Search PubMed⌕ Search

Biomedical subjects

D C White

Publications and source records attributed to D C White.

At least 91 records · Page 5Linked to original sources
PubMed1993

Components of the inspiratory-arterial isoflurane partial pressure difference.

We have measured the partial pressure of isoflurane simultaneously in inspired gas (PIiso), end-expired gas (PE'iso), mixed-expired gas (PEiso), arterial (Paiso) and mixed venous blood (Pviso) in six patients (aged 57-79 yr) anaesthetized with nitrous oxide, oxygen and isoflurane before surgery and after PE'iso had been stable for at least 15 min. We related these changes to the various indices of pulmonary maldistribution to determine if they were sufficient to explain reported differences between PE'iso and Paiso. Alveolar deadspace dilution of end-expired gas was calculated for carbon dioxide and this dilution factor used to calculate the "ideal" alveolar Piso (PAiso) from the observed inspired and end-expired concentrations. Shunt fraction was measured for oxygen and then used to calculate the partial pressure of isoflurane in the pulmonary end-capillary blood (Pc'iso) from the partial pressure in arterial and mixed venous blood. Mean (SE) values were: PIiso 0.69 (0.05) kPa; PE'iso 0.52 (0.04) kPa; PAiso 0.50 (0.04) kPa; Pc'iso 0.38 (0.04) kPa; Paiso 0.35 (0.03) kPa and Pviso 0.22 (0.02) kPa; Paiso: PE'iso 0.66 (0.02) kPa. The mean "ideal" alveolar to pulmonary end-capillary Piso difference was 0.12 (0.01) kPa and highly significant (P < 0.001). Paiso was substantially less than PE'iso but, for isoflurane, the difference was reasonably constant (range 0.14-0.22 kPa). The difference was attributable in part to the effects of shunt and deadspace, but also a failure of equilibration of isoflurane between the alveolar gas and pulmonary end-capillary blood. It is likely to be different for other anaesthetics. We conclude that, while PE'iso may adequately reflect Paiso for isoflurane, it cannot be assumed that the relation between end-expiratory gas and arterial partial pressures is the same for all anaesthetics.

Aged↗
PubMed1993

Isolation and characterization of an N-methylcarbamate insecticide-degrading methylotrophic bacterium.

A gram-negative bacterium which hydrolyzed aryl N-methylcarbamate insecticides was isolated from an agricultural soil which quickly degraded these pesticides. This organism, designated strain ER2, grew on carbofuran as a sole source of carbon and nitrogen with a doubling time of 3 h in a mineral salts medium. The aromatic nucleus of the molecule was not metabolized, and carbofuran 7-phenol accumulated as the end product of metabolism. The insecticides carbaryl, bendiocarb, and propoxur were similarly hydrolyzed, with each yielding the corresponding phenol. Strain ER2 contained two plasmids (120 and 130 kb). A probe cloned from the pDL11 plasmid of Achromobacter sp. strain WM111, which encodes the carbofuran hydrolase (mcd) gene (P. H. Tomasek and J. S. Karns, J. Bacteriol. 171:4038-4044, 1989), hybridized to the 120-kb plasmid. Restriction fragment profiles of pDL11 and strain ER2 plasmid DNAs suggested that the 120-kb plasmid of strain ER2 is very similar to pDL11. On the basis of the results of biochemical tests, 16S rRNA sequence analysis, and membrane lipid analyses, strain ER2 was found to be a phylogenetically unique type II methylotroph. The constitutive carbofuran hydrolase activity in glucose-grown cells increased sevenfold when strain ER2 was grown in the presence of 100 mg of carbofuran per liter as the sole source of carbon and nitrogen or as the sole nitrogen source in the presence of glucose. Growth on carbofuran resulted in the induction of enzymes required for methylamine-dependent respiration and the serine pathway of formaldehyde assimilation. These results indicate that the carbofuran hydrolase mcd gene is conserved on a plasmid found in organisms from different geographic areas and that the specific activity of carbofuran degradation may increase in response to carbofuran treatment.

Alcaligenes↗
PubMed1993

Survival of subsurface microorganisms exposed to UV radiation and hydrogen peroxide.

