Assist device

Other efforts have led to the development of ventricular assist devices to support the heart for several months and intra-aortic balloon pumps (lABPs) which are widely used to unload and stabilize the heart. 

Biomaterials for Cardiovascular Devices. Perhaps the most advanced field of biomaterials is that for cardiovascular devices. For several decades bodily parts have been replaced or repaired by direct substitution using natural tissue or selected synthetic materials. The development of implantable-grade synthetic polymers, such as siHcones and polyurethanes, has made possible the development of advanced cardiac assist devices (see... 

Ca.rdia.c-AssistDevices. The principal cardiac-assist device, the intra-aortic balloon pump (lABP), is used primarily to support patients before or after open-heart surgery, or patients who go into cardiogenic shock. As of the mid-1990s, the lABP was being used more often to stabilize heart attack victims, especially in community hospitals which do not provide open-heart surgery. The procedure consists of a balloon catheter inserted into the aorta which expands and contracts to assist blood flow into the circulatory system and to reduce the heart s workload by about 20%. The disposable balloon is powered by an external pump console. 

The worldwide market for vascular grafts was approximately 150 million and growing at about 5% annuaUy as of 1995. The vascular graft area has tremendous market potential in development of smaU-diameter grafts of 3—4 mm for coronary bypass surgery. The total market for the intra-aortic baUoon pump, a cardiac-assist device, is ca 80 million worldwide. About 75,000 patients were supported by these baUoon pumps in 1994. This market is thought to have peaked. 

Poly(tetramethylene oxide) polyols (PTMEG) are high performance polyethers that are crystalline waxes at molecular weights above 650 and liquids at lower molecular weights. They are only available as diols, but they produce adhesives with good hydrolysis resistance and moisture resistance, which is why these adhesives are even used in medical devices, blood bags, catheters, and heart-assist devices [25]. Certain thermoplastic polyurethane adhesives and solvent-borne adhesives are also based on PTMEG s. 

The ventricular assist device (VAD) is a surgically implanted pump that reduces or replaces the work of the right, left, or both ventricles. Ventricular assist devices are currently indicated for short-term support in patients refractory to pharmacologic therapies, as long-term bridge therapy (a temporary transition treatment) in patients awaiting cardiac transplant, or in some instances, as the destination therapy (treatment for patients in lieu of cardiac transplant for those who are not appropriate candidates for transplantation).1 The most common complications are infection and thromboembolism. Other... 

Cardiac transplantation is one option for patients with severe heart failure. Candidates for cardiac transplantation generally present with New York Heart Association (NYHA) class III or IV symptoms and have an ejection fraction of less than 25%.1,3 The general indications for cardiac transplantation include rapidly declining cardiac function and a projected 1-year mortality rate of greater than 75%. Mechanical support with an implantable left ventricular assist device may be appropriate while patients await the availability of a viable organ.1,3 Some additional reasons for heart transplant include ... 

Occupational and physical therapy may help patients to preserve joint function, extend joint range of motion, and strengthen joints and muscles through strengthening exercises. Patients with joint deformities may benefit from the use of mobility or assistive devices that help to minimize disability and allow continued activities of daily living. In situations where the disease has progressed to a severe form with extensive... 

Referral to a physical or occupational therapist may be helpful, particularly in patients with functional disabilities. Physical therapy is tailored to the patient and may include assessment of muscle strength, joint stability, and mobility use of heat (especially prior to episodes of increased physical activity) structured exercise regimens and implementation of assistive devices, such as canes, crutches, and walkers. The occupational therapist ensures optimal joint protection and function, energy conservation, and use of splints and other assistive devices. 

Acute myocardial infarction Angiopathy Aortic aneurysm Aortic balloon assist devices Giant hemangiomas Peripheral vascular disease Postcardiac arrest Prosthetic devices Raynaud s syndrome Infectious Arbovirus Aspergillus Candida albicans Cytomegalovirus Ebola virus... 

The introduction of newer and better elastomers for use in the rubber diaphragm of circulatory assist devices is currently hampered by a lack of shortterm fatigue tests to evaluate candidate materials. 

The development of cardiac assist devices and other instrumentation and components which come in contact with the cardiovascular system requires materials which will perform in a physiological environment. One particularly difficult application is the diaphragm for blood pumps, which requires an elastomer to undergo cyclic deformation and/or flexing while in contact with blood. 

More recently, the National Institutes of Health have been emphasizing hearts and assist devices capable of mechanical or electrical operation. Most of these devices have a pusher plate that moves back and forth to displace the diaphragm a fixed (but adjustable) distance, generally independent of the pressure of each stroke. The fatigue test which most closely mimics this condition will deform the test specimens to a fixed deformation or strain in each cycle. This is the type of fatigue test machine that MRC has constructed for this program. 

Snyder TA, Tsukui H, Kihara S et al (2007) Preclinical biocompatibility assessment of the EVAHEART ventricular assist device coating comparison and platelet activation. J Biomed Mater Res A 81 85-92... 

Adequate rest, weight reduction if obese, occupational therapy, physical therapy, and use of assistive devices may improve symptoms and help maintain joint function. 

Patients with treatment refractory symptoms at rest despite maximal medical therapy (e.g., patients requiring recurrent hospitalization or who cannot be discharged without mechanical assist devices or inotropic therapy)... 

SECTION 2 Cardiovascular Disorders Ventricular Assist Devices... 

Ventricular assist devices are surgically implanted and assist, or in some cases replace, the pumping functions of the right and/or left ventricles. 

Ventricular assist devices can be used in the short-term (days to several weeks) for temporary stabilization of patients awaiting an intervention to correct the underlying cardiac dysfunction. They can also be used long term (several months to years) as a bridge to heart transplantation. Permanent device implantation has recently become an option for patients who are not candidates for heart transplantation. 

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