bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of glutamine in cerebral nitrogen metabolism and ammonia neurotoxicity
Authors: Cooper Arthur J.L.
Published: August 2002

Ammonia enters the brain by diffusion from the blood or cerebrospinal fluid, or is formed in situ from the metabolism of endogenous nitrogen‐containing substances. Despite its central importance in nitrogen homeostasis, excess ammonia is toxic to the central nervous system and its concentration in the brain must be kept low. This is accomplished by the high activity of glutamine synthetase, which is localized in astrocytes and which permits efficient detoxification of incoming or endogenously generated ammonia. The location also permits the operation of an intercellular glutamine cycle. In this cycle, glutamate released from nerve terminals is taken up by astrocytes where it is converted to glutamine. Glutamine is released to the extracellular fluid to be taken up into the nerve cells, where it is converted back to glutamate by the action of glutaminase. Most extrahepatic organs lack a complete urea cycle, and for many organs, including the brain, glutamine represents a temporary storage form of waste nitrogen. As such, glutamine was long thought to be harmless to the brain. However, recent evidence suggests that excess glutamine is neurotoxic. Hyperammonemic syndromes (e.g., liver disease, inborn errors of the urea cycle, Reye's disease) consistently cause astrocyte pathology. Evidence has been presented that hyperammonemia results in increased formation of glutamine directly in astrocytes, thereby generating an osmotic stress to these cells. This osmotic stress results in impaired astrocyte function, which in turn leads to neuronal dysfunction. In this review a brief overview is presented of the role of glutamine in normal brain metabolism and in the pathogenesis of hyperammonemic syndromes. MRDD Research Reviews 2001;7:280–286. © 2001 Wiley‐Liss, Inc.
Estimation of local aortic elastic properties with MRI
Authors: Vulliémoz Serge , Stergiopulos Nikos , Meuli Reto
Published: August 2002

Aortic compliance and pulse wave velocity (PWV) are important determiners of heart load, and are clinically useful indices of cardiovascular risk. Most direct methods to derive them require invasive pressure measurement. In this work a noninvasive technique to evaluate aortic compliance and PWV using MRI is proposed. MRI magnitude and phase images to measure area and flow in the ascending aorta were acquired in a group of 13 young healthy subjects. Assuming that the early systolic part of the wave was unidirectional and reflectionless, PWV was determined as the ratio between flow and area variations at early systole. Our results were compared to pulse wave velocities derived from a direct transit time, and to one using ascending aortic area and peripheral brachial pulse pressure. The new method proved to be accurate and in good agreement with the transit time method, as well as with previously published results. Magn Reson Med 47:649–654, 2002. © 2002 Wiley‐Liss, Inc.
Assessment of a potential tumor‐seeking manganese metalloporphyrin contrast agent in a mouse model
Authors: Takehara Yasuo , Sakahara Harumi , Masunaga Hatsuko , Isogai Satoshi , Kodaira Nami , Sugiyama Masahiro , Takeda Hiroyasu , Saga Tsuneo , Nakajima Susumu , Sakata Isao
Published: August 2002

The performance of a newly developed potential tumor‐seeking magnetic resonance (MR) contrast agent α‐Aqua‐13,17‐bis(1‐carboxypropionyl) carbamoylethyl‐3,8‐bis(1‐phenethyloxyethyl)‐β‐hydroxy‐2,7,12,18‐tetramethyl‐porphyrinato manganese (III) (HOP‐8P) was tested using a mouse model. Tumor‐bearing (SCC‐VII) mice were imaged using a 1.5T MR imager before and after intravenous administration of 0.1 mmol/kg of HOP‐8P. A biodistribution analysis was performed using an optical emission spectrometer. Significant enhancement of the transplanted tumor was observed in MR images 24 h after intravenous injection of HOP‐8P. The biodistribution assessment of manganese also correlated with the results of the imaging study. During the 24‐h period following contrast administration, HOP‐8P was consistently cleared from the circulation, liver, kidneys, and muscle; however, it was progressively accumulated within the tumor. HOP‐8P is a promising tumor‐seeking metalloporphyrin MR contrast agent with a wide imaging window. Magn Reson Med 47:549–553, 2002. © 2002 Wiley‐Liss, Inc.
In vivo 1H2O T measurement in the human occipital lobe at 4T and 7T by Carr‐Purcell MRI: Detection of microscopic susceptibility contrast
Authors: Bartha Robert , Michaeli Shalom , Merkle Hellmut , Adriany Gregor , Andersen Peter , Chen Wei , Ugurbil Kamil , Garwood Michael
Published: August 2002

A high‐resolution spin‐echo imaging method is presented (called CP‐LASER) which exploits the spin refocusing capability of an adiabatic Carr‐Purcell (CP) pulse sequence to measure apparent 1H2O transverse relaxation (T) and generate contrast based on microscopic tissue susceptibility. High‐resolution CP‐LASER images of the human occipital lobe were acquired at four different echo times from six subjects at 4T and eight subjects at 7T to investigate the effect of magnetic field strength (B0) and the CP interpulse time (τcp) on T. Susceptibility contrast was identified and T was quantified for long τcp (>10 ms) and short τcp (7 ms at 4T and 6 ms at 7T) in gray matter, white matter, and cerebral spinal fluid. The 1H2O relaxation rate constants (1/T) of gray and white matter each increased approximately linearly with field strength and T was inversely related to τcp. The average T value of gray matter was 19% and 9% smaller than that of white matter at 4T and 7T, respectively. These results are consistent with higher levels of compartmentalized ferritin and increased blood volume in gray matter compared to white matter in this region of the brain. Magn Reson Med 47:742–750, 2002. © 2002 Wiley‐Liss, Inc.
Noninvasive in vivo oximetric imaging by radiofrequency FT EPR
Authors: Subramanian Sankaran , Yamada Ken‐Ichi , Irie Akira , Murugesan Ramachandran , Cook John A. , Devasahayam Nallathamby , Van Dam Gootzian M. , Mitchell James B. , Krishna Murali C.
Published: August 2002

