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Biomedical subjects

K R Nielsen

Publications and source records attributed to K R Nielsen.

At least 19 recordsLinked to original sources
PubMed1997

[A case of acute intermittent porphyria].

A case of an acute attack of porphyria acuta intermittens is presented. A patient was admitted with severe abdominal pain and hypertension. He had excessive excretion of porphobilinogen (PBG) and aminolaevulinicacid (ALA) in the urine and a reduced activity of ery-PBG deaminase (PBGD). The patient was not aware that he was a member of a large "porphyria-family". DNA-analysis showed that he had a hitherto underscribed G to A mutation. This paper shows: 1) The importance of family studies: 2) The risk of developing neurogenic attacks among gene carriers if exposed to precipitating factors. 3) The significance of having the diagnosis of porphyria in mind in every uncertain case of abdominal pain, progressive paresis and psychiatric disease.

Humans↗
PubMed1996

[Suicide among the elderly in the county of Arhus. A 10-year retrospective study of suicide among persons aged 65 and over].

During a ten year period (1983 to 1992) 337 suicides (188 men and 149 women) were registered among people over 65 years of age in the county of Aarhus. The suicide rate (number of deaths per 100,000 living people) decreased during the period from 1983 to 1990. For men the rate was highest over the age of 80, whereas for women the rate was highest before the age of 70. The analyses showed, that the majority of the suicides were committed with violent methods. Previous attempts were registered in 25%. The decision to commit suicide was not associated with health conditions. The percentage of suicide victims living in nursing-homes was slightly higher than that of the background population. In 25% of the 116 suicides a farewell letter was found, despondency was slated as the main cause - not painful or incurable diseases. Prevention of suicide among elderly people is not clarified in this study.

Age Factors↗
PubMed1994

Organ modeling in the quantitation of planar images for distribution studies.

BACKGROUND: The advantage of whole-body imaging for distribution studies is that it accounts for all activities. The problem, however, is that the classic approach to determining distribution from planar images does not accommodate overlapping structures. That approach assumes implicitly that the sampling region is a prismoid whose cross-section, parallel to the detector plane, is defined by a region of interest and whose sides are orthogonal to the detector plane. METHODS: In the proposed organ-model approach, the region of interest is assumed explicitly to be the projected shadow of an organ or structure, whose general shape is known from anatomic generality, and whose size or specific shape variation is defined by the shadow or region of interest. If "j" is a pixel in the organ shadow "i", a fraction "Vij" of the volume of organ "i" is assumed to project orthogonally in "j". More than one organ shadow can overlap, in which case the volumes projecting in "j" are the sum of "Vij" over "i". The activity "Aj" (count rate density) in any location "j" is defined by the linear combination of volumes "Vij" and concentrations "Ci". For all the pixels in the image, this defines an overdetermined set of linear equations that can be solved by matrix inversion for "Ci", the organ concentrations. RESULTS: The organ-model method was tested on simulated and phantom data. It proved, on serial and repeat processing, to be robust (not subject to large errors due to small variations) if the images had sufficient contrast. This method was found to be superior to the classic approach in evaluating the same data, because in the classic approach, the border regions are too heavily weighted, and therefore, the size of the sampling region is critical. Furthermore, the expression of the results in concentrations is more relevant to dosimetry, the derivation of which is based on cumulative concentrations. CONCLUSION: Modeling organ shadows is a viable improvement on the use of regions of interest to quantify tracer distribution in planar imaging.

Models, Biological↗
PubMed1994

Human thyroxine absorption: age effects and methodological analyses.

Experience with the use of simultaneous oral and iv radioiodine tracers of thyroxine (T4) to measure T4 absorption was reviewed to determine the effect of advanced age on T4 absorption and to search for acceptable simplifications in the measurement methodology. (1) Age effect: In control subjects, T4 absorption did not differ with age between 21 and 69 years; it averaged 62.8 +/- 13.5% (SD) in subjects over age 70 compared with 69.3 +/- 11.9% in subjects aged 21-69 (p < 0.001). We conclude that, because of this small but significant reduction in T4 absorption efficiency in the elderly, it is especially important to monitor individual response to replacement T4 doses in this age group. (2) Methodology studies: Intrasubject coefficient of variation for T4 absorption in triplicate studies averaged 8.9%, when an identical method was used at weekly intervals (n = 3). When the 3 studies were done by 3 separate methods (sequential po and i.v. 123I-labeled T4, sequential 125I-labeled T4 po and i.v., and simultaneous po and i.v. doses of different tracers), the intrasubject coefficient of variation averaged 9.8% (n = 8). When the absorption calculation used only one serum sample, taken after isotopic equilibrium was achieved at 24 h [the double isotope (eq) method], calculated T4 absorption differed little from that calculated in the same subjects using a full serum time-activity curve and a noncompartmental analysis [the double isotope (AUC) method]. Compared with a compartmental model solution, both methods slightly overestimated T4 absorption. In 4 subjects given i.v. radioiodide as a third tracer at the same time demonstrated that, as long as radioiodide contamination of the T4 tracers is measured and accounted for in the standards, contaminating radioiodide has no clinically significant effect on T4 absorption measurements. When an oral tracer of T4 was considered alone, without an i.v. tracer to correct for T4 metabolism, the estimates of T4 absorption correlated in a curvilinear fashion with T4 absorption as measured by the double isotope method. Except at very low absorption levels, the oral tracer alone is a poor predictor of T4 absorption. We conclude that, when using a double isotope method to measure T4 absorption, it is acceptable to rely on a single serum sample taken at 24 h, a time when isotopic equilibrium between the two tracers has been reached.(ABSTRACT TRUNCATED AT 400 WORDS)

Administration, Oral↗
PubMed1994

Localization of bronchopleural fistula using ventilation scintigraphy.

