Biomedical subjects

D A Christensen

Publications and source records attributed to D A Christensen.

At least 19 recordsLinked to original sources

PubMed2001

Calculation of electric fields induced in the human knee by a coil applicator.

Calculations are presented of the induced electric fields and current densities in the cartilage of the knee produced by a coil applicator developed for applying pulsed magnetic fields to osteoarthritic knees. This applicator produces a sawtooth-like magnetic field waveform composed of a series of 260-micros pulses with a peak to peak magnitude of approximately 0.12 mT in the cartilage region. The simulations were performed using a recently developed 3 dimensional finite difference frequency domain technique for solving Maxwell's equations with an equivalent circuit model. The tissue model was obtained from the anatomically segmented human body model of Gandhi. The temporal peak electric field magnitude was found to be -153 mV/m, averaged within the medial cartilage of the knee for the typical dB/dt excitation levels of this coil. The technique can be extended to analyze other excitation waveforms and applicator designs.

Bone and Bones↗

PubMed2001

Manipulation of cattle growth to target carcass quality.

Two trials were conducted to determine the effects of breed type, backgrounding program, and backfat end point (USBFEP) as determined by ultrasound on the performance and carcass characteristics of feedlot steers. Trial 1 utilized 144 large-framed Charolais- (304.6 +/- 16.3 kg) and 144 medium-framed Hereford-cross steers (294.8 +/- 20.9 kg). Trial 2 utilized 88 medium-framed Angus (289.5 +/- 15.0 kg), 88 large-framed Charolais- (299.8 +/- 17.7 kg), and 88 medium-framed Hereford-cross (291.1 +/- 20.9 kg) steers. Within breed type, short- (70 d) or long-term (126 d) backgrounding programs (Trial 1) and 6- or 12-mm USBFEP (Trials 1 and 2) were assigned. In both trials, carcass size was greater (P < 0.05) for the large-framed Charolais-cross steers, longer backgrounding, and fatter USBFEP treatments. Lean meat yield was greater (P < 0.05) for Charolais- than Hereford-cross steers (Trial 1) and for the leaner USBFEP (Trials 1 and 2). Marbling was greater (P < 0.05) for Angus- (Trial 2) and Charolais- (Trials 1 and 2) than Hereford-cross steers (Trials 1 and 2) and for the fatter end point (Trials 1 and 2). It was concluded that breed type, backgrounding program, and USBFEP were effective in altering growth and could be used to target carcass traits of interest for value-based marketing programs.

Animal Husbandry↗

PubMed2001

Evaluation of the 1996 NRC beef model under western Canadian environmental conditions.

Two feedlot trials were conducted to evaluate the 1996 NRC beef model under western Canadian conditions. In the first trial, 144 Charolais- (304.6 +/- 16.3 kg) and 144 Hereford- (295.1 +/- 20.8 kg) cross steers were used, whereas the second trial used 88 Angus- (289.7 +/- 15.0 kg), 88 Charolais- (299.8 +/- 17.9 kg), and 88 Hereford- (291.1 +/- 20.9 kg) cross steers. Diets were based on barley silage, rolled barley grain, canola meal, and cereal straw and were analyzed according to the 1996 NRC methodologies. Animal performance and environmental data were collected for 24 pens of steers per trial for the backgrounding and finishing periods. Levels 1 and 2 of the 1996 NRC model were used to generate predictions of DMI and ADG for each pen. Results showed that actual finishing DMI was accurately predicted for Trial 1 and for the combined trials but not for Trial 2. Predicted ADG was lower (P < 0.05) than actual ADG for all feeding periods except Level 1 of the Trial 1 finishing period. All ADG residuals were significant (P < 0.05), indicating inaccurate prediction of ADG in all feeding periods. The 1996 NRC model consistently predicted that protein was not limiting gain. Further investigations and model refinement regarding animal energy requirements under cold weather conditions and effects of limit feeding are required to increase the accuracy of the 1996 NRC model in predicting animal performance.

Animal Feed↗

PubMed2000

Factors affecting acoustically triggered release of drugs from polymeric micelles.