A novel method, called relaxo‐oximetry, for rapid spatially resolved in vivo measurements of oxygen concentration using time‐domain radiofrequency (RF) electron paramagnetic resonance (EPR) is described. Time‐domain data from triaryl methyl (TAM)‐based single‐electron contrast agents were processed by systematic deletion of the initial time points to arrive at T‐weighted discrimination of signal amplitudes. In experiments involving phantoms, the line widths [∼ (T)−1] increased as a function of oxygen, and the slope (line width/pO2) was the same for both absorption‐ and magnitude‐mode line shapes. Line widths derived from T weighting and the computed pO2 values agreed favorably with the measured ones from phantoms of known oxygen tension. In vivo relaxo‐oximetry was performed on C3H mice, and it was found that the liver was more hypoxic than the kidneys. For tumors, 2D oxygen maps were generated while the animal breathed room air or Carbogen® (95% O2/5% CO2). Carbogen® enhanced oxygen concentration within the tumor, and the pO2 histograms showed considerable heterogeneity. Clark electrode oxygen measurements on organs and tumors were in good agreement with tissue oxygen measurements done by relaxo‐oximetry. Thus, from a single spatial image data set, pO2 measurements can be done noninvasively by relaxo‐oximetry, and 3D imaging can be performed in less than 3 min. Magn Reson Med 47:1001–1008, 2002. © 2002 Wiley‐Liss, Inc.
Integral method for numerical simulation of MRI artifacts induced by metallic implants
Authors: Balac S. , Caloz G. , Cathelineau G. , Chauvel B. , de Certaines J.D.
Published: August 2002

Numerical simulation is a valuable tool for the study of magnetic susceptibility artifacts from metallic implants. A major difficulty in the simulation lies in the computation of the magnetic field induced by the metallic implant. A new method has been designed and implemented to compute the magnetic field induced by metallic objects of arbitrary shape. The magnetic field is expressed pointwise in terms of a surface integral. Efficient quadrature schemes are proposed to evaluate this integral. Finally, the method is linked to an artifact reconstruction model to simulate the images. Magn Reson Med 45:724–727, 2001. © 2001 Wiley‐Liss, Inc.
7T vs. 4T: RF power, homogeneity, and signal‐to‐noise comparison in head images
Authors: Vaughan J.T. , Garwood M. , Collins C.M. , Liu W. , DelaBarre L. , Adriany G. , Andersen P. , Merkle H. , Goebel R. , Smith M.B. , Ugurbil K.
Published: August 2002

Signal‐to‐noise ratio (SNR), RF field (B1), and RF power requirement for human head imaging were examined at 7T and 4T magnetic field strengths. The variation in B1 magnitude was nearly twofold higher at 7T than at 4T (∼42% compared to ∼23%). The power required for a 90° pulse in the center of the head at 7T was approximately twice that at 4T. The SNR averaged over the brain was at least 1.6 times higher at 7T compared to 4T. These experimental results were consistent with calculations performed using a human head model and Maxwell's equations. Magn Reson Med 46:24–30, 2001. © 2001 Wiley‐Liss, Inc.
Real‐time interactive coronary MRA
Authors: Nayak Krishna S. , Pauly John M. , Yang Phillip C. , Hu Bob S. , Meyer Craig H. , Nishimura Dwight G.
Published: August 2002

An interactive real‐time imaging system capable of rapid coronary artery imaging is described. High‐resolution spiral and circular echo planar trajectories were used to achieve 0.8 × 1.6 mm2 resolution in 135 ms (CEPI) or 1.13 × 1.13 mm2 resolution in 189 ms (spirals), over a 20‐cm FOV. Using a sliding window reconstruction, display rates of up to 37 images/sec were achieved. Initial results indicate this technique can perform as a high‐quality 2D coronary localizer and with SNR improvement may enable rapid screening of the coronary tree. Magn Reson Med 46:430–435, 2001. © 2001 Wiley‐Liss, Inc.
Development of biocompatible oxygen‐permeable films holding paramagnetic carbon particles: Evaluation of their performance and stability in EPR oximetry
Authors: He Jiang , Beghein Nelson , Ceroke Paul , Clarkson R.B. , Swartz Harold M. , Gallez Bernard
Published: August 2002

