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Biomedical subjects

D A Christensen

Publications and source records attributed to D A Christensen.

At least 55 records · Page 3Linked to original sources
PubMed1988

Trypsin inhibitors and nutritive value in cereals.

Chemical assays demonstrated that rye and barley cultivars contained relatively high levels of trypsin inhibitor activity as compared to oat and wheat cultivars, and there was a low degree of stability to prolonged wet treatment. In feeding trials with broiler chicks, incorporation of 67% raw barley or 50% raw rye in the rations enhanced feed intake and weight gains, and the marginal increases in pancreas weight were not reversed by feeding autoclaved cereals. Raw rye cultivars fed at the 75% level in mouse diets reduced weight gains, feed efficiency, protein digestibility, protein efficiency ratio and biological value. Autoclaving to inactivate trypsin inhibitors, or ether extraction to remove the resorcinols, failed to improve the nutritive value of rye diets for mice. It appeared that the protease inhibitors in the four cereals were relatively weak inhibitors of trypsin in the digestive system despite stability to dry heat and acid pH.

Animals↗
PubMed1986

Influence of age and breed of equid on plasma copper and zinc concentrations.

Plasma ceruloplasmin activities and plasma Cu and Zn concentrations were determined in 215 clinically normal equids of various ages and breeds. Newborn foals, regardless of breed, were hypocupremic, compared with adolescent and mature horses. The mean plasma Cu concentration of newborn Standardbred-Thoroughbred (STD-TB) foals was 2.9 mumol/L, which was about one-sixth of plasma Cu concentrations of mature horses. Newborn draft-cross foals had higher (4.6 mumol/L) plasma Cu concentrations than did newborn STD-TB foals, but plasma Cu content was only one-fifth of the dams' concentrations. Draft-cross horses, regardless of age, had plasma Cu concentrations 15% to 40% higher than did STD-TB horses. Plasma Cu concentrations of Quarter Horse yearlings were similar to those in draft-cross yearlings. Plasma ceruloplasmin activities revealed a curvilinear relationship to plasma Cu concentrations. Plasma Zn concentrations of newborn and 1-week-old STD-TB foals were 30% to 80% higher than those for yearling and mature STD-TB horses. There were no differences between draft-cross neonates and their dams in plasma Zn concentration. Plasma Zn concentrations of neonatal and mature draft-cross horses were 22% higher than those obtained for all other equids. Age and breed of equid should be a consideration in interpretations of plasma Cu and Zn concentrations in equids.

Age Factors↗
PubMed1985

Variability of heating patterns in animals by magnetic induction hyperthermia.

In a test of electromagnetic induction hyperthermia to deep viscera of a live dog model, we found that heating was not uniform to any depth, but was quite variable. In general, there was a thermal gradient between peripheral and central portions of the transposed spleen of about 1 degree C. Though heat generation within the abdomen was not uniform, its temperature pattern in the alive animal resulted in significant heating of that part of the organ that had been surgically placed at the center of the animal. This heating could not be explained by perfusion with regionally heated core blood. Our results indicate that extensive investigations in living systems and complex dynamic phantoms will be necessary before individual patient response can be predicted.

Abdomen↗
PubMed1985

Zinc levels of hospitalized elderly.

Zinc status was evaluated in 99 consecutive elderly patients admitted to a geriatric assessment unit. The assessment of zinc status was based on measurement of plasma, erythrocyte, and urinary zinc levels by atomic absorption spectrophotometry; serum lactic dehydrogenase and alkaline phosphatase by standard laboratory methods; and dietary intake by the food frequency questionnaire method. Mean (+/- standard deviation) plasma zinc concentration was 72 +/- 16 micrograms/100 ml (N = 91). Although 67% of the group had plasma zinc levels in the deficient range, only three patients had values below the normal range for erythrocyte zinc and none fell below the reference range for urinary zinc per 24 hours (N = 15) or the urinary zinc:creatinine ratio. Mean values for the other parameters of zinc status were 1.27 +/- 0.26 micrograms/10(9) RBC for erythrocyte zinc, 285 +/- 217 micrograms/24 hours for urinary zinc, and 588 +/- 309 micrograms/gm for the urinary zinc:creatinine ratio. Serum alkaline phosphatase and lactic dehydrogenase were not specific indicators of zinc status. Forty-six percent had adequate and 54% inadequate dietary intakes (N = 46). Twenty percent were receiving an inadequate intake of meat products, suggesting that the majority (80%) were ingesting an adequate supply of zinc-rich foods. Zinc status appeared to be adequate in this population.

Aged↗
PubMed1985

The effect of cow's dietary copper intake, sire breed, age on her copper status and that of her fetus in the first ninety days of gestation.

The liver copper concentration of the bovine fetus and the hepatic and plasma copper concentrations of its dam during the first trimester of pregnancy were studied. The effect of the dam's dietary copper intake, age, sire breed and stage of pregnancy on her copper status and that of her fetus was also investigated. Simmental sired heifers had the lowest plasma copper concentration. The younger cows (two, three and four years) had significantly lower liver copper concentration than the older cows (six and seven years). The bovine fetal liver copper concentration was approximately 3.1 mmol/g DM and was not affected by dam's age, breed, stage of pregnancy, or copper status.

Animal Feed↗
PubMed1984

Calculated power absorption patterns for hyperthermia applicators consisting of electric dipole arrays.

