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Biomedical subjects

S A Nielsen

Publications and source records attributed to S A Nielsen.

At least 19 recordsLinked to original sources
PubMed2002

A multi-domain Chebyshev collocation method for predicting ultrasonic field parameters in complex material geometries.

The use of ultrasound to measure elastic field parameters as well as to detect cracks in solid materials has received much attention, and new important applications have been developed recently, e.g., the use of laser generated ultrasound in non-destructive evaluation (NDE). To model such applications requires a realistic calculation of field parameters in complex geometries with discontinuous, layered materials. In this paper we present an approach for solving the elastic wave equation in complex geometries with discontinuous layered materials. The approach is based on a pseudospectral elastodynamic formulation, giving a direct solution of the time-domain elastodynamic equations. A typical calculation is performed by decomposing the global computational domain into a number of subdomains. Every subdomain is then mapped on a unit square using transfinite blending functions and spatial derivatives are calculated efficiently by a Chebyshev collocation scheme. This enables that the elastodynamic equations can be solved within spectral accuracy, and furthermore, complex interfaces can be approximated smoothly, hence avoiding staircasing. A global solution is constructed from the local solutions by means of characteristic variables. Finally, the global solution is advanced in time using a fourth order Runge-Kutta scheme. Examples of field prediction in discontinuous solids with complex geometries are given and related to ultrasonic NDE.

Journal Article↗
PubMed1992

Absorption of wheat starch in patients resected for left-sided colonic cancer.

Bacterial fermentation of carbohydrate in the colon, producing short-chain fatty acids (SCFA)--and especially butyrate--has been shown possibly to impede cell proliferation and regulate cell differentiation of colonocytes. In patients with diverticular disease or benign polyps in the colon a hyperabsorption of potato starch in the small intestine has been found. We have investigated the absorption of wheat starch in 15 patients radically resected for cancer in the descending or sigmoid colon, and the results were compared with those of 15 healthy controls. The starch malabsorption was quantified by the hydrogen breath test. The patients malabsorbed 2-14 g (median, 8 g) of 100 g wheat starch ingested, and the control group malabsorbed 3-11 g (median, 6 g) (P greater than 0.1). Mouth-to-cecum transit time for wheat starch and lactulose and the hydrogen production capacity after the lactulose standards were also similar in patients and controls. The results do not support the theory that hyperabsorption of starch is characteristic of patients with malignant disease in the large intestine.

Adult↗
PubMed1991

Studies on the possible role of cattle nuisance flies, especially Hydrotaea irritans, in the transmission of summer mastitis in Denmark.

The summer mastitis pathogens Actinomyces pyogenes, Peptococcus indolicus, Bacteroides melaninogenicus ss. levii, Fusobacterium necrophorum and Streptococcus dysgalactiae were isolated from the polyphagous symbovine dipterans Hydrotaea irritans (Fallén) and Morellia sp. caught around dairy heifers on pasture, but not from the haematophagous species Haematobia irritans (L.), Haematobosca stimulans (Meigen), Culicoides sp. and Simulium sp. Secretions from clinical cases of summer mastitis proved to be sources of summer mastitis bacteria for more than 3 weeks despite antibiotic treatment and teat amputation. Taking into account the seasonal activity pattern of Hydrotaea irritans and its topographical distribution on grazing cattle, it appears evident that this fly may play a central role in the establishment and maintenance of the bacterial contamination with summer mastitis pathogens on the teats of healthy cattle. In the present study the survival of A.pyogenes and P.indolicus for 7 days in experimentally infected Hydrotaea irritans, as demonstrated by the recovery of these microorganisms from agar plates exposed to live infected flies, is described. However, experimental transmission of summer mastitis from sick to healthy heifers by Hydrotaea irritans proved unsuccessful.

Actinomyces↗
PubMed1988

Short-term prophylaxis with cefotaxime in colorectal surgery. A prospective, randomized trial.

