bluuebunny/crossref_metadata_2025 huggingface dataset:
Screen Printable Dielectric for Field Emission Displays
Authors: Bouchard Robert J. , Cheng Lap‐Tak , Roach David H. , Moffett Paul J. , Hang Kenneth W.
Published: May 2005

A system of an insulating Bi2O3‐based frit and a conductive SnO2:Sb has been developed for printing and firing on glass substrates. Resistivity can be progressively decreased from >200 GΩ to the megaohm region by adding micron size SnO2:Sb in the thick film formulation. More SnO2:Sb is required for a given resistivity when alumina is added as a filler, and resistivity is dependent on alumina particle size. Controllably reducing resistivity of a dielectric is useful in field emission display applications to eliminate charging between emitter lines and to function as a ballast resistor layer.
Characterization of Ceramics by X‐Ray and Neutron Small‐Angle Scattering
Authors: Allen Andrew J.
Published: May 2005

This paper reviews some recent advances in small‐angle X‐ray and neutron scattering methods and their application to address complex issues in ceramic systems of technological importance. It is shown how small‐angle scattering (SAS) can be applied to ceramic systems in order to extract statistically representative microstructure information (e.g., void volume fraction size distributions, internal surface areas, pore morphologies) that complements the information obtained from diffraction methods, X‐ray microtomography, or electron microscopy. It is demonstrated how SAS studies provide insights, not obtainable by other means, on the processing–microstructure–property relationships that frequently govern technological performance.
Selected Internet Sites for Transcultural Health Questions
Authors: Sobralske Mary
Published: May 2005

Are you new to the Internet and want some tips on findings sites that will help you in clinical practice? Maybe you are Internet savvy, but don't have the time to go searching for sites on transcultural health. Want the work done for you? This is a handy guide that discusses some selected Internet sites on questions you may have about your patients’ health beliefs and their culture. Here are tips for improving communication and assessment of your ethnically and culturally diverse patients.
A Unique Set of Interactions: The MSU Sustained Partnership Model of Nurse Practitioner Primary Care
Authors: Dontje Katherine , Corser William , Kreulen Grace , Teitelman Anne
Published: May 2005

Purpose

To present a unified conceptual model that identifies the integral processes of nurse practitioner (NP) care delivery and that integrates major structural influences and potential outcomes. The model is further characterized to delineate the unique and “value‐added” nature of NP primary care and to describe how this nature may be correlated with specific clinical outcomes.

Data Sources

Extensive review of the literature, relevant conceptual models, clinical experiences of the authors, and two sets of qualitative data exploring differences between NP practice and other practices.

Conclusions

The basis of NP primary care is the unique provider‐client relationship that develops within the primary care setting. This relationship is oriented toward (a) helping clients become empowered to more appropriately manage their own care in a way that will best meet their needs, (b) encouraging mutual decision making, (c) ensuring clients’ continuity of care, and (d) providing a holistic approach to primary care. The major structural influences are NP role components, interdisciplinary practice relationships, budget resources and payer mix, and environmental characteristics. The potential outcomes are increased healthpromoting behaviors, improved utilization of care, higher client satisfaction levels, and improved health status.

Implications for Practice

NPs can use this model to articulate the unique contribution of NP practice and its interrelationships within the broader primary care setting. Practicing NPs can use this framework to better understand the complexities of their current and future primary care practices. Faculty can utilize the concepts to help guide students’ understanding of their prospective roles as advanced practice nurses. Finally, this conceptual framework can inform research about specific NP processes and related outcomes. A clearly delineated model that accurately depicts structures, processes, and outcomes relevant to NP primary care can strengthen NP education, distinguish NP practice, and advance evidenced‐based research linking NP practice and outcomes.
Different effects of cardiac versus skeletal muscle regulatory proteins on in vitro measures of actin filament speed and force
Authors: Clemmens Emilie Warner , Entezari Michelle , Martyn Donald A. , Regnier Michael
Published: May 2005

Mammalian cardiac and skeletal muscle express unique isoforms of the thin filament regulatory proteins, troponin (Tn) and tropomyosin (Tm), and the significance of these different isoforms in thin filament regulation has not been clearly identified. Both in vitro and skinned cellular studies investigating the mechanism of thin filament regulation in striated muscle have often used heterogeneous mixtures of Tn, Tm and myosin isoforms, and variability in reported results might be explained by different combinations of these proteins. Here we used in vitro motility and force (microneedle) assays to investigate the influence of cardiac versus skeletal Tn and Tm isoforms on actin–heavy meromyosin (HMM) mechanics. When interacting with skeletal HMM, thin filaments reconstituted with cardiac Tn/Tm or skeletal Tn/Tm exhibited similar speed–calcium relationships and significantly increased maximum speed and force per filament length (F/l) at pCa 5 (versus unregulated actin filaments). However, augmentation of F/l was greater with skeletal regulatory proteins. Reconstitution of thin filaments with the heterogeneous combination of skeletal Tn and cardiac Tm decreased sliding speeds at all [Ca2+] relative to thin filaments with skeletal Tn/Tm. Finally, for filaments reconstituted with any heterogeneous mix of Tn and Tm isoforms, force was not potentiated over that of unregulated actin filaments. Combined the results suggest (1) that cardiac regulatory proteins limit the allosteric enhancement of force, and (2) that Tn and Tm isoform homogeneity is important when studying Ca2+ regulation of crossbridge binding and kinetics as well as mechanistic differences between cardiac and skeletal muscle.
Calcitonin gene‐related peptide‐induced suppression of luteinizing hormone pulses in the rat: the role of endogenous opioid peptides
Authors: Bowe J. E. , Li X. F. , Kinsey‐Jones J. S. , Paterson S. , Brain S. D. , Lightman S. L. , O'Byrne K. T.
Published: May 2005

