The improving hematologic picture in long-term surviving calves with total artificial hearts

Old, new and Revised Aspects of Artificial Organs

Retrograde perfusion of the coronary veins with oxygenated blood is effective. Closed chest transarterial left ventricular bypass was developed by Hans Zwart to support the failing left ventricle. Transapical left ventricular bypass started by Alex Kralios, later studied by Jeffrey Peters et al, became effective when filters were introduced into the system –- first surviving patient! One must be prepared to support both ventricles. Retrograde transpulmonary bypass (Kralios) is as yet only experimental. The blood is pumped from one occluded pulmonary artery into the aorta. Plasmapheresis removes particles with a molecular weight of 7 to 45,000 which may be harmful in patients with burns or oxygenators since they blind the leukocytes. Starling's Law will regulate the total artificial heart. The future is for the electrohydraulic artificial heart by Robert Jarvik. However, air driven hearts may offer a life of sufficient quality to people now doomed to die. All types of hemodialyzers or peritoneal dialyzers should be made portable or wearable. The «mouse» is a good peritoneal access device. It makes recirculating peritoneal dialysis practical.

Artificial heart and left ventricular assist devices

We believe there will be a place in cardiac surgery for a variety of assist and replacement devices. The extracorporeal assist devices, with or without extracorporeal membrane oxygenation, will be needed for acute situations requiring time for diagnosis and prognosis to be determined. There will also be a place for intrathoracic paraventricular assist devices that may temporarily or permanently support the right or left ventricle. Finally, we believe that there will be a number of patients whose native cardiac function is of no help at all and whose hearts probably should be removed to make room for an improved blood pump of human design. Pneumatic ventricles are presently available and we should see increasing use of them over the next couple of years. The convenience for a patient of electrical wires instead of pneumatic hoses coming out of the chest is obvious. However, the complexity and cost of the overall system is considerably greater, further testing and development is needed. Dr. William Pierce already has kept an animal alive for over 6 months with an electrically driven heart. Clearly, the electrically driven systems are the pumps for the next decade.

Effects of implantation on the mechanical properties of the polyurethane diaphragm of left ventricular assist devices

Tensile properties of blood pump diaphragms made from a segmented polyether polyurethane (Toyobo TM5) were studied after implanting in goats for variable periods of time up to 72 days. The implantation decreased the tensile strength and ultimate elongation at break, while the elastic modulus increased very slightly. These changes in the strength and ductility were primarily caused by the contact of material with blood rather than by the mechanical fatigue of material. Mechanical stability was greatly improved by removing residual oligomers from the material by a refining procedure. The refined polyurethane has characteristics favourable for blood pump applications.

Mechanical stability of elastomeric polymers for blood pump applications

As a series of studies on the mechanical properties of materials used in cardiac prostheses, static and dynamic characteristics and stability of five kinds of elastomeric polymers have been studied by uniaxial tensile and fatigue tests in air at room temperature and in saline solution at 37 degrees C. Of all materials tested in this study, Texin MD85A, a segmented polyether polyurethane, has the lowest flexibility under static and dynamic conditions, with relatively high strength. Hexsyn, a polyolefin rubber, is highly flexible with little stress relaxation. However, this material has very low tensile strength and short elongation, and shows unstable change in the elastic modulus during cyclic deformation. Avcothane 51, a copolymer of polyurethane and silicon, has unstable mechanical properties and gradually stiffens upon cyclic deformation. On the other hand, Biomer, a segmented polyether polyurethane, has high flexibility and shows the most stable behavior during cyclic deformation regardless of test environment. Toyobo TM5, a similar segmented polyurethane to Biomer, has higher strength and ductility than Biomer, although its static and dynamic flexibility are slightly worse and less stable than those of Biomer. These results indicate that Biomer and Toyobo TM5 are more suitable for flexible components of cardiac prostheses.

Effects of immersion in cholesterol-lipid solution on the tensile and fatigue properties of elastomeric polymers for blood pump applications

Tensile and fatigue properties were studied on three kinds of segmented polyether polyurethanes developed for blood pump applications. To study the effects of plasma constituents, specimens were immersed in a cholesterol-lipid solution whose composition is similar to that of plasma. The results obtained were compared with those observed in a saline solution which had been reported previously. Immersion in the cholesterol-lipid solution has influence on the mechanical properties of Toyobo TM5 polyurethane and Avcothane 51: Its effect is enhanced by cyclic deformation. Cholesterol-lipids change the mechanical characteristics of Avcothane 51 more remarkably than those of Toyobo TM5 polyurethane possibly because the former contains about 10% silicone. On the other hand, there is little effect of the constituents of the cholesterol-lipid solution on the static and dynamic mechanical properties of Biomer, although moisture and cyclic deformation have some influence on the mechanical characteristics.

Design of pusher-plate-type left ventricular assist device based on mechanical analyses

A permanently implantable left ventricular assist device (LVAD) pump of the pusher-plate type was designed based on mechanical analyses. A series of three different segmented polyether polyurethanes was utilized for the diaphragm, cannulae, and their blood-contacting surfaces, considering each material's characteristics. The span and thickness of the pump diaphragm were determined so as to minimize the stress developed by the bending and blood pressure forces. The inflow and outflow cannulae were designed using fundamental equations that describe the operation of a piston-type reciprocating pump. The pump diameter was determined considering the required flow for the average Japanese person. In vitro and in vivo experiments showed good pump performance, which satisfied the design specifications. No failure was observed in the designed diaphragm. The Hall effect sensor incorporated in the pump was very useful in monitoring the cardiac output of the pump.

Possible causes for the calcification of glutaraldehyde-treated tissue heart valves and blood contacting elastomers during prolonged use in medical devices: a physico-chemical view

Calcification of glutaraldehyde-treated porcine tissue heart valves (xenografts) is not a unique phenomenon but characteristic of a variety of synthetic elastomers and to a lesser extent of non-elastomeric polymers. The main commonality between them is their relative flexibility, permeability, and porosity, and differing capability to adsorb and to absorb various blood components. Although the possibility of biochemical factors involving calcium homeostasis and vitamin K-dependent protein carboxylation as recently proposed by others should not be ignored, it should be noted that calcification of synthetic elastomers has been reported with or without continuous anticoagulation with coumarin derivatives. This paper presents a physico-chemical view showing that despite the observed calcifications with a small number of xenograft valves, their otherwise impressive performance in the physiological environment is due to a significant extent to thermodynamic, molecular and supramolecular factors. The longevity of glutaraldehyde-treated tissue valves can be further improved by special methods. Calcification is especially characteristic for flexing and otherwise moving and pulsating surfaces, typical of many experimental circulatory assist devices and artificial hearts intended for long-term uses.