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At least 271 records · Page 15Linked to original sources
PubMed2002

Fully endoscopic vascular decompression of the glossopharyngeal nerve.

Microvascular decompression of the glossopharyngeal nerve is an effective treatment of patients with glossopharyngeal neuralgia in whom compression of the nerve by a blood vessel is implicated in the pathogenesis of the disease. The standard surgical technique uses a binocular operating microscope for intra-operative visualization. Growing experience with posterior fossa endoscopy, however, has suggested that endoscopes may provide more comprehensive anatomical views of cerebellopontine angle. This report describes the case of a patient suffering from glossopharyngeal neuralgia who underwent fully endoscopic vascular decompression of the glossopharyngeal nerve. During this procedure the endoscope was used to survey the posterior fossa, guide the placement of insulating sponges, and conduct a final assessment of the intervention. We found the endoscope ideally suited to the constricted operating space of the posterior fossa, allowing for accurate localization and careful separation of the pathological vascular conflict with minimal brain retraction and no damage to surrounding structures. The versatility of endoscopy allows for superior visual appreciation of neurovascular conflicts in the posterior fossa. To date, endoscopy has primarily been used to supplement microscopy in cranial nerve decompression surgery. This report demonstrates how the endoscope can be used as the sole imaging modality in glossopharyngeal nerve decompression, with excellent results.

Adult↗
PubMed1998

Metabolic interaction of n-hexane and methyl ethyl ketone in vitro in a head space rat liver S9 vial equilibration system.

Methyl ethyl ketone pretreatment induced rat liver cytochrome P450 and increased significantly the in vitro metabolism of n-hexane and the formation of 2,5-hexanedione in rat liver S9. No significant changes were, however, found in the levels of the intermediate metabolites 2-hexanol, 2,5-hexanediol or methyl n-butyl ketone. Methyl ethyl ketone added in vitro to untreated (non-induced) liver S9 inhibited in a non-competitive pattern the metabolism of n-hexane and decreased significantly and in a dose-dependent way the levels of methyl n-butyl ketone and 2,5-hexanedione. When methyl ethyl ketone and n-hexane were added in vitro to in vivo methyl ethyl ketone pretreated (induced liver S9, the significant increase in the formation of 2,5-hexanedione was maintained, an increase which was only to a minor extent influenced by the in vitro addition of methyl ethyl ketone. These findings are in agreement with an in vivo induction by methyl ethyl ketone of key enzyme(s) in a generally minor metabolic pathway for the conversion of n-hexane to 2,5-hexanedione in rat liver, a pathway which is not influenced by the presence of methyl ethyl ketone itself. The results obtained in this study indicate that the head space equilibration technique is well suited for screening studies of metabolic interactions between organic solvents.

Animals↗
PubMed2004

Experimental verification of dispersed fringe sensing as a segment phasing technique using the Keck telescope.

Dispersed fringe sensing (DFS) is an efficient and robust method for coarse phasing of segmented primary mirrors (from one quarter of a wavelength to as much as the depth of focus of a single segment, typically several tens of microns). Unlike phasing techniques currently used for ground-based segmented telescopes, DFS does not require the use of edge sensors in order to sense changes in the relative heights of adjacent segments; this makes it particularly well suited for phasing of space-borne segmented telescopes, such as the James Webb Space Telescope. We validate DFS by using it to measure the piston errors of the segments of one of the Keck telescopes. The results agree with those of the Shack-Hartmann-based phasing scheme currently in use at Keck to within 2% over a range of initial piston errors of +/-16 microm.

Journal Article↗
PubMed2005

Analysis of stellar interferometers as wave-front sensors.

The basic principle and theoretical relationships of an original method are presented that allow the wave-front errors of a ground or spaceborne telescope to be retrieved when its main pupil is combined with a second, decentered reference optical arm. The measurement accuracy of such a telescope-interferometer is then estimated by means of various numerical simulations, and good performance is demonstrated, except in limited areas near the telescope pupil's rim. In particular, it permits direct phase evaluation (thus avoiding the use of first- or second-order derivatives), which will be of special interest for the cophasing of segmented mirrors in future giant-telescope projects. Finally, the useful practical domain of the method is defined, which seems to be better suited for periodic diagnostics of space- or ground-based telescopes or to real-time scientific observations in some specific cases (e.g., the central star in instruments that search for extrasolar planets).

