PubMed Health⌕ Search

Biomedical subjects

A Schreyer

Publications and source records attributed to A Schreyer.

12 recordsLinked to original sources
PubMed2005

Comparative analysis of the structure of sterically stabilized ferrofluids on polar carriers by small-angle neutron scattering.

Results of experiments on small-angle neutron scattering from ferrofluids on polar carriers (pentanol, water, methyl-ethyl-ketone), with double-layer sterical stabilization of magnetic nanoparticles, are reported. Several types of spatial structural organization are observed. The structure of highly stable pentanol-based samples is similar to that of stable ferrofluids based on organic non-polar carriers (e.g., benzene) with mono-layer covered magnetic nanoparticles. At the same time, the effect of the interparticle interaction on the scattering is stronger in polar ferrofluids because of the structural difference in the surfactant shell. The structure of the studied methyl-ethyl-ketone- and water-based ferrofluids essentially different from the previous case. The formation of large (>100 nm in size) elongated or fractal aggregates, respectively, is detected even in the absence of external magnetic field, which corresponds to weaker stability of these types of ferrofluids. The structure of the fractal aggregates in water-based ferrofluids does not depend on the particle concentration, but it is sensitive to temperature. A temperature increase results in a decrease in their fractal dimension reflecting destruction of the aggregates. In addition, in water-based ferrofluids these aggregates consist of small (radius approximately 10 nm) and temperature-stable primary aggregates.

Colloids↗
PubMed2003

[Evaluation of radiological teaching programs in the Internet].

PURPOSE: Evaluation of web based training programs, which can be contacted from the homepages of radiological departments of German universities. MATERIAL AND METHOD: From June 2000 to January 2002 the 75 web based training programs of 57 providers,which can be contacted from the web pages of the radiological departments of German universities were evaluated in a prospective study. A medical student experienced in using the world wide web examined each training program three times in an interval of six months using the following criteria: availability of the web sites, target group, kind of training program, contents and structure and the technical solution. RESULTS: 51 of the 57 the homepages were fully available at each visit. 64 of the 75 web based training programs which could be connected from these sites were available at all three visits.One program was only partially available at one spot check. 8 of the 75 programs were designed for physicians and medically trained personal, 23 were made for medical students and 44 addressed both target groups (partially more than once mentioned). The number of the presented cases ranged between one single and 3700. In 31 of 75 training programs links to other teaching files were found. A complete presentation of cases was presented by 48 of the 75 web sites.5 of the 75 web sites offered physiological images for comparison. In 20 training programs the pathological changes were optically marked in the x-ray images. A logical and didactical structure was found in 24 teaching files, 14 gave the possibility to check the learning results. No provider made use of the possibility to pass credits to the students or physicians account with regard to official training programs. Multimedia techniques were used in 15 training programs.43 sites used data reduced preview images (thumbnails). The latest update of the site is mentioned in 55 of the 75 web sites. 19 of 57 providers had either no possibility of contact or did not answer to an e-mail. CONCLUSION: From the homepages of the departments of diagnostic radiology of German universities 75 teaching files can be contacted. There is a great variety in quantity and quality. Most sites offer collections of cases. A web based training program which is comparable in quality to a CD-ROM teaching program could not be found. No program used the possibility to give credits to the users with regard to official training programs.

Computer-Assisted Instruction↗
PubMed2002

Determination of lopinavir and nevirapine by high-performance liquid chromatography after solid-phase extraction: application for the assessment of their transplacental passage at delivery.

An adaptation of the HPLC method previously described for the simultaneous assay of amprenavir, ritonavir, indinavir, saquinavir, nelfinavir and efavirenz after solid-phase extraction is proposed here for the separate analysis of the newer PI lopinavir (LPV) and the NNRTI nevirapine (NVP). After viral inactivation by heat (60 degrees C for 60 min), plasma (600 microl), with clozapine added as internal standard, is diluted 1+1 with phosphate buffer pH 7 and subjected to a solid-phase extraction on a C(18) cartridge. Matrix components are eliminated with 2 x 500 microl of a solution of 0.1% H(3)PO(4) neutralised with NaOH to pH 7. LPV and NVP are eluted with 3 x 500 microl MeOH. The resulting eluate is evaporated under nitrogen at room temperature and is reconstituted in 100 microl MeOH 50%. A 40-microl volume is injected onto a Nucleosil 100, 5 microm C(18) AB column. LPV and NVP are analysed separately using a gradient elution program with solvents constituted of MeCN and phosphate buffer adjusted to pH 5.07 and containing 0.02% sodium heptanesulfonate. LPV and NVP are detected by UV at 201 and 282 nm, respectively. The calibration curves are linear up to 10 microg/ml. The mean absolute recovery of LPV and NVP is 91% and 88%, respectively. The method is precise with mean inter-day C.V.s within 2.1-6.6% and 0.9-1.7% for LPV and NVP, and accurate (range of inter-day deviations -1.1 to +2.4%, and -1.9 to +0.8%, for LPV and NVP, respectively). The method has been validated and is currently applied to the monitoring of LPV and NVP in HIV patients, and has been notably applied in a study aimed at assessing the extent of transplacental passage of nevirapine and PIs, notably lopinavir, at the time of delivery in pregnant HIV-infected women.

