Twenty-four-hour heparin-free veno-right ventricular ECMO: an experimental study.

Platelets and coagulation factors were studied during 24-hour heparin-free veno-right ventricular extracorporeal membrane oxygenation (ECMO) in 6 healthy pigs. An endpoint attached and covalently bonded heparin-coated ECMO system was used in these experiments. The veno-right ventricular ECMO supplied the total lung function of the animals, and after 24 hours, all the animals were successfully weaned from ECMO. Lung function and central hemodynamics were not affected by the procedure. Because all the animals showed a significant reduction in plasma volume, the concentration of measured coagulation variables was corrected both for plasma volume changes and for hemodilution. The platelet count and the plasma-free hemoglobin level were not significantly altered by ECMO. Similarly, the prothrombin complex, antithrombin, thrombin-antithrombin complex, factor XII, and the urinary excretion of 2,3-dinor-thromboxane B2 were not significantly altered. Fibrinogen and fibrin monomer increased significantly, whereas von Willebrand factor was significantly decreased after ECMO. In summary, 24-hour heparin-free veno-right ventricular total extracorporeal lung assistance does not affect the platelets and the coagulation system significantly in healthy juvenile pigs.     

Low power CO2 laser-assisted microvascular anastomosis: an experimental study

Low power CO2 laser-assisted microvascular anastomosis (LAMA) was used for saphenous artery autotransplantation in 40 rabbits. Eighty end-to-end anastomoses were performed by three methods (conventional interrupted suture, stay suture + laser, laser without stay suture). The long term patency rate in the three types of anastomosis is 93%, 93%, and 100%, respectively. The time needed for the laser procedure is half to one-third of that required for the interrupted suture method. The tensile strength of the bonding site can withstand up to 250 mm Hg of arterial pressure. We have demonstrated that the CO2 laser can be used in microvascular anastomosis with or without stay sutures. Aneurysm formation is a potential risk of LAMA. Accurate coaptation of the transected vessel, precise control of laser energy, and minimal area exposed to the laser beam are the key points for further improving anastomotic quality.     

Fundus microvascular flow monitoring during retrograde cerebral perfusion: an experimental study

BACKGROUND: Retrograde cerebral perfusion (RCP) through the superior vena cava was clinically introduced as a supportive technique to protect the brain during deep hypothermic circulatory arrest. This study searched for a direct monitor of cerebral blood flow to evaluate the effect of cerebral perfusion. METHODS: Retinal microvascular perfusions were studied in six piglets using fundus fluorescein angiography (FFA) and color Doppler sonography before cardiopulmonary bypass and retrograde cerebral perfusion during deep hypothermic circulatory arrest. RESULTS: FFA showed initial filling of the fundus venae in 2.5 minutes, and complete filling in 4.5 minutes with partial filling of the arteriae. Arteriae completely filled in 8 minutes, and all of the arteriae and venae filled from 15 to 17 minutes. Color Doppler sonography showed that flow signals were detected in all of the fundus vessels during RCP. CONCLUSIONS: FFA and color Doppler sonography are direct and sensitive methods for observing cerebral blood flow and assessing the effect of cerebral perfusion.     

