EUS-guided radiofrequency ablation in the pancreas: results in a porcine model.

BACKGROUND: Our aim in this study was to investigate the feasibility and safety of performing radiofrequency (RF) ablation in the pancreas with endoscopic ultrasound (EUS). METHODS: RF was applied to normal pancreatic tissue in 13 anesthetized Yorkshire pigs with specially modified 19-gauge needle electrodes (1.0 to 1.5 cm tip). The pancreas was localized with EUS and punctured through a transgastric approach. RF current (285 +/- 120 mA) was delivered for 6 minutes. Diagnostic imaging (EUS and CT) and serum amylase and lipase levels were obtained at baseline, immediately after ablation, and 1 to 14 days after the procedure. Pigs were killed immediately (n = 5), 1 to 2 days after ablation (n = 2), and 2 weeks after the procedure (n = 6). Pathologic examination was performed. RESULTS: Sixteen ablations were performed. During ablation, round hyperechoic foci (diameter to 1.0 cm) gradually surrounded the tip of the electrode. Immediately after the procedure CT demonstrated 1 cm hypodense foci that did not enhance with iodinated contrast. In pigs killed immediately and 1 to 2 days after ablation, pathologic examination showed discrete, well-demarcated spherical foci of coagulation necrosis measuring 8 to 12 mm in diameter surrounded by a 1 to 2 mm rim of hemorrhage. Radiologic-pathologic correlation was within 2 mm. In 4 of 6 (67%) pigs killed on day 14, retraction of the coagulated focus was observed. A 1 to 3 mm fibrotic capsule surrounded the coagulated tissue in the remaining 2 pigs. One pig had mild hyperlipasemia, a focal zone of pancreatitis (<1 cm), and later a pancreatic fluid collection. Biochemical parameters were normal in the remaining pigs. Other complications included three gastric and one intestinal burn caused by improper electrode placement. CONCLUSIONS: EUS-guided RF ablation can be used safely to produce discrete zones of coagulation necrosis in the porcine pancreas. Potential clinical uses of this technology include management of small neuroendocrine tumors and possibly palliation of unresectable pancreatic adenocarcinoma.     

Evaluation of liver parenchymal pressure and portal endothelium damage during radio frequency ablation in an in vivo porcine model.

BACKGROUND/AIMS: We previously developed a multi-step, incremental expansion method (multi-step method) for radio frequency ablation (RFA) in vitro, which prevented increases in pressure and reduced the ablation time as compared with other methods. In this study, we evaluated liver parenchymal pressure and portal endothelium damage during RFA with different devices and protocols in an in vivo porcine model. METHOD: Nine healthy female pigs were anaesthetized. RFA was performed with two different devices and protocols; one involved the use of a LeVeen needle with a single-step full expansion method or a multi-step method, and the other used a cool-tip needle with 40 or 60 W power. We measured the pressure in the liver parenchyma and the gallbladder during RFA. We also evaluated portal endothelium damage by NADH staining. RESULTS: The multi-step method with the LeVeen electrode resulted in the lowest parenchymal and intra-gallbladder pressures (multi-step method相似文献   

门静脉回流的胰肾联合移植大鼠模型制备

目的探索建立大鼠胰肾联合移植（SPK）模型的手术技巧。方法以雄性健康近交封闭群SD大鼠作为供体，Wistar大鼠作为受体，行整块胰肾十二指肠移植。采用供体腹主动脉和受体腹主动脉端侧吻合，供体门静脉和受体肠系膜上静脉端侧吻合，供体肾静脉和受体肾静脉袖套式吻合，供体输尿管膀胱瓣与受体膀胱吻合，最后将十二指肠近端结扎，远端腹壁造瘘。结果共正式实验40例，手术成功率为85％。供体肾、胰植入受体后立即恢复良好的血液循环，移植后24h血糖、肌酐降为正常，术后移植胰腺具有内分泌功能。结论此模型切实可行，手术成功率高，术后并发症少，可用于SPK基础方面的研究。     

