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Biomedical subjects

M Boller

Publications and source records attributed to M Boller.

At least 19 recordsLinked to original sources
PubMed2006

Characteristics of particle-associated PAHs in a first flush of a highway runoff.

Runoff monitoring of six rainfall events was carried out in a highway, Winterthur, Switzerland focusing on first flush (runoff volume up to 2.88 mm). Six runoff events were used to investigate the characteristics of particle-associated PAHs in first flush. The fine fraction (< 45 microm) had a relatively higher contribution than the coarse fraction. A significant contribution of the coarse fraction was observed at some periods when the runoff flow rapidly increased. Fluctuation of PAH content during a runoff event was significant in the coarse fraction and, in contrast, the PAH content in the fine fraction was less fluctuating. The weighted average PAH content in each event ranged from 17 to 62 microg/g in total SS, from 23 to 54 microg/g in the fine fraction and from 16 to 84 microg/g in the coarse fraction. The loading of particle-associated PAHs from the first flush of highway runoff ranged from 0.06 to 0.22 g/ha in a total of 12 PAH species.

Air Pollutants↗
PubMed2006

Treatment of source-separated urine by a combination of bipolar electrodialysis and a gas transfer membrane.

Urine contains nutrients which can be applied usefully as a fertiliser in agriculture, but the relatively high pH can lead to ammonia evaporation. Electrodialysis with bipolar membranes was combined with an additional mass transfer unit in order to render a product containing ammonium and phosphate at a low pH. In one case, the additional mass transfer unit consisted of bubble columns placed in acid and basic concentrate streams, connected with a circulating gas phase. In the other case, the unit consisted of a gas-filled (hydrophobic) membrane placed in between the circulating acid and basic concentrate streams. The results showed that ammonia was transferred through the gas phase, but also carbonate, which is present in stored urine originating from the hydrolysis of urea. Although the pH in the product stream decreases initially, it rises above pH 7 at longer operation times. This pH increase can be attributed to a combination of proton compensating effects. The use of ammonia-selective membranes for the transfer into the acid concentrate could provide a solution to generate an ammonium phosphate product at low pH and high recoveries.

Dialysis↗
PubMed2006

Copper and zinc removal from roof runoff: from research to full-scale adsorber systems.

Large, uncoated copper and zinc roofs cause environmental problems if their runoff is infiltrated into the underground or discharged into receiving waters. Since source control is not always feasible, barrier systems for efficient copper and zinc removal are recommended in Switzerland. During the last few years, research carried out in order to test the performance of GIH-calcite adsorber filters as a barrier system. Adsorption and mass transport processes were assessed and described in a mathematical model. However, this model is not suitable for practical design, because it does not give explicit access to design parameters such as adsorber diameter and adsorber bed depth. Therefore, for e.g. engineers, an easy to use design guideline for GIH-calcite adsorber systems was developed, mainly based on the mathematical model. The core of this guideline is the design of the depth of the GIH-calcite adsorber layer. The depth is calculated by adding up the GIH depth for sorption equilibrium and the depth for the mass transfer zone (MTZ). Additionally, the arrangement of other adsorber system components such as particle separation and retention volume was considered in the guideline. Investigations of a full-scale adsorber confirm the successful application of this newly developed design guideline for the application of GIH-calcite adsorber systems in practice.

Adsorption↗
PubMed2005

Dynamic behavior of fractional suspended solids and particle-bound polycyclic aromatic hydrocarbons in highway runoff.

A long-term continuous runoff monitoring was carried out in a highway in Winterthur, Switzerland. The total suspended solids (TSS) samples were fractionated into fine (< 45 microm) and coarse (> 45 microm) fraction and their wash-off behavior was studied. The fine and coarse fraction showed different wash-off behaviors. During the runoff the concentration of the fine fraction was less fluctuated compared to coarse. The fluctuation of the coarse fraction was more influenced by TSS concentration. The PAH content measurement in fine fraction showed less fluctuation compared to the coarse fraction. The PAH content in the coarse fraction was found decreasing with increasing the coarse fraction contribution to TSS.

