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Biomedical subjects

D Hansen

Publications and source records attributed to D Hansen.

At least 109 records · Page 6Linked to original sources
PubMed1990

Prechilling and vacuum mixing not suitable for all bone cements. Handling characteristics and exotherms of bone cements.

Nine bone cements were tested for handling characteristics, intrusion, doughing time, setting time, and exothermic temperature. Comparative studies were made of manual mixing and vacuum mixing of cement components stored at room temperature or chilled to 5 degrees C. Vacuum mixing of cement packages stored at room temperature was inapplicable except for the low-viscosity brands, as the cements became too viscous to mold test specimens. Prechilling and vacuum mixing prolonged the setting time and preserved a lower viscosity during the handling period. Palacos R and Palacos G were most suitable for this method, whereas a considerable increase in exothermic temperature was experienced with the other brands. The method might, however, be considered for Zimmer and Cerafix also, as the exotherm was of the same magnitude as for Palacos brands.

Bone Cements↗
PubMed1990

[Long-term antidepressive medication-- an increased anesthetic risk?].

Antidepressants inhibit the re-uptake of norepinephrine at the monoaminergic synapse from the synaptic fissure, leading in this way to an increased sensitivity to catecholamines. In addition, antidepressants have alpha1-, H1- and H2-receptor blocking effects and also anticholinergic effects; the tricyclic antidepressants in particular are known for these properties. A few animal experiments and some case reports indicate that a long-term treatment with these substances can lead to intra-operative blood pressure fluctuations, tachycardia and arrhythmias. Therefore a number of authors recommend that antidepressants be withdrawn 3 days before a planned operation. In view of the pharmacokinetics of these substances and the long-term adapting processes at the monoaminergic synapse this period is certainly too short to achieve complete loss of effectiveness. Other authors think preoperative withdrawal is not indicated if there is careful intraoperative monitoring. We agree with the latter opinion. Inhalation anesthesia with isoflurane or enflurane should be preferred. The muscle relaxant pancuronium should not be used, and exogenous intake of catecholamines should be avoided. Opiates seem to have a positive effect on cardiac stability. Benzodiazepines show the least interactions with antidepressants and are therefore recommended for premedication. In the postoperative period the possibility of an anticholinergic syndrome has to be considered.

Anesthesia↗
PubMed1990

Malignant intestinal schwannoma. Case report.

Malignant schwannoma of the small intestine is rare and diagnosis often late. Histologic distinction from fibrosarcoma and leiomyosarcoma may require electron microscopy. The primary treatment is surgical. Close postoperative observation is recommended because of the tendency to recurrence. Remission after chemotherapy has been reported, but without controlled studies. The 5-year survival rate is unknown. Two cases are presented.

Aged↗
PubMed1988

Thermal denaturation of engineered tet repressor proteins and their complexes with tet operator and tetracycline studied by temperature gradient gel electrophoresis.

The effects of Trp to Phe exchanges in the Tet repressor on the thermal stability of the proteins and their complexes with operator DNA and inducer have been studied by temperature gradient polyacrylamide gel electrophoresis. The denaturation temperatures obtained by this method are compared with the results from temperature-dependent fluorescence and binding activities of the proteins. It is established that exchanging the interior Trp75 to Phe reduces the thermal stability of the Tet repressor by 8 degrees C while exchanging the exterior Trp43 to Phe has no effect on the stability of the protein. Binding of the inducer tetracycline increases the thermal stability of wild-type and Trp43 to Phe mutant Tet repressors by 5 degrees C, while the ones with the Trp75 to Phe mutation are stabilized by 10 degrees C. The stabilizing effect of operator binding is 20 degrees C in the Trp75 to Phe mutant and only 9 degrees C in the ones with the Trp43 to Phe exchange. In addition to the denaturation temperatures, the gel mobility shifts observed in temperature gradient gel electrophoresis reveal also information about the intermediates of the denaturation reaction. The free proteins and their complexes with the inducer tetracycline exhibit monophasic transitions upon denaturation. The operator complexes of wild-type and Trp75 to Phe mutant repressors denature in more complex reactions. At low temperature they exhibit a stoichiometry of two repressor dimers per tandem tet operator DNA. Upon elevating the temperature they form complexes with only one repressor dimer per DNA fragment. When the temperature is further increased the double-stranded DNA begins to melt from one end resulting in a complex with partially single-stranded DNA which exists only in a narrow temperature range. Finally, the denatured protein and single-stranded DNA are formed at high temperature. The associated mobility shifts are analyzed by changing the ionic strength and characterizing multiphasic melting of a pure DNA fragment by temperature gradient gel electrophoresis.