Calcitonin gene‐related peptide (CGRP) is involved in a variety of stress responses in the rat. Central administration of CGRP activates the hypothalamo–pituitary–adrenal axis resulting in increased corticosterone secretion. We have previously shown that central CGRP suppresses the gonadotrophin‐releasing hormone (GnRH) pulse generator, specifically LH pulses. Endogenous opioid peptides (EOPs) have been shown to play an important role in stress‐induced suppression of the reproductive axis. The aim of the present study was to test the hypothesis that EOPs mediate CGRP‐induced suppression of pulsatile LH secretion. Ovariectomized rats were implanted with intracerebroventricular (i.c.v.) and i.v. cannulae. Intravenous administration of the opioid antagonist naloxone (250 μg) completely blocked the suppression of LH pulses induced by 1.5 μg i.c.v. CGRP and significantly attenuated the suppression of pulsatile LH secretion induced by 5 μg i.c.v. CGRP. Furthermore, intravenous administration of naloxone was found to immediately restore normal LH pulse frequency in animals treated 90 min earlier with 1.5 μg i.c.v. CGRP. Co‐administration (i.c.v.) of CGRP (1.5 μg) with the μ and κ opioid receptor‐specific antagonists naloxone (10 μg) and norbinaltorphimine (5 μg), respectively, blocked the CGRP‐induced suppression of LH pulses, whilst i.c.v. co‐administration of CGRP (1.5 μg) with the δ opioid receptor‐specific antagonist naltrindole (5 μg) did not. These data provide evidence that EOPs play a pivotal role in mediating the inhibitory effects of CGRP on pulsatile LH secretion in the rat. They also suggest that the μ and κ, but not the δ, opioid receptors may be responsible for mediating the effects of CGRP on LH pulses.
Specificity of TRH receptor coupling to G‐proteins for regulation of ERG K+ channels in GH3 rat anterior pituitary cells
Authors: Miranda Pablo , Giráldez Teresa , De La Peña Pilar , Manso Diego G. , Alonso‐Ron Carlos , Gómez‐Varela David , Domínguez Pedro , Barros Francisco
Published: May 2005

The identity of the G‐protein coupling thyrotropin‐releasing hormone (TRH) receptors to rat ether‐à‐go‐go related gene (r‐ERG) K+ channel modulation was studied in situ using perforated‐patch clamped adenohypophysial GH3 cells and dominant‐negative variants (Gα‐QL/DN) of G‐protein α subunits. Expression of dominant‐negative Gαq/11 that minimizes the TRH‐induced Ca2+ signal had no effect on r‐ERG current inhibition elicited by the hormone. In contrast, the introduction of dominant‐negative variants of Gα13 and the small G‐protein Rho caused a significant loss of the inhibitory effect of TRH on r‐ERG. A strong reduction of this TRH effect was also obtained in cells expressing either dominant‐negative Gαs or transducin α subunits, an agent known to sequester free G‐protein βγ dimers. As a further indication of specificity of the dominant‐negative effects, only the dominant‐negative variants of Gα13 and Rho (but not Gαs‐QL/DN or Gαt) were able to reduce the TRH‐induced shifts of human ERG (HERG) activation voltage dependence in HEK293 cells permanently expressing HERG channels and TRH receptors. Our results demonstrate that whereas the TRH receptor uses a Gq/11 protein for transducing the Ca2+ signal during the initial response to TRH, this G‐protein is not involved in the TRH‐induced inhibition of endogenous r‐ERG currents in pituitary cells. They also identify Gs (or a Gs‐like protein) and G13 as important contributors to the hormonal effect in these cells and suggest that βγ dimers released from these proteins may participate in modulation of ERG currents triggered by TRH.
The role of central 5‐HT3 receptors in vagal reflex inputs to neurones in the nucleus tractus solitarius of anaesthetized rats
Authors: Jeggo Ross D. , Kellett Daniel O. , Wang Yun , Ramage Andrew G. , Jordan David
Published: May 2005

