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Biomedical subjects

W Zingg

Publications and source records attributed to W Zingg.

At least 37 records · Page 2Linked to original sources
PubMed1985

Parallel flow arteriovenous shunt for the ex vivo evaluation of heparinized materials.

The patency of heparin-polyvinyl alcohol (hep-PVA) coated polyethylene tubing was found to be significantly longer than control tubes coated with polyvinyl alcohol (PVA) but without heparin at low flow rates in dogs using a novel parallel flow arteriovenous shunt designed to avoid surgical artifacts. A standard Silastic chronic shunt (3.18 mm i.d.) was inserted between the iliac artery and vein of a dog. After a 2-week recovery period, a small diameter coated polyethylene tube (1.14 mm i.d.) was connected in parallel with the exteriorized portion of the chronic shunt through a pair of Silastic Y-connectors, so that less than 3% of the shunt flow was diverted into the test tube. The chronic shunt was reused many times over a greater than 6 month patency period, eliminating the need for frequent surgery and reducing interanimal variability in the results. The difference in patency between heparinized and control tubes was greater at higher mainshunt flow rates indicating the presence of a significant effect of the Y-connectors on platelet adhesion or aggregation. This effect was manifested in a time-dependent reduction in circulating platelet count. Scanning electron microscopy (SEM) examination of the midportion of the heparinized tubes after occlusion demonstrated the absence of platelet and fibrin deposits, unlike the control tubes without heparin. Although the Y-connectors played a significant role, they did not dominate the thrombotic processes occurring in this shunt and consequently the biological effectiveness of the immobilized heparin could be demonstrated.

Animals↗
PubMed1985

Determination of the surface tension of various species of erythrocytes by means of the solidification front technique.

The solidification front technique is employed to determine the surface tension of fixed erythrocytes of dog, horse, human, chicken, and turkey. The results range from 65.5 erg/cm2 for dog erythrocytes to 67.6 erg/cm2 for turkey erythrocytes. A detailed error analysis shows that the differences obtained are statistically significant. Since cellular interactions are governed to a considerable extent by surface tension effects, it is concluded that caution needs to be exercised when results obtained for one species are used to predict the behavior of cells of another species.

Animals↗
PubMed1985

Modification of platelet adhesion by antiplatelet drugs helps prevent cardiovascular complications of diabetes mellitus.

If it could be shown that: The abnormal platelet function in diabetes contributes to the development of cardiovascular complications of diabetes, the abnormal platelet function is a consequence of the diabetic state, the level of blood sugar control or insulin administration, antiplatelet drugs improve the abnormal platelet function independent of the diabetic state and its treatment, the altered platelet function induced by antiplatelet drugs diminishes the evolution of cardiovascular complications, the addition of antiplatelet drugs to the management of diabetes may be reasonable. Specifically designed animal experiments are necessary to provide the scientific basis for designing appropriate clinical trials.

Animals↗
PubMed1985

DIAG: a computer-assisted dermatologic diagnostic system--clinical experience and insight.

Over the past few decades, the computer has been utilized in various ways to assist physicians in formulating their differential diagnoses, usually on an experimental basis. Following a review of the three major technics employed in computer-assisted diagnosis, statistical pattern classification, production rules, and cognitive models, a new system (DIAG) is described. The sole function of DIAG is to assist in the formulation of the differential diagnosis of skin diseases. At the beginning of the fourth year of development, the accuracy of the program in reaching diagnoses has been shown, on many occasions, to be comparable to its expert counterparts. However, it has been demonstrated that the system is not utilized within the dermatology clinic routinely. In response to this, aspects of DIAG have been modified in order to improve its clinical acceptability. Until this acceptance is achieved, these tools will not fulfill their potential to affect patient care.

Diagnosis, Computer-Assisted↗
PubMed1983

The electro-osmotic actuation of implantable insulin micropumps.

