Mesenteric VeinsPortal VeinMesenteric Vascular OcclusionVeinsPortal SystemSplenic VeinRenal VeinsFemoral VeinSaphenous VeinIliac VeinHepatic VeinsSplanchnic CirculationVaricose VeinsVenous ThrombosisVena Cava, InferiorPulmonary VeinsJugular VeinsVisceraPancreaticoduodenectomyIofetamineHypertension, PortalNorepinephrineMesenteric ArteriesLiver CirculationPortasystemic Shunt, SurgicalMesenteric Artery, SuperiorAdrenergic alpha-2 Receptor AntagonistsUmbilical VeinsEsophageal and Gastric VaricesAmphetaminesMuscle, Smooth, VascularThrombosisTomography, X-Ray ComputedDogsAnastomosis, SurgicalBudd-Chiari Syndrome