Mechanical prostheses

Hea.rt Va.Ives. Since the early 1960s nearly 50 different heart valves have been developed. The most commonly used valves as of the mid-1990s include mechanical prostheses and tissue valves. Nearly 75,000 of these prosthetic valves are implanted aimually worldwide, and about 30,000 in the United States alone. Caged-baH, caged disk, and til ting-disk heart valves are the types most widely used. 

The in vivo and jji vitro pressure measurements indicate that like other ball valves, due to its centrally occluding design, the Starr-Edwards ball valves are moderately stenotic in the medium to larger sizes. In the smaller sizes the valves are very stenotic. Patients with this prosthesis would not be able to lead very strenuous life styles. The prosthesis does have low regurgitant volumes, the lowest among mechanical prostheses in current clinical use. The in vivo and in vitro data seem to indicate that the instability of the silicone rubber poppet (1200/1260, 6120) could lead to larger pressure drops across the prosthesis. 

Mechanical prostheses Prostheses made of non-biological material. 

Mechanical and animal models, in CPR, 18-11-18-12 Mechanical heart valves, 44-2-44-8, 44-7 Mechanical interlock fixation method, 45-11 Mechanical prostheses, 44-2 Mechanical work in humans, fectors affecting, 66-1-66-9... 

The long-term chnical durability of bioprosthetic valves is the major impediment to their use. Before long-term durabihty data became available, improvement of hemodynamic performance was the focus of development. The chnical introduction of the bovine pericardial valve solved the hemodynamic problem, and such valves exhibit hemodynamics equal to or better than some mechanical prostheses. 

Rizzoli, G. et al.. Biological or mechanical prostheses in tricuspid position A meta-analysis of intra-institutional results. Ann Thorac Surg, 2004. 77(5) p. 1607-14. 

Vicchio, M. et al.. Tissue versus mechanical prostheses Quality of life in octogenarians. Amm Thorac Surg, 2008. 85(4) p. 1290-5. 

Fig. 9.25. Three possible adaptronic control systems for biomedical applications, a Open-loop solid line) adaptronic system with closed-loop option dashed line), as e. g. applied in the neural/muscular control of a mechanical prosthesis (open-loop) or a drug delivery system (closed-loop), b control depends on two variables, namely the biological system and the ambiance sensor input, c signal is encoded from an ambiance input to achieve an effector response in the biological system. Biosensing delivers state variables for adaptive control...

Fig. 9.27. Open-loop adaptronic system for controlling the movements of a mechanical prosthesis...

Hammermeister, K.E. et al.. Comparison of outcome after valve replacement with a bioprosthesis versus a mechanical prosthesis Initial 5 year results of a randomized trial. / Am Coll Cardiol, 1987. 10(4) p. 719-32. 

While it would be difficult to enumerate all of the efforts in the area of implants where plastics are involved, some of the significant ones are (1) the implanted pacemaker, (2) the surgical prosthesis devices to replace lost limbs, (3) the use of plastic tubing to support damaged blood vessels, and (4) the work with the portable artificial kidney. The kidney application illustrates an area where more than the mechanical characteristics of the plastics are used. The kidney machine consists of large areas of a semi-permeable membrane, a cellulosic material in some machines, where the kidney toxins are removed from the body fluids by dialysis based on the semi-permeable characteristics of the plastic membrane. A number of other plastics are continually under study for use in this area, but the basic unit is a device to circulate the body fluid through the dialysis device to separate toxic substances from the blood. The mechanical aspects of the problem are minor but do involve supports for the large amount of membrane required. 

Bioactive materials can be used as powders for filling small defects and as coatings that enhance metallic prosthesis fixation. However, when considering bioactive materials for bone regeneration in medium and large defects, bioactive pieces with appropriate mechanical properties are required. At this point, the key is to keep the properties provided by the nanostructure when processing a piece at the macroscopic... 

Adverse effects of prosthesis insertion include early and late onset infection, mechanical failure, and erosion of the rods through the penis. 

The artificial hip has been used to replace the human hip because the hip is easily worn out over a lifetime of mechanical stress resulting from normal activity. The first artificial hip implant was made by Thermistokles Gluck in 1891 in Berlin. This implant made use of a femoral head of ivory fixed with plaster of paris and glue (Gluck, 1890, 1891). The results were not good due to severe infection problems and adverse foreign body tissue reactions. To develop better hip replacement prosthesis, many materials and procedures were examined between 1925 and 1953. 