A study using an electro-osmotic cell suitable for actuating an implantable insulin micropump showed that controlled variable flow rates in the order of 0.2 mL/day are possible. The cell functioned continuously with low energy and power requirements and long service life. The principle of operation is compatible with achieving the very low flow rates necessary if highly concentrated insulin is to be used to avoid frequent insulin reservoir refilling. An electro-osmotic cell, Ag/AgCl/NaCl(aq)/cation exchange membrane/NaCl(aq)/AgCl/Ag, was connected to a constant current power supply which reversed the direction of the current every 10 mins causing a to-and-fro transport of fluid through the membrane. Flow rates of 0.15-0.60 microL/min were achieved with currents of 2.5-10 mA. At the low flow rate, energy consumption was 6.4 X 10(-2) J/microL and peak power requirement was less than 2.0 X 10(-4) W. Fluid was transported against a pressure gradient of 52 cm Hg. The cell contained a total electrolyte volume of less than 0.25 mL. The membrane showed no change in properties after 10,000 current reversals (69 days). To function as an actuator for an implantable insulin micropump, the electro-osmotic cell requires a switching and valving assembly; a suitable design for this is briefly considered.

Insulin Infusion Systems↗
PubMed1983

Surface thermodynamics of bacterial adhesion.

The adhesion of five strains of bacteria, i.e., Staphylococcus aureus (strain 049), Staphylococcus epidermidis (strain 047), Escherichia coli (strains 055 and 2627), and Listeria monocytogenes, to various polymeric surfaces was studied. The design of the experimental protocol was dictated by thermodynamic considerations. From the thermodynamic model for the adhesion of small particles from a suspension onto a solid substratum, it follows that the extent of adhesion is determined by the surface properties of all three phases involved, i.e., the surface tensions of the adhering particles, of the substrate, and of the suspending liquid medium. In essence, adhesion is more extensive to hydrophilic substrata (i.e., substrata of relatively high surface tension) than to hydrophobic substrata, when the surface tension of the bacteria is larger than that of the suspending medium. When the surface tension of the suspending liquid is larger than that of the bacteria, the opposite pattern of behavior prevails. Suspensions of bacteria at a concentration of 10(8) microorganisms per ml were brought into contact with several polymeric surfaces (Teflon, polyethylene, polystyrene, and acetal and sulfonated polystyrene) for 30 min at 20 degrees C. After rinsing, the number of bacteria adhering per unit surface area was determined by image analysis. The surface tension of the suspending medium. Hanks balanced salt solution, was modified through the addition of various amounts of dimethyl sulfoxide. It was found that the number of bacteria adhering per unit surface area correlates well with the thermodynamic predictions and that these data may be used to determine the surface tension of the different bacterial species. The surface tensions of the bacteria obtained in this fashion are in excellent agreement with those obtained by other methods.

Acetals↗
PubMed1983

Determination of the surface tension of protein coated materials by means of the advancing solidification front technique.

We investigated whether substrates with different surface tensions would induce a different degree of conformational change in adsorbed protein molecules, which would be reflected by differences in the surface tension of the adsorbed layers. The solidification front technique allowed this study without requiring to expose the protein coated-particle to an air interface which would induce conformational changes in the adsorbed protein layer. With a low bulk albumin concentration (0.1%) decreasing surface tension of the adsorbed protein layer with increasing hydrophobicity of the substrate, suggested more extensive conformational changes on the more hydrophobic surfaces. At high bulk concentrations (0.5% and above) the surface tension of the adsorbed albumin layer was independent of the substrate material and increased to a value of approximately 70.2 ergs/cm2. This was consistent with the surface tension of albumin derived from other independent techniques such as contact angle measurements on thick layers of the protein material or from adsorption data. Freezing front measurements with albumin (BSA or HSA), immunoglobulin G (IgG), and fibrinogen adsorbed onto one and the same substrate material, octyl-sepharose beads, indicate that the hydrophobicity of the protein coated sepharose increased in the following order: BSA less than HSA less than IgG less than Fibrinogen. This was in good agreement with the relative hydrophobicity of these proteins determined by other independent methods.

