Prevention of postoperative pericardial adhesions by closure of the pericardium with absorbable polymer patches. An experimental study.

Pericardial adhesions after cardiac operations are a widely known phenomenon. They may severely complicate reoperations, making reentry hazardous, increasing bleeding, and prolonging the operation time. The anatomic orientation and visibility of both bypass grafts and coronary arteries are also impaired. With the aim of minimizing pericardial adhesions after cardiac operations, we studied the course of tissue regeneration after implantation of a new absorbable patch made from poly-hydroxy-butyrate. A total of 23 sheep were studied. Of these, 18 formed the test group and five served as control animals. The animals were killed at intervals of 2 to 30 months after the operation. In 14 of the 18 test animals no adhesions developed. In three animals loose adhesions were found, and in one with signs of postoperative infection there were moderate, generalized adhesions. All control sheep showed moderate adhesions; no infection was noted in this group. Light microscopy in the test group revealed a layer of mesothelium-like cells facing the epicardial side; this was already present in the early specimens. Poly-hydroxy-butyrate appeared to be slowly phagocytosed by polynucleated macrophages, which were still found occasionally in the late samples. Lymphocytes and platelets were rare. Scanning electron microscopy showed, on the epicardial side of the regenerated tissue, a mesothelium-like lining that completely covered the underlying collagen layer. The surface cell morphology grossly resembled that of native pericardium. It was concluded that in this animal model poly-hydroxy-butyrate pericardial patches decreased adhesions and preserved coronary anatomy. The findings in the control group demonstrated that pericardial surgery in the sheep was associated with adhesion formation.

Arterial regeneration following polyglactin 910 suture mesh grafting.

A suture mesh of polyglactin 910 [Vicryl (polyglactin 910) suture mesh] was placed as a patch graft into the thoracic aorta of 23 growing pigs. In three other pigs the mesh was grafted in the form of a tube to replace a short aortic defect. The biological processes taking place in the grafted area were studied by morphological methods. The following observations were made: (1) Hemostasis readily occurred by fibrin, platelet, and erythrocyte embedding of the mesh. (2) Early outgrowth of smooth muscle cells around the mesh took place from the normal aortic media and from a newly formed subintimal smooth muscle layer. (3) The newly formed arterial tissue was completely endothelialized within 20 days. (4) The polyglactin mesh had disappeared almost completely at 40 days, but the new wall seemed to retain sufficient strength throughout the observation time. (5) Only irregular deposition of elastic fibrils occurred, but in other respects the new tissue structurally resembled normal arterial tissue.

A simple infusion method for measurement of intraoperative peripheral vascular runoff resistance.

A simple infusion system to assess the status of distal runoff was investigated on both hindlimbs of five mongrel dogs. Infusion catheters were placed in the superficial femoral arteries and the origin of the lower leg arteries was exposed for anatomic manipulation of the distal runoff. Saline solution was infused through the superficial femoral arteries at 64, 129, and 193 cm levels to calculate volume flow and index of resistance to flow. The in vitro part of the study was undertaken to analyze the effect of different-size catheters on flow rates in a rigid undistensible model. In the hindlimb study the flow differed significantly between two- and one-vessel runoff status at 50 and 100 mm Hg infusion pressures. In the in vitro study, in contrast to the hindlimb study, index of resistance to flow values for different-size catheters remained almost unchanged as the infusion pressure increased, demonstrating the distensibility of the runoff bed in dogs. A preliminary clinical study in 13 patients undergoing infrainguinal bypass surgery demonstrated a good correlation between angiographic runoff evaluation and intraoperative flow values. Valuable information can be obtained about the status of the distal runoff by this simple infusion method, which might be used to improve the prediction of outcome of infrainguinal bypass surgery.

A new method of angiographic runoff evaluation in femorodistal reconstructions. Significant correlation with early graft patency.

In 62 patients undergoing femorodistal bypass surgery, the foot vessel runoff was analyzed with a new grading system based on intraoperative postreconstruction serial angiography. The patients were divided into two groups according to the level of the distal anastomosis (proximal or low). Good runoff was defined as integrity of the anterior and/or posterior foot arch in proximal femorodistal grafts and integrity of both arches in low bypasses. In the proximal group, runoff was classified as poor when the arches were deficient or occluded, and in the low group, when only one arch was intact. The patency rate after 6 months was 81% in the good runoff group, whereas all grafts in patients with poor runoff were occluded. The new method allowed better prediction of the early outcome than does the primary and secondary pedal arch integrity concept.