门静脉回流的胰肾联合移植大鼠模型制备

目的 探索建立大鼠胰肾联合移植(SPK)模型的手术技巧.方法 以雄性健康近交封闭群SD大鼠作为供体,Wistar 大鼠作为受体,行整块胰肾十二指肠移植.采用供体腹主动脉和受体腹主动脉端侧吻合,供体门静脉和受体肠系膜上静脉端吻合,供体肾静脉和受体肾静脉袖套式吻合,供体输尿管膀胱瓣与受体膀胱吻合,最后将十二指肠近端结扎,远端腹壁造瘘.结果 共正式实验40例,手术成功率为85%.供体肾、胰体入受体后立即恢复良好的血液循环,移植后24h血糖、肌酐降为正常,术后移植胰腺具有内分泌功能.结论此模型切实可行,手术成功率高,术后并发症少,可用于SPK基础方面的研究.     

The effect of augmenting portal venous inflow on intrahepatic pressure and resistance in the isolated perfused porcine liver

BACKGROUND/AIMS: The literature regarding the relationship between portal venous flow and pressure is controversial. The aim of this study was to examine the effects of doubling portal venous inflow on hepatic hemodynamics. METHODOLOGY: Portal venous pressure, intrahepatic portal venous resistance, hepatic arterial pressure and intrahepatic arterial resistance were assessed during basal portal venous inflow (756 +/- 142 mL/min; mean +/- SD) and enhanced portal venous inflow (1512 +/- 284 mL/min) in an isolated perfused normal porcine liver model (n = 6). Hepatic arterial flow was maintained constant throughout the experiments. RESULTS: During the period of enhanced portal venous flow there was an increase in: portal venous pressure (from 9 +/- 2 to 22 +/- 7 mm Hg, P = 0.0076); the difference between portal venous and hepatic venous pressures (from 2 +/- 2 to 10 +/- 5 mm Hg; P = 0.0289); hepatic arterial pressure (from 84 +/- 9 to 151 +/- 33 mm Hg, P = 0.0019); and intrahepatic arterial resistance (from 0.3488 +/- 0.0637 to 0.6387 +/- 0.2020, P = 0.0046). CONCLUSIONS: The increases in hepatic artery pressure and intrahepatic arterial resistance are a result of the hepatic arterial 'buffer response', a phenomenon not previously demonstrated in vitro. The magnitude of the observed changes in portal venous and hepatic venous pressure leads to the conclusion that, in the porcine liver, the intrahepatic venous resistance sites react by constricting to increases in portal venous inflow.     

Cystic echinococcosis of the liver and lung treated by radiofrequency thermal ablation： An ex-vivo pilot experimental study in animal models

AIM： To evaluate radiofrequency thermal ablation （RTA） for treatment of cystic echinococcosis in animal models （explanted organs）.
METHODS： Infected livers and lungs from slaughtered animals, 10 bovine and two ovine, were collected. Cysts were photographed, and their volume, cyst content, germinal layer adhesion status, wall calcification and presence of daughter or adjacent cysts were evaluated by ultrasound. Some cysts were treated with RTA at 150 W, 80℃, 7 min. Temperature was monitored inside and outside the cyst. A second needle was placed inside the cyst for pressure stabilization. After treatment, all cysts were sectioned and examined by histology. Cysts were defined as alive if a preserved germinal layer at histology was evident, and as successfully treated if the germinal layer was necrotic.
RESULTS： The subjects of the study were 17 cysts （nine hepatic and eight pulmonary）, who were treated with RTA. Pathology showed 100% success rate in both hepatic （919） and lung cysts （8/8）; immediate volume reduction of at least 65%; layer of host tissue necrosis outside the cyst, with average extension of 0.64 cm for liver and 1.57 cm for lung; and endocyst attached to the pericystium both in hepatic and lung cysts with small and focal de novo endocyst detachment in just 3/9 hepatic cysts.
CONCLUSION： RTA appears to be very effective in killing hydatid cysts of explanted liver and lung. Bile duct and bronchial wall necrosis, persistence of endocyst attached to pericystium, should help avoid or greatly decrease in v/vo post-treatment fistula occurrence and consequent overlapping complications that are common after surgery or percutaneous aspiration, injection and reaspiration. In vivo studies are required to confirm and validate this new therapeutic approach.     

