A-V shunt

In the previous papers(12,13), we reported on the vessel access type, i.e. tubular type, glucose sensor. It consisted of a glucose electrode system with a GOX enzyme immobilized Nylon membrane and a glucose semipermeable membrane, and a reference oxygen electrode system. The sensor could directly measure up to 700 mg/dl of BGL in an arterial blood stream when it was placed into an external A-V shunt. This sensor, however, has some problems such as thrombus during in vivo testing without heparin and clinical complexity associated with implanting the sensor in a blood stream. 

Be Scheerder (58) 1997 Self-designed Duraflo 11 Rat A-V shunt pig coronary art Bare stent Yes No... 

Chronos N, Robinson K, White D, et al. Heparin coating dramatically reduces platelet deposition on incompletely deployed Plamaz-Schatz in the baboon A-V shunt [abstr]. J Am Coll Cardiol 1996 27 84A. 

A method for the direct observation of extracorporal thrombus formation has been introduced by Rowntree and Shionoya (1927). These first studies could provide evidence that anticoagulants like heparin and hirudin do inhibit thrombus development in arteriovenous shunts. Since today, the A-V-shunt thrombosis models have been often used to evaluate the antithrombotic potential of new compounds in different species including rabbits (Knabb et al. 1992), rats (Hara et al. 1995), pigs (Scott et al. 1994), dogs and cats (Best et al. 1938), and non-human primates (Yokoyama et al. 1995). 

In 80-90% of cases, focal nodular hyperplasia shows a typical, radial (spoke-like) arrangement of coiled vessels in the area of the tumour, which originate from a circular artery. Occasionally, fine a.v. shunts are present. The smooth-edged lesion is hypervascular. The parenchymal phase, with its homogeneous concentration of contrast medium, allows the lesion to be clearly demarcated from healthy liver tissue. (156) Hepatic adenoma is generally hypervascular. Displaced vessels are frequently visible. 

Percutaneous splenoportography has lost its importance. Should a direct procedure be indicated, laparoscopic splenoportography is a possible alternative. Recently, a new technique has been described. (134) The percutaneous splenic puncture is performed using a thin needle under screen control, with the needle directed at the splenic hilus. The pressure of the splenic pulp can be measured directly in order to estimate the portal vein pressure. Contrast medium is injected manually or by a special device. From this depot in the red pulp, the splenic vein, the portal vein and the intrahepatic branches of the portal vein are contrasted within a few seconds, (s. fig. 8.12) Complications resulting from percutaneous splenoportography include afterbleeding from the spleen, bilateral rupture of the spleen, arterial aneurysms and a.v. shunts — these complications are serious in nature, but rare. Contraindications for the procedure should be carefully observed, (s. tab. 8.6)... 

Plasma polymers of hydrocarbon (CHJ and perfluorocarbons were insaled into an A-V shunt in a baboon. Clot formation was examined by a r-camera, and the platelet half-life was compared against that of a control experiment according to a previously established standard procedure. Some glow disdiarge polymers of perfluorocarbons showed excellent athrombogenic characteristics, i.e., no clot forntation was observed and platelet half-life was identical to the control value. 

Fig. 11 SEM photographs of PVA hydrogels and PVC surfaces after exposure to blood at an A-V shunt system for different times.

In other advances, we see polymers and natural tissue in competition. For example, in small diameter blood vessel repair, the saphenous vein is still the best. However, we are now approaching the first human implantation of small diameter synthetic polymer vascular prostheses to help those patients who have no useable saphenous vein. The ball and disc type of heart valve prostheses are still not as good as the processed natural tissue porcine valve. Yet even here we use a polymeric or metal stint to support the porcine tissue. The artificial kidney has been miniaturized, but in terms of patient well-being it has improved very little since the 1940 s. Also, the A/V shunts have given way to A/V fistulas since we do not have good polymers for long-term access. Peritoneal dialysis is becoming a better dialysis procedure for the patient, primarily because of the improvement of a polymeric access to the peritoneal cavity. 

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