In vitro measurement and calculation of drag force on iliac limb stentgraft in a compliant arterial wall model

Interventional treatment of aortic aneurysms using endovascular stentgrafting is a minimally invasive technique. Following device implantation, transient drag forces act on the stentgraft. When the drag force exceeds the fixation force, complications like stentgraft migration, endoleaks and stentgraft failure occur. In such a scenario the device becomes unstable, causing concern over the long-term durability of endovascular repairs. The objective of this study is: (1) to measure the drag force on iliac limb stentgraft, having a distal diameter that is half the size of the proximal end, in an in vitro experiment; (2) to calculate the drag force using blood flow-compliant arterial wall interaction model and compare it with the measured values on the stentgraft for the in vitro experiment; (3) to calculate drag force on the stentgraft using physiological flow conditions. Experimental data for a stentgraft within a silicon tubing, representing a compliant artery, shows a peak drag force of 2.79 N whereas the calculation predicts a peak drag force of 2.57 N; thus a percentage difference of 7.8% is observed. When physiological flow and pressure pulse are used for the blood flow-compliant arterial wall computations, a peak drag force of 0.59 N is obtained for the same stentgraft that was used in the experiment. The outer cavity between the distal end of the iliac limb stentgraft and the arterial wall reduces the drag force. These forces can be used as design guideline for determining the fixation force needed for the stentgraft under physiological pulsatile flow.     

Analysis of biomechanical factors affecting stent-graft migration in an abdominal aortic aneurysm model

Focusing on a representative abdominal aortic aneurysm (AAA) with a bifurcating stent-graft (SG), a fluid-structure interaction (FSI) solver with user-supplied programs has been employed to solve for blood flow, AAA/SG deformation, sac pressure and wall stresses, as well as the downward forces acting on the SG. Simulation results indicate that implanting a SG can significantly reduce sac pressure, mechanical stress, pulsatile wall motion, and maximum diameter change in AAAs; hence, it may restore normal blood flow and prevent AAA rupture effectively. The transient SG drag force is similar in trend as the cardiac pressure. Its magnitude depends on multi-factors including blood flow conditions, as well as SG and aneurysm geometries. Specifically, AAA neck angle, iliac bifurcation angle, neck aorta-to-iliac diameter ratio, SG size, and blood waveform play important roles in generating a fluid flow force potentially leading to SG migration. It was found that the drag force can exceed 5N for an AAA with a large neck or iliac angle, wide aortic neck and narrow iliac arteries, large SG size, and/or abnormal blood waveform. Thus, the fixation of self-expandable or balloon-expandable SG contact may be inadequate to withstand the forces of blood flowing through the implant and hence means of extra fixation should be considered. A comprehensive FSI analysis of the coupled SG-AAA dynamics provides physical insight for evaluating the luminal hemodynamics, and maximum AAA-stresses as well as biomechanical factors leading potentially to SG migration.     

Finite element analysis of the biomechanical interaction between coronary sinus and proximal anchoring stent in coronary sinus annuloplasty

Recent clinical studies of the percutaneous transvenous mitral annuloplasty (PTMA) devices have shown a short-term reduction of mitral regurgitation after implantation. However, adverse events associated with the devices such as compression and perforation of vessel branches, device migration and fracture were reported. In this study, a finite element analysis was carried out to investigate the biomechanical interaction between the proximal anchor stent of a PTMA device and the coronary sinus (CS) vessel in three steps including: (i) the stent release and contact with the CS wall, (ii) the axial pull t the stent connector and (iii) the pressure inflation of the vessel wall. To investigate the impact of the material properties of tissues and stents on the interactive responses, the CS vessel was modelled with human and porcine material properties, and the proximal stent was modelled with two different Nitinol materials with one being stiffer than the other. The results indicated that the vessel wall stresses and contact forces imposed by the stents were much higher in the human model than the porcine model. However, the mechanical differences induced by the two stent types were relatively small. The softer stent exhibited a better fatigue safety factor when deployed in the human model than in the porcine model. These results underscored the importance of the CS tissue mechanical properties. Vessel wall stress and stent radial force obtained in the human model were higher than those obtained in the porcine model, which also brought up questions as to the validity of using the porcine model to assess device mechanical function. The quantification of these biomechanical interactions can offer scientific insight into the development and optimisation of the PTMA device design.     