Environmental Monitoring↗
PubMed2003

Analytical electron microscopy and focused ion beam: complementary tool for the imaging of copper sorption onto iron oxide aggregates.

Nanometre-scale electron spectroscopic imaging has been applied to characterize the operation of a copper filtration plant in environmental science. Copper washed off from roofs and roads is considered to be a major contributor to diffuse copper pollution of urban environments. A special adsorber system has been suggested to control the diffusion of copper fluxes by retaining Cu with a granulated iron hydroxide. The adsorber was tested over an 18-month period on facade runoff. The concentrations range of Cu in the runoff water was measured between 10 and 1000 p.p.m. and could be reduced by between 96% and 99% in the adsorption ditch. Before the analysis of the adsorber, the suspended material from the inflow was ultracentrifuged onto TEM grids and analysed by energy-filtered transmission electron microscopy (EFTEM). Copper was found either as small precipitates 5-20 nm in size or adsorbed onto organic and inorganic particles. This Cu represents approximately 30% of the total dissolved Cu, measured by atomic emission spectrometry. To locate where the copper sorption takes place within the adsorber, the granulated iron oxide was analysed by analytical electron microscopy after exposure to the roof run-off water. A section of the granulated iron hydroxide was prepared by focused ion beam milling. The thickness of the lamina was reduced to 100 nm and analysed by EFTEM. The combination of these two techniques allowed us to observe the diffusion of Cu into the aggregate of Fe. Elemental maps of Fe and Cu revealed that copper was not only present at the surface of the granules but was also sorbed onto the fine particles inside the adsorber.

Journal Article↗
PubMed2002

Closure of large patent ductus arteriosus with a self-expanding duct occluder in two dogs.

Of the different catheterisation methods described for closure of patent ductus arteriosus (PDA), coil embolisation is most commonly used in dogs. However, for a PDA larger than 4 to 5 mm in diameter, coil implantation is difficult. For these cases, the Amplatzer duct occluder (ADO) offers an alternative method. This report describes the successful implantation of an ADO in two dogs with large PDAs of approximately 6 mm diameter. The self-expandible device attached to an implantation wire was advanced through a long sheath antegrade to the femoral vein through the right heart and pulmonary artery to the duct and delivered into the PDA. Thereafter the device was released by unscrewing it from the delivery cable. The large PDA in both dogs was totally occluded by these means without any residual shunt. Thus, the ADO is a controlled release implant that also allows occlusion of a large PDA. Its high costs limit its general use in veterinary medicine at the present time.

Angiography↗
PubMed2002

Dynamic behavior of suspended pollutants and particle size distribution in highway runoff.

Continuous runoff quality monitoring was conducted for one month at urban highway drainage with an area of 8.4 ha. Dynamic change of suspended solids and heavy metal concentrations were investigated during first flush periods, taking the particle size distribution into consideration. Except for Pb, the concentrations of TSS and heavy metals in runoff were within the range of the EMC reported in recent highway runoff research. Particle-bound heavy metals (Zn, Pb, and Cu) accounted for more significant pollutant loads than soluble fractions. Their content decreased with increasing total SS concentration in runoff samples. The results of particle size distribution (PSD) analysis of runoff samples indicate that high TSS concentration samples contained coarser particles. Based on the PSD results, a stepwise wash-off phenomenon of TSS under varying runoff rate conditions was explained by the different washoff behavior of fine (< 20 microm) and coarser particles.

Environmental Monitoring↗
PubMed2001

Disinhibition in rat superior colliculus mediated by GABAc receptors.

