Biomedical subjects

H Ahlfeldt

Publications and source records attributed to H Ahlfeldt.

29 records · Page 2Linked to original sources

PubMed1991

Distribution patterns of ventricular premature complexes in long-term electrocardiographic recordings and their usefulness in disclosing modulated parasystole.

Long-term electrocardiographic recordings from 25 patients with abundant ventricular premature complexes (VPCs) were screened with a computer program for sequences of interectopic intervals with the number of sinus beats consistent with manifest or concealed bigeminy/trigeminy. On average, 19.0% of VPCs in this patient series were followed by an uninterrupted sequence of greater than or equal to 10 interectopic intervals with concealed bigeminy. The corresponding figure for concealed trigeminy was 2.2%, for manifest bigeminy 9.6%, and for manifest trigeminy 0.8%. The longest sequence with concealed bigeminy comprised 149 interectopic intervals. The corresponding figure for concealed trigeminy was 135 interectopic intervals. The sequences of concealed bigeminy occurred at significantly lower heart rates than those of concealed trigeminy. These findings can be explained by the entrainment phenomena described in experimental models of modulation of a ventricular parasystolic focus across a zone of impaired conduction.

Adult↗

PubMed1989

Deduction of biphasic phase response curves from ventricular parasystole.

The mechanisms behind ventricular premature beats may be divided into two main categories, reentry and modulated parasystole. Although it is relatively easy to distinguish among arrhythmia generating mechanisms on the cellular level, it is far more difficult in the clinic. Modulation of ventricular parasystole by sinus beats has been shown to result in a biphasic phase response curve. Two cases are reported where the deduction of such phase response curves from long-term ECG recordings is discussed and described as a stepwise procedure.

Aged↗

PubMed1989

Deduction of triphasic phase response curves from ventricular parasystole.

Modulation of ventricular parasystole by sinus beats has been shown to result in a biphasic phase response curve. Some reports also indicate that the modulation effect could be described by a triphasic response with an early phase of acceleration, which would correspond to the supernormal phase of excitability. Two cases of such triphasic phase response curves are reported. The coexistence of ventricular couplets and parasystole is also discussed. The second beat of the couplet has often been explained by reentry or reflection, but could also be interpreted as due to supernormal modulation, resulting in an accelerated second ectopic response.

Aged↗

PubMed1989

Teaching medical informatics to biomedical engineering students: experiences over 15 years.

The Departments of Biomedical Engineering and Medical Informatics at Linköping University in Sweden were established in 1972-1973. The main purpose was to develop and offer courses in medicine, biomedical engineering and medical informatics to students in electrical engineering and computer science, for a specialization in biomedical engineering and medical informatics. The courses total about 400 hours of scheduled study in the subjects of basic cell biology, basic medicine (terminology, anatomy, physiology), biomedical engineering and medical informatics. Laboratory applications of medical computing are mainly taught in biomedical engineering courses, whereas clinical information systems, knowledge based decision support and computer science aspects are included within the medical informatics courses.

Biomedical Engineering↗

PubMed1988

Computer simulation of cardiac pacing.

A mathematical model of the cardiac conduction system, including external pacemakers, has been developed. The heart is modeled as a network in which the impulse propagation is described by differential equations; several arrhythmia-generating mechanisms, such as modulated parasystole, reflection, macro and micro re-entry and block, can be simulated. Different kinds of pacemaker modes have been incorporated in the model, thus making it possible to simulate the interaction between the heart and the pacemaker. The model can be tuned by the user according to electrophysiological data so that pacemaker programs can be tested under different underlying conditions. During a simulation, the program generates ECG signals and pacemaker diagnostic diagrams. This model can be used for training and testing, and also as a support system when searching for the optimal pacing therapy for a particular patient.

Computer Simulation↗

PubMed1987

Computer simulation of cardiac arrhythmias.

A mathematical model of the cardiac conduction system has been developed. The mechanisms of cardiac arrhythmias are described mathematically, and the heart is modeled as a network, where each element is defined by a unique set of time parameters from the action potential. The mathematical description is separated from the network structure, thus making it possible to run the model with different network sizes. Simulated ECG curves are produced in each case. This model is especially suited for rhythm studies, and a variety of different cardiac arrhythmia mechanisms has been simulated such as reentry, reflection, modulated parasystole, and different kinds of block.

Action Potentials↗

PubMedDate not supplied

Modelling and reclassification of surgical procedures--experiences from the use of GALEN methods in the domain of thoracic surgery.