Long-term in vivo experience of an electrochemical sensor using the potential step technique for measurement of mixed venous oxygen pressure.

An implantable amperometric blood oxygen sensor was developed to improve rate adaptation of heart pacemakers. Two different working electrode materials in direct contact with the blood were tested, smooth glassy carbon and gold. Reference electrodes of Ag/AgCl and porous pyrolytic carbon were evaluated. A counter electrode being the titanium housing of the pulse generator was partly coated with carbon. An implantable pacemaker system with chronocoulometric oxygen detection was developed. Heart synchronous potential steps were periodically applied to the 7.5 mm2 working electrode in the atrium. Both single and double potential step techniques were evaluated. The oxygen diffusion limited current was used to calculate the stimulation rate. Bench tests and studies on 31 animals were performed to evaluate long-term stability and biocompatibility. In five dogs, the AV node was destroyed by RF ablation to create a realistic animal model of a pacemaker patient. Sensor stability and response to exercise was followed up to a maximum implantation time of 4 years. Post-mortem examinations of the electrode surfaces and tissue response were performed. The results show that a gold electrode is more stable than glassy carbon. The Ag/AgCl reference was found not to be biocompatible, but activated carbon was stable enough for use as reference for the potentiostat. Double potential steps stabilize the sensor response in comparison to single steps. Blood protein adsorption on the gold surface decreased the oxygen transport but not the reaction efficacy. No adverse tissue reactions were observed.

Bypass grafting to the popliteal artery in limbs with occluded crural arteries.

Intraoperative completion angiograms of 47 femoropopliteal bypasses in limbs with occluded crural arteries were reviewed to identify the angiographic determinants of early outcome. Of 28 limbs in which the foot vessels were available for analysis, only 2 (7%) had an intact pedal circulation, and 18 limbs demonstrated no crural arteries suitable for distal reconstruction. The overall cumulative patency rate was 51% with a 76% limb salvage rate at 12 months. All seven grafts performed onto a popliteal artery segment of less than 8 cm occluded in the early period. The status of crural and foot arteries and the number of collaterals did not correlate well with early patency. Limbs with no patent crural artery that were analyzed in the poor angiographic runoff group, according to our previously reported classification, demonstrated relatively higher patency rates than the other subgroups with poor runoff. In cases where angiography demonstrates a poor runoff for distal revascularization, popliteal bypass with occluded crural arteries might achieve acceptable patency rates.

Influence of twist on vein and PTFE graft hemodynamics: an ex vivo experimental study.

OBJECTIVE: In an ex vivo infusion model, the effect of different factors affecting the critical level of twist in vein and PTFE grafts was analysed. SETTING: University Hospital, Department of Surgery. EXPERIMENTAL DESIGN: Saline perfusion of grafts with various diameter and length under constant high (90 ml/min) and low (50 ml/min) flow rates against various peripheral resistance was performed. MEASURES: The pressure changes in the grafts were measured at increasing increments of twisting. RESULTS: The critical level of twist appears to be dependent on the diameter, length, stretching, status of peripheral resistance, amount of volume flow and the type of graft material, varying between 90 to more than 360 degrees. In vein grafts critical twisting appeared earlier with a decrease in diameter, shortening in length, high peripheral resistance, high flow rate and stretching. PTFE grafts especially with external spiral support were resistant to twist. CONCLUSIONS: These data suggest that the critical level of graft twist is dependent upon multiple factors and moderate or even high grade twist with especially externally supported PTFE grafts regardless of length and long mobilized vein grafts do not lead to hemodynamic changes. On the other hand total cessation of flow occurs at lower degrees of twist in stretched, short vein grafts.

Efficient biliary excretion of susalimod, probably via the bromosulphthalein carrier, studied in a chronic bile fistula model in dogs.