Chemoreflexes: an experimental study

HYPOTHESIS: Transmyocardial laser revascularization (TMLR) will not denervate the heart, because it does not destroy all of the afferents. This study was designed to determine if stimulation of cardiac sympathetic and vagal afferents from an area of the left ventricle treated with TMLR could evoke reflex effects, and thus whether TMLR would denervate the heart. METHODS: The effect of TMLR on reflexes evoked by chemically stimulating cardiac afferents was examined in 9 dogs. Bradykinin and capsaicin were applied topically or injected into the left anterior descending coronary artery before and after TMLR and after bilateral vagotomy and sympathectomy. Aortic (AoP) and left ventricular pressures (LVP) and electrocardiography were monitored. The first derivatives of LVP (dP/dt) were calculated. RESULTS: Topical bradykinin elicited variable hemodynamic responses. Topical capsaicin evoked pressor responses, increasing mean (+/- SEM) AoP (105+/-9 to 115+/-9 mm Hg; P<.001) and positive dP/dt (+dP/dt) (1032+/-81 to 1159+/-10 mm Hg/s; P<.01) before TMLR. Intracoronary capsaicin evoked a depressor response before TMLR. Pressor responses remained intact after TMLR with increases in mean AoP and +dP/dt (115+/-6 to 128+/-5 mm Hg and 1039+/-98 to 1136+/-100 mm Hg/s, respectively; P<.01). Depressor responses also remained intact after TMLR (91+/-10 vs 101+/-11 mm Hg [P<.02], and 865+/-104 vs 931+/-104 mm Hg/s [P<.05], respectively). Hemodynamic responses were diminished after bilateral vagotomy and abolished after bilateral sympathectomy. CONCLUSION: Since activation of cardiac afferent nerves and reflex responses remained intact after TMLR, but changed after vagotomy or sympathectomy, TMLR does not denervate the heart sufficiently to be the cause of improved angina after TMLR.     

Influence of flow disturbance on an anastomotic intimal hyperplasia: experimental and clinical study

Experimental and clinical studies were made of the localization and morphology of anastomotic intimal hyperplasia (AIH) at the end-to-side anastomosis in relation to flow disturbances. In vitro experimental findings showed that boundary layer separation (BLS) became prominent as proximal outflow segment (POS) flow increased. An aorto-right iliac bypass was performed on 30 dogs using 22 Biografts, 3 EPTFES and 5 Dacron grafts. Distal end-to-side anastomoses were made at 3 different angles, i.e., 30 degrees (Group I), 90 degrees (Group II) and 150 degrees (Group III). BLS was likely to occur at the toe in Group I because POS flow exceeded 50%, while not in Group III. Up to 35 months observation, AIH was noted to develop at the toe 36% in Group I, 25% in Group II but in none in Group III. Thirty five reconstructions using Biograft in which angiography was performed later than 6 months postoperatively were chosen for clinical study. Invariably in all cases of AIH occurring following a femoropopliteal bypass, severe stenosis was noted to occur at the toe and heel of the distal end-to-side anastomosis. In conclusion, a disproportionate increase in POS flow was considered a likely cause of marked BLS and, consequently, an important precipitating cause of AIH. When POS flow exceeds 50%, a distal anastomosis dividing flow distribution should be considered as a salvage operation of potential usefulness.     

Blood substitution: an experimental study

Priming fluids for cardiopulmonary bypass have been extremely varied, with resultant hemodilution. Furthermore, major surgeries utilizing cardiopulmonary bypass require multiple postoperative transfusions of blood and blood products. The appeal of having a readily available blood substitute for major cardiovascular and neurosurgical operations could prove to be a life saver, while also eliminating the risk of diseases transmitted by transfusion. Blood substitutes could also lessen the reported complications resulting from blood damage due to prolonged circulation of the blood by the extracorporeal pump. A technique was examined in 15 dogs using hypothermia for maximum metabolic suppression, incorporating an aqueous blood substitute (Cryomedical Sciences, Inc., Rockville, MD). The anesthetized animals were cannulated for extracorporeal pump oxygenation. As temperature was lowered the dogs were exsanguinated and volume replaced with blood substitute to lower the hematocrit to less than 1%. After 3 hours of cardiac arrest and continuous perfusion at a core temperature less than 10 degrees C, rewarming began. When temperature reached greater than or equal to 10 degrees C, the blood substitute was drained and the animals were autotransfused. The heart was started at 15 degrees C and spontaneous respiration resumed at 29 degrees C. Using the first generation blood substitute the survival rate was maximal (100%) at 2.5 hrs under 10 degrees C and 3 hours of cardiac arrest. Research is underway on a new blood substitute, which is to serve as a universal hypothermic preservation solution (in situ organ preservation).(ABSTRACT TRUNCATED AT 250 WORDS)     