A custom ultrasonic exposure chamber with real-time fluorescence detection was used to measure acoustically-triggered drug release from Pluronic P-105 micelles under continuous wave (CW) or pulsed ultrasound in the frequency range of 20 to 90 kHz. The measurements were based on the decrease in fluorescence intensity when drug was transferred from the micelle core to the aqueous environment. Two fluorescent drugs were used: doxorubicin (DOX) and its paramagnetic analogue, ruboxyl (Rb). Pluronic P-105 at various concentrations in aqueous solutions was used as a micelle-forming polymer. Drug release was most efficient at 20-kHz ultrasound and dropped with increasing ultrasonic frequency despite much higher power densities. These data suggest an important role of transient cavitation in drug release. The release of DOX was higher than that of Rb due to stronger interaction and deeper insertion of Rb into the core of the micelles. Drug release was higher at lower Pluronic concentrations, which presumably resulted from higher local drug concentrations in the core of Pluronic micelles when the number of micelles was low. At constant frequency, drug release increased with increasing power density. At constant power density and for pulse duration longer than 0.1 s, peak release under pulsed ultrasound was the same as stationary release under CW ultrasound. Released drug was quickly re-encapsulated between the pulses of ultrasound, which suggests that upon leaving the sonicated volume, the non-extravasated and non-internalized drug would circulate in the encapsulated form, thus preventing unwanted drug interactions with normal tissues.

Antibiotics, Antineoplastic↗

PubMed2000

Influence of particle size on the effectiveness of the fiber in barley silage.

We used eight multiparous Holstein cows in a 4 x 4 Latin square design to evaluate the effects and possible interactions between silage particle size and concentrate level on chewing activities and productivity of cows fed barley-based total mixed rations (TMR). Diets were designed with two forage-to-concentrate ratios (low forage, 45:55, high forage 55:45), combined with two theoretical chop lengths of barley silage (short = 4.68 mm and long = 18.75 mm). Diets were formulated to provide similar and above-minimum neutral detergent fiber recommended for cows in early lactation. Increasing silage particle size of the forage did not affect dry matter intake. The 3.5% fat-correct milk and fat yields trended higher for increased particle size. Percent milk protein was higher for short particle size. Increasing the concentrate levels in the diets increased proportions of milk protein and lactose, but not milk fat. Cows fed short silage spent 90 min less per day chewing and ruminating than did those on long silage. Total chewing activity per kilogram of forage intake was higher for cows on long silage compared with those on short silage diets. Although a reduction in silage particle size did not depress milk fat, rumination and chewing activity were significantly reduced. These results suggest that particle size of the silage may have dominant control over chewing activity despite adequate neutral detergent fiber intakes.

Animal Feed↗

PubMed2000

Effects of pea, barley, and alfalfa silage on ruminal nutrient degradability and performance of dairy cows.

Six Holstein cows in early lactation were used in a double 3 x 3 Latin square design to determine the effects of feeding diets with pea silage, relative to barley silage, or alfalfa silage. Cows were fed rations formulated to contain 50:50 forage:concentrate ratio. Two ruminally fistulated cows were used in a randomized complete block design to determine ruminal nutrient degradability for pea silage relative to barley and alfalfa silages. Pea silage contained lower neutral detergent fiber (NDF), acid detergent fiber, and starch concentrations but higher crude protein than barley silage. Compared with alfalfa silage, pea silage had higher starch and NDF but lower crude protein content. Pea and alfalfa silage had similar effective ruminal degradability of dry matter, which was higher than that of barley silage. The rate of degradation and effective ruminal degradability of NDF was highest for alfalfa silage, intermediate for pea silage and lowest for barley silage. Results of the lactation trial showed that dry matter intake and milk yield were not affected by forage source. Milk composition was similar for cows fed pea or barley silage; however, cows fed pea silage produced milk with a higher fat and a lower protein percentage than those fed the alfalfa silage. Pea silage can replace barley or alfalfa silage as a forage source for dairy cows in early lactation.

Animal Nutritional Physiological Phenomena↗

PubMed1999

Multiple-analyte fluoroimmunoassay using an integrated optical waveguide sensor.

A silicon oxynitride integrated optical waveguide was used to evanescently excite fluorescence from a multianalyte sensor surface in a rapid, sandwich immunoassay format. Multiple analyte immunoassay (MAIA) results for two sets of three different analytes, one employing polyclonal and the other monoclonal capture antibodies, were compared with results for identical analytes performed in a single-analyte immunoassay (SAIA) format. The MAIA protocol was applied in both phosphate-buffered saline and simulated serum solutions. Point-to-point correlation values between the MAIA and SAIA results varied widely for the polyclonal antibodies (R2 = 0.42-0.98) and were acceptable for the monoclonal antibodies (R2 = 0.93-0.99). Differences in calculated receptor affinities were also evident with polyclonal antibodies, but not so with monoclonal antibodies. Polyclonal antibody capture layers tended to demonstrate departure from ideal receptor-ligand binding while monoclonal antibodies generally displayed monovalent binding. A third set of three antibodies, specific for three cardiac proteins routinely used to categorize myocardial infarction, were also evaluated with the two assay protocols. MAIA responses, over clinically significant ranges for creatin kinase MB, cardiac troponin I, and myoglobin agreed well with responses generated with SAIA protocols (R2 = 0.97-0.99).

