Simple Traction

Complications such as cardiac perforation and tamponade are also possible using this technique. 

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The characteristic feature of all Amplatzer devices is the nitinol wire mesh. There are two possible methods of implantation. Either the device is placed entirely into the appendage or the distal disc is expanded in the neck and the proximal disc in the left atrium. The risk of residual shunting around the device is increased when it is totally inserted into the LAA with no part protruding into the atrium. The Amplatzer occluder series holds the widest spectrum of device sizes (4 to 40 mm), The device is attached to a delivery cable and can simply be opened or recollapsed into the delivery catheter. Release is by unscrewing the device after first testing stability with simple traction. 

Lead removal is removal of a pacing or defibrillator lead using any technique. It includes two completely different procedures lead explant and lead extraction. Lead explant is the removal of a lead using simple traction techniques, which is usually possible for leads implanted for less than 1 year. Lead extraction is removal of a lead implanted for more than 1 year or that requires the assistance of specialized equipment in order to be removed. Lead extraction is by far the more complex procedure. As it carries some risks for the patient, clear indications, expertly trained personnel, adequate tools, and appropriate environment and facilities are mandatory for its safe removal [1, 2]. 

The shorter implant time, different characteristics of lead insulation, and absence of a fixation mechanism can explain the substantial ease of transvenous removal of LV leads. Regardless of the ease of lead removal by simple traction, binding sites into the CS are present in most patients as evidenced by findings during LV lead reimplantation. These include CS stenosis, presence of thrombi, and obliteration of venous branches. These observations suggest that, due to their different characteristics, it may be easier to slip LV leads through adhesions than the other leads. On the other hand, these observations and clinical experiences suggest that the use of fixation mech-... 

From Simple Traction to Internal Transjugular Approach... 

There are three fundamental anatomic approaches for lead extraction (23,24,37). The first is retrieval by the implant vein, frequently called the superior approach. This approach can include simple traction. Buck s traction, the use of locking stylets with traction, or the use of locking stylets with countertraction sheaths. The second approach is transfemoial, frequently called the inferior approach. This approach may involve several distinct techniques. When this involves entangling a lead with a pigtail catheter, the catheter is passed from below. When free open ends present themselves, a wire-loop system may be used with traction. Both the Dotter retriever and Dormia basket may also be applied for traction from below. Finally, the lead to be removed may be extracted by the Byrd Femoral Work Station with the use of a combination of snares and wire loops. The third and final approach is retrieval of leads by a limited thoracotomy. 

Epicardial leads can be used in a standard bipolar or unipolar configuration. Pacing and sensing thresholds tend to deteriorate over several days. Epicardial leads with specially designed epicardial electrodes (as opposed to uninsulated braided wire) provide lower pacing thresholds (54, 55). The leads are removed by simple traction. The use of temporary epicardial wires is generally safe. In one series of more than 9,000 patients no complications were observed other than inability to remove the electrode in three patients in all three patients the lead wire was simply clipped at the skin without sequelae. The effectiveness and safety of the epicardial system have led to widespread use. 

In a uniaxial stress state, as in the specimen under simple traction, Eq. (9.21) yield... 

FIGURE 22.13 Simple analytical model of hysteresis friction of rubber moving over a rough road profile left). Tire on a wet road track, where hysteresis energy losses dominate the traction behavior right). (From Kluppef M. and Heinrich, G., Kautschuk, Gummi, Kunststojfe, 58, 217, 2005. With permission.)... 

At the instant of contact between a sphere and a flat specimen there is no strain in the specimen, but the sphere then becomes flattened by the surface tractions which creates forces of reaction which produce strain in the specimen as well as the sphere. The strain consists of both hydrostatic compression and shear. The maximum shear strain is at a point along the axis of contact, lying a distance equal to about half of the radius of the area of contact (both solids having the same elastic properties with Poisson s ratio = 1/3). When this maximum shear strain reaches a critical value, plastic flow begins, or twinning occurs, or a phase transformation begins. Note that the critical value may be very small (e.g., in pure simple metals it is zero) or it may be quite large (e.g., in diamond). 

Microstructures are generally too complex for exact models. In a polycrystalline microstructure, grain-boundary tractions will be distributed with respect to an applied load. Microstructures of porous bodies include isolated pores as well as pores attached to grain boundaries and triple junctions. Nevertheless, there are several simple representative geometries that illustrate general coupled phenomena and serve as good models for subsets of more complex structures. 

This is the simplest case, and for the idealised loading of uniform tractions on the ends of the bar we obtain the simple relation a = eE, where o is the stress on the cross-section, e the strain and E the Young modulus in the direction of strain. 

The fiber is suspended in the liquid, which means that due to small time scales given by the pure viscous nature of the flow, the hydrodynamic force and torque on the particle are approximately zero [26,51]. Numerically, this means that the velocity and traction fields on the particle are unknown, which differs from the previous examples where the velocity field was fixed and the integral equations were reduced to a system of linear equations in which velocities or tractions were unknown, depending on the boundary conditions of the problem. Although computationally expensive, direct integral formulations are an effective way to find the velocity and traction fields for suspended particles using a simple iterative procedure. Here, the initial tractions are assumed and then corrected, until the hydrodynamic force and torque are zero. 

The direct boundary integral formulation was used to simulate suspended spheres in simple shear flow. The viscosity was then calculated by integration of the surface tractions on the moving wall. Figure 10.28 shows a typical mesh for the domain and spheres for these simulations in this mesh, the box has dimensions of 1 x 1 x 1 (Length units)3 and 40 spheres of radius of 0.05 length units. 

From the simple exercise given above, we conclude that if the craze lentil shape remained constant with an unchanging aspect ratio p, the craze traction would always be less than the applied stress and the craze tip driving force ... 

The Cauchy stress principle arises through consideration of the equilibrium of body forces and surface tractions in the special case of the infinitesimal tetrahedral volume shown in fig. 2.7. Three faces of the tetrahedron are perpendicular to the Cartesian axes while the fourth face is characterized by a normal n. The idea is to insist on the equilibrium of this elementary volume, which results in the observation that the traction vector on an arbitrary plane with normal n (such as is shown in the figure) can be determined once the traction vectors on the Cartesian planes are known. In particular, it is found that = crn, where a is known as the stress tensor, and carries the information about the traction vectors associated with the Cartesian planes. The simple outcome of this argument is the claim that... 

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