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G A Davis

Publications and source records attributed to G A Davis.

At least 19 recordsLinked to original sources
PubMed2001

Search for large extra dimensions in dielectron and diphoton production.

We report a search for effects of large extra spatial dimensions in pp collisions at a center-of-mass energy of 1.8 TeV with the D0 detector, using events containing a pair of electrons or photons. The data are in good agreement with the expected background and do not exhibit evidence for large extra dimensions. We set the most restrictive lower limits to date, at the 95% C.L. on the effective Planck scale between 1.0 and 1.4 TeV for several formalisms and numbers of extra dimensions.

Journal Article↗
PubMed2000

Acute-onset nontraumatic paraplegia in childhood: fibrocartilaginous embolism or acute myelitis?

Fibrocartilaginous embolus causing acute spinal cord infarction is a rare cause of acute-onset paraplegia or quadriplegia. Few cases of survivors have been reported in the neurosurgical literature, with most reports involving postmortem or biopsy findings. There is little information on MRI findings in such patients. We present the youngest patient ever reported, and discuss the important differences between fibrocartilaginous embolus and acute myelitis of childhood. A 6-year-old girl with a history of back pain presented with sudden-onset nontraumatic paraplegia, with a clinical anterior spinal artery syndrome. Initial MRI scan revealed intervertebral disc disease at L1-2 and an incidental thoracic syrinx, but no cause for her acute-onset paraplegia was identified. Cerebrospinal fluid and other investigations were all negative. Sequential MRI scans revealed development of spinal cord expansion from T10 to the conus medullaris, with increased cord signal in the anterior aspect of the spinal cord. The intervertebral disc disease was unchanged. The imaging and clinical findings were caused by fibrocartilaginous embolus, which meant there was no need for spinal cord biopsy. The report describes the clinical and imaging criteria for diagnosis of fibrocartilaginous embolus, highlighting the case for avoiding an unnecessary biopsy. The clinical pattern in the paediatric group is discussed, with features differentiating it from acute myelitis of childhood.

Acute Disease↗
PubMed2000

Accident reduction factors and causal inference in traffic safety studies: a review.

Accident reduction factors are used to predict the change in accident occurrence which a countermeasure can be expected to cause. Since ethical and legal obstacles preclude the use of randomized experiments when evaluating traffic safety improvements, empirical support for the causal effectiveness of accident countermeasures comes entirely from observational studies. Drawing on developments in causal inference initiated by Donald Rubin, it is argued here that the mechanism by which sites are selected for application of a countermeasure should be included as part of a study's data model, and that when important features of the selection mechanism are neglected, existing methods for estimating accident reduction factors become inconsistent. A promising, but neglected, way out of these difficulties lies in developing rational countermeasure selection methods which also support valid causal inference of countermeasure effects.

Accidents, Traffic↗
PubMed2000

Delayed presentation of transorbital intracranial pen.

A 13 year old Fijian boy sustained a stab wound to the left orbit 3 years ago. It was not appreciated by the treating physicians in Fiji that the plastic pen had crossed from the left orbit, through the nose, right orbit and right optic nerve, into the right middle cranial fossa and lodged in the right temporal lobe and that the pen remained in situ for the past 3 years. The boy presented to Australia with a discharge from the entry wound in his left lower eyelid. The retained foreign body was not detected on computed tomography imaging, but was detected on subsequent magnetic resonance image. A combined neurosurgery/plastic surgery craniofacial approach was undertaken with successful complete removal of the retained pen, and preservation of vision in his only seeing eye.

Child↗
PubMed1999

Microbial population changes during bioremediation of an experimental oil spill.

Three crude oil bioremediation techniques were applied in a randomized block field experiment simulating a coastal oil spill. Four treatments (no oil control, oil alone, oil plus nutrients, and oil plus nutrients plus an indigenous inoculum) were applied. In situ microbial community structures were monitored by phospholipid fatty acid (PLFA) analysis and 16S rDNA PCR-denaturing gradient gel electrophoresis (DGGE) to (i) identify the bacterial community members responsible for the decontamination of the site and (ii) define an end point for the removal of the hydrocarbon substrate. The results of PLFA analysis demonstrated a community shift in all plots from primarily eukaryotic biomass to gram-negative bacterial biomass with time. PLFA profiles from the oiled plots suggested increased gram-negative biomass and adaptation to metabolic stress compared to unoiled controls. DGGE analysis of untreated control plots revealed a simple, dynamic dominant population structure throughout the experiment. This banding pattern disappeared in all oiled plots, indicating that the structure and diversity of the dominant bacterial community changed substantially. No consistent differences were detected between nutrient-amended and indigenous inoculum-treated plots, but both differed from the oil-only plots. Prominent bands were excised for sequence analysis and indicated that oil treatment encouraged the growth of gram-negative microorganisms within the alpha-proteobacteria and Flexibacter-Cytophaga-Bacteroides phylum. alpha-Proteobacteria were never detected in unoiled controls. PLFA analysis indicated that by week 14 the microbial community structures of the oiled plots were becoming similar to those of the unoiled controls from the same time point, but DGGE analysis suggested that major differences in the bacterial communities remained.