Yeast flocculation mechanism can be described as a phenomenon of adhesion to certain surfaces. The ability to adhere to surfaces and to form biofilm is the basis of the pathogenicity of Candida species. Pathogens adhere to mucous membranes and wounds, they stick to medical instruments and prosthesis, and thus contaminate surfaces in food processing facilities. The high mortality rate in disseminated fungal infections caused an increase in the amount of research on the molecular basis of the adhesive phenomena in Candida. This research discovered a considerable overlap in the molecular regulation of all forms of adhesive behavior. ... 

Decreased INR associated with the use of P. ginseng was reported in a 47-year-old patient who had been stabilized on warfarin (25). Another case of inadequate anticoagulation with ginseng product resulting in thrombosis on a mechanical aortic valve prosthesis was reported in a 58-year-old patient (26). Additional details of these two case reports are discussed in Chapter 5. 

Implantation materials, which are in direct contact with blood, have to meet a particularly large range of requirements bio- and blood compatibility, mechanical strength against blood pressure, impermeability to the blood and its constituents, and sterilizability. In addition, the healing process that takes place on the inner and the outer surface of the artificial vessel is very different. The inner surface of the biomaterial should not stimulate adhesion of cellular blood components but should be covered with endothelial cells, whereas the outer surface of the prosthesis should be wrapped with connective tissue. 

Orthopaedic prosthesis Mechanism of wear of Ultra-high molecular weight polyethylene currently used in total hip and knee joint implants— see J. Mater. Set. 28 1045-1058 (1993). 

Potentiation of the effect of warfarin by danshen (the root of Salvia miltiorrhizd), a widely used traditional Chinese herbal medicine, particularly for cardiovascular complaints, has been described in a 62-year-old man with a mechanical mitral valve prosthesis (159). 

Both allergic and irritant mechanisms have been proposed as explanations for nasal symptoms. Measures that have successfully been used include nasal swabs (eosinophils), nasal lavage or biopsy, acoustic rhinometry (nasal volume), anterior and posterior rhinomanometry (plethysmography), and measures of nasal hyperreactivity (visual, using a dental prosthesis as a head fixative, and using an ear surgery microscope to measure distances and swelling). 

The inflatable prosthesis has several parts, inclnding two inflatable rods and a pnmp-reservoir mechanism. When activated, the device pnmps saline solntion from the reservoir into the rods, cansing inflation. The inflatable prosthesis prodnces a more natnral erection, in that the patient only develops an erection when the device is activated. Some newer advances in inflatable prosthesis technology have resulted in devices with the pump, reservoir, and rods aU in one nnit, and these can be placed dnring shorter snrgical procednres and are less likely to malfunction (Fig. 81-9). 

Adverse effects of prosthesis insertion can occnr early or late after the surgical procedure. The most common early comphcation is infection. Late complications include mechanical failnre of the prosthesis, particularly when inflatable prostheses have been inserted. With improved technology, the mechanical failure rate has decreased to 5%. Other late complications include erosion of the rods through... 

As noted earlier, many joint prostheses are held in place by a polymeric cement. This cement is usually a pasty mixture of a methyl methacrylate copolymer and monomeric methyl methacrylate with an added redox initiating system. The paste is pressed into the excavated bone region and polymerized in situ to produce a polymeric mass that then holds the prosthesis by mechanical entrapment. This... 

American Medical Association as much as possible amorphous material ambulate ambulatory arm muscle circumference age-related macular degeneration acute megokaryoblastic leukemia acoustic myography acute myocardial infarction acute myelogenous leukemia agnogenic myeloid metaplasia acute myelomonoblastic leukemia amniocentesis acute monoblastic leukemia amputation ampule Austin-Moore prosthesis alternating motor rates acute mountain sickness amylase assisted mechanical ventilation... 

The surface of the implant or prosthesis is grit blasted not only to establish a mechanical bond between the substrate and the coating, but also to establish a stronger mechanical bond with bone once the HAp has been resorbed. A surface roughness, Ra, as little as 1 pm can lead to a twofold increase in the removal torque of an implant from... 

Bioadhesion, i.e. biofihn formation resulting in a fouling surface, is required for biomaterial to be considered as a part of the body (e.g., orthopedic prosthesis, hard tissue) to enhance its incorporation and its biomechanical response. Examples are in the rebuilding of bones, recolonization, and hybrid implants composed of two parts, a synthetic one (with polymers as the mechanical sub-... 

In many cases the hemolysis caused by the prosthesis is mild or moderate, and is generally compensated for quite adequately by natural regeneration in the bone-marrow. Cloth covering on the valve superstructure (such as with the Starr-Edwards and Beall valves) will lead to an increase in hemolysis depending on the structure and surface characteristics of the fabric. Hemolysis, however mild, is not innocuous. It is the forerunner in one of the proposed mechanisms for platelet aggregation and coagulation, which in turn could lead to the formation of thromboemboli. 

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