A dedicated compression device for high resolution X-ray tomography of compressed gas diffusion layers.

We present an experimental approach to study the three-dimensional microstructure of gas diffusion layer (GDL) materials under realistic compression conditions. A dedicated compression device was designed that allows for synchrotron-tomographic investigation of circular samples under well-defined compression conditions. The tomographic data provide the experimental basis for stochastic modeling of nonwoven GDL materials. A plain compression tool is used to study the fiber courses in the material at different compression stages. Transport relevant geometrical parameters, such as porosity, pore size, and tortuosity distributions, are exemplarily evaluated for a GDL sample in the uncompressed state and for a compression of 30 vol.%. To mimic the geometry of the flow-field, we employed a compression punch with an integrated channel-rib-profile. It turned out that the GDL material is homogeneously compressed under the ribs, however, much less compressed underneath the channel. GDL fibers extend far into the channel volume where they might interfere with the convective gas transport and the removal of liquid water from the cell.

[Control of aspirin effect in chronic cardiovascular patients using two whole blood platelet function assays. PFA-100 and Multiplate]. / Vollblutaggregometrie zur Kontrolle der Wirksamkeit von Azetylsalizylsäure bei Patienten mit koronarer Herzkrankheit. Vergleich von PFA-100 und Multiplate.

In this study two aspirin sensitive platelet function tests which are based on the analysis of whole blood were evaluated and correlated with each other. In vitro bleeding time was determined using the PFA-100 analyzer (Dade Behring, Marburg, Germany) using the collagen/epinephrine cartridge and citrated blood. Whole blood aggregometry was performed using the Multiplate analyzer (Dynabyte medical, Munich, Germany) using hirudin blood (25 mug/ml). Aggregatin was triggered using arachidonic acid (ASPItest), collagen (COLtest) or TRAP-6 (thrombin receptor activating peptide, TRAPtest). Following informed consent citrated blood and hirudin blood was drawn from 76 cardiovascular patients which were on long-term aspirin therapy (aspirin patients). In addition hirudin blood was drawn from 57 healthy blood donors for assessment of whole blood aggregometry. PFA-100 closure times of the aspirin patients were 273 +/- 49 s. Based on the cut-off of 170 s a non response to the aspirin therapy was detected in 5 of 76 patients. Whole blood aggregation was comparable in the aspirin patients vs the blood donors AUC values in the TRAP test, whereas in COLtest and ASPItest significantly reduced aggregations were detected (p < 0.05). Of the five patients that had a normal PFA-100 closure time only one had normal aggregation in ASPItest, and also only one had a normal aggregation in COLtest. The high rate of response to the aspirin therapy which was found in PFA-100 and ASPItest can be explained by the assumed high level of compliance of the cohort. In the applied tests different patients were stratified as aspirin-non-responders. This highlights the importance of the assay conditions for the diagnosis of an aspirin-non-response.

Detection limit, cut-off and specificity of an improved rapid assay for cardiac troponin T.

The performance of an improved version of the troponin T rapid test TROPT Sensitive was investigated in a multicentre evaluation at twelve centres. The detection limit and the cut-off were determined in a method comparison with Elecsys Troponin T using a total of 365 samples from patients with suspected acute coronary syndromes and 91 samples from healthy blood donors or non-cardiological patients. The analytical specificity was determined by measuring 1271 blood samples from blood donors without any myocardial injury. The test cut-off (90% of results positive) is 0.08 microg/L, and the detection limit is about 0.05 microg/L. The analytical specificity of the test is between 99.7 and 99.9%. With its small area of undefined significance between positive and negative results and its high sensitivity and specificity, TROPT Sensitive is very well suited to the reliable detection of troponin T positive patients with acute coronary syndromes.

The tobacco apocytochrome b gene predicts sensitivity to the respiratory inhibitors antimycin A and myxothiazol.

The potential for use of the cytochrome-pathway electron-transfer inhibitors antimycin A and myxothiazol in the selection of plant mitochondrial genome transformants was investigated. The net growth of Nicotiana tabacum L. (tobacco) suspension-culture cells was reduced by these inhibitors, but complete repression of cell growth occurred only in the presence of both cytochrome and alternative electron-transfer-pathway inhibitors. Antimycin A and myxothiazol bind to and block electron transfer through different sites in the cytochrome b (COB) subunit of the mitochondrial bc1 respiratory complex (complex III). The nucleotide sequence of the tobacco cob gene was determined and found to predict highly conserved glycine and phenylalanine residues that are associated with sensitivity to antimycin A and myxothiazol, respectively. These residues are altered by mutations that confer resistance to antimycin A or myxothiazol in diverse organisms. Tobacco cob cDNA clones were constructed and sequenced, revealing eight full and 11 partial RNA-editing sites. RNA editing did not, however, alter codons for the conserved glycine and phenylalanine residues associated with sensitivity to the respiratory inhibitors. Antimycin A or myxothiazol, in conjunction with a modified cob gene, may therefore be useful in the selection of tobacco cells carrying a genetically transformed mitochondrial genome.