Computational analysis of biomechanical contributors to possible endovascular graft failure

This paper evaluates numerically coupled blood flow and wall structure interactions in a representative stented abdominal aortic aneurysm (AAA) model, leading potentially to endovascular graft (EVG) failure. A total of 12 biomechanical contributors to possible EVG migration were considered. The results show that after EVG insertion for the given model, the peak AAA sac-pressure was reduced to 14.2 mmHg (11.8% of p_lumen), and hence the maximum von Mises wall stress and wall deformation dropped by factors of 20 and 10, respectively. Thus, an EVG can significantly reduce sac pressure, mechanical stress, pulsatile wall motion, and the maximum diameter in AAAs and hence prevent AAA rupture effectively. In the absence of endoleaks, elevated sac-pressure can still be caused by fluid-structure interactions between the EVG, stagnant blood, and AAA wall. EVG migration forces vary from 1.4 to 7 N for different EVG geometries, material properties, and hemodynamic conditions. AAA-neck angle, iliac bifurcation angle, neck aorta-to-iliac diameter ratio, EVG size, aorto-uni-iliac EVG, and hypertension play important roles in generating forces potentially leading to EVG migration.     

In-stent graft helical flow intensity reduces the risk of migration after endovascular aortic repair

During the last years endovascular aneurysm repair (EVAR) became the elective treatment for abdominal aortic aneurysms (AAAs) thanks to lower mortality and morbidity rates than open surgery. In face of these advantages, stent-graft performances are still clinically suboptimal. In particular, post-surgical complications derive from device migration as a consequence of the hemodynamic forces acting on the endograft. In this regard, while the importance of hemodynamic surface forces is well recognized, the role of the in-stent flow is still unclear. Here we hypothesize that in-stent helical blood flow patterns might influence the distribution of the displacement forces (DFs) acting on the stent-graft and, ultimately, the risk of stent migration. To test this hypothesis, the hemodynamics of 20 post-EVAR models of patients treated with two different commercial endografts was analyzed using computational hemodynamics.The main findings of the study indicate that: (1) helical flow intensity decreases the risk of endograft migration, as given by an inverse correlation between helicity intensity (h₂) and time-averaged displacement forces (TADFs) (p < 0.05); (2) unbalanced counter-rotating helical structures in the legs of the device contribute, in particular along the systole, to significantly suppress TADFs (p < 0.01); (3) as expected, helical flow intensity is positively correlated with pressure drop and resistance to flow (p < 0.001). The findings of this study suggest that a design strategy promoting in-stent helical flow structures could contribute to minimize the risk of migration of implanted EVAR devices.     

Analysis of blood flow behaviour in custom stent grafts

Endovascular aneurysm repair (EVAR) is an attractive alternative to open surgery for treating abdominal aortic aneurysms (AAAs). However, the implantation of stent grafts into AAAs can result in post-operative complications such as stent graft migration, rupture or endoleak. EVAR has therefore been carried out only on selected patients. Stent grafts are usually standard commercial stent grafts (CSGs); however, custom made stent grafts (cmSGs) of various shapes and sizes are sometimes used to fit patients’ anatomies. In the present study, the cmSGs were specially designed and fabricated by the surgeons at the Pitié-Salpétriére hospital in Paris. Two patients carrying cmSGs with unfavourable geometries showing tortuous shapes, angulation, widening, narrowing, curvature and kinking and one patient with a cmSG with a more favourable geometry resembling a straight tube were examined. These three clinical cases were investigated using three-dimensional numerical simulations, and the results showed that even when the cmSG geometries are unfavourable, the drag forces to which they are subjected are of a similar magnitude to those exerted on CSGs, or even smaller. The hemodynamic analysis carried out on the two unfavourable cmSGs showed the occurrence of low velocity values in the main trunk of the cmSGs, high velocities linked to recirculation areas downstream from kinking and strong distal narrowing. These flow patterns are liable to induce thrombus. However, since cmSG implantation can save the lives of patients for whom neither classical stent grafts nor open surgery are indicated, it can be concluded that these devices are useful in some cases.     