Calibration↗
PubMed1998

The effects of birth on urinary continence mechanisms and other pelvic-floor characteristics.

OBJECTIVE: To determine the effects of delivery on bladder and anorectal functions. METHODS: One hundred forty-nine nulliparas were studied once during pregnancy and again about 9 weeks after delivery by means of questionnaire, clinical examination, perineal sonography, urethral pressure profiles, and recording of intravaginal and intra-anal pressures during pelvic-floor contraction. RESULTS: Stress urinary incontinence was present in 46 patients (31%) during pregnancy and persisted in ten of them after delivery. After vaginal delivery, urinary and fecal incontinence were present in 36% and 4% of forceps-delivered women, respectively, and in 21% and 5.5% of spontaneously delivered women. Bladder neck mobility was increased significantly after all vaginal births, whereas bladder neck position at rest was lowered only in forceps-delivered women. Functional urethral length was decreased in the supine and standing positions after spontaneous and forceps deliveries. Otherwise, indices of urethral sphincter function were unchanged or improved after vaginal delivery. A significant decrease in intravaginal pressure and in intra-anal pressure was observed in all vaginally delivered women. The intra-anal pressure decrease correlated significantly with infant weight (r=0.24, P=.01). Women who underwent cesarean had no specific complaints and only slight modifications of these measurements. CONCLUSION: After spontaneous and instrumental deliveries, 21% and 34% of women complained of stress urinary incontinence and 5.5% and 4% reported fecal incontinence, respectively. Substantial bladder neck hypermobility was present together with diminished functional urethral length and intravaginal and intra-anal pressures. Only 22% of patients with stress urinary incontinence during pregnancy had such incontinence after delivery.

Adult↗
PubMed1998

Stimulated pressure profile at rest: a noninvasive method for assessing urethral sphincter function.

OBJECTIVES: To validate a method for assessing urethral sphincter muscle function by recording rises in intraurethral pressure during repetitive pudendal nerve stimulations. METHODS: A supine urethral pressure profile at rest was performed on 12 stress-continent and 28 stress-incontinent patients during repetitive pudendal nerve stimulations applied near the ischial spine, and the intraurethral pressure increases were calculated for each third of the urethral functional length. RESULTS: No significant difference in intraurethral pressure increases was seen between continent and stress-incontinent women. On the various regression curves, the intraurethral pressure increases showed a significant correlation with maximal urethral closure pressure values at rest and at stress (r = 0.36 to 0.54) and with the patient's age (r = 0.46), but not with pudendal nerve conduction times to the urethral sphincter on either side (r = 0.14 and 0.19). CONCLUSIONS: This method (1) measures intraurethral pressure increases that correlate well with the anatomic location of the urethral sphincter muscle, (2) shows there is no significant difference between them in continent and stress-incontinent patients, except in patients with a low-pressure urethra, and (3) demonstrates that they correlate well with the maximal urethral closure pressure and the patient's age, but not with pudendal motor latencies to the urethral sphincter. This method gives us a mapping of the urethral sphincter activity, explaining why some patients with a low-pressure urethra have less urinary loss than others with the same urethral closure pressure.

Adult↗
PubMed1996

The assessment of bladder neck position and mobility in continent nullipara, mulitpara, forceps-delivered and incontinent women using perineal ultrasound: a future office procedure?

