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H Förster

Publications and source records attributed to H Förster.

At least 19 recordsLinked to original sources
PubMed2006

Full-counting statistics for voltage and dephasing probes.

We present a stochastic path integral method to calculate the full-counting statistics of conductors with energy conserving dephasing probes and dissipative voltage probes. The approach is explained for the experimentally important case of a Mach-Zehnder interferometer, but is easily generalized to more complicated setups. For all geometries where dephasing may be modeled by a single one-channel dephasing probe we prove that our method yields the same full-counting statistics as phase averaging of the cumulant generating function.

Journal Article↗
PubMed2004

Investigations of the formation of explosive mixtures in dryers for coatings.

In the following we will discuss a specific problem of explosion protection in dryers for coatings. It is mainly encountered in chamber dryers as these pose specific problems as regards occupational safety and health. During the drying process of most coatings, solvent vapours are released most of which can form explosive mixtures when a specific concentration, the lower explosion limit, is reached. The European Standard EN1539:2000 requires explosion venting areas for most of these dryers without adequate explosion protection measures such as appropriate limitation of the solvent input being taken into account. Different aspects of the model underlying the calculations are evaluated, and it will be shown that this model is still reliable in most applications. The investigations consisted of three parts. At first there have been made investigations of the operating conditions in different enterprises aimed to get information about specific parameters, problems and failures. Laboratory experiments have been made to investigate in detail the major influencing parameters. Attempts to set up a simple but basic physical model for the experimental data have also been made. Evaporation and diffusion have been examined. The numerical models have been kept as simple as possible to be a potential tool for designers/manufacturers and users.

Diffusion↗
PubMed2002

[Severe adverse event following iv administration of 10 ml 6% Dextran60 (0.6 g) in a healthy volunteer].

We describe the case of a 24-year-old healthy volunteer who underwent a dextran-induced anaphylactic/anaphylactoid reaction (DIAR) type III after administration of 10 ml 6% Dextran60 (0.6 g) during a preliminary examination. There were no specific incidents in the medical history or any infusions of any colloids. In contrary to other DIAR case reports of anaphylactic reactions, in this case we observed a latency period after intravenous application of Dextran60 to the first clinical symptoms of anaphylactic shock of about 5 min. The initial decrease of systolic blood pressure to less than 90 mmHg and consecutive increase in heart rate to higher than 90 bpm returned to normal after therapy with head-down position, iv injection of 2 mg Clemastin, 100 mg hydrocortisone and infusion of 500 ml hydroxyethyl starch after approximately 8 min. During this period responsiveness was unsatisfactorily although the volunteer complained about warming of the skin, paresthesia and nausea. Immediate shock symptoms that normally belong to antigen-antibody reactions were not observed. It is therefore still unclear whether this case was caused by antibody reactions. Nevertheless, to provide DIAR it is still absolute necessary to give 20 ml Promit((R)) 15% in advance. It is not an acceptable alternative to infuse the first 100 ml of dextran as a bolus and it must remain a point of discussion as to whether the reactions described could have been due to a bolus administration of the first 100 ml Dextran. It is absolutely necessary to accurately monitor the first 10 min after an infusion even if only small volumes of dextran (i.e. 0.6 g) are infused. This is becoming more and more important due to the increasing use of "small volume resuscitation", solutions containing dextran (RescueFlow((R)), Biophausia AB, Uppsala, Schweden) or cryoconservation with dextran.

Adult↗
PubMed2002

[Thrombelastographic coagulation analysis following in vitro and in vivo haemodilution with hydroxyethyl starch (HES)].

In the study presented the effects of in vitro hemodilution with HES on coagulation are compared with the effects of in vivo hemodilution using thrombelastography (TEG). The in vivo hemodilution was performed by the i. v. infusion of 1000 ml 6 % solution of hydroxyethyl starch HES (2 formulations with HES 130/0.4 and one formulation with HES 200/0.5) in healthy volunteers during 30 min. The in vitro hemodilution was performed with blood samples taken from the volunteers before the infusion was started. These samples were diluted with HES-solution until the same hemoglobin concentration measured at the end of the infusion was attained. The in vivo TEG-parameters remained in the reference range of the method, however all in vitro TEG-parameters are out of the range of normal values. The isolated interpretation of the in vitro data shows an impairment of blood coagulation. The shortening of the reaction time as an indicator for the initiation of blood clotting points to activated coagulation by in vivo hemodilution with HES, whereas in vitro the prolongation of the reaction time is indicative for retardation of clotting. The evaluation of the TEG-parameters and of other clotting parameters determined prior to the beginning of the infusion, at the end of the infusion and four hours after termination of the infusion of HES 130/0.4 and of HES 200/0.5 to healthy volunteers show alterations of blood coagulation parameters caused mainly by dilutional effects. The more pronounced alterations found in vitro cannot be interpreted as impairment of haemostasis in vivo. On the other hand, the likewise haemodilution in vitro causes an impairment of coagulation. Therefore, the effects of in vitro hemodilution with HES on coagulation differ qualitatively and quantitatively from the effects of in vivo hemodilution.