Journal Article↗
PubMed2001

Remarks on the inner ear of elasmobranchs and its interpretation from skeletal labyrinth morphology.

The structure and function of the craniate inner ear is reviewed, with 33 apomorphic characters of the membranous labyrinth and associated structures identified in craniates, gnathostomes, and elasmobranchs. Elasmobranchs are capable of low-frequency semi-directional phonoreception, even in the absence of any pressure-to-displacement transducer such as ear ossicles. The endolymphatic (parietal) fossa, semicircular canals, and crista (macula) neglecta are all adapted toward phonoreception. Some (but not all) of the morphological features associated with phonoreception can be inferred from the elasmobranch skeletal labyrinth. Endocranial spaces such as the skeletal labyrinth also provide suites of morphological characters that may be incorporated into phylogenetic analyses, irrespective of how closely these spaces reflect underlying soft anatomy. The skeletal labyrinths of Squalus and Notorynchus are compared using silicone endocasts and high-resolution CT-scanning. The latter procedure offers several advantages over other techniques; it is more informative, nondestructive, preserves relationships of surrounding structures, and it can be applied both to modern and fossil material.

Animals↗
PubMed1996

[Epidurography: comparison with CT, spiral CT and MR epidurography].

PURPOSE: The purpose of this study was to explain the origin of image patterns demonstrated by conventional epidurography, which is a controversially discussed topic in recent literature. MATERIAL AND METHODS: After introduction of thoracic epidural catheters and iopamidol injection, conventional epidurography and CT-epidurography were performed on 25 preoperative patients. After injection of Gadolinium-DTPA MR-epidurography was performed in two patients treated for chronic pain with already introduced epidural catheters. Three volunteers also underwent identical imaging after introduction of thoracic epidural catheters and in addition helical-CT epidurography using twin-beam technology. RESULTS: 40% of the patients demonstrated the railroad track phenomenon. We were able to prove that it is a sign of a rhythmically variable filling of segments of the lateral epidural space with contrast medium 76% of the patients demonstrated no ventral epidural space at the thoracic level. 56% of the patients showed a medial area of translucence combined with a band-shaped contrasting of the epidural space in the standard ap view. This was proven in all cases to be a plica mediana dorsalis by CT. In all volunteers who underwent helical-CT and MR epidurography we observed the railroad track phenomenon and the filling defect of the anterior thoracic epidural space. CONCLUSION: CT epidurography is well suited for obtaining new insights into the interpretation of findings obtained by conventional epidurography.

Analgesia, Epidural↗
PubMed2003

Distributed coding of sound locations in the auditory cortex.

Although the auditory cortex plays an important role in sound localization, that role is not well understood. In this paper, we examine the nature of spatial representation within the auditory cortex, focusing on three questions. First, are sound-source locations encoded by individual sharply tuned neurons or by activity distributed across larger neuronal populations? Second, do temporal features of neural responses carry information about sound-source location? Third, are any fields of the auditory cortex specialized for spatial processing? We present a brief review of recent work relevant to these questions along with the results of our investigations of spatial sensitivity in cat auditory cortex. Together, they strongly suggest that space is represented in a distributed manner, that response timing (notably first-spike latency) is a critical information-bearing feature of cortical responses, and that neurons in various cortical fields differ in both their degree of spatial sensitivity and their manner of spatial coding. The posterior auditory field (PAF), in particular, is well suited for the distributed coding of space and encodes sound-source locations partly by modulations of response latency. Studies of neurons recorded simultaneously from PAF and/or A1 reveal that spatial information can be decoded from the relative spike times of pairs of neurons - particularly when responses are compared between the two fields - thus partially compensating for the absence of an absolute reference to stimulus onset.