This paper reports on experiences from the evaluation of GALEN methods for mapping of follow-up categories in the domain of thoracic surgery to an existing classification of surgical procedures. The mapping of the aggregated levels or groups of thoracic procedures presents a genuine problem in relation to strict hierarchical classifications, since the follow-up categories do not necessarily fit in the pre-set structure of the classification. Experiences from modelling of the traditional classification and of the follow-up categories are reported, and an analysis of the results is presented along with a discussion of opportunities and potential problems and pitfalls when applying GALEN models and tools.

Cardiac Surgical Procedures↗

PubMedDate not supplied

Vestibulo-oculomotor disturbances in humans exposed to styrene.

Several reports indicate that disturbances of the vestibulo-oculomotor ability are a manifestation of the toxic action on the central nervous system exerted by some industrial solvents. The aim of the present investigation was to examine the vestibulo-oculomotor system during exposure to styrene, which is extensively used in the production of plastics. Healthy volunteers were exposed to styrene for one hour. Rotatory and optokinetic nystagmus, visual suppression as well as speed, latency and accuracy of saccades were tested before, during, and one hour after the exposure. The pulmonary uptake and the blood level of the solvent were continuously analysed by gas chromatography. The styrene blood concentration was equivalent to that which may well be reached after serveral hours of hard work in an industrial environment with a concentration of styrene within permitted limits. No spontaneous nystagmus appeared. The rotatory and optokinetic nystagmus was not influenced by styrene. However, the speed of the saccade was significantly enhanced. The visual suppression was disturbed, shown by an increased gain after styrene exposure. The experiments thus indicate that styrene given to healthy test persons induced disturbances, thus consistent with the theory that some organic solvents block the cerebellar inhibition of the vestibulo-oculomotor system.

Adult↗

PubMedDate not supplied

Query-handling in MLM-based decision support systems.

Arden Syntax for Medical Logic Modules is a standard specification for creation and sharing of knowledge bases. The standard specification focuses on knowledge that can be represented as a set of independent Medical Logic Modules (MLMs) such as rules, formulas and protocols. The basic functions of an MLM are to retrieve patient data, manipulate the data, come to some decision, and possibly perform an action. All connections to the world outside an MLM are collected in the data-slot of the MLM. The institution specific parts of these connections are inside the notation of curly brackets ([]) to facilitate sharing of MLM between institutions. This paper focuses on some of the problems that occur in relation to Arden Syntax and connections to a patient database such as database queries. Problems related to possibilities of moving one or several module(s) are also discussed, with emphasis on database connections. As an example, an MLM based Decision Support System (DSS) developed at Linköping University is described.

Artificial Intelligence↗

PubMedDate not supplied

Terminology support for development of sharable knowledge modules.

Lack of an agreed infrastructure for terminology is identified as one of the major barriers to interchange of knowledge modules and integration of knowledge bases with other clinical information systems. The goal of the GALEN project is to bridge this gap between different terminology systems through the construction of a terminology server, which is based on a rich conceptual model with mapping facilities to natural language expressions and coding schemas. The long term goal is to support communication between medical information systems. Arden Syntax is a standard format for the creation of knowledge modules, with sharability as one of the main objectives. Since Arden Syntax is based on a data-driven approach, the data items used need to be adapted to locally available terminology. The GALEN approach appears to be complementary to Arden Syntax and to the development of sharable knowledge modules. The major theme of this paper is utilization of the GALEN terminology server for knowledge module authoring. Two systems are presented, a knowledge base manager and a client to the terminology server, allowing the user to navigate in the semantic network and to import concept definitions and terms into the knowledge modules. The benefit of the terminology server, allowing the user to navigate in the semantic network and to import concept definitions and terms into the knowledge modules. The benefit of the terminology services is discussed.

Artificial Intelligence↗

PubMedDate not supplied

The connection between terms used in medical records and coding system: a study on Swedish primary health care data.

Implementation of problem lists and their relation to standardized coding systems have been approached and analysed in different ways. Most evaluations concern quantitative aspects such as content coverage in a specific domain. In order to reveal the qualitative aspects of diagnostic coding, medical record texts from primary health care encounters were compared with terms from a coding system that was used for describing them statistically. The records were coded by six general practitioners, and in some cases, an applied diagnostic term was found within the text, while other record text-coding system relationships were categorized as synonyms, alternative terms, and interpretations. Thus, the categories roughly corresponded to a measure of semantic distance between the terms in the record text and the rubrics of the coding system, and there was a correlation between semantic distance and inter-rater agreement. The subcategories of this scheme corresponded fairly well to recently published desiderata for clinical terminology servers, including functionality such as word normalization and spelling correction. However, not all problems could have been automatically coded by means of lexical methods, which can be partly explained by the fact that diagnostic coding also relies on clinical knowledge. In addition, proper automation relies on context representation within the records.

Abstracting and Indexing↗