Brainstem 5‐hydroxytryptamine (5‐HT, serotonin)‐containing neurones modulate cardiovascular reflex responses but the differing roles of the many 5‐HT receptors have not been thoroughly investigated. The present experiments on anaesthetized rats investigated the role of 5‐HT3 receptors in modulating vagal afferent evoked activity of nucleus tractus solitarius (NTS) neurones. Recordings were made from 301 NTS neurones receiving an input at long (> 20 ms) minimum onset latency from stimulation of the vagus nerve. These included 140 neurones excited by activating non‐myelinated cardiopulmonary afferents by right atrial injection of phenylbiguanide (PBG). Ionophoretic application of PBG, a highly selective 5‐HT3 receptor agonist, significantly increased activity (from 2.4 ± 0.4 to 5.5 ± 0.8 spikes s−1) in 96 of 106 neurones tested and in all 17 neurones tested the increase in activity (3.4 ± 1.1 to 7.0 ± 1.9 spikes s−1) was significantly attenuated (3.0 ± 0.9 to 3.8 ± 1.1 spikes s−1) by the selective 5‐HT3 receptor antagonist granisetron. Ionophoretic application of PBG potentiated responses to vagus nerve and cardiopulmonary afferent stimulation, and granisetron significantly attenuated this cardiopulmonary input (20.2 ± 5.7 to 10.6 ± 4.1 spikes burst−1) in 9 of 10 neurones tested. Ionophoretic application of AMPA and NMDA also excited NTS neurones and these excitations could be selectively antagonized by the non‐NMDA and NMDA receptor antagonists DNQX and AP‐5, respectively. At these selective currents, DNQX and AP‐5 also attenuated PBG‐ and cardiopulmonary input‐evoked increases in NTS activity. These data are consistent with the hypothesis that vagal inputs, including non‐myelinated cardiopulmonary inputs to the NTS, utilize a 5‐HT‐containing pathway which activates 5‐HT3 receptors. This excitatory response to 5‐HT3 receptor activation may be partly a direct postsynaptic action but part may also be due to facilitation of the release of glutamate which in turn acts on either non‐NMDA or NMDA receptors to evoke excitation.
Rhythmicity in arterial smooth muscle
Authors: Haddock Rebecca E. , Hill Caryl E.
Published: May 2005

Many arteries and arterioles exhibit rhythmical contractions which are synchronous over considerable distances. This vasomotion is likely to assist in tissue perfusion especially during periods of altered metabolism or perfusion pressure. While the mechanism underlying vascular rhythmicity has been investigated for many years, it has only been recently, with the advent of imaging techniques for visualizing intracellular calcium release, that significant advances have been made. These methods, when combined with mechanical and electrophysiological recordings, have demonstrated that the rhythm depends critically on calcium released from intracellular stores within the smooth muscle cells and on cell coupling via gap junctions to synchronize oscillations in calcium release amongst adjacent cells. While these factors are common to all vessels studied to date, the contribution of voltage‐dependent channels and the endothelium varies amongst different vessels. The basic mechanism for rhythmical activity in arteries thus differs from its counterpart in non‐vascular smooth muscle, where specific networks of pacemaker cells generate electrical potentials which drive activity within the otherwise quiescent muscle cells.
Nociceptive stimulation activates locus coeruleus neurones projecting to the somatosensory thalamus in the rat
Authors: Voisin D. L. , Guy N. , Chalus M. , Dallel R.
Published: May 2005

In the thalamus, noradrenergic output from the pontine nucleus locus coeruleus (LC) may actively shape the response properties of various sensory networks en route to the cortex. Little is known, however, about the involvement of ascending noradrenergic innervation of the somatosensory thalamus in the processing of nociceptive information. To address this question, we combined the study of Fos expression upon nociceptive tooth pulp stimulation in the anaesthetized rat, with the detection of retrogradely traced neurones from the somatosensory thalamus. Cell bodies labelled retrogradely from the left thalamus were observed on both sides of the LC, with an ipsilateral predominance (n= 8). Electrical stimulation of the right incisor pulp (n= 4) provoked a significantly stronger Fos expression (around twice) than sham surgery (n= 4), in both the ipsi‐ and contralateral LC. Significantly larger numbers of double labelled neurones were counted in the LC of tooth‐pulp‐stimulated animals (representing around 30% of retrogradely labelled cells in LC) than in the LC of sham animals. They were found bilaterally, but with a clear, significant, ipsilateral (i.e. left) predominance. The present data offer an anatomical framework to understand how the LC is involved in the sensory processing of nociceptive information in the thalamus. For the first time, it is shown that nociceptive stimulation activates LC neurones projecting to the somatosensory thalamus. This suggests a new role for LC in modulating nociception within the thalamus.
Structure and function of parallel pathways in the primate early visual system
Authors: Callaway Edward M.
Published: May 2005

Parallel processing streams in the primate visual system originate from more than a dozen anatomically and functionally distinct types of retinal ganglion cells (RGCs). A central problem in determining how visual information is processed is understanding how each of these RGC types connects to more central structures, including the lateral geniculate nucleus (LGN) of the thalamus and (via the LGN) the primary visual cortex. Neverthelss, the available functional and anatomical evidence linking together specific cell types across these structures is surprisingly indirect. This review evaluates the available evidence and assesses the strength of the many inferences that can be made from these observations. There is strong evidence that parasol RGCs are the provenance of the magnocellular (M) visual pathway and that midget RGCs give rise to the parvocellular (P) pathway. Furthermore, the M and P pathways remain segregated up to the input layer of primary visual cortex. The relationships between the numerous other RGC types and cell types in the LGN remain less certain. and there remains ambiguity about how best to define additional pathways, such as the koniocellular (K) pathway, which probably arise from these other, less common, RGC types.
Molecular determinants of glycine receptor αβ subunit sensitivities to Zn2+‐mediated inhibition
Authors: Miller Paul S. , Beato Marco , Harvey Robert J. , Smart Trevor G.
Published: May 2005

