Pulsatile flow tests

The functionality of the valve has been tested with equipment which has been made in our laboratory. Pulsatile flow tests on a mock circulatory system, flow patterns, measurements of steady retrograde flow and pressure drop across the valve, in vivo tests have been carried out. By the pulsatile flow tests, the shapes of curves referring to ventricular and aortic pressure and to flow rate, similar to that shown by other kinds of valves, have been observed. 

Rote et al. (1993, 1994) used a carotid thrombosis model in dogs. A calibrated electromagnetic flow meter was placed on each common carotid artery proximal to both the point of insertion of an intravascular electrode and a mechanical constrictor. The external constrictor was adjusted with a screw until the pulsatile flow pattern decreased by 25 % without altering the mean blood flow. Electrolytic injury to the intimal surface was accomplished with the use of an intravascular electrode composed of a Teflon-insulated silver-coated copper wire connected to the positive pole of a 9-V nickel-cadmium battery in series with a 250000 ohm variable resistor. The cathode was connected to a subcutaneous site. Injury was initiated in the right carotid artery by application of a 150 xA continuous pulse anodal direct current to the intimal surface of the vessel for a maximum duration of 3 h or for 30 min beyond the time of complete vessel occlusion as determined by the blood flow recording. Upon completion of the study on the right carotid, the procedure for induction of vessel wall injury was repeated on the left carotid artery after administration of the test drug. 

The tigue tester used in this study was specially designed and built by our team for this research project. The test system consists of a peristaltic pump, which generates the pulsatile flow (Figure 3). 

A number of studies based on PGA/P4HB have confirmed the importance of dynamic cell culture conditions that reproduce physiological mechanical stress and of pulsatile flow to achieve optimally functional scaffolds [43,45, 46,255,259]. A bioreactor that includes dynamic flexure as a major mode of deformation in the native heart valve cusp has been tested on PGA/P4HB and PLLA/P4HB composite scaffolds [270]. 

Heart valve scaffolds with conduit and leaflets made entirely from P3HO-3HH porous films [287] were tested in vitro imder static and pulsatile flow cell culture conditions [44,281]. A larger number of vascular cells, together with the formation of an oriented and confluent cell layer, was found on scaffolds exposed to pulsatile flow [281]. The P3HO-3HH heart valves, preseeded with vascular cells under static conditions, were tested for up to 17 weeks in the pulmonary position in a lamb model. The valves showed good functionality... 

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