Acoustic Stimulation↗
PubMed1991

Human exploration of Mars.

The human exploration of Mars has the potential to return a rich harvest of scientific information about that planet, its possible past biological history and the prospects for future habitation by Earthly life. The realization of that potential will require new approaches and new technologies--a whole new paradigm in space exploration. Picture yourself exploring the surface of Mars, where your task involves conducting a detailed investigation of features larger than the United States in order to uncover a record of planetary history spanning over four billion years.

Atmosphere↗
PubMed1993

Orthostatic stress by lower body negative pressure and its body fluid distribution kinetics under microgravity.

To support the hypothesis that interstitial fluid loss is one of the components of the "cardiovascular deconditioning" induced by space flight, a series of three experiments was performed in one subject, after 5 days in space: 1) standard thigh cuffs were inflated up to suprasystolic pressure values (CUFF I) for two minutes, 2) Half an hour later a lower body negative pressure test (LBNP) followed with -15 mmHg for 15, -30 mmHg for 5, and -40 mmHg for 15 minutes, 3) Twenty minutes after that, the CUFF maneuver was repeated (CUFF II). Body fluid shifts were detected by quadripole segmental electrical impedance (BIM) and by electrical impedance tomography (APT). The APT electrodes were placed directly under one of the thigh cuffs. Cardiovascular reaction patterns were observed by continuous ECG-recordings and by minute-by-minute arm cuff blood pressure measurements. By means of segmental impedance the expected body fluid change in the abdominal, thigh, and calf regions could be detected. The thoracic segment showed no significant changes in microgravity. However, the calf increased its electrical impedance roughly by 50%. The interstitial fluid in the skin and musculature, detected by APT during CUFF I, was reduced more than 50%. The LBNP-maneuver was able to refill this interstitial space. However, only the higher levels (LBNP > 15 mmHg) showed the outward filtration component during the constant LBNP levels. In addition, the LBNP-experiment clearly showed the reduced ability to cope with orthostatic stress. Pulse pressure dropped and heart rate increased much more than on ground. The fluid displacement during CUFF I showed a similar hemodynamic response, which had not been seen on ground before. The CUFF II maneuver after LBNP showed that the reaction had returned to normal. This leads to the conclusions that LBNP can counteract cardiovascular deconditioning, but only higher LBNP-levels are able to transfer fluid into the interstitial spaces of the legs, if they are emptied by the loss of gravitational forces.

Aerospace Medicine↗
PubMed1994

Preinflation before acceleration on tolerance to simulated Space Shuttle reentry G profiles in dehydrated subjects.

This study was conducted to determine if preinflation of a standard five-bladder anti-g suit 10 minutes before exposure to a centrifuge simulation of a Space Shuttle reentry would provide significantly better protection against orthostasis than the standard symptomatic inflation regimen. This study differed significantly from prior studies: The rate of g onset was slower, peak g was lower, duration of exposure was longer, and the subjects were dehydrated to mimic conditions observed in astronauts immediately postflight. Preinflation demonstrated physiological advantages as determined by arterial blood pressure and heart rate changes in seven healthy male, experienced centrifuge subjects.

Acceleration↗
PubMed1991

[Use of personal protective equipment by pathologists and legal physicians working with particularly dangerous infectious diseases].

The possibility of pneumosuit use constructed in the Institute to protect the pathology department staff at the hospitals for infectious diseases from HIV virus was studied. The suit is a hose-type suit for protection of respiratory organs and skin using the ventilated underhood space and autonomic air supply. Both the detailed description of this suit and its disinfection scheme developed and tested by authors are presented. The comparative physio-hygienic assessment of pneumosuit and standard antiplaque suit demonstrated a number of advantages of the former during 2 hours work at pathology department. The authors recommend the pneumosuit as an equipment for the protection of skin and respiratory organs of pathologists and legal physicians working with particularly dangerous infections.

Forensic Medicine↗
PubMed1993

Implementation of biological elements in life support systems: rationale and development milestones.