We have applied the plane-wave spectrum method to obtain a technique for calculating the internal fields in a lossy dielectric half-space irradiated by rather arbitrary sources. We used the technique to calculate power absorption profiles of some idealized aperture sources to gain insight into how the source parameters affect the power absorption profile. With this insight, we next calculated power absorption profiles of some linear electric dipole antenna arrays. From these results we developed a simpler method of optimizing the antenna parameters by calculating their field pattern in an infinite water medium, which does not require the PWS method and is therefore faster and cheaper. Using this technique, we found an antenna array with reasonably practical parameters that produces an appealing calculated power absorption profile. We also made some calculations based on a simple approximate model that indicate that a three-element dipole array on the front of a patient and a similar one on the back could produce deep central heating. Although our calculations are based on a somewhat crude dielectric half-space model of the body, the results provide valuable insight about power absorption profiles and indicate that practical systems for producing deep internal heating without overheating the surface of the body could be developed.

Absorption↗
PubMed1983

Power deposition patterns in magnetically-induced hyperthermia: a two-dimensional low-frequency numerical analysis.

The electric fields and power deposition patterns generated in two-dimensional inhomogenous models exposed to the axially directed uniform magnetic fields of an infinitely long solenoid are calculated numerically. The fields are calculated using the method of moments (Galerkin procedure) with linear basis and weighting functions. This low-frequency analysis is useful for studying the power deposition patterns attributable to solenoidal inductive applicators operated at frequencies up to 13.56 MHz. For the models we have studied, the ratio of power per volume deposited into the tumor to power per volume deposited into the immediately surrounding tissue is largest for tumors in the lung, although the power per volume deposited into the outermost layer is still much larger than the power per volume deposited into the tumor; it may be possible, however, to cool this region adequately from the body surface. When the complex permittivity of the tumor model is similar to that of the region in which it is embedded, the currents in the torso and tumor circulate primarily around the center of the body, as has been previously calculated for concentric cylinders. When the complex permittivity of the tumor is much greater than the region in which it is embedded, the currents in the tumor circulate primarily around the center of the tumor.

Diathermy↗
PubMed1981

The effect of insulin on net metabolism of glucose and amino acids by the bovine mammary gland.

Previous work has shown that insulin is necessary for lactation. In this study, the short term effects of insulin on the net metabolism of glucose and amino acids by the bovine mammary gland were examined in six experiments in lactating cows. To prevent insulin-induced hypoglycemia from masking the direct effects of insulin, glucose (50--75 g/h) was infused with insulin 12 U/h). The insulin plus glucose infusion (2 h) was followed by a 2-h infusion of glucose alone (75 g/h). Throughout the control and infusion periods, arterial and mammary venous blood samples were obtained to measure venoarterial concentration differences of glucose and amino acids across the mammary gland. During the insulin plus glucose infusion, insulin concentrations increased from basal values of 9 +/- 1 to 38 +/- 6 mu U/ml (mean +/- SE). During glucose infusion alone, the insulin concentration was 15 +/- 2 mu U/ml. Glucagon concentrations were not significantly altered by the treatments. The extraction of glucose by the mammary gland was not altered significantly by insulin, nor was the extraction altered during the infusion of glucose alone. During the infusion of insulin plus glucose and glucose alone, the extraction ratios [(A -- V)/A] of isoleucine, leucine, tyrosine, aspartate, and valine were increased 10--20%. Thus, it appears that insulin does not influence glucose extraction and only moderately may enhance the extraction of some amino acids by the bovine mammary gland.

Amino Acids↗
PubMed1981

Trace mineral deficiencies in cattle: a review.

This review discusses the biological role of copper, zinc and selenium in ruminant nutrition. Soil, climate, plant and animal interactions are discussed in relationship to trace mineral availability. A review of the clinical symptoms associated with copper, zinc and selenium deficiences are also presented.

Animal Feed↗
PubMed1979

Thermal dosimetry and temperature measurements.

A crucial ingredient of any hyperthermia procedure is the accurate measurement of achieved temperature. In this paper, we present some accuracy and resolution suggestions and address the problem of temperature measurements when electromagnetic energy is used as the mode of heating. In such cases, conventional metallic thermometers can cause severe errors due to reradiated fields, high internal healing, and electronic interference. To avoid these problems, several groups have developed either high-resistance lead thermometers or optical-fiber probes using a variety of sensors, including birefringent and semiconductor crystals. A new noninvasive approach uses ultrasound-computed tomography and relies upon the change in the speed of sound versus temperature to achieve maps of internal tissue temperature.

Electromagnetic Fields↗
PubMed1976

Rapeseed meal in complete feeds for dairy cows.

Three complete feeds containing low glucosinolate, low erucic acid rapeseed meal (Cultivar "1788"), high glucosinolate, low erucic acid rapeseed meal (Cultivar "Span"), or soybean meal as protein supplement were evaluated with lactating Holstein cows in a double 3 X 3 Latin square design. Lactation performance, hematology, blood chemistry, serum-free amino acids, rumen volatile fatty acid concentrations, and milk fatty acid composition were measured. The 1788 ration tended to increase yield of milk and of total solids. Hematology, blood chemistry, and serum-free amino acid data showed no differencein utilization of nitrogen. Concentrations of volatile fatty acids were not different. Feeding of the high glucosinolate Span ration did not reduce feed intake. However, there were indications that Span-fed cows may have experienced hypothyroidism. No differences were in erucic acid content of milk fat, and concentrations were low. Rapeseed meals 1788 and Span and soybean meal were equal as protein supplements.

Amino Acids↗