulses and the elimination of the necessity for hardware such as nonlinear gradient coils.

Algorithms↗
PubMed2003

High-sensitivity quantitation of cabergoline and pergolide using a triple-quadrupole mass spectrometer with enhanced mass-resolution capabilities.

Quantitative analysis of pharmaceuticals with low systemic plasma levels requires the utmost in sensitivity and selectivity from the analytical method used. A recently introduced triple-quadrupole mass spectrometer with unique enhanced mass-resolution capability was evaluated in the analysis of two such drugs, cabergoline and pergolide, in plasma. Liquid chromatographic/electrospray ionization selected reaction monitoring determination of cabergoline in plasma at unit mass-resolution demonstrated improved sensitivity (50 fg on-column), coupled with suitable accuracy and precision over a broad linear dynamic range covering five orders of magnitude (50 fg to 5 ng on-column). Liquid chromatographic/atmospheric pressure chemical ionization selective reaction monitoring determination of pergolide in plasma also attained a high level of sensitivity (500 fg on-column) at unit mass-resolution, with accuracy and precision values well within pharmaceutical industry standards. Again, a linear dynamic range covering five orders of magnitude (500 fg to 50 ng on-column) was achieved for the assay. Utility of the enhanced mass-resolution feature of the triple-quadrupole mass spectrometer in the determination of pergolide resulted in an improvement in analyte sensitivity (250 fg on-column) and linear dynamic range (250 fg to 50 ng on-column).

Animals↗
PubMed2026

Evaluation and Optimization of Different Digestion Strategies for In-Depth Proteomic Characterization of Residual Host Cell Proteins in rAAV-Based Gene Therapy Products.

Recombinant adeno-associated virus vectors (rAAVs) are the most important vectors for in vivo gene therapies, yet their safety relies on low levels of residual host cell proteins (HCPs). While mass spectrometry-based proteomics enables sensitive and untargeted HCP profiling, it faces challenges with matrix interferences from purification buffers and the high dynamic range between abundant viral capsids and trace HCPs. Although sample preparation methods that address these challenges are well-established for antibody products, their adaptation to rAAV purification stages and products remains largely unexplored. In this study, we systematically evaluated three widely used proteomic sample preparation workflows&#x2500;In-Solution, FASP, and SP3&#x2500;across different stages of rAAV purification. In addition, each workflow was tested under both standard denatured digestion conditions and a "native" digestion strategy designed to reduce dynamic range by preserving capsid integrity while selectively digesting HCPs. This comparison identified the native FASP protocol as the most effective sample preparation method for overcoming matrix interference and dynamic range challenges, consistently outperforming other workflows in HCP identification across purification stages. Further optimization of the native FASP workflow enhanced its performance, achieving the highest host cell (HC) proteome depth, particularly in highly purified drug substance samples. This optimized sample preparation strategy provides a robust and easy-to-use framework for deep characterization of the host cell proteome in rAAV samples. By enabling deeper insights into the HCP profile, this approach supports improved understanding of the rAAV purification process and facilitates the development of targeted strategies to enhance product quality and safety.

Dependovirus↗
PubMed2000

A comparison of fluorescent Ca2+ indicator properties and their use in measuring elementary and global Ca2+ signals.

Quantifying the magnitude of Ca2+ signals from changes in the emission of fluorescent indicators relies on assumptions about the indicator behaviour in situ. Factors such as osmolarity, pH, ionic strength and protein environment can affect indicator properties making it advantageous to calibrate indicators within the required cellular or subcellular environment. Selecting Ca2+ indicators appropriate for a particular application depends upon several considerations including Ca2+ binding affinity, dynamic range and ease of loading. These factors are usually best determined empirically. This study describes the in-situ calibration of a number of frequently used fluorescent Ca2+ indicators (Fluo-3, Fluo-4, Calcium Green-1, Calcium Orange, Oregon Green 488 BAPTA-1 and Fura-Red) and their use in reporting low- and high-amplitude Ca2+ signals in HeLa cells. All Ca2+ indicators exhibited lower in-situ Ca2+ binding affinities than suggested by previously published in-vitro determinations. Furthermore, for some of the indicators, there were significant differences in the apparent Ca2+ binding affinities between nuclear and cytoplasmic compartments. Variation between indicators was also found in their dynamic ranges, compartmentalization, leakage and photostability. Overall, Fluo-3 proved to be the generally most applicable Ca2+ indicator, since it displayed a large dynamic range, low compartmentalization and an appropriate apparent Ca2+ binding affinity. However, it was more susceptible to photobleaching than many of the other Ca2+ indicators.

Aniline Compounds↗
PubMed2003

The medullary dorsal reticular nucleus enhances the responsiveness of spinal nociceptive neurons to peripheral stimulation in the rat.

