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Biomedical subjects

A W Hahn

Publications and source records attributed to A W Hahn.

At least 91 records · Page 5Linked to original sources
PubMed1989

Arrhythmia analysis with an expert system.

We have developed a rule based expert system which was designed to diagnose electrocardiographic arrhythmias in several species. The program, called ECG-X, is written in OPS5 and runs under MS-DOS 2.1 and higher on an IBM-PC or AT type machine. The program uses the paper speed, the species, the temporal relationships between the P waves and the QRS complexes as well as basic information about the P and QRS morphology, and provides the user with a rhythm diagnosis consistent with rules provided by contemporary cardiac electrophysiologic knowledge.

Animals↗
PubMed1988

The influence of Encephalitozoon cuniculi on neural tissue responses to implanted biomaterials in the rabbit.

Laboratory rabbits are commonly used for testing the tissue response of neural device biomaterials. Rabbits of many colonies in the U.S. are infected by the intracellular microsporidian parasite, Encephalitozoon cuniculi, with rates of infection ranging from 15 to 76% (1). Several authors have suggested that infection by this parasite may alter immune system response and experimental results. We report that infection by E. cuniculi made the interpretation of results more difficult and altered the animals' responsiveness to implanted platinum wires coated with various polymers such as glow discharge methane, Parylene C, or polyimide. Edema, neuronal and glial reaction, and inflammatory responses to the coated wires were quantitated at four sites in each animal. Inconsistency of response in all measured parameters was found, both between animals and between sites in infected animals. Infected animals showed the greatest variability, primarily in the degree of inflammatory reaction. Parylene C was found to induce the most severe inflammatory reaction, an unexpected finding. No consistent reaction to any of the coating materials was found in this study. We believe that this variability in response was primarily due to infection by E. cuniculi. Our results suggest that rabbits should not be used for tissue compatibility testing of neural device biomaterials until the animals are free of E. cuniculi infestation as demonstrated by serologic screening.

Animals↗
PubMed1987

Electrical insulation of implantable devices by composite polymer coatings.

Protection of implanted integrated circuits has required hermetic sealing, usually in metal containers and usually in package sizes that would preclude implantation in small and confined areas of the body. We have developed a method whereby ultrathin (10 micron) composite films consisting of glow discharge and vapor deposited polymers can be placed directly over integrated circuit substrates to provide protection from water and ions for up to 30 days (our present test limits). Our paper describes the reactor, surface preparation, and polymerization conditions necessary to obtain the water/ion resistant coatings. Results indicate little change in leakage current when comb patterns with 10 micron line widths and our insulating composite coatings are exposed to physiological saline solution and a 3 VDC bias.

Adhesiveness↗
PubMed1986

Factor VIII complex in canine plasma after submaximal treadmill exercise.

Exercise-induced changes in the plasma concentrations of coagulation factor VIII and von Willebrand factor were evaluated, using 8 random-source adult dogs that exercised on a treadmill for 5 to 10 minutes (mean running time = 8.3 minutes). Maximum treadmill speeds attained by the dogs were 11 to 18 km/hr, and the mean of the maximum individual speeds was 14.3 km/hr. Maximum heart rates of individual dogs during exercise were 190 to 250 beats/min with a mean of 218 beats/min (a 2.4-fold increase over the mean preexercise rate). Exercise did not induce significant increases in plasma concentrations of factor VIII coagulant activity, coagglutinin co-factor activity, or factor VIII-related antigen. Results indicated that submaximal exercise does not induce increases in plasma concentrations of coagulation factor VIII or von Willebrand factor in the dog.

Animals↗
PubMed1984

Biochemical and cellular identification of HLA-Bw44 subtypes.

