Biomedical subjects

C Werner

Publications and source records attributed to C Werner.

At least 91 records · Page 5Linked to original sources

PubMed2000

Resistance of L132 lung cell clusters to glyoxal-induced apoptosis.

Glyoxal is a highly reactive glycating agent involved in the formation of advanced glycation end products (AGEs) and known to induce apoptosis. AGE-mediated apoptosis may be an important mechanism of alveolar epithelial remodelling in pulmonary fibrosis. In this study, we investigated the cytotoxic effect of glyoxal on the fetal human epithelial lung cell line L132 under serum-free conditions. This type of culture, which forces the cells to grow as spheroids, also excludes effects of preformed AGEs by the reaction of glyoxal with fetal calf serum proteins. Our results showed that in cells treated with 200 microM glyoxal, the intercellular contacts in spheroids were disrupted, i.e. cells became totally dissociated. Immunocytochemical analysis revealed a dose-dependent accumulation of the AGE product epsilonN-(carboxymethyl)lysine (CML) in cells detached from cell clusters. The loss of cell attachment was associated with decreased expression of beta1-integrins and CD44 as revealed by laser scanning cytometry (LSC). Increasing concentrations of glyoxal induced an increase in the number of apoptotic cells which were identified by the immunoreactivity for active caspase-3. Remaining cell clusters showed resistance to both CML formation and apoptosis. The present findings demonstrate that cells treated with glyoxal undergo possibly anoikis, a specific mode of apoptosis caused by loss of cell adhesion.

Anoikis↗

PubMed2000

Benzoxazinoids-cyclic hydroxamic acids, lactams and their corresponding glucosides in the genus Aphelandra (Acanthaceae).

An improved method of sample preparation and simultaneous HPLC separation was developed that allowed the separation of 2,4-dihydroxy-1,4-benzoxazine-3(4H)-one (DIBOA), 2,4-dihydroxy-7-methoxy-1,4-benzoxazine-3(4H)-one (DIMBOA), 2-hydroxy-1,4-benzoxazine-3(2H)-one (HBOA), 2-hydroxy-7-methoxy-1,4-benzoxazine-3(2H)-one (HMBOA) and their corresponding glucosides as well as the benzoxazolinones BOA and MBOA. The amount and distribution of these compounds was determined in the roots of Aphelandra squarrosa and A. fuscopunctata plants. There is a significant difference in the amount and distribution of this substance class in the two species analyzed. The results are discussed in relation to their function as defence compounds and allelochemicals.

Benzoxazines↗

PubMed2000

A mechanized gait trainer for restoring gait in nonambulatory subjects.

OBJECTIVE: To construct an advanced mechanized gait trainer to enable patients the repetitive practice of a gaitlike movement without overstraining therapists. DEVICE: Prototype gait trainer that simulates the phases of gait (by generating a ratio of 40% to 60% between swing and stance phases), supports the subjects according to their ability (lifts the foot during swing phase), and controls the center of mass in the vertical and horizontal directions. PATIENTS: Two nonambulatory, hemiparetic patients who regained their walking ability after 4 weeks of daily training on the gait trainer, a 55-year-old woman and a 62-year-old man, both of whom had a first-time ischemic stroke. INTERVENTION: Four weeks of training, five times a week, each session 20 minutes long. MAIN OUTCOME MEASURES: Functional ambulation category (FAC, levels 0-5) to assess gait ability and ground level walking velocity. Rivermead motor assessment score (RMAS, 0-13) to assess gross motor function. RESULTS: Patient 1: At the end of treatment, she was able to walk independently on level ground with use of a walking stick. Her walking velocity had improved from .29m/sec to .59m/sec. Her RMAS score increased from 4 to 10, meaning she could walk at least 40 meters outside, pick up objects from floor, and climb stairs independently. Patient 2: At end of 4-week training, he could walk independently on even surfaces (FAC level 4), using an ankle-foot orthosis and a walking stick. His walking velocity improved from .14m/sec to .63m/sec. His RMAS increased from 3 to 10. CONCLUSION: The gait trainer enabled severely affected patients the repetitive practice of a gaitlike movement. Future studies may elucidate its value in gait rehabilitation of nonambulatory subjects.