Susalimod is a structural analogue of sulphasalazine, known to be extensively excreted in the bile in various animal species and for inducing bile duct hyperplasia after long-term treatment of the dog with doses exceeding 25 mg kg(-1). In this study local concentrations of susalimod in the bile duct were determined after oral administration in dogs. A chronic bile fistula experimental model was designed to affect the bile duct as little as possible. The dogs received repeated oral doses of 25-150 mg kg(-1) day(-1) for 5 days; these doses had been used in previous toxicology studies. Extremely high biliary concentrations of unchanged susalimod (20,000-43,000 microM) were measured. Biliary excretion approached saturation at the higher doses, resulting in super-proportional increases in peripheral plasma concentrations as the dose was increased. The maximal bile/plasma concentration ratio was 4300. The high biliary clearance was indicative of almost complete first-pass elimination at doses below saturation of the elimination process. Interaction studies with the biliary excretion marker bromosulphthalein (BSP) demonstrated that susalimod and BSP probably share the same carrier transport system in biliary excretion. The elimination of BSP from plasma was prolonged 20 times and the biliary excretion rate was markedly reduced when susalimod was co-administered with BSP. These results show that susalimod is highly enriched in the bile, in a saturable manner, after oral administration. The compound interacts with the biliary excretion of BSP, suggesting that it shares the same carrier-mediated transport system.

Renal complications to left renal vein ligation in abdominal aortic surgery.

Postoperative renal complications have been investigated in 31 patients subjected to left renal vein ligation during abdominal aortic surgery (11 ruptured and 18 non-ruptured aneurysms, 2 occlusive diseases). A marked increase in s-creatinine values was found in all patients after left renal vein ligation. The increase was significantly longer (p less than 0.01) and higher (p less than 0.005) as compared with control patients subjected to abdominal aortic surgery without ligation of the left renal vein. A sustained increase in postoperative s-creatinine values was found in 6 patients, one of whom had a total loss of left kidney function. Left-sided nephrectomy was necessary in 2 patients to control bleeding from the kidney. Acute haemorrhagic infarction and subinfarction of the left kidney were seen in 2 patients. A restricted application of left renal vein ligation during abdominal aortic surgery is recommended.

Surgical treatment of pararenal abdominal aortic aneurysms.

Thirty patients with juxtarenal infrarenal and 16 patients with suprarenal abdominal aortic aneurysms underwent elective (58%) or urgent (42%) repair. Twenty-three patients were hypertensive and 20 had impaired renal function preoperatively. Nineteen patients required combined aortic and renal artery reconstruction, in which reimplantation was the most common technique used. The perioperative mortality rate was 7.4% in the elective group and 36.8% in the urgent group. Rupture of the aneurysm and a preoperative high serum creatinine level were risk factors correlating to early mortality. Among survivors, 61% showed a rise in serum creatinine in the early postoperative period. In all but one the transient renal insufficiency was resolved within one month. Of the hypertensive patients 64% were cured or under control with medication following combined reconstruction. These results demonstrate that surgical repair of pararenal abdominal aortic aneurysms can be performed with an acceptable mortality and morbidity.

In vitro and in vivo biodurability of a compliant microporous vascular graft.

Polyurethanes have unique mechanical and biologic properties that make them ideal for many implantable devices. However, certain polyurethanes are affected by some in vivo degradation mechanisms. For example, poly(ester)urethanes are subject to hydrolytic degradation and are no longer used in long-term implanted devices. Poly(ether)urethanes while hydrolytically stable, are subject to oxidative degradation in several forms, including environmental stress cracking and metal ion oxidation. We have developed a second-generation poly(carbonate)urethane with superior biostability. This material has been fabricated by our patented method into small diameter microporous vascular grafts. We evidenced the biodurability of our vascular graft by in vitro qualification tests which compared the poly(carbonate)urethane with a traditional poly(ether)urethane. This poly(carbonate)urethane graft has also proven to be biodurable in in vivo experimental implants up to twenty months duration with no evidence of hydrolysis or environmental stress cracking (ESC).

Development of a microporous compliant small bore vascular graft.

