Cardiovascular applications Heart

Since PTFE is highly inert and nontoxic, it finds use in medical applications for cardiovascular grafts, heart patches, ligaments for knees, and others.12... 

Application -Cardiovascular application (Hemocompat-ibility] [88] -Cardiovascular application (similarity of mechanical properties to those of porcine aorta and aortic heart valve] [89]... 

FIGURE 19.2 Polymeric prostheses for cardiovascular applications, (a) Design (i) and prototype (ii) of a synthetic heart valve fabricated with POSS-PCU nanocomposite polymer, (b) Schematics of an ePTFE vascular graft with heparin immobilized on the surface for anticoagulant effects. Panel (a) Adapted from Kidane et al. [67] with permission from Elsevier, copyright (2009). Panel (b) Adapted from Hoshi et al. [122] with permission from Elsevier, copyright (2013). 

Both of these approaches are important steps towards the creation of PVA-C tissue hybrids for cardiovascular applications and specifically for heart valves and vascular grafts. 

Biomaterials have many cardiovascular applications (that is, pertaining to the heart, blood, and blood vessels). Heart valve implants are often mechanical devices. The presentation of a smooth surface is important, to reduce blood clotting and the loss of red blood cells. Vascular grafts are commonly constructed of Dacron a polyester material that integrates with surrounding tissues. Artifi-... 

Metals share excellent mechanical and conductivity (electrical and thermal) properties ideal for high stress apphcations such as heart valves. Titanium—nickel alloys have become the most common material for metaUic cardiovascular applications (stents and valves) due to unique properties shape memory effect, super-elasticity, high degree of biocompatibility moreover, they are almost completely inert and nonmagnetic. 

Wan mimics the mechanical behavior of cardiovascular tissues, such as aorta and heart valve leaflets. The stress-strain properties for porcine aorta are matched by microbial cellulose-poly(vinyl alcohol) nanocomposite in both the circumferential and the axial tissue directions. Relaxation properties of the nanocomposite, which are important for cardiovascular applications, were also studied and found to relax at a faster rate and to a lower residual stress than the tissues they might replace. The study showed that this nanocomposite is a promising material for cardiovascular soft tissue replacement applications. The aim of a study by Mohammadi et al. was to mimic not only the nonlinear mechanical properties displayed by porcine heart valves, but also their anisotropic behavior, by applying a controlled strain to the samples while imdergoing low-temperature thermal cycling, in order to induce oriented mechanical properties. 

Biomaterials have played a vital role in the treatment of cardiovascular diseases, examples of applications including heart valve prostheses, vascular grafts, stents, indwelling catheters, ventricular assist devices, total implantable artificial heart, pacemakers, automatic internal cardioverter defibrillator, intraaortic balloon pump, and more. A key requirement for materials in cardiovascular applications, particularly blood-contacting devices, is blood compatibility, that is, nonthrombogenic. Additional requirements include mechanical and surface properties that are application specific. Surveying the field of polymers used in cardiovascular applications reveals that PUs, polyethylene terephthalate (PET), and expanded PTFE (ePTFE) are the most commonly used. This section will review each of the three polymers followed by a brief introduction of other emerging polymers for use in the cardiovascular area. 

Other examples of PDE inhibitors with possible clinical usefulness are inhibitors of PDE3 or PDE4 (Table 21-1). Based on the localization of PDE3 to heart and vascular tissue and the role of cAMP in regulating heart muscle contraction and smooth muscle relaxation, a large number of PDE3 inhibitors have been developed for possible clinical applications in cardiovascular medicine. 

Cardiovascular Effects. The only information available is the case of an investigator who self-applied an amount of ointment containing 100 mg 1,3-DNB three times over a 24-hour period (White and Hay 1901). After the third application, he noticed that his heart rate had increased to about 100-120 beats per minute and did not return to pre-exposure rate (not specified) until 3 days later. No further information was provided. 

Adrenoceptors of the /3-subtype are important mediators of the sympathetic activation of the heart, kidney, and bronchi. /3-Adrenoceptors are also found in other organs and tissues such as blood vessels and the central nervous system. Accordingly, /3-adrenoceptor antagonists or jS-blockers inhibit the stimulating influence of the endogenous catecholamines (noradrenaline, adrenaline) on the various organs and tissues which are subject to sympathetic innervation. In cardiovascular medicine the /3-blockers are used in particular to blunt the sympathetic activation of the heart and kidneys. These effects are mediated by the /3i-subtype of the /3-adrenoceptors. The currently used /3-blockers are all competitive antagonists of the /3i-adrenoceptor, which is the basis of their therapeutic application. 

The NEP and APN levels are moderate on heart [74,75] while the concentration of both peptidases is higher in vascular endothelium or vagus nerve terminals [76-78]. However, the mechanisms and site of action (central or peripheral) involved in the cardioprotective effects of the endogenous opioid peptides remain unknown. Nevertheless, owing to their lack of narcotic effects, inhibition of endogenous enkephalin catabolism and subsequent stimulation of delta receptor could have interesting clinical applications in the cardiovascular domain. 

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