Neo-arterial walls of Dacron vascular prostheses were examined under both optical and electron microscopes from 1 to 1184 days after implantation in the thracic aorta of 146 dogs. Complete endothelialization of the grafts was observed in all specimens of more than 20 weeks after implantation and no fibrin layer nor thrombus was deposited on them. The essential structure of the neo-arterial wall could be divided into four laminae: (1) the most inner coat, the tunica intima, whose structural elements resembled the endothelium of an aorta, serving to inhibit the formation of thrombi; (2) the next coat, a smooth muscle cells layer; (3) the third coat, the tunica media, which consisted of a foreign body (Dacron fibers) granuloma at an end stage, served for forming the conduit framework of neoarterial walls; (4) the outer coat, a loose connective tissue layer, which was the medium surrounding the neo-arterial walls and neighbouring organs. It resisted the local mechanical stress. These observations revealed the fundamental structure of neo-arterial walls at stable stage, which was one of cellulofibrous tissues, quite similar to the cellulofibrous thickening of intima at arteriosclerosis.
Evaluation was made of 18 mongrel dogs who underwent conduit reconstruction of the right ventricular outflow tract with woven Dacron prosthesis containing a Tilting SAM valve. This conduit was implanted as a bypass between right ventricular outflow and distal pulmonary artery by the partial clamp method. Antibiotics were given for one week after operation, but anticoagulats were not used. Eight of these animals died on the operating table, 5 as aresult of hemorrhage and 3 from sever clotting on the prosthesis. Among the 10 survivors, 9 were sacrificed after follow-up periods of one to 24 monhts for evaluation of prosthesis. In 2 dogs of them, Tilting SAM valves were found to be fixed at open position by excessive tissue growing. But in another 7 dogs, valve function was kept perfectly without over-growing tissue. Remaining one dog is living well now for 34 months after operation without identifiable evidence of valve dysfunction. These satisfactory experimental results have encouraged us to use this easily obtainable and versatile form of valved conduit in clinic.
In the course of the studies in total heart replacement systems the authors took up the problem of output flow control of artificial hearts from the angle of control engineering and systems engineering. Here, they tentatively regarded the cardiovascular system, which was assumed to be the control object, as a closed multiport system. Then they analyzed the characteristics of the cardiovascular system as a circulatory system with bond graph designation method. On the basis of bond graph designation, mathematical and mechanical models similar to the cardiovascular system were developed. To test whether dynamic behaviors of the mechanical model were similar to those of living dog or not, the data on the model were compared with the hemodynamics of the experimental dog, whose heart was totally replaced by the authors' blood pumps. Under the same output flow condition, the hemodynamics data from the simulator and experimental dog showed high resemblance to each another. Though there remain several issues in their present models, theirs would as such be available to fundamental researches on the cardiovascular system, especially on artificial heart control systems.
Based upon an experimental hypothesis that an ideal biomedical material should meet the following conditions: 1) proper tissue regeneration in a proper period, 2) complete replacement by reciepients tissue, 3) no cartinogenicity and 4) sufficient functions of the regenerated organs, we have performed several experimental studies before. Our standpoints are that a well controlled dissolvable synthetic or modified natural material might meet these conditions and we expect to be able to selectively tailor materials and introduce new properties by chemical or enzymatic treatments. We choosed the bovine pericardium as original material and performed several kinds of chemical treatments on it. Reconstractions of rabbit bladders were performed with these chemically treated bovine pericardiums after 70% resection of natural urinary bladder. Aceton pretreated 70% acetic anhydride and 30% acecti acid treated bovine pricardium showed acceptable resulst in substitution of the bladder tissue. Methylated and methyl-acetylated bovine pericardiums were also expected good biomedical materials in this study.