Platelet function analysis with PFA-100 in patients medicated with acetylsalicylic acid strongly depends on concentration of sodium citrate used for anticoagulation of blood sample.

Our data from 214 patients after cessation of long-term therapy with 100 mg/d ASA demonstrate that the determination of platelet-related primary hemostasis in citrated whole blood with PFA-100 is a reliable and sensitive method for the detection of ASA-induced platelet dysfunction. However, the sensitivity of the method is strongly dependent on concentration of sodium citrate used as anticoagulant. The results of PFA-100 testing show a clearly enhanced sensitivity for ASA when blood samples were collected with 0.129 M rather than 0.106 M sodium citrate. According to sample stability, PFA-100 results can only be confirmed up to 1 hour postcollection when blood was anticoagulated with 0.129 M but not with 0.106 M sodium citrate. Therefore, we recommend that testing with PFA-100 in patients with suspected ASA-induced platelet dysfunction should be performed exclusively in blood collected in buffered 0.129 M sodium citrate.

[The reliability of stroke scales. The german version of NIHSS, ESS and Rankin scales]. / Untersuchung zur Reliabilität von Schlanganfallskalen. Die deutschen Versionen von NIHSS, ESS und Rankin Scale.

Aim of the study was the translation of three frequently used stroke scales ("National Institutes of Health Stroke Scale" NIHSS, "European Stroke Scale" ESS and "Rankin Scale") into German and the analysis of the interrater reliability of the respective German versions. The translation process followed the protocol of the Medical Outcomes Trust (Boston) and included two independent forward, one backward translation and a consensus conference for the German versions. Interrater reliability was assessed using the weighted kappa statistic. For this study 43 patients with an ischemic stroke determined by computed tomography or magnetic resonance imaging were recruited from two university hospitals. Excluded were patients with an intracerebral hemorrhage or TIA. The interrater reliability of the three German versions was substantial to excellent. Mean Kappa for the NIHSS was 0.80, for the ESS 0.79 and 0.76 for the Rankin Scale using simple weights in the analysis. Additional analysis revealed the influence of preselected weights on the results of the kappa statistic. The use of German versions of frequently used stroke scales can reduce bias that is introduced by different levels of knowledge of the English language and thus improve the standardised assessment of neurological deficits in stroke.

Gestational age-dependent reference values for iron and selected proteins of iron metabolism in serum of premature human neonates.

The diagnosis and treatment of fetal and neonatal diseases requires knowledge of gestational age-dependent reference ranges for most laboratory values. It was the aim of the present study to establish reference values for serum iron, transferrin, ferritin and ceruloplasmin concentrations in premature neonates, thereby paying attention to the possible changes with gestational age. Blood samples were taken from 100 premature neonates within the first hour of life. Total serum iron, transferrin, ferritin and ceruloplasmin concentrations were determined, transferrin saturation was calculated. Newborns who developed a presumed oxygen radical disease of prematurity were excluded from the study (n = 37), because previous investigations could demonstrate significantly lower serum transferrin and ceruloplasmin concentrations in prematures suffering one of these disorders. Related to gestational age, only serum transferrin concentration showed a statistically significant increase and correlation (r = 0.47; p < 0.0001) with rising age. Although statistically not significant, even serum ferritin concentration increased with rising age of the neonates. None of the investigated laboratory values correlated with birth weight. Only ferritin showed a slight, but statistically not significant increase with higher body mass. We conclude that gestational age-dependent changes of serum transferrin levels must be considered in the judgement of fetal and neonatal diseases, whereas total serum iron and ceruloplasmin concentrations remain rather constant at least during the last weeks of gestation.

[Factors affecting the primary stability of acetabular components. An in vitro study]. / Einflussgrössen der Primärstabilität acetabulärer Komponenten. Eine In-vitro-Studie.

The aim of the present study was to investigate the micromotion under physiological loading of various acetabular components with and without screws, to determine the most suitable anchoring, cup design and optimal surface structure. Six acetabular components with varying cup geometry and surface configuration were implanted with a 2 mm press-fit into polyethylene pelves. In the first set of trials, the uncemented cups with two peripheral screws were tested under an axial load of 240 kg (2,354 N). The screws were then removed and the cups, held in place only by press fit, were tested again. None of the uncemented cups achieved the high initial stability of the cemented reference cups. It was not possible to determine an optimal cup design. In this study, titanium plasma-spray-coated cups achieved the best results. Stability is determined only in part by the configuration of the prosthesis. Of equal importance is the quality of the preparation of the cup bed. The use of screws cannot be unreservedly recommended. With a good press fit, the use of screws enhances stability only minimally.

