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Biomedical subjects

K M Hanson

Publications and source records attributed to K M Hanson.

At least 19 recordsLinked to original sources
PubMed1998

Epidermal trans-urocanic acid and the UV-A-induced photoaging of the skin.

The premature photoaging of the skin is mediated by the sensitization of reactive oxygen species after absorption of ultraviolet radiation by endogenous chromophores. Yet identification of UV-A-absorbing chromophores in the skin that quantitatively account for the action spectra of the physiological responses of photoaging has remained elusive. This paper reports that the in vitro action spectrum for singlet oxygen generation after excitation of trans-urocanic acid mimics the in vivo UV-A action spectrum for the photosagging of mouse skin. The data presented provide evidence suggesting that the UV-A excitation of trans-urocanic acid initiates chemical processes that result in the photoaging of skin.

Animals↗
PubMed1998

Risk factors associated with Corynebacterium pseudotuberculosis infection in California horses.

A case-control study was designed using equine medical records from the UC Davis Veterinary Medical Teaching Hospital (VMTH) and data derived through a mailed survey. The objective was to evaluate the associations between horse demographics, horse-management factors, and equine Corynebacterium pseudotuberculosis infection in California. Horses admitted to the VMTH between July 1 1992 and June 30 1994 served as the study base for case identification and simple random sampling of 800 controls. A questionnaire was mailed to the owners of all horses enrolled in the study to collect data on demographics, management and health-related questions. A logistic-regression model containing age, outdoor activity level, other locations in California, insect-control measures, contact with other horses, and summer pasture was developed. The final model was adjusted for the suspected confounding variables admission type, regular teaching hospital patient and breed. Horses of age between 1 and 2 yrs and between 3 and 5 yrs, and horses in contact with other horses or horses on summer pasture had significantly increased odds (p < 0.05) of being diagnosed with C. pseudotuberculosis infection. The results support the hypotheses that the disease predominantly affects young-adult horses of all breeds and both sexes, and that management factors play an important role in occurrence of the disease. Since the existing serological test system is not reliable and destruction of infected animals is not feasible, the most-logical approach for disease prevention is the early identification and isolation of clinical cases and the implementation of management changes like improvement of stable hygiene and insect control and change of pasture practices.

Animals↗
PubMed1998

Tomographic reconstruction using 3D deformable models.

We address the issue of reconstructing the shape of an object with uniform interior activity from a set of projections. We estimate directly from projection data the position of a triangulated surface describing the boundary of the object while incorporating prior knowledge about the unknown shape. This inverse problem is addressed in a Bayesian framework using the maximum a posteriori (MAP) estimate for the reconstruction. The derivatives needed for the gradient-based optimization of the model parameters are obtained using the adjoint differentiation technique. We present results from a numerical simulation of a dynamic cardiac imaging study. A first-pass exam is simulated with a numerical phantom of the right ventricle using the measured system response of the University of Arizona FASTSPECT imager, which consists of 24 detectors. We demonstrate the usefulness of our approach by reconstructing the shape of the ventricle from 10,000 counts. The comparison with an ML-EM result shows the usefulness of the deformable model approach.

Bayes Theorem↗
PubMed1998

The origin of the wavelength-dependent photoreactivity of trans-urocanic acid.

Two-color, pulsed-laser photoacoustic calorimetry is used to distinguish between multiple rotamer or electronic state contributions to the absorption spectrum of the epidermal chromophore trans-urocanic acid. The data definitively show that the wavelength-dependent photochemistry of trans-urocanic acid results from the presence of two distinct, weakly coupled electronic states absorbing between 264 nm and 310 nm.

Calorimetry↗
PubMed1997

Socioeconomic and demographic factors are associated with worldwide patterns of stunting and wasting of children.

We estimated the variability among nations in the prevalence of stunting and wasting, evaluated which national factors are associated with stunting and wasting and examined the relationship of stunting with wasting. The World Health Organization Global Database on Child Growth, a comprehensive conceptual model and a database of national factors were used with variance components and regression analyses. There was substantial variability among nations and among provinces within nations. Most national variability for stunting (76%) and wasting (66%) was explained by national factors and geographic region. Higher energy availability, female literacy and gross product were the most important factors associated with lower prevalence of stunting. The association of health expenditures and stunting differed by region. Higher immunization rate and, for Asia only, energy availability were the most important factors associated with lower prevalence of wasting. Regional differences in the relationship between stunting and wasting were accounted for by national factors. Some factors associated with stunting and wasting differ at the national level. Child malnutrition within a household is greatly influenced by issues at national and provincial levels, and intervention should be considered at all three levels.

Child Nutritional Physiological Phenomena↗
PubMed1995

Enzyme inhibitors: new and known polybrominated phenols and diphenyl ethers from four Indo-Pacific Dysidea sponges.

Extracts and pure compounds isolated from four samples of Dysidea sp. sponges collected from two geographically distinct regions of the Indo-Pacific (Chuuk Atoll and Fiji) were assayed against five different enzyme assays, four of which are relevant to anticancer drug discovery and one of which (15-lipoxygenase) may detect compounds significant in modulating the development of atherosclerotic plaque. The pure compounds that inhibited various enzymes were polybrominated phenols and polybrominated phenoxyphenols. Fourteen of these phenols were isolated, six of which were new compounds. A variety of the phenols inhibited inosine monophosphate dehydrogenase (IMPDH), guanosine monophosphate synthetase, and 15-lipoxygenase. No activity was observed with protein tyrosine kinase pp60v-src or matrix metalloprotease.