Equipment Design↗

PubMed2000

Increasing isoflurane concentration may cause paradoxical increases in the EEG bispectral index in surgical patients.

We have studied the effects of increases in isoflurane concentration on the EEG bispectral index (BIS) in 70 patients anaesthetized with isoflurane-nitrous oxide-sufentanil for major abdominal surgery. During surgery, baseline BIS was recorded at 0.8% end-tidal isoflurane with nitrous oxide in oxygen (FIO2 0.35). After this, end-tidal isoflurane was increased to 1.6% for 15 min and decreased subsequently to 0.8% for 20 min to assess recovery. In 20 patients, BIS decreased from a mean value of 40 (SD 9) during baseline to 25 (10) at 1.6% isoflurane. In contrast, BIS did not change in 23 patients and increased in 27 patients from 35 (6) to 46 (8) as isoflurane was increased to 1.6%. In all patients, BIS recovered to baseline values at 0.8% isoflurane. The changes in BIS with increasing isoflurane concentration were not related to drugs or differences in physiological variables, which did not differ between groups. Patients with a decrease in BIS were significantly younger (38 (range 18-68) yr) than those with unchanged (55 (26-70) yr) or increased (60 (40-70) yr) BIS values (P < 0.001). It is possible that the paradoxical increase in BIS is related to continuous pre-burst EEG patterns consisting of high-frequency activity. This suggests that the use of BIS as a guide for isoflurane administration may be misleading in some patients undergoing surgical procedures.

Abdomen↗

PubMed2000

Effects of xenon on cerebral blood flow and autoregulation: an experimental study in pigs.

We have investigated the effects of xenon on regional cerebral blood flow (rCBF) and autoregulation in pigs sedated with propofol 4 mg kg-1 h-1. Balloon-tipped catheters were placed into the descending aorta and inferior vena cava of 15 Göttingen Minipigs for manipulation of arterial pressure and blood sampling. rCBF was measured using the sagittal sinus outflow technique. Xenon was adjusted randomly to end-tidal fractions (FE'Xe) of 0, 0.30, 0.50 and 0.70. After baseline measurements of heart rate (HR), mean arterial pressure (MAP), rCBF, sagittal sinus pressure (SSP) and calculation of regional cerebrovascular resistance (rCVR) at each respective FE'Xe, autoregulation was tested in the MAP range 60-120 mm Hg. Increasing FE'Xe had no effect on HR, MAP, rCBF or SSP. rCVR increased with increases in MAP, regardless of FE'Xe. Autoregulation was not impaired. We conclude that xenon inhalation had no effect on rCBF and autoregulation in our model, which could suggest that xenon is an adequate adjunct for neurosurgical anaesthesia.

Anesthetics, Inhalation↗

PubMed2000

Preanesthetic train-of-four fade predicts the atracurium requirement of myasthenia gravis patients.

BACKGROUND: The most sensitive diagnostic criterion of myasthenia gravis is a decrement in the muscular response to repetitive stimulation. The authors hypothesized that myasthenia gravis patients who show a train-of-four ratio (T4/T1) < 0.9 in the preanesthetic period will have increased sensitivity to nondepolarizing neuromuscular blocking agents compared with myasthenia gravis patients with preanesthetic T4/T1 > or = 0.9. METHODS: After institutional review board approval was obtained, 20 electrophysiologically documented myasthenia gravis patients were studied. Current pyridostigmine therapy was continued until the morning of surgery. Before induction of anesthesia, neuromuscular transmission was recorded from the hypothenar muscles using electromyography with train-of-four stimulation of the ulnar nerve. According to the T4/T1 ratio, patients were assigned to the "normal" group (T4/T1 > or = 0.9) or the "decrement" group (T4/T1 < 0.9). After induction of intravenous anesthesia, the effective dose to achieve a 95% neuromuscular blockade (ED95) for atracurium was assessed with a cumulative bolus technique. Postoperatively, pyridostigmine was titrated to obtain a T4/T1 > 0.75 and to treat residual myasthenic symptoms. RESULTS: In 14 patients, preanesthetic T4/T1 was > or = 0.9 (normal), whereas 6 patients presented with T4/T1 < 0.9 (decrement). Decrement patients had a lower ED95 of 0.07 +/- 0.03 mg/kg atracurium (mean +/- SD) compared with normal patients with an ED95 of 0.24 +/- 0.11 mg/kg atracurium (P = 0.002). All patients were extubated within 30 min after surgery. Postoperative pyridostigmine infusion did not differ significantly between groups. CONCLUSIONS: The requirement for atracurium is significantly reduced in myasthenia gravis patients with a T4/T1 ratio < 0.9 before anesthesia. This study indicates that routine neuromuscular monitoring in myasthenia gravis patients should be extended into the preinduction period to identify patients who require less atracurium.