Adult↗
PubMed2001

[Acetyl starch as volume substitute, a possible alternative to HES].

OBJECTIVES: Pharmacokinetics and tolerability of acetyl starch (ACS) in comparison to hydroxyethyl starch (HES) were investigated after repeated intravenous infusions. METHODS AND COHORTS: A 500 ml solution of ACS (n = 8) or HES (n = 9) was infused to male volunteers (Age 25-42 Years) over four hours on five consecutive days. RESULTS: Comparing the pharmacokinetic parameters, marked differences were found between ACS and HES. A continuos increase of Cmax, AUC0-24 and t1/2 over the five days caused by administration of HES was due to an accumulation of HES in serum. However, after administration of ACS all these parameters remained unaltered. The repeated infusion of 50 g ACS did not cause any changes of the acid-base-status. The influence of ACS on the coagulation parameters was comparable to that of HES and due to dilution effects. The acetic acid concentration increased up to 2.96 +/- 0.67 mg/dl following ACS infusion. The blood glucose concentration was not influenced by the infusion of HES or of ACS. The repeated ACS infusions were well tolerated. In contrast to HES, ACS did not accumulate in serum. CONCLUSION: According to these data ACS is an alternative to HES for volume replacement. Well-known side effects due to long storage of HES in tissues may not occur following application of ACS. However, the wide usage of ACS is restricted by the limited stability of ACS solutions at room temperature. ACS solutions are thus only stable during storage at lower temperatures.

Adult↗
PubMed2001

Coniferyl alcohol metabolism in conifers -- I. Glucosidic turnover of cinnamyl aldehydes by UDPG: coniferyl alcohol glucosyltransferase from pine cambium.

UDPG: coniferyl alcohol glucosyltransferase (CAGT; EC 2.4.1.111) isolated from cambial tissues of Pinus strobus was able to convert cinnamyl aldehydes as well as dihydroconiferyl alcohol into their corresponding 4-O-beta-D-glucosides in vitro. Cinnamyl aldehydes were glucosylated with comparable efficiency to coniferyl alcohol, the physiological substrate for CAGT. Seasonal patterns of CAGT activity for aldehydes were similar to those of coniferyl alcohol. Formation of cinnamyl aldehyde and additional monolignol glucosides indicates that precursor flux and availability for lignification is likely greater than previously recognized.

Aldehydes↗
PubMed2001

Coniferyl alcohol metabolism in conifers -- II. Coniferyl alcohol and dihydroconiferyl alcohol biosynthesis.

Coniferaldehyde and NADPH when incubated with microsomes isolated from developing xylem of Pinus strobus yielded coniferyl alcohol and dihydroconiferyl alcohol in vitro. D-(+)-Pinitol was also found to be a microsomal constituent. Endogenous E-coniferyl alcohol content, quantified in dormant buds, cambium, bark and needles of Pinus resinosa and P. strobus by isotope-dilution combined gas chromatography mass spectrometry (GC/MS) using ring-(13)C(6)-coniferyl alcohol, was at a level similar to that of endogenous indol 3-ylacetic acid (IAA). Wounding (branch girdling) induced more than a 10-fold increase in content of endogenous E-coniferyl alcohol in dormant non-lignifying cambium, a clear indication that monolignol biosynthesis is not coupled to lignification.

Gas Chromatography-Mass Spectrometry↗
PubMed2001

[The in vivo molecular weight and renal threshold of hydroxyethyl starch in the example of molar substituted HES70/0/5].