Animals↗
PubMed1992

Solvent and temperature effects on the excited singlet state absorption of diphenylbutadiene.

Nanosecond excited state absorption spectra of all-trans-1,4-diphenyl-1,3-butadiene (DPB) and a rigid s-cis DPB analog, 1,4-diphenyl-1,3-cyclopentadiene, were obtained in several hydrocarbon solvents at room temperature and low temperatures. Analysis of the excited state absorption spectra of these two molecules suggests the presence of excited state s-cis rotamers in DPB at room temperature.

Butadienes↗
PubMed1991

Optimization of the constrained Algebraic Reconstruction Technique for the performance of a variety of visual tasks.

This work demonstrates the application of a method to optimize image reconstruction algorithms on the basis of the performance of specific visual tasks that are to be accomplished using the reconstructed images. The evaluation of task performance is numerically realized by a Monte Carlo simulation of the complete imaging chain, including the final inference based on the reconstructions. Fundamental to this evaluation is that it yields an average response by consideration of many initial scenes. It is shown that the use of the nonnegativity constraint in the Algebraic Reconstruction Technique can significantly improve performance in situations where there is a severe lack of measurements when the relaxation factor is optimized. There is no indication in any of the cases studied hitherto that the nonnegativity constraint can improve performance in situations where the data are complete, but noisy. It is also shown that neither the rms error nor the L1 error in constrained reconstructions are good predictors of task performance.

Algorithms↗
PubMed1980

On the optimality of the filtered backprojection algorithm.

It is shown that under certain conditions the filtered backprojection algorithm produces a computed tomographic reconstruction for which the statistical accuracy attainable in the amplitude estimation of large-area objects meets the general lower bound derived by Tretiak. In this sense, filtered backprojection is an optimum algorithm.

Computers↗
PubMed1980

Alpha-adrenergic blocking agents and the cardiovascular response to pharmacological doses of vasopressin.

The effects of alpha-adrenergic blockade with phentolamine or dibenamine on the cardiovascular response to pharmacological doses of vasopressin were studied in anesthetized dogs. Some observations were also made on the combined effects of vasopressin and norepinephrine. Changes in mean systemic arterial pressure, portal pressure, and resistance in the prehepatic splanchnic vasculature during vasopressin infusion were noted. A total of 97 dogs were used. alpha-Blockade appeared to enhance the response of arterial pressure to vasopressin, possibly because of loss of baroreceptor-mediated buffering action which normally attenuates its pressor action. Effects of vasopressin on mesenteric vascular resistance and portal pressure were unchanged or somewhat less after alpha-blockade, hence no evidence that its therapeutic effect would be improved by this combination. Vasopressin and norepinephrine when given together result in an additive pressor response with little or no evidence of potentiation.

Adrenergic alpha-Antagonists↗
PubMed1977

Treatment of severe drug overdosage with charcoal hemoperfusion.

Mortality from severe poisoning remains excessively high in patients managed conservatively. In this report, charcoal hemoperfusion was used as a therapeutic aid to active drug removal in 10 patients (9 of whom were in Grade IV coma) intoxicated with a variety of drugs and a further 3 patients poisoned with the highly lethal herbicide, paraquat. All 10 patients who ingested drugs recovered. One of the 3 patients ingesting paraquat survived. The hemoperfusion treatments were associated with demonstrated drug removal. Complications associated with hemoperfusion were minor. Decreases in platelet levels were observed but were not accompanied by clinically important bleeding. The technique of hemoperfusion is simple and provides a therapeutic aid in the care of the severely poisoned patient.

Adolescent↗
PubMed1977

Species specificity and other aspects of chymotrypsin inhibition by plasma.

The inhibition of chymotrypsin activity by pig, dog, human and rat blood plasma was studied. N-Benzoyl-L-tyrosyl-p-amino-benzoate (PABA-peptide) was used as the substrate. Crystalline bovine chymotrypsin as well as activated lyophilized human, pig, rat and chicken pancreatic secretions were used as enzyme sources. Certain species differences were noted. Swine plasma had no effect on bovine or human chymotrypsin while it inhibited that of the chicken by 67%. Dog plasma was a potent inhibitor of chymotrypsin activity from all sources tested. An acute pancreatitis model using the rat was also developed in which pancreatic juice flow was blocked without interference with biliary flow. After 24 h, these animals had increased plasma amylase activity, decreased plasma protease inhibitor and decreased hematocrit. By 72 h, amylase, trypsin inhibitor and hematocrit had nearly recovered while chymotrypsin inhibitor had actually increased above control levels. In rats subjected to hepatectomy or to hepatectomy plus pancreatic blockage, plasma protease inhibitor was even more severely depressed and remained so.

Acute Disease↗
PubMed1976

A new substrate for the rapid evaluation of enteric microbial overgrowth.

The possibility of a new approach to diagnosis of intestinal bacterial overgrowth has been evaluated in laboratory animals. The diagnostic test involves oral administration of an enzyme-labile substrate consisting of para-aminobenzoic acid (PABA) conjugated to a bile acid. In the presence of enteric bacteria, PABA is split from the bile acid and is rapidly absorbed and excreted in the urine. The amount of PABA recovered during the 6 hr following the administered dose of the conjugate may be used as an index of bacterial overgrowth in the upper-gastrointestinal tract. The procedure has been shown to be a reliable index of this condition in laboratory animal models.

Aminobenzoates↗