Strength and fatigue tests were extracorporeally performed on silicone rubber, one of the materials of the artificial heart device pump, and the following results were obtained. 1) It is necessary to sandwich two mesh sheets between the silicone rubber membranes and to limit the directional expansion and contraction to a minimum level. 2) The connection between the housing and chamber was found to have sufficient strength through motion model tests performed 10 million times. In the fatigue test, fatigue associated with frequency of motion could not be demonstrated.
Experimental and clinical studies have been made on various types of mechanical cardiac massage as a method to assist circulation, but in this study the authors made a number of improvements on the heretofore employed assister cup and using this improved assister cup conducted basic experiments with the purpose of resuscitation from cardiac insufficiency, preparatory and assisted circulation prior to artificial heart transplant and organ preservation on the premise of transplantation. A review was made on its effectiveness and on the method of producing this improved cup.
The causes distrurbing the circulatory autoregulation during artificial heart pumping were studied. Employing two mathematical models of the prosthetic hearts, i.e., the sac and diaphragm type models, the stroke volume sensitivity to the venous pressure were analyzed by numerical computations. The depressive effects of increased inflow valve resistance, increased pump vacuum pressure, decreased elasticity of the ventricular sac or diaphragm and decreased sizes of the ventricle were demonstrated. In the experiments of the total prosthetic heart replacement in calves, the resistances at the connecting part of the right heart to the natural atrium were measured varying the pump vacuum pressure. When the vacuum pressure exceeded —20mmHg, these resistances became about 4 times of the inflow valve used. It was concluded that thep rosthetic heart shculd be designed to provide sufficient flow with pump vacuum pressure at least not exceeding —20mmHg.
Resistance of silicone rubber membranes to oxygen transfer was measured by use of a specially designed apparatus. In membrane oxygenators the membrane resistance is generally much smaller than the blood phase resistance. Thus, any design which minimizes the blood phase resistance would enhance the gas exchange rate significantly. Rates of oxygen absorption into saline solutions and blood were measured in a membrane oxygenator in which screens were placed in the blood channels between the membranes for the purpose of reducing the blood phase resistance. The oxygen absorption rate in the new oxygenator is substantially higher than those in the conventional membrane oxygenators. Increases in the rate of hemolysis and formation of emboli in the oxygenator due to the presence of the screens are slight.
For a purpose of nonthrombogenic artificial heart, antithrombogenicity of Tetoron velour covered with fibroblasts of human embryo was studied. As the fibroblasts did not grow well and their viability tend to decrease after 48 hours incubation on the Tetoron velour, seeding of the fibroblasts (5×105/cm2) was added after 24 hours. After 48 hours incubation, Tetoron velour was inserted into the SVC of the mongrel dogs. After 2 hours exposure to blood stream, surface of neointima formed on the cell cultured Tetoron velour was thinner and smoother than that of the controls. Utilizing Helmholtz-Smoluchowski's formula, zeta potential of cell covered Tetoron velour was calculated, which revealed slightly positive. Adsorption of ion to cell membrane or bovine serum of culture medium were thought to be the cause of positive zeta potential. It is concluded that fibroblasts cultured on the Tetoron velour inhibits thrombus formation in early phase, though positively charged bioelectrically.
Our comparative studies of fluorinated materials which was used as the vascular prostheses for large caliber veins disclosed that surface properties and porosity highly corresponded with the thickness of the layer of thrombus in the inner surface. In the nonoporous prostheses (polytetrafluoroethylene-hexafluoropropylene, polytetrafluoroethylene-hexafluoropropylene-methylmetacryate.) initial platelet adhesion was seen from 24 hours to 120 hours after insertion into superior vena cava and inferior vena cava, and thrombus formation was seen in only one case during this period. In expanded poly-tetrafluoroethylene prostheses of 2-4 microns pore size, thin layer of thrombus which might be changed into the neointima was seen. On the other hand in ex-panded polytetrafluoroethylene prostheses of 7-10 microns pore size, thick layer of thrombus which could be enough to occlude the lumen was seen.
Complications and follow-up study of 75 pacemaker implants in 54 patients done since 1966 were reported. The series included 24 males and 30 females. The age ranged from 11 months to 79 years with an average of 50 years. High grade A-V block was present in 48 patients, S-A block in 4 and tachycardia-bradycardia syndrome in 2. Stokes-Adams seizures were noted in 46 patients, heart failure in 6 and chest pain in 2. Endocardial leads were used in 45 patients and epicardial leads in 10. Fixed rate pacemaker were used in 14 patients, demand pacemaker in 51 and P wave synchronous pacemaker in 1. Endocardial leads and demand pacemarkers were used as a rule since 1971. Complications were noted 27 times in 19 patients, which consisted of 4 generator failure, 4 electrode trouble and miscellaneous complications related to patient's condition. Generator failure consisted of 3 early exhaustion of mercury cells and one runaway pacemaker. These were all relieved with emergency replacement of generators. Electrode trouble consisted of 3 displacement of endocardial electrode and one fracture of epicardial electrade. Complications related to patient's condition, such as twitching of diaphragm, wound infection, ventricular fibrillation, pulmonary emboli were seen 19 times in 15 patients. Death occured in 9 partients and 5 of them were unrelated to pacemaker implantation. Follow up of surviving patients comprises 93 years. Rehabilitation of survivors was excellent except 3 patients who were still in NYHA 2 because of other reasons.
The membrane oxygenator has been recognized as the ideal artificial lung. It must be uniform in capacities, and easy to be handled and industrialized. In these points of view, we compare the three types of the oxygenators, i. e. multi-tube-type, pack-type and coil-type. 1) multi-tube-type: Because of the limitation of the size of a silicon tube itself, the oxygen mustt be sent in the tube and intermittent compression system is neccessory to get a thin blood film and better oxygenation. 2) pack-type: An artificial kidney (Kiil type) is modified and used as an artificial lung. In this type, as the blood flow increases, the blood film becomes thicker, resulting in poorer oxygenation. 3) coil-type: Another artificial kidney (Kolff type) is also utilized as above. This type is the best among the three in oxygenation; and the size is the smallest and the easiest to be handled. Unfortunately, however, it is very difficult to provide the uniform lungs in present state. Nevertheless, this type will be the most hopefull in many points of view.