To ensure the complete autonomy of man in space, biological life support technologies must be developed. A survey of today's knowledge in biotechnology has been performed and technologies suited to long-duration manned missions in space have been identified. Regardless of whether they are to be used in a space vehicle or at a lunar or planetary base, most of those technologies require development times of 20 to 30 years. It is therefore essential to start development now to ensure that the life support system is ready when development of Moon or Mars bases begins.

Air Conditioning↗
PubMed2005

Extravehicular mobility unit training and astronaut injuries.

BACKGROUND: Astronaut spacewalk training can result in a variety of symptom complaints and possible injuries. This study quantified and characterized signs, symptoms, and injuries resulting from extravehicular activity spacesuit training at NASA's Neutral Buoyancy Laboratory, Johnson Space Center, Houston, TX, immersion facility. METHODS: We identified the frequency and incidence of symptoms by location, mechanisms of injury, and effective countermeasures. Recommendations were made to improve injury prevention, astronaut training, test preparation, and training hardware. At the end of each test, a questionnaire was completed documenting signs and symptoms, mechanisms of injury, and countermeasures. RESULTS: Of the 770 tests, there were 190 in which suit symptoms were reported (24.6%). There were a total of 352 reported suit symptom comments. Of those symptoms, 166 were in the hands (47.16%), 73 were in the shoulders (20.7%), and 40 were in the feet (11.4%). Others ranged from 6.0% to 0.28%, respectively, from the legs, arms, neck, trunk, groin, and head. Causal mechanisms for the hands included moisture and hard glove contacts resulting in fingernail injuries; in the shoulders, hard contact with suit components and strain mechanisms; and in the feet, hard boot contact. The severity of symptoms was highest in the shoulders, hands, and feet. CONCLUSIONS: Most signs and symptoms were mild, self-limited, of brief duration, and were well controlled by available countermeasures. Some represented the potential for significant injury with consequences affecting astronaut health and performance. Correction of extravehicular activity training-related injuries requires a multidisciplinary approach to improve prevention, medical intervention, astronaut training, test planning, and suit engineering.

Arm Injuries↗
PubMed1994

A novel use of differential equations to fit exponential functions to experimental data.

A procedure for fitting multi-exponential functions to experimental data is described. It is fast, requires no initial parameter estimates and is particularly suited to sums of several closely spaced exponentials. The method comprises the application of three well tried numerical techniques: (i) the signal is smoothed by representing it as an abbreviated Legendre series; (ii) the coefficients of a certain kind of differential equation are determined such that it's solution is the closest fit to the smoothed signal; and (iii) the amplitudes of the exponential components are determined, given the calculated values of the exponential rate constants. The method is computationally efficient, since determination of amplitudes and exponents involves the use of linear techniques, and therefore does not require multiple iterations, and the smoothed signal is contained in a handful of coefficients rather than as a lengthy time series. The severe ill-conditioning that is unavoidable in this problem is contained within the well-understood procedures of inverting a matrix and determining the roots of a polynomial. This method is particularly appropriate for analysis of data that may be modelled by a scheme of linked first-order reactions, describing for example the stochastic behaviour of ion channels, a chemical reaction, or the uptake and distribution of a drug within body compartments.

Data Interpretation, Statistical↗
PubMed1993

In vivo noradrenaline release evoked in the anteroventral thalamic nucleus by locus coeruleus activation: an electrochemical study.