The correlation of segment accelerations and impact forces with knee angle in jump landing

Impact forces and shock deceleration during jumping and running have been associated with various knee injury etiologies. This study investigates the influence of jump height and knee contact angle on peak ground reaction force and segment axial accelerations. Ground reaction force, segment axial acceleration, and knee angles were measured for 6 male subjects during vertical jumping. A simple spring-mass model is used to predict the landing stiffness at impact as a function of (1) jump height, (2) peak impact force, (3) peak tibial axial acceleration, (4) peak thigh axial acceleration, and (5) peak trunk axial acceleration. Using a nonlinear least square fit, a strong (r = 0.86) and significant (p < or = 0.05) correlation was found between knee contact angle and stiffness calculated using the peak impact force and jump height. The same model also showed that the correlation was strong (r = 0.81) and significant (p < or = 0.05) between knee contact angle and stiffness calculated from the peak trunk axial accelerations. The correlation was weaker for the peak thigh (r = 0.71) and tibial (r = 0.45) axial accelerations. Using the peak force but neglecting jump height in the model, produces significantly worse correlation (r = 0.58). It was concluded that knee contact angle significantly influences both peak ground reaction forces and segment accelerations. However, owing to the nonlinear relationship, peak forces and segment accelerations change more rapidly at smaller knee flexion angles (i.e., close to full extension) than at greater knee flexion angles.     

Applicability of different endovascular methods for treatment of refractory Budd-Chiari syndrome

The study’s objective was to evaluate the applicability of different endovascular methods for treatment of refractory type of Budd–Chiari syndrome (BCS) under specific scenarios frequently encountered in patients. The treatment methods were evaluated in 197 patients with the following four types of refractory BCS: lesions of the inferior vena cava (IVC) including a special shape diaphragm (e.g., a knife- or a vertically shaped diaphragm, etc.), occlusion of the long segment of IVC, IVC obstruction combined with thrombosis, and occlusion of the hepatic vein. The choice of endovascular treatment depended on the degree of difficulty to puncture the membrane after spatial orientation. There was a need to adjust the curvature of the device to fit the natural angle of IVC. When IVC lesions were combined with thrombosis, the treatment was adjusted depending on the freshness of the thrombus. Different routes were used to rupture the membrane and expand the lesion. The majority of patients recovered without complications. The few complications observed were the following: 1 case of death due to a postoperative stress ulcer, 1 case of a successfully treated pericardial tamponade, 1 case of stent migration, and 3 cases of failure to stent and re-occlusion that occurred in the follow-up period. To conclude, BCS is preferably treated via endovascular intervention; however, the particular choice depends on individual circumstances.     

Flow around cells adhered to a microvessel wall. I. Fluid stresses and forces acting on the cells

To evaluate the fluid forces acting on cells adhered to a microvessel wall, we numerically studied the flow field around adherent cells and the distribution of the stresses on their surfaces. For simplicity, the cells were modeled as rigid particles attached to a wall of a circular cylindrical tube regularly in the flow direction, in a row or two rows. It was found that not the detailed shape of the model cells but their height from the vessel wall is a key determinant of the fluid forces and torque acting on them. In both arrangements of one row and two rows, the axial spacing between neighboring adherent cells significantly affects the distributions of the stresses on them, which results in drastic variations of the fluid forces with the axial spacing and the relative positions with respect to their neighboring cells. The drag force acting on an adherent cell in the vessel was evaluated to be larger than the value in the 2D chamber flow at the same wall shear stress, mainly due to much larger variations of the pressure distribution on the cell surface in the vessel flow.     

