No abstract

Continuing investigations of vascular graft materials suggest that unacceptable graft complications continue and that the ideal graft material has not yet been found. We have developed and tested a biologic vascular graft material, small intestine submucosa (SIS), in normal dogs. This material, when used as an autograft, allograft, or xenograft has demonstrated biocompatibility and high patency rates in aorta, carotid and femoral arteries, and superior vena cava locations. The grafts are completely endothelialized at 28 days post-implantation. At 90 days, the grafts are histologically similar to normal arteries and veins and contain a smooth muscle media and a dense fibrous connective tissue adventitia. Follow-up periods of up to 5 years found no evidence of infection, intimal hyperplasia, or aneurysmal dilation. One infection-challenge study suggested that SIS may be infection resistant, possibly because of early capillary penetration of the SIS (2 to 4 days after implantation) and delivery of body defenses to the local site. We conclude that SIS is a suitable blood interface material and is worthy of continued investigation. It may serve as a structural framework for the application of tissue engineering technologies in the development of the elusive ideal vascular graft material.

Small-intestinal submucosa (SIS) has been shown to induce tissue remodelling in vivo when used as a vascular graft. The present study investigated in physical and mechanical properties of remodeled aortic grafts derived from xenogeneic SIS material. Eight infrarenal aortic grafts were implanted in mongrel dogs. The grafts were explanted at 1 or 2 months and tested for compliance and hoop mechanical properties. The morphologic changes within the grafts were also characterized. The remodeling process produced graft structures which were significantly stronger than both the normal artery (P = .012) and the original SIS graft (P = .0001), and the compliance of these structures was one third that of normal artery and similar to the original SIS grafts. The remodeled grafts were > 10 times the thickness of the implanted SIS. Immunohistochemical analysis of remodeled tissues suggest that the SIS material was degraded and resorbed over time. The remodeling process transformed a material which was physically and mechanically quite different from normal aorta into a blood conduit which had the physical and mechanical properties needed to function in this mammalian arterial system.

No abstract

Autoregulatory responses to alterations in arterial or venous perfusion pressure were determined for individual arterioles within the rat cremaster muscle. The cremaster muscle of pentobarbital anesthetized rats (50 mg/kg, ip) was surgically exposed and maintained in a controlled tissue bath for visualization by in vitro television microscopy. Cremaster bath PO2 was controlled at either a high (approximately 70 mm Hg) or low (approximately 19 mm Hg) level. Inside diameter and red blood cell velocity were measured for individual first (1A), second (2A), or third (3A) branching order arterioles, and instantaneous blood flows within each arteriole were calculated. To measure the autoregulatory responses, we decreased arterial perfusion pressure to the microvascular bed by gradually occluding the sacral aorta. Significant autoregulation was observed in all orders of vessels, but, in general, autoregulation was more pronounced at all vessel levels when bath PO2 was low, and the autoregulatory gain was greater for the smaller vessels compared to the larger vessels. Elevation of venous pressure within the vascular bed by gradual occlusion of the inferior vena cava led to a significant vasoconstriction of the smaller vessels, suggesting that a significant myogenic component was present. The vasoconstriction response to elevated venous pressure was more pronounced when bath PO2 was high. Our data are not consistent with a purely myogenic or purely metabolic mechanism, but suggest that both mechanisms are simultaneously contributing to the local vascular regulation.