PURPOSE: To produce biodurable small diameter microporous vascular grafts with self-sealing properties for vascular access, for peripheral vascular and potentially for coronary artery bypass. The prosthesis should retain compliance and pulsatile flow in situ using a unique modus operandi permitting wall compression which accommodates changes in volume. METHOD: We have utilized efficient low temperature coagulation technology to develop a unique range of small diameter microporous vascular grafts using ChronoFlex, a biodurable polycarbonate urethane. RESULTS: Grafts have been subjected to a range of in vitro and in vivo testing, demonstrating excellent physical and mechanical characteristics, self-sealing, maintenance of compliance and pulsatile flow in situ and patency up to twenty-two weeks.

Peroperative assessment in arterial surgery--flow determination or angiography?

Complete data from flow measurement and intraoperative angiography were obtained in 70 femoro-popliteal vein by pass procedures. The results were compared in respect to their predictability of early outcome after arterial reconstruction. A correct prediction was given in 65 of 70 cases (92 per cent) by angiography. The corresponding figure for flowmeter determination was 52 of 70 (74 per cent). Angiography was found to be preferable to flow determination especially when low flow values were registered.

Rupture of an abdominal aortic aneurysm into the vena cava.

Aortic abdominal aneurysm combined with aorto-caval fistula is a rare condition with a high mortality. We discuss here the sympatomatology and treatment of one such patient.

Electric stimulation of a transsected nerve does not seem to prevent loss of sensory neurons: an experimental study in cats.

Injury to a sensory nerve often results in a clinically poor long term outcome, possibly as a result of the extensive loss of neurons within the dorsal root ganglia (DRG), which has been shown in several experimental studies. This loss is possibly caused by interruption of the sensory input and axonal transport in the damaged afferent nerve. To investigate the importance of sensory afferent input into a nerve a pulsed electric stimulation was applied on the proximal part of the superficial radial nerve after transsection and microsurgical repair. The purpose was to simulate nerve impulses and thereby mask the severity of the injury. To test this hypothesis a pilot study was undertaken in eight cats. The neuronal tracer showed that the median neuronal loss was 38% of the neurons of the dorsal root ganglia that received afferents from the nerve investigated, which corresponds to the figure in a previous study in which electric stimulation was not used. Artificial sensory stimulation during regeneration in a transsected and repaired peripheral nerve therefore does not seem to reduce neuronal loss.

The vitreous after C3F8 gas instillation: long-term histologic findings after spontaneous reabsorption of the gas in rabbit eyes.

Perfluoropropane gas (C3F8) was injected intravitreally into rabbit eyes to displace the vitreous. Histologic examination by light and scanning electron microscopy revealed the vitreous material slowly expanded up to a nearly normal configuration during a follow-up of 6 months. Neither posterior vitreous detachment nor liquefaction of the vitreous could be observed.

Microproliferations in proliferative diabetic retinopathy and their relationship to the vitreous: corresponding light and electron microscopic studies.

Using a special embedding method, autopsied eyes with proliferative diabetic retinopathy were studied. In areas with no posterior vitreous detachment, small proliferations may arise multifocally and grow within the vitreous cortex. The fibrous material of the vitreous cortex is densely interconnected with and obviously incorporated into the newly formed proliferated tissue, a process which causes coarse traction lines on the vitreous cortex lamellae. The clinical consequences of these findings are discussed.

Pulmonary microembolism during and after aortic cross-clamping in heparinized and non-heparinized pigs.

The occurrence of pulmonary microembolism after aortic clamping and declamping was investigated in 21 young pigs. The prophylactive effect of heparin was also examined. Eight animals were heparinized, while 13 did not receive heparin. In 15 pigs the plasma concentration of fibrinogen was determined before, during and after clamping of the aorta. External detection of 51Cr-labelled platelets and 125I-labelled fibrinogen was performed. Lung tissue from these animals was homogenized and analysed for radioactivity. Specimens were taken from the lungs of all animals for morphological investigation. A significant decrease in plasma fibrinogen concentration was noted during the aortic clamping in non-heparinized animals. Morphological studies of lung tissue revealed numerous fibrin/platelet thrombi, leukocyte and platelet aggregates, atelectases and bleedings. In homogenized lung tissue, areas with elevated radioactivity were found, indicating fibrin/platelet entrapment. No such changes were seen in pigs pretreated with heparin. It was found that pulmonary microembolism occurs frequently after aortic clamping if heparin is not given at an early stage of the procedure.