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Biomedical subjects

U Hahn

Publications and source records attributed to U Hahn.

At least 55 records · Page 3Linked to original sources

Medical knowledge reengineering--converting major portions of the UMLS into a terminological knowledge base.

We describe a semi-automatic knowledge engineering approach for converting the human anatomy and pathology portion of the UMLS metathesaurus into a terminological knowledge base. Particular attention is paid to the proper representation of part-whole hierarchies, which complement taxonomic ones as a major hierarchy-forming principle for anatomical knowledge. Our approach consists of four steps. First, concept definitions are automatically generated from the metathesaurus, with LOOM as the target language. Second, integrity checking of the emerging taxonomic and partonomic hierarchies is automatically carried out by the terminological classifier. Third, terminological cycles and inconsistencies are manually eliminated and, in the last step, the knowledge base built this way is incrementally refined by a medical expert. Our experiments were run on a terminological knowledge base which is composed of 164,000 concepts and 76,000 relations. Empirical evidence for the lack of logical consistency, adequacy and improper granularity of the UMLS knowledge source is given, and finally, assessments of what kind of efforts are needed to render the formal target representation structures complete and empirically adequate.

Anatomy↗

New strategies in platelet inhibition in noncoronary interventions.

Thrombembolic complications frequently occur during and after endovascular procedures because of associated arterial injury and thrombotic characteristics of implanted devices such as stents. New strategies in platelet aggregation inhibition are now available blocking the final and common pathway of platelet aggregation, the glycoprotein IIb/IIIa receptor. This treatment modality seems to be more effective for prophylaxis and prevention of thrombembolic complications than standard antiplatelet therapy. Most of the data provided for glycoprotein IIb/IIIa receptor blockade are derived from studies of coronary interventions. This report reviews the pharmacodynamic differences of classic and new drugs for platelet inhibition and the basic considerations for antiplatelet therapy in noncoronary interventions.

Arteries↗

[Endovascular therapy of renal artery stenosis: technical results with the Palmaz-Corinthian stent].

OBJECTIVE: To evaluate the technical performance and delivery characteristics of the Palmaz-Corinthian stent for endovascular therapy of atherosclerotic renovascular disease. METHODS: 61 patients underwent implantation of 76 Palmaz-Corinthian (PC) stents in 72 arteries. 50 original PC and 26 PC stents with the modified IQ-design were employed. The indications comprised primary stenting of ostial (n = 49) or truncal (n = 1) stenosis or occlusion (n = 3), and selective stenting following complicated (dissection, n = 4) or unsuccessful (n = 8) angioplasty. The remaining stents were placed in patients with recurrent stenosis (n = 5) or acute aortic dissection (n = 2) involving the renal artery. Mean severity and length of stenosis were 81.3% and 9.8 mm, respectively. 39 lesions were rated eccentric or calcified. Data on technical success, complication rate, delivery characteristics and ease of placement compared to standard renal stents were retrieved from a prospective multicenter registry. RESULTS: Stent delivery was successful in all patients, major complications were not reported. Stent placement was suboptimal in 7 of 72 cases: 4 stents were located too distally in the renal artery, necessitating proximal coaxial overstenting in 2 cases. The distal part of the stenosis was incompletely covered and the orifice of a segmental branch inappropriately overstented in one case each. One stent was dislodged from the balloon, resulting in stent protrusion in the aortic lumen. Significant residual stenosis after stenting was not observed. Overall stent deliverability, trackability and potential repositioning inside the stenosis were rated positive, radio-opacity was rated superior for the IQ design. CONCLUSION: Technical performance and delivery characteristics of the Palmaz-Corinthian stent have been significantly improved compared to the Palmaz design, allowing mostly correct placement in renal artery stenoses with a low complication rate.

Angiography, Digital Subtraction↗

[2D-phase contrast flow evaluation and contrast-enhanced MR angiography for perioperative assessment of internal mammary artery grafts].