It can be difficult to localize or even lateralize the site of persistent bronchopleural fistula in patients who have undergone thoracotomy. If the site of persistent air leak can be identified noninvasively, it may be possible to repair the leak with thoracoscopic techniques and thereby avoid repeat thoracotomy. This article reports experience using 99mTc-DTPA ventilation scintigraphy to localize persistent bronchopleural fistulas in six patients. The site of bronchopleural fistula was identified in four patients. In the other two patients, no leak was identified, and the clinical course confirmed that a significant bronchopleural fistula did not exist.

Adult↗
PubMed1990

Ultrasonically guided percutaneous drainage of breast abscesses.

Four patients with breast abscesses developed during lactation were successfully treated by ultrasonically guided percutaneous drainage under local anaesthesia. Three patients continued nursing during and after the period of treatment and 2 patients were treated as out-patients. The cosmetic results were excellent. No recurrence of abscess was observed following the treatment. Ultrasonically guided percutaneous drainage as an alternative to surgery is discussed.

Abscess↗
PubMed1988

The effect of intravesically administered Cetiprin on bladder spasms after transurethral resection of the prostate. A double-blind randomized study.

A double-blind study of the short-term effects of intravesically administered emepronium bromide (Cetiprin) versus placebo on bladder spasms after transurethral prostatectomy was done in 40 male patients. In the Cetiprin group there was a significant decline in the need for analgesia, and significantly fewer catheter problems. The use of intravesically instilled Cetiprin is recommended only in cases of severe postoperative bladder spasms.

Administration, Intravesical↗
PubMed1988

Discrete analysis of spatial-sensitivity models.

The visual representation of spatial patterns begins with a series of linear transformations: the stimulus is blurred by the optics, spatially sampled by the photoreceptor array, spatially pooled by the ganglion-cell receptive fields, and so forth. Models of human spatial-pattern vision commonly summarize the initial transformations by a single linear transformation that maps the stimulus into an array of sensor responses. Some components of the initial linear transformations (e.g., lens blurring, photoreceptor sampling) have been estimated empirically; others have not. A computable model must include some assumptions concerning the unknown components of the initial linear encoding. Even a modest sketch of the initial visual encoding requires the specification of a large number of sensors, making the calculations required for performance predictions quite large. We describe procedures for reducing the computational burden of current models of spatial vision that ensure that the simplifications are consistent with the predictions of the complete model. We also describe a method for using pattern-sensitivity measurements to estimate the initial linear transformation. The method is based on the assumption that detection performance is monotonic with the vector length of the sensor responses. We show how contrast-threshold data can be used to estimate the linear transformation needed to characterize threshold performance.

Humans↗
PubMed1985

Application of a computable model of human spatial vision to phase discrimination.

We have used a computable model of human spatial vision to make predictions for phase-discrimination experiments. This model is being developed to deal with a broad range of problems in vision and was not specifically formulated to deal with phase discrimination. In the model, cross correlation of the stimuli with an array of sensors produces feature vectors that are operated on by a position-uncertain ideal observer to simulate detection and discrimination experiments. In this report the stimuli are compound sinusoidal gratings composed of a fundamental and a higher-frequency component added in various phases. We compare model predictions with three key results from the literature: the effect of the contrast of the fundamental on phase discrimination, threshold phase difference as a function of the fundamental frequency, and the contrast required for phase discrimination as a function of the frequency ratio of the two grating components. In the first two cases, the predictions capture the main features of the data, although quantitative discrepancies remain. In the third case, the model fails, and this failure suggests additional restrictions on the combination of information across sensors.

Discrimination Learning↗
PubMed1984

Vertical image registration in stereopsis.

Most computational theories of stereopsis require a registration stage prior to stereo matching to reduce the matching to a one-dimensional search. Even after registration, it is critical that the stereo matching process tolerate some degree of residual misalignment. We have studied the tolerance to vertical disparity in situations in which false targets abound and corrective eye movements are eliminated. Our main results are: vertical disparity of only the central "figure" part of a random dot stereogram can be tolerated up to about 3.5', and vertical disparity of the "figure + ground" is tolerated up to about 6.5' in the presence of monocular cues to vertical disparity. Our data suggest that this tolerance is attained by two non-motor mechanisms: the spatial average performed by the receptive fields that filter the two images prior to stereo matching, and a non-motor shift mechanism that may be driven at least in part by monocular cues.

Computers↗
PubMed1978

Neonatal and maternal lymphocytes in whole-blood cultures: absence of strong interaction.

The relative growth of neonatal and maternal lymphocytes was studied in PHA-stimulated mixed short-time whole-blood cultures, with particular regard to a possible inhibition of the maternal cells. For comparison, neonatal and maternal cells were grown separately. No uniform inhibition was observed, although there was an average 34% depression of growth of the maternal cells in the mixed cultures.

Female↗