Biochemical analysis of HLA-Bw44 antigens by two-dimensional gelelectrophoresis and one-dimensional isoelectric focusing (IEF) from serologically heterozygous and homozygous donors allows the identification of two distinct types of HLA-Bw44 molecules, designated as Bw44-I and Bw44-II. These results are in concordance with the data obtained by CML-typing where at least two types of Bw44 target cells can be distinguished clearly as well. The antigen of type I has a more acidic isoelectric point (IEP) than that of type II. The difference in IEP are not due to differences in sialic acid content.

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PubMed1981

The adhesion of glow--discharge polymers, Silastic and Parylene to implantable platinum electrodes: results of tensile pull tests after exposure to isotonic sodium chloride.

Thin organic coatings commonly are used for insulating microelectrodes and electronic packages designed for implant applications. The adherence of these coatings to the underlying substrates is a key parameter in their selection for various devices. Instron pull tests were performed on glow-discharge polymerized monomers, Parylene-N, medical-grade Silastic and various epoxies. The application of a thin coating of glow-discharge polymerized methane under a thicker Parylene-N coating improved the adhesion of the latter to the underlying substrate in isotonic sodium chloride solution and during accelerated testing conditions done by boiling.

Adhesiveness↗
PubMed1979

Bioevaluation of plasma polymerized films in skeletal muscle.

Plasma polymerized ethylene (PPE), styrene (PPS), and chlorotrifluoroethylene (PPCTFE) were synthesized by exposing the monomeric gases to an inductively coupled radio frequency "glow-discharge" field. The polymer films were deposited on poly(dimethyl) siloxane (medical grade Silastic), which was then surgically implanted in rat paravertebral muscle for periods up to 84 weeks. The biocompatibility of the plasma deposited films and uncoated Silastic was evaluated by qualitative (graded inflammatory cell response) and quantitative (connnective tissue capsule thickness) techniques as a function of time. The morphological features of the connective tissue capsule and the plasma polymerized films were examined by SEM after 75 weeks of implantation. Results showed that the acute inflammatory cell migration around PPS and PPCTFE was at a maximum in 2 weeks, decaying to control levels in 4 to 8 weeks. The PPE response was judged as less than the control response up to 4 weeks. After 8 weeks no qualitative difference could be detected between the plasma polymerized films and Silastic. On the other hand, a quantifiable change in fibrous capsule response as a function of time and material was noted until 24 weeks. From these data we conclude that these types of films do not elicit an untoward foreign body reaction at a skeletal muscle implant site in rats.

Animals↗
PubMed1978

Performance of implanted biogalvanic pacemakers.

Seventeen unipolar cardiac pacemakers powered by hybrid biogalvanic cells were implanted in dogs. Long term clinical effects and electrical performance in vivo of the generators were investigated. The biogalvanic cells were designed to provide 50 years of generator operation. No systemic pathological changes which would be attributed to the generator or the biogalvanic cell were observed. Local reaction to implants was mild and not significantly different from the one observed in conventional pacemaker implantations to date. The electrical performance of the biogalvanic cells was very encouraging. Final steady-state cell voltage levels of .65V to .75V were reached in 100--150 days after implantation and remained constant in 3 units to date which represents over 36 months after implantation for each generator.

Animals↗
PubMed1978

Patent ductus arteriosus in the dog: a retrospective study of radiographic, epidemiologic, and clinical findings.

Twenty-seven cases of patent ductus arteriosus (PDA) in the dog, which were confirmed by cardiac catheterization, surgical exploration, or at necropsy, were reviewed. A machinery murmur, electrocardiographic evidence of left ventricular enlargement, and radiographic evidence of cardiomegaly with an aortic and a pulmonary artery dilatation were consistent features. Surgical repair was successful in 65% of the dogs. The postoperative radiographic and electrocardiographic changes are described. A concomitant congenital defect was present in 2 dogs. The epidemiologic features of 532 dogs identified as having PDA and submitted to the National Cancer Institute's Veterinary Medical Data Program were reviewed. Miniature and Toy Poodles, Pomeranians, and Shetland Sheepdogs were identified as being at high risk for PDA. An excess of females over males was noticed.

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