EPR oximetry using paramagnetic particles relies on the measurement of the EPR linewidth, which is directly related to the pO2. It was previously found that some of the paramagnetic materials with optimal EPR spectroscopic properties in vitro may lose their responsiveness to oxygen in tissues (change of the calibration curve of the EPR linewidth as a function of the pO2). We hypothesized that coating paramagnetic particle materials could improve the stability of response, as well as the biocompatibility. In this study, very thin films holding paramagnetic materials were prepared with different biopolymers (cellulose acetate, cellulose triacetate, cellulose nitrate, silicone, and polyurethane) that already are accepted for clinical applications. Their performance was evaluated in EPR oximetry by measuring the stability of the calibration curves (EPR linewidth as a function of pO2) after a prolonged period in an aqueous environment
(1 week in saline) or in vivo (implantation for 3 weeks under the skin of mice). We found that one type of silicone film was able to stabilize the responsiveness of an intrinsically unstable carbon material (a wood char). Magn Reson Med 46:610–614, 2001. © 2001 Wiley‐Liss, Inc.
Modified block uniform resampling (BURS) algorithm using truncated singular value decomposition: Fast accurate gridding with noise and artifact reduction
Authors: Moriguchi Hisamoto , Duerk Jeffrey L.
Published: August 2002

The block uniform resampling (BURS) algorithm is a newly proposed regridding technique for nonuniformly‐sampled k‐space MRI. Even though it is a relatively computationally intensive algorithm, since it uses singular value decomposition (SVD), its procedure is simple because it requires neither a pre‐ nor a postcompensation step. Furthermore, the reconstructed image is generally of high quality since it provides accurate gridded values when the local k‐space data SNR is high. However, the BURS algorithm is sensitive to noise. Specifically, inaccurate interpolated data values are often generated in the BURS algorithm if the original k‐space data are corrupted by noise, which is virtually guaranteed to occur to some extent in MRI. As a result, the reconstructed image quality is degraded despite excellent performance under ideal conditions. In this article, a method is presented which avoids inaccurate interpolated k‐space data values from noisy sampled data with the BURS algorithm. The newly proposed technique simply truncates a series of singular values after the SVD is performed. This reduces the computational demand when compared with the BURS algorithm, avoids amplification of noise resulting from small singular values, and leads to image SNR improvements over the original BURS algorithm. Magn Reson Med 46:1189–1201, 2001. © 2001 Wiley‐Liss, Inc.
Idiopathic bilateral diaphragmatic paralysis
Authors: Valls‐Solé Josep , Solans Margarita
Published: August 2002

A 41‐year‐old man complained of subacute onset of dyspnea and pain in the neck and chest. He was diagnosed with bilateral diaphragmatic paralysis, based on clinical inspection of the breathing pattern and transdiaphragmatic pressure recording, and was trained to use a portable bi‐level positive airway pressure apparatus (BiPAP). Needle electromyography showed profuse fibrillation potentials and positive waves in the diaphragm, more abundant on the right than left side, and no response to phrenic nerve stimulation. Other muscles were not involved. Follow‐up examinations, performed at 9 and 12 months after onset of paralysis, demonstrated a slow but progressive improvement of the patient's respiratory function, together with the appearance of reinnervation potentials in the diaphragm, and polyphasic, long‐latency responses to phrenic nerve stimulation. The subacute onset of the paralysis associated with local pain, and its subsequent recovery, suggest bilateral proximal lesions in the phrenic nerves. In the absence of traumatic or metabolic causes, these findings suggest that the phrenic nerve can be a target in idiopathic neuritis. © 2002 Wiley Periodicals, Inc. Muscle Nerve 25: 000–000, 2002.
Gender, body mass and age as risk factors for ulnar mononeuropathy at the elbow
Authors: Richardson James K. , Green Donald F. , Jamieson Sarah C. , Valentin F. Clifford
Published: August 2002

Factors that predispose patients to ulnar mononeuropathy at the elbow (UME) are poorly defined. We compared 112 electrodiagnostic reports which met criteria for definite or probable UME to 104 reports which excluded UME. Male gender was strongly associated with definite (OR = 6.9, 95% CI = 2.4–20.4; P < 0.001) and all UME (OR = 2.2, 95% CI = 1.2–4.1; P = 0.010) after controlling for age and body mass index (BMI). Among men, UME was associated with increasing age (P = 0.008) but not a decreased BMI. Women, however, demonstrated an association between decreased BMI and UME (OR = 2.3, 95% CI = 1.3–4.2 for BMI ≤22.0 versus >22.0). These findings, in conjunction with gender differences in ulnar motor nerve parameters among UME subjects and controls, suggest that the pathophysiology of UME differs with gender. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24:551–554, 2001
Sodium influx during action potential in innervated and denervated rat skeletal muscles
Authors: Kotsias Basilio A. , Venosa Roque A.
Published: August 2002