The intravascular changes of the in vivo molecular weight of HES 70/0.5 were investigated on healthy volunteers. A repeated daily infusion of 835 ml of 6% HES solution (50 g HES 70/0.5; Rheohes) during four hours on five consecutive days was performed. The analysis of the distribution of the molecular masses in serum and urine was performed by SEC-HPLC with MALLS/RI detection. The in vivo average molecular weight (Mw) of HES was found to be 58,000 Da at the end of the infusion. This was lower than the Mw of 66,000 Da as measured initially in the HES solution. In the time following the infusion Mw increased steadily up to 64,000 Da because of renal elimination of low molecular HES. However, in the morning before the start of the next infusion of HES, the average molecular weight Mw of HES was even higher up to 71,000 Da. In the first collected portion of urine (i.e. up to 8 h after beginning the infusion) the average molecular weight of HES was as low as 17,000 Da. During the next hours (i.e. in the second collection period lasting from 8 up to 24 h after start of the HES infusion) Mw of HES increased up to 28,000 Da. The top fraction of the first period showed molecular masses of 27,000 Da, in the second collection period top fraction of molecular masses measured 40,000 Da. According to the presented data it is concluded that the renal threshold for medium substituted HES is independent of the initial Mw and related primarily to the molar substitution of the HES used. This renal threshold for medium substituted HES is determined to be at 40,000 Da. The in vivo Mw of HES is variable and related to the sampling time and predicted predominantly by the molar substitution of the HES used. The in vivo Mw, therefore, is not suited for characterisation of HES.

Adult↗
PubMed2000

Protein-protein interactions of the primase subunits p58 and p48 with simian virus 40 T antigen are required for efficient primer synthesis in a cell-free system.

DNA polymerase alpha-primase (pol-prim, consisting of p180-p68-p58-p48), and primase p58-p48 (prim(2)) synthesize short RNA primers on single-stranded DNA. In the SV40 DNA replication system, only pol-prim is able to start leading strand DNA replication that needs unwinding of double-stranded (ds) DNA prior to primer synthesis. At high concentrations, pol-prim and prim(2) indistinguishably reduce the unwinding of dsDNA by SV40 T antigen (Tag). RNA primer synthesis on ssDNA in the presence of replication protein A (RPA) and Tag has served as a model system to study the initiation of Okazaki fragments on the lagging strand in vitro. On ssDNA, Tag stimulates whereas RPA inhibits the initiation reaction of both enzymes. Tag reverses and even overcompensates the inhibition of primase by RPA. Physical binding of Tag to the primase subunits and RPA, respectively, is required for these activities. Each subunit of the primase complex, p58 and p48, performs physical contacts with Tag and RPA independently of p180 and p68. Using surface plasmon resonance, the dissociation constants of the Tag/pol-prim and Tag/primase interactions were 1.2 x 10(-8) m and 1.3 x 10(-8) m, respectively.

Antibodies, Monoclonal↗
PubMed2000

Sample optimization and identification of signal patterns of amino acid side chains in 2D RFDR spectra of the alpha-spectrin SH3 domain.

Future structural investigations of proteins by solid-state CPMAS NMR will rely on uniformly labeled protein samples showing spectra with an excellent resolution. NMR samples of the solid alpha-spectrin SH3 domain were generated in four different ways, and their (13)C CPMAS spectra were compared. The spectrum of a [u-(13)C, (15)N]-labeled sample generated by precipitation shows very narrow (13)C signals and resolved scalar carbon-carbon couplings. Linewidths of 16-19 Hz were found for the three alanine C(beta )signals of a selectively labeled [70% 3-(13)C]alanine-enriched SH3 sample. The signal pattern of the isoleucine, of all prolines, valines, alanines, and serines, and of three of the four threonines were identified in 2D (13)C-(13)C RFDR spectra of the [u-(13)C, (15)N]-labeled SH3 sample. A comparison of the (13)C chemical shifts of the found signal patterns with the (13)C assignment obtained in solution shows an intriguing match.

Alanine↗
PubMed2000

[The use of lithium hydroxide for carbon dioxide absorption prevents formation of compound A during sevoflurane anesthesia].

