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.

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.

Diabetic vitreopathy--findings using the celloidin embedding technique.

BACKGROUND: To evaluate the role of the vitreous in diabetic eyes, autopsy eyes from diabetic patients have been examined by means of light and electron microscopy. METHODS: Twenty-five eyes were obtained from 19 patients. The duration of diabetes was from 8 to 26 years (average 17 years). All patients had type II diabetes. The glycerol-dehydrated globes were embedded in celloidin and hardened with chloroform. For light microscopy, areas of interest were cut from 200-microm-thick celloidin sections and embedded in paraffin, and 10-microm sections were cut. Such 200-microm and 10-microm sections were also used for scanning electron microscopy. For transmission electron microscopy, areas of interest were cut from thick celloidin sections and embedded in Epon for thin sectioning. RESULTS: The vitreous in diabetic eyes exhibits delayed senile degeneration in case of early onset of diabetes. It shows intensified staining of the vitreous cortex. Posterior detachment is often incomplete without collapse. The vitreous collagen fibers are coarse and aggregated in the centrally located cortical region of the vitreous. Hyalocytes in diabetic eyes have a different shape than normally, and their number seems to be increased. All these structural changes were not demonstrated in nondiabetic eyes. CONCLUSION: The vitreous in diabetic patients is morphologically different from normal vitreous. Features of the diabetic vitreous are aggregated collagen fibers, increased density of the vitreous cortex and morphological changes of hyalocytes. It is discussed whether these findings arise from nonenzymatic glycosylation of collagen molecules resulting in diabetic vitreopathy.

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).

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.

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.

A biodegradable patch used as a pericardial substitute after cardiac surgery: 6- and 24-month evaluation with CT.

Biodegradable patches made of polyhydroxybutyrate (PHB) were recently shown to limit postoperative pericardial adhesions when inserted into the pericardium in sheep. The present study was carried out to evaluate the presence of post-operative retrosternal adhesions after cardiac surgery in patients operated on with the PHB patch compared with those operated on without the insertion of such a patch. 50 patients admitted for CABG and/or valvular replacement were randomised to treatment either with pericardial closure with a patch or with the pericardium left open. In 39 of these (19 with and 20 without a PHB patch) computerised tomography was carried out six and twenty-four months postoperatively. Computerised tomography indicated a lower incidence (p < 0.05) of postoperative adhesions between the patch and the cardiac surface in the patch group, compared with the corresponding area in the non-patch group. A reduction of patch size in 27% (p = 0.003) was also seen.

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.

Comparative analysis of patency, limb salvage and survival in diabetic and non-diabetic patients undergoing infrainguinal bypass surgery.

In 92 diabetic and 175 non-diabetic patients undergoing 336 femoropopliteal or femorodistal bypass procedures, 1- and 3-year cumulative life-table patency, limb salvage, and survival rates were comparatively analysed. The peroperative mortality rate was significantly higher in diabetic patients (5% compared to 1.4%, p < 0.001). The cumulative graft patency rates were 61% at 12 months and 46% at 36 months in diabetic patients compared to 64 and 52% in non-diabetic patients. Significantly better patency rates were observed in limbs with good runoff compared to limbs with poor runoff in both groups. The limb salvage rates at 3 years were 70% in diabetic patients and 62% in non-diabetic patients. The survival rate at 3 years was significantly lower in diabetic patients, 62% compared to 86% in non-diabetic patients. Diabetic patients with poor runoff demonstrated a significantly lower survival rate after 36 months compared to diabetic patients with good runoff (48% and 74%, respectively). The results of this study demonstrate that the early and intermediate patency and limb salvage rates are similar in diabetic and non-diabetic patients. On the other hand the survival rate in diabetic patients, especially in those with poor distal runoff, is significantly lower than non-diabetic patients.

A new dual chamber single lead system.

A DDD pacing system normally requires the introduction and positioning of two separate electrode leads. A VDD system may use a single lead with a ventricular electrode at the tip and at least one atrial ring electrode. The disadvantage of VDD systems is that the full range of DDD stimulation and detection alternatives is not available. The present animal study was made to evaluate a new single lead design with the distal electrode placed in the atrium and the proximal ring electrode in the right ventricle. This design permits the full range of DDD options including atrial stimulation. Acute stimulation thresholds and sensing amplitudes were stable and comparable to conventional DDD systems. Long-term studies are on-going.

Enlargement of the right ventricular outflow tract and the pulmonary artery with a new biodegradable patch in transannular position.