Adult↗

PubMed2000

Identification of novel serine/threonine protein phosphatases in Trypanosoma cruzi: a potential role in control of cytokinesis and morphology.

We cloned two novel Trypanosoma cruzi proteins by using degenerate oligonucleotide primers prepared against conserved domains in mammalian serine/threonine protein phosphatases 1, 2A, and 2B. The isolated genes encoded proteins of 323 and 330 amino acids, respectively, that were more homologous to the catalytic subunit of human protein phosphatase 1 than to those of human protein phosphatase 2A or 2B. The proteins encoded by these genes have been tentatively designated TcPP1alpha and TcPP1beta. Northern blot analysis revealed the presence of a major 2.3-kb mRNA transcript hybridizing to each gene in both the epimastigote and metacyclic trypomastigote developmental stages. Southern blot analysis suggests that each protein phosphatase 1 gene is present as a single copy in the T. cruzi genome. The complete coding region for TcPP1beta was expressed in Escherichia coli by using a vector, pTACTAC, with the trp-lac hybrid promoter. The recombinant protein from the TcPP1beta construct displayed phosphatase activity toward phosphorylase a, and this activity was preferentially inhibited by calyculin A (50% inhibitory concentration [IC(50)], approximately 2 nM) over okadaic acid (IC(50), approximately 100 nM). Calyculin A, but not okadaic acid, had profound effects on the in vitro replication and morphology of T. cruzi epimastigotes. Low concentrations of calyculin A (1 to 10 nM) caused growth arrest. Electron microscopic studies of the calyculin A-treated epimastigotes revealed that the organisms underwent duplication of organelles, including the flagellum, kinetoplast, and nucleus, but were incapable of completing cell division. At concentrations higher than 10 nM, or upon prolonged incubation at lower concentrations, the epimastigotes lost their characteristic elongated spindle shape and had a more rounded morphology. Okadaic acid at concentrations up to 1 microM did not result in growth arrest or morphological alterations to T. cruzi epimastigotes. Calyculin A, but not okadaic acid, was also a potent inhibitor of the dephosphorylation of (32)P-labeled phosphorylase a by T. cruzi epimastigotes and metacyclic trypomastigote extracts. These inhibitor studies suggest that in T. cruzi, type 1 protein phosphatases are important for the completion of cell division and for the maintenance of cell shape.

Amino Acid Sequence↗

PubMed2000

[A simple model for describing pressure-volume curves in free balloon dilatation with reference the dynamics of inflation hydraulic aspects].

We propose a simple model to describe pressure-time and pressure-volume curves for the free balloon (balloon in air) of balloon catheters, taking into account the dynamics of the inflation device. On the basis of our investigations of the flow rate-dependence of characteristic parameters of the pressure-time curves, the appropriateness of this simple model is demonstrated using a representative example. Basic considerations lead to the following assumptions: (1) the flow within the shaft of the catheter is laminar, and (ii) the volume decrease of the liquid used for inflation due to pressurization can be neglected if the liquid is carefully degassed prior to inflation, and if the total volume of the liquid in the system is less than 2 ml. Taking into account the dynamics of the inflation device used for pumping the liquid into the proximal end of the shaft during inflation, the inflation process can be subdivided into the following three phases: initial phase, filling phase and dilatation phase. For these three phases, the transformation of the time into the volume coordinates is given. On the basis of our model, the following parameters of the balloon catheter can be determined from a measured pressure-time curve: (1) the resistance to flow of the liquid through the shaft of the catheter and the resulting pressure drop across the shaft, (2) the residual volume and residual pressure of the balloon, and (3) the volume compliance of the balloon catheter with and without the inflation device.

