An Innovative Ski-Boot: Design,Numerical Simulations and Testing

The present work is concerned with the design of an innovative ski-boot. In order to optimize ergonomics and biomechanical behavior of the ski-boot it is important to take into account the orientation of the leg with respect to the ground. The SGS system (Stance Geometry System) developed in this work allows the skier to adjust for posture in the frontal plane by rotating the sole of the boot about the antero-posterior axis (ski-boot is then locked in the desired position before skiing). A simplified model of the effect of ski-boot deformation on skiing behavior is used to evaluate the minimal stiffness the system must have. An experimental analysis on the ski slopes was carried out to provide ski-boot deformations and loading data in different skiing conditions, to be used in numerical simulations. Finite Elements Method (FEM) simulations were performed for optimal design of the joint between ski-boot and sole. The active loads and local ski-boot deformations during small- and large-radius turns were experimentally determined and used to validate a FEM model of the ski-boot. The model was used to optimize the design for maximum stiffness and to demonstrate the efficacy of virtual design supported by proper experimental data. Mean loads up to 164% body weight were measured on the outer ski during turning. The new SGS design system allows the adjustment of lateral stance before using the ski-boot, optimizing the ski-boot stiffness through FEM analysis. Innovative aspects of this work included not only the stance geometry system ski-boot but also the setup of a virtual design environment that was validated by experimental evidence. An entire dataset describing loads during skiing has been obtained. The optimized SGS ski-boot increases intrinsic knee stability due to proper adjustment of lateral stance, guaranteeing appropriate stiffness of the ski-boot system.

Key Points

• Load acting during different phases of active skiing have been investigated in both qualitative and quantitative ways.
• The effects of ski-boot - ski-boot sole stiffness during skiing has been investigated.
• A ski-boot stance geometry system and an innovative design environment have been developed to make skiing easier and safer.

Key Words: Stance geometry system, stiffness, virtual design environment, FEM analysis, skiing performance     

3D Simulations of Blood Flow Dynamics in Compliant Vessels: Normal,Aneurysmal, and Stenotic Arteries

Arterial diseases such as aneurysm and stenosis may result from the mechanical and/or morphological change of an arterial wall structure and correspondingly altered hemodynamics. The development of a 3D computational model of blood flow can be useful to study the hemodynamics in major blood vessels and may provide an insight into the noninvasive technique to detect arterial diseases in early stage. In this paper, we present a three-dimensional model of blood flow in the aorta, which is based on the immersed boundary method to describe the interaction of blood flow with the aortic wall. Our simulation results show that the hysteresis loop is evident in the pressure-diameter relationship of the normal aorta when the arterial wall is considered to be viscoelastic. In addition, it is shown that flow patterns and pressure distributions are altered in response to the change of aortic morphology.     

Lumped Parameter Outflow Models for 1-D Blood Flow Simulations: Effect on Pulse Waves and Parameter Estimation

Several lumped parameter, or zero-dimensional (0-D), models of the microcirculation are coupled in the time domain to the nonlinear, one-dimensional (1-D) equations of blood flow in large arteries. A linear analysis of the coupled system, together with in vivo observations, shows that: (i) an inflow resistance that matches the characteristic impedance of the terminal arteries is required to avoid non-physiological wave reflections; (ii) periodic mean pressures and flow distributions in large arteries depend on arterial and peripheral resistances, but not on the compliances and inertias of the system, which only affect instantaneous pressure and flow waveforms; (iii) peripheral inertias have a minor effect on pulse waveforms under normal conditions; and (iv) the time constant of the diastolic pressure decay is the same in any 1-D model artery, if viscous dissipation can be neglected in these arteries, and it depends on all the peripheral compliances and resistances of the system. Following this analysis, we propose an algorithm to accurately estimate peripheral resistances and compliances from in vivo data. This algorithm is verified against numerical data simulated using a 1-D model network of the 55 largest human arteries, in which the parameters of the peripheral windkessel outflow models are known a priori. Pressure and flow waveforms in the aorta and the first generation of bifurcations are reproduced with relative root-mean-square errors smaller than 3%.     

