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Biomedical subjects

S Hyun

Publications and source records attributed to S Hyun.

16 recordsLinked to original sources
PubMed2003

Hemodynamics simulation and identification of susceptible sites of atherosclerotic lesion formation in a model abdominal aorta.

Employing the rabbit's abdominal aorta as a suitable atherosclerotic model, transient three-dimensional blood flow simulations and monocyte deposition patterns were used to evaluate the following hypotheses: (i) simulation of monocyte transport through a model of the rabbit abdominal aorta yields cell deposition patterns similar to those seen in vivo, and (ii) those deposition patterns are correlated with hemodynamic wall parameters related to atherosclerosis. The deposition pattern traces a helical shape down the aorta with local elevation in monocyte adhesion around vessel branches. The cell deposition pattern was altered by an exercise waveform with fewer cells attaching in the upper abdominal aorta but more attaching around the renal orifices. Monocyte deposition was correlated with the wall shear stress gradient and the wall shear stress angle gradient. The wall stress gradient, the wall shear stress angle gradient and the normalized monocyte deposition fraction were correlated with the distribution of monocytes along the abdominal aorta and monocyte deposition is correlated with the measured distribution of monocytes around the major abdominal branches in the cholesterol-fed rabbit. These results suggest that the transport and deposition pattern of monocytes to arterial endothelium plays a significant role in the localization of lesions.

Animals↗
PubMed2002

Multifunctional composites: optimizing microstructures for simultaneous transport of heat and electricity.

Composite materials are ideally suited to achieve multifunctionality since the best features of different materials can be combined to form a new material that has a broad spectrum of desired properties. Nature's ultimate multifunctional composites are biological materials. There are presently no simple examples that rigorously demonstrate the effect of competing property demands on composite microstructures. To illustrate the fascinating types of microstructures that can arise in multifunctional optimization, we maximize the simultaneous transport of heat and electricity in three-dimensional, two-phase composites using rigorous optimization techniques. Interestingly, we discover that the optimal three-dimensional structures are bicontinuous triply periodic minimal surfaces.

Journal Article↗
PubMed2002

Cross-mapping the ICNP with NANDA, HHCC, Omaha System and NIC for unified nursing language system development. International Classification for Nursing Practice. International Council of Nurses. North American Nursing Diagnosis Association. Home Health Care Classification. Nursing Interventions Classification.

Nursing language plays an important role in describing and defining nursing phenomena and nursing actions. There are numerous vocabularies describing nursing diagnoses, interventions and outcomes in nursing. However, the lack of a standardized unified nursing language is considered a problem for further development of the discipline of nursing. In an effort to unify the nursing languages, the International Council of Nurses (ICN) has proposed the International Classification for Nursing Practice (ICNP) as a unified nursing language system. The purpose of this study was to evaluate the inclusiveness and expressiveness of the ICNP terms by cross-mapping them with the existing nursing terminologies, specifically the North American Nursing Diagnosis Association (NANDA) taxonomy I, the Omaha System, the Home Health Care Classification (HHCC) and the Nursing Interventions Classification (NIC). Nine hundred and seventy-four terms from these four classifications were cross-mapped with the ICNP terms. This was performed in accordance with the Guidelines for Composing a Nursing Diagnosis and Guidelines for Composing a Nursing Intervention, which were suggested by the ICNP development team. An expert group verified the results. The ICNP Phenomena Classification described 87.5% of the NANDA diagnoses, 89.7% of the HHCC diagnoses and 72.7% of the Omaha System problem classification scheme. The ICNP Action Classification described 79.4% of the NIC interventions, 80.6% of the HHCC interventions and 71.4% of the Omaha System intervention scheme. The results of this study suggest that the ICNP has a sound starting structure for a unified nursing language system and can be used to describe most of the existing terminologies. Recommendations for the addition of terms to the ICNP are provided.

International Council of Nurses↗
PubMed2002

Computational analysis of a human inhalation test chamber for dosimetry-and-health effect studies.