Transient bisalbuminemia: separation by isoelectric focusing of human albumin fractions linked to different numbers of benzylpenicilloyl groups.

The behavior of modified human serum albumin (HSA) from penicillin-treated patients and in vitro conjugated samples was studied by isoelectric focusing in the absence and presence of 8 M urea. It is shown that samples classified as bisalbuminemic after separation under native conditions display a spectrum of several major bands with decreasing pIs when focusing is done in the presence of 8 M urea. In this spectrum, the distances between two consecutive major bands are as expected from a 2-unit charge difference. Since this result is compatible with the blockage of a lysine residue with a benzylpenicilloyl (BPO) group, each major band can be interpreted as representing an HSA fraction covalently linked to different numbers of benzylpenicilloyl groups. The separation methods presented therefore seem to constitute simple and reliable tools for a detailed assessment of the extent of BPO covalent binding to HSA both in vivo and in vitro.

Thrombin-based antithrombin assays show overestimation of antithrombin III activity in patients on heparin therapy due to heparin cofactor II influence.

An extensive comparison has been performed on the clinical chemistry automate Hitachi 717 between thrombin- and Factor Xa-based methods for determination of antithrombin III activity. In 460 patients who did not receive any heparin therapy the agreement between assays was in general close although the thrombin-based methods resulted in slightly higher assignments of 0.3-2.6% antithrombin III activity. The discrepancy was, however, substantial in plasmas from patients receiving heparin of > or = 20000 IU/day, resulting in plasma levels of heparin of 0.8-1.2 IU/ml. Thus, analysis of 102 patients showed that the thrombin-based methods resulted in, on average, 7-16% higher assignment of antithrombin III activity as compared to the Factor Xa-based method used. Addition of antibodies to antithrombin III and heparin cofactor II revealed that the discrepancy was primarily due to contribution of heparin cofactor II activity in the thrombin-based methods. The results thus suggest that the Factor Xa-based antithrombin III activity method provides more valid results in patients on heparin therapy.

Androstenedione therapy reinstates normal, not supernormal, song structure in castrated adult male zebra finches.

In previous studies, androstenedione (AE) replacement therapy restored the highest levels and intensities of courtship song displays in castrated male zebra finches of any hormone tested. Furthermore, female zebra finches responded strongly to AE-treated males and preferred intact males given small AE implants to unsupplemented males. In this study, we asked whether AE treatment might alter song structure, since male song is an important cue in mate choice by female zebra finches. Songs of adult males were recorded. The males were then castrated and given AE therapy and recorded again. No differences were found between the courtship or undirected songs males sang before castration and after AE treatment. As in previous studies, the structure of a male's courtship song differed significantly from his undirected song, and the structural differences between these two song types were not altered by AE treatment.

Song acquisition in photosensitive and photorefractory male European starlings.

We tested the ability of 1-year-old European starlings (Sturnus vulgaris) to acquire songs while in different physiological states. Photorefractory males, with low testosterone levels, learned songs as completely and as accurately as photosensitive males in full reproductive condition. This indicates that song acquisition in 1-year-old males does not depend on high levels of androgens. The ability to learn songs during the nonbreeding season may reflect the high song output of potential tutors through most of the year, including the photorefractory period, and may facilitate increases in song repertoire size in adulthood.

Effects of human thyroxine-binding globulin and prealbumin on the reverse flow of thyroid hormones from extravascular space into the bloodstream in rabbits.

A plasma fraction rich in thyroid hormone-binding globulin (hTBG, human thyropexin) was injected iv into rabbits in order to see whether thyroid hormone concentrations in plasma would increase by return of T3 and T4 from the extravascular space. For this purpose, both [125I]T3 and [131I]T4 were simultaneously injected. After 1 h, or after 16 h in another series of experiments, 50 mg hTBG were injected iv. Thereafter, the mean radioactivity of both [125I]T3 and [131I]T4 in the plasma rose, and reached its peak 20-30 min after hTBG injection; [125I]T3 and [131I]T4 returned to the preinjection value slowly, after more than 3 h. When hTBG was injected 15-16 h after the radioactive hormones, the mean radioactivity of [125I]T3 reached its peak about 1 h after hTBG injection and returned to the base value after approximately 5.5 h, [131I]T4 reached its peak about 1 h after hTBG injection and returned to the base value within 12 h. After injection of hTBG, total T4 and T3 concentrations in plasma increased about 3- to 5-fold over the base values. At the same time, the percentage of both, free T4 and free T3 dropped instantly whereas absolute free T4 and free T3 values remained almost constant. After injection of 500 mg transthyretin (hTBPA), a similar flux of [125I]T3 and [131I]T4 was observed, whereas 500 mg human serum albumin were ineffective. These marked effects of injected hTBG and hTBPA on the serum levels of [125I]T3, [131I]T4, and total T3 indicate that reentry of T3 and T4 into the intravascular compartment is an important component of thyroid hormone distribution and transport. As can be anticipated from the animal experiments, the efficiency of plasmapheresis or hemofiltration methods may be improved by previous application of large doses of hTBPA or hTBG in cases of thyrotoxicosis.