Radiofrequency Tissue Ablation: Effect of Hepatic Blood Flow Occlusion on Thermal Injuries Produced in Cirrhotic Livers

Background: Radiofrequency thermal ablation has been used as a treatment for several types of hepatic malignancies. Many of these lesions exist in the presence of cirrhosis. Limitations exist to the size of the ablations and, subsequently, the efficacy of treatment. Hepatic vascular inflow occlusion has been advocated as an adjunctive measure to increase the efficacy of the ablation. We present a model in the human cirrhotic liver that demonstrates the advantage of blood flow occlusion during radiofrequency ablation.Methods: Five patients with advanced endstage liver disease scheduled to have orthotopic liver transplantation were enrolled in this study. After laparotomy and before hepatectomy, radiofrequency ablation was performed without and with hepatic blood flow occlusion. After hepatectomy, the liver was sectioned, the area of ablation was measured in three dimensions, and the volume of ablation calculated.Results: Three of the patients had had previously placed transjugular intrahepatic portosystemic shunt. The mean volume of the ablation without blood flow occlusion was 22.5 ± 7.4 cm³ and that with blood flow occlusion was 48.4 ± 24.0 cm³ (P = .05).Conclusions: Ablation area is increased significantly with hepatic blood flow occlusion in the human cirrhotic liver. This result may have application in the treatment of larger (>3 cm) hepatic malignancies.     

A Parallel Computational Model for Three-Dimensional,Thermo-Mechanical Stokes Flow Simulations of Glaciers and Ice Sheets

This paper focuses on the development of an efficient, three-dimensional, thermo-mechanical, nonlinear-Stokes flow computational model for ice sheet simulation. The model is based on the parallel finite element model developed in [14] which features high-order accurate finite element discretizations on variable resolution grids. Here, we add an improved iterative solution method for treating the nonlinearity of the Stokes problem, a new high-order accurate finite element solver for the temperature equation, and a new conservative finite volume solver for handling mass conservation. The result is an accurate and efficient numerical model for thermo-mechanical glacier and ice-sheet simulations. We demonstrate the improved efficiency of the Stokes solver using the ISMIP-HOM Benchmark experiments and a realistic test case for the Greenland ice-sheet. We also apply our model to the EISMINT-II benchmark experiments and demonstrate stable thermo-mechanical ice sheet evolution on both structured and unstructured meshes. Notably, we find no evidence for the "cold spoke" instabilities observed for these same experiments when using finite difference, shallow-ice approximation models on structured grids.     

Bjorken Flow Revisited: Analytic and Numerical Solutions in Flat Space-Time Coordinates

In this work we provide analytic and numerical solutions for the Bjorkenflow, a standard benchmark in relativistic hydrodynamics providing a simple modelfor the bulk evolution of matter created in collisions between heavy nuclei.We consider relativistic gases of both massive and massless particles, working ina (2+1) and (3+1) Minkowski space-time coordinate system. The numerical resultsfrom a recently developed lattice kinetic scheme show excellent agreement with theanalytic solutions.     

Ventricular Fibrillation: Its Effect on Myocardial Flow,Distribution, and Performance

Subendocardial ischemia develops in hearts that are fibrillated during cardiopulmonary bypass when: (1) the normal ventricle is fibrillated with a sustained electrical stimulus, (2) the hypertrophied ventricle is allowed to fibrillate spontaneously, (3) the fibrillating heart becomes distended, or (4) the perfusion pressure is reduced to approximately 50 mm Hg. Myocardial hypothermia reduces cardiac oxygen requirements during fibrillation but does not prevent ischemia when perfusion pressure falls to levels frequently attained during clinical open-heart operations. The ischemia occurs because flow cannot rise sufficiently to meet the metabolic demands of ventricular fibrillation. The forces interacting to impede adequate flow to the subendocardium during ventricular fibrillation are: (1) the compressive forces exerted on subendocardial muscle by the strength of fibrillation, (2) the compressive forces resulting from raised intracavitary pressure due to occlusion or malfunction of the ventricular vent, and (3) the evolution of myocardial edema as ischemia is prolonged.We have abandoned the use of ventricular fibrillation in clinical open-heart operations and now allow the heart to beat continually with adequate perfusion pressure. We have not needed to use inotropic drugs postoperatively after aortic or mitral valve replacement since adopting this technique.     