PURPOSE: To evaluate LV functional parameters, graft flow and patency in patients with IMA grafts using a combined MR protocol with phase-contrast technique and contrast enhanced MR angiography. MATERIAL AND METHODS: Using a 1.5 T MR system 27 patients with 27 left internal mammary artery (LIMA) and 41 venous grafts were examined before and 6 months after CABG surgery. A T(1)w-TSE sequence (slice thickness 5 mm) was applied for morphological imaging. LV function (EF, CO) was evaluated on cine images (segmented FLASH 2D, TR(eff) 11 ms, TE 4.8 ms, flip angle 25 degrees ). A phase-contrast FLASH 2D (TR 24 ms, TE 5 ms, flip angle 20 degrees ) sequence was applied for aortic and IMA flow measurements. Postoperatively, a contrast enhanced FLASH 3D MR angiography (TR 3.8 ms, TE 1.4 ms, flip angle 30 degrees ) with 25 ml Gd-DTPA was performed to assess bypass patency. RESULTS: In patients with reduced LV function (ejection fraction < 50 %) an improvement of the ejection fraction from 38.4 +/- 10.3 % to 49.8 +/- 15.3 % (p < 0.05) was found postoperatively. LIMA grafts were occluded in 1/27 patients, while 6/41 venous grafts were occluded. Distal LIMA anastomoses were demonstrated in 33 % by MRA. Flow of LIMA decreased from 21.2 +/- 11 ml/min/m(2) preoperatively to 14.4 +/- 9.6 ml/min/m(2) postoperatively (p < 0.01). CONCLUSION: MR imaging allows accurate combined assessment of LV function, bypass patency and flow. The protocol of this study may be applicable for perioperative follow-up studies in patients after CABG surgery.

Aged↗

[Multidetector CT Angiography - is it a valuable screening tool to detect significant renal artery stenosis?].

PURPOSE: To evaluate the diagnostic value of multidetector CT angiography (MDCTA) of the renal arteries. METHODS: 27 patients underwent MDCTA of the renal arteries. Scan parameters were: collimation 4 x 1 mm, pitch 1.5, effective slice thickness 1.25 mm, reconstruction increment 0.8 mm, circulation time measurement, power injection of 80 ml iomeprol 400, flow 4 ml/sec. Independent reading on laser film was done by two radiologists using edited maximum intensity projections, multiplanar reconstructions and source images. Standard of reference was a 3D-FLASH MR angiography (1.5 T, 3.9/1.2, 10 degrees 0.2 mmol GdDTPA/kg bw) in 10 and intraarterial angiography in 17 patients. RESULTS: Analysing 63 arteries, sensitivity, specificity, positive predictive value and negative predictive value in terms of detection of moderate and high grade renal artery stenosis (n = 10) were 90, 98, 90 and 98 % for reader A, and 90 % each for reader B, respectively (kappa = 0.91 interobserver agreement). 1/11 accessory renal arteries was missed by both angiography and MDCTA. Image quality was graded as excellent or good in 26/27 of cases by both readers. CONCLUSION: MDCTA proved to be a highly accurate tool in the detection of therapeutically relevant renal artery stenosis.

Aged↗

Peripheral artery occlusion: treatment with abciximab plus urokinase versus with urokinase alone--a randomized pilot trial (the PROMPT Study). Platelet Receptor Antibodies in Order to Manage Peripheral Artery Thrombosis.

PURPOSE: To evaluate the combination of a platelet glycoprotein IIb/IIIa complex receptor inhibitor and urokinase for treatment of recent (<or=6 weeks) arterial occlusion of the legs. MATERIALS AND METHODS: Seventy patients with lower extremity arterial occlusion of less than 6 weeks duration were randomly separated into two treatment groups: urokinase plus abciximab or urokinase plus placebo. Primary end points were the rate of major complications at 30 days after randomization and the rates of amputation-free survival and survival without open surgery or major amputation at follow-up of 90 days. Two readers unaware of the patients' treatment group assignments analyzed digital subtraction angiograms as they related to the study end points, with a final consensus reading. RESULTS: Thrombolysis relative to clot length was faster in the urokinase-plus-abciximab group (odds ratio, 0.52; 95% CI: 0.35, 0.76; P < .001). There were no procedure-related deaths or intracranial hemorrhages, but the rate of nonfatal major bleeding was higher with urokinase plus abciximab (four of 50 patients) than with urokinase alone (none of 20 patients; P = .32). At 90 days, amputation-free survival was 96% (48 of 50 patients) in the urokinase-plus-abciximab group compared with 80% (16 of 20 patients) in the urokinase alone group. The hazard ratio for the two Kaplan-Meier curves was 0.42 (95% CI: 0.16, 0.96; P = .04). CONCLUSION: In patients with lower extremity arterial occlusion who were undergoing urokinase thrombolysis, adjunctive abciximab treatment resulted in faster thrombus dissolution and improved amputation-free survival, despite an increase in major bleeding.

Abciximab↗

Fluorescence correlation spectroscopy as a new method for the investigation of aptamer/target interactions.

Fluorescence correlation spectroscopy is an attractive tool for monitoring molecular interactions in solution. We report here a new and highly sensitive method for studying the interaction of aptamers with their targets using this technique. In vitro selection technology is a combinatorial method for the generation of nucleic acid receptors (aptamers) that are capable of binding to various target molecules. Using the in vitro selection approach we isolated RNAs which bind to the antibiotic moenomycin with high affinity. The formation of RNA-moenomycin complexes was studied by fluorescence correlation spectroscopy with a tetramethylrhodamine-labeled derivative of moenomycin.