Animals↗

PubMed1999

Pupil-size effects in fiber optic stellar interferometry.

The effects of finite telescope pupil sizes on the measurement of fringe visibility in fiber optic stellar interferometry are described. It is shown theoretically that the measured fringe visibility is equal to the cross correlation of the magnitude of the source's mutual coherence function with the cross correlation of the telescopes' effective pupil functions. If the telescopes' effective pupil diameters are not small compared with the width of the source's mutual coherence function, then the measured fringe visibility will be correspondingly distorted. The theoretical results are verified experimentally in a fiber optic Mach-Zehnder interferometer.

Extraterrestrial Environment↗

PubMed1999

Evaluation of wheat-based thin stillage as a water source for growing and finishing beef cattle.

Two trials were conducted to evaluate the nutritional value of wheat-based thin stillage as a water source for cattle. In Trial 1, 20 large-framed steers were fed a basal diet based primarily on barley grain and barley silage, with ad libitum access to water or thin stillage at one of three DM concentrations (2, 4, and 6.7%) in a completely randomized design. The trial consisted of a 70-d growing period and a finishing phase. In Trial 2, total-tract nutrient digestibility coefficients of the basal diet and water treatments fed in the growing period were determined in a randomized complete block design using 12 medium-framed steers. The results showed that when only DMI from the basal diet was considered, there was a linear reduction (P<.01) in DMI and a linear improvement (P<.01) in the gain:feed ratio with no effect on daily gain as thin stillage DM concentration increased. No differences were detected in DMI or efficiency of gain when total DMI (basal diet and thin stillage) was considered. Carcass traits indicated a trend toward increased (P<.06) carcass fat with increasing thin stillage DM concentration. Results of Trial 2 indicated a linear improvement (P<.05) in apparent digestibility of DM, CP, NDF, and energy of the total diet (basal diet and thin stillage) as thin stillage DM concentration increased. We concluded that supplementing growing and finishing cattle with thin stillage reduced the amount of the basal diet required for gain and improved nutrient utilization.

Animals↗

PubMed1999

Feeding value of wheat-based thin stillage: in vitro protein degradability and effects on ruminal fermentation.

Two experiments were conducted to evaluate the nutritive value of wheat-based thin stillage as a fluid source for ruminants. In vitro CP degradability of thin stillage was estimated relative to canola meal and heated canola meal in a completely randomized design. Four ruminally cannulated steers were used in a double cross-over design to determine the effects of consuming thin stillage or water as drinking sources on ruminal fermentation traits. The in vitro CP degradability of thin stillage (55.4%) was lower (P<.05) than that of canola meal (59.4%) and higher than that of heated canola meal (31.6%). Ruminal pH for steers consuming thin stillage was higher (P<.05) at 1000 and 1100 and lower (P<.05) at 1900 and 2000 than that for steers consuming water. Total VFA followed a pattern that was the reverse of that reported for pH. Ruminal NH3 N levels were higher (P<.05) for steers fed thin stillage than for water-fed steers through most of the collection period. Ruminal fluid and particulate matter passage rates were not affected by treatment and averaged .165 and .06 /h, respectively. The amount of thin stillage and water that did not equilibrate with the ruminal fluid and, thus, was considered to bypass the rumen was estimated to be 51.9 and 59.2% of total fluid consumed, respectively. Feeding wheat-based thin stillage had no adverse effects on ruminal metabolism.

Animals↗

PubMed1997

Calculation of electric fields induced near metal implants by magnetic resonance imaging switched-gradient magnetic fields.

Electric (E) fields induced near metal implants by MRI switched-gradient magnetic fields are calculated by a new equivalent-circuit numerical technique. Induced E-field results are found for a metallic spinal-fusion implant consisting of two thin wires connected to the metallic case of a current generator as well as for its subsections: a bare U-shaped wire, an insulated U-shaped wire, a cut insulated wire, and a generator. The presence of the metallic implants perturbs the E field significantly. Near the ends of the bare U-shaped wire, the E field is 89.7 times larger than in the absence of the wire. The greatest E field concentration occurs near the ends of the cut insulated wire, where the E field is 196.7 times greater than in the absence of the wire. In all cases, the perturbation of the induced E field by the implanted wire is highly localized within a few diameters of the wire.

