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   Dr. Pavcnik
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   Dr. Barnwell
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Dotter Interventional Institute

IR Laboratory Research - Second Decade

Experimental model for traumatic thoracic aorta dissection

Laboratory research in the Institute from 2000 to 2010 expanded into new areas. These included exploration of a new biomaterial – small intestinal submucosa (SIS), development of venous and aortic valves, devices for closure of heart defects, new techniques for peripheral embolism protection and arterial closure devices. To explore these areas, we first developed experimental models for venous insufficiency, percutaneous creation of atrial septal defect, tricuspid valve regurgitation, traumatic thoracic aortic dissection and endoleaks after abdominal aorta stentgrafting. Presently a model for percutaneous creation of patent ductus arteriosus is being developed.

SIS was found to be useful for both construction of a venous valve, and for covering bare stents used in aortic endografting and treatment of injured iliac arteries and tracheas. It also proved useful for percutaneous venous ablation, aneurysm sac embolization, closure of fallopian tubes and as a plug for nephrostomy tracts. SIS was not satisfactory in carotid artery grafting, in the biliary system and as a cover for TIPS stentgrafts.

Good function of SIS valve in the jugular vein at 5 weeks on venograms (A,B) and in vitro venoscopy (C,D)

Significant effort was placed into developing a bioprosthetic venous valve that consisted of SIS attached to different types of square stent frames. The third generation valve showed excellent short-term experimental and promising early clinical results. But, SIS fibrous remodeling and neointimal hyperplasia leading to thickening of the SIS leaflets compromised long-term valve function. Presently, research efforts are directed to modifying the SIS leaflet surface with the goal of preventing neointimal hyperplasia and enhancing long-term valve function. Bioengineering methods are now used to capture endothelial progenitor cells on the valve leaflets intended to prevent neointimal hyperplasia. This research is being performed under an NIH grant. Promising results with long-term valve function were also obtained with another technique - experimental percutaneous autogenous venous valve transplantation.

An exciting new device, the Biodisk, was developed to close patent foramen ovales (PFO). It consists of a metal frame covered with an SIS membrane. The Biodisk is easy to deliver percutaneously. Long-term PFO occlusion has been achieved experimentally. Modifications of the Biodisk for occlusion of atrial septal defects is presently undergoing detailed experimental studies to lead to its clinical approval.

Experimental research in endovascular treatment of abdominal aortic aneurysms and prevention of endoleaks yielded useful information for clinical practice. SIS sandwiched stentgrafts resulted in efficient treatment of ruptured abdominal aorta aneurysms. Pressure measurements in the aneurysm sac following endografting were useful in detecting the presence of an endoleak. Aneurysm sac embolization with SIS foam was found to be very effective for endoleak prevention at the time of endograft placements and also to treat endoleaks post endografting.

Pathologic and histologic study of the femoral artery after double wall puncture and manual compression hemostasis

We also tested arterial closure devices, mainly bandages based on the procoagulant chitosan. Used with manual compression, the hemostatic bandages resulted in rapid hemostasis with fewer complications than conventional manual compression. We documented that closure of the arterial access site occurs by formation of a platelet rich fibrin thrombus. This thrombus is often large. The thrombus also can extend significantly into the arterial lumen and has a tendency to embolize peripherally.

Additional research projects in the second decade included: Evaluation of optional IVC filters and their retrievability; comparison of endothelization of various stent cover materials in the venous and arterial systems; evaluation of lipiodol distribution during liver embolization; and effects of blood flow and ventilation restriction during radiofrequency lung ablation.

Laboratory work with visiting researchers also increased during the second decade. Dr. Stan Cope developed a technique to create a gastrointestinal anastomosis percutaneously. Dr. Michael Conlin, an OHSU urologist, introduced an SIS plug for closure of large tracts after endoscopic stone retrieval. Dr. Kent Hermsmeyer, an OHSU research cardiologist, worked on prevention and treatment of coronary artery spasm. Drs. Peregrin and Sochman from the Clinical Research Institute in Prague, Czech Republic, developed a pericardiotom for facilitating pericardial punctures; a cone valve for percutaneous replacement of dysfunctional aortic valves; and a twin valve caval stent for palliation of tricuspid insufficiency.

Fifteen United States patents were issued to Institute researchers documenting their inventiveness and creativity in developing new devices and techniques. Four other patents are presently being processed. Dr. Pavcnik is the lead researcher for most of these patents.