Aerobic and microaerophilic subsurface bacteria were screened for resistance to UV light. Contrary to the hypothesis that subsurface bacteria should be sensitive to UV light, the organisms studied exhibited resistance levels as efficient as those of surface bacteria. A total of 31% of the aerobic subsurface isolates were UV resistant, compared with 26% of the surface soil bacteria that were tested. Several aerobic, gram-positive, pigmented, subsurface isolates exhibited greater resistance to UV light than all of the reference bacterial strains tested except Deinococcus radiodurans. None of the microaerophilic, gram-negative, nonpigmented, subsurface isolates were UV resistant; however, these isolates exhibited levels of sensitivity similar to those of the gram-negative reference bacteria Escherichia coli B and Pseudomonas fluorescens. Photoreactivation activity was detected in three subsurface isolates, and strain UV3 exhibited a more efficient mechanism than E. coli B. The peroxide resistance of four subsurface isolates was also examined. The aerobic subsurface bacteria resistant to UV light tolerated higher levels of H2O2 than the microaerophilic organisms. The conservation of DNA repair pathways in subsurface microorganisms may be important in maintaining DNA integrity and in protecting the organisms against chemical insults, such as oxygen radicals, during periods of slow growth.

Bacteria, Aerobic↗
PubMed1993

Phylogenetic analysis of a bacterial aerobic degrader of azo dyes.

Eubacterial consensus oligonucleotide primers were used to amplify by polymerase chain reaction the nearly full-length 16S rRNA gene of isolate C7, a gram-negative rod capable of aerobic degradation of azo dyes. The DNA product was cloned and sequenced. Phylogenetic analysis based upon this DNA sequence places C7 within the alpha subdivision of proteobacteria, most closely related to Caulobacter subvibrioides. The phospholipid fatty acid pattern resembles that of caulobacters, with monounsaturated 16- and 18-carbon fatty acids predominating. C7 is unusual in having a monounsaturated branched fatty acid in the phospholipids and exclusively 2-hydroxy fatty acids in the lipid-extracted residue. This organism is of potential use in bioreactors operated for azo dye degradation.

Aerobiosis↗
PubMed1991

Kinetics of ATP release and Pi binding during the ATPase cycle of lethocerus flight muscle fibres, using phosphate-water oxygen exchange.

Rate constants have been obtained using oxygen isotope exchange techniques for steps controlling ATP release and Pi binding in the ATPase cycle of insect flight muscle fibres from the giant waterbug Lethecerus. The new exchange data for Pi binding and ATP release are compatible with a model developed previously in which only the rate constants controlling Pi and ATP release change during fibre activation. Phosphate-water oxygen exchange occurs into ATP remaining after partial hydrolysis by chemically skinned fibres in (18O) water. For fully activated fibres, the results are compatible with a single set of rate constants controlling this exchange and give a rate constant for ATP release of 1 s-1 (21 degrees C, pH 7.0 I = 120 mM). Oxygen exchange also occurs between (18O4)Pi in the medium and water during ATP hydrolysis. There is a strong correlation between the measured rate constant of exchange and the value of keat for the ATPase activity at different levels of activation. For fibres fully activated by oscillation or strain, the rate constant for Pi binding to an actomyosin. ADP state is greater than 960 M-1 s-1.

Adenosine Diphosphate↗
PubMed1991

Development of a differential volume reactor system for soil biodegradation studies.

A bench scale experimental system was developed for the analysis of polycyclic aromatic hydrocarbon (PAH) degradation by mixed microbial cultures in PAH contaminated Manufactured Gas Plant (MGP) soils and on sand. The reactor system was chosen in order to provide a fundamental protocol capable for evaluating the performance of specific mixed microbial cultures on specific soil systems by elucidating the important system variables and their interactions. The reactor design and peripherals are described. A plug flow differential volume reactor (DVR) was used in order to remove performance effects related to reactor type, as opposed to system structure. This reactor system could be well represented mathematically. Methods were developed for on-line quantitative determination of PAH liquid phase concentrations. The mathematical models and experimental data are presented for the biodegradation of naphthalene on artificial and MGP soils.

Bacteria↗
PubMed1991

Effect of ventilation and cardiac output on the uptake of anaesthetic agents from different breathing systems: a theoretical study.

We have investigated the influences of ventilation and cardiac output on uptake of anaesthetic with different breathing systems, by analysis of simple equations and by computer simulation. Increases in cardiac output and ventilation increased uptake from those systems which provided a constant inspired concentration, but not from completely closed systems with the vaporizer out of the circle (VOC), or when using the technique described by Lowe and Ernst. When the vaporizer was inside the circle, uptake increased with ventilation but not with cardiac output. With servo control of endtidal concentration, uptake increased with cardiac output but not with ventilation. When the fresh gas flow to VOC systems was increased from basal, independence of uptake from ventilation was well maintained until fresh gas flow approached alveolar ventilation, but the independence of uptake from cardiac output was lost much sooner.

Anesthesia, Closed-Circuit↗
PubMed1991

Membrane fatty acids as phenotypic markers in the polyphasic taxonomy of methylotrophs within the Proteobacteria.