Endogenous hypercholecystokininemia model in the hamster: trophic effect on the exocrine pancreas.

Using Syrian golden hamsters, we studied the effect of pancreaticobiliary diversion (PBD) on plasma cholecystokinin (CCK) and exocrine pancreatic tissue over 5, 10, and 24 days. As compared with sham-operated controls, PBD-operated animals had increased plasma CCK concentrations by 228, 318, and 207% at 5, 10, and 24 days, respectively. Correspondingly, pancreatic wet weight increased by 24, 61, and 87%; total pancreatic protein by 6, 57, and 73%; and total pancreatic DNA by 35, 52, and 98%, respectively. At 5 days, but not at 10 and 24 days, there was a significant increase in the pancreatic tissue DNA concentration (p less than 0.01) and [3]H-thymidine incorporation into DNA (p less than 0.02). Autoradiography showed increased [3]H-thymidine labeling index in acinar cells at 5 and 10 days after PBD (p less than 0.01 and p less than 0.005). Although not significant, ductal cell labeling index was also increased at 5 and 10 days. These findings provide evidence that, as in the rat, PBD in the hamster induces hypercholecystokininemia with ensuing pancreatic hyperplasia and hypertrophy. The hamster model may be useful for studies on the effect of endogenous CCK on pancreatic ductal cell carcinogenesis and diseases of the gallbladder, neither of which can be studied in the rat.     

Radiofrequency ablation in a porcine liver model： Effects of transcatheter arterial embolization with iodized oil on ablation time, maximum output, and coagulation diameter as well as angiographic characteristics

AIM:To evaluate the effects of combined radiofrequen-cy ablation and transcatheter arterial embolization with iodized oil on ablation time,maximum output,coagula-tion diameter,and portal angiography in a porcine liver model. METHODS: Radiofrequency ablation (RFA) was applied to in vivo livers of 10 normal pigs using a 17-gauge 3.0 cm expandable LeVeen RF needle electrode with or with-out transcatheter arterial embolization (TAE) with iodized oil (n = 5). In each animal,2 areas in the liver were ab-lated. Direct portography was performed before and af-ter RFA. Ablation was initiated at an output of 30 W,and continued with an increase of 10 W per minute until roll-off occurred. Ablation time and maximum output until roll-off,and coagulated tissue diameter were compared between the 2 groups. Angiographic changes on portog-raphy before and after ablation were also reviewed. RESULTS: For groups with and without TAE with iodized oil,the ablation times until roll-off were 320.6 ± 30.9 seconds and 445.1 ± 35.9 seconds,respectively,maxi-mum outputs were 69.0 ± 7.38 W and 87.0 ± 4.83 W and maximal diameters of coagulation were 41.7 ± 3.85 mm and 33.2 ± 2.28 mm. Significant reductions of abla-tion time and maximum output,and significantly larger coagulation diameter were obtained with RFA following TAE with iodized oil compared to RFA alone. Portography after RFA following TAE with iodized oil revealed more occlusion of the larger portal branches than with RFA alone. CONCLUSION: RFA following TAE with iodized oil can increase the volume of coagulation necrosis with lower output and shorter ablation time than RFA alone in nor-mal pig liver tissue.     

