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Biomedical subjects

T Kristiansen

Publications and source records attributed to T Kristiansen.

At least 19 recordsLinked to original sources
PubMed1992

External fixator pin design.

The integrity of the bone-pin interface is the critical link in the stability of external fixation systems. External fixation pins placed in cancellous metaphyseal bone frequently loosen over time, resulting in fixation failure and an increased risk of infection. To design an external fixation pin with optimal bone-metal interface strength in cancellous bone, a systematic study of various thread design features was performed. Combinations of pitch, tooth profile, and minor diameter in 5 mm self-tapping half pins were evaluated in coaxial pullout testing using a fresh bovine cancellous bone. A significant increase in pullout strength was found with a decrease in minor diameter. No statistical differences were found in pullout strength attributable to thread profile and pitch. There were no significant interactions between minor diameter and tooth profile or minor diameter and pitch. The data obtained suggest significantly greater holding power in cancellous bone can be achieved by using an external fixation pin with a smaller minor diameter or a larger interference. Additional pullout testing of five commercially available external fixator pins was performed. Of these, the two pins with the largest interference demonstrated greater pullout strength. Therefore, within a range of acceptable major diameters and adequate minor diameters for the torsional strength requirements, an optimal interference for cancellous pin application may exist and it may well be larger than that present in currently available external fixation pins.

Animals↗
PubMed1990

Mechanical evaluation of external fixators used in limb lengthening.

Four external fixator systems (five configurations) used for limb lengthening were tested to determine the fixator stiffness and the fracture gap rigidity. There was a statistical difference between fixators in all modes of loading with respect to stiffness, shear, and axial motion. The fixators were graded to determine their relative stiffness, shear rigidity, and axial rigidity. The EBI Orthofix proved to be the most rigid fixator relative to the configurations tested with minimal shear or axial motion at the fracture site. The Ilizarov tibial configuration was the least rigid, demonstrating more shear and axial motion at the fracture gap. The Ilizarov femoral system combined excellent stability and shear resistance with preservation of axial dynamization. Fixators with a high stiffness provide less motion at the fracture site, which may cause stress shielding of the osteotomy. Fixators that provide more motion at the fracture gap are less stable. These data may be useful in determining which fixator may be ideal for a particular clinical situation.

Biomechanical Phenomena↗
PubMed1989

A biomechanical analysis of the Ilizarov external fixator.

Five configurations of the Ilizarov fixator were analyzed in vitro. The overall stiffness, shear stiffness, and axial motion of the fracture site were determined. The data were compared with the results of eight conventional one-half frame fixators previously tested in the same manner. The Ilizarov fixator allowed significantly more axial motion at the fracture site during axial compression than the other fixators tested. The overall stiffness and shear rigidity of the Ilizarov external fixator were similar to those of the one-half pin fixators in bending and torsion. The stability of the Ilizarov fixator was a function of bone position within the fixator rings and fixation wire tension. The use of olive stop wires increased the shear resistance of the Ilizarov system.

Biomechanical Phenomena↗
PubMed1984

Determination of 25-hydroxyvitamin D3 in serum by high performance liquid chromatography and isotope dilution-mass spectrometry.

Four different HPLC methods for analysis of 25-hydroxyvitamin D3 in serum were evaluated with a method based on isotope dilution-mass spectrometry (ID-MS). Method I utilized Sephadex LH-20 chromatography as the only prepurification step. No correlation with the ID-MS method was obtained. Method II utilized Sephadex LH-20 chromatography and a subsequent reversed phase HPLC step as prepurification. The correlation coefficient was 0.99 (regression coefficient 1.2 and intercept - 3.9 micrograms/l). Method III included open silicic acid chromatography and straight phase HPLC as prepurification. The correlation when compared with the ID-MS method was 0.94 (regression coefficient 1.2 and intercept - 0.4 micrograms/l). In method IV Sep-pak C18 chromatography and open silicic acid chromatography were used as prepurification. The correlation coefficient when compared with the ID-MS method was 0.97 (regression coefficient 0.8 and intercept 0.1 microgram/l). It is concluded that a single Sephadex LH-20 step is not sufficient as prepurification and that method IV had an accuracy sufficient for its intended use to analyse 25-hydroxyvitamin D3 in serum from cattle.

Calcifediol↗
PubMed1983

Bovine viral diarrhea virus: purification of surface proteins in detergent-containing buffers by fast protein liquid chromatography.

Bovine viral diarrhea virus was purified by lectin chromatography. The glycoprotein peplomers were dissociated from the virion by treatment with detergent. By a second lectin gel chromatography the glycoconjugates containing terminal galactose were prepared. In combination with lectin affinity chromatography, ion-exchange chromatography on Mono-Q in the presence of the low-UV-absorbing detergent Berol 172 proved to be a powerful technique both for analytical and preparative applications.

Chromatography, Affinity↗
PubMed1982

Purification and partial characterization of an agglutinin from Phaseolus coccineus var. 'alubia'.

An agglutination from seeds of 'alubia', a Mexican strain of Phaseolus coccineus, has been purified by affinity chromatography using physically entrapped stroma. The protein appears to be homogeneous by electrophoresis, molecular sieve chromatography and ultracentrifugation. A molecular species of approx. Mr 112,000, with S values of 6.25, 4.52, 4.63 and 4.65 at pH 2.5, 4.5, 7.0 and 9.5, respectively, consisting of four similar subunits (28 kDa), and containing 20% W/W glucosamine, is found to be responsible for the hemagglutinating capacity of 'alubia' extracts. No sugar able to inhibit agglutination has been found. The possibility that hemagglutination by Ph. coccineus var. 'alubia' involves cell receptors other than simple carbohydrate structures must therefore be considered.