Bacteria↗
PubMed1999

Comparison of common cytotypesof Andropogon gerardii(Andropogoneae, Poaceae).

Many plant species contain populations with more than one polyploid cytotype, but little is known of the mechanisms maintaining several cytotypes in a population. Andropogon gerardii cytotypes were compared to evaluate different models of autopolyploid cytotype coexistence. The enneaploid (90 chromosome, 9x) cytotype was found to be larger and taller than the hexaploid (60 chromosome, 6x) cytotype. Seed production is significantly more efficient in hexaploids, but seed production per area was not significantly different. The two cytotypes are not exomorphologically separable in the field because of great plasticity in response to environmental variation and wide variation within each cytotype. These data suggest cytotypic variation is maintained by natural selection.

Journal Article↗
PubMed1998

Evaluation of aminoglycoside pharmacokinetics in postpartum patients using Bayesian forecasting.

Many postpartum women have suboptimal serum concentrations after standard doses of aminoglycosides. The purpose of this study was to characterize the pharmacokinetics of aminoglycosides in postpartum patients through the use of Bayesian forecasting and to test the ability of these subpopulation parameters to predict actual aminoglycoside serum concentrations. In phase I, 28 postpartum patients who received empiric gentamicin therapy were identified and Bayesian subpopulation parameters generated. In phase II, additional gentamicin concentrations (peaks and troughs) were evaluated to test bias and precision of Bayesian subpopulation versus traditional estimates in predicting actual aminoglycoside serum concentrations. In phase I, 56 gentamicin serum concentrations in 28 patients, (age, 26 +/- 7 years; actual body weight [ABW], 84.3 +/- 18.4 kg; ideal body weight [IBW], 54.6 +/- 5.1 kg; dosing weight [DW], 66.3 +/- 9.4 kg; creatinine clearance [Clcr], 140.4 +/- 34.0 ml/min / 1.73 m2), were evaluated to calculate subpopulation pharmacokinetic parameters of volume of distribution (Vd) 0.29 +/- 0.07 l/kg (DW); elimination rate constant (ke) 0.29 +/- 0.05 h-1 and half-life (t1/2) 2.5 +/- 0.5 hours. In phase II, 50 gentamicin serum concentrations in 25 patients (age, 23 +/- 4 years; ABW 79.4 +/- 17.5 kg; IBW 55.0 +/- 7.3 kg; DW 64.8 +/- 9.6 kg; Clcr 139.7 +/- 29.3 ml/min/1.73 m2) were evaluated to calculate subpopulation pharmacokinetic parameters of Vd 0.30 +/- 0.04 l/kg (DW); ke 0.27 +/- 0.06 h-1; and t1/2 2.9 +/- 0.8 hours. Predictive performance tests (95% confidence intervals) demonstrate that subpopulation postpartum Bayesian parameters show greater precision for peak concentrations and less bias for trough concentrations than do traditional population estimates (p < 0.05). Definition of the Bayesian subpopulation parameters will allow us to dose aminoglycosides optimally in postpartum patients who have fragmented data.

Adult↗
PubMed1998

Validation of the Hartford nomogram in trauma surgery patients.

