The dura mater valve: in vitro characteristics and pathological changes after implantation in calves.

Human dura mater valves of various sizes with rigid and flexible stents were tested in an in vitro pulsatile mock circulatory system. A 22-mm flexible stent valve incorporating a new fabrication technique showed almost the same pressure gradient as a 28-mm rigid stent valve. The backflow/stroke volume ratio was about 4% at a net flow of 10 L/min. One hundred and five rigid stent-mounted dura mater valves were used in 51 pump implantations for up to 316 days. Collagen fiber degeneration began three months after implantation. Microscopic and macroscopic calcification of the valve tissue was seen in eight out of 105 valves, giving an overall incidence of 7.6%. The calcified degeneration was dystrophic in nature, not accompanied by cellular reactions, and was seen in the areas of the valve under stress. The degenerative changes were more severe in the left side than in the right side of the total artificial heart. These findings suggest that mechanical damage to the tissue plays an important role in the pathogenesis of calcification.