Combinatorial Chemistry Techniques↗

RNase-stable RNA: conformational parameters of the nucleic acid backbone for binding to RNase T1.

An RNA sequence showing high stability with respect to digestion by ribonuclease T1 (RNase T1) was isolated by in vitro selection from an RNA library. Although ribonuclease T1 cleaves single-stranded RNA specifically after guanosine residues, secondary structure calculations predict several guanosines in single-stranded areas. Two of these guanosines are part of a GGCA-tetraloop, a recurring structure element in the secondary structure predictions. Molecular dynamics simulations of the conformation space of the nucleotides involved in this tetraloop show on the one hand that the nucleic acid backbone of the guanosines cannot realise the conformation required for cleavage by RNase T1. On the other hand, it could be shown that an RNA molecule not forced into a tetraloop occupies this conformation several times in the course of the simulation. The simulations confirm the GGCA-tetraloop as an RNase-stable secondary structure element. Our results show that, besides the known prerequisite of a single-stranded RNA, RNase T1 has additional demands on the substrate conformation.

Base Sequence↗

A new device for percutaneous suture-mediated closure of arterial puncture sites using exteriorized needles: initial experience.

PURPOSE: To assess the feasibility and initial clinical results of Closer (Perclose, Redwood City, California), a new device for percutaneous suture-mediated closure of arterial puncture sites. METHODS: Vascular interventions were performed using 6 and 7 French sheaths in 22 consecutive patients. All patients underwent suture-mediated percutaneous closure with the new device. Patients were followed by physical examination the day after the procedure. RESULTS: Immediate hemostasis was achieved in 20/22 patients (91%). In 3 out of 5 antegrade closures, only one suture was captured. In two cases, this was managed by reinsertion of a second device. In another patient, hemostasis was not achieved by the device due to knot entrapment. No major complications were observed. The overall rate of minor complications was 9% (2/22) due to hematomas without the need for blood transfusions. CONCLUSION: Percutaneous suture with this new device is an acceptably safe and effective method to achieve immediate hemostasis of the arterial access site after interventional procedures with minimized manipulation of the puncture track.

Adult↗

Indexing medical WWW documents by morphemes.

Assisting users to search medical information on the WWW is here considered from two perspectives--the linguistic complexity of medical terms, nominal compounds in particular, and cross-lingual relationships between monolingual medical terminologies. In order to solve the first problem, we present an approach to automatic indexing in which medically plausible morphological units are used. Semantic value is added to these index terms by a compact domain-specific thesaurus. We further discuss tools for morphological segmentation and morphosemantic normalization of HTML documents, as well as an adaptation of a standard WWW search engine for morpheme-based retrieval. The second problem, cross-lingual medical document retrieval, is dealt with by defining cross-lingual equivalence relations on the emerging morpheme sets.

Abstracting and Indexing↗

[A condylar plate in distal femoral fractures].

Up to the seventies, the surgical treatment of supra- and bicondylar femoral fractures was difficult and was accompanied by a lot of complications. In most studies conservative treatment was recommended. In the last 30 years the clinical outcome after surgical treatment has improved. This was a result of the development of new implants and improved surgical techniques. Today, the primary surgical treatment is the therapy of choice. We reviewed from 1986 to 2000 105 distal femoral fractures which in 32 cases were treated with a condylar blade plate. The final results were rated using the system that was described by Neer. The averaged follow up time was 9 years. Low postoperative infection rates and in 75% excellent and satisfactory results combined with low cost are the state of art which has to be the reference for new methods and new implants in the future.

Adult↗

Subword segmentation--leveling out morphological variations for medical document retrieval.

Many lexical items from medical sublanguages exhibit a complex morphological structure that is hard to account for by simple string matching (e.g., truncation). While inflection is usually easy to deal with, productive morphological processes in terms of derivation and (single-word) composition constitute a real challenge. We here propose an approach in which morphologically complex word forms are segmented into medically significant subwords. After segmentation, both query terms and document terms are submitted to the matching procedure. This way, problems arising from morphologically motivated word form alterations can be eliminated from the retrieval procedure. We provide empirical data which reveals that subword-based indexing and retrieval performs significantly better than conventional string matching approaches.

Information Storage and Retrieval↗

Empirical data for the semantic interpretation of prepositional phrases in medical documents.

We report on the results from an empirical study deal-ing with the semantic interpretation of prepositional phrases in medical free texts. We use a small number of semantic interpretation schemata only, which operate on well-defined configurations in dependency graphs. We provide a quantitative analysis of the performance of the semantic interpreter in terms of recall/precision data, and consider, in qualitative terms, the impact semantic interpretation patterns have on the construction of the underlying medical ontology.

