Assessment of PEO/PTMO multiblock copolymer/segmented polyurethane blends as coating materials for urinary catheters: in vitro bacterial adhesion and encrustation behavior

The effective long-term use of indwelling urinary catheters has often been hindered by catheter-associated infection and encrustation. In this study, the suitability of poly(ethylene oxide) (PEO)-based multiblock copolymer/segmented polyurethane (SPU) blends as coating materials for the commercial urinary catheters was assessed by measuring swellability, bacterial adhesion, and encrustation behavior. When exposed to PBS (pH 7.4), the blends absorbed a significant amount of water, which was proportional to the copolymer content. It was demonstrated from bacterial adhesion tests that compared to bare SPU, the blend surfaces could significantly reduce the adhesion of E. coli, P. mirabilis, and S. epidermidis; the number of adherent bacteria correlated with the amount of copolymer additive. indicating that the swellability of the blends affected bacterial adhesion. Of the bacteria studied, the greatest effect of the copolymer additive was observed in S. epidermidis adhesion, in which there was an 85% decrease compared to bare SPU with a small amount of copolymer additive as low as 5% based on a dried blend. By using an artificial bladder model, allowing the catheter to be blocked by encrustation, it was revealed that the blend surfaces could effectively resist encrustation. The duration of patency was extended up to 20 +/- 3.1 h on the blend surface containing 10% of the copolymer additive, whereas the silicone-coated catheter, a control, required the least time for blockage, 7.8 +/- 3.1 h. The superior characteristics of the blends compared to other surfaces might be attributed to their PEO-rich surfaces, produced by the migration of PEO phase in the copolymer chain of the blends in an aqueous environment, and provide promising potential as a coating material on the urinary catheter for long-term catheterization.     

An assessment of an automated fluorimetric blood phenylalanine technique for phenylketonuria screening and for accurate estimations

An assessment of the automated fluorimetric technique for the estimation of phenylalanine, using blood collected and stored on filter paper, indicated that its accuracy and precision compared favourably with those of other methods, including the bacteriological inhibition assay. The method appeared to offer advantages, both in the detection of phenylketonuria and for the more accurate determinations required in the further investigation and control of known cases.     

An automated technique for measuring the area of contrasted bronchi

Central Scientific-Research Institute for Tuberculosis. Institute for Problems of Information Transmission, Moscow. Translated from Meditsinskaya Tekhnika, No. 3, pp. 30–32, May–June, 1992.     

An automated screening technique for the detection of sickle-cell haemoglobin

An automated technique is described which is capable of detecting sickle-cell haemoglobin and differentiating the sickle-cell trait from sickle-cell anaemia. The method is based upon the Itano solubility test and utilizes Technicon equipment.     

An EEG averaging technique for automated sleep-wake stage identification in the rat

An automated on-line sleep-wake classification system based on an averaging technique of the running EEG is described. It operates for three rats simultaneously and is able to discriminate every 5 sec between wakefulness, light slow-wave sleep, deep slow-wave sleep, and paradoxical sleep. The hippocampal EEG and nuchal EMG are used as input parameters. The EEG is bandpass filtered after which a microcomputer samples and averages the filtered EEG and constructs spectrograms. The variability, the theta-delta ratio and the amplitude of the delta waves are obtained from these spectrograms. Together with the amplitude index of the EMG, these three EEG indices are subjected to decision rules for the identification of sleep-wake states. A first evaluation study showed 93% agreement between visual inspection and computer classification. In a second evaluation study 24-hr recordings were made. Clear circadian patterns emerged especially during the light period: deep slow-wave sleep was enhanced during the initial hours, while paradoxical sleep tended to increase over the latter hours. The outcome of these studies is compared with the results obtained with other automated sleep identification procedures.     