Proper air flow and tracer gas distribution or contaminant ventilation are of great importance in biomedical test chambers or industrial workrooms. The focus is on mass transfer in an inhalation test chamber with a breathing subject on a bike exposed to a tracer gas environment (e.g., carbon monoxide). This is an environmentally realistic setup for dosimetry-and-health effect studies, which require controlled, near-uniform pollutant concentrations. However, unmodified test chambers exhibit a strong single vortex in the larger breathing zone, which, depending upon the subject's location, implies possible trace gas depletion during inhalation, foreign particle entrainment, excessive air velocities, and so on. Employing a commercial finite-volume code with user-enhanced Fortran programs, the transient three-dimensional turbulent momentum, mass, and heat transfer equations have been solved and the configurations of a suitable flow redirection device, different man-machine locations, and thermal effects have been analyzed. As a result, the best air flow device configuration and man-machine orientation have been determined to achieve high and consistent trace gas concentrations inhaled by the subject, for example, 96 percent of the CO concentration at the chamber inlet is inhaled by the subject for the optimal scenario.

Administration, Inhalation↗
PubMed2001

Computational particle-hemodynamics analysis and geometric reconstruction after carotid endarterectomy.

Transient three-dimensional laminar incompressible dilute suspension flow in rigid in-plane carotid artery bifurcations has been solved with a user-enhanced finite-volume program. Instantaneous velocity vector and wall shear stress vector fields illustrate strong "disturbed flow" patterns. Implications of elevated surface contours of hemodynamic wall parameters, indicating such disturbed flows, and particle deposition sites are discussed and a relative comparison in terms of indicator functions between the endarterectomized carotid artery bifurcation and two design improvements is shown. Although the combined perioperative mortality and non-fatal stroke rate for carotid endarterectomy ranges only from 2% to 7%, the final geometric design recommendation presented merits consideration because it may significantly lower the chances of post-operative complications such as stroke, ischemic attack, or even death. The new carotid artery bifurcation design is based on the overall reduction of "disturbed flow" indicator functions, including the time-averaged wall shear stress angle deviation and a wall deposition parameter for critical blood particles, such as monocytes.

Carotid Stenosis↗
PubMed2001

Hemodynamic parameters and early intimal thickening in branching blood vessels.

Intimal thickening due to atherosclerotic lesions or intimal hyperplasia in medium to large blood vessels is a major contributor to heart disease, the leading cause of death in the Western World. Balloon angioplasty with stenting, bypass surgery, and endarterectomy (with or without patch reconstruction) are some of the techniques currently applied to occluded blood vessels. On the basis of the preponderance of clinical evidence that disturbed flow patterns play a key role in the onset and progression of atherosclerosis and intimal hyperplasia, it is of interest to analyze suitable hemodynamic wall parameters that indicate susceptible sites of intimal thickening and/or favorable conditions for thrombi formation. These parameters, based on the wall shear stress, wall pressure, or particle deposition, are applied to interpret experimental/clinical observations of intimal thickening. Utilizing the parameters as "indicator" functions, internal branching blood vessel geometries are analyzed and possibly altered for different purposes: early detection of possibly highly stenosed vessel segments, prediction of future disease progression, and vessel redesign to potentially improve long-term patency rates. At the present time, the focus is on the identification of susceptible sites in branching blood vessels and their subsequent redesign, employing hemodynamic wall parameters. Specifically, the time-averaged wall shear stress (WSS), its spatial gradient (WSSG), the oscillatory shear index (OSI), and the wall shear stress angle gradient (WSSAG) are compared with experimental data for an aortoceliac junction. Then, the OSI, wall particle density (WPD), and WSSAG are segmentally averaged for different carotid artery bifurcations and compared with clinical data of intimal thickening. The third branching blood vessel under consideration is the graft-to-vein anastomosis of a vascular access graft. Suggested redesigns reduce several hemodynamic parameters (i.e., the WSSG, WSSAG, and normal pressure gradient [NPG]), thereby reducing the likelihood of restenosis, especially near the critical toe region.

Animals↗
PubMed2000

Fringe forms a complex with Notch.