OBJECTIVE: To validate the Hartford nomogram for once-daily aminoglycoside dosing in trauma surgery patients. METHODS: A chart review was performed in trauma surgery patients who were started on once-daily aminoglycoside therapy. A peak aminoglycoside concentration was drawn 30 minutes after the end of the first or second infusion, and a random concentration was drawn approximately 10 hours after the dose. The 10-hour random concentration was used to validate the Hartford nomogram by predicting the actual dosing interval (determined by extrapolating the peak and random concentrations to achieve a trough concentration <1 mg/L). The percentage of intervals accurately predicted by the nomogram was determined. RESULTS: Forty-nine patients (34 men and 15 women), age 43.0+/-15.9 y, total body weight 81.3+/-24.5 kg, ideal body weight 68.1+/-10.7 kg, dosing body weight (DBW) 72.0+/-14.4 kg, and estimated creatinine clearance [Cl(cr)] 89.5+/-20.6 mL/min/1.73 m2 were evaluated. Patients received 505+/-105 mg (7.0+/-0.4 mg/kg) of either gentamicin or tobramycin per dose. The concentration 30 minutes after the infusion was 22.4+/-5.9 mg/L, the concentration at the end of the dosing interval was 0.20+/-0.46 mg/L, the 10-hour random concentration was 2.6+/-1.8 mg/L, the elimination rate constant was 0.26+/-0.08 h(-1), the elimination half-life was 3.0+/-1.2 hours, and the volume of distribution was 19.9+/-7.9 L (0.28+/-0.09 L/kg of DBW). Ninety-eight percent (48/49) of the intervals were accurately predicted by the nomogram. CONCLUSIONS: In trauma surgery patients with Cl(cr) of more than 60 mL/min/1.73 m2, the Hartford nomogram using a single random aminoglycoside concentration accurately predicted the same once-daily aminoglycoside intervals as determined by two concentrations. Less aggressive therapeutic drug monitoring in this patient subpopulation can lead to significant cost savings.

Adult↗
PubMed1998

Clinical pharmacokinetics in the 21st century. Does the evidence support definitive outcomes?

Clinical pharmacokinetics emerged as a clinical discipline in the late 1960s and early 1970s. Clinical pharmacokinetic monitoring (CPM) helped many pharmacists to enter the clinical arena, but the focus was more on the pharmacists and tools. With the widespread acceptance of pharmaceutical care and patient-focused pharmacy, we now must take a sobering look at how clinical pharmacokinetics fits into the pharmaceutical care process. The existing literature is laden with articles that evaluate the effect of CPM on surrogate end-points. Many pharmacists have also had personal experiences that attest to the usefulness of CPM. Decreased mortality, decreased length of treatment, decreased length of hospital stay, decreased morbidity, and decreased adverse effects from drug therapy have been examined in an effort to measure and evaluate the impact of CPM on patient outcomes. While many of these studies demonstrated significant positive outcomes, several showed that CPM did not have a significant impact on specific patient outcomes. A few studies even found a negative impact on specific patient outcomes. Ultimately, there is good evidence in only a few specific patient groups to support the benefit of CPM. Despite the limitations of data supporting the routine use of CPM in managing drug therapy in diverse populations, many pharmacists continue to expend considerable time and effort in this activity. We need to define those patients who are most likely to benefit from CPM and incorporate this into our provision of pharmaceutical care, while minimising the time and money spent on CPM that provides no value. In redefining the patients who will benefit from CPM, we need to critically re-evaluate clinical studies on the relationship between drug concentration and response. Similarly, we need to pay special attention to recent studies evaluating the impact of CPM on outcomes in specific subpopulations. In the absence of specific studies demonstrating the value of CPM in particular patients, we propose that a more comprehensive decision-making process be undertaken that culminates in the quintessential question: 'Will the results of the drug assay make a significant difference in the clinical decision-making process and provide more information than sound clinical judgement alone?' We also need to consider opportunities to expand the use of CPM for new drugs and where new evidence suggests benefit. Even when there is strong evidence that CPM is useful in managing therapy in particular patient groups, clinicians need to remember that the therapeutic range is no more than a confidence interval and, therefore, we need to 'treat the patient and not the level'. We need to incorporate the patient-specific and outcome-oriented principles of pharmaceutical care into our CPM, even as we utilise CPM as an essential tool in pharmaceutical care.

Drug Monitoring↗
PubMed1997

General versus subpopulation values in Bayesian prediction of aminoglycoside pharmacokinetics in hematology-oncology patients.

The predictive performance of Bayesian estimates incorporating pharmacokinetic values for hematology-oncology patients was compared with that of Bayesian estimates incorporating general population values. In study phase 1, medical records were reviewed for 50 adult patients with a hematologic or oncologic diagnosis who had received i.v. gentamicin or tobramycin. Aminoglycoside pharmacokinetic values were calculated for the patients by using a modified two-point Sawchuk-Zaske method, and the subpopulation mean for each variable was determined. In phase 2, data for 10 other hematology-oncology patients receiving aminoglycosides were entered into the Abbottbase Bayesian pharmacokinetics program. Aminoglycoside pharmacokinetic values and serum concentrations for each of these 10 patients were estimated, first using the program's general population values and then repeating the analysis using the subpopulation means for volume of distribution and renal clearance slope obtained in phase 1. The serum aminoglycoside concentrations predicted by each Bayesian method were compared with the actual peaks and troughs. Both the peak and trough predictions of the Abbottbase program using the subpopulation values for volume of distribution and renal clearance slope were significantly less biased than those predicted by the Abbottbase program incorporating the general population values. The methods did not differ significantly in precision. Use of subpopulation pharmacokinetic values in Bayesian predictions of serum aminoglycoside concentrations in hematology-oncology patients reduced bias significantly but had no significant effect on precision.