The stratum griseum superficiale (SGS) of the superior colliculus contains a high concentration of the recently described GABA(C) receptor. In a previous study, it was postulated that activation of these receptors on inhibitory interneurons functions to disinhibit projection cells that relay visual information to the thalamus and brainstem. To test this model, we used in vitro whole-cell patch-clamp methods to measure effects of GABA and muscimol on EPSCs and IPSCs evoked in rat SGS by electrical optic layer stimulation. The neurons were filled with biocytin for later morphological characterization. As expected, bath applications of GABA and muscimol always strongly depressed evoked PSCs at concentrations of >100 and >1 micrometer, respectively. However, at lower agonist concentrations, which most likely activate GABA(C) but not GABA(A) receptors, effects were not uniform. Evoked responses were suppressed by both agonists in 48% of the neurons, whereas the remaining cells exhibited enhanced responses with increased evoked EPSCs, decreased evoked IPSCs, or both types of change. Most morphologically identified cells with suppressed responses (14 of 17 cells) had morphological characteristics of putative GABAergic interneurons, whereas almost all cells with enhanced responses (8 of 10 cells) had morphological characteristics of projection cells. Finally, all effects of GABA and muscimol at low concentrations were blocked by (1,2,5,6-tetrahydropyridine-4-yl) methylphosphinic acid, a specific GABA(C) receptor antagonist, but not by the specific GABA(A) receptor antagonist bicuculline. Taken together, these results indicate that in SGS, GABA(C) receptors are predominantly expressed by GABAergic neurons and that activation of these receptors leads to disinhibition of SGS projection cells.

Animals↗
PubMed2001

Postnatal maturation of GABA(A) and GABA(C) receptor function in the mammalian superior colliculus.

In the stratum griseum superficiale (SGS) of the mammalian superior colliculus, GABA(C) receptors seem to control the excitability of projection neurons by selective inactivation of local GABAergic interneurons. As the onset of visual responses to SC begins well after birth in the rat, it is possible to study developmental changes in GABAergic mechanisms that are linked to the onset of visual information processing. In order to analyse postnatal changes in inhibitory mechanisms that involve GABA receptor function, we used extracellular field potential (FP) recordings and single cell patch-clamp techniques in slices from postnatal day 4 (P4) to P32 and examined the effects of GABA and muscimol on electrically evoked SGS cell activity. While GABA(A) receptor activation affected FP amplitudes throughout postnatal development, GABA(C) receptor activation did not significantly change FP amplitudes until the third postnatal week. Results from patch-clamping single cells, however, clearly demonstrate that GABA(C) receptors are already functional at P4--similar to GABA(A) receptors. Throughout postnatal development, activation of GABA(C) receptors leads to a strong inhibition of inhibitory postsynaptic activity, indicating that GABA(C) receptors are expressed by inhibitory interneurons. Furthermore, the proportion of neurons that show decreased excitatory postsynaptic activity during GABA(C) receptor activation correlates with the proportion of GABAergic interneurons in SGS. Our patch-clamp results indicate that the functional expression of GABA(C) receptors by GABAergic interneurons does not change significantly during postnatal development. However, our measurements of FP amplitudes indicate that the maturation of the efferent connections of these GABAergic neurons within SGS during the third postnatal week strongly changes GABA(C) receptor function.

Aging↗
PubMed2001

Clinical comparison of preanaesthetic intramuscular medetomidine and dexmedetomidine in domestic sheep.

Medetomidine and its active d-enantiomer, dexmedetomidine, are highly selective alpha-2 agonists with potent sedative, anaesthetic-sparing and analgesic effects. These properties make them an ideal pre-anaesthetic medication for noxious surgical procedures. However, sheep can develop adverse hypoxaemic effects after intravenous alpha-2 agonists. Objective of the present study was to compare intramuscular injection of medetomidine or dexmedetomidine at equipotent doses as preanaesthetic medication prior to isoflurane anaesthesia in sheep. Nineteen healthy, adult, non-pregnant, female sheep of various breeds were used. The study was carried out as a randomised, blind trial. Group A received 15 micrograms/kg bwt dexmedetomidine and group B received 30 micrograms/kg bwt medetomidine intramuscularly (i.m.) 30 minutes prior to induction of anaesthesia. Anaesthesia was induced with ketamine (2.0 mg/kg bwt i.v.) and maintained with isoflurane in 100% oxygen. End expired anaesthetic concentration (FEiso), respiratory frequency (fR), direct arterial blood pressures and heart rates (HR) were measured. Arterial blood samples were taken at intervals. Data were averaged over time (sum of measurements/number of measurements) and tested for differences between groups by independent t-tests, and ANOVA for repeated measures followed by Bonferroni corrected t-tests. There were no differences in demographic data between the groups. Duration of anaesthesia [A: 170 (42) minutes, B: 144 (33) minutes] and duration of surgery [A: 92 (32) minutes, B: 85 (31) minutes] were similar in both groups. Average FEiso concentrations required to maintain a surgical plane of anaesthesia were not significantly different between groups [A: 0.82 (0.14)%; B: 1.00 (0.25)%]. Mean average fR, did not differ between groups [A: 31 (14), B: 37 (15)]. Heart rates were significantly lower in group B over the course of the anaesthesia. Mean arterial blood pressures (MAP) were not significantly different between the groups. The PaO2 was less variable in group A than in group B. Individual minimum values were 19.1 kPa and 7.9 kPa in group A and B, respectively. There were no significant differences in PaCO2 and paH between the groups and over time. In conclusion, intramuscular application of dexmedetomidine at 15 micrograms/kg bwt and medetomidine at 30 micrograms/kg bwt prior to isoflurane anaesthesia induced similar changes in clinically monitored cardiorespiratory parameters. The observed differences (heart rates, PaO2) between dexmedetomidine and medetomidine at the chosen dose relationship can be considered clinically not significant. At the chosen dose rates individual animals responded with a transient drop in blood oxygenation, therefore careful monitoring is required. In addition, in compromised sheep medetomidine and dexmedetomidine should be used carefully.