Glycine receptors exhibit a biphasic sensitivity profile in response to Zn2+‐mediated modulation, with low Zn2+ concentrations potentiating (< 10 μm), and higher Zn2+ concentrations inhibiting submaximal responses to glycine. Here, a substantial 30‐fold increase in sensitivity to Zn2+‐mediated inhibition was apparent for the homomeric glycine receptor (GlyR) α1 subunit compared to either GlyR α2 or α3 subtypes. Swapping the divergent histidine (H107) residue in GlyR α1, which together with the conserved H109 forms part of an intersubunit Zn2+‐binding site, for the equivalent asparagine residue present in GlyR α2 and α3, reversed this phenotype. Co‐expression of heteromeric GlyR α1 or α2 with the ancillary β subunit yielded receptors that maintained their distinctive sensitivities to Zn2+ inhibition. However, GlyR α2β heteromers were consistently 2‐fold more sensitive to inhibition compared to the GlyR α2 homomer. Comparative studies to elucidate the specific residue in the β subunit responsible for this differential sensitivity revealed instead threonine 133 in the α1 subunit as a new vital component for Zn2+‐mediated inhibition. Further studies on heteromeric receptors demonstrated that a mutated β subunit could indeed affect Zn2+‐mediated inhibition but only from one side of the intersubunit Zn2+‐binding site, equivalent to the GlyR α1 H107 face. This strongly suggests that the α subunit is responsible for Zn2+‐mediated inhibition and that this is effectively transduced, asymmetrically, from the side of the Zn2+‐binding site where H109 and T133 are located.
Fibre‐type specificity of interleukin‐6 gene transcription during muscle contraction in rat: association with calcineurin activity
Authors: Banzet Sébastien , Koulmann Nathalie , Simler Nadine , Birot Olivier , Sanchez Hervé , Chapot Rachel , Peinnequin André , Bigard Xavier
Published: May 2005

In this study, we quantified the transcription of the interleukin‐6 (IL‐6) gene in individual fibres and the associated changes in calcineurin activity assessed at the cellular level during prolonged muscle contraction. Individual myofibres were isolated from plantaris and soleus muscles of rats at the end of an exhaustive running exercise test (n= 10), categorized according to their myosin heavy chain isoform content, and compared to those of resting rats (n= 10). Using real‐time PCR analysis in individual fibres, a marked rise in IL‐6 transcript levels occurred in type I and IIa fibres at the end of exercise (P < 0.05). Transcription of the gene encoding for the modulatory calcineurin‐interacting protein‐1 (MCIP‐1), a sensitive indicator of calcineurin activity, also mainly increased in type I and IIa fibres (P < 0.05). Moreover, a slight increase in MCIP‐1 mRNA levels was observed in type IIx (P < 0.05). Fibre types determined by immunohistochemistry were qualitatively examined for glycogen content using periodic acid–Shiff staining, and no direct relationship was found, at the cellular level, between glycogen content, fibre‐type and IL‐6 transcription. Our data clearly suggest that IL‐6 gene transcription was mainly observed in early recruited myofibres and that contraction‐induced IL‐6 transcription could be associated with enhanced calcineurin activity.
NHERF family and NHE3 regulation
Authors: Donowitz Mark , Cha Boyoung , Zachos Nicholas C. , Brett Christopher L. , Sharma Annu , Tse C. Ming , Li Xuhang
Published: May 2005

The intestinal and renal proximal tubule brush border (BB) Na+–H+ exchanger NHE3 binds to members of the NHERF (Na+–H+ exchanger regulatory factor) family. These are four proteins (current most used names include NHERF1, NHERF2, PDZK1 and IKEPP) which are related to each other, are present in locations in or close to the BB, and scaffold a variable series of proteins in NHE3‐containing complexes in a dynamic manner that is altered by changes in signal transduction which affects NHE3 activity. The specific roles of these proteins in terms of NHE3 regulation as well as interactions with each other and with their many other substrates are only now being defined. Specificity for only one member of the NHERF family in one example of NHE3 regulation, inhibition by elevation in cGMP, is used to describe how NHERF family proteins are involved in NHE3 complex formation and its regulation. In this case, NHERF2 directly binds cGKII in the brush border to form an NHE3 complex, with cGKII also associating with the BB via its myristoylation.
Binocular visual responses in cells of the rat dLGN
Authors: Grieve Kenneth L.
Published: May 2005

In the mammalian visual system the output of the retina reaches the cerebral cortex by means of a synaptic link within the thalamus, the dorsal lateral geniculate nucleus (dLGN). In higher mammals this structure is visibly laminated, such that input from the two eyes remains segregated, binocular responses in essence being seen first in the cerebral cortex. In the rat this segregation is less obvious. With only around 3–10% of retinal ganglion cells projecting axons to the ipsilateral dLGN, the dLGN may be considered basically monocular; however, these ipsilaterally projecting axons contact cells in a region described as the ‘hidden lamina’, whose physiological properties have not been well described. In the anatomical literature, there is some debate as to the possibility of cross‐over between the terminations of the two eyes. Here, a population of cells physiologically receiving input from the ipsilateral eye is described – surprisingly, the majority (63%) had powerful, excitatory input from both eyes, suggesting a simple form of binocular integration at a stage earlier than previously described for other, more ‘visually developed’ species, in which thalamic binocular integration is complex.
Simulation of Fretting Wear at Orthopaedic Implant Interfaces
Authors: Ebramzadeh Edward , Billi Fabrizio , Sangiorgio Sophia N. , Mattes Sarah , Schmoelz Werner , Dorr Lawrence
Published: May 2005

