Mechanical patency

In addition to the above general criteria, the mechanical properties of implants also play an important role in determining their success. Four major properties of interest are strength, bending stiffness or, conversely, flexibility, abrasion resistance and durability or long-term mechanical patency. These are now examined along with the factors that can be used to optimize them. 

Criteria for understanding and characterizing the mechanical patency of an implant, (a) An ideally elastic material with indefinite fatigue life, and (b) and (c) visco-elastic materials with limited fatigue life. 

Self-expanding stents with a higher radial force (e.g., WingSpan, Boston Scientific Corp.) will probably play a key role in acute stroke cases related to intracranial atherosclerotic disease. Antegrade flow is essential for the maintenance of vascular patency, as particularly evident in patients with severe proximal stenoses who commonly develop rethrombosis after vessel recanalization. Furthermore, stenting of the proximal vessels may be required in order to gain access to the intracranial thrombus with other mechanical devices or catheters. In a recent series, 23 of 25 patients (92%) with acute n = 15) or subacute n = 10) ICA occlusions were successfully revascularized with this technique. " ... 

Considering the second requirement, that is, good dynamic mechanical properties ePTFE-based arterial prostheses must satisfy to improve their functional patency, there are not so many ways to reach this goal. Unfortunately, and due to the intrinsic mechanical characteristics of PTFE, the mechanical behaviour of these prostheses cannot be easily modified. However, different ways have been explored on the one hand, an optimisation of the design of the prostheses... 

Note Hemostasis refers to a complex homeostatic mechanism within blood and on blood vessels that serves to maintain the patency of vessels after injury, while preserving the fluidity of blood. 

Some alternative theories seem less probable. Tubal patency tests have established that lUDs do not cause mechanical obstruction or spasm... 

Efforts to decrease the time until therapy was initiated to maximize both the rate of success of lytic therapy [fresher clots are more susceptible to lysis, especially with nonfibrin-specific agents (5)] and the impact of reperfusion on myocardial salvage led to a shift to intravenous administration of these drugs, which could be performed in the coronary care unit (CCU) or the emergency department (ED), saving 1-2 hours between diagnosis and the initiation of therapy. Trials performed with angiographic assessment after the initiation of thrombolytic therapy are patency studies infarct-related vessels found to be patent will include those that contained clot that was successfully dissolved by the therapy delivered, those that contained clot that resolved because of the body s own fibrinolytic mechanisms before therapy was instituted, and those that never had intracoronary thrombus as an occlusive event. 

Preexisting airway damage (such as that caused by prior toxic inhalant exposure) may seriously compromise the respiratory system s normal protection and clearance mechanisms. Specifically, there may be depletion of critical enzyme systems. Cigarette smoking may severely compromise airway function with respect to both airway patency and clearance mechanisms. Hyperreactive airways (asthma in varying degrees) are seen in up to 15% of the adult population. Toxic inhalant exposures... 

Stylet wires (Fig. 4.2) are used to stiffen leads for removal. Moreover, stylet wires can be used to debride foreign matter inside the lead body, confirm patency, and measure lead length. Stylet wires improve the effectiveness of lead removal when using either direct traction or mechanical sheaths. 

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