The effectiveness of a cardiovascular stent depends on many factors, such as its ability to sustain the compression applied by the vessel wall, minimal longitudinal contraction when it is expanded, and its ability to flex when navigating tortuous blood vessels. The long-term reaction of the tissue to the stent is also device dependant; in particular some designs provoke in-stent restenosis (i.e., regrowth of the occlusion around the stent). The mechanism of restenosis is thought to involve injury or damage to the vessel wall due to the high stresses generated around the stent when it expands. Because of this, the deflection of the tissue between the struts of the stent (called prolapse or "draping") has been used as a measure of the potential of a stent to cause restenosis. In this paper, uniaxial and biaxial experiments on human femoral artery and porcine aortic vascular tissue are used to develop a hyperelastic constitive model of vascular tissue suitable for implementation in finite-element analysis. To analyze prolapse, four stent designs (BeStent 2, Medtronic AVE; NIROYAL, Boston Scientific; VELOCITY, Cordis; TETRA, Guidant) were expanded in vitro to determine their repeating-unit dimensions. This geometric data was used to generate a finite element model of the vascular tissue supported within a repeating-unit of the stent. Under a pressure of 450 mm Hg (representing the radial compression of the vessel wall), maximum radial deflection of 0.253 mm, 0.279 mm, 0.348 mm and 0.48 mm were calculated for each of the four stents. Stresses in the vascular wall were highest for the VELOCITY stent. The method is proposed as a way to compare stents relative to their potential for restenosis and as a basis for a biomechanical design of a stent repeating-unit that would minimize restenosis.
Peoples' perception of the necessity of their involuntary admissions is not stable over time and risk of involuntary readmission is associated with recovery style.
This article examines the ability of young Irish graduates to enact mobility as a form of personal and career development both during economic expansion and recession. Of particular interest is the observation that Irish graduates are much more mobile than those in other countries which were also badly affected by the recession. Drawing from a study of recent Irish graduate emigrants (Irish Graduate Abroad Study), the article demonstrates how Irish graduates have successfully negotiated routes into global labour markets, facilitated by the relatively straightforward recognition of their qualifications, their ability to speak English and the visa permissions that enable such movement. Irish graduates have incredible global networks generated through a family history of migration. Irish graduates also have a considerable prior culture of mobility facilitated through institutionally mediated mobility programmes. Taken together, Irish graduates have amongst the lowest barriers globally to actually enact global careers. In the context of limited opportunities in Ireland due to its size and its current economic situation, mobility is an attractive choice with far more to gain than lose for many young Irish graduates.
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