A new methodology to measure load transfer through the forearm using multiple universal force sensors

Previous approaches to measuring forces in the forearm have made the assumption that forces acting in the radius and ulna are uniaxial near the wrist and elbow. To accurately describe forces in the forearm and the forces in the interosseous ligament, we have developed a new methodology to quantitatively determine the 3-D force vectors acting in forearm structures when a compressive load is applied to the hand. A materials testing machine equipped with a six degree-of-freedom universal force–moment sensor (UFS) was employed to apply a uniaxial compressive force to cadaveric forearms gripped at the hand and humerus. Miniature UFSs were implanted into the distal radius and proximal ulna to measure force vectors there. A 3-D digitizing device was used to measure transformations between UFS coordinate systems, utilized for calculating the force vectors in the distal ulna, proximal radius, and the interosseous ligament (IOL). This method was found to be repeatable to within 3 N, and accurate to within 2 N for force magnitudes. Computer models of the forearm, generated from CT scans, were used to visualize the force vectors in 3-D. Application of this methodology to eight forearm specimens showed that the radius carries most of the load at the wrist while force in the IOL relieves load acting in the radius at the mid-forearm. For a 136 N applied hand force, the force in the IOL was 36±21 N. Advantages of this methodology include the determination of 3-D force vectors, especially those in the IOL, as well as computer generated 3-D visualization of results.     

The effects of stent interaction on porcine urinary bladder matrix employed as stent-graft materials

Deployment of stent-grafts, derived from synthetic biomaterials, is an established minimally invasive approach for effectively treating abdominal aortic aneurysms (AAAs). However, a notable disadvantage associated with this surgical technique is migration of the deployed stent-graft due to poor biocompatibility and inadequate integration in vivo. Recently, tissue-engineered extracellular matrices (ECMs) have shown early promise as integrating stabilisation collars in this setting due to their ability to induce a constructive tissue remodelling response after in vivo implantation. In the present study the effects of stent loading on an ECM?s mechanical properties were investigated by characterising the compression and loading effects of endovascular stents on porcine urinary bladder matrix (UBM) scaffolds. Results demonstrated that the maximum stress was induced when the stent force was 8-times higher than a standard commercially available stent-graft and this represented about 20% of the failure strength of the UBM material. In addition, the influence of stent shape was also investigated. Findings demonstrated that the stress induced was higher for circular stents at low forces and a higher stress was induced on square stents when increased force was applied. Our findings demonstrate that porcine UBM possesses sufficient mechanical strength to withstand the compression and loading effects of commercially available stent-grafts in the setting of endovascular aneurysm repair.     

The influence of gravity and wind on land plant evolution

Aspects of the engineering theory treating the elastic stability of vertical stems and cantilevered leaves supporting their own weight and additional wind-induced forces (drag) are reviewed in light of biomechanical studies of living and fossil terrestrial plant species. The maximum height to which arborescent species can grow before their stems elastically buckle under their own weight is estimated by means of the Euler-Greenhill formula which states that the critical buckling height scales as the 1/3 power of plant tissue-stiffness normalized with respect to tissue bulk density and as the 2/3 power of stem diameter. Data drawn from living plants indicate that progressively taller plant species employ stiffer and lighter-weight plant tissues as the principal stiffening agent in their vertical stems. The elastic stability of plants subjected to high lateral wind-loadings is governed by the drag torque (the product of the drag force and the height above ground at which this force is applied), which cannot exceed the gravitational bending moment (the product of the weight of aerial organs and the lever arm measured at the base of the plant). Data from living plants indicate that the largest arborescent plant species rely on massive trunks and broad, horizontally expansive root crowns to resist drag torques. The drag on the canopies of these plants is also reduced by highly flexible stems and leaves composed of tissues that twist and bend more easily than tissues used to stiffen older, more proximal stems. A brief review of the fossil record suggests that modifications in stem, leaf, and root morphology and anatomy capable of simultaneously coping with self-weight and wind-induced drag forces evolved by Devonian times, suggesting that natural selection acting on the elastic stability of sporophytes occurred early in the history of terrestrial plants.     