Bacterial Proteins↗
PubMed1988

Femoral shaft fracture after hip arthroplasty.

Femoral shaft fractures after hip arthroplasties were treated in 74 noncemented hemiarthroplasties and 65 cemented arthroplasties. In loose prostheses the best clinical results and the least number of operations were achieved with revision arthroplasty with a long-stem prosthesis, combined with simple internal fixation methods when applicable. In firmly fixed prostheses the results of revision arthroplasty and traction treatment were similar. Cemented revision arthroplasty did not interfere with fracture union. Internal fixation with the prosthesis in situ cannot be recommended because of a large number of secondary revision arthroplasties and nonunions. Removal of the femoral stem prosthesis and internal fixation nearly always require a secondary revision and cannot be recommended.

Adult↗
PubMed1988

Production and immunohistochemical characterization of monoclonal antibodies directed against renal basement membranes of rats.

Basement membranes were separated from rat glomeruli and purified by mild procedures, which led to a highly enriched basement membrane fraction. Here, the production and characterization of five monoclonal antibodies against tubular and glomerular basement membranes are described. These antibodies were analyzed immunohistochemically on frozen sections of rat, bovine, and human kidneys as well as on rat embryos. One monoclonal antibody (BM O II) exclusively recognized the glomerular basement membranes, another one (BM O VII) bound to tubular basement membranes and to Bowman's capsule. Three antibodies (BM O IV, BM M II, BM M III) recognized their antigens in both glomerular and tubular basement membranes as well as in mesangial cells. The BM O II antibody showed a stringent species specificity and bound only to glomerular basement membranes of the rat. The other four antibodies cross-reacted with human and bovine glomerular basement membrane and mesangial antigens; they also bound to other tissues in the developing rat embryo. Antibody binding to specific purified components of the basement membranes such as collagen type IV, laminin, heparan sulphate proteoglycan, and fibronectin was investigated by enzyme-linked immunosorbent assay (ELISA). None of these antibodies reacted with any of these known basement membrane components, indicating that the antibodies may serve as useful tools in future investigations of so far unidentified components of basement membranes.

Animals↗
PubMed1987

Engineered Tet repressor mutants with single tryptophan residues as fluorescent probes. Solvent accessibilities of DNA and inducer binding sites and interaction with tetracycline.

Mutants of the Tn10-encoded Tet repressor containing single or no tryptophan residues were constructed by oligonucleotide-directed mutagenesis. The Trp-75 to Phe exchange reduces the dissociation rate of the complex with the inducer tetracycline by a factor of 2. The Trp-43 to Phe exchange has no effect on inducer binding. The fluorescence emission spectra of both tryptophan residues are quenched to a different extent by binding of tetracycline: Trp-75 is quenched to zero and Trp-43 to only 50%. It is concluded that Trp-75 is in the vicinity of the inducer binding site. The different fluorescence emission spectra of both tryptophan residues depend on the native structure of Tet repressor. Quenching studies with iodide indicate that the DNA binding motif is solvent exposed in free repressor and moves towards the interior of the protein upon inducer binding. The inducer binding site is in the interior of the protein. The fluorescence of tetracycline is enhanced upon binding to Tet repressor. The excitation at 280 nm results mainly from the change in environment and in part from energy transfer from tryptophan to the drug.

Bacterial Proteins↗
PubMed1987

Tryptophan in alpha-helix 3 of Tet repressor forms a sequence-specific contact with tet operator in solution.