Antibiotic resistance ofPseudomonas aeruginosa colonizing a urinary catheter in vitro

A modified Robbins Device was used to establish coherent biofilms ofPseudomonas aeruginosa on the surface of catheter material in an artificial urine milieu and the ability of an antibiotic to penetrate the biofilm and kill the enclosed bacteria was assessed. ThePseudomonas aeruginosa strain used had been isolated from a patient with urinary tract infection. Although planktonic (floating) cells of thePseudomonas aeruginosa strain were inhibited by less than 1 mg/l of tobramycin and killed by 50 mg/l, contact with 1,000 mg/l of tobramycin for 12 h failed to kill all the sessile (adherent) bacteria in the biofilms on the surface of the catheter material. Surviving sessile bacteria recovered directly from the exposure to 1,000 mg/l of tobramycin were inhibited by 0.4 mg/l of this agent when tested as dispersed planktonic cells by standard MIC methods. It is suggested that growth within thick adherent biofilms confers upon cells ofPseudomonas aeruginosa a large measure of resistance to aminoglycosides and other antibiotics that may help to explain the frequent failure of antibiotic chemotherapy in catheter-associated urinary tract infections.     

Deflation of the 'obstinate' Foley's urinary catheter balloon: a new technique

We have successfully deflated "obstinate" Foley's urinary catheter balloons in 15 cases in the last six months with the help of a simple bedside procedure using an angiographic guide-wire.     

An automated technique for SPECT marker-based image registration in radionuclide therapy

An automated technique for marker-based image registration in radionuclide therapy is described. This technique is based on localization of the centroids of external markers and on establishing correspondence between the individual markers of the two studies to be registered. Localization of the centroids of markers relies on segmenting the markers using iterative thresholding. Thresholding is locally adaptive in order to account for study-dependent conditions (e.g. crossover between adjacent markers and markers with varying radioactive concentrations). Following marker segmentation, the centroids of the markers are computed based on an intensity-weighted method. Finally, prior to the least-squares fit registration, the markers of the two sets are matched to achieve one-to-one correspondence. The technique was applied to both simulated and patient studies resulting in mean residual three-dimensional registration errors (+/- 1SD) of 1.7 +/- 0.1 mm and 3.5 +/- 0.3 mm respectively. The technique was compared with a semi-automated approach and no significant difference was found between the mean residual three-dimensional registration errors (t = 0.281. p = 0.8). This automated marker-based image registration technique provides robust and accurate registration. Although it was developed as part of a programme to generate three-dimensional dose distributions for radionuclide therapy, it could be useful for other clinical applications.     

An evaluation of the automated assay of urinary oestrogens in pregnant women

An automated assay suitable for estimating urinary oestrogens in pregnant women has been investigated. Fluorimetry was found to have considerable advantages over colorimetry. The fluorimetric assay was simpler, more precise, more sensitive, and eliminated the need for correction for non-specific chromogens; in the assay of oestriol in pregnant women there was no need for correction for non-specific fluorescence. Spectrofluorimetric and photometric analyses, recoveries, and reproducibility show that the method offers a robust means of providing values for urinary oestrogen in pregnant women on a scale of up to 100 tests a day, the time of the assay being one and a half hours.     

An automated technique for analysis of current transitions in multilevel single-channel recordings

Detailed kinetic studies of ion channel gating are best carried out using the patch-clamp technique which permits the measurement of the ionic current through individual channels. Typical patch-clamp recordings show the current signal, in the form of a sequence of rectangular pulses (analogous to a random telegraph signal), riding on slow baseline drift, partially obscured by high-frequency noise and distorted by filtering. In order to analyze such recordings, we have developed a set of interactive Pascal programs based on a feature-detection algorithm capable of identifying current transitions in multiple-channel recordings in the presence of substantial levels of noise and drift. Software operation is largely automated but includes provisions for examination and correction of the output. The software was optimized and systematically evaluated using simulated data with variable amounts of noise and drift. Results indicate that satisfactory performance is obtained for signal-to-noise ratio as low as four even with uncommonly large baseline drift. Steady-state processing speeds varied from 1000 to 4000 samples per second depending on data complexity.     