Single-unit spinal recordings combined with application of glutamate into the medullary dorsal reticular nucleus were used to assess the action of this nucleus upon deep dorsal horn neurons in rats. Injection of high glutamate concentrations (10 and 100 mm) induced a dramatic and long-lasting increase of the responses of wide-dynamic range neurons to electrical stimulation of the sciatic nerve in the noxious range, without affecting ongoing discharges. Post-stimulus time histograms revealed that this increase concerned the post-discharge, but not A- or C-fibre-mediated responses, which remained unchanged independently of the stimulation frequency applied. The onset of the glutamate-induced response enhancement occurred with a concentration-dependent time delay and developed slowly until its maximum. These data indicate that the medullary dorsal reticular nucleus exerts a facilitating action upon deep dorsal horn wide-dynamic range neurons by enhancing their capacity to respond to peripheral stimulation through prolongation of their discharge. This action is accompanied by the strengthening of wind-up of deep dorsal horn wide-dynamic range neurons, hence providing a plausible substrate for chronic pain states. These results are in agreement with previous behavioural studies suggesting a pronociceptive role for the dorsal reticular nucleus [Almeida et al. (1996) Brain Res. Bull., 39, 7-15; Almeida et al. (1999) Eur. J. Neurosci., 11, 110-122], and support the involvement of a reverberating circuit, previously described in morphological studies [Almeida et al. (1993) Neuroscience, 55, 1093-1106; Almeida et al. (2000) Eur. J. Pain, 4, 373-387], which probably operates only at a certain threshold of activation.

Animals↗
PubMed1993

Long-term dysfunctions of neural stereoscopic mechanisms after unilateral extraocular muscle proprioceptive deafferentation.

1. Neural correlates of the permanent deficits in depth perception that occur when extraocular muscle proprioceptive (EMP) afferents are interrupted unilaterally in kittens were investigated by performing extracellular recordings in the primary visual cortex (area 17) in adulthood. Unilateral section of the ophthalmic branch of the trigeminal nerve (V1 nerve) were performed in 11 cats when they were between 5 and 12 weeks of age (uni-V1 group). Electrophysiological results were compared with those obtained in 17 normal adult cats (control group). 2. Binocular interactions were assessed by testing the sensitivity of cortical neurons to dichoptic presentations of moving sine-wave gratings whose interocular positional phase relationship was randomly varied. The amplitude modulation between the minimum and the maximum binocular responses defined the dynamic range. The degree of binocular suppression or facilitation was assessed by comparing these binocular response limits with the optimal monocular responses evoked through either eye at the best spatial frequency. The variability of both monocular and binocular responses was estimated by using the variation coefficient. 3. In uni-V1 cats, both the dynamic range and the degree of binocular suppression were significantly less pronounced than in controls, whereas binocular facilitation was not affected. The variability of the binocular responses was significantly increased, unlike monocular responses, whose variability was similar to control values. 4. From Fourier analysis of the poststimulus time histograms, two clear-cut categories of cells emerged that were differentially affected in the uni-V1 group. The "modulated" cells showed significantly less binocular suppression than in controls, and the "unmodulated" cells had binocular responses that were significantly more variable than in controls. Results from "simple" cells were similar to those of modulated cells, and results from "complex" cells were similar to those of unmodulated cells. However, in the unmodulated population, which was composed of both simple and complex cells, it was shown that the increase of variability was due to that of complex cells. 5. A nonparametric statistical test was applied on the interocular phase shift tuning curves to determine the minimum stimulus change necessary to elicit a significant change in the neural response. Two categories of cells were determined: the "discriminative" cells (80% in controls but 45% in uni-V1 cats) combined pronounced binocular suppression and dynamic range with relatively low variability. The reverse was true in the case of "nondiscriminative" cells (20% in controls and 55% in uni-V1 cats). 6. In uni-V1 cats, about half of the cells were monocularly activated.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed2006

Sensitivity measurement and compensation in spectral imaging.

BACKGROUND: The ImageStream system combines advances in CCD technologies with a novel optical architecture for high sensitivity and multispectral imaging of cells in flow. The sensitivity and dynamic range as well as a methodology for spectral compensation of imagery is presented. METHODS: Multicolored fluorescent beads were run on the ImageStream and a flow cytometer. Four single color fluorescent control samples of cells were run to quantify spectral overlap. An additional sample, labeled with all colors was run and compensated in six spectral channels. RESULTS: Analysis of empirical data for sensitivity and dynamic range matched theoretical predictions. The ImageStream system demonstrated fluorescence sensitivity comparable to a PMT-based flow cytometer. A methodology for addressing spectral overlap, individual pixel anomalies, and multiple imaging modalities was demonstrated for spectral compensation of K562 cells. Imagery is shown pre- and post-compensation. CONCLUSIONS: Unlike intensity measurements made with conventional flow cytometers, object size impacts both dynamic range and fluorescence sensitivity in systems that utilize pixilated detection. Simultaneous imaging of alternate modalities can be employed to increase fluorescent sensitivity. Effective compensation of complex multimode imagery spanning six spectral bands is accomplished in a semi-automated manner.