The Fringe protein of Drosophila and its vertebrate homologues function in boundary determination during pattern formation. Fringe has been proposed to inhibit Serrate-Notch signalling but to potentiate Delta-Notch signalling. Here we show that Fringe and Notch form a complex through both the Lin-Notch repeats and the epidermal growth factor repeats 22-36 (EGF22-36) of Notch when they are co-expressed. The Abruptex59b (Ax59b) and AxM1 mutations, which are caused by missense mutations in EGF repeats 24 and 25, respectively, abolish the Fringe-Notch interaction through EGF22-36, whereas the l(1)N(B) mutation in the third Lin-Notch repeat of Notch abolishes the interaction through Lin-Notch repeats. Ax mutations also greatly affect the Notch response to ectopic Fringe in vivo. Results from in vitro protein mixing experiments and subcellular colocalization experiments indicate that the Fringe-Notch complex may form before their secretion. These findings explain how Fringe acts cell-autonomously to modulate the ligand preference of Notch and why the Fringe-Notch relationship is conserved between phyla and in the development of very diverse structures.

Animals↗
PubMed2000

Hemodynamics analyses of arterial expansions with implications to thrombosis and restenosis.

It is assumed that critical hemodynamic factors play an important role in the onset, localization and degree of post-operative complications, for example, thrombosis and restenosis. Of special interest are sudden expansion flows, which may occur in straight artery segments such as the common carotid after endarterectomy or end-to-end anastomoses. Sudden expansion geometries are possible origins of early post-operative emboli and significant myointimal hyperplasia resulting in early or late complications. Transient laminar axisymmetric and fully three-dimensional blood flows were simulated employing a validated finite volume code in conjunction with a Runge-Kutta particle tracking technique. Disturbed flow indicators, which may predict the onset of thrombosis and/or restenosis, were identified and employed to evaluate 90 degrees -step and smooth expansion geometries. Smooth expansion geometries have weaker disturbed flow features than step expansion geometries. Specifically, the regions near the expansion wall and the reattachment point are susceptible to both atherosclerotic lesion and thrombi formations as indicated by non-uniform hemodynamic indicators such as near-zero wall shear stress and elevated wall shear stress gradients as well as blood particle accumulation and deposition. A new parameter, the wall shear stress angle deviation (WSSAD) has been introduced, which indicates areas of abnormal endothelial cell morphology and particle wall deposition. In turn, regions of low wall shear stress and high wall shear stress gradients are recognized as susceptible sites for arterial diseases. Thus, it is interesting to note that high WSSAD surface areas cover low wall shear stress, high wall shear stress gradient locations as well as high wall particle deposition.A gradual change in step expansion geometry provides better results in terms of WSSAD values and hence potentially reducing atherosclerosis as well as thrombi formation.

Arteries↗
PubMed2000

Aerosol transport and deposition in sequentially bifurcating airways.

Deposition patterns and efficiencies of a dilute suspension of inhaled particles in three-dimensional double bifurcating airway models for both in-plane and 90 deg out-of-plane configurations have been numerically simulated assuming steady, laminar, constant-property air flow with symmetry about the first bifurcation. Particle diameters of 3, 5, and 7 microns were used in the simulation, while the inlet Stokes and Reynolds numbers varied from 0.037 to 0.23 and 500 to 2000, respectively. Comparisons between these results and experimental data based on the same geometric configuration showed good agreement. The overall trend of the particle deposition efficiency, i.e., an exponential increase with Stokes number, was somewhat similar for all bifurcations. However, the deposition efficiency of the first bifurcation was always larger than that of the second bifurcation, while in general the particle efficiency of the out-of-plane configuration was larger than that of the in-plane configuration. The local deposition patterns consistently showed that the majority of the deposition occurred in the carinal region. The distribution pattern in the first bifurcation for both configurations were symmetric about the carina, which was a direct result of the uniaxial flow at the inlet. The deposition patterns about the second carina showed increased asymmetry due to highly nonuniform flow generated by the first bifurcation and were extremely sensitive to bifurcation orientation. Based on the deposition variations between bifurcation levels and orientations, the use of single bifurcation models was determined to be inadequate to resolve the complex fluid-particle interactions that occur in multigenerational airways.

Aerosols↗
PubMed2000

Computer simulation and geometric design of endarterectomized carotid artery bifurcations.