In a controlled, randomized study the effect of penicillin and streptomycin on postoperative septic complications in colorectal surgery (penicillin, 2 ml, IU, intramuscularly, three times daily for a period of six days and concomitantly streptomycin, 0.5 gm, intramuscularly, two times daily for a period of four days) was compared with the effect of cefotaxime, 2 gm, intravenously, three times on the day of surgery. One hundred patients completed the study: 48 were treated with penicillin and streptomycin (Group 1) and 52 with cefotaxime (Group 2). Wound infection occurred in one patient (2.1 percent) in Group 1, but not in Group 2 (0%, N.S.). Rupture of the wound occurred in one patient in each group (2.1 percent vs. 1.9 percent, N.S.). Insufficiency of the anastomosis occurred in four patients in Group 1 (8.3 percent) and in one patient in Group 2 (1.9 percent). It is concluded that short-term prophylaxis with cefotaxime is as effective as long-term prophylaxis with penicillin and streptomycin.

Adult↗
PubMed1985

The effects of a glycine antagonist (strychnine) on cortically induced rhythmical jaw movements in the anesthetized guinea pig.

We have investigated the effects of systemic administration of a glycine antagonist, strychnine, on rhythmical jaw movements (RJMs) induced by repetitive stimulation of the masticatory area of the guinea pig cerebral cortex. It was found that after strychnine administration (0.4 mg/kg), the frequency of the cortically induced RJMs was minimally affected, whereas the burst durations of the digastric EMG during the jaw opening phase of the RJM cycle were dramatically increased. These data suggest that the neuronal network (central pattern generator (CPG)) which is responsible for the production of rhythmical jaw movements is not critically dependent upon glycine for the genesis of the basic oscillatory rhythm. On the other hand, glycine synapses are involved with the neuronal mechanisms which are responsible for controlling the burst durations of the digastric muscle during the jaw opening phase of each rhythmic jaw movement cycle.

Animals↗
PubMed1978

Gastric ulcer in old age.

One hundred and eleven (16%) of 701 patients with gastric ulcers, admitted to Kommunehospitalet, Copenhagen, from 1955 to 1964, were 70 years of age of older. Of those elderly patients, 43 were treated surgically, 68 non-surgically. The incidences of hemorrhage and extragastric diseases were significantly greater in older patients, whereas the incidence of pain, site of pain, ulcer size, and location, incidence of combined ulcers and gastric retention did not differ from those observed in younger patients. The duration of symptoms was shorter in the aged, though the difference was not significant. Prognosis was less favourable in the aged, largely due to a higher incidence of hemorrhage (47%) and of accessory diseases (47%). The mortality in elderly patients suffering from hemorrhage and accessory diseases was 64% during hospitalization, but only 4% in patients without accessory diseases. Follow-up and autopsy studies of discharged patients revealed that ulcers healed in only half of the non-surgical patients and that surgery was ultimately necessary in 50% of these. It was concluded that the factors which prescribed surgical treatment in elderly patients with gastric ulcers did not differ considerably from those in younger patients. The risk was greater, but this was also true in non-surgical treatment. Close cooperation between surgeon and physician was essential, both pre- and postoperatively, since accessory diseases were very significant for the outcome.

Age Factors↗
PubMed1977

The diagnosis of pancreatic cyst by endoscopic retrograde pancreatography and ultrasonic scanning.

Fourteen patients with verified pancreatic cysts were examined by both preoperative endoscopic retrograde pancreatography (ERP) and ultrasonic scanning. ERP showed filling of a cyst in 4 patients and raised suspicion of a cyst in 8. In two patients it was not possible to visualize the pancreatic duct. Ultrasonic scanning showed a cyst in 12 patients. There were two false negative ultrasonic diagnoses. These two were correctly diagnosed by ERP. Ultrasonically guided percutaneous puncture was carried out on 19 occasions in 8 patients. Cysts down to 2 cm in diameter were punctured without difficulty. There were no clinically significant complications due to the punctures. One patient was followed for 20 months without ultrasonically demonstrable recurrence of a large cyst aspirated, showing that definite therapy is possible by this method. Puncture can be used to verify the diagnosis and as treatment in patients where surgery is contraindicated.

Diagnosis, Differential↗
PubMed1975

Causes of death in patients with gastric ulcers.