Simultaneous use of endoscopic resection and radiofrequency ablation is not safe in an esophageal porcine model

Radiofrequency ablation (RFA) is safe and effective for eradication of Barrett's esophagus after endoscopic resection (ER) of neoplasia. Widespread ER, however, is likely to induce stenosis, hampering subsequent circumferential RFA. A ‘single step’ procedure with ER and circumferential RFA in the same session may avoid this problem. Two variants are possible: circumferential RFA of Barrett's esophagus including the lesion followed by ER of the ablated lesion (‘RFA→ER’), or ER of the lesion directly followed by circumferential RFA of remaining Barrett's esophagus including the resection wound (‘ER→RFA’). First aim was to evaluate perforation risk of ‘ER→RFA’ using increasing RFA energies. Second aim was to compare stenosis rate after ‘ER→RFA’ versus ‘RFA→ER’. In Experiment 1, 24 areas in six pigs underwent widespread ER directly followed by circumferential RFA with increasing energies (2 x 10, 2 x 12‐6 x 12 J/cm²) in the esophagus. In Experiment 2, eight pigs each had four treatment areas randomized: ‘ER→RFA’, RFA alone, ER alone, and ‘RFA→ER’. No acute perforations occurred when ablating ER wounds. Two delayed perforations occurred: one in experiment 1, another in experiment n2 at the ‘ER→RFA’ area. The remaining seven pigs in experiment 2 showed stenosis in all ‘ER→RFA’ and ‘RFA→ER’ areas versus 5/7 RFA alone areas, and 0/7 ER alone areas. In conclusion, the ‘single step’ variant ‘ER→RFA’ is not safe in this porcine model and seems therefore not ethical to evaluate in humans at this stage. Given the high rate of stenosis after ‘RFA→ER’ and RFA alone, one might question the validity of the porcine model for this type of experiments.     

Microwave ablation in a hepatic porcine model: correlation of CT and histopathologic findings

Background. Thermal ablative techniques have gained increasing popularity in recent years as safe and effective options for patients with unresectable solid malignancies. Microwave ablation has emerged as a relatively new technique with the promise of larger and faster burns without some of the limitations of radiofrequency ablation (RFA). Here we study a new microwave ablation device in a living porcine model using gross, histologic, and radiographic analysis. Materials and methods. The size and shape of ablated lesions were assessed using six pigs in a non-survival study. Liver tissue was ablated using 2, 4, and 8 min burns, in both peripheral and central locations, with and without vascular inflow occlusion. To characterize the post-ablation appearance, three additional pigs underwent several 4 min ablations each followed by serial computed tomography (CT) imaging at 7, 14, and 28 days postoperatively. Results. The 2 and 4 min ablations resulted in lesions that were similar in size, 33.5 cm³ and 37.5 cm³, respectively. Ablations lasting 8 min produced lesions that were significantly larger, 92.0 cm³ on average. Proximity to hepatic vasculature and inflow occlusion did not significantly change lesion size or shape. In follow-up studies, CT imaging showed a gradual reduction in lesion volume over 28 days to 25–50% of the original volume. Discussion. Microwave ablation with a novel device results in consistently sized and shaped lesions. Importantly, we did not observe any significant heat-sink effect using this device, a major difference from RFA techniques. This system offers a viable alternative for creating fast, large ablation volumes for treatment in liver cancer.     

Computer simulation of portal venous shunting and other isolated hepatobiliary defects of the enterohepatic circulation of bile acids using a physiological pharmacokinetic model

The effect of three isolated defects in the enterohepatic circulation of bile acids on the size and distribution of the bile acid pool, plasma bile acid levels and bile acid secretion into the intestine was simulated using a linear multicompartmental physiological pharmacokinetic model previously used to simulate these aspects of bile acid metabolism in healthy man. Stepwise increases in portal-systemic shunting (with a reciprocal decrease in hepatic blood flow) caused an exponential increase in systemic plasma concentrations of bile acids, but no other major changes in bile acid metabolism. When the effect of varying fractional hepatic extraction was simulated, it was found that the greater the fractional hepatic extraction, the greater the elevation observed for systemic plasma bile acid levels for a given degree of portal-systemic shunting. When total hepatic blood flow was restored to normal by simulating "arterialization," systemic plasma levels of bile acids decreased strikingly, yet remained elevated. For cholate with a fractional hepatic extraction of 0.9 and 100% portal-systemic shunting, arterialization caused a decrease from a 20-fold elevation to a 5-fold elevation. This simulation thus defined the effect of the presence of the portal venous system per se on plasma bile acid levels and also quantified the circulatory route by which substances reach the liver when portal-systemic shunting is present. An isolated defect in hepatic uptake of bile acids caused little change in overall bile acid metabolism other than modestly increased plasma levels. Loss of bile acid storage by the gallbladder caused the majority of the bile acid pool to move from the gallbladder compartments to the proximal small intestine during fasting but had little effect on the dynamics of the enterohepatic circulation during eating. The results of these novel simulations of isolated defects in bile acid transport should aid in the interpretation of the more complex changes in bile acid metabolism which are likely to occur in hepatic or biliary disease.     