A polyphasic approach to bacterial taxonomy attempts to integrate phylogenetic relationships with phenotypic marker analysis. This study describes the application of membrane fatty acids as a phenotypic marker for methylotrophs. Detailed phospholipid, ester-linked fatty acid (PLFA) profiles are reported for 17 methylotrophic eubacterial strains. These profiles included verification of double bond positions and geometries, both critical features for this analysis. Multivariate cluster analysis was used to indicate groupings of these strains along with literature values of both methylotrophs and non-methylotrophs based on the PLFA phenotype. Like many phenotypic characteristics, PLFA profiles were influenced by environmental conditions. The instabilities displayed, however, were predictable from physiological studies including increased trans/cis and cyclopropyl/cis ratios. Cluster analysis of PLFA profiles generated by separate investigators with different culture conditions indicated reproducibility by strain and species. The PLFA phenotype relationships compare favourably with phylogenetic associations based on 16S rRNA data for methylotrophs and will continue to be a valuable phenotypic marker for Proteobacteria taxonomy.

Cell Membrane↗
PubMed1991

Low-flow anaesthesia. Practice, cost implications and acceptability.

An 8-week survey was conducted to determine whether the introduction of low-flow anaesthesia (a fresh gas flow of 4 litres/minute or less) into routine use would be acceptable to members of a representative anaesthetic department and if the consequent reduction in use of volatile anaesthetics would result in financial savings. The hourly consumption of the volatile agents was measured during anaesthesia conducted using either conventional or low fresh gas flows. Anaesthetists' acceptance of low-flow anaesthesia was assessed using a questionnaire. Data were gathered on 286 patients undergoing inhalational anaesthesia for routine operative procedures. A 54.7% reduction in the consumption of isoflurane and a 55.9% reduction in that of enflurane was found. Of the 28 anaesthetists at the hospital, 21 would use low-flow anaesthesia routinely. The routine use of low-flow anaesthesia would therefore be acceptable and could result in annual savings of 26,870 pounds at Northwick Park Hospital.

Anesthesia, Inhalation↗
PubMed1991

Evaluation of the Lamtec anaesthetic agent monitor.

The Lamtec agent monitor is a compact anaesthetic analyser designed to measure halothane, isoflurane and enflurane. It shows good linearity and stability. The faster model can be used for end-tidal measurements up to 25 breaths per minute. Calibration using a standard of the gas to be measured is recommended.

Anesthesia, Inhalation↗
PubMed1991

Aerobic mineralization of vinyl chloride by a bacterium of the order Actinomycetales.

A gram-positive branched bacterium isolated from a trichloroethylene-degrading consortium mineralized vinyl chloride in growing cultures and cell suspensions. Greater than 67% of the [1,2-14C]vinyl chloride was mineralized to carbon dioxide, with approximately 10% of the radioactivity appearing in cell biomass and another 10% appearing in 14C-aqueous-phase products.

Actinomycetales↗
PubMed1991

Archaebacterial ether lipid diversity analyzed by supercritical fluid chromatography: integration with a bacterial lipid protocol.

A strategy has been developed for archaebacterial lipid analysis which provides three times the information to describe archaebacterial isolates and is compatible with simultaneous eubacterial/eukaryotic lipid analysis of environmental samples. Eubacterial and micro-eukaryotic biomass, community structure, and nutritional status have been routinely defined in environmental samples by lipid analysis. Lipid profiles are also useful in eubacterial identification and taxonomy. Polar lipid or whole cell ester-linked fatty acids are generally analyzed by gas chromatography-mass spectroscopy. Archaebacteria are characterized by their ether-linked membrane lipids. There is, however, less diversity in the side chains of archaebacterial membrane lipids as compared the eubacterial ester-linked membrane lipids. The information content of the archaebacterial lipid profile was increased by separately analyzing the polar lipid, glycolipid, and lipid-extracted residue fractions. Identification and quantification were performed by supercritical fluid chromatography. Results are presented for three species of methanogens and four thermoacidophile isolates, and compared with a literature review.

Archaea↗
PubMed1990

Alteration in crossbridge kinetics caused by mutations in actin.

The generation of force during muscle contraction results from the interaction of myosin and actin. The kinetics of this force generation vary between different muscle types and within the same muscle type in different species. Most attention has focused on the role of myosin isoforms in determining these differences. The role of actin isoforms has received little attention, largely because of the lack of a suitable cell type in which the myosin isoform remains constant yet the actin isoforms vary. An alternative approach would be to examine the effect of actin mutations, however, most of these cause such gross disruption of muscle structure that mechanical measurements are impossible. We have now identified two actin mutations which, despite involving conserved amino acids, can assemble into virtually normal myofibrils. These amino-acid changes in actin significantly affect the kinetics of force generation by muscle fibres. One of the mutations is not in the putative myosin-binding site, demonstrating the importance of long-range effects of amino acids on actin function.

Actins↗
PubMed1990

Physiological properties of the dorsal longitudinal flight muscle and the tergal depressor of the trochanter muscle of Drosophila melanogaster.

A prerequisite for using muscle mutants to study contraction in Drosophila melanogaster is a description of the mechanics of wild-type muscles. Here we describe the mechanics of two different wild-type muscles; the dorsal longitudinal flight muscle which is asynchronous (nerve impulses are not synchronised with each contraction), and a leg muscle, the tergal depressor of the trochanter, which is synchronous. We have compared their mechanics to those of the asynchronous flight and the synchronous leg muscle from the giant waterbug Lethocerus indicus. We found that the mechanics of the asynchronous flight muscles from the two species were similar. At rest length both muscles had a high relaxed stiffness, were partially activated by Ca2+ (low steady-state active tension) and, once activated, had a large delayed increase in tension, which was well maintained, in response to a rapid stretch. The rate constant for the delayed increase in tension was about 10 times greater for D. melanogaster than for L. indicus under the same conditions. The mechanics of the synchronous leg muscles from both species were different from those of the flight muscles and resembled those of other synchronous muscles such as vertebrate striated muscle. At rest length, both muscles had a lower relaxed stiffness than the flight muscles, were fully activated by Ca2+ (high steady-state active tension) and, once activated, had a small delayed increase in tension, which was less well maintained, in response to a rapid stretch. The rate constant for the delayed increase in tension was similar for the leg muscles of both species. The different mechanical properties of the flight and leg muscles must arise from differences in their contractile proteins. The demonstration that satisfactory mechanical responses can be obtained from the small (less than 1 mm long) muscles of D. melanogaster will enable future responses from mutant muscles to be tested.

Animals↗
PubMed1990

Biodegradation of trichloroethylene in continuous-recycle expanded-bed bioreactors.

Experimental bioreactors operated as recirculated closed systems were inoculated with bacterial cultures that utilized methane, propane, and tryptone-yeast extract as aerobic carbon and energy sources and degraded trichloroethylene (TCE). Up to 95% removal of TCE was observed after 5 days of incubation. Uninoculated bioreactors inhibited with 0.5% Formalin and 0.2% sodium azide retained greater than 95% of their TCE after 20 days. Each bioreactor consisted of an expanded-bed column through which the liquid phase was recirculated and a gas recharge column which allowed direct headspace sampling. Pulses of TCE (20 mg/liter) were added to bioreactors, and gas chromatography was used to monitor TCE, propane, methane, and carbon dioxide. Pulsed feeding of methane and propane with air resulted in 1 mol of TCE degraded per 55 mol of substrate utilized. Perturbation studies revealed that pH shifts from 7.2 to 7.5 decreased TCE degradation by 85%. The bioreactors recovered to baseline activities within 1 day after the pH returned to neutrality.

Journal Article↗
PubMed1989

Differences in fatty acid composition between vegetative cells and N(2)-fixing vesicles of Frankia sp. strain CpI1.

When growing on N(2), actinomycetes from the genus Frankia form multicellular structures that contain nitrogenase. The structures are referred to as vesicles and are indistinguishable from vesicles formed when Frankia sp. are in root-nodule symbioses. Vesicles isolated from N(2)-grown cells of Frankia sp. strain CpI1 had a significantly higher amount and different composition of fatty acids than did vegetative cells recovered from NH(4) (+)-containing medium. Lipids from vesicles, whole cells grown on N(2), and whole cells grown on NH(4) (+) were fractionated by silicic acid chromatography into neutral lipids, glycolipids, and polar lipids. The fatty acids were transesterified by methanolysis and analyzed by gas chromatography and mass spectrometry. Vesicles had considerably higher amounts of fatty acids in the neutral and glycolipid fractions but lower amounts of polar lipid fatty acids than did vegetative cells. Polar lipids from vesicles had a higher proportion of mono-unsaturated and cyclopropane fatty acids and a lower proportion of isobranched fatty acids than did polar lipids from NH(4) (+)-grown or N(2)-grown cells. The neutral lipid and glycolipid fractions contained several long-chain compounds with molecular ions at m/z 408 and 410. The proportions of these compounds were significantly higher in the lipids from vesicles than from vegetative cells. These results suggest that lipids in vesicles might be involved in the protection of nitrogenase from O(2) and suggest a parallel with the glycolipids involved in protecting nitrogenase from O(2) in the cyanobacterial heterocysts.

Journal Article↗