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Biomedical subjects

A Bylock

Publications and source records attributed to A Bylock.

At least 19 recordsLinked to original sources
PubMed1994

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.

6-Ketoprostaglandin F1 alpha↗
PubMed1992

Preliminary results of intraoperative excimer laser angioplasty: phase 1: an adjunct to coronary artery bypass surgery.

The excimer laser underwent phase I clinical trials at three centers to determine its safety for intraoperative coronary laser angioplasty as an adjunct to coronary artery bypass grafting. A 308-nm Xenon-Chloride, pulsed-wave excimer laser was used to perform angioplasty in 30 patients undergoing coronary artery bypass surgery. Forty vessels (30 patients) were treated, in which the extent of occlusion ranged from 30% to 100%, with complete occlusion in 40% of all vessels. Improvement in vessel luminal caliber was achieved in 33 (79%) vessels, with perforations occurring in 4 (12%) vessels, 2 of which required surgical repair. The lumens of the remaining 8 (19%) vessels were not enlarged, and 2 (5%) of these vessels were perforated. Luminal enlargement was most often achieved in totalled occluded vessels in which 16/17 (94%) were recanalized. No patients died within 30 days postoperatively. Five patients demonstrated biochemical and electrocardiographic evidence of myocardial injury 48 hr postoperatively, and one patient died of cardiac arrest 139 days postoperatively. On the basis of these results, we believe that excimer laser angioplasty can be performed safely to improve coronary luminal patency, even in totally occluded vessels, in an operative setting. The long-term value of this procedure remains to be elucidated.

Aged↗
PubMed1992

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.

Animals↗
PubMed1992

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.

Animals↗
PubMed1992

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.

6-Ketoprostaglandin F1 alpha↗
PubMed1988

Seeding of ePTFE carotid interposition grafts in sheep and dogs: species-dependent results.

Autologous endothelial seeding of thin-walled ePTFE vascular prostheses (I.D.4 mm), interposed in the carotid artery, was performed in 10 dogs and 14 sheeps. Aspirin (250 mg/day) and dipyridamole (75 mg/twice daily) were given throughout the study as antiplatelet therapy. Animals were killed 2 and 5 weeks after surgery. Patency rates for seeded grafts in dogs were 75% (6:8) and 83% (10:12) at 2 and 5 weeks, respectively. In control grafts the patency rates were identical. Patency rates for seeded grafts in sheep were 0% (0:5) and 11% (1:9) at 2 and 5 weeks, respectively. Control grafts in sheep had a patency rate of 40% (2:5) and 0% (0:9) at corresponding times. Scanning electron microscopy showed an almost complete endothelialization of seeded grafts in dogs after 5 weeks. Platelet deposition was studied in the dogs by means of chromium-51-labeled autologous platelets. Significantly fewer platelets accumulated on seeded grafts, and the ratio of 6-keto-PCF1 alpha to thromboxane B2 was significantly higher, compared with unseeded grafts, which indicated the presence of a functionally active endothelial lining in seeded grafts. Differences in the hemostatic system could account for the high clotting incidence in sheep, compared with that in dogs. Such species differences make extrapolations to the clinical situation from autologous endothelial seeding in experimental animals hazardous.

Animals↗
PubMed1986

Extravascular lung water measurement in septic sheep.

Sheep were prepared with a chronic lung lymph fistula and studied unanesthetized following septicemia by infusion of live Escherichia coli 10(9) ml/kg bw or injection of oleic acid 0.05 ml/kg bw. Extravascular lung water (EVTV) was measured with thermal-dye technique and compared to gravimetrically measured lung water (EVWV). Septic sheep had increased pulmonary artery pressure, reduced mean arterial blood pressure and reduced cardiac output. In control animals there was a correlation between EVTV-EVWV of r = 0.70. In animals given oleic acid lungs were macroscopically edematous and the correlation was r = 0.93. In septic sheep, however, no correlation could be found between EVTV and EVWV (r = -0.25). The thermal-dye technique was found to give erroneously high values. This finding could probably be due to erythrostasis and leukocyte plugging with uneven perfusion and prolonged transit times due to reduced cardiac output.