Angioplasty, Balloon, Coronary↗

PubMed1999

Screening postmortem blood and tissues for nine classes [correction of cases] of drugs of abuse using automated microplate immunoassay.

A commercially available enzyme-linked immunosorbant assay (ELISA) was evaluated as a screening procedure for the detection of nine classes of abused drugs in postmortem blood and tissue specimens. Specifically, postmortem blood, fluid and/or tissue homogenates were screened for amphetamine (AMP), methamphetamine (MET), barbiturates (BARB), benzodiazepines (BZD), cannabinoids (CNB), cocaine (benzoylecgonine; BE), morphine-specific (MOR), opiates (class; OPI), phencyclidine (PCP) and lysergic acid diethylamide (LSD) by ELISA and by coated tube radioimmunoassay (CTR) (BARB, BE, OPI, PCP, LSD) or double-antibody radioimmunoassay (DAR) (AMP/METH, BZD, CNB). Specimens that screened 'positive' by any method were confirmed and quantitated by gas chromatography/mass spectrometry (GC/MS). The only assay that appeared to perform less optimally than RIA was the MOR assay (five false negatives). However, this assay is very specific for free morphine while the GC/MS confirmation method provided a total morphine value. The OPI assay was more sensitive, producing fewer false negatives, and is recommended for broad class opiate screening. EIA is an adequate alternative to RIA for screening postmortem specimens, including blood and tissue, for nine major classes of drugs.

Amphetamine↗

PubMed1999

Tributaries of West Antarctic Ice Streams Revealed by RADARSAT Interferometry.

Interferometric RADARSAT data are used to map ice motion in the source areas of four West Antarctic ice streams. The data reveal that tributaries, coincident with subglacial valleys, provide a spatially extensive transition between slow inland flow and rapid ice stream flow and that adjacent ice streams draw from shared source regions. Two tributaries flow into the stagnant ice stream C, creating an extensive region that is thickening at an average rate of 0.49 meters per year. This is one of the largest rates of thickening ever reported in Antarctica.

Journal Article↗

PubMed1999

Prevention of osteoporosis after cardiac transplantation: a prospective, longitudinal, randomized, double-blind trial with calcitriol.

BACKGROUND: Accelerated bone loss is a well-recognized complication after cardiac transplantation (HTx) due to immunosuppressive therapy. The purpose of this prospective, longitudinal, randomized, placebo-controlled, double-blind study was to investigate the effect of calcitriol (1,25-dihydroxyvitamin D3) in the prevention of bone loss and fracture rate after HTx. METHODS: Basic therapy included 1000 mg of calcium daily and sex hormone replacement in hypogonadal patients. A total of 132 patients (111 male, 21 female; mean age: 51+/-10 years; 35+/-25 months after HTx) were randomized to 0.25 microg of calcitriol or placebo. Bone mineral density (BMD, g/cm2; T score, %) of the lumbar spine and x-rays for the assessment of vertebral fractures were performed at baseline and after 12, 24, and 36 months. Biochemical indexes of mineral metabolism were measured every 3 months. RESULTS: Overall BMD was significantly decreased after HTx (T score 87+/-13%). BMD increased continuously within the study period in the calcitriol group (1 year: 2.2+/-4.8%; 2 years: 3.9+/-5.4%; 3 years: 5.7+/-4.4%) as well as in the placebo group (1 year: 1.8+/-4.9%; 2 years: 3.7+/-6.5%; 3 years: 6.1+/-7.8%) without statistical difference between the groups. Fracture incidence was low during the study interval (1 year: 2.0%; 2 years: 3.4%; 3 years: 0%). Hypogonadism (20%) was associated with a lower BMD (78+/-12% vs. 88+/-12%; P<0.01) and a higher increase (35%) after hormone replacement in comparison to normogonadal patients. Increased intact parathyroid hormone and bone resorption markers decreased significantly during therapy. CONCLUSIONS: Calcium supplementation and sex hormone replacement in hypogonadism proved a sufficient long-term prevention therapy to improve decreased BMD and to prevent fractures after HTx. Besides immunosuppression, both concomitant hypogonadism and secondary hyperparathyroidism play a major role in the long-term bone loss and should therefore be monitored and treated adequately. Low-dose calcitriol demonstrated no significant extra benefit regarding BMD and fracture rate in the long-term period after HTx.