Force acting on spheres adhered to a vessel wall

To evaluate the force and torque acting on leukocytes attached to the vessel wall, we numerically study the flow field around the leukocytes by using rigid spherical particles adhered to the wall of a circular cylindrical tube as a model of adherent leukocytes. The adherent particles are assumed to be placed regularly in the flow direction with equal spacings, in one row or two rows. The flow field of the suspending fluid is analyzed by a finite element method applied to the Stokes equations, and the drag force and torque acting on each particle, as well as the apparent viscosity, are evaluated as a function of the particle to tube diameter ratio and the particle arrangements. For two-row arrangements of adhered particles where neighboring particles are placed alternately on opposite sides of the vessel, the drag and the torque exerted on each particle are higher than those for single-row arrangements, for constant particle to tube diameter ratio and axial spacing between neighboring particles. This is enhanced for Larger particles and smaller axial spacings. The apparent viscosity of the flow through vessels with adhered particles is found to be significantly higher than that without adhered particles or when the particles are freely floating through the vessels.     

Monophasic synovial sarcoma presenting as a primary ileal mass: a case report and review of the literature

Introduction

Iliocaval fistulas can complicate an iliac artery aneurysm. The clinical presentation is classically a triad of hypotension, a pulsatile mass and heart failure. In this instance, following presentation with multiorgan failure, management included the immediate use of an endovascular stent graft on discovery of the fistula.

Case presentation

A 62-year-old Caucasian man presented to our tertiary hospital for management of iatrogenic trauma due to the insertion of a central venous line into his right common carotid artery, causing transient ischemic attack. Our patient presented to a peripheral hospital with fever, nausea, vomiting, acute renal failure, acute hepatic dysfunction and congestive heart failure. A provisional diagnosis of sepsis of unknown origin was made. There was a 6.5 cm×6.5 cm right iliac artery aneurysm present on a non-contrast computed tomography scan. An unexpected intra-operative diagnosis of an iliocaval fistula was made following the successful angiographic removal of the central line to his right common carotid artery. Closure of the iliocaval fistula and repair of the iliac aneurysm using a three-piece endovascular aortic stent graft was then undertaken as part of the same procedure. This was an unexpected presentation of an iliocaval fistula.

Conclusion

Our case demonstrates that endovascular repair of a large iliac artery aneurysm associated with a caval fistula is safe and effective and can be performed at the time of the diagnostic angiography. The presentation of an iliocaval fistula in this case was unusual which made the diagnosis difficult and unexpected at the time of surgery. The benefit of immediate repair, despite hemodynamic instability during anesthesia, is clear. Our patient had two coronary angiograms through his right femoral artery decades ago. Unusual iatrogenic causes of iliocaval fistulas secondary to previous coronary angiograms with wire and/or catheter manipulation should be considered in patients such as ours.     

Advanced Age and Disease Predict Lack of Symptomatic Improvement after Endovascular Iliac Treatment in Male Veterans