Resting Na+ influx (JiNa) was measured in innervated and denervated (1–6 days) rat extensor digitorum longus muscle in the absence and presence of 2 μmol/L tetrodotoxin (TTX).The mean value of Na+ permeability (PNa) in innervated muscles was 49.6 ± 2.6 pm.s−1. At the second day postdenervation, it decreased by about 45%. This was followed, between the second and fourth days, by a sharp rise, which by the sixth day reached a steady value ∼2.5 times greater than that of innervated muscles. This, most likely, generated the 30% increase in internal [Na+] concentration ([Na+]I) observed at this time. Tetrodotoxin reduced PNa of both innervated and denervated muscles by about 25%. In 6‐day denervated muscles, virtually all the TTX effect on PNa represents the blockage of TTX‐resistant Na+ channels. Denervation produced a depolarization of about 20 mV by the sixth day. The extra JiNa per action potential (AP) decreased monotonically with time after denervation from 20.0 ± 3.8 in innervated to 11.1 ± 1.0 nmol.g−1.AP−1 in 6‐day denervated muscles. The overshoot of the AP decreased from 15 ± 1 in innervated to 7 ± 1 mV in 6‐day denervated muscles. Likewise, the maximum rate of rise (+dV/dt), an expression of the inward Na+ current, fell from 305 ± 14 in innervated to 188 ± 18 V.s−1 in 6‐day denervated muscles. The estimated 6‐day denervated/innervated ratio of peak Na+ conductance (gNa) was 0.67. The changes in AP parameters promoted by denervation were substantially reduced when both innervated and denervated fibers were hyperpolarized to −90 mV. These results suggest that the depolarization, mainly due to the increase in PNa /PK ratio, increases Na+ inactivation and consequently reduces peak gNa , in spite of the absolute increment in resting TTX‐sensitive PNa. This, in addition to the moderate reduction in the inward driving force on Na+, decreases the inward Na+ current and the extra JiNa per AP. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 1026–1033, 2001
Influence of age and height on nerve conduction
Authors: Rivner Michael H. , Swift Thomas R. , Malik Khalid
Published: August 2002

Previous studies demonstrated age‐ and height‐related slowing of nerve conduction velocity (NCV) and reduction in nerve response amplitude. Unfortunately, many studies examined discontinuous populations, preventing regression analysis. The correlation coefficients of available studies vary widely, preventing clear conclusions. We retrospectively examined 3969 clinically normal subjects ranging in age from 20 to 95 years from a total of 22,420 electrodiagnostic studies done between 1986 and 1998. The correlation of NCV with height was stronger than with age. Regression equations using both factors account for 12–27% of the variance. Responses were seen in the majority of patients aged 70 years and older, but the percentage of normals who had no response increased with advancing age. Age was strongly inversely correlated with the amplitudes of both sensory and motor responses, accounting for 7–16% of the variance. Regression equations using both height and age improved this correlation, accounting for 7–22% of the variance. Therefore, both height and age must be taken into consideration when normal values are developed. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 1134–1141, 2001
Nerve lesions and the generation of pain
Authors: Campbell James N.
Published: August 2002

This review addresses the issue of how axotomy of peripheral nerve fibers leads to pain and hyperalgesia. The point of axotomy (the nerve injury site), the dorsal root ganglia, and the dorsal horn of the spinal cord are candidate sites for generation of the pain signal that is likely to be critical for maintaining the neuropathic pain state. This review considers neuropathic pain from a “systems” perspective, tracing concepts of neuropathic pain from the work of Henry Head to the present. Surprisingly, the nerve injury site and the dorsal root ganglion belonging to a transected spinal nerve do not give rise to spontaneous activity in putative C‐fiber nociceptors. The intact nociceptor belonging to adjacent uninjured spinal nerves, however, does acquire abnormal spontaneous activity and a chemical sensitivity to catechols. It is suggested that partially denervated tissues in the nerve, skin, and other locations may release substances that, in turn, sensitize the intact nociceptors. These abnormalities in the intact nociceptor, which arise in the context of Wallerian degeneration, probably play a role in creating or maintaining the abnormal pain state. These considerations probably also apply to the understanding of pain arising in other neuropathies. The findings relative to the “intact” nociceptor provide a rationale by which to understand how therapies distal to the nerve injury site may diminish pain. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 1261–1273, 2001.
Multiphase model for inclusion‐reinforced geostructures: Application to rock‐bolted tunnels and piled raft foundations
Authors: Sudret Bruno , de Buhan Patrick
Published: August 2002

A multiphase model is proposed to describe the mechanical behaviour of geomaterials reinforced by linear inclusions. This macroscopic approach considers the reinforced soil or rock mass as the superposition of continuous media. Equations of motion and constitutive laws of the model are first derived. Its implementation in a finite element computer code is then detailed. A modified implicit algorithm for elastoplastic problems is proposed. The model and its implementation are fully validated for rock‐bolted tunnels (comparison with scale model experiments) and piled raft foundations (comparison with the classical ‘hybrid method’). The Messeturm case history is finally presented to assess the handiness of the approach for real structures. Copyright © 2001 John Wiley & Sons, Ltd.
A phenomenological constitutive model for rocks with shear failure mode
Authors: Zhou G. L. , Tham L. G. , Lee P. K. K. , Tsui Y.
Published: August 2002

In this paper, a phenomenological constitutive model is proposed to simulate the stress–strain behaviours of intact rocks with shear failure mode. The model captures a wide range of behaviours of rock material such as elastic, plastic, strain softening, ‘Class II’, strain localization, elastic modulus degradation, etc. The sensitivity of the stress–strain relation on the parameters is also investigated. Typical results obtained by testing a number of granite and marble specimens are used to validate the proposed model. Copyright © 2001 John Wiley & Sons, Ltd.
Volumetric sand production model and experiment
Authors: Papamichos E. , Vardoulakis I. , Tronvoll J. , Skjærstein A.
Published: August 2002