Anaphylaxis in the Monkey: Respiratory Mechanics, Acid-base Status and Blood Gases

Aggregate anaphylaxis was induced by intravenous injection of the specific antigen in eight ovalbumin-sensitized monkeys. Changes in respiratory mechanics, acid-base status and blood gases were studied during the following half hour. Within 1 minute after challenge, a short period of respiratory depression, probably reflex-mediated, was observed. This was followed by hyperventilation, and arterial PCO2 decreased. There was a rapid increase in pulmonary resistance (Rpulm) and a concomitant decrease in pulmonary dynamic compliance (Cdyn), suggesting constriction of smooth muscles in the lung. Rpulm returned to the control value but Cdyn remained depressed, as a result of constriction of small airways and pulmonary congestion. Oxygen saturation in arterial blood decreased slightly due to a marked desaturation of mixed venous blood and increased venous admixture. Progressive metabolic acidosis developed, indicating poor tissue oxygenation and perfusion. The changes observed in this study were not severe enough to cause any major disturbance of the gas exchange in the lungs, despite a severe anaphylactic shock.     

Controlled Hypotension with Sodium Nitroprusside: Effects on Cerebral Blood Flow and Cerebral Venous Blood Gases in Patients Operated for Cerebral Aneurysms

The effect on cerebral haemodynamics of arterial hypotension induced by sodium nitroprusside infusion was studied in nine patients at the end of operations for intracranial aneurysms under N2O-O2-halothane anaesthesia. Cerebral blood flow (CBF), using the intraarterial 133Xe injection method, and cerebral jugular venous blood gases were monitored before, during and after the induced hypotension. CBF and jugular venous oxygen tension (PvO2) remained constant during the hypotensive period. Following its termination, a 13% increase in CBF occurred (P less than 0.05) and PvO2 showed the same trend, a 5% increase (P less than 0.30). Regional CBF recordings (rCBF) in 16 small areas within the cerebral hemisphere were obtained at each measurement. In four of the patients, rCBF abnormalities were present in the form of hyperaemic regions, probably induced by the operation or the disease itself. The focal abnormalities were not accentuated during hypotension nor were ischaemic regions disclosed. It is concluded that sodium nitroprusside has only a minor influence on cerebral haemodynamics in the anaesthetized state.     

Numerical Simulation of the Motion of Inextensible Capsules in Shear Flow Under the Effect of the Natural State

In this paper, a computational model for the natural state of an inextensible capsule has been successfully combined with a spring model of the capsule membrane to simulate the motion of the capsule in two-dimensional shear flow. Besides the viscosity ratio of the internal fluid and external fluid of the capsule, the natural state also plays a role for having the transition between two well known motions, tumbling and tank-treading (TT) with the long axis oscillates about a fixed inclination angle (a swinging mode), when varying the shear rate. Between tumbling and tank-treading, the intermittent behavior has been obtained for the capsule with a biconcave rest shape. The estimated critical value of the swelling ratio for having the intermittent transition behavior is less than 0.7, i.e., the capsules with rest shape closer to a full disk do not have the intermittent behavior in shear flow. The intermittent dynamics of the capsule in the transition region is a mixture of tumbling and TT with a swinging mode. Just like the motion of TT with a swing mode, which can be viewed as a tank-treading with an incomplete tumbling, the membrane tank-treads backward and forward within a small range during the tumbling motion.     

Linear Stability Analysis and Gas Kinetic Scheme (GKS) Simulations of Instabilities in Compressible Plane Poiseuille Flow

