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Biomedical subjects

V Hartmann

Publications and source records attributed to V Hartmann.

At least 19 recordsLinked to original sources
PubMed2003

The influence of antimicrobial treatments on the cytocompatibility of polyurethane biosensor membranes.

The cytocompatibility of polyurethane membranes was tested following ultraviolet or gamma irradiation as well as treatment with hydrogen peroxide or glutaraldehyde containing solutions. Despite the fact that all of the methods had been recommended for antimicrobial treatment of glucose biosensors, the treatments investigated significantly influenced cytocompatibility characteristics. Cytotoxicity of membrane eluates was not observed following irradiation treatments. This was also the case when the membranes were repeatedly washed following chemical treatment. Cell growth upon the membranes was stimulated to a different extent after gamma and UV irradiation as well as following hydrogen peroxide treatments. Residues of an urea-based hydrogen peroxide inclusion compound caused a restriction in cell growth upon the membranes as was similarly observed with 2 and 4% glutaraldehyde solutions acting over 2 and 4 h, respectively. It is concluded that cytocompatibility in vitro reflecting the host response against a biomaterial in vivo does not only depend upon the material itself but also upon antimicrobial treatments which could have consequences for its bioperformance characteristics.

Animals↗
PubMed2002

Sterilization of enzyme glucose sensors: problems and concepts.

A useful method of enzyme glucose sensor sterilization has not only to ensure the needs of sterility assurance but has also to guarantee the functional stability of the sensors. The action of 2 or 3% alkalinized glutaraldehyde solution, as well as gamma irradiation with a dose of 25 kGy caused changes of the in vitro functionality and polymer material irritations, respectively. After a combined treatment by 0.6% hydrogen peroxide solution acting over 4 days with 7 kGy gamma irradiation only a slight loss of sensitivity must be registered. The combination of a specially designed universal homogeneous ultraviolet irradiation over 300 s with a 3 days lasting treatment by an inclusion compound of hydrogen peroxide with tensides in urea (0.15% effective hydrogen peroxide concentration) did not cause any influence on the glucose sensor function in vitro. With all methods tested here, a Bacillus subtilis spore reduction over 8 log(10) cycles from 10(6) to 10(-2) spores per test object on an average could be proved experimentally. In general, if non-thermal methods must be used it seems to be impossible to guarantee a sterility assurance level of 10(-6) as it is demanded by the pharmacopoeias. Consequently, effective concepts to produce sterile glucose biosensors for medical and biological applications should be based not only on final product treatments but should include germ reducing measures in every manufacturing step.

Biosensing Techniques↗
PubMed2001

Determination of the disintegration behavior of magnetically marked tablets.

The disintegration behavior of different tablets that were marked as magnetic dipoles by the incorporation of ferromagnetic black iron oxide and subsequent magnetization was studied using a specially developed measurement setup. This novel apparatus records the magnetic induction generated by the magnetic dipole moment of the tablets during their disintegration. It was found that the observed decrease of the magnetic induction can be used for a quantitative determination of the disintegration of tablets. In particular, it could be shown that the magnetic data provide information about the disintegration mechanism. For tablets with a minor influence of swelling on the disintegration mechanism a linear decline of the magnetic fluxes was observed. After addition of swelling disintegrants (crospovidone) the decline of the magnetic flux could be fitted by an exponential function, indicating the involvement of a disintegration force. Furthermore, the data demonstrate that using modern multichannel biomagnetic measurement equipment the monitoring of the disintegration behavior of magnetically marked tablets in humans will be possible.

Ferric Compounds↗
PubMed2000

Physico-chemical, in vitro and in vivo characterisation of polymers for ocular use.

The influence of artificial tear fluid (AT) on ionic and nonionic ophthalmic polymer excipients was rheologically established. In usual concentrations polyvinylalcohol, polyvinylpyrrolidone, dextran, hydroxypropylmethylcellulose, hydroxyethylcellulose and methylcellulose did not show any changes. In contrast, solutions of polyacrylic acid, sodium hyaluronate (S-Hya), sodium alginate (S-Alg) and chitosan decrease the apparent viscosity in contact with AT, while gellan solution increases the viscosity and shows thixotropy. The adhesion of selected polymers (polysaccharides) on mucin was evaluated using a rheological method and resulted in the order S-Hya > Gellan > S-Alg > dextran. Miosis testing of Gellan containing pilocarpine HCl formulations in rabbits shows a possible reduction of drug concentration from 2% to 0.5% obtaining the same bioavailability.