An in vitro technique to assess oxygenator potential for respiratory failure therapies

To assess microporous membrane oxygenators (MMO) for long-term respiratory support, an in vitro test of 4 days duration has been developed. The objective is to screen oxygenators before they undergo expensive animal trials. As a sensitive indicator of performance change, CO2 transfer rates (VCO2) are determined with fresh bovine blood at the start, after 48 hours and after 96 hours of perfusion. Blood is used only for gas exchange evaluation and is replaced with plasma in the intervening periods. Data are obtained at blood flow rates (QB) of 1.0, 1.5 and 2.0 l/min for gas: blood flow ratios (QG:QB) of 2:1 and 5:1. The test has been conducted on Bentley BOS-CM50 oxygenators (n = 10). With heated dry air ventilation there was no significant change in VCO2 with time for all QB and QG:QB combinations. Plasma leakage did not occur into the gas compartment of the MMO. Similar results were obtained with heated humidified air ventilation. The findings are in agreement with existing animal studies of 4-7 days duration.     

The cytotoxicity assessment of the novel latex urinary catheter with prolonged antimicrobial activity

The purpose of this study was to evaluate the in vitro biocompatibility of the novel Sparfoxacin (SPA)-treated latex catheter with previously performed prolonged antimicrobial activity. Rectangular-shaped test samples of silicone latex catheter were fabricated according to patented procedure permitting the immobilization of SPA on heparin (HP)-coated catheter by means of mixed, covalent and non-covalent bonds. Samples subjected to cytotoxicity assay were divided into four groups: (1) the untreated catheter, (2) HP-coated catheter, (3) HP-coated catheter with SPA immobilized in low SPA concentration solution (SPA-L treated sample), and (4) high SPA concentration solution (SPA-H treated sample). Then the samples were placed directly into green monkey kidney (GMK) cell monolayer for 24 h. After the incubation period, cytotoxicity was determined by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. The degree of cytotoxicity of each sample was evaluated according to the reference value represented by the control cells cultured without catheter sample. Statistical significance was determined by repeated t-test (P < 0.05). The cytotoxic effect of treated and untreated catheters was also estimated by microscopic observations of GMK cells morphological changes. SPA-treated catheters demonstrated high survival rates in MTT assay (>93%) on the contrary to the untreated catheters (6.13%) and HP-coated catheters (80.90%). Moreover, microscopic observation of GMK cells exposed to SPA-treated samples revealed no morphological changes and no cell growth reduction. We suggest that SPA-treated latex catheters are biofilm formation resistant (as we revealed in our previous work), considerably less toxic than untreated ones, and can be undoubtedly used in urological practice.     

An electrical impedance technique for assessment of wheals

In previous studies of the electrical impedance of the skin, we introduced a set of physical indices which could be used to distinguish between the cutaneous effects produced by different irritants and allergic contact reactions. In this study, wheals were induced in 10 allergic patients by performing prick tests on the forearm with the relevant allergen and histamine, respectively. Normal skin was used for control. The wheals were evaluated by visual scoring, laser Doppler, and electrical impedance. As expected, there was a close agreement between the visual and laser Doppler readings. Compared to the controls, there were significant changes in the electrical impedance of the wheals, especially in the index related to the phase angle. The changes in the indices were found to follow a particular pattern, which diverged from those obtained in contact skin reactions of both allergic and irritant type. Our results indicate that, by the application of the impedance technique, it will be possible to characterize objectively and quantify the wheal reaction. The results also suggest that cutaneous reactions of completely different causes, such as allergic skin reactions of the late and immediate type, and irritant contact reactions, may be distinguished on the basis of their effects on the electrical impedance of the skin.     

Novel approach to in vitro drug susceptibility assessment of clinical strains of Leishmania spp