ABO Blood-Group System↗
PubMed1982

Prevention of parturient hypocalcemia: effect of a single oral dose of 1,25-dihydroxyvitamin D3.

Norwegian Red cows 4 yr or older were fed a high calcium diet the last 2 to 4 wk before calving to increase the severity of hypocalcemia at parturition. An oral dose of pellets of fat-encapsulated 1,25-dihydroxyvitamin D3 (500 micrograms) was given to 15 cows and placebo pellets to 12 cows. Treated cows were grouped according to time of treatment, 1) 4 cows treated within 24 h of calving, 2) 8 cows treated 1 to 3 days before, and 3) 3 cows treated 4 to 5 days before calving. Minerals in blood plasma were measured from day -10 to day +10 (calving: day 0). Average calcium concentration of cows treated 1 to 3 days before calving decreased from 2.6 to 2.4 and of placebo treated from 2.5 to 1.8 mmol/liter from day -1 to day +1. Treatment with 1,25-dihydroxyvitamin D3 at other times did not protect against hypocalcemia. Average concentrations of 1,25-dihydroxyvitamin D in plasma were 200 to 250 pg/ml on days -2 and -1 in 5 cows treated on days -3 and -2. Similar concentrations were reached by placebo cows 1 to 2 days after parturition. A single oral dose of 500 micrograms 1,25-dihydroxyvitamin D3 given 1 to 3 days before parturition can prevent hypocalcemia at calving. Difficulties in judging actual time for parturition led to optimal treatment of only 8 of 15 cows.

Administration, Oral↗
PubMed1982

Skiing and spinal trauma.

Spinal injury in skiers can either be acute or chronic. Acute spinal injury accounts for 3 to 3.6 per cent of all injuries occurring in Alpine skiing. Fewer acute injuries occur in cross-country skiing, and those that do usually are the result of a sudden, compressive force from a seated fall. The prevalence of chronic spinal trauma in skiing is unknown. Both cross-country and Alpine skiers appear to have greater complaints of mild to moderate low back pain as compared with their nonskiing counterparts. These differences may be the result of a complex interaction between recreational and occupational activities. Theoretical analyses suggest a risk for low-grade torsional injury to the Alpine skier's spine, whereas in cross-country skiing significant shear forces are applied to lumbar discs during the kick but not the double-poling phase.

Acute Disease↗
PubMed1981

Bovine viral diarrhea virus: affinity chromatography on Crotalaria juncea lectin.

Attempts were made to purify bovine viral diarrhea virus by chromatography on Crotalaria juncea lectin coupled to Sepharose 2B. A recovery of abut 65% of viral infectivity after desorption was obtained. Electron microscopy revealed mostly de-enveloped particles, rather uniform in appearance but differing in size. Immunodiffusion tests with immune calf sera showed precipitation lines of identity between the desorbed virus and extracts from infected cell cultures.

Antigens, Viral↗
PubMed1980

Medium conditioned for 24 hours by mononuclear human blood cells contains an inducer of granulopoiesis lacking colony stimulating activity.

Regulation of granulocyte and macrophage formation was studied by a modified CFU-C assay. Mouse bone marrow cells were cultured in methylcellulose in vitro. After colony counting on d 7, the cells were washed out to determine the total cell number per plate, and the distribution of granulocytes and macrophages in smears. By this procedure it was possible to study pathway-specific regulators. The colony stimulating factor in medium conditioned by mouse L-cells appeared specific for the macrophage cell line; 99% of the colony cells were macrophages. Medium conditioned for 24 h by mononuclear cells from human blood, had no colony forming capacity, but increased colony size and generated significant granulocyte production when combined with L-CSF. This granulopoiesis inducing factor was thermo-labile, and was mostly retained by an Amicon filter separating molecules at 100 000 daltons.

Animals↗
PubMed1979

Hydrophobicity of lectins. I. The hydrophobic character of concanavalin A.

The hydrophobicity of Concanavalin A has been estimated by its tendency to adsorb to hydrophobic adsorbents. Experiments varying temperature, salt concentration and hydrophobicity of the absorbent were consistent with accepted criteria of hydrophobic interaction between biomolecules and hydrophobic ligands. The biological significance of the hydrophobic character of Concanavalin A is also discussed.

Adsorption↗
PubMed1979

Assay of 1,25-dihydroxy vitamin D3 by isotope dilution--mass fragmentography.

We describe a specific assay of 1,25-dihydroxy vitamin D3 in human serum, based on isotope dilution-mass fragmentography. We added [26-2H3]-1,25-dihydroxy vitamin D3 to a fixed amount of serum. The steroids were extracted with chloroform/methanol and purified by liquid chromatography. The purified materal was converted into the trimethylsilyl ether and analyzed. Unlabeled 1,25-dihydroxy vitamin D3 was quantitated from the ratio between the tracings at m/e 452 and 455. The two ions used correspond to loss of two trimethylsilyloxo functions from the molecular ion. Essentially the same results, with some problems of interference, were obtained when we used the more intense ions at m/e 131 and 134 (corresponding to cleavage between C-24 and C-25). The detection limit was about 5 ng/L of serum; the coefficient of variation was about 6%. The accuracy of the method was assessed by recovery experiments. 1,25-Dihydroxy vitamin D3 in sera from 15 healthy subjects was found to average 55 +/- 10 ng/L(+/- SD). We believe this represents the first determination of 1,25-dihydroxy vitamin D3 in serum by use of a method not based on radioimmunoassay or receptor assay. Slightly lower values have been reported by those latter techniques.

Chromatography, High Pressure Liquid↗