Cell Line, Tumor↗
PubMed2005

A CMOS image sensor with programmable pixel-level analog processing.

A prototype of a 34 x 34 pixel image sensor, implementing real-time analog image processing, is presented. Edge detection, motion detection, image amplification, and dynamic-range boosting are executed at pixel level by means of a highly interconnected pixel architecture based on the absolute value of the difference among neighbor pixels. The analog operations are performed over a kernel of 3 x 3 pixels. The square pixel, consisting of 30 transistors, has a pitch of 35 microm with a fill-factor of 20%. The chip was fabricated in a 0.35 microm CMOS technology, and its power consumption is 6 mW with 3.3 V power supply. The device was fully characterized and achieves a dynamic range of 50 dB with a light power density of 150 nW/mm2 and a frame rate of 30 frame/s. The measured fixed pattern noise corresponds to 1.1% of the saturation level. The sensor's dynamic range can be extended up to 96 dB using the double-sampling technique.

Algorithms↗
PubMed2000

[Functional gait adaptations in patients with painful hip].

PURPOSE OF THE STUDY: This prospective study was conducted to analyze the mechanisms of gait compensation in patients with painful hip and to search for correlations with preoperative clinical and radiographic findings. MATERIAL AND METHODS: Optoelectronic and multicomponent force-plate datas were used to calculate joint motion, moments and intersegmental forces for 26 patients with unilateral hip pain and 20 normal age and sex-matched patients. Height was similar in the two groups but mean weight in the study group (83 kg) was greater than in the controls (68 kg). The preoperative Harris score was 53 in the study group and 16 patients had a permanent flexion contracture of the knee (mean 15 degrees, range 5-30 degrees). Radiographically, there were 22 cases of osteo-arthritis hip disease and 4 cases of necrosis. RESULTS: Gait analysis showed a significant 0.66 +/- 0.06 m (12 p. 100) reduction in step length. Patients who had severe hip pain walked with a decreased dynamic range of motion (18 +/- 5 degrees, p<0.0001) with a curve reversal as they extended the hip. They also reduced dynamic range of motion of the knee and ankle. Patients who presented a reversal in their dynamic hip range of motion had a greater passive flexion contracture and a greater loss in range of motion during gait than those with a smooth regular pattern (p<0.0001). Patients with hip pain walked with significantly decreased external extension, adduction, and internal and external rotation moments (p<0.0001). They also unloaded the ipsilateral knee and ankle. The decreased hip extension moment was significantly correlated with an increased level of pain (p<0.0001). There was no correlation with radiological findings. DISCUSSION: Reversal of dynamic hip range of motion was interpreted as a mechanism to increase effective hip extension during stance phase through increased anterior pelvic tilt and lumbar lordosis. CONCLUSION: Patients with painful hip walked with a manner that was asymmetric. These gait modifications were related to hip limitation in passive motion and pain. Patients with flexion contracture adopted a compensatory gait mechanism. This study confirms relation between hip pain and forces across the hip joint.

Adaptation, Physiological↗
PubMed2001

Far-field responses to stimulation of the cochlear nucleus by microsurgically placed penetrating and surface electrodes in the cat.

OBJECT: A new generation of penetrating electrodes for auditory brainstem implants is on the verge of being introduced into clinical practice. This study was designed to compare electrically evoked auditory brainstem responses (EABRs) to stimulation of the cochlear nucleus (CN) by microsurgically implanted surface electrodes and insertion electrodes (INSELs) with stimulation areas of identical size. METHODS: Via a lateral suboccipital approach, arrays of surface and penetrating microelectrodes with geometric stimulation areas measuring 4,417 microm2 (diameter 75 microm) were placed over and inserted into the CN in 10 adult cats. After recording the auditory brainstem response (ABR) at the mastoid process, the CN, and the level of the inferior colliculus, EABRs to stimulation of the CN were recorded using biphasic, charge-balanced stimuli with phase durations of 80 microsec, 160 microsec, and 240 microsec at a repetition rate of 22.3 Hz. Waveform, threshold, maximum amplitude, and the dynamic range of the responses were compared for surface and penetrating electrodes. The EABR waveforms that appeared for both types of stimulation resembled each other closely. The mean impedance was slightly lower (30 +/- 3.4 kohm compared with 31.7 +/- 4.5 kohm, at 10 kHz), but the mean EABR threshold was significantly higher (51.8 microA compared with 40.5 microA, t = 3.5, p = 0.002) for surface electrode arrays as opposed to penetrating electrode arrays. Due to lower saturation levels of the INSEL array, dynamic ranges were almost identical between the two types of stimulation. Sectioning of the eighth cranial nerve did not abolish EABRs. CONCLUSIONS: Microsurgical insertion of electrodes into the CN complex may be guided and monitored using techniques similar to those applied for implantation of surface electrodes. Lower thresholds and almost equivalent dynamic ranges indicate that a more direct access to secondary auditory neurons is achieved using penetrating electrodes.

Animals↗