Humans↗

Epicatechin and catechin are O-methylated and glucuronidated in the small intestine.

There is considerable interest in the bioavailability of polyphenols and their bioactivity in vivo. We have studied the absorption and metabolism of catechin and epicatechin in the small intestine and the comparative transfer across the jejunum and ileum. Perfusion of isolated jejunum with the flavanols resulted in glucuronidation ( approximately 45%), O-methylation: 3'-O-Methyl- and 4'-O-methyl- ( approximately 30%), and O-methyl-glucuronidation ( approximately 20% of total flavanols identified) during transfer across the enterocytes to the serosal side. This demonstrates the activity of catechol-O-methyl transferases in the metabolism of flavanols and suggests that these metabolites and conjugates are likely to enter the portal vein. In contrast, in the case of the ileum, the majority of the flavanols appeared on the serosal side unmetabolised and the total percentage of flavanols transferred was higher than that in the jejunum ( approximately fivefold).

Animals↗

Resveratrol is absorbed in the small intestine as resveratrol glucuronide.

We have studied the absorption and metabolism of resveratrol in the jejunum in an isolated rat small intestine model. Only small amounts of resveratrol were absorbed across the enterocytes of the jejunum and ileum unmetabolised. The major compound detected on the serosal side was the glucuronide conjugate of resveratrol (96.5% +/- 4.6 of the amount absorbed) indicating the susceptibility of resveratrol to glucuronidation during transfer across the rat jejunum. The presence of the glucuronide was confirmed using HPLC-PDA and nanoES-MS/MS techniques. These findings suggest that resveratrol is most likely to be in the form of a glucuronide conjugate after crossing the small intestine and entering the blood circulation. This will have important implications for the biological functions of resveratrol in vivo.

Animals↗

Nano-electrospray mass spectrometry with a modified commercial IonSpray source

Electrospray mass spectrometry is a standard tool for the investigation of biological samples. Due to the high flowrates of the standard sources, large sample amounts are required and it is almost impossible to spray physiological solutions due to their aqueous medium. The introduction of microelectrospray sources has made it possible to decrease the sample amounts needed and enabled the use of buffered solutions. In this work, a nanoES-like source based on a modification of an existing IonSpray source is introduced. In contrast to other nanoES sources available, the modification presented allows a fast change between the nanoES and the normal IonSpray modes. Copyright 2000 John Wiley & Sons, Ltd.

Journal Article↗

German inflection: single route or dual route?

The German plural system has recently become a focal point for conflicting theories of language, both linguistic and cognitive. Marcus et al. (1995) highlight the German plural as support for the dual-route account of inflectional morphology first proposed by Pinker and colleagues (Pinker & Prince, 1988). On the dual-route account, inflectional morphology is universally subserved by a symbolic rule route which deals with regular inflection and an associative memory component which deals with irregular inflection. This contrasts with single-route connectionist systems. We seek to counter supposed evidence for the dual-route account through large-scale simulations as well as through experimental data. We argue that, in its current form, the dual-route account is incapable of generating experimental data provided by Marcus et al. (1995) as support. Finally, we provide direct quantitative comparisons between single-route and dual-route models of German plural inflection and find single-route performance superior on these tests.

Humans↗

[Polytopic manifestations of paragangliomas. Diagnosis, differential diagnosis and indications for therapy].

Paragangliomas of the glomus caroticum are relatively rare, but highly vascularized neoplasmas, which develop from chemoreceptors. They can be develop at any age, but most often in the third or fourth decade of life. Paragangliomas grow very slowly and are most always of benign origin. There is a familial predisposition, and an autosomal-dominant transmission is presumed. They are commonly located in the jugular region; in rare cases a polytopic manifestation is found. We describe the case of a 47-year-old male patient who was referred to our department because of a progressive swelling of the neck on both sides. Contrast-enhanced computed tomography had displayed soft tissue tumors in the jugular regions. We performed an operative exploration, which showed a highly vascularized tumor. Histopathologic analysis revealed the diagnosis of a paraganglioma. An angiography of the neck and thoracic region, furthermore, revealed an additional paraganglioma in the anterior mediastinum. Using a surgical approach via lateral cervicotomies and thoracotomy the paragangliomas were extirpated. Our case report demonstrates the rare polytopic manifestation of paragangliomas. This perivascular neoplasms have to be removed before haemodynamic complications develop. The extent of this tumors is clearly illustrated by use of an angiography. Because of the familial predisposition, clinical and radiological examinations of relatives are mandatory.

Carotid Body↗