Of 701 patients with gastric ulcers admitted to hospital within the period 1955-64, 180 died within a five-year period calculated from the time of admission. Causes of death were established at autopsy in 66%, and otherwise were derived from death certificates. The mortality in our series is grouped after the sex and age of the patients, and the causes of death are compared with the corresponding sex and age groups of the Copenhagen population. Mortality was significantly higher than expected in both men and women, particularly high in the first year after actual admission, but falling thereafter to about the same level as the expected mortality. Gastric ulcer itself was the most usual cause of death, but other disease was also significant. Thus mortality from suicide was significantly higher than expected in women. That there is a relationship between operation and suicide seems unlikely--all concerned had psychiatric histories. In men, pulmonary disease involved a significantly higher mortality than expected, and some connection between ulcer disease and pulmonary disease seems possible. If patients dying from cancer of the stomach within a two-year period are excluded, mortality from this disease was not significantly higher than expected. Thus the study gives no support to that theory that benign gastric ulcers are prone to malignant degeneration.

Adolescent↗
PubMedDate not supplied

Biochemical and clinical effects of an antioxidative supplementation of geriatric patients. A double blind study.

Ninety seven geriatric patients from two Danish homes for old people accepted to participate in a blinded experiment designed to counteract ageing phenomena. The subjects were split into two groups, i.e., the verum and the placebo group. The verum group received daily for one year an antioxidative cocktail consisting of: 300 micrograms selenium as L-selenomethionine, 45 mg zinc, 270 mg vitamin C, 2.7 mg vitamin A, 6 mg vitamin B-6, and 465 mg vitamin E (d-alfatocopherol). Furthermore, in order to enhance exchange in polyenoic acids, each subject received daily 250 mg gamma-linolenic acid. The placebo groups received similar looking pills and capsules without the active components. During one year in the verum group, the whole blood selenium, the hydrogen-dependent glutathione peroxidase (GSH-Px) of erythrocytes, and the vitamin E level in serum was found increased compared to the pretreatment values and to the placebo group. No change could be traced in the t-butylhydroperoxide dependent GSH-Px, an enzyme that also assays the glutathione-s-transferase. During the same period of time, the fasting levels of serum fatty acids and the content of lipofuscin in erythrocytes were estimated. Compared to the pretreatment values, the lipofuscin level declined significantly and the level of w-3 penta- and hexaenoic acids increased in the verum, but not in the placebo group. During the study period, slight, but significant improvements in psychological scores could be traced. Furthermore, the assays of bloodflow in different areas of the brain surface (i.e., the ISI values) revealed a general trend to improvement in all areas, when the ISI values were compared during treatment with the pretreatment values and the values in the placebo group.

Adult↗
PubMedDate not supplied

Comparison of whole blood selenium values and erythrocyte glutathione peroxidase activities of normal individuals on supplementation with selenate, selenite, L-selenomethionine, and high selenium yeast.

The selenium levels and the glutathione peroxidase activity GSH-PX of whole blood and of erythrocytes, respectively, were determined in 139 normal Danes and related to sex and smoking habits. No differences were found in relation to sex apart from a higher GSH-PX activity of females when assayed with tertiary butyl hydroperoxide. Smokers showed significantly lower selenium values than non-smokers (p less than 0.05), but the two groups had identical GSH-PX activities. Individuals from the above-mentioned group were divided into four groups, receiving daily oral doses of 200 micrograms of selenium in the form of selenite, selenate, L-selenomethionine, and selenium as contained in yeast. Whole blood selenium values and the erythrocyte glutathione peroxidase activities were determined during three months of supplementation followed by a withdrawal period of four months. Both the inorganic selenium compounds and the organic derivatives gave rise to steady state levels of GSH-PX after one month of supplementation. However, the selenium levels in the groups receiving organic selenium showed a steady rise during the whole period, whereas those supplemented with inorganic selenium leveled off after a period of one to three months. The data for smokers and nonsmokers revealed identical results when organic selenium was supplemented. However, selenite gave rise to significantly higher selenium levels and GSH-PX activities in smokers than in non-smokers. Less significant (p less than 0.08) elevations of both parameters were also observed among the smokers in the selenate group. By taking both the selenium level and the GSH-PX activity into consideration, organic selenium (i.e., L-(+) selenomethionine) was judged to be more bioavailable than selenite and selenate.

Adult↗