Bone Wires↗

PubMed1997

Use of real-time ultrasound to evaluate live animal carcass traits in young performance-tested beef bulls.

Young bulls were ultrasonically scanned to 1) study breed differences for 12th rib fat depth (USFAT) and longissimus muscle area (USREA), 2) evaluate the nature and predictability of USFAT and USREA development, and 3) determine the effect of age (YFAT and YREA, respectively) or weight (WREA) adjustments on USFAT and USREA. Angus (AA), Charolais (CH), Hereford (HH), Shorthorn (SS), and Simmental (SM) bulls (n = 886) were studied in 2 yr at two stations. Breed differences were observed for end of test USFAT (AA = SS > HH > CH = SM, P < .05) and USREA (CH = SM > SS = AA > HH, P < .05). Within-breed coefficients of variation were 29.8 to 48.4% for end of test USFAT and from 9.0 to 10.8% for end of test USREA. In most bulls, USFAT development was neither linear nor quadratic (P > .05), but USREA development was linear (P < .05). Prediction equations were characterized by low r2 and high residual standard deviation (RSD) values, although those for d-84 USREA had r2 values from .63 to .70 and RSD values from 4.09 to 5.80 cm2. High associations were obtained between end of test USFAT with YFAT (r = .83 to .91, P < .05) and USREA with YREA (r = .74 to .84, P < .05) but not for end of test USREA with WREA (r = .31 to .56, P < .05). These results indicate that end of test ultrasound measurements may be a useful addition to performance testing programs.

Adipose Tissue↗

PubMed1996

Femtomolar sensitivity using a channel-etched thin film waveguide fluoroimmunosensor.

A dual channel, evanescent fluoroimmunoassay format is used to detect femtomolar analyte concentrations (i.e. less than 1 part per trillion [w/w]) on an etched channel siliconoxynitride thin film integrated optical waveguide. Two assays are used to demonstrate the dose-response behaviour of the sensor: (1) a direct assay of a fluorescently-labeled protein ligand binding to an immobilized protein receptor, and (2) an indirect sandwich assay of a non-fluorescent protein ligand binding to an immobilized protein receptor, as detected by the binding of a fluorescently-labeled secondary receptor protein. A red-emitting cyanine dye (Cy-5), which minimized background fluorescence and scatter losses of the waveguide, was used in both assays. To our knowledge, this is the first report of femtomolar sensitivity in an immunosensing instrument.

Biosensing Techniques↗

PubMed1996

The effects of weak extremely low frequency magnetic fields on calcium/calmodulin interactions.

Mechanisms by which weak electromagnetic fields may affect biological systems are of current interest because of their potential health effects. Lednev has proposed an ion parametric resonance hypothesis (Lednev, 1991, Bioelectromagnetics, 12:71-75), which predicts that when the ac, frequency of a combined dc-ac magnetic field equals the cyclotron frequency of calcium, the affinity of calcium for calcium-binding proteins such as calmodulin will be markedly affected. The present study evaluated Lednev's theory using two independent systems, each sensitive to changes in the affinity of calcium for calmodulin. One of the systems used was the calcium/calmodulin-dependent activation of myosin light chain kinase, a system similar to that previously used by Lednev. The other system monitored optical changes in the binding of a fluorescent peptide to the calcium/calmodulin complex. Each system was exposed to a 20.9 microT static field superimposed on a 20.9 microT sinusoidal field over a narrow frequency range centered at 16 Hz, the cyclotron frequency of the unhydrated calcium ion. In contrast to Lednev's predictions, no significant effect of combined dc-ac magnetic fields on calcium/calmodulin interactions was indicated in either experimental system.

Animals↗

PubMed1995

Structure of the fibre-forming protein pilin at 2.6 A resolution.

The crystallographic structure of Neisseria gonorrhoeae pilin, which assembles into the multifunctional pilus adhesion and virulence factor, reveals an alpha-beta roll fold with a striking 85 A alpha-helical spine and an O-linked disaccharide. Key residues stabilize interactions that allow sequence hypervariability, responsible for pilin's celebrated antigenic variation, within disulphide region beta-strands and connections. Pilin surface shape, hydrophobicity and sequence variation constrain pilus assembly to the packing of flat subunit faces against alpha 1 helices. Helical fibre assembly is postulated to form a core of coiled alpha 1 helices banded by beta-sheet, leaving carbohydrate and hypervariable sequence regions exposed to solvent.