The fundamental nature of flow instability in wall bounded flows changeswith Mach number. The objectives of this study are two-fold, (i) compute the instability modes in high Mach number Poiseuille flows using linear stability analysis (LSA)and, (ii) perform direct numerical simulations (DNS) of the instability developmentusing a solver based on gas kinetic method (GKM) for the purpose of code validationby comparison against LSA results. The LSA and DNS are performed for the case ofPoiseuille flow over a range of Mach numbers – from moderately supersonic to hypersonic speeds. First, LSA is employed to identify the most unstable mode over the rangeof Mach numbers. We then perform two sets of GKM-DNS to corroborate the LSA results over the Mach number range. In the first set of simulations, the background fieldis initially perturbed with the most unstable mode identified by LSA and the evolutionis monitored. It is shown that GKM-DNS accurately captures the exponential growthin kinetic energy for all Mach numbers. The second set of GKM-DNS simulations isperformed by superposing the background pressure field with random initial perturbations. After an initial transient period, the modes predicted by LSA dominate theDNS flow field evolution. The wave-vector and mode shapes of the dominant instability are well replicated by GKM-DNS at each Mach number. These insights in thelinear regime of high speed Poiseuille flow and validation of GKM are important forunderstanding and simulating wall bounded flows.     

Channels, carriers, and pumps in the pathogenesis of sodium-sensitive hypertension

Sodium-sensitive hypertension is thought to be dependent on primary alterations in renal tubular sodium reabsorption. The major apical plasma membrane Na(+) transporters include the proximal tubular Na(+)-H(+) exchanger, the thick ascending limb Na(+)-K(+)-2Cl(-) cotransport system, the distal tubular Na(+)-Cl(-) cotransporter, and the collecting duct epithelial sodium channel (ENaC). This article explores the role of each transporter in the pathogenesis of hypertension. Although the contribution of the proximal tubule Na(+)-H(+) exchanger is not yet defined completely, more convincing data have been generated about the importance of the Na(+)-K(+)-2Cl(-). Indeed at least 2 forms of hypertension appear to be related to the up-regulation of the transporter: the so-called programmed hypertension induced by low-protein diet during pregnancy and the early phase of hypertension in the Milan strain of rats. With respect to the Na(+)-Cl(-) cotransporter this may be overactive caused by inactivating mutation of WNK4 as in the Gordon syndrome, although it is the main actor for the maintenance phase of the hypertension found in the Milan strain of rats. Finally, the contribution of the ENaC has been established clearly; indeed, in the Liddle syndrome the mutation of the ENaC gene leads to a longer retention of the channel on the cell surface of collecting duct principal cells, thus inducing stronger sodium reabsorption along this segment. All these examples clearly indicate that renal sodium transporters may be responsible for various types of sodium-sensitive hypertension.     

Ion Channels and Gap Junctions: Their Role in Erectile Physiology, Dysfunction, and Future Therapy

A flurry of research and clinical activity during this past decade has documented that the tonicity and synchronicity of the corporal smooth muscle cells of the penis are major determinants of erectile capacity and function. Specifically, the effects of diverse and bifurcating intracellular signal transduction pathways on the activity of nonjunctional ion channels such as potassium (K(+)), calcium (Ca(2+)), and chloride (C(1-)) govern the former, whereas intercellular communication through gap junctions provides the anatomic substrate for the latter. Recent studies at the tissue, cellular, subcellular, and molecular levels have verified this supposition and provided important insight into how subtle alterations in the balance between contraction and relaxation of the corporal smooth muscle cells can predispose a man to erectile failure. This report reviews the available information concerning the participation of gap junctions and K(+), Ca(2+), and C(1-) channels in the erectile process and describes their importance as potential molecular targets for the future therapy of erectile dysfunction (ED). It is argued that a major goal should now be to proceed on at least two fronts simultaneously: (1) to capitalize on these new mechanistic insights by developing novel treatments for ED centered on the modulation of ion channel activity; and (2) simultaneously to take advantage of the unique therapeutic opportunities afforded by the presence and ubiquitous distribution of gap junction channels in the human corpora. One strategy that fulfils both criteria will be briefly reviewed, that is, gene therapy with the maxi-K(+) channel subtype.     