Animals↗
PubMed1986

Surface morphology of unused and used Hydromer-coated intravenous catheters.

Hydromer-coated polyurethane (Erythroflex) catheters, unused, or intravenously inserted for 2-20 days, were studied by scanning electron microscopy (SEM). Both unfixed and fixed (2% glutaraldehyde in phosphate buffer), and air-or critical-point dried (CPD) specimens were investigated. The catheter segments were sputter-coated with approx. 20 nm gold and studied at an accelerating voltage of 20 kV. The specimens were examined for surface depositions, thickness and structure of the Hydromer layers, and occurrence of adhering and embedded bacteria. The outer Hydromer layer showed, in the unused specimens, scratches and fissures, as well as adhering foreign bodies. In used specimens, the layer was swollen, with cracks (like "dried earth"), and, occasionally, amorphous substances and coccoid bacteria were seen adhering. Damage to the layer, or even its total disappearance was also noted in some specimens. The inner (luminal) Hydromer layer was, in unused specimens, clean and slightly wavy. In used catheters, it was thicker, possibly swollen, with small, isolated or agglomerated protrusions, like a "lunar landscape". Adhering platelets and amorphous substances were also occasionally seen. The results suggest that the Hydromer is a fragile material in both its dry and wet forms. Thus, the Hydromer-coated catheters should neither be stored in flexible packs, nor inserted by the Seldinger technique. The findings do not support the belief that the Hydromer-coating can prevent either thrombus formation, or intraluminal occlusion of the in-situ catheters.

Catheters, Indwelling↗
PubMed1986

Endothelial surface ultrastructure following hypoxia and hyperoxia.

Effects of hypoxia and hyperoxia on the ultrastructure of aortic endothelial cells were studied in rats. Rats were subjected to FIO2 0.05, 0.06 or 0.1 for various period times. Hypoxia was followed by nuclei protrusion, appearance of holes through the luminal membranes of individual cells. Some cells showed signs of partial of total disintegration. Hyperoxia (FIO2 = 1.0) were followed by slight morphological changes notable after 8 hours but most pronounced after 24 hours. The present study corroborated previous studies in that both hypoxia and hyperoxia can alter endothelial integrity.

Animals↗
PubMed1985

"Half-way" venous catheters. IV. Clinical experience and thrombogenicity.

"Half-way", Secalon-Seldy, soft venous catheters, 40 cm long, were inserted by basilic (n = 90) and cephalic (n = 31) veins at the fossa cubiti in 121 patients (71 men and 50 women) aged between 19 and 88 years whose heights varied from 152-197 cm. The inserted catheter lengths approximated 1/5 of the patient's height. Sixty-five per cent of 106 radiologically investigated catheter tips were located proximally in the axillary veins, and 34% distally in the subclavian veins. The duration of catheterization varied from 1 to 44 (mean 9 +/- 7) days (means +/- 1 s.d.). Perfect function was recorded in 93 of 121 catheters. No serious, but some minor complications were registered such as temporary interruption of infusion flow with movements of the arm (n = 12), partial or total catheter occlusion (n = 16), leakage of the infusate at the insertion site (n = 1), and pain along the vein during infusion (n = 2). Five patients (4%) developed thrombophlebitis 2-.10 days after insertion. Pull out phlebographies at catheter withdrawal (4-35 days after insertion) were performed in 36 patients. Radiological thrombi were small and similar to those recorded in another 53 phlebographies of "long-way" brachial catheters of similar stiffness. Neither local infection nor episodes of sepsis were registered over a period of 1,081 catheter days. "Half-way" catheters proved able to take over all the functions of both peripheral and central venous catheters, lacking the frequent complications (phlebitis and infection) of the former, and the serious mechanical complications (pneumothorax, vein perforations, and injuries of the ductus thoracicus, nerves, arteries, and heart) of the latter.