Adult↗

PubMed1999

Desflurane and isoflurane improve neurological outcome after incomplete cerebral ischaemia in rats.

We have investigated the effects of isoflurane and desflurane on neurological outcome in a rat model of incomplete cerebral ischaemia. We studied 40 non-fasted male Sprague-Dawley rats, anaesthetized, intubated and ventilated mechanically with isoflurane and nitrous oxide in oxygen (FlO2 0.3). Arterial and venous catheters were inserted for measurement of arterial pressure, drug administration and blood sampling. A biparietal electroencephalogram (EEG) was recorded continuously using subdermal platinum electrodes. At completion of surgery, administration of isoflurane was discontinued (with the exception of those animals receiving isoflurane as treatment) and rats were allowed an equilibration period of 30 min according to the following procedure: group 1 (n = 10), 66% nitrous oxide in oxygen and fentanyl (bolus 10 micrograms kg-1 i.v. followed by infusion at a rate of 25 micrograms kg-1 h-1); group 2 (n = 10), 1.0 MAC of isoflurane in oxygen (FlO2 0.3) and air; groups 3 and 4 (n = 10 per group), 1.0 MAC or 1.5 MAC of desflurane in oxygen (FlO2 0.3) and air, respectively. Ischaemia was produced by combined unilateral common carotid artery ligation and haemorrhagic hypotension to 35 mm Hg for 30 min. Functional neurological deficit was evaluated for 3 days after cerebral ischaemia. At baseline, brain electrical activity was higher with fentanyl-nitrous oxide, 1.0 MAC of isoflurane and 1.0 MAC of desflurane (groups 1-3) compared with 1.5 MAC of desflurane (group 4). Neurological outcome was improved in isoflurane and desflurane anaesthetized animals (groups 2-4), regardless of the concentration used compared with fentanyl-nitrous oxide anaesthesia (group 1). The increase in plasma epinephrine and norepinephrine concentrations during ischaemia was significantly higher in fentanyl-nitrous oxide anaesthetized animals (group 1) compared with animals who received volatile anaesthetics (groups 2-4). These data suggest that cerebral protection produced by isoflurane and desflurane appears to be related to reduction in sympathetic activity rather than suppression of cerebral metabolic rate.

Anesthetics, Inhalation↗

PubMed1999

Diagnostic epididymal and testicular sperm recovery and genetic aspects in azoospermic men.

Various procedures for sperm recovery in azoospermic men have been described, from open testicular biopsy to simple needle aspiration from the epididymis and the testis. Fifty-one obstructive and 86 non-obstructive azoospermic men were treated to compare the recovery of spermatozoa obtained by percutaneous aspiration from the epididymis (PESA) and aspiration/extraction from the testis (TESA, TESE) with histopathology. If TESA failed, the work up proceeded with TESE. All patients were karyotyped. Spermatozoa were recovered by PESA or TESA in all obstructive men (51/51 patients). In 22 out of 86 patients with non-obstructive azoospermia, testicular spermatozoa could be successfully recovered by TESA. In five additional patients TESE was successful in recovering spermatozoa where TESA had failed. In 43 patients, neither TESA nor TESE was successful. Sixteen patients chose not to proceed with TESE. Seven out of 86 patients had an abnormal karyotype in the non-obstructive group (8%), none in the obstructive group. In the non-obstructive patient group testicular histopathology showed hypospermatogenesis, incomplete maturation arrest and germ cell aplasia with focal spermatogenesis in cases where spermatozoa were recovered and complete germ cell aplasia, complete maturation arrest and fibrosis in cases where no spermatozoa were found. Spermatozoa were recovered by PESA or TESA from all patients with obstructive azoospermia and from approximately 40% of patients with non-obstructive azoospermia by TESA or TESE. Retrieval of viable spermatozoa in the infertility work-up was highly predictable for sperm recovery in subsequent ICSI cycles. TESA performed under local anaesthesia seems almost as effective as more invasive procedures in recovering testicular spermatozoa, both in obstructive and non-obstructive azoospermic men.