The main goal of this computational study is to establish surgical guidelines for optimal geometries of carotid endarterectomy reconstructions that may measurably reduce postoperative complications, that is, thrombosis, stroke, and/or restenosis. The underlying hypotheses are that nonuniform hemodynamics, or "disturbed flows," are linked to arterial diseases and consequently that minimization of "disturbed flow" indicators leads to geometric bifurcation designs that lower postoperative complication rates. Considering transient 3-D laminar blood flow in partially occluded, in-plane, rigid-wall carotid artery bifurcations, the results presented include time-averaged indicators of "disturbed flow", such as the wall shear stress, spatial wall shear stress gradient, and wall shear stress angle deviation. In addition, trajectories and deposition patterns of critical blood particles (i.e., monocytes) are shown and evaluated. Within given physiological constraints, the vessel geometry was then changed in order to reduce the magnitudes of key indicators associated with thrombosis (i.e., blood clot formation) or restenosis (e.g., renewed atherosclerosis and/or hyperplasia). The quantitative results and knowledge base generated will be crucial for future clinical trials.

Blood Flow Velocity↗
PubMed1998

Establishment and characterization of cell lines constitutively expressing hepatitis B virus X-protein.

We prepared human hepatoma cell lines, which expressed the human hepatitis B virus-X gene product. The plasmid pMAMneo-X, containing an HBV-X gene promoter, an enhancer and a structural gene was constructed. Transfected HBV-X gene integration and expression were detected by Southern and Northern blotting, as well as by chloramphenicol acetylase transferase (CAT) assay using various kinds of promoter-CAT reporter systems. HBV-X protein expression in stable transfectants was confirmed by immunofluorescence microscopy. Transfected cell lines showed permanent expression of HBV-X proteins. The HBV-X transfectant activated its target promoters in promoter-CAT constructs as reporters. The HBV-X transfectant enhanced AP-1 transcription factor binding to its target DNA. Therefore, X-transfectants are not only stable, but also have specific biological functions. Cell cycle analysis by flow cytometry showed that the majority of the transfectant cells are arrested in the G1 or G2 phase of the cell cycle. These cell lines may be useful in analyzing the biological functions of HBV-X and its functional role in the formation of hepatocellular carcinomas.

Carcinoma, Hepatocellular↗
PubMed1994

Elevated in vivo and in vitro secretion of CD8-alpha molecules in patients with systemic lupus erythematosus.

Endogenously activated CD8+ cells contribute to the aberrant immune regulation that characterizes SLE. Because stimulation of CD8+ cells with lectin/Ag triggers release of CD8-alpha molecules (sCD8), we measured, in patients with SLE, serum sCD8 content, its correlation with disease activity, and the in vitro release of sCD8 by SLE PBMCs. sCD8 levels, measured by ELISA in sera of 50 SLE patients, were higher than normal in 16 out of 21 mildly active and 15 out of 15 active SLE patients. sCD8 correlated positively with the clinical index for disease activity (r = 0.57, p = 0.001) and with sIL-2R levels (r = 0.52, p < 0.0001), and negatively with serum C3 levels (r = -0.5, p < 0.04). Freshly isolated SLE PBMCs had higher than normal CD8-alpha mRNA levels and secreted high levels of sCD8 in vitro (p < 0.05 vs control PBMC). sCD8 in vitro release by SLE PBMCs may be modulated by non-CD8+ cells. Thus, anti-CD2 mAb inhibited sCD8 release, whereas anti-HLA mAb increased it in unseparated PBMCs, but not in CD8+ enriched cultures. Moreover, sCD8 release increased significantly in PBMC cultures enriched for CD8+ DR+ cells by negative selection. Added-back monocytes decreased sCD8 to original levels, but not after glutaraldehyde fixation, nor in the presence of anti-HLA mAb. Further, lectin-induced IgG production and proliferation were reduced in the presence of sCD8, suggesting that the soluble CD8 molecules may be immunoregulatory. Because the high sCD8 levels in sera of active SLE likely reflect pathogenic cell activation, serum CD8 content may be an additional serologic activity marker, and its study could provide insights into mechanisms of disease.

CD8 Antigens↗