A sand production model was developed for volumetric sand production predictions that take into account the effects of the external stresses and fluid flow rate. The model couples the poro‐mechanical behaviour of the solid–fluid system with the erosion behaviour of the solids due to fluid flow. It predicts reasonably experimental volumetric sand production data from a hollow cylinder test on a weak sandstone. The test results show that in weak and compactive sandstones, sand production is associated with decohesioning and plasticification of a zone around the inner hole which can then be mobilized by the hydrodynamic forces of the fluid flow. The sand production rate increases both with external applied stress and fluid flow rate but it is constant with time under constant external stress and fluid flow rate. In both cases a critical lower limit has to be exceeded for sand production initiation. Copyright © 2001 John Wiley & Sons, Ltd.
Analytical simulation of the dynamic compressive strength of a granite using the sliding crack model
Authors: Li H. B. , Zhao J. , Li T. J. , Yuan J. X.
Published: August 2002

A sliding crack model is employed to simulate rock strength under dynamic compression. It is assumed that the growth and nucleation of a sliding crack array presented results in the shear fault failure and dominate the mechanical properties of rock material. The pseudo‐tractions method is used to calculate the stress intensity factor of the sliding crack array under compression. With the utilization of a dynamic crack growth criterion, the growth of the sliding crack array is studied and the simulated strengths of a granite under dynamic compression are correspondingly obtained. It is concluded that the simulated rock strengths increase with increasing strain rates at different confining pressures, and the rising rates have a trend to decrease with increasing confining pressures. It is also indicated that the simulated rock strengths increase with increment of confining pressure at different strain rates, and the rising rates are almost identical at different strain rates. The simulation results are validated by the experimental data for the granite. Copyright © 2001 John Wiley & Sons, Ltd.
A constitutive model for crushed salt
Authors: Olivella S. , Gens A.
Published: August 2002

A constitutive model for crushed salt is presented in this paper. A creep constitutive model is developed first and compared with test results. The constitutive model presented here concentrates on creep deformation because saline media behave basically in a ductile and time‐dependent way. An idealized geometry is used as a common framework to obtain stress–strain macroscopic laws based on two deformation mechanisms: fluid‐assisted diffusional transfer creep and dislocation creep. The model is able to predict strain rates that compare well with results from laboratory tests under isotropic and oedometric conditions. Macroscopic laws are written using a non‐linear viscous approach, which incorporates also a viscoplastic component, based on critical state theory. The viscoplastic term is intended for non‐creep deformation mechanisms such as grain reorganization and crushing. Copyright © 2002 John Wiley & Sons, Ltd.
Bulbocavernosus muscle responses after suprapubic stimulation: Analysis and measurement of suprapubic bulbocavernosus reflex latency
Authors: Amarenco Gerard , Bayle Beatrice , Ismael Samer Sheikh , Kerdraon Jacques
Published: August 2002

Our objective was to describe pelvic floor responses with measurement of reflex latency after suprapubic mechanical stimulation. Twenty‐one patients without neurological disease were studied. They were 14 women and seven men. The mean age was 51 (SD = 14.2). Motor responses were recorded with a needle electrode inserted in the left bulbocavernosus muscle. Stimulation was delivered with an electromechanical hammer, tapping directly on the suprapubic area. A polyphasic muscular response was always easily elicited in all patients. The man latency was 67.5 milliseconds (SD = 14.7). The reproducibility between the first and second mechanical responses was good with no statistical difference (r=0.966;P = 0.0001). In three patients who underwent cystometry, no rise in detrusor pressure was observed during mechanical stimulation of the suprapubic area. Our study clearly demonstrates a suprapubic bulbocavernosus reflex (SBR). Tapping the suprapubic area is a strong stimulus, reflexively mediated, used in the management of neurogenic bladder to determine a bladder contraction. However, the reflex consisting of pelvic floor muscle contraction after suprapubic stimulation was not specifically studied in humans. Many arguments can be put forth for a polysynaptic reflex (polyphasic response, habituation and short latency of the reflex, mean latency in the habitual values of R2 responses after electrical stimulation of the dorsal nerve of the penis). We hypothesize that the true stimulus is the stimulation of the bladder wall tensoreceptors, the integration level of the SBR is the sacral segments and the efferent limb the pudendal nerve, and afferent pathways could be conducted by pelvic nerve fibers. Competition between a preponderant (or exaggerated) SBR and a bladder contraction after suprapubic tapping may constitute an equivalent of detrusor‐sphincter dyssynergia in some suprasacral bladders. Neurourol. Urodynam. 21:210–213, 2002. © 2002 Wiley‐Liss, Inc.
1H NMR spectroscopy as a tool to evaluate key metabolic functions of primary porcine hepatocytes after cryopreservation
Authors: Dabos Konstantinos J. , Parkinson John A. , Hewage Chandralal , Nelson Leonard J. , Sadler Ian H. , Hayes Peter C. , Plevris John N.
Published: August 2002