The anteroventral thalamic nucleus is innervated by noradrenergic terminals exclusively originating in the locus coeruleus, a densely packed cell group located in the dorsotegmental part of the pons. In urethane-anaesthetized rats, electrical stimulations of locus coeruleus axons (dorsal noradrenergic bundle; 14 Hz, 20 s) evoked a rapid increase in the signal (catechol oxidation current) measured within the anteroventral thalamic nucleus by the use of carbon fibre electrodes combined with electrochemistry. This effect was reproducible and immediately reversible. Evoked changes in this current were found to be due to oxidation of noradrenaline released from terminals. The amplitude of the evoked noradrenaline release varied non-linearly with the frequency of stimulation. We investigated the influence of locus coeruleus activation on noradrenaline release measured in the anteroventral thalamic nucleus every second by means of differential pulse amperometry: (i) chemical activation of locus coeruleus by local injection of glutamate (0.2-0.8 nmol) immediately and consistently evoked noradrenaline release in a dose-dependent manner; and (ii) peripheral stimulation of the sciatic nerve (20 s)--known to enhance the firing rate of locus coeruleus neurons-evoked a noradrenaline release similar to that produced by a stimulation of the dorsal noradrenergic bundle at 8-10 Hz. Pharmacological and kinetic characteristics of the noradrenaline release were the same for central or peripheral stimulation of locus coeruleus neurons. Our results indicate that in vivo electrochemistry, because of its sensitivity and its high space and time resolution, is well suited for studies of evoked noradrenaline release from locus coeruleus terminals. This approach allowed us to describe the characteristics of central noradrenaline release evoked by central and peripheral stimulations of short duration. In particular, we observed a very close relationship between impulse flow and evoked noradrenaline release.

Animals↗
PubMed2004

Imaging in head and neck oncology.

Evaluation of head and neck cancer with imaging is a topic that is far more extensive than can be covered in this article. The main reason for head and neck imaging is to evaluate the true extent of disease to best determine surgical and therapeutic options. This process includes evaluation of the size, location, and extent of tumor infiltration into surrounding vascular and visceral structures. Important anatomic variants must be pointed out so the surgeon can avoid potential intraoperative complications. These variant scan be evaluated with the appropriate multiplanar and three-dimensional images to provide as much information as possible to the surgeon preoperatively. Second, nodal staging should be assessed in an effort to increase the number of abnormal nodes detected by physical examination and, more important, to precisely define their location by a standard classification system that can be understood and consistently applied by the radiologist, surgeon, radiation oncologist, and pathologist. Although secondary to the previously described tasks, imaging frequently enables a limitation of the diagnostic and histologic possibilities based on lesion location and signal-attenuation characteristics, which may lead the clinical investigation along a different path. saving the patient unnecessary risk and shortening the time to diagnosis and ultimate treatment. This article has attempted to detail the current state of the controversy between CT, MRI, and other modalities, and has emphasized the constant evolution of this controversy because of the evolving imaging technology. Although CT and MRI are both well suited to evaluation of the deep spaces and submucosal spaces of the head and neck, each has some limitations.MRI has the advantages of higher soft tissue contrast resolution, the lack of iodine-based contrast agents, and high sensitivity for perineural and intracranial disease. The disadvantages of MRI include lower patient tolerance, contraindications in pacemakers and certain other implanted metallic devices, and artifacts related to multiple causes, not the least of which is motion. CT is fast, well tolerated, and readily available but has lower contrast resolution and requires iodinated contrast and ionizing radiation. The current authors' practice is heavily centered on CT for initial evaluation, preoperative planning, biopsy targeting, and postoperative follow-up. They reserve MRI for tumors that are suspicious for perineural,cartilaginous, or bony invasion on CT, or for tumors such as adenoid cystic carcinoma that are highly likely to spread by way of these routes. For patients who have head and neck cancer, a radiologist who is educated in the treatment options, patterns of tumor growth, and important surgical landmarks, and who has a well-established pattern of communication with the head and neck clinical services, including surgery, radiation oncology,and pathology, is key in providing accurate and useful image interpretation.

Carcinoma, Squamous Cell↗
PubMed1970

Neuroglia: biophysical properties and physiologic function.

The membrane time constant of neocortical glial cells is abolut 385 microseconds, less than one-twentieth the known value for the Betz cell. Glial membrane specific resistance is low (approximately 200 to 500 ohm centimeters squared. Neuroglial cells are ideally suited to buffer the immediate extraneuronal space at areas of synaptic contact against the increases in external potassium ion concentration that accompany postsynaptic and spike activity and to minimize the spread of potassium ions to other pre- and postsynaptic regions.

Animals↗