Osteolysis due to wear debris is a primary cause of failure of total joint replacements. Although debris produced by the joint articulating surfaces has been studied and simulated extensively, fretting wear debris, produced at nonarticulating surfaces, has not received adequate attention. We developed a three-station fretting wear simulator to reproduce in vivo motion and stresses at the interfaces of total joint replacements. The simulator is based on the beam bending theory and is capable of producing cyclic displacement from 3to1000microns, under varying magnitudes of contact stresses. The simulator offers three potential advantages over previous studies: The ability to control the displacement by load, the ability to produce very small displacements, and dynamic normal loads as opposed to static. A pilot study was designed to test the functionality of the simulator, and verify that calculated displacements and loads produced the predicted differences between two commonly used porous ingrowth titanium alloy surfaces fretting against cortical bone. After 1.5 million cycles, the simulator functioned as designed, producing greater wear of bone against the rougher plasma-sprayed surface compared to the fiber-mesh surface, as predicted. A novel pin-on-disk apparatus for simulating fretting wear at orthopaedic implant interfaces due to micromotion is introduced. The test parameters measured with the fretting wear simulator were as predicted by design calculations, and were sufficient to measure differences in the height and weight of cortical bone pins rubbing against two porous ingrowth surfaces, plasma-sprayed titanium and titanium fiber mesh.
Subject-Specific Finite Element Model of the Pelvis: Development, Validation and Sensitivity Studies
Authors: Anderson Andrew E. , Peters Christopher L. , Tuttle Benjamin D. , Weiss Jeffrey A.
Published: May 2005

A better understanding of the three-dimensional mechanics of the pelvis, at the patient-specific level, may lead to improved treatment modalities. Although finite element (FE) models of the pelvis have been developed, validation by direct comparison with subject-specific strains has not been performed, and previous models used simplifying assumptions regarding geometry and material properties. The objectives of this study were to develop and validate a realistic FE model of the pelvis using subject-specific estimates of bone geometry, location-dependent cortical thickness and trabecular bone elastic modulus, and to assess the sensitivity of FE strain predictions to assumptions regarding cortical bone thickness as well as bone and cartilage material properties. A FE model of a cadaveric pelvis was created using subject-specific computed tomography image data. Acetabular loading was applied to the same pelvis using a prosthetic femoral stem in a fashion that could be easily duplicated in the computational model. Cortical bone strains were monitored with rosette strain gauges in ten locations on the left hemipelvis. FE strain predictions were compared directly with experimental results for validation. Overall, baseline FE predictions were strongly correlated with experimental results (r2=0.824), with a best-fit line that was not statistically different than the line y=x(experimental strains=FEpredicted strains). Changes to cortical bone thickness and elastic modulus had the largest effect on cortical bone strains. The FE model was less sensitive to changes in all other parameters. The methods developed and validated in this study will be useful for creating and analyzing patient-specific FE models to better understand the biomechanics of the pelvis.
Effect of Combined Cyclic Stretch and Fluid Shear Stress on Endothelial Cell Morphological Responses
Authors: Owatverot Tomas B. , Oswald Sara J. , Chen Yong , Wille Jeremiah J. , Yin Frank C-P
Published: May 2005

Endothelial cells in vivo are normally subjected to multiple mechanical stimuli such as stretch and fluid shear stress (FSS) but because each stimulus induces magnitude-dependent morphologic responses, the relative importance of each stimulus in producing the normal in vivo state is not clear. Using cultured human aortic endothelial cells, this study first determined equipotent levels of cyclic stretch, steady FSS, and oscillatory FSS with respect to the time course of cell orientation. We then tested whether these levels of stimuli were equipotent in combination with each other by imposing simultaneous cyclic stretch and steady FSS or cyclic stretch and oscillatory FSS so as to reinforce or counteract the cells’ orientation responses. Equipotent levels of the three stimuli were 2% cyclic stretch at 2%∕s, 80dynes∕cm2 steady FSS and 20±10dynes∕cm2 oscillatory FSS at 20dyne∕cm2-s. When applied in reinforcing fashion, cyclic stretch and oscillatory, but not steady, FSS were additive. Both pairs of stimuli canceled when applied in counteracting fashion. These results indicate that this level of cyclic stretch and oscillatory FSS sum algebraically so that they are indeed equipotent. In addition, oscillatory FSS is a stronger stimulus than steady FSS for inducing cell orientation. Moreover, arterial endothelial cells in vivo are likely receiving a stronger stretch than FSS stimulus.
Elastic Deformation of Mineralized Collagen Fibrils: An Equivalent Inclusion Based Composite Model
Authors: Akkus Ozan
Published: May 2005