Proton NMR spectroscopy of biological fluids has produced interesting results lately. We used the technique to investigate the effects of cryopreservation on primary porcine hepatocytes as successful cryopreservation of primary porcine hepatocytes is of importance to the development of bioartificial liver support systems. After isolation 108 hepatocytes were cryopreserved for 1 week in Williams E/10% DMSO, either by quick freezing (−5 to −30 °C/min), slow freezing (−0.3 to −3 °C/min) or stepwise freezing protocols on cell suspensions and confluent cell plates. Plating efficiency was assessed by percentage LDH release. Metabolic functions of cryopreserved hepatocytes at 24 h post‐thawing were compared with those of fresh hepatocyte cultures at 48 h. 1H nuclear magnetic resonance spectroscopy of the culture medium post‐incubation, using the presaturation technique, assessed the following: glucose metabolism, transamination and glutamine synthesis and succinate synthesis. Freshly isolated cells had a viability of 82 ± 4.3% and a plating efficiency of 87 ± 3.8%. All cryopreservation protocols resulted in significantly reduced viability and plating efficiency. No significant differences were observed between different cryopreservation media or protocols. When comparing cryopreserved with freshly isolated cells, we observed that metabolism of acetyl‐CoA precursors was significantly impaired in cryopreserved cells. Lactate and pyruvate production was also significantly less, although glucose consumption was similar. No differences were observed in gluconeogenic amino acid metabolism, transamination and urea synthesis. 1H NMR spectroscopy can be used to provide information about metabolic activity and functions of cultured primary cells. Copyright © 2002 John Wiley & Sons, Ltd.
Approximate inverse computation using Frobenius inner product
Authors: Montero G. , González L. , Flórez E. , García M. D. , Suárez A.
Published: August 2002

Parallel preconditioners are presented for the solution of general linear systems of equations. The computation of these preconditioners is achieved by orthogonal projections related to the Frobenius inner product. So, minM∈𝒮∥AM−I∥ F and matrix M0∈𝒮 corresponding to this minimum (𝒮 being any vectorial subspace of ℳ︁n(ℝ)) are explicitly computed using accumulative formulae in order to reduce computational cost when subspace 𝒮 is extended to another one containing it. Every step, the computation is carried out taking advantage of the previous one, what considerably reduces the amount of work. These general results are illustrated with the subspace of matrices M such that AM is symmetric. The main application is developed for the subspace of matrices with a given sparsity pattern which may be constructed iteratively by augmenting the set of non‐zero entries in each column. Finally, the effectiveness of the sparse preconditioners is illustrated with some numerical experiments. Copyright © 2002 John Wiley & Sons, Ltd.
Modelling crack growth by level sets in the extended finite element method
Authors: Stolarska M. , Chopp D. L. , Moës N. , Belytschko T.
Published: August 2002

An algorithm which couples the level set method (LSM) with the extended finite element method (X‐FEM) to model crack growth is described. The level set method is used to represent the crack location, including the location of crack tips. The extended finite element method is used to compute the stress and displacement fields necessary for determining the rate of crack growth. This combined method requires no remeshing as the crack progresses, making the algorithm very efficient. The combination of these methods has a tremendous potential for a wide range of applications. Numerical examples are presented to demonstrate the accuracy of the combined methods. Copyright © 2001 John Wiley & Sons, Ltd.
An updated Lagrangian finite element sensitivity analysis of large deformations using quadrilateral elements
Authors: Srikanth Akkaram , Zabaras Nicholas
Published: August 2002

A continuum parameter and shape sensitivity analysis is presented for metal forming processes using the finite element method. The sensitivity problem is posed in a novel updated Lagrangian framework as suitable for very large deformations when remeshing operations are performed during the analysis. In addition to exploring the issue of transfer of variables between meshes for finite deformation analysis, the complex problem of transfer of design sensitivities (derivatives) between meshes for large deformation inelastic analyses is also discussed. A method is proposed that is shown to give accurate estimates of design sensitivities when remeshing operations are performed during the analysis. Sensitivity analysis for the consistent finite element treatment of near incompressibility within the context of the assumed strain methods is also proposed. In particular, the performance of four‐noded quadrilateral elements for the sensitivity analysis of large deformations is studied. The results of the continuum sensitivity analysis are validated by a comparison with those obtained by a finite difference approximation (i.e. using the solution of a perturbed deformation problem). The effectiveness of the method is demonstrated by applications in the design optimization of metal forming processes. Copyright © 2001 John Wiley & Sons, Ltd.
Convergence study of the truncated Karhunen–Loeve expansion for simulation of stochastic processes
Authors: Huang S. P. , Quek S. T. , Phoon K. K.
Published: August 2002

A random process can be represented as a series expansion involving a complete set of deterministic functions with corresponding random coefficients. Karhunen–Loeve (K–L) series expansion is based on the eigen‐decomposition of the covariance function. Its applicability as a simulation tool for both stationary and non‐stationary Gaussian random processes is examined numerically in this paper. The study is based on five common covariance models. The convergence and accuracy of the K–L expansion are investigated by comparing the second‐order statistics of the simulated random process with that of the target process. It is shown that the factors affecting convergence are: (a) ratio of the length of the process over correlation parameter, (b) form of the covariance function, and (c) method of solving for the eigen‐solutions of the covariance function (namely, analytical or numerical). Comparison with the established and commonly used spectral representation method is made. K–L expansion has an edge over the spectral method for highly correlated processes. For long stationary processes, the spectral method is generally more efficient as the K–L expansion method requires substantial computational effort to solve the integral equation. The main advantage of the K–L expansion method is that it can be easily generalized to simulate non‐stationary processes with little additional effort. Copyright © 2001 John Wiley & Sons, Ltd.
An analysis for the compressible Stokes equations by first‐order system of least‐squares finite element method
Authors: Kim Sang Dong , Lee EunJung
Published: August 2002