Background: Endovascular angioplasty and stent placement is currently the most frequent treatment for iliac artery occlusive disease. However, despite a successful endovascular procedure, some patients do not experience symptomatic improvement and satisfaction with their care. This study seeks to identify patient-related factors associated with lack of symptomatic improvement after endovascular iliac artery treatment in male veterans.Methods: Retrospective review of patients treated with endovascular methods for iliac artery occlusive disease between January 2008 and July 2012 at VA Connecticut Healthcare System. Symptomatic improvement on the first post-operative visit was evaluated, with bilateral treatments counted separately.Results: Sixty-two patients had 91 iliac arteries treated with angioplasty and stent placement. Forty-seven (52 percent) legs had critical limb ischemia, and 77 (85 percent) had at least two-vessel distal runoff. Angiographic success was 100 percent. Patient-reported symptomatic improvement at the first post-operative visit was 55 percent (50/91). Lack of symptomatic improvement correlated with older age (OR 1.09 [1.03-1.17], p = 0.008), presence of critical limb ischemia (OR 3.03 [1.09-8.65], p = 0.034), and need for additional surgical intervention (OR 5.61 [1.65-17.36], p = 0.006). Survival, primary and secondary patency, and freedom from restenosis were comparable between patients who reported symptomatic improvement and those who did not.Conclusions: Despite angiographically successful revascularization, patients who are older or have critical limb ischemia who are treated with isolated endovascular iliac artery intervention are more likely to require additional interventions and less likely to experience symptomatic improvement. These patients may need more extensive infra-inguinal revascularization than isolated iliac angioplasty and stent placement, despite a preserved ankle-brachial index. Quality of life needs to be measured with formal instruments after iliac artery endovascular treatment, especially to determine long term outcomes.     

Endovascular Repair of Arterial Iliac Vessel Wall Lesions with a Self-Expandable Nitinol Stent Graft System

Objective

To assess the therapeutic outcome after endovascular repair of iliac arterial lesions (IALs) using a self-expandable Nitinol stent graft system.

Methods

Between July 2006 and March 2013, 16 patients (13 males, mean age: 68 years) with a self-expandable Nitinol stent graft. A total of 19 lesions were treated: nine true aneurysms, two anastomotic aneurysms, two dissections, one arteriovenous fistula, two type 1B endoleaks after endovascular aneurysm repair, one pseudoaneurysm, and two perforations after angioplasty. Pre-, intra-, and postinterventional imaging studies and the medical records were analyzed for technical and clinical success and postinterventional complications.

Results

The primary technical and clinical success rate was 81.3% (13/16 patients) and 75.0% (12/16), respectively. Two patients had technical failure due to persistent type 1A endoleak and another patient due to acute stent graft thrombosis. One patient showed severe stent graft kinking on the first postinterventional day. In two patients, a second intervention was performed. The secondary technical and clinical success rate was 87.5% (14/16) and 93.8% (15/16). The minor complication rate was 6.3% (patient with painful hematoma at the access site). The major complication rate was 6.3% (patient with ipsilateral deep vein thrombosis). During median follow-up of 22.4 months, an infection of the aneurysm sac in one patient and a stent graft thrombosis in another patient were observed.

Conclusion

Endovascular repair of various IALs with a self-expandable Nitinol stent graft is safe and effective.     

Flow patterns in an endovascular stent-graft for abdominal aortic aneurysm repair

Endovascular exclusion of the abdominal aortic aneurysm (AAA) has been carried out in selected patients during the past decade. The deployment of a complex multicomponent endovascular device in an aneurysmal aorta may alter the local haemodynamics and lead to thrombosis and intimal hyperplasia development. The aim of this in vitro study was to investigate the flow patterns using flow visualisation and laser Doppler anemometry in a commercial bifurcated stent-graft. Two configurations of the stent-graft, endo-stent and exo-stent, were investigated in an idealised planar AAA model. The flow structures in the main trunk in both configurations of the stent-graft are three-dimensional with complex secondary structures. However, these flow structures were not entirely caused by the stent-graft. The stent struts in the endo-stent configuration cause localised alteration in the flow pattern but the overall flow structures were not significantly affected. Low velocity regions in the main trunk and flow separation in the stump region and the curved segment of the iliac limbs were observed. These areas are associated with thrombosis in the clinical situation. Improvements in the design of endovascular devices may remove these areas of unfavourable flow patterns and lead to better clinical performance.     