Adrenergic alpha-Agonists↗
PubMed1999

GABA(A) and GABA(C) receptors have contrasting effects on excitability in superior colliculus.

We have recently found that GABA(C) receptor subunit transcripts are expressed in the superficial layers of rat superior colliculus (SC). In the present study we used immunocytochemistry to demonstrate the presence of GABA(C) receptors in rat SC at protein level. We also investigated in acute rat brain slices the effect of GABA(A) and GABA(C) receptor agonists and antagonists on stimulus-evoked extracellular field potentials in SC. Electrical stimulation of the SC optic layer induced a biphasic, early and late, potential in the adjacent superficial layer. The late component was completely inhibited by 6-cyano-7-nitroquinoxaline-2,3-dione or CoCl(2), indicating that it was generated by postsynaptic activation. Muscimol, a potent GABA(A) and GABA(C) receptor agonist, strongly attenuated this postsynaptic potential at concentrations >10 microM. In contrast, the GABA(C) receptor agonist cis-aminocrotonic acid, as well as muscimol at lower concentrations (0.1-1 microM) increased the postsynaptic potential. This increase was blocked by (1,2,5, 6-tetrahydropyridine-4-yl)methylphosphinic acid, a novel competitive antagonist of GABA(C) receptors. Our findings demonstrate the presence of functional GABA(C) receptors in SC and suggest a disinhibitory role of these receptors in SC neuronal circuitry.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1994

Comparative effects of the dihydropyridine-type calcium-agonists (-)-S-Bay K 8644, (+/-)-Bay-W 5035 and (+/-)-Bay-T 5006 on human platelet aggregability.

1. Human platelet aggregation induced by collagen is concentration-dependently inhibited by dihydropyridine (DHP)-type calcium(Ca)-agonists. 2. There was no significant difference between the maximal anti-aggregatory effects or the anti-aggregatory potencies of (-)-S-Bay-K 8644 (EC50: 5.3 +/- 1.5 x 10(-5) M), (+/-)-Bay-W 5035 (EC50: 14.9 +/- 8.8 x 10(-5) M) or (+/-)-Bay-T 5006 (EC50: 2.7 +/- 1.9 x 10(-5) M) (P > 0.05). 3. Antiaggregatory effects of DHP-type Ca-agonists seem to be independent of Ca-channel activation.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1994

The calcium modulator nifedipine exerts its antiaggregatory property via a nitric oxide mediated process.