髋臼发育不良动物模型的建立及其临床意义

目的探讨髋臼发育不良在先天性髋关节脱位发病过程中的意义。方法将１２只幼犬通过外科手术造成单侧髋关节脱位,术后３、４周通过大体标本、组织学及Ｘ线摄片,观察髋臼变化。结果术后３周幼犬实验性髋关节脱位侧即出现髋臼发育不良,髋臼上部呈斜坡状,髋臼浅,Ｘ线片上可见髋臼指数增大,由实验前平均１３２±１３度增大为平均２７８±１５度,组织学观察见髋臼软骨退行变化。结论髋臼发育不良为髋关节脱位的继发病变,不是髋关节脱位的原因;如果髋关节脱位或髋关节松驰得到及时治疗,髋臼发育不良可以恢复正常     

Effects of xenon on cerebral blood flow and autoregulation: an experimental study in pigs

We have investigated the effects of xenon on regional cerebral blood flow (rCBF) and autoregulation in pigs sedated with propofol 4 mg kg-1 h-1. Balloon-tipped catheters were placed into the descending aorta and inferior vena cava of 15 Gottingen Minipigs for manipulation of arterial pressure and blood sampling. rCBF was measured using the sagittal sinus outflow technique. Xenon was adjusted randomly to end- tidal fractions (FE'Xe) of 0, 0.30, 0.50 and 0.70. After baseline measurements of heart rate (HR), mean arterial pressure (MAP), rCBF, sagittal sinus pressure (SSP) and calculation of regional cerebrovascular resistance (rCVR) at each respective FE'Xe, autoregulation was tested in the MAP range 60-120 mm Hg. Increasing FE'Xe had no effect on HR, MAP, rCBF or SSP. rCVR increased with increases in MAP, regardless of FE'Xe. Autoregulation was not impaired. We conclude that xenon inhalation had no effect on rCBF and autoregulation in our model, which could suggest that xenon is an adequate adjunct for neurosurgical anaesthesia.      

Low flow enhances platelet activation after acute experimental arterial injury

Purpose: Vascular smooth muscle cell (VSMC) proliferation and migration to the subintima or intimal hyperplasia (IH) occur after arterial injury and are thought to be induced by mitogenic factors released from activated platelets. Because low flow (LF) and shear have been attributed to the localization and progression of IH, we postulated that hemodynamic factors may regulate the degree of platelet activation, as measured by plasma thromboxane B₂ (TXB₂) and platelet-derived growth factor-AB (PDGF-AB) release at regions of experimental arterial injury. Methods: The right common carotid artery (CCA) was subjected to balloon injury in 18 New Zealand White male rabbits. Flow in the injured CCA was reduced by out-flow ligation (LF group, n = 6) or increased by ligation of the left CCA (high flow [HF] group, n = 6). In six other animals, flow was preserved (normal flow [NF] group). Mean blood flow and pressure in the right CCA were measured thereafter at 10 and 30 minutes. Plasma TXB₂ and PDGF-AB levels were determined with the enzyme-linked immunosorbent assay method in each animal with blood samples taken systematically before injury (baseline) and in the distal CCA at similar time points. Results: At 10 minutes, mean blood flow was reduced from 20 ± 2 ml/min in the NF group to 7 ± 1 ml/min in the LF group animals (p < 0.01) and increased to 32 ± 2 ml/min in the HF group animals (p < 0.05). Mean arterial blood pressure did not differ among the groups. Hemodynamic parameters were similar at 10 and 30 minutes. TXB₂ levels were more than fourfold greater in the LF group than in the HF and NF groups at both time points (p < 0.05). In addition, there was a twofold increase in plasma PDGF-AB level at 10 minutes in the LF group compared with baseline levels (p < 0.05). Conclusion: Platelet activation at regions of acute vascular injury was determined to be flow dependent. Upregulated platelet activity in low flow conditions may be due to increased platelet exposure time to subendothelial collagen and is greatly attenuated if normal or increased flow is present.(J Vasc Surg 1998;27:910-8.)     

Secondary sclerosing cholangitis: an experimental study

An experimental study on rabbit sclerosing cholangitis (SC) secondary to direct injection into the biliary tract of the chemical substances commonly employed for intraoperative sterilization of the hydatid cyst content is reported. Among the various substances utilized, 10% formalin and 30% hypertonic solution caused gross and microscopic lesions compatible with less advanced forms of sclerosing cholangitis. The authors present their hypothesis on the development of SC in operated hydatid cysts of the liver.     