Epididymis↗

PubMed1999

Non-velocity-related effects of a rigid double-stopped ankle-foot orthosis on gait and lower limb muscle activity of hemiparetic subjects with an equinovarus deformity.

BACKGROUND AND PURPOSE: This study investigated the non-velocity-related effects of a 1-bar rigid ankle-foot orthosis on the gait of hemiparetic subjects, with particular emphasis on the muscle activity of the paretic lower limb. METHODS: Twenty-one hemiparetic subjects who had been using an ankle-foot orthosis for equinovarus deformity for <1 week participated. Patients walked cued by a metronome at a comparable speed with and without the orthosis. Dependent variables were basic, limb-dependent cycle parameters, gait symmetry, vertical ground reaction forces, sagittal ankle excursions, and kinesiological electromyogram of several lower limb muscles. RESULTS: The use of the caliper was associated with more dynamic and balanced gait, characterized by longer relative single-stance duration of the paretic lower limb, better swing symmetry, better pivoting over the stationary paretic foot, and better ankle excursions (P<0.05). The functional activity of the paretic quadriceps muscles increased, while the activity of the paretic tibialis anterior muscle decreased (P<0.05). CONCLUSIONS: The orthosis led to a more dynamic and balanced gait, with enhanced functional activation of the hemiparetic vastus lateralis muscle. The study further supports the functional benefits of a rigid ankle-foot orthosis in hemiparetic subjects as an integral part of a comprehensive rehabilitation approach. However, the reduced activity in the tibialis muscle may lead to disuse atrophy and hence long-term dependence on the orthosis.

Adult↗

PubMed1999

Surface characterization of polymers for medical devices.

A survey is given on analytical techniques currently applied to the surface characterization of biomedical polymers. The techniques include spectroscopies, thermodynamic and electrochemical measurements and microscopies, respectively. To illustrate the motivation for surface analysis, the hypotheses on the correlations between surface parameters and hemocompatibility of polymers are briefly examined. The applications of the examined methods are illustrated by a number of examples. These examples include the characterization of cellulose membranes (low-flux hemodialysis membranes) by streaming potential measurements and by inverse contact angle measurements. The use of surface spectroscopies (ATR-FTIR and XPS) is demonstrated by considering the optimization of surface modification procedures of vascular prostheses made from poly(tetrafluoroethylene). Furthermore, the characterization of water-swollen cellulose membranes by scanning force microscopy is shown. Finally, the extended application of physico-chemical surface analysis to the investigation of protein adsorption is considered. An example deals with in situ spectroscopic ellipsometry used to study the adsorption of fibrinogen onto a plasma-deposited hydrophobic fluoropolymer and onto poly(ethyleneoxide)-grafted fluoropolymer, respectively.

Biocompatible Materials↗

PubMed1999

[In Process Citation]

This paper was intended to settle the question whether the so-called gentle sectio caesarea with a high skin incision as described by Cohen in 1972 [2] could be applied in combination with a sectio on the level of the classic Pfannenstiel's incision which would be more satisfying cosmetically. Furthermore a comparison was to be drawn between the postoperative condition of those patients on whom this surgical method had been performed and the condition following a classic Pfannenstiel's incision. Between January 1997 and July 1997 we compared the classic method of Pfannenstiel's incision with the variant of Cohen's method as described above in a prospective randomised study. On applying this surgical technique, the abdomen was opened according to Cohen's method using a surgical knife but for the skin, and the tissue layers underneath were opened blunt with two fingers. Following the extraction of the child only three sutures were made: Uterus, fascia and skin. Redon drainages were not inserted. We were able to show that this method of applying mainly blunt "incision" to sectio caesarea the tissue is at least equal to the sharp opening of the abdominal cavity. In some respects, such as the early postoperative mobilisation, it is, in fact, superior, because the blunt opening causes less bleeding and the reduction to three sutures only, deliberately leaving the two peritoneal membranes open, as well as leaving away the redon drainages, considerably increases the patients' postoperative well-being. It is for these reasons that we call for this method to become part of the routine procedures in caesarean sectio.