Adhesiveness↗
PubMed1995

Streptomyces ghanaensis plasmid pSG5: nucleotide sequence analysis of the self-transmissible minimal replicon and characterization of the replication mode.

The naturally temperature-sensitive plasmid pSG5 of Streptomyces ghanaensis DSM 2932 is the basis replicon of the "pGM-vectors." The nucleotide sequence of the pSG5 minimal replicon was determined. Only one single open reading frame (rep) with high coding probability is located on the minimal replicon. The deduced Rep protein consists of 378 aa and contains motifs characteristic of initiation proteins for rolling-circle-type replication. Sequence similarity indicated that the Rep protein of pSG5 is related to the Rep proteins of the pC194 plasmid family. Accumulation of large amounts of single-stranded plasmid DNA was shown for all small pGM vectors. A minus origin for the lagging strand synthesis was localized outside of the pSG5 minimal replicon. Although the sequenced pSG5 fragment is self-transmissible, it seems not to carry further genes in addition to the rep gene. This suggests that the transfer mechanism of plasmid pSG5 differs from that of other Streptomyces plasmids, which all encode specific transfer genes.

Amino Acid Sequence↗
PubMed1995

[Not Available].

Explore the source record for details and available documents.

Expeditions↗
PubMed1994

Transfer and establishment of DNA in Streptomyces (a brief review).

Based on endogenous Streptomyces plasmids we have constructed various multiple purpose vectors for cloning in streptomycetes. Since replication of the S. ghanaensis plasmid pSG5 is inherently temperature-sensitive, pGM-vectors derived from pSG5 can be used for gene disruption/replacement and mutational cloning. The 1.6-kb minimal replication region of pSG5 encodes only one polypeptide, an initiation protein (Rep) for single stranded DNA-replication. Different internal fragments of sequenced genes of the Ptt-biosynthetic pathway were cloned into pGM-vectors to study both, the function of the biosynthetic genes and recombination in Streptomyces. The observed recombination frequencies were very high, up to 80% of the cells carried single or multiple copies of the plasmid integrated into the chromosome. Replacement experiments revealed that the frequency of marker exchange and plasmid integration, respectively, lies in the same order of magnitude. The region of homology which is required for homologous recombination could at least be reduced to 200 bp.

Cloning, Molecular↗
PubMed1992

Tissue PO2 and growth rate in early chick embryos.

We determined dry mass, frequency distribution of tissue PO2 and microvascular density of head and trunk of early chick embryos between day 4 and day 6 of incubation. During this period the percentage of the dry mass of the head on total dry mass increased from 31% to 48% indicating that the head grows faster than the trunk. Tissue PO2 values ranged between zero and arterial PO2. About half of the numbers were less than 5 Torr. Mean tissue PO2 was significantly higher in the head than in the trunk. This was paralleled by a significantly higher microvascular density in the head. The high frequency of low tissue PO2 values found at each day at all measuring sites suggests that the embryonic tissue of both head and trunk extracts as much oxygen from the capillary blood as possible. Consequently, growth rate strongly depends on oxygen availability. Since the arterial PO2 is the same in the head and in the trunk (Meuer and Baumann, 1988), the diversity of tissue PO2 and growth rate found in this study is probably caused by differences in the structure of the microvascular bed resulting in variations of tissue blood perfusion, capillary transit time and diffusion distance.

Animals↗
PubMed1986

Bronchodilator effect of theophylline preparations and aerosol fenoterol in stable asthma.

To compare the acute bronchodilator effect of increasing doses of intravenous theophylline and inhaled beta adrenergic agonists, we administered intravenous theophylline dissolved in ethylenediamine or proxyphylline and diprophylline or placebo in a double blind fashion to nine asthmatics on three different days. At each session, 100 mg theophylline or placebo were given during each of five subsequent periods of 30 minutes' duration and followed by inhalation of 0.4 mg fenoterol. In contrast to placebo, 500 mg theophylline in ethylenediamine or proxyphylline and diprophylline significantly decreased mean specific airway resistance (SRaw in cmH2O.s) from 31.2 to 23.6 or 34.2 to 23.5 at theophylline serum concentrations of 14.4 or 16.6 mg/L, respectively. Fenoterol lowered SRaw to about 40 percent of the respective baseline values independent of theophylline or placebo pretreatment. We conclude that the acute bronchodilator effect of theophylline is weak in comparison to inhaled beta agonists. Furthermore, proxyphylline and diprophylline cause a weak but not significant bronchodilation when compared to ethylenediamine.