Mineralized collagen fibrils are the basic building blocks of bone tissue at the supramolecular level. Several disease states, manipulation of the expression of specific proteins involved in biomineralization, and treatment with different agents alter the extent of mineralization as well as the morphology of mineral crystals which in turn affect the mechanical function of bone tissue. An experimental assessment of mineralized fibers’ mechanical properties is challenged by their small size, leaving analytical and computational models as a viable alternative for investigation of the fibril-level mechanical properties. In the current study the variation of the elastic stiffness tensor of mineralized collagen fibrils with changing mineral volume fraction and mineral aspect ratios was predicted via a micromechanical model. The partitioning of applied stresses between mineral and collagen phases is also predicted for normal and shear loading of fibrils. Model predictions resulted in transversely isotropic collagen fibrils in which the modulus along the longer axis of the fibril was the greatest. All the elastic moduli increased with increasing mineral volume fraction whereas Poisson’s ratios decreased with the exception of ν12(=ν21). The partitioning of applied stresses were such that the stresses acting on mineral crystals were about 1.5, 15, and 3 times greater than collagen stresses when fibrils were loaded transversely, longitudinally, and in shear, respectively. In the overall the predictions were such that: (a) greatest modulus along longer axis; (b) the greatest mineral/collagen stress ratio along the longer axis of collagen fibers (i.e., greatest relief of stresses acting on collagen); and (c) minimal lateral contraction when fibers are loaded along the longer axis. Overall, the pattern of mineralization as put forth in this model predicts a superior mechanical function along the longer axis of collagen fibers, the direction which is more likely to experience greater stresses.
Effectiveness, Active Energy Produced by Molecular Motors, and Nonlinear Capacitance of the Cochlear Outer Hair Cell
Authors: Spector Alexander A.
Published: May 2005

Cochlear outer hair cells are crucial for active hearing. These cells have a unique form of motility, named electromotility, whose main features are the cell’s length changes, active force production, and nonlinear capacitance. The molecular motor, prestin, that drives outer hair cell electromotility has recently been identified. We reveal relationships between the active energy produced by the outer hair cell molecular motors, motor effectiveness, and the capacitive properties of the cell membrane. We quantitatively characterize these relationships by introducing three characteristics: effective capacitance, zero-strain capacitance, and zero-resultant capacitance. We show that zero-strain capacitance is smaller than zero-resultant capacitance, and that the effective capacitance is between the two. It was also found that the differences between the introduced capacitive characteristics can be expressed in terms of the active energy produced by the cell’s molecular motors. The effectiveness of the cell and its molecular motors is introduced as the ratio of the motors’ active energy to the energy of the externally applied electric field. It is shown that the effectiveness is proportional to the difference between zero-strain and zero-resultant capacitance. We analyze the cell and motor’s effectiveness within a broad range of cellular parameters and estimate it to be within a range of 12%–30%.
Flow Mixing Enhancement from Balloon Pulsations in an Intravenous Oxygenator
Authors: Guzmán Amador M. , Escobar Rodrigo A. , Amon Cristina H.
Published: May 2005

Computational investigations of flow mixing and oxygen transfer characteristics in an intravenous membrane oxygenator (IMO) are performed by direct numerical simulations of the conservation of mass, momentum, and species equations. Three-dimensional computational models are developed to investigate flow-mixing and oxygen-transfer characteristics for stationary and pulsating balloons, using the spectral element method. For a stationary balloon, the effect of the fiber placement within the fiber bundle and the number of fiber rings is investigated. In a pulsating balloon, the flow mixing characteristics are determined and the oxygen transfer rate is evaluated. For a stationary balloon, numerical simulations show two well-defined flow patterns that depend on the region of the IMO device. Successive increases of the Reynolds number raise the longitudinal velocity without creating secondary flow. This characteristic is not affected by staggered or non-staggered fiber placement within the fiber bundle. For a pulsating balloon, the flow mixing is enhanced by generating a three-dimensional time-dependent flow characterized by oscillatory radial, pulsatile longitudinal, and both oscillatory and random tangential velocities. This three-dimensional flow increases the flow mixing due to an active time-dependent secondary flow, particularly around the fibers. Analytical models show the fiber bundle placement effect on the pressure gradient and flow pattern. The oxygen transport from the fiber surface to the mean flow is due to a dominant radial diffusion mechanism, for the stationary balloon. The oxygen transfer rate reaches an asymptotic behavior at relatively low Reynolds numbers. For a pulsating balloon, the time-dependent oxygen-concentration field resembles the oscillatory and wavy nature of the time-dependent flow. Sherwood number evaluations demonstrate that balloon pulsations enhance the oxygen transfer rate, even for smaller flow rates.
Numerical Study on the Thawing Process of Biological Tissue Induced
by Laser Irradiation
Authors: Zhou Jianhua , Liu Jing , Yu Aibing
Published: May 2005