Biomechanical factors affecting fracture stability and femoral bursting in closed intramedullary rod fixation of femur fractures

Intramedullary rodding of femur fractures, although a safe and rapidly performed procedure, can result in several complications. If the rod fit is too loose, fracture instability, rod migration, and delayed union may result. If the rod fit is too tight, cracking of the femur may occur during rod insertion. These complications were investigated in terms of geometric and mechanical parameters of the bone-implant system. Results showed that rods of the same nominal size from different manufacturers showed more than twofold difference in flexural rigidity and a threefold difference in torsional modulus. These differences appear to be due to differences in cross sectional shape and wall thickness of the rods. Measurements of pushout force and hoop stress in cadaver femora showed a large difference in pushout force with different rods, and significantly lower forces in distal than in proximal femoral fracture components. Pushout force decreased with fracture component length proximally and dropped to zero in distal components less than 170 mm long. An increase in ream diameter in the distal components of just 1 mm was found to decrease the mean pushout force from 740N to 90N. The most significant variable was found to be anterior offset of the starting hole more than 6 mm from the centerline of the medullary canal which resulted in consistent lifting of the anterior cortex during insertion of the rod.     

Patient-specific analysis of displacement forces acting on fenestrated stent grafts for endovascular aneurysm repair

Treatment options for abdominal aortic aneurysm (AAA) include highly invasive open surgical repair or minimally invasive endovascular aneurysm repair (EVAR). Despite being minimally invasive, some patients are not suitable for EVAR due to hostile AAA morphology. Fenestrated-EVAR (F-EVAR) was introduced to address these limitations of standard EVAR, where AAA is treated using a Fenestrated Stent Graft (FSG). In order to assess durability of F-EVAR, displacement forces acting on FSGs were analysed in this study, based on patient-specific geometries reconstructed from computed tomography (CT) scans. The magnitude and direction of the resultant displacement forces acting on the FSG were numerically computed using computational fluid dynamics (CFD) with a rigid wall assumption. Although displacement force arises from blood pressure and friction due to blood flow, numerical simulations elucidated that net blood pressure is the dominant contributor to the overall displacement force; as a result, time dependence of the resultant displacement force followed pressure waveform very closely. The magnitude of peak displacement force varied from 1.9 N to 14.3 N with a median of 7.0 N. A strong positive correlation was found between inlet cross-sectional area (CSA), anterior/posterior (A/P) angle and the peak displacement force i.e. as inlet CSA or A/P angle increases, the magnitude of resultant displacement increases. This study manifests that while loads exerted by the pulsatile flow dictates the cyclic variation of the displacement force, its magnitude depends not only on blood pressure but also the FSG morphology, with the latter determining the direction of the displacement force.     

Measurement of finger joint angles and maximum finger forces during cylinder grip activity

Finger joint angles and finger forces during maximal cylindrical grasping were measured using multi-camera photogrammetry and pressure-sensitive sheets, respectively. The experimental data were collected from four healthy subjects gripping cylinders of five different sizes. For joint angles, an image analysis system was used to digitize slides showing markers. During the calibration of the camera system, both the nonlinear least square and the direct linear transform methods were applied and compared, the former providing the fewer errors; it was used to determine joint angles. Data were collected from the pressure-sensitive grip films by using the same image analysis system as used in the collection of the joint angle data. The method of using pressure-sensitive sheets provided an estimation of the weighted centre of the phalangeal forces. Results indicate that finger flexion angles at the metacarpophalangeal and proximal interphalangeal joints gradually increase as cylinder diameter decreases, but that at the distal interphalangeal joint the angle remains constant throughout all cylinder sizes. It was also found that most of the radio-ulnar deviation and the axial rotation angles at the finger joints deviate from zero, but the deviations are small. For the force measurement, it was found that total finger force increases as cylinder size decreases, and the phalangeal force centres are not located at the mid-points of the phalanges. The data obtained in this experiment would be useful for muscle force predictions and for the design of handles.