Animals↗
PubMed1983

The effect of temperature on the extent of platelet adhesion to foreign surfaces.

For a given temperature the extent of platelet adhesion increased with increasing substrate surface tension, in agreement with earlier findings. For a given substrate platelet adhesion decreases linearly with decreasing temperature. Morphometric evaluation of the adhering platelets indicated that the extent of platelet spreading as a function of temperature follows the same pattern as the extent of platelet adhesion. Smaller quantities of ADP were required to induce aggregation at the reduced temperatures. Substrate roughness did not appear to influence the extent of platelet adhesion to any of the surfaces for any of the temperatures examined.

Biocompatible Materials↗
PubMed1982

Continuous ambulatory peritoneal dialysis in diabetics with end-stage renal disease.

Twenty diabetics with end-stage renal disease who had never previously received dialysis treatment were treated with continuous ambulatory peritoneal dialysis for periods of two to 36 months (average, 14.5). Intraperitoneal administration of insulin achieved good control of blood sugar. Even though creatinine clearance decreased significantly (P = 0.001), control of blood urea nitrogen and serum creatinine was adequate. Hemoglobin and serum albumin levels increased significantly (P = 0.005 and 0.04, respectively). Similarly, there was a significant increase in serum triglycerides and alkaline phosphatase (P = 0.02 and 0.05). Blood pressure became normal without medications in all but one of the patients. Retinopathy, neuropathy, and osteodystrophy remained unchanged. Peritonitis developed once in every 20.6 patient-months--a rate similar to that observed in nondiabetics. The calculated survival rate was 93 per cent at one year; the calculated rate of continuation on ambulatory peritoneal dialysis was 87 per cent. We conclude that continuous ambulatory dialysis with intraperitoneal administration of insulin is a good alternative treatment for diabetics with end-stage renal disease.

Adult↗
PubMed1982

Surface thermodynamics of phagocytic ingestion of non-opsonized bacteria by granulocytes in liquids of different surface tensions.

The free energy of engulfment of four bacterial species by human granulocytes is calculated from contact angle data as a function of the surface tension gamma LV of the suspending liquid. The resulting curves predict that at low liquid surface tensions gamma LV, the phagocytic ingestion increases with decreasing hydrophobicity of the bacteria while at high surface tensions gamma LV, it increases with increasing hydrophobicity. Furthermore, these curves reach a minimum at values of gamma LV equal to the surface tension gamma LV of the bacteria. The experimental results support these predictions. Thus, the determination of the surface tension of the suspending medium at which phagocytic ingestion becomes minimum represents a novel technique to establish the surface tension of ingested particles, such as bacteria. The results obtained in this fashion for the four bacterial species are in good agreement with those obtained from contact angles, as well as those derived from bacterial adhesion experiments.

Bacterial Physiological Phenomena↗
PubMed1982

Effect of surface roughness on platelet adhesion under static and under flow conditions.

Normal blood clots when exposed to surfaces other than endothelial. Various unsuccessful attempts have been made to find a synthetic material that is compatible with blood. Both platelets and clotting factors are involved in thrombosis at foreign surfaces. The authors are concerned with platelet adhesion as a first step in thrombus formation. The determination of the number of platelets adhering per unit area, therefore, appears to be a useful criterion for the choice of appropriate biomaterials contacting blood. However, laboratory tests are often carried out with specially prepared, well-defined biomaterials with a smooth surface, whereas biomaterials in clinical use may have a variable degree of roughness. In this paper the authors present data on platelet adherence to a hydrophilic (glass) and to a hydrophobic (silane) material, with smooth and rough surfaces. Additional data are presented that document the extent of platelet adhesion to a wide range of smooth polymer materials having a large variation in surface hydrophobic quality. There was no difference in platelet adherence between the smooth and rough surfaces when tested under static conditions. When the surfaces were tested in a laminar flow cell, the addition of roughness caused a decrease in platelet adhesion on the hydrophilic surface and an increase in platelet adhesion on the hydrophobic surface.

Animals↗