Effect of Synchronous and Asynchronous Pulsatile Flow During Left, Right, and Biventricular Bypass

Ventricular assist devices augment flow from the left atrium to the aorta and/or from the right atrium to the pulmonary artery. Most devices are used in the asynchronous full-to-empty mode (asynchronous) but may also be used in a synchronous counterpulsation mode (synchronous). This study determines the optimal assist modes to reduce myocardial oxygen consumption (MVO2) and metabolism. Twelve pigs were instrumented with carotid artery and Baim coronary sinus catheters for determination of MVO2 and myocardial lactate production (LACT). Six were implanted with a Pierce-Donachy left ventricular assist device (LVAD) and 6 with both right and left ventricular assist devices (BIVAD). Two periods each of control, synchronous, and asynchronous bypass were instituted, the midanterior descending coronary artery (LAD) was ligated, and the sequence was repeated. After each period, MVO2 and LACT were determined and myocardial biopsy specimens were obtained for tissue, lactate, and ATP assay. Following LAD ligation, biopsy specimens were obtained from both the infarct and noninfarct zones of the heart. MVO2 decreased (p < 0.05) in the asynchronous BIVAD mode compared with control. MVO2 was unchanged in synchronous BIVAD or either LVAD mode. Tissue ATP and tissue lactate were unaffected by any mode of bypass. Only BIVAD in the asynchronous mode reduced MVO2. When ventricular assist devices are utilized to aid recovery of the natural heart, two devices should always be inserted to allow biventricular assist. Synchronous counterpulsation offers no advantage.     

Phase Field Model of Thermo-Induced Marangoni Effects in the Mixtures and Its Numerical Simulations with Mixed Finite Element Method

In this paper, we study the Marangoni effects in the mixture of two Newtonian fluids due to the thermo-induced surface tension heterogeneity on the interface. We employ an energetic variational phase field model to describe its physical phenomena, and obtain the corresponding governing equations defined by a modified Navier-Stokes equations coupled with phase field and energy transport. A mixed Taylor-Hood finite element discretization together with full Newton's method are applied to this strongly nonlinear phase field model on a specific domain. Under different boundary conditions of temperature, the resulting numerical solutions illustrate that the thermal energy plays a fundamental role in the interfacial dynamics of two-phase flows. In particular, it gives rise to a dynamic interfacial tension that depends on the direction of temperature gradient, determining the movement of the interface along a sine/cosine-like curve.     

不同血气管理与红细胞压积在深低温停循环中对乳猪脑损伤的影响

目的用近红外分光仪(NIRS)观察不同的血气管理和红细胞压积(HCT)对乳猪深低温停循环(DHCA)中脑损伤的影响。方法将24只乳猪根据DHCA期间所采用不同的血气管理和HCT分为4组。A组术中HCT0.25～0.30,降温期pH稳态管理血气,其余各期采用alpha稳态管理血气;B组术中HCT0.25～0.30,alpha稳态管理血气;C组术中HCT0.20～0.25,降温期pH稳态管理血气;D组术中HCT0.20～0.25,alpha稳态管理血气。用NIRS连续监测脑氧合情况,术后6h脑组织固定于甲醛中,并进行组织学评分判断脑损伤程度。结果NIRS指标中,D组脑氧合血红蛋白(HbO2)和总血红蛋白(HbT)在降温期明显低于A组和B组(P<0.05),A组DHCA期间HbO2最低点持续时间(HbO2-NT)明显短。所有HbO2-NT小于25min的乳猪均无脑组织损伤的病理改变。结论DHCA期间采用pH稳态联合高HCT能减轻术后脑损伤。     

Permanent Charge Effects on Ionic Flow: A Numerical Study of Flux Ratios and Their Bifurcation

Ionic flow carries electrical signals for cells to communicate with each other.The permanent charge of an ion channel is a crucial protein structure for flow properties while boundary conditions play a role of the driving force. Their effects on flowproperties have been analyzed via a quasi-one-dimensional Poisson-Nernst-Planckmodel for small and relatively large permanent charges. The analytical studies haveled to the introduction of flux ratios that reflect permanent charge effects and have auniversal property. The studies also show that the flux ratios have different behaviorsfor small and large permanent charges. However, the existing analytical techniquescan reveal neither behaviors of flux ratios nor transitions between small and large permanent charges. In this work we present a numerical investigation on flux ratios tobridge between small and large permanent charges. Numerical results verify the analytical predictions for the two extremal regions. More significantly, emergence of non-trivial behaviors is detected as the permanent charge varies from small to large. Inparticular, saddle-node bifurcations of flux ratios are revealed, showing rich phenomena of permanent charge effects by the power of combining analytical and numericaltechniques. An adaptive moving mesh finite element method is used in the numericalstudies.