Absorbable, nonwoven patches made from polyhydroxybutyrate (PHB) were implanted as transannular patches into the right ventricular outflow tract and pulmonary artery in 13 weanling sheep, the test group. Six sheep, in which a transannular Dacron patch was implanted, served as control group. The test and the control patches were harvested 3-24 months later. The results were documented macroscopically, by histological examination, and by scanning electron microscopy. The 6-keto-PGF1 alpha activity was measured in the regenerated tissue and compared with that in the native pulmonary artery. No aneurysms were noted. Regeneration of a neointima and a neomedia, comparable to native arterial tissue, was observed in the test group. In the control group, a neointimal layer was present but no neomedia comparable to native arterial tissue. Scanning electron microscopy disclosed differences in the endothelial structure between the test and control groups. 6-keto-PGF1 alpha activity was present in both the test and control groups. It is concluded that absorbable, nonwoven patches of PHB can be used as a scaffold for tissue regeneration in low-pressure systems. The regenerated vessel had structural and biochemical qualities in common with the native pulmonary artery.

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.

Urethral reconstruction with a new synthetic absorbable device. An experimental study.

Four centimeters of the canine urethra was replaced by a graft consisting of a polyglactin fiber mesh tube, coated with polyhydroxybutyric acid. Microscopic examination 8-12 months later showed almost complete regeneration of the urethral epithelium and the adjacent connective tissue. The neo-urethra was patent and there were no anastomotic strictures, nor was there any inflammatory reaction around the urethra. The validity of this concept in humans remains to be proved.

Regeneration of pericardial tissue on absorbable polymer patches implanted into the pericardial sac. An immunohistochemical, ultrastructural and biochemical study in the sheep.

A new absorbable polymer prepared from polyhydroxybutyrate (PHB) was inserted as a pericardial patch in sheep to serve as a temporary scaffold for regeneration of pericardial tissue. Postoperative adhesions were rare or absent. The present study focuses on characterization of the regenerated surface cells. The luminal surface of the regenerated tissue was covered with a complete layer of mesothelium-like cells which at light and scanning electron microscopy resembled those in native pericardium. Immunohistochemical stainings for cytokeratin and thrombomodulin were positive in these cells. Heparan sulfate proteoglycan was found in a basement-membrane-like structure beneath the surface cells, as in the normal pericardium. Transmission electron microscopy of the regenerated surface revealed cells with the characteristics of mesothelium. Prostacyclin production in the regenerated tissue was similar to that in native pericardium. The results indicate regeneration of a mesothelial layer with many of the important functions of native mesothelial cells. This may explain the presently and previously observed prevention of pericardial adhesions after cardiac surgery in this field. Clinical testing of PHB patches as pericardial substitutes is warranted in cardiac surgery when pericardial closure is desired.

A new biodegradable patch for closure of atrial septal defect. An experimental study.

Biodegradable patches made from polyhydroxybutyrate (PHB) were used to close experimentally induced atrial septal defect in six calves. The implants were evaluated after 3-12 months macroscopically and by light and scanning electron microscopy with regard to regeneration of tissue and degradation of the polymer. At implant degradation, complete endothelial layers facing the right and left atrium were observed, with a subendothelial layer of collagen and some smooth-muscle cells. The patch was degraded by polynucleated macrophages, and 12 months postoperatively no polymer material was identifiable at ordinary light microscopy, but in polarized light small particles of polymer with persisting foreign body reaction were still seen. Scanning electron microscopy revealed a complete layer of surface cells with morphologic signs of endothelium. There was no shunt or sign of infection. Biodegradable PHB patches implanted in atrial septal defects in this experimental model thus prompted formation of regenerated tissue that macroscopically and microscopically resembled native atrial septal wall. The total degradation time exceeded 12 months.

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.

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.

Angiographic criteria for prediction of early graft failure of secondary infrainguinal bypass surgery.

Complete intraoperative postreconstruction angiograms were obtained during 93 reoperations after failed femoropopliteal and femorodistal bypass grafts to evaluate the predictive value of a new method of angiographic runoff assessment. Good runoff was defined as patency of two or three lower leg arteries to the foot, or one patent vessel continuous with an intact anterior or posterior foot arch in femoropopliteal and proximal femorodistal bypasses, and integrity of both arches in low femorodistal bypasses. All other outflow patterns were considered poor. The cumulative 1-year patency rate was 61% with a 79% limb salvage rate after reoperations performed in limbs with good runoff. In reoperations with poor runoff, the patency rate was only 5% with a 22% limb salvage rate. In reoperations with good runoff, and 85% patency rate of vein grafts compared to 43% of prosthetic grafts clearly demonstrated the importance of graft material on early outcome. The improved prediction of early outcome with this new method of angiographic runoff evaluation might allow more rational management of patients with failed infrainguinal grafts.

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.