UNLABELLED: Aim of the study was the clinical investigation of sevoflurane degradation when using water-free lithiumhydroxide versus moist Drägersorb 800 for carbon dioxide absorption. METHODS: Concentrations of Compound A in the inspiratory gas mix and serum fluoride levels were measured in two groups of 8 patients each. RESULTS: When water-free lithiumhydroxide was used for carbon dioxide absorption, concentration of Compound A in the inspiratory gas mix was ca. 1 ppm (near minimal level of detection) as compared to ca. 20 ppm for moist Drägersorb 800. The concentration of fluoride increased during sevoflurane anesthesia (15.0 +/- 4.8 mumol/l with lithiumhydroxide versus 21.9 +/- 4.0 mumol/l with Drägersorb 800 after 60 mins). CONCLUSIONS: When lithiumhydroxide is used, there is only minimal formation of compound A from sevoflurane degradation. Since serum fluoride levels increased in both patient groups, we conclude that this is caused mainly by metabolism of sevoflurane. Capacity of lithiumhydroxide for carbon dioxide absorption is similar to that of Drägersorb 800. Therefore, the use of lithiumhydroxide increases patient safety.

Absorption↗
PubMed2000

Pharmacodynamics and tolerability of acetyl starch as a new plasma volume expander in patients undergoing elective surgery.

OBJECTIVE: Acetyl starch (ACS) is a new synthetic colloid solution for plasma volume expansion and is now undergoing phase II clinical trials. We compared the pharmacodynamics and tolerability of ACS with those ofhydroxyethyl starch (HES) in 32 patients (American Society of Anesthesiologists physical status I and II) undergoing elective surgery. SUBJECTS, MATERIAL AND METHODS: In this prospective, randomized, double-blind trial patients received either 15 ml/kg ACS 6% (average molecular weight (Mw) 200,000/molar substitution (MS) 0.5) or HES 6% (Mw 200,000/MS 0.5) i.v. up to a maximum dose of 1000 ml. Hemodynamic parameters, rheologic parameters, volume effect, acid-base status as well as effects on hemostasis were studied. RESULTS: After infusion of ACS and HES there was a similar increase in central venous pressure and mean arterial pressure in both groups. Acid-base status was not significantly altered after the end of the colloid infusions. After ACS infusion, plasma acetate concentration increased from 0.13+/-0.16 mg/dl to 2.87+/-1.13 mg/dl, however, after 24 h there was no significant difference in plasma acetate concentration compared to HES. The volume effect ranged from 104-116%(ACS) and from 88-118% (HES) of the colloid dose administered. These differences were not statistically significant. Partial thromboplastin time (aPTT) was only slightly increased after ACS infusion (from 38.6+/-5.7 sec to 41.4+/-5.1 sec), but was significantly increased after HES infusion (from 38.7+/-5.7 sec to 46.1+/-7.0 sec). CONCLUSION: ACS and HES are equally effective plasma volume expanders; ACS might be a new, alternative colloid solution with fewer coagulation side-effects than HES.

Adolescent↗
PubMed1999

[Ketoacidosis in a 14 month old child caused by fasting].

Preoperative starvation in order to prevent pulmonary aspiration is mandatory in elective pediatric surgery. Hypoglycemia, thirst and unwellness have been reported as undesired side effects. The metabolic response towards decreasing blood-glucose concentrations in fasting children includes gluconeogenesis and production of ketone bodies to meet the energetic demand. Accumulation of beta-hydroxybutyrate und acetoacetate in blood can lead to ketoacidosis. We report a case of a severe intraoperative ketoacidosis in a fourteen months old child complicating 36 hours of starvation.

Acid-Base Equilibrium↗
PubMed1999

[The accumulation of different substituted hydroxyethyl starches (HES) following repeated infusions in healthy volunteers].

AIM OF THE STUDY: Accumulation of hydroxyethyl starch (HES) after repeated applications of starches with different molar substitution and similar molecular weight was investigated. METHODS: Treatment with five consecutive infusions of hydroxyethyl starch was carried out using two medium molecular weight hydroxyethyl starches with a molar substitution of 0.5 and 0.62. Healthy volunteers received 500 ml 6% HES 200/0.62 (30 g) or 500 ml 10% HES 200/0.5 per day over a period of five consecutive days. Blood samples were taken in the morning before infusions were started (7.A.M.) and at each hour during the infusion period of 4 hours post infusionem until 4 hours after the infusions. During the first 10 days and on the 20th and on the 30th day after the last infusion blood samples were taken. RESULTS: Both HES solutions were subjectively and objectively well tolerated by healthy volunteers. No side effects were observed. However, pharmacokinetics of the investigated HES-formulations were significantly different. The model-independent calculated elimination half life time (T1/2) increased from day to day. During the five days T1/2 was prolonged for 20 h by high substituted HES (200/0.62) and for 2.5 h for medium substituted HES (200/0.5). The half life times related to the three compartment model calculation were with 0.6 h, 11.6 h and 211 h for HES 200/0.62 two fold higher than the times for HES 200/0.5 with 0.39 h, 6.98 h and 113 h. Plasma clearance for HES 200/0.5 (4.86 ml/min) was five fold higher than that from HES 200/0.62 with 0.98 ml/min. With the exception of the first day of infusion serum concentrations of HES 200/0.5 although only 30 g HES 200/0.6 versus 50 g HES 200/0.5 were infused. No difference of the hemodilution effects between the two HES-formulations were observed. The hemorheologic parameters were similar in both groups with the exception of plasma viscosity which was significantly higher after infusion of HES 200/0.62. CONCLUSION: High substituted HES accumulate in serum more than medium substituted HES. Especially when HES must be applied in multiple doses, high substituted HES should not be used or the infusion interval must be adapted to the elimination half life time of the used HES.