Adult↗
PubMed1984

Effect of venous stasis on vessel wall fibrinolysis.

The effects of prolonged venous stasis on release of plasminogen activators (PA) from the caval vein of rats were studied. PA activity was continuously reduced in the intimal layer and after 8 hr of stasis the reduction was statistically significant. After 2 and 3 days no intimal PA activity was found. The PA activity in the adventitial vasa vasorum was unchanged during the experimental period.

Animals↗
PubMed1984

Dynamics of thrombophlebitis in central venous catheterization via basilic and cephalic veins.

The incidence distribution of thrombophlebitis after central catheterization via basilic and cephalic veins was investigated, using 227 catheters made of various plain or heparin-coated materials and with differing stiffness and surface structures. The platelet-adhesion stimulating properties were measured in vitro. Thrombophlebitis showed similar incidence patterns with all catheter types. The maximum incidence of venous reaction was found one to ten days after catheter insertion (central tendency 3-8 days with a peak at 5 days). After ten days the risk of thrombophlebitis fell significantly. The results supported the view that central venous catheters inserted via basilic or cephalic veins should not be withdrawn or exchanged as prophylaxis against thrombophlebitis, at any rate when long-term catheterization is intended. For conclusive comparisons between catheter materials regarding induction of clinically apparent thrombophlebitis, all the patients in the trial should be catheterized for ten days or more, unless symptoms of venous reaction arise earlier.

Adolescent↗
PubMed1983

Local fibrinolytic activity and its structural basis in experimental gastric ulcers.

The stomach contains plasminogen activators localized to submucosal vessels and to the mucosa. To study the release of plasminogen activators from mucosal cells, we induced mucosal damage by pyloric ligature and instillation of 0.5 mol/l HCl in rats. After 4 h, all rats developed focal necrotic lesions and a diffuse mucosal damage, as studied both by light microscopy and by scanning electron microscopy. Diffuse mucosal damage was accompanied by significant increase (P less than 0.001) in mucosal fibrinolytic activity based on plasminogen activators. This activity was probably derived from injured mucosal cells since focal necrotic lesions (erosions and ulcers) with total denudation of the mucosal epithelium lacked fibrinolytic activity. The results obtained in this study support the hypothesis that plasminogen activators are released during cellular degeneration.

Animals↗
PubMed1983

The effect of balloon catheter trauma on surface ultrastructure and fibrinolytic activity in the caval vein in rats.

Surgical procedures in veins such as thrombectomy are followed by a high complication rate. Re-occlusion is not uncommon in spite of primarily successful thrombectomy. The venous endothelium is damaged by the thrombotic process and the mechanical trauma from the balloon will be additive. The endothelial cells are the source of fibrinolytic activators. The present study compared changes in fibrinolytic activity in the vessel walls from the caval veins in rats to ultrastructural changes as seen in the scanning electron microscope. The balloon caused an almost complete denudation of the intima and the lesions were fully covered with platelets 1 hour after trauma. After 3 days reendothelialization had started. The fibrinolytic activity was significantly decreased at 1 and 24 hours following trauma. Reendothelialization was accompanied by return to normal fibrinolytic activity.

Animals↗
PubMed1981

Early reactions of the arterial wall, following mechanical trauma. A scanning and transmission electron microscopy study.

Endothelial injury has for a long time been suggested to be an important factor for the development of atherosclerotic lesions. In this study, a superficial, circumferential, injury to the aortic intima was induced via a catheter covered with small stones, introduced into the femoral artery of rabbits. The immediate answer of the arterial wall and the formed elements of the blood was studied with combined scanning and transmission electron microscopy. De-endothelialization was noted and the denuded areas were almost immediately covered by platelets, spreading over the surface and releasing the contents of their granules by time. At some locations deeper injuries to the elastic laminae of the wall could be noted. Especially frequent around these areas, but also common all over the de-endothelialized surface, leukocytes were seen. Both neutrophils, lymphocytes and monocytes could be found. A demarcation of the border of the injury was noted three days after catheterization.

Animals↗