Reinforced graft-to-artery anastomosis: an experimental study

This experiment was designed to study the effects of reinforcing graft-to-artery anastomoses. A section of infrarenal aorta was replaced with a Dacron graft in 24 dogs. In eighteen animals one anastomosis was reinforced with a cuff of Dacron graft material, while the remaining six dogs both anastomoses were reinforced, one with graft material and the other with Dacron mesh. The animals were sacrificed at three week to six month intervals. The grafts were examined grossly and microscopically, and the tensile strength of the anastomosis determined. There was no difference in tensile strength or in the luminal healing. There was only limited fibrous healing under the graft material cuff whereas there was full incorporation of the mesh cuff. Conclusions: Reinforcement is not required routinely. When used, the cuff should be made with mesh rather than graft material.     

Subperiosteal tissue expansion: an experimental study

Periosteal flaps have been used to cover bone defects. There are no sufficient data on whether expanded periosteum can be used to repair bone defects after subperiosteal tissue expansion. In this experimental study, 14 male dogs, which were 2 years-old and weighed 14.5–16.0 kg, were used to investigate the repair of bony defects with expanded periosteum. Rectangular tissue expanders, measuring 50 mm in width, 70 mm in length, and 20 mm in height (volume: 20 ml) were used. The dogs were divided into two groups each of seven dogs: one control group and one experimental group. In each dog, a pocket, 50×70 mm in size, was prepared in parietal area, and a periosteal area, 30×40 mm in size, was marked out. A rectangular tissue expander was inserted into the pocket. In the control group, the tissue expanders were not inflated. On the seventh postoperative day, the tissue expander inflation with normal saline (5 ml per 2 days) was started in the experimental group. After 15 days, the previously marked out periosteal area was measured. A specimen was taken from this periosteal tissue for histopathological evaluation. A bone defect, 20×20 mm in size, was created beneath expanded periosteal tissue, and this defect was covered with the expanded periosteal tissue. After 15 days, a histopathological evaluation was carried out. Statistical analysis was carried out using the Mann–Whitney U-test. The area of periosteum expanded was more in the experimental group than that of the control group (p>0.05). After removal of the tissue expander, both in the control and subperiosteal tissue expansion group, osteoblastic lining of the expanded periosteum, increased vascularity, and granulation tissue was noted. Following 15 days, woven and lamellated bone tissue was formed both in the control and subperiosteal expansion group. In the subperiosteal expansion group, there was greater bone formation, the expanded periosteum was thickened, and thickened lamellated bone was covered by active osteoblasts. It is concluded that subperiosteal tissue expansion may be worthwhile to provide large periosteal flaps for the repair of large bone defects, by increasing osteogenic capacity.     

Arterialization of the portal blood with a new model of flow diversion: an experimental study

Arterialization of the portal blood with double shunts, cavo-mesenteric venous and femoro-femoral arterio-venous, was attempted in dogs. The experimental model was studied in three groups. Group-I was concerned with the condition immediately after establishment of the model. Group-II-A was referred to the study on the established model with hepatic artery ligation for seven days. Group-II-B was evaluated under hepatic artery ligation and absent participation in arterialization and shunts. The ratio of portal venous flow (PVF) to cardiac output (CO) in group-I revealed significant increase from 23 +/- 6% to 56 +/- 9% (p less than 0.01). Portal venous PO2 (PVO2) also increased from 48 +/- 7 mmHg to 65 +/- 9 mmHg (p less than 0.01). Portal venous pressure, however, remained below 200 mmH2O. Persistent increase of CO (150% of the control) and PVF/CO were seen in observation of group-II-A. Histopathological appearance of the liver was normal in group-II-A. Group-II-B revealed a high mortality rate (8/9) with necrosis of the liver by seventh postoperative day. The experimental model provides the useful flow diversion with arterialized blood to the portal flow. The arterialization of the portal flow may play an important role in the recovery of the ischemic liver cell in the preservation of the liver graft and in hepatic regeneration after extended resection.