Adult↗
PubMed1999

The elimination of sodium and potassium hydroxides from desiccated soda lime diminishes degradation of desflurane to carbon monoxide and sevoflurane to compound A but does not compromise carbon dioxide absorption.

UNLABELLED: Normal (hydrated) soda lime absorbent (approximately 95% calcium hydroxide [Ca(OH)2], the remaining 5% consisting of a mixture of sodium hydroxide [NaOH] and potassium hydroxide [KOH]) degrades sevoflurane to the nephrotoxin Compound A, and desiccated soda lime degrades desflurane, enflurane, and isoflurane to carbon monoxide (CO). We examined whether the bases in soda lime differed in their capacities to contribute to the production of these toxic substances by degradation of the inhaled anesthetics. Our results indicate that NaOH and KOH are the primary determinants of degradation of desflurane to CO and modestly augment production of Compound A from sevoflurane. Elimination of these bases decreases CO production 10-fold and decreases average inspired Compound A by up to 41%. These salutary effects can be achieved with only slight decreases in the capacity of the remaining Ca(OH)2 to absorb carbon dioxide. IMPLICATIONS: The soda lime bases used to absorb carbon dioxide from anesthetic circuits can degrade inhaled anesthetics to compounds such as carbon monoxide and the nephrotoxin, Compound A. Elimination of the bases sodium hydroxide and potassium hydroxide decreases production of these noxious compounds without materially decreasing the capacity of the remaining base, Ca(OH)2, to absorb carbon dioxide.

Absorption↗
PubMed1998

The pharmacokinetics of acetyl starch as a plasma volume expander in patients undergoing elective surgery.

UNLABELLED: Acetyl starch (ACS) is a new synthetic colloid solution for plasma volume expansion and is now undergoing phase 2 clinical trials. We compared the pharmacokinetics of ACS with those of hydroxyethyl starch (HES) in 32 patients (ASA physical status I and II) undergoing elective surgery. In this randomized, double-blind trial, patients received either 15 mL/kg ACS 6% (average molecular weight [Mw] 200,000/molar substitution [MS] 0.5) or HES 6% (Mw 200,000/MS 0.5) i.v. up to a maximal dose of 1000 mL. Plasma colloid concentrations were measured by repetitive arterial blood sampling over 24.5 h. Plasma colloid concentrations were detected using a high-pressure liquid chromatography controlled enzymatic test. Standard pharmacokinetics were calculated, including initial half-life (t(1/2init)), i.e., the time required for a 50% decline of the maximal plasma colloid concentration at the end of drug infusion. Whereas HES was eliminated by second-order kinetics, ACS followed first-order characteristics. In the first hours after i.v. administration, t(1/2init) and clearances were similar in both groups. However, the terminal half-life of HES was significantly longer than that of ACS (9.29 +/- 1.43 h vs 4.37 +/- 1.06 h). After 16.5 and 24.5 h, ACS showed significantly lower plasma concentrations than HES, which indicates that the final degradation of ACS by esterases and amylase was significantly more rapid. ACS might be an alternative plasma volume expander, which avoids the accumulation of persisting macromolecules. IMPLICATIONS: We studied the pharmacokinetics of acetyl starch, a newly developed colloid solution for plasma volume substitution, compared with hydroxyethyl starch in 32 surgical patients undergoing elective major general surgical procedures. In contrast to hydroxyethyl starch, this new agent undergoes rapid and nearly complete enzymatic degradation.

Adolescent↗