Most of the laser applications in medicine and biology involve thermal effects. The laser-tissue thermal interaction has therefore received more and more attentions in recent years. However, previous works were mainly focused on the case of laser heating on normal tissues (37 °C or above). To date, little is known on the mechanisms of laser heating on the frozen biological tissues. Several latest experimental investigations have demonstrated that lasers have great potentials in tissue cryopreservation. But the lack of theoretical interpretation limits its further application in this area. The present paper proposes a numerical model for the thawing of biological tissues caused by laser irradiation. The Monte Carlo approach and the effective heat capacity method are, respectively, employed to simulate the light propagation and solid-liquid phase change heat transfer. The proposed model has four important features: (1) the tissue is considered as a nonideal material, in which phase transition occurs over a wide temperature range; (2) the solid phase, transition phase, and the liquid phase have different thermophysical properties; (3) the variations in optical properties due to phase-change are also taken into consideration; and (4) the light distribution is changing continually with the advancement of the thawing fronts. To this end, 15 thawing-front geometric configurations are presented for the Monte Carlo simulation. The least-squares parabola fitting technique is applied to approximate the shape of the thawing front. And then, a detailed algorithm of calculating the photon reflection/refraction behaviors at the thawing front is described. Finally, we develop a coupled light/heat transport solution procedure for the laser-induced thawing of frozen tissues. The proposed model is compared with three test problems and good agreement is obtained. The calculated results show that the light reflectance/transmittance at the tissue surface are continually changing with the progression of the thawing fronts and that lasers provide a new heating method superior to conventional heating through surface conduction because it can achieve a uniform volumetric heating. Parametric studies are performed to test the influences of the optical properties of tissue on the thawing process. The proposed model is rather general in nature and therefore can be applied to other nonbiological problems as long as the materials are absorbing and scattering media.
Effect of Blood Flow on Gas Transport in a Pulmonary Capillary
Authors: Merrikh Ali A. , Lage José L.
Published: May 2005

The effects of blood velocity on gas transport within the alveolar region of lungs, and on the lung diffusing capacity DL have for many years been regarded as negligible. The present work reports on a preliminary, two-dimensional investigation of CO convection-diffusion phenomenon within a pulmonary capillary. Numerical simulations were performed using realistic clinical and morphological parameter values, with discrete circular red blood cells (RBCs) moving with plasma in a single capillary. Steady-state simulations with stationary blood (RBCs and plasma) were performed to validate the model by comparison with published data. Results for RBCs moving at speeds varying from 1.0mm∕s to 10mm∕s, and for capillary hematocrit (Ht) from 5% to 55%, revealed an increase of up to 60% in DL, as compared to the stationary blood case. The increase in DL is more pronounced at low Ht (less than 25%) and high RBC speed and it seems to be caused primarily by the presence of plasma. The results also indicate that capillary blood convection affects DL not only by improving the plasma mixing in the capillary bed but also by replenishing the capillary with fresh (zero concentration) plasma, providing an additional reservoir for the consumption of CO. Our findings cast doubt on the current belief that an increase in the lung diffusing capacity of humans (for instance, during exercising), with fixed hematocrit, can only be accomplished by an increase in the lung volume effectively active in the respiration process.
One-Dimensional and Three-Dimensional Models of Cerebrovascular Flow
Authors: Moore S. M. , Moorhead K. T. , Chase J. G. , David T. , Fink J.
Published: May 2005

The Circle of Willis is a ring-like structure of blood vessels found beneath the hypothalamus at the base of the brain. Its main function is to distribute oxygen-rich arterial blood to the cerebral mass. One-dimensional (1D) and three-dimensional (3D) computational fluid dynamics (CFD) models of the Circle of Willis have been created to provide a simulation tool which can potentially be used to identify at-risk cerebral arterial geometries and conditions and replicate clinical scenarios, such as occlusions in afferent arteries and absent circulus vessels. Both models capture cerebral haemodynamic autoregulation using a proportional–integral (PI) controller to modify efferent artery resistances to maintain optimal efferent flow rates for a given circle geometry and afferent blood pressure. The models can be used to identify at-risk cerebral arterial geometries and conditions prior to surgery or other clinical procedures. The 1D model is particularly relevant in this instance, with its fast solution time suitable for real-time clinical decisions. Results show the excellent correlation between models for the transient efferent flux profile. The assumption of strictly Poiseuille flow in the 1D model allows more flow through the geometrically extreme communicating arteries than the 3D model. This discrepancy was overcome by increasing the resistance to flow in the anterior communicating artery in the 1D model to better match the resistance seen in the 3D results.
Precision Assessment of Biofluid Viscosity Measurements Using Molecular Rotors
Authors: Akers Walter J. , Haidekker Mark A.
Published: May 2005

Blood viscosity changes with many pathologic conditions, but its importance has not been fully investigated because the current methods of measurement are poorly suited for clinical applications. The use of viscosity-sensitive fluorescent molecular rotors to determine fluid viscosity in a nonmechanical manner has been investigated recently, but it is unknown how the precision of the fluorescence-based method compares to established mechanical viscometry. Human blood plasma viscosity was modulated with high-viscosity plasma expanders, dextran, pentastarch, and hetastarch. The samples were divided into a calibration and a test set. The relationship between fluorescence emission and viscosity was established using the calibration set. Viscosity of the test set was determined by fluorescence and by cone-and-plate viscometer, and the precision of both methods compared. Molecular rotor fluorescence intensity showed a power law relationship with solution viscosity. Mechanical measurements deviated from the theoretical viscosity value by less than 7.6%, while fluorescence-based measurements deviated by less than 6%. The average coefficient of variation was 6.9% (mechanical measurement) and 3.4% to 3.8% (fluorescence-based measurement, depending on the molecular rotor used). Fluorescence-based viscometry exhibits comparable precision to mechanical viscometry. Fluorescence viscometry does not apply shear and is therefore more practical for biofluids which have apparent non-Newtonian properties. In addition, fluorescence instrumentation makes very fast serial measurements possible, thus promising new areas of application in laboratory and clinical settings.
Using Mass Distribution Information to Model the Human Thigh for Body Segment Parameter Estimation
Authors: Durkin Jennifer L. , Dowling James J. , Scholtes Laura
Published: May 2005