This article applies the first‐order system least‐squares (fosls) finite element method developed by Cai, Manteuffel and McCormick to the compressible Stokes equations. By introducing a new dependent velocity flux variable, we recast the compressible Stokes equations as a first‐order system. Then it is shown that the ellipticity and continuity hold for the least‐squares functionals employing the mixture of H−1 and L2, so that the fosls finite element methods yield best approximations for the velocity flux and velocity. © 2001 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 17:689–699, 2001
Randomized trial of a home recovery intervention following coronary artery bypass surgery
Authors: Moore Shirley M. , Dolansky Mary A.
Published: August 2002

For this study a randomized clinical trial was designed to test the effects of an early home recovery information intervention on physical functioning, psychological distress, and symptom frequency 1 month following coronary artery bypass graft surgery (CABG). Recovery outcomes were compared between two groups: those receiving an audiotape of information on expected physical sensations and their management (Cardiac Home Information Program [CHIP]) in addition to the usual care, and those receiving the usual cardiac discharge information protocol. A nonprobability sample of 180 patients (84 women and 96 men; mean age = 62 years) was equally distributed between the two study groups. When controlling for age, comorbidity, and cardiac functional status, the results showed positive effects on physical functioning in women and psychological distress, vigor and fatigue in men. Consistent with other studies, women had worse physical functioning and more symptom frequency than men. These findings indicate that the CHIP intervention is an effective method to prepare CABG patients for home recovery. © 2001 John Wiley & Sons, Inc. Res Nurs Health 24: 93–104, 2001
Using diversity indices to measure changes in prey choice at the Shag River Mouth site, southern New Zealand
Authors: Nagaoka Lisa
Published: August 2002

As in the rest of Polynesia, human colonization of New Zealand marked the beginning of tremendous change for the native flora and fauna resulting in significant habitat destruction and numerous extinctions. The loss of numerous native vertebrates, especially economically important taxa such as moas and seals, must have greatly affected the foraging economy of southern New Zealand. The effect that declining abundances of native fauna had on subsistence can be understood through the use of foraging theory models. The prey choice model, in particular, can be used to examine how foragers choose the resources they exploit. From this model we can predict changes in the diet that occur with the loss of important resources. In this paper, I explore the use of diversity indices as one means of measuring these dietary changes. Richness and evenness measures of the faunal data from the Shag River Mouth site are used to evaluate predictions made by the prey choice model about changing diet breadth and foraging efficiency. Copyright © 2001 John Wiley & Sons, Ltd.
At the threshold between governance and management: community‐based natural resource management in Southern Africa
Authors: Fortmann Louise , Roe Emery , van Eeten Michel
Published: August 2002

In this article, we use the threshold‐based management framework to analyse and make policy recommendations for community‐based natural resource management (CBNRM). We introduce the concept, present two examples from Southern Africa, and lay out the fundamentals of the threshold‐based resource management approach. We then analyse the two cases using the framework to assess whether it can provide solutions to CBNRM implementation problems or whether the conditions characterizing many CBNRM sites would preclude use of the approach.

We suspect that John Cohen, in whose memory we are dedicating this article, would have been very pleased with our focus on management and governance, but would have greatly regretted the pretensions of high theory some may read into our framework. Copyright © 2001 John Wiley & Sons, Ltd.
Decentralization, local governance and ‘recentralization’ in Africa
Authors: Wunsch James S.
Published: August 2002

Although Many African states have pursued substantial decentralization reforms in the previous twenty years, many of these reforms are still experiencing problems in bringing about effective local governance. Often these problems grow from the difficulty in translating general reform initiatives into specific working arrangements at the local level that are effective in several key processes and operations. Specifically these include planning and capital investment, budgeting and fiscal management, personnel systems and management, and finance and revenue. A combination of central reluctance to relinquish authority in these key areas and the complexity of organizational redesign to support decentralization seem to explain these problems. Copyright © 2001 John Wiley & Sons, Ltd.
The fetal cerebellar vermis: normal development as shown by transvaginal ultrasound
Authors: Malinger G. , Ginath S. , Lerman‐Sagie T. , Watemberg N. , Lev D. , Glezerman M.
Published: August 2002

Objective

To determine the normal appearance and development of the fetal cerebellar vermis using mid‐sagittal planes obtained by transvaginal sonography.

Subjects and Methods

A total of 101 fetuses were evaluated by transvaginal sonography between 21 and 39 weeks of gestation. The mid‐sagittal antero‐posterior and cranio‐caudal vermian diameters, circumference and surface area were measured and calculated. Nomograms were produced.

Results

The vermis was observed in 96% of the cases and all the measurements were performed in 92%. The vermis grows in a linear fashion throughout pregnancy. The growth pattern correlates well with gestational age, biparietal diameter, head circumference and transverse cerebellar diameter.