The in vitro effect of nifedipine, a calcium channel blocker of the dihydropyridine (DHP) type, on platelet aggregation was reinvestigated considering especially the capability of platelets to form endogenous nitric oxide (NO). We studied the dose-dependent antiaggregatory property of nifedipine in porcine platelet rich plasma. Aggregation was stimulated by collagen (7.5 micrograms/ml). Nifedipine inhibited collagen-induced platelet aggregation with an IC50 of 380 nmol/l. The antiaggregatory effect of nifedipine could be significantly diminished by N-nitro-L-arginine (NNA) in a concentration dependent manner, whereas oxy haemoglobin (4 microM), a NO scavenger, totally abolished the effect of nifedipine. L-Arginine, the precursor of NO, dose-dependently inhibited the collagen-induced platelet aggregation but did not potentiate the effects of nifedipine. Therefore, we propose that in platelet rich plasma the nifedipine induced inhibition of platelet aggregation is mediated by NO, a potent endogenous inhibitor of aggregation. We could confirm this hypothesis by measuring NO directly with a specific electrode.

Animals↗
PubMed1989

Beta-adrenergic modulation of transient inward current in guinea-pig cardiac myocytes. Evidence for regulation of Ca2(+)-release from sarcoplasmic reticulum by a cyclic AMP dependent mechanism.

Transient inward current (Iti) indicating Ca2(+)-release from the sarcoplasmic reticulum and L-type Ca2(+)-current (ICa) were studied in atrial and ventricular myocytes from hearts of adult guinea-pigs by means of whole-cell voltage-clamp. The increase of ICa caused by beta-adrenergic stimulation using isoprenaline (ISO) or related experimental manoeuvres such as superfusion with forskolin (FORSK) was used as a qualitative monitor of an increase of intracellular cAMP. Changes of Iti were used to manifest changes of sarcoplasmic Ca2(+)-release. In myocytes dialysed with citrate-based (60 mM) pipette filling solution containing 100 microM EGTA spontaneous transient inward currents were recorded at a constant holding potential of -50 mV in the majority of myocytes. Superfusion with a solution containing ISO (greater than or equal to 5 x 10(-8) M) increased the amplitude of spontaneous Iti and reduced its time-to-peak. The effects of ISO on Iti developed in parallel to stimulation of ICa. In myocytes which did not show spontaneous cyclic Ca2(+)-release in the above condition, this could be evoked de novo by ISO. Spontaneous Iti was suppressed in the majority of cells by increasing the concentration of EGTA in the dialysing solution to 200 microM. Brief (50 ms) activation of ICa by voltage steps from -50 to +10 mV usually failed to trigger Ca2(+)-release from the SR. The increase of ICa-amplitude upon administration of ISO went ahead with the induction of Ca2(+)-release by brief activation of ICa. The effects of ISO could be mimicked by FORSK or intracellular dialysis with 3'5'-cyclic adenosine monophosphate. The effects on ICa and SR Ca2(+)-release were dependent o the concentration of the stimulating substance. In a given cell changing superfusion from a low to a high concentration of ISO or FORSK resulted in an increase of the number of Ca2(+)-release events per number of Ca2(+)-currents elicited and a shortening of time-to-peak of Iti's. The stimulating effects of ISO or FORSK on Ca2(+)-release were only partially due to an increase of the triggering ICa. Ca2(+)-currents too small to trigger Ca2(+)-release before beta-adrenergic stimulation could evoke Ca2(+)-release after augmentation of intracellular cAMP. Whereas the effects of ISO and FORSK on ICa were reversible, the stimulatory effects on Ca2(+)-release persisted after washing out the substances. The results give support to the hypothesis that beta-adrenoceptor-mediated positive inotropic and arrhythmogenic effects are, at least partly, due to a cyclic AMP-dependent regulatory mechanism modulating sarcoplasmic Ca2(+)-release.

Animals↗
PubMed1985

Computed tomographic evaluation of compression of the superior vena cava and its tributaries.

Observations on computed tomography (CT) of 15 patients with compression of the superior vena cava (SVC) and its tributaries are reported and compared with clinical, radiographic and surgical findings. The site of compression in 14 patients was accurately determined by CT, which could delineate the presence of intraluminal clot and extrinsic compression of venous structures, as well as associated mediastinal masses. Collateral superficial vessels were identified in nine patients with contrast-enhanced scans. Contrast-enhanced mediastinal and chest CT was shown to provide detailed anatomic and physiologic information about the etiology of SVC syndrome.

Adult↗