The purpose of this study was to assess the effects of spontaneous and instrumented deliveries, the baby's birthweight, the presence of stress incontinence and the woman's age and weight on bladder neck (BN) position and mobility using perineosonography, a simple non-invasive method, and to compare these results with those from continent nulliparous controls. Two hundred and fourteen women, including 74 nullipara, 29 para-1, 64 para-2 and 3, 16 with previous forceps deliveries and 32 with stress incontinence, underwent perineosonography with measurements of BN position and backwards/downwards displacement of BN using a two-axis calculation system. Results showed that bladder neck position undergoes a significantly backwards and downwards displacement on assuming an upright position. When compared with nulliparous controls, the bladder neck position at rest was the same in all groups of parous women in the supine/standing positions, but lower in patients having undergone forceps delivery (standing position) and in stress incontinent patients (both supine and standing); the bladder neck position during Valsalva was significantly lower in all groups of patients in the standing position, but the only significant difference in the supine position was seen in stress incontinent patients; the extent of bladder neck displacement was not significantly different between the groups, except in stress incontinent patients. A strong correlation (r = 0.66) was found between the relative importance of backwards and downwards displacement, but no correlation was found between bladder neck displacement and baby's birth-weight or patient's weight. It was concluded that compared to nulliparous continent patients, normal and instrumented delivery induces no modifications of BN position at rest, but is responsible for a lower bladder neck position during Valsalva in the standing position only. The extent of BN displacement is virtually the same in all groups of patients in both positions, except for stress incontinent patients, who have a significantly lower and more mobile bladder neck, the values of which overlap to a great extent (sensitivity of 78%/75% for a displacement > 14 mm) within those seen in continent nulliparous women. The correlation between the importance of backwards and downwards displacement is strong, making superfluous a two-dimensional coordinate system for routine BN position/mobility assessment.

Age Factors↗
PubMed1991

ATP-dependent transport of taurocholate across the hepatocyte canalicular membrane mediated by a 110-kDa glycoprotein binding ATP and bile salt.

Direct photoaffinity labeling of liver plasma membrane subfractions enriched in sinusoidal and canalicular membranes using [35S]adenosine 5'-O-(thiotriphosphate) ([35S]ATP gamma S) allows the identification of ATP-binding proteins in these domains. Comparative photoaffinity labeling with [35S]ATP gamma S and with the photolabile bile salt derivative (7,7-azo-3 alpha, 12 alpha-dihydroxy-5 beta-[3 beta-3H]-cholan-24-oyl-2'- aminoethanesulfonate followed by immunoprecipitation with a monoclonal antibody (Be 9.2) revealed the identity of the ATP-binding and the bile salt-binding canalicular membrane glycoprotein with the apparent Mr of 110,000 (gp110). The isoelectric point of this glycoprotein was 3.7. Transport of bile salt was studied in vesicles enriched in canalicular and sinusoidal liver membranes. Incubation of canalicular membrane vesicles with [3H] taurocholate in the presence of ATP resulted in an uptake of the bile salt into the vesicles which was sensitive to vanadate. ATP-dependent taurocholate transport was also observed in membrane vesicles from mutant rats deficient in the ATP-dependent transport of cysteinyl leukotrienes and related amphiphilic anions. Substrates of the P-glycoprotein (gp170), such as verapamil and doxorubicin, did not interfere with the ATP-dependent transport of taurocholate. Reconstitution of purified gp110 into liposomes resulted in an ATP-dependent uptake of [3H]taurocholate. These results demonstrate that gp110 functions as carrier in the ATP-dependent transport of bile salts from the hepatocyte into bile. This export carrier is distinct from hitherto characterized ATP-dependent transport systems.

ATP-Binding Cassette Transporters↗
PubMed1991

Fluorescent derivatives of bile salts. I. Synthesis and properties of NBD-amino derivatives of bile salts.

In order to visualize bile salt transport, fluorescent bile salt derivatives were synthesized by introduction of the relatively small fluorescent 4-nitrobenzo-2-oxa-1,3-diazol (NBD)-amino group in either the 3-, 7-, or 12-position of the steroid structure, thus providing a complete set of diastereomeric derivatives, 3 alpha-NBD-amino-7 alpha,12 alpha-dihydroxy-5 beta-cholan-24-oic acid, 3 beta-NBD-amino-7 alpha,12 alpha-dihydroxy-5 beta-cholan-24-oic acid, 7 alpha-NBD-amino-3 alpha,12 alpha-dihydroxy-5 beta-cholan-24-oic acid, 7 beta-NBD-amino-3 alpha,12 alpha-dihydroxy-5 beta-cholan-24-oic acid, 12 alpha-NBD-amino-3 alpha,7 alpha-dihydroxy-5 beta-cholan-24-oic acid, 12 beta-NBD-amino-3 alpha,7 alpha-dihydroxy-5 beta-cholan-24-oic acid, as well as their taurine conjugates. Their optical properties with absorption maxima at about 490 nm and emission maxima at 550 nm make them suitable for fluorescent microscopic studies. Fluorescence of the NBD-derivatives is strongly dependent on polarity of the solvent, on the concentration of the bile salt derivatives, and only slightly on temperature.

Bile Acids and Salts↗