The Tn10-encoded Tet repressor contains two tryptophan residues at positions 43 and 75. The typical tryptophan fluorescence is decreased upon binding of tet operator. The Tet repressor gene was engineered to replace either or both of the Trp codons by Phe codons. The resulting single tryptophan mutants are called F43 and F75 and the double mutant F43F75. The mutant proteins were purified to homogeneity. They recognize tet operator DNA only in the absence of the inducer tetracycline, indicating an intact tertiary structure of the engineered proteins. F75 and wild-type bind tet operator with the same association constant. The association constants of F43 and F43F75 with tet operator are about 3 orders of magnitude smaller. This indicates that Trp43 is important for tet operator recognition. Trp43 fluorescence is completely quenched in the complex with tet operator DNA while Trp75 remains unaffected. Binding to nonspecific DNA leads only to a 40% decrease of Trp43 fluorescence. This is interpreted as the contribution of the changed environment while the complete quench reflects a tight sequence-specific contact of tryptophan 43 to tet operator DNA. Trp43 is solvent-exposed, while Trp75 is buried in the hydrophobic interior of the protein. These results are discussed in light of the alpha-helix turn-alpha-helix DNA binding motif deduced from homology to other repressor proteins.

Base Sequence↗
PubMed1986

Hemi-arthroplasty of the hip followed by ipsilateral fracture of the femoral shaft.

In a series of 74 ipsilateral fractures of the femoral shaft in relation to hemi-arthroplasties, treatment by a cemented long-stem total hip replacement was found to be superior to conservative treatment or internal fixation without removal of the prosthesis. Acceptable clinical results were obtained in 89 per cent of these cases.

Aged↗
PubMed1986

Identification of Mycobacterium tuberculosis antigens in Seibert fractions by immunoblotting.

Seibert fractions prepared from Mycobacterium tuberculosis culture filtrates were evaluated by immunoblotting with a serum pool from patients with active pulmonary tuberculosis. Antibody activity was observed primarily with antigens in the polysaccharide II and A protein fractions; these fractions were further evaluated by immunoblotting with sera from individual patients with tuberculosis, from individuals without tuberculosis and positive for the purified protein derivative antigen skin test, and from individuals negative for the purified protein derivative antigen skin test. The antigens identified in the protein A fraction, a 32,000-molecular-weight antigen and a heterogeneous high-molecular-weight antigen, reacted with antibody found in sera from all patients with tuberculosis and with antibody from over 25% of the control individuals. A 10,000-molecular-weight antigen, a 30,000- to 44,000-molecular-weight antigen, and a heterogeneous high-molecular-weight antigen were observed in the polysaccharide II fraction; these antigens reacted with serum antibody from 70% or more of the patients with tuberculosis and with antibody from 20 to 70% of the control individuals. One of the antigens, with a molecular weight ranging from 17,000 to 28,000 in the polysaccharide II fraction, reacted with antibody in 64% of the sera from patients with tuberculosis but with only 1 of 15 control normal sera. This antigen may elicit an antibody response specifically associated with tuberculosis.

Antigens, Bacterial↗
PubMed1986

First-stage palliation of hypoplastic left heart syndrome. The importance of coarctation and shunt size.

After Norwood's initial report of successful first-stage palliation of hypoplastic left heart syndrome in neonates, an improved understanding of both the pathologic anatomy and physiology of this common condition has led to improving surgical results. Twenty-five neonates have been treated by modifications of the Norwood procedure, and the early mortality between January, 1984, and July, 1985, has been 24% (six deaths). Two premature neonates weighing less than 2 kg died, as did two neonates who could not be resuscitated with prostaglandin E1 and had cardiac arrests immediately preoperatively. There have been four late deaths. The frequent occurrence (80%) of a juxtaductal coarctation or coarctation shelf necessitates alteration of surgical technique. Failure to do so will be reflected in an early persistent postoperative metabolic acidosis with an arterial oxygen tension greater than 35 to 40 mm Hg in the operating room or greater than 40 to 45 mm Hg in the intensive care unit. A similar acid-base derangement will be seen if the systemic-to-pulmonary shunt is excessively large. Careful ventilatory and pharmacologic management of the ratio of pulmonary to systemic vascular resistance is an essential part of the perioperative management of these neonates with two parallel competing circulations. Late postoperative catheterization findings have emphasized the importance of a wide atrial septectomy, because restrictive atrial septal defects have developed in a number of children, despite partial surgical atrial septectomy. Central pulmonary artery reconstruction must be carefully performed to avoid distorted hypoplastic pulmonary arteries that would be unsuitable for a second-stage modified Fontan procedure.

Acid-Base Imbalance↗