Steady state of an ATP-driven calcium pump: limitations on kinetic and thermodynamic parameters.

A numerical analysis was carried out to explore limitations on kinetic and thermodynamic parameters for an ATP-driven Ca pump. A conventional pump reaction cycle was employed, with a transport stoichiometry of two Ca ions per cycle. Rigid requirements were imposed to represent the needs of physiological function, defined as the ability to maintain the cytoplasmic Ca concentration below 10(-7) M against a 3 mM concentration on the opposite side of the membrane. Realistic physical limits were placed on the magnitudes of rate constants for individual reaction steps. Reversibility under laboratory conditions was assumed. The results show that these requirements can be satisfied simultaneously only if the equilibrium constant for binding Ca from the cytoplasmic (uptake) side of the membrane is much larger than the binding constant on the discharge side. More generally, the results demonstrate that limitations on rate constants make it possible for the pump to maintain an adequate rate only if steady-state levels of kinetically important (slowly reacting) reaction intermediates do not become too disparate. Experimental data for the sarcoplasmic reticulum calcium pump support these theoretical conclusions.     

Immune function in patients with extrahepatic portal venous obstruction and the effect of splenectomy

Abnormalities of cell-mediated immunity-anergy to delayed hypersensitivity skin testing, diminished T-lymphocyte concentrations and mitogen responsiveness, and the presence of serum inhibitors--have been shown to be present in patients with portal venous obstruction and normal hepatic function. In contrast, tests of humoral immunity--antibody titiers to viral and bacterial antigens and immunoglobulin concentrations--were normal. These abnormalities in cell-mediated immunity are probably the result of the development of portal hypertension, portosystemic shunting, and congestive splenomegaly. These studies raise the possibility that qualitatively similar defects in patients with chronic liver disease and portal hypertension may, in part, be attributable to the same mechanisms.     

Radiofrequency ablation combined with reduction of hepatic blood flow: effect of Lipiodol on coagulation diameter and ablation time in normal pig liver

BACKGROUND/AIMS: We evaluated the effectiveness of radiofrequency (RF) ablation combined with transarterial embolization using Lipiodol and gelatin sponge. METHODOLOGY: A total of 18 normal pig liver lobes were randomly assigned to the following three different RF ablation groups, 1) combined with TAE using Lipiodol and gelatin sponge as "LpTAE group"; 2) combined with TAE using gelatin sponge only as "TAE group"; 3) ablation alone as "control group". Ablations were performed under open laparotomy using an RF generator and a 2-cm expandable needle. The diameter of coagulation and the ablation time were compared among the three groups. RESULTS: The characteristic shape of coagulated area differed among the three groups. The long-axis diameter showed no significant difference among the three groups (27.5mm, 27.5mm, 26.7mm; respectively), while the short-axis diameter was significantly larger in the LpTAE group compared with the control groups (25.2mm vs. 20.5mm; p < 0.05). The total ablation time was significantly shorter in the LpTAE and TAE groups compared with the control group (166, 204 seconds vs. 309 seconds; p = 0.001, p = 0.01). CONCLUSIONS: RF ablation combined with LpTAE produced larger and more spherical areas of coagulation in a shorter ablation time. Such an advantage could potentially enhance the clinical effectiveness of RF ablation.