Accurate estimations of body segment inertial parameters (BSPs) are required to calculate the kinetics of motion. The purpose of this study was to develop a geometric model of the human thigh segment based on mass distribution properties determined from dual energy x ray absorptiometry (DEXA). One hundred subjects from four populations underwent a DEXA scan and anthropometric measurements were taken. The mass distribution properties of the thigh segment were determined for 20 subjects, a geometric model was developed, and the model was applied to the remaining 80 subjects. The model was validated by comparing to benchmark DEXA measurements. Four other popular models in the literature were also evaluated in the same manner. No one set of predictors performed best for a particular group or BSP, however modeling the mass distribution properties of the segment allows the assumption of constant density while still accurately representing the inertial properties of the segment and provides promise for future development of BSP models.
Effect of Mercury Column on the Microdynamics of the Piezo-Driven Pipettes
Authors: Ediz Kerem , Olgac Nejat
Published: May 2005

This study is on an interesting phenomenon concerning cellular microinjection procedures which are used for various biomedical applications, and in particular intracytoplasmic sperm injection. Recent years have brought considerable practical improvements in these operations. One of them suggests aspirating a very small quantity of mercury in the injection pipettes prior to piercing into cells. This process is proven to enhance the rate of success considerably. We present a unique study in determining the influence of mercury on the microdynamics of the pipette. The effort contains both numerical simulations and corresponding experimental verification. Ultimately we offer two critical results: (1) The mercury column increases the mass loading and expectedly decreases the natural frequencies of the pipette and (2) The lateral oscillations, which play a destructive role in piercing, are subdued in amplitude due to the mass loading of mercury. Simulation results are presented, which are also verified experimentally using high-speed digital imaging. As a consequence of these findings we also propose some alternative design directions for future microinjection devices.
Nucleus Implant Parameters Significantly Change the Compressive Stiffness of the Human Lumbar Intervertebral Disc
Authors: Joshi Abhijeet , Mehta Samir , Vresilovic Edward , Karduna Andrew , Marcolongo Michele
Published: May 2005

Nucleus replacement by a synthetic material is a recent trend for treatment of lower back pain. Hydrogel nucleus implants were prepared with variations in implant modulus, height, and diameter. Human lumbar intervertebral discs (IVDs) were tested in compression for intact, denucleated, and implanted condition. Implantation of nucleus implants with different material and geometric parameters into a denucleated IVD significantly altered the IVD compressive stiffness. Variations in the nucleus implant parameters significantly change the compressive stiffness of the human lumbar IVD. Implant geometrical variations were more effective than those of implant modulus variations in the range examined.
Development and Validation of a Computed Tomography-Based Methodology to Measure Carpal Kinematics
Authors: Pfaeffle Jamie , Blankenhorn Brad , Stabile Kathryne , Imbriglia Joseph , Goitz Robert , Robertson Douglas
Published: May 2005

Motion of the wrist bones is complicated and difficult to measure. Noninvasive measurement of carpal kinematics using medical images has become popular. This technique is difficult and most investigators employ custom software. The objective of this paper is to describe a validated methodology for measuring carpal kinematics from computed tomography (CT) scans using commercial software. Four cadaveric wrists were CT imaged in neutral, full flexion, and full extension. A registration block was attached to the distal radius and used to align the data sets from each position. From the CT data, triangulated surface models of the radius, lunate, and capitate bones were generated using commercial software. The surface models from each wrist position were read into engineering design software that was used to calculate the centroid (position) and principal mass moments of inertia (orientation) of (1) the capitate and lunate relative to the fixed radius and (2) the capitate relative to the lunate. These data were used to calculate the helical axis kinematics for the motions from neutral to extension and neutral to flexion. The kinematics were plotted in three dimensions using a data visualization software package. The accuracy of the method was quantified in a separate set of experiments in which an isolated capitate bone was subjected to two different known rotation/translation motions for ten trials each. For comparison to in vivo techniques, the error in distal radius surface matching was determined using the block technique as a gold standard. The motion that the lunate and capitate underwent was half that of the overall wrist flexion-extension range of motion. Individually, the capitate relative to the lunate and the lunate relative to the radius generally flexed or extended about 30 deg, while the entire wrist (capitate relative to radius) typically flexed or extended about 60 deg. Helical axis translations were small, ranging from 0.6 mm to 1.8 mm across all motions. The accuracy of the method was found to be within 1.4 mm and 0.5 deg (95% confidence intervals). The mean error in distal radius surface matching was 2.4 mm and 1.2 deg compared to the use of a registration block. Carpal kinematics measured using the described methodology were accurate, reproducible, and similar to findings of previous investigators. The use of commercially available software should broaden the access of researchers interested in measuring carpal kinematics using medical imaging.