Resistance to antimonial drugs has been documented in Leishmania isolates transmitted in South America, Europe, and Asia. The frequency and distribution of resistance to these and other antileishmanial drugs are unknown. Technical constraints have limited the assessment of drug susceptibility of clinical strains of Leishmania. Susceptibility of experimentally selected lines and 130 clinical strains of Leishmania panamensis, L. braziliensis, and L. guyanensis to meglumine antimoniate and miltefosine was determined on the basis of parasite burden and percentage of infected U-937 human macrophages. Reductions of infection at single predefined concentrations of meglumine antimoniate and miltefosine and 50% effective doses (ED(50)s) were measured and correlated. The effects of 34°C and 37°C incubation temperatures and different parasite-to-host cell ratios on drug susceptibility were evaluated at 5, 10, and 20 parasites/cell. Reduction of the intracellular burden of Leishmania amastigotes in U-937 cells exposed to the predefined concentrations of meglumine antimoniate or miltefosine discriminated sensitive and experimentally derived resistant Leishmania populations and was significantly correlated with ED(50) values of clinical strains (for meglumine antimoniate, ρ = -0.926 and P < 0.001; for miltefosine, ρ = -0.906 and P < 0.001). Incubation at 37°C significantly inhibited parasite growth compared to that at 34°C in the absence of antileishmanial drugs and resulted in a significantly lower ED(50) in the presence of drugs. Susceptibility assessment was not altered by the parasite-to-cell ratio over the range evaluated. In conclusion, measurement of the reduction of parasite burden at a single predetermined drug concentration under standardized conditions provides an efficient and reliable strategy for susceptibility evaluation and monitoring of clinical strains of Leishmania.     

Biofilm formation by Candida species on the surface of catheter materials in vitro.

A model system for studying Candida biofilms growing on the surface of small discs of catheter material is described. Biofilm formation was determined quantitatively by a colorimetric assay involving reduction of a tetrazolium salt or by [3H]leucine incorporation; both methods gave excellent correlation with biofilm dry weight (r = 0.997 and 0.945, respectively). Growth of Candida albicans biofilms in medium containing 500 mM galactose or 50 mM glucose reached a maximum after 48 h and then declined; however, the cell yield was lower in low-glucose medium. Comparison of biofilm formation by 15 different isolates of C. albicans failed to reveal any correlation with pathogenicity within this group, but there was some correlation with pathogenicity when different Candida species were tested. Isolates of C. parapsilosis (Glasgow), C. pseudotropicalis, and C. glabrata all gave significantly less biofilm growth (P < 0.001) than the more pathogenic C. albicans. Evaluation of various catheter materials showed that biofilm formation by C. albicans was slightly increased on latex or silicone elastomer (P < 0.05), compared with polyvinyl chloride, but substantially decreased on polyurethane or 100% silicone (P < 0.001). Scanning electron microscopy demonstrated that after 48 h, C. albicans biofilms consisted of a dense network of yeasts, germ tubes, pseudohyphae, and hyphae; extracellular polymeric material was visible on the surfaces of some of these morphological forms. Our model system is a simple and convenient method for studying Candida biofilms and could be used for testing the efficacy of antifungal agents against biofilm cells.     

An epidemiologic assessment of genomic profiling for measuring susceptibility to common diseases and targeting interventions

Purpose: The current clinical value of genomic profiling (testing for genotypes at multiple loci) for assessing susceptibility to common diseases and targeting behavioral and medical interventions is questionable. As common diseases result from many gene-environment interactions, epidemiologic studies should be used to examine the value of genomic profiling in terms of clinical validity (future disease positive and negative predictive value stratified by exposure), clinical utility (targeted interventions to reduce disease risk among persons with the profile) and public health utility (comparing reduction of disease burden in the population based on genomic profiling to population-wide interventions).Methods: We investigate these parameters for a hypothetical common disease (5% lifetime risk), for which 3 genetic variants at different loci and one environmental exposure are risk factors.Results: We show that even for modest effects of each variant alone (risk ratios from 1.5–3.0) and modest interactions between the exposure and the genes, the disease predictive value for people with 2 or more variants (especially 3) can be quite high (50–100%) in the presence of a modifiable exposure. Individual risks can then be reduced by targeted exposure intervention among persons with the genotype. However, the predictive value for multiple genotypes is much lower for rarer diseases (< 1 per 1000). Also, with increasing number of genes in a profile, the population impact of disease reduction for targeted intervention based on genotype will be smaller, especially for rare genotypes, weak associations, and weak interactions.Conclusion: To assess the value of genomic profiling, well-designed epidemiologic studies are needed to quantify disease risks, in addition to costs, benefits, and risks for testing and interventions.