Airway Resistance↗
PubMed1985

Effect of diltiazem on histamine- and carbachol-induced bronchospasm in normal and asthmatic subjects.

Recently, several transmembrane calcium-channel blockers have been used in experimental models to investigate the mechanisms through which Ca++ ions contribute to the regulation of the contractile response of airway smooth muscle and to determine the therapeutic use of these drugs in bronchial asthma. Since the data from these studies are inconsistent and inconclusive, we studied the effect of diltiazem, a calcium-channel blocker previously not examined to our knowledge, on histamine- and carbachol-induced bronchoconstriction in healthy and in asymptomatic allergic bronchial asthma. The study was performed in a double-blind, randomized, placebo-controlled fashion, using a single oral dose of 60 mg of diltiazem. Airway reactivity to histamine and carbachol expressed by PD35SGaw was significantly but weakly attenuated by diltiazem in the asthmatic, but not in the normal subjects. Baseline lung function was not significantly influenced by diltiazem. We concluded that the effect of diltiazem on unspecific airway hyperresponsiveness in asthmatic subjects is too weak to justify a recommendation as therapy.

Adult↗
PubMed1984

Influence of diltiazem on bronchoconstriction induced by cold air breathing during exercise.

Since the calcium antagonists nifedipine and verapamil have been shown to diminish exercise induced asthma, the effect of oral diltiazem, a calcium channel blocker not previously investigated in this context, was studied. Ten patients with bronchial asthma were given 60 mg diltiazem or placebo four hours before the challenge in a double blind, randomised, crossover fashion. Exercise was performed on a cycle ergometer while the subjects were breathing cold air, resulting in a respiratory heat exchange which was similar at the two study sessions. FEV1 and specific conductance (sGaw) were recorded before and three, 10, 15, and 30 minutes after the challenge. No significant differences were found between placebo and diltiazem days in the fall of FEV1 or sGaw after exercise. Thus unlike other calcium antagonists diltiazem, in a dose of 60 mg given orally four hours before exercise, failed to protect against exercise induced asthma.

Adult↗
PubMed1984

[Liver biopsy in surgery of the gallbladder].

Biopsy of the liver with the menghini needle was done as a routine diagnostic procedure during surgery in 581 cases. During earlier decades morphological changes of the liver could be demonstrated by that procedure in 80-100% of the patients. In contrast such changes could be found only in 55% of our cases; in 5,5% these changes were severe. From these numbers it should be concluded that liver biopsy during gall bladder surgery is not necessary as a routine procedure. If patients are selected for biopsy on the basis of history, ultrasonography, laboratory data and intraoperative microscopical liver findings this procedure is necessary only in 14% of the cases, complication rate being 0,09%. In this particularly selected group changes of the liver can be found in 90,4%, severe changes in 33% of the cases. Pathological changes of the liver are likely to occur in 65-91% of patients with complicated gall stone disease and/or accompanying diseases like diabetes, obesitas, alcoholism, or a history of hepatitis. In this particular group biopsy and histological examination during surgery seem to be indicated as it was the case before.

Biopsy↗
PubMed1983

Histamine receptor blocking effects of cimetidine in the airways.

We investigated the modification of histamine-induced bronchoconstriction by the H2-antagonist cimetidine in conscious sheep. One hundred breaths of 5% histamine aerosol increased mean (SD) pulmonary resistance (RL) by 5.6 (1.4) cmH2O/l/sec. This increase in RL was completely blocked by intravenous clemastine (0.5 mg), a specific H1-antagonist, indicating that the histamine-induced bronchoconstriction was mediated by H1-receptors. Intravenous cimetidine caused a dose-dependent enhancement of the histamine response between 1 and 1000 mg with a mean peak delta RL of 15.3 (5) cmH2O/l/sec (p less than 0.05) at the 1000 mg dose, while it blocked the histamine response at a dose of 2400 mg [delta RL = 1.9 (2) cmH2O/l/sec, p = NS]. This paradoxic effect was not related to an anticholinergic mechanism as intravenous cimetidine (2400 mg) failed to block carbachol-induced (25 breaths of 1% solution) bronchoconstriction. We conclude that in the ovine airway, cimetidine is a selective H2-histamine receptor blocker at lower tissue concentrations, and a combined H2- and H1-histamine receptor blocker at high tissue concentrations.

Airway Resistance↗