Adult↗
PubMed1997

Referential cohesion and logical coherence of narration after right hemisphere stroke.

A group with right hemisphere dysfunction was compared to neurologically intact controls regarding the referential cohesion and logical coherence of narrative production. A somewhat varied sample of six stories was obtained with tasks of cartoon-elicited story-telling and auditory-oral retelling. We found deficits in the patient group with respect to referential cohesion, logical coherence, and accuracy of narration, but the occurrence of deficits depended on the condition in which narration was produced and, to some extent, on the particular story used in each condition. The primary implications of this study pertain to the attention given by researchers to the feature of discourse production being studied.

Adult↗
PubMed1996

Neuroanatomical distribution of androgen and estrogen receptor-immunoreactive cells in the brain of the male roughskin newt.

Immunohistochemistry was used to investigate the neuroanatomical distribution of androgen and estrogen receptors in brains of adult male roughskin newts, Taricha granulosa, collected during the breeding season. Immunoreactive cells were found to be widely distributed in specific brain areas of this urodele amphibian. Androgen receptor-immunoreactive (AR-ir) cells were observed in the olfactory bulbs, habenula, pineal body, preoptic area, hypothalamus, interpeduncular nucleus, area acusticolateralis, cerebellum, and motor nuclei of the medulla oblongata. Estrogen receptor-immunoreactive (ER-ir) cells were found in the lateral septum, amygdala pars lateralis, pallium, preoptic area, hypothalamus, and dorsal mesencephalic tegmentum. This immunocytochemical study of the newt brain reveals AR-ir and ER-ir cells in several regions that have not been previously reported to contain androgen and estrogen receptors in non-mammalian vertebrates. Additionally, the distribution of AR-ir and ER-ir cells in the newt brain, in general, is consistent with previous studies, suggesting that the distribution of sex steroid receptor-containing neurons in some brain regions is relatively conserved among vertebrates.

Animals↗
PubMed1996

Comparison of creatinine clearance estimation methods in patients with trauma.

The abilities of a modified Cockcroft-Gault equation and the standard equation to estimate creatinine clearance (CLcr) in trauma patients were compared. The medical records of patients with stable renal function who had been treated for trauma and had had a 24-hour urine collection for creatinine measurement were reviewed. Creatinine concentrations in urine and serum were used to calculate the actual CLcr, which was normalized to 1.73 sq m. CLcr was estimated by the modified equation (which normalized body weight to 72 kg) and by the standard equation using ABW, IBW, and dosing body weight (DBW). Values derived with the standard equation were normalized to 1.73 sq m. The predictive performances of the modified and standard equations in estimating the actual CLcr were then compared. Fifty patients were enrolled. The standard equation using IBW or DBW produced estimates that differed significantly from the actual CLcr. The modified equation and the standard equation using ABW did not differ significantly in bias or precision, but both were significantly less biased than the standard equation using IBW or DBW. The only significant difference among equations in precision was between the modified equation (the more precise) and the standard equation using IBW. There were no clinically significant differences among methods in gentamicin dosing simulations. The modified Cockcroft-Gault equation can be used to estimate CLcr in trauma patients with stable renal function.

Adult↗
PubMed1996

Implementing a distributed intranet-based information system.

The article discusses Internet and intranet technologies and describes how to install an intranet-based information system using the Merle language facility and other readily available components. Merle is a script language designed to support decentralized medical record information retrieval applications on the World Wide Web. The goal of this work is to provide a script language tool to facilitate construction of efficient, fully functional, multipoint medical record information systems that can be accessed anywhere by low-cost Web browsers to search, retrieve, and analyze patient information. The language allows legacy MUMPS applications to function in a Web environment and to make use of the Web graphical, sound, and video presentation services. It also permits downloading of script applets for execution on client browsers, and it can be used in standalone mode with the Unix, Windows 95, Windows NT, and OS/2 operating systems.

Computer Communication Networks↗
PubMed1995

Comparison of fluid volumes with whole bowel irrigation in a simulated overdose of ibuprofen.

OBJECTIVE: To determine the effect of 2 different fluid volumes of polyethylene glycol whole bowel irrigation (WBI) solution on absorption of an ingested toxin in a simulated overdose model. DESIGN: Prospective, randