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Biomedical subjects

D G Williams

Publications and source records attributed to D G Williams.

At least 19 recordsLinked to original sources
PubMed2006

The sensitivity of ecosystem carbon exchange to seasonal precipitation and woody plant encroachment.

Ongoing, widespread increases in woody plant abundance in historical grasslands and savannas (woody encroachment) likely will interact with future precipitation variability to influence seasonal patterns of carbon cycling in water-limited regions. To characterize the effects of woody encroachment on the sensitivity of ecosystem carbon exchange to seasonal rainfall in a semi-arid riparian setting we used flux-duration analysis to compare 2003-growing season NEE data from a riparian grassland and shrubland. Though less seasonally variable than the grassland, shrubland NEE was more responsive to monsoon rains than anticipated. During the 2004-growing season we measured leaf gas exchange and collected leaf tissue for delta(13)C and nitrogen content analysis periodically among three size classes of the dominant woody-plant, Prosopis velutina and the dominant understory species, Sporobolus wrightii, a C(4) bunchgrass, present at the shrubland. We observed size-class and plant functional type independent patterns of seasonal plant performance consistent with greater-than-anticipated sensitivity of NEE in the shrubland. This research highlights the complex interaction between growing-season precipitation, plant-available alluvial groundwater and woody plant abundance governing ecosystem carbon balance in this semi-arid watershed.

Analysis of Variance↗
PubMed2006

Best practice in primary care pathology: review 6.

This sixth best practice review examines four series of common primary care questions in laboratory medicine: (1) laboratory monitoring in hypertension and heart failure abnormalities; (2) markers of inflammatory joint disease; (3) laboratory investigation of chronic diarrhoea; and (4) mumps and chickenpox. The review is presented in question-answer format, referenced for each question series. The recommendations represent a precis of guidance found using a standardised literature search of national and international guidance notes, consensus statements, health policy documents and evidence-based medicine reviews, supplemented by Medline Embase searches to identify relevant primary research documents. They are not standards but form a guide to be set in the clinical context. Most are consensus based rather than evidence based. They will be updated periodically to take account of new information.

Arthritis↗
PubMed2006

Influence of soil texture on hydraulic properties and water relations of a dominant warm-desert phreatophyte.

We investigated hydraulic constraints on water uptake by velvet mesquite (Prosopis velutina Woot.) at a site with sandy-loam soil and at a site with loamy-clay soil in southeastern Arizona, USA. We predicted that trees on sandy-loam soil have less negative xylem and soil water potentials during drought and a lower resistance to xylem cavitation, and reach E(crit) (the maximum steady-state transpiration rate without hydraulic failure) at higher soil water potentials than trees on loamy-clay soil. However, minimum predawn leaf xylem water potentials measured during the height of summer drought were significantly lower at the sandy-loam site (-3.5 +/- 0.1 MPa; all errors are 95% confidence limits) than at the loamy-clay site (-2.9 +/- 0.1 MPa). Minimum midday xylem water potentials also were lower at the sandy-loam site (-4.5 +/- 0.1 MPa) than at the loamy-clay site (-4.0 +/- 0.1 MPa). Despite the differences in leaf water potentials, there were no significant differences in either root or stem xylem embolism, mean cavitation pressure or Psi(95) (xylem water potential causing 95% cavitation) between trees at the two sites. A soil-plant hydraulic model parameterized with the field data predicted that E(crit) approaches zero at a substantially higher bulk soil water potential (Psi(s)) on sandy-loam soil than on loamy-clay soil, because of limiting rhizosphere conductance. The model predicted that transpiration at the sandy-loam site is limited by E(crit) and is tightly coupled to Psi(s) over much of the growing season, suggesting that seasonal transpiration fluxes at the sandy-loam site are strongly linked to intra-annual precipitation pulses. Conversely, the model predicted that trees on loamy-clay soil operate below E(crit) throughout the growing season, suggesting that fluxes on fine-textured soils are closely coupled to inter-annual changes in precipitation. Information on the combined importance of xylem and rhizosphere constraints to leaf water supply across soil texture gradients provides insight into processes controlling plant water balance and larger scale hydrologic processes.

Circadian Rhythm↗
PubMed2006

Antecedent moisture and seasonal precipitation influence the response of canopy-scale carbon and water exchange to rainfall pulses in a semi-arid grassland.

The influences of prior monsoon-season drought (PMSD) and the seasonal timing of episodic rainfall ('pulses') on carbon and water exchange in water-limited ecosystems are poorly quantified. *In the present study, we estimated net ecosystem exchange of CO(2) (NEE) and evapotranspiration (ET) before, and for 15 d following, experimental irrigation in a semi-arid grassland during June and August 2003. Rainout shelters near Tucson, Arizona, USA, were positioned on contrasting soils (clay and sand) and planted with native (Heteropogon contortus) or non-native invasive (Eragrostis lehmanniana) C4 bunchgrasses. Plots received increased ('wet') or decreased ('dry') monsoon-season (July-September) rainfall during 2002 and 2003. Following a June 2003 39-mm pulse, species treatments had similar NEE and ET dynamics including 15-d integrated NEE (NEE(pulse)). Contrary to predictions, PMSD increased net C uptake during June in plots of both species. Greater flux rates after an August 2003 39-mm pulse reflected biotic activity associated with the North American Monsoon. Furthermore, August NEE(pulse) and ecosystem pulse-use efficiency (PUE(e) = NEE(pulse)/ET(pulse)) was greatest in Heteropogon plots. PMSD and rainfall seasonal timing may interact with bunchgrass invasions to alter NEE and ET dynamics with consequences for PUE(e) in water-limited ecosystems.

Arizona↗
PubMed2006

Sprayable microencapsulated sex pheromone formulation for mating disruption of oriental fruit moth (Lepidoptera: Tortricidae) in Australian peach and pear orchards.

Areawide mating disruption treatments have been effective in controlling infestation of oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), in Australian pome and stone fruit orchards. Although successful, the areawide mating disruption program has been an expensive approach by using hand-applied Isomate dispensers. Sprayable microencapsulated (MEC) pheromone formulations that can be applied with standard spray equipment could substantially reduce the cost of application. Field trials conducted during two consecutive seasons (2002-2004) demonstrated that monthly applications of MEC-OFM phase V (3M Canada, London, Ontario, Canada) at a rate of 125 ml/ha (37.1 g [AI]/ha) in replicated 2-ha blocks of both peaches and pears reduced oriental fruit moth shoot tip and fruit damage as effectively as a single application of Isomate OFM Rosso hand-applied dispensers (500 dispensers per ha) and as or more effectively than standard broad-spectrum insecticide sprays. Fruit protection was achieved despite high oriental fruit moth population densities in both crops as measured by moth catches in terpinyl acetate food and pheromone traps. Similar numbers of oriental fruit moths were captured among all treatments in food traps but captures of males in pheromone traps were disrupted (96-99%) in pheromone-treated blocks relative to controls. The results of this study suggest that microencapsulated formulations of pheromone could be effectively used in areawide mating disruption programs for oriental fruit moth in Australia as a cost-saving alternative to reservoir-style dispensers requiring labor-intensive hand application.

Aerosols↗
PubMed2004

Ropivacaine in neonates and infants: a population pharmacokinetic evaluation following single caudal block.

BACKGROUND: The aims of this study were to evaluate pharmacokinetics, efficacy and safety of ropivacaine in infants aged 0-12 months following a single caudal injection. METHODS: Term ASA I-III patients, scheduled for surgery, with a body weight of > or = 2500 g received a caudal block with ropivacaine 2 mg x ml(-1), 1.0 ml x kg(-1). Plasma samples were collected at different time intervals up to 30 h, for analysis of total and unbound ropivacaine and alpha-1-acid glycoprotein (AAG). Pharmacokinetic data were characterized by population analysis. Unbound and total concentrations from 35 patients, median (min-max) postnatal age of 66 (4-351) days, were included in the nonlinear mixed effects modeling to provide estimates of pharmacokinetic parameters and the exploration of covariate relationships. Simulations were made to test the predictive performance of the final model and to describe the effect of significant covariates on systemic exposure. RESULTS: The mean (min-max) peak plasma concentration of total ropivacaine was 0.83 (0.05-1.57) mg x l(-1) at 0.5-5.7 h (median: 1.0 h) and the plasma concentration of unbound ropivacaine was 0.042 (0.012-0.081) mg x l(-1) within 0.5-1 h. The observed unbound fraction in plasma was 6% (1%-14%). A one-compartment open model with first-order absorption and elimination, incorporating a linear-binding model of ropivacaine to AAG best described the data. The only significant covariate relationship was that of age on Clu/F according to the following relationship Clu/F = 3.01 x e0.00474 x Age. This predicts a Clu/F of 3.5 l x h(-1) x kg(-1) at 30 days and 10.8 l x h(-1) x kg(-1) at 270 days with corresponding terminal half-lives of 6.7 and 2.2 h. The interindividual variability (coefficient of variation, CV) in Clu/F was 39%. The population estimate (CV) of ka was 1.65 h(-1) (30%), Vu/F was 33.6 (l x kg(-1)) (45%) and Ka was 1.78 l x mg(-1) (14%). Thirty-five infants received supplementary analgesics (mostly paracetamol). The median time to first supplementary analgesic (based on all 37 patients) was 3.9 h. No safety concerns or signs of systemic toxicity were observed. CONCLUSIONS: Following a caudal block with ropivacaine 2 mg x kg(-1) plasma concentrations of unbound ropivacaine were well below threshold levels for toxicity in adults. Apparent volume of distribution is unchanged, apparent unbound clearance increases and the terminal half-life decreases with age in 0-12-month-old neonates and infants. The postoperative pain management provided adequate analgesia and was well tolerated.

Amides↗
PubMed2003

Contrasting patterns of hydraulic redistribution in three desert phreatophytes.

We measured sap flow in taproots, lateral roots and stems within a single individual in each of three co-occurring tree species in a Chihuahuan desert arroyo to assess the seasonality and magnitude of hydraulic redistribution. Nocturnal reverse flow (hydraulic redistribution) was detected in shallow lateral roots of Fraxinus velutina and Juglans major during periods when surface soils were dry. Reverse flow in the Fraxinus lateral root ranged from near zero to 120 g h(-1), and was inversely correlated with nighttime vapor pressure deficit (D), suggesting that nighttime transpiration may have inhibited hydraulic redistribution. Reverse flow in the Juglans lateral root ranged from near zero to 18 g h(-1). There was no relationship between reverse flow and nighttime D in the Juglans lateral root, despite a weak positive relationship between nighttime D and rates of basipetal flow (flow towards the stem) in the taproot. Reverse flow in Fraxinus and Juglans ceased when surface soils were wetted by monsoon rains and flooding. We found no reverse flow or seasonal variation in root sap flow in Celtis reticulata. However, basipetal sap flow in Celtis roots continued throughout most of the evening, even during periods when D was near zero, and commenced in the morning more than two hours after the onset of sap flow in the main stem. Patterns of nocturnal root sap flow in Celtis may have been facilitated by the diurnal withdrawal from, and refilling of above ground storage compartments (i.e. above ground diurnal storage capacity), which may have prevented hydraulic redistribution. Species differences in nocturnal root function may have significant impacts on ecosystem hydrological fluxes, and should be considered when scaling fluxes to catchment, landscape, and regional levels.

Biological Transport↗
PubMed2003

Epidural analgesia in children. A survey of current opinions and practices amongst UK paediatric anaesthetists.

BACKGROUND: Despite the widespread use of epidural analgesia in children its place in paediatric pain management has not been clearly established. In order to investigate the current practice of paediatric epidural analgesia in the UK paediatric anaesthetists and paediatric pain management teams were surveyed. METHODS: Questionnaires were sent to the members of the Association of Paediatric Anaesthetists (APA) working within the UK and to lead clinicians and clinical nurse specialists for acute pain in the 26 designated major paediatric centres. RESULTS: The response rate was 72%. There was little consensus regarding drugs and drug combinations used for epidural analgesia. A total of 36% of paediatric centres did not audit their epidural practice, and of those that did the reported incidences of side-effects showed wide variation. Important differences in practice were also identified in the areas of patient selection, informed consent, the use of epidural test doses, drug delivery systems, monitoring and the management of side-effects. Twelve per cent of specialist paediatric hospitals did not have an acute pain team and elsewhere the provision was often limited to staff with few or no specialist skills. CONCLUSION: There is wide variation in the practice of paediatric epidural analgesia in the UK. Inconsistencies are likely to be related to the poor evidence base available to guide clinical decision making and the lack of a specialized paediatric acute pain service in some centres. More research is required to determine the optimal management of epidural analgesia, and suitable clinical support for paediatric pain control should be more widely available.

Analgesia, Epidural↗
PubMed2003

Hydraulic redistribution by deep roots of a Chihuahuan Desert phreatophyte.

Downward redistribution of soil water through plant roots has important consequences for water and nutrient balance of arid and semi-arid ecosystems. Nevertheless, information on the seasonal patterns and magnitudes of redistribution is lacking for all but a few plant species. We measured sap flow in the taproot and three main lateral roots of a 10-year-old Juglans major Torr. tree, on an ephemeral catchment in southeastern Arizona, to determine how patterns of redistribution respond to pulses of summer precipitation. Groundwater was beyond rooting depth and a hardpan prevented recharge of surface water to deep soil layers. Reverse flow (hydraulic descent) commenced in the taproot and deep lateral roots in early August after a series of moderate precipitation events, and abruptly ceased after all shallow roots were experimentally severed in mid-August. On some days, hydraulic descent continued in the deep lateral roots during periods of daytime transpiration, and the daily volume of hydraulic descent (deep lateral roots plus taproot) ranged from 10 to nearly 60% of daily transpiration. The persistent pattern of reverse flow demonstrates that, in some plants, water potential gradients from soil to leaf during transpiration are often smaller than those between soil layers within the rooting zone. Hydraulic descent may be an important component of the water balance of phreatophytic trees by facilitating root growth in deep soil layers and by transferring water away from shallow-rooted competitors.

Arizona↗
PubMed2002

An unexpected difficult laryngoscopy.

A case of unexpected difficult laryngoscopy in a patient with gross hydrocephalus and generalized hypertonus is described. The 30-month-old girl had no antecedent history of such difficulty, having had two recent uneventful anaesthetics. We suggest that the reason for our inability to open the patient's mouth was a result of contracture of the temporalis muscle. The patient was managed using a laryngeal mask airway with controlled ventilation.

Anesthesia↗
PubMed2002

Pharmacogenetics of codeine metabolism in an urban population of children and its implications for analgesic reliability.

BACKGROUND: Codeine analgesia is wholly or mostly due to its metabolism to morphine by the cytochrome P450 enzyme CYP2D6, which shows significant genetic variation in activity. The aims of this study were to investigate genotype, phenotype and morphine production from codeine in children undergoing adenotonsillectomy, and to compare analgesia from codeine or morphine combined with diclofenac. METHODS: Ninety-six children received either codeine 1.5 mg kg(-1) or morphine 0.15 mg kg(-1) in a randomized, double-blind design. Genetic analysis was performed and plasma morphine concentrations at 1 h were determined. Postoperative analgesia and side-effects were recorded. RESULTS: Forty-seven per cent of children had genotypes associated with reduced enzyme activity. Mean (SD) morphine concentrations were significantly lower (P<0.001) after codeine [4.5 (0.3) ng ml(-1)] than after morphine [24.7 (1.5) ng ml(-1)], and morphine and its metabolites were not detected in 36% of children given codeine. There was a significant relationship between phenotype and plasma morphine (P=0.02). More children required rescue analgesia after codeine at both 2 (P<0.05) and 4 h after administration (P<0.01). Fifty-six per cent of children vomited after morphine and 29% after codeine (P<0.01). Neither phenotype nor morphine concentration was correlated with either pain score or the need for rescue analgesia (r=-0.21, 95% confidence interval -0.4, -0.01). CONCLUSIONS: Reduced ability for codeine metabolism may be more common than previously reported. Plasma morphine concentration 1 h after codeine is very low, and related to phenotype. Codeine analgesia is less reliable than morphine, but was not well correlated with either phenotype or plasma morphine in this study.

Analgesia↗
PubMed2002

Carbon isotope discrimination and bundle sheath leakiness in three C(4) subtypes grown under variable nitrogen, water and atmospheric CO(2) supply.

The changes in composition and productivity of semi-arid C(4) grassland, anticipated with rising atmospheric CO(2), will depend on soil water and nutrient availability. The interactive effects of soil resource limitation and elevated CO(2 )on these grasses, furthermore, may vary among C(4) biochemical subtypes (NADP-ME, NAD-ME, PCK) that differ in bundle sheath leakiness (Phi) responses to drought and nitrogen supply. To address C(4) subtype responses to soil resource gradients, the carbon isotope discrimination (Delta), bundle sheath leakiness (Phi), leaf gas exchange (A, g(s), c(i)/c(a)) and above-ground biomass accumulation were measured on three dominant grasses of semi-desert grassland in south-eastern Arizona. Bouteloua curtipendula (PCK), Aristida glabrata (NADP-ME) and the non-native Eragrostis lehmanniana (NAD-ME) were grown in controlled-environment chambers from seed under a complete, multi-factorial combination of present ambient (370 ppm) and elevated (690 ppm) CO(2) concentration and under high and low water and nitrogen supply. E. lehmanniana (NAD-ME) had the highest photosynthetic rate (A) and lowest Phi compared to the other two grasses when grown under low nitrogen and water availability. However, favourable water and nitrogen supply and elevated atmospheric CO(2) enhanced photosynthetic performance and above-ground biomass production of B. curtipendula (PCK) to a greater extent than in A. glabrata and E. lehmanniana. Contrary to pre vious studies, Phi and Delta in the NADP-ME subtype (A. glabrata) were most affected by changing environmental conditions compared to the other subtypes; deviations from the classic NADP-ME anatomy in Aristida could have accounted for this result. Overall, response of semi-arid grasslands to rising atmospheric CO(2) may depend more on species-specific responses to drought and nitrogen limitation than on general C(4) subtype responses.

Algorithms↗
PubMed2001

Demonstrative validation study employing a packed column pressurized fluid chromatography method that provides assay, achiral impurities, chiral impurity, and IR identity testing for a drug substance.

Assay development, assay validation, and documentation are reported here for a single packed column pressurized fluid chromatographic/ultraviolet (UV) method that provides: (1) simultaneous detection and quantification for the chiral drug, the chiral impurity and seven achiral impurities; and (2) a Fourier transform infrared (FT-IR) spectrometric identification test result for the Searle drug substance sample, xemilofiban. The separation is achieved in less than 30 min with three columns in tandem and a gradient of CO2-CH3OH. The post-column flow is split between UV (assay) and FT-IR (identification). Precision and accuracy are consistent within figures of merit obtained by liquid chromatographic-ultraviolet assays on analogous drug substances. The reported procedure combines three typical drug substance tests into one test (e.g. chiral impurities, achiral impurities, and infrared identification).

Chromatography, Liquid↗
PubMed1999

Side-chain specificities and molecular modelling of peptide determinants for two anti-Sm B/B' autoantibodies.

Autoantibodies binding the Sm B and B' peptides (B/B') are commonly associated with systemic lupus erythematosus in man and in MRL lpr/lpr mice. The linear antigenic regions of two anti-Sm B/B' murine monoclonal auto-antibodies have been mapped using overlapping octapeptides. Unique epitopes are identified by each antibody. Monoclonal KSm-5 recognizes the peptide, PPPGMRPP, which is repeated three times in the Sm B polypeptide. KSm 3 preferably binds to two similar, almost neighboring octapeptides, PPPGIRGP and PGIRGPPP. The two monoclonal antibodies do not cross react. These regions of Sm B/B' are major areas of antigenicity in human sera. Amino acid deletion and substitution in antigenic octapeptides show that binding to the KSm-5 epitope is lost with most modifications. Molecular dynamic modelling suggests that when PPPGMRPP is substituted in the sixth position arginine, KSm/5 binding may be associated with a shared peptide backbone structure rather than charge or hydrophobicity of the substituted amino acid. In contrast, binding of KSm-3 to PPPGIRGP is abolished when the sixth position arginine is substituted by any other amino acid. Substitution at arginine and modelling experiments, therefore, suggest very different mech-anisms of binding. Autoantibodies may bind quite different features of similar peptide structures.

Amino Acid Sequence↗
PubMed1999

Rheumatoid factor isotype switch and somatic mutation variants within rheumatoid arthritis synovium.

The presence of clonally-related B-lymphocyte aggregates within synovial lining tisue of rheumatoid arthritis (RA) patients suggests a germinal centre-like reaction, which may hold implications for disease pathogenesis and the causes of chronic inflammation. We studied 250 rheumatoid factor (RF) heavy-chain sequences cloned from the synovium of three patients with RA, to determine whether they undergo both somatic mutation and isotype switching consistent with this hypothesis. Size analysis of immunoglobulin heavy-chain cDNAs from synovial RF+ B cells revealed oligoclonal RF+ populations and identically-sized VH-D-JH transcripts of different immunoglobulin isotypes. Sequencing of individual inserts selected from cloned immunoglobulin heavy-chain cDNAs demonstrated a clonal relationship between immunoglobulin M (IgM) RF and IgA RF, suggesting that this isotype switch occurred in synovium. Furthermore, most somatic mutations were found to have occurred after this isotype switch. This finding suggests that the RA synovial microenvironment sustains somatic mutation and isotype switching in RF-specific B lymphocytes akin to secondary lymphoid organs.

Aged↗
PubMed1998

Molecular modeling of an anti-DNA autoantibody (V-88) and mapping of its V region epitopes recognized by heterologous and autoimmune antibodies.

Anti-DNA autoantibodies are a characteristic feature of human systemic lupus erythematosus (SLE) and lupus diseases in the mouse. V-88 is an IgG1/kappa ssDNA-binding Ab, derived from a lupus mouse, that bears a cross-species, cross-reactive Id (CRI) that has been implicated in the pathogenesis of both human and murine disease. A linear epitope map of V-88 has been determined with anti-idiotypic antisera obtained from rabbits, and candidate sequences for the idiotopes of the CRI have been proposed. We now report the modeling of the three-dimensional structure of the V regions of Ab V-88, to map the location of these idiotopes. The V region framework structure was derived from those of crystallographically determined Ab structures, and the complementarity determining region (CDR) structures were based upon the set of canonical structures adopted by these loop regions in Abs of known structure. One of the idiotopes is an extensive, highly accessible epitope consisting of framework regions spatially adjacent to CDR2 in the heavy chain. Epitopes recognized by an anti-idiotypic rabbit antiserum were compared with those recognized by autoimmune sera from SLE-prone mice, and common features were identified. By analogy with the crystal structure of an anti-DNA Ab BV04-01 complexed with a trinucleotide, the modeled structure also suggests a mode of binding of ssDNA to V-88. The location of the candidate CRI, although within the framework region of VH, is such that it could influence Ag specificity.

Amino Acid Sequence↗
PubMed1998

Characterization and specificity of B-cell responses in lupus induced by Mycobacterium bovis in NOD/Lt mice.

A single dose of pasteurized Mycobacterium bovis administered intravenously to prediabetic non-obese diabetic (NOD) mice prevented the onset of type 1 diabetes but precipitated a systemic 'autoimmune rheumatic disease' (ARD) similar to systemic lupus erythematosus. This syndrome was characterized by haemolytic anaemia, anti-dsDNA and anti-Smith antigen (Sm) antinuclear autoantibodies, increased severity of sialadenitis and glomerular immune complex deposition. Here, we examine the specificity of the autoantibody responses in M. bovis-treated NOD mice. Large amounts of antibody were detected to the Sm/ribonucleoprotein (RNP) complex, of which the 28 000 MW polypeptide appeared to be immunodominant. The IgG subclass involved in the anti-Sm response was primarily IgG2a. Antibodies against dsDNA were also detected, but the subclass of this response was mixed, with IgG2a and IgG2b being present in equal amounts. Together, these findings argue against a role for immune deviation towards T helper type 2 (Th2) responses in pathogenesis of the disease. The anti-dsDNA and anti-Sm reactivities were not mediated by polyreactive antibodies since neither antigen could cross-compete plasma antibody binding to the other in competitive enzyme-linked immunosorbent assay. The role of polyclonal B-cell activation was examined by measuring total gamma-globulin as well as IgG reactive with other nuclear antigens including Ro60, Ro52 and La, which although not a major component of the autoantibody responses in these mice, did show small but significant increases following immunization with M. bovis. Thus polyclonal stimulation, while likely to be occurring, was not directly responsible for production of anti-Sm antibodies.

Animals↗