Journal Article↗

PubMed1999

[Pressure-volume recording of PTCA catheters with balloons of lower and higher compliance].

In this report, the results of complementary studies of pressure-volume (p-V) measurements on balloon catheters with balloons of low (LC) and high compliance (HC) used for percutaneous transluminal coronary angioplasty are discussed. The measurements were performed with balloons unconfined in air (free dilatation) and also confined in different shells. In the case of rigid shells, a surprisingly high self-expansion of the catheters was found. Although this self-expansion does not contribute to the radial dilatation, it cannot be neglected, but must be taken into account when the success of balloon dilatation is determined on the basis of measured p-V curves. The investigations performed using wrapped shells clearly show the different dilatation properties of LC and HC balloons. The results provide important information on the feasibility of controlled balloon dilatation on the basis of p-V measurements performed on-line during PTCA.

Angioplasty, Balloon, Coronary↗

PubMed1998

Extended Electrokinetic Characterization of Flat Solid Surfaces.

An experimental setup has been developed and applied for the combined determination of the electrokinetic potential and the surface conductivity of flat surfaces. The key feature of the new device (designated as microslit electrokinetic setup) is the variability of the distance between two parallel flat sample surfaces (10 mm x 20 mm) forming a slit channel. The setup allows us to decrease this distance down to about 1 µm keeping the surfaces parallel. In consequence, streaming potential measurements can be performed at a given solid/liquid interface both at conditions where surface conductivity is negligible and at conditions where surface conductivity significantly contributes to the total channel conductivity. The zeta potential is calculated at different channel geometries based on streaming potential and channel conductivity data and, alternatively, based on streaming current measurements and the dimensions of the cross section of the slit channel. The results obtained were found to agree well if correct conductivity values for the calculation of the zeta potential based on the streaming potential data are used. The surface conductivity is determined from the extrapolation of the channel conductance values gained at a number of sufficiently small distances between the parallel sample surfaces to the distance zero. An additional feature of the developed microslit electrokinetic setup is the assessability of the hydrodynamic thickness of adsorbed layers of macromolecules or particles at the investigated flat surface. In a series of measurements a plasma-deposited fluoropolymer (PDFP) layer on top of a glass carrier and an adsorption layer of the blood protein fibrinogen on top of the PDFP layer were characterized by zeta potential and surface conductivity measurements in different aqueous electrolyte solutions (KCl, KOH, HCl). For the PDFP/solution interfaces zeta potential up to -100 mV were obtained in solutions of neutral pH exclusively due to preferential ion adsorption. After adsorption of fibrinogen the zeta potential is considerably reduced. For the PDFP/solution interfaces surface conductivities were determined in the range of (1-2) x 10(-9) S. The contribution of the diffuse layer to the surface conductivity has been calculated from the zeta potential according to the approach of Bikerman (Kolloid Z. 72, 100 (1935)) and compared with the experimentally determined surface conductivity. Based on this comparison ions in hydrodynamically immobile interfacial layers were concluded to contribute considerably to the surface conductivity in all investigated cases. This so-called additional surface conductivity is attributed to the accumulation of hydroxide and hydronium ions in the Stern layer. Both the high specific mobility of these ions (as compared to the potassium and the chloride ions) and the conductivity of the charge determining species may contribute to the experimental observations. After adsorption of fibrinogen onto the PDFP surface the additional surface conductivity is increased by about an order of magnitude. The latter fact is assumed to be caused by the presence of mobile ions in the interfacial volume of the adsorbed protein layer. In addition to the electrochemical characterization of the adsorbed protein layer its hydrodynamic thickness has been determined by means of liquid flow measurements with the microslit electrokinetic setup. The obtained value of 48 +/- 5 nm correlates well with the protein dimensions given in the literature and is in the order of magnitude of the optical layer extension determined by ellipsometry. Copyright 1998 Academic Press.

Journal Article↗