Conclusion

Transvaginal sonography is a valuable tool in the study of the fetal vermis during the second half of pregnancy. Knowledge of its normal appearance may help identify developmental anomalies and enable accurate prenatal counseling. Copyright © 2001 John Wiley & Sons, Ltd.
Prenatal diagnosis: does it alter outcome?
Authors: Thomas D. F. M.
Published: August 2002

The prenatal detection of urinary tract anomalies is changing paediatric practice but in many areas the impact on clinical outcome remains difficult to quantify. However it is already apparent that termination of pregnancy has reduced the numbers of infants with lethal pulmonary hypoplasia and renal dsyplasia who would previously have been liveborn but destined to succumb as neonates. Similarly, referrals of major non lethal abnormalities such as bladder exstrophy are declining as parents increasingly opt for termination. Fetuses at greatest risk of early onset postnatal renal failure can now be identified with considerable accuracy on prenatal ultrasound. Termination, prompted by quality of life considerations, could result in reduced numbers of infants and young children requiring end stage renal failure treatment in the first few years of life. Pre natal detection of anomalies such as PUJ obstruction and reflux undoubtedly provides an opportunity to avert functional deterioration and minimise urinary infection. But the proportion of children who genuinely benefit has proved difficult to assess. The prenatal detection of mild dilatation is of doubtful benefit in all but a minority of cases. Clinically significant underlying pathology is rare yet this common prenatal finding often generates disproportionate parental anxiety. Copyright © 2001 John Wiley & Sons, Ltd.
Prenatal diagnosis of Joubert syndrome: a case report
Authors: Aslan Halil , Ulker Volkan , Gulcan E. Mahir , Numanoglu Ceyhun , Gul Ahmet , Agar Mehmet , Ark H. Cemal
Published: August 2002

Joubert syndrome is a rare, autosomal recessive condition, first described by Joubert in 1969. We present a case of Joubert syndrome from a consanguineous family in which, apart from the cerebellar vermis agenesis, ventriculomegaly, bilateral postaxial polydactyly of hands and right foot and micropenis, episodes of fetal breathing pattern with an increased respiratory rate were also demonstrated by prenatal ultrasound scan. At birth the infant showed an odd face and bilateral fleshy nodules of the tongue. He had an abnormal breathing pattern of alternating tachypnea and apnea. Cranial MRI showed molar tooth sign, hydrocephalus and Dandy–Walker malformation. He had nystagmus, and electroretinography showed retinal dystrophy. Copyright © 2002 John Wiley & Sons, Ltd.
Multicenter epidemiologic and health services research on therapeutics in the HMO Research Network Center for Education and Research on therapeutics
Authors: Platt Richard , Davis Robert , Finkelstein Jonathan , Go Alan S. , Gurwitz Jerry H. , Roblin Douglas , Soumerai Stephen , Ross‐Degnan Dennis , Andrade Susan , Goodman Michael J. , Martinson Brian , Raebel Marsha A. , Smith David , Ulcickas‐Yood Marianne , Chan K. Arnold
Published: August 2002

Research and education programs in therapeutics that combine the data, organizational capabilities, and expertise of several managed care organizations working in concert can serve an important role when a single organization is not large enough to address a question of interest, when diversity in populations or delivery systems is required, and when it is necessary to establish consistency of results in different settings. Nine members of the HMO Research Network, a consortium of health maintenance organizations (HMOs) that perform public domain research, have formed a Center for Education and Research on Therapeutics (CERT), sponsored by the Agency for Healthcare Research and Quality, to conduct multicenter research in therapeutics. The CERT uses a distributed organizational model with shared leadership, in which data reside at the originating organization until they are needed to support a specific study. Extraction of data from the host computer systems, and some manipulation of data, is typically accomplished through computer programs that are developed centrally, then modified for use at each site. For complex studies, pooled analysis files are created by a coordinating center, and then analysed by investigators throughout the HMOs. It is also possible to contact HMO members when necessary. This multicenter environment has several benefits, addressing: (1) a wide array of questions about the safety and effectiveness of therapeutics, (2) the impact of efforts to change clinicians' and patients' behavior, and (3) pharmacoeconomic and pharmacogenetic questions. Copyright © 2001 John Wiley & Sons, Ltd.
Estimation of incidence and prevalence of Parkinson's disease in the elderly using pharmacy records
Authors: van de Vijver D. A. M. C. , Roos R. A. C. , Jansen P. A. F. , Porsius A. J. , de Boer A.
Published: August 2002

Purpose

We determined the prevalence and incidence of Parkinson's disease among persons aged 55 years and older in pharmacy records.

Methods

Data came from the PHARMO database which includes information on drug dispensing for all residents of six Dutch cities. We selected all persons aged 55 years and older who had used antiparkinsonian drugs, and calculated a chance for having Parkinson's disease with use of a previously validated logistic regression model. We used a cut‐off of 0.5 (sensitivity 62%, positive predictive value 92%). Prevalence was estimated on the first Wednesday of October 1997, incidence on the first Wednesday of October 1993 until 1997. A patient was incident, if the first prescription for an antiparkinsonian drug was dispensed at least 180 days after entry into PHARMO. Prevalence and incidence were standardized to the Netherlands population of 1 January 1998. The prevalence was adjusted for the sensitivity and positive predictive value of the model.

Results

The unadjusted prevalence (per 100 000) for those aged 55–64 years was 111, 65–74 years 598, 75–84 years 1551 and for persons aged 85 years and older 1847. The adjusted and standardized prevalence was 970 per 100 000 (95% confidence interval 869 to 1071). The incidence (per 100 000 person years) for persons aged 55–64 years was 12, 65–74 years 108, 75–84 years 257 and for persons aged 85 years and older 247. The standardized incidence was 109 per 100 000 person years (96 to 121).

Conclusions

Prevalence and incidence were in range with the literature. Pharmacy records therefore seem to be a useful tool for continuous monitoring of incidence and prevalence of Parkinson's disease. Copyright © 2001 John Wiley & Sons, Ltd.