Evaluation of a new alpha-amylase assay using 4.6-ethylidene-(G7)-1-4-nitrophenyl-(G1)-alpha-D-maltoheptaoside as substrate.

The determination of alpha-amylase activity using an ethylidene-blocked 4-nitrophenyl-maltoheptaoside (EPS) has been evaluated in five laboratories on eight different analysers at 25 degrees C, 30 degrees C and 37 degrees C. The protecting ethylidene group inhibits hydrolysis at the non-reducing end of the substrate molecule by the auxiliary enzyme, alpha-glucosidase. The combined reagent is therefore stable for at least 10 days at 2-8 degrees C. HEPES is used, because the molar absorbance of 4-nitrophenol is independent of temperature in the presence of this buffer. Compared with the method using unprotected substrate 4-nitrophenyl-alpha-D-maltoheptaoside (4NP-G7), the present method is equal or better with respect to the imprecision, linearity and interlaboratory transferability of results in human and control sera. Since the protected and unprotected substrates differ in their turnover rate, the new assay yields activities which differ from those of the 4-nitrophenyl-alpha-D-maltoheptaoside method. Based on the homogeneous results obtained in method comparisons between EPS and 4-nitrophenyl-alpha-D-maltoheptaoside, and in order to maintain the 4-nitrophenyl-alpha-D-maltoheptaoside reference values, a conversion factor was derived to eliminate the above differences: activityEPS x 2.50 = activity4NP-G7. The temperature and instrument independence of this relationship was demonstrated in a total of 720 human sera and plasmas.

Macro lipase--a new member of the family of immunoglobulin-linked enzymes.

This first report describes a variant form of lipase in the serum of a woman suffering from a malignant non-Hodgkin lymphoma. Activity measurements of serum lipase and amylase showed persistently elevated activities of lipase with simultaneously normal activities of amylase. Results of exclusion chromatography and immunological investigations clearly demonstrate that the atypical time-course of lipase activity is not due to injury of the pancreas or alterations of the patient's lipase, but rather due to the presence of lipase-binding autoantibodies, resulting in the formation of immune complexes with high molecular mass (Mr greater than 200,000) between lipase and immunoglobulin G lambda. A clinical significance, if any, of this macro lipase has yet to be determined.

Analytical patterns and biochemical properties of macro creatine kinase type 2.

Here we describe our findings for 105 patients' sera containing macro creatine kinase (CK) type 2, as confirmed by exclusion chromatography. Depending on the technique used for determining isoenzyme CKs (electrophoresis, ion-exchange chromatography, immunoinhibition), this variant CK shows characteristic patterns and interferes in CK-MB assays by different mechanisms and to various degrees, thus complicating test interpretation. Macro CK type 2 evidently is not of cytoplasmic origin; rather it is a separate CK activity of human serum, characterized by its heat stability and, especially, by its increased molecular mass and high energy of activation. These latter characteristics have never been associated with the normal-size, dimeric cytoplasmic CK isoenzymes, but are typical for mitochondrial CK isolated from human tissues. We conclude that mitochondrial CK released after severe cell damage usually appears in blood in macromolecular forms (macro CK type 2), not in a dimeric form.

Macro creatine kinase type 2: results of a prospective study in hospitalized patients.

We determined total CK activity with the N-acetylcysteine-activated method and residual activity after immunoinhibition of the CK-M subunits in the sera of 2018 patients consecutively admitted to our university hospital for internal diseases, and of 936 outpatients, regardless of the patients' diagnoses. We could detect not more than two types of macro CK: macro CK type 2, which we observed in the sera of 85 patients (prevalence, 3.7% for hospitalized patients), and macro CK type 1. Most patients showing macro CK type 2 were older than 50 years, but we additionally observed a second peak at 20-30 years of age. We saw no preponderance by sex. We detected macro CK type 2 predominantly in severely ill patients of all ages, mainly those with malignant tumors or cirrhosis of the liver. Our findings support the assumption that macro CK type 2 is the manifestation of mitochondrial CK in serum. Occasionally, macro CK type 2 disappeared from the circulation after amelioration of the associated disease. Its occurrence in serum nevertheless is a sign of a serious illness with high mortality but not inevitably a sign of impending death.