Amino Acid Sequence↗

PubMed1993

The effect of sulphate on thiamine-destroying activity in rumen content cultures in-vitro.

The effect of sulphur on thiamine-destroying activity was studied in native or thiamine-spiked rumen content cultures. The treatments consisted of water [control (Ctrl)], sodium chloride (NaCl) and sodium sulphate (Na2SO4). A net gain (relative to 0 h) of thiamine in native cultures was observed for at least 48 h at levels of S ranging from 0.25 to 8 mg S added per ml of the culture and also in the Ctrl and respective NaCl cultures. However, after 48 h of incubation thiamine concentration was lower (p < 0.05) in native cultures treated with Na2SO4 relative to Ctrl and NaCl treatments. There was a linear (p < 0.03) time trend indicating an effect of Na2SO4 over time on changes in thiamine concentration in native rumen cultures. In thiamine-spiked rumen content cultures, the cultures treated with Na2SO4 produced higher (p < 0.05) thiamine-destroying activity. There was no effect of cation (Na) on thiamine-destroying activity. Initial heat treatment of thiamine-spiked cultures inactivated part of the thiamine-destroying activity. There were no differences among treatments in heat treated cultures. It is concluded that sulphate increases thiamine-destroying activity in the rumen content and the destructive mechanism involves thermolabile factor(s), however, the ruminal synthesis of thiamine is not affected by sulphate.

Animals↗

PubMed1992

Role of thiamine status in sulphur induced polioencephalomalacia in sheep.

The effects of excess dietary sulphur were studied in sheep supplemented and unsupplemented with thiamine. The diets contained either 0.19 per cent sulphur (LS) or 0.63 per cent sulphur (HS) in combinations with 14 mg kg-1 thiamine (LB1) or 243 mg kg-1 thiamine (HB1). A total of 56 two-month-old lambs were used. Groups consisting of nine, nine, 22 and 16 lambs were fed LS-LB1, LS-HB1, HS-LB1 and HS-HB1 diets, respectively for 14 weeks. Out of 22 lambs fed the HS-LB1 diet, seven lambs developed neurological signs between the third and eighth week of the trial. Two of these lambs died, three that were in extremis were euthanased, and two recovered completely. All clinically affected animals had extensive malacic lesions in the cerebral cortex, midbrain and brainstem. None of the lambs from the LS groups or HS-HB1 group developed clinical signs. Several clinically normal lambs from the HS-LB1 group had necrotic lesions in their brains at gross and microscopic examination. Supplementation with dietary thiamine prevented development of clinical signs, but did not totally prevent development of microscopic brain lesions. Brain thiamine concentration, transketolase activity and thiamine pyrophosphate (TPP) effect were not different (P greater than 0.05) among groups. There was a strong effect (P less than 0.0001) of dietary thiamine supplementation on blood thiamine concentration and TPP effect. Blood thiamine concentration was higher whereas TPP effect was lower in the thiamine supplemented sheep. Blood and tissue thiamine concentrations in sheep exposed to high dietary sulphur did not indicate either systemic or local thiamine deficiency per se. Increased TPP effect in sheep fed the HS-LB1 diet indicated mild to moderate metabolic thiamine deficiency. Thiamine inadequacy may be an effect of an increased requirement for thiamine in animals exposed to excess dietary sulphur.

Animals↗

PubMed1991

The effects of thiamine and EDTA on biliary and urinary lead excretion in sheep.

Relative efficacy of thiamine (B1) and/or calcium disodium ethylinediaminetetraacetate (EDTA) administration on lead (Pb) excretion via bile and urine was studied in Pb-loaded sheep. The sheep were administered B1 s.c., 75 mg/kg body wt., EDTA i.v., 110 mg/kg body wt., and a combination of B1-EDTA at rates as above. Each treatment was followed by 69 h sampling of blood, bile, and urine. Urinary Pb excretion increased following B1-EDTA greater than EDTA greater than B1 administration. Thiamine and B1-EDTA treatments increased biliary Pb excretion. Overall, B1, EDTA and B1-EDTA administration increased Pb excretion via bile and urine by 72%, 595%, and 842% respectively over basal level (mean +/- SE: 20.1 +/- 2.9 micrograms Pb/h). It has been concluded that thiamine enhances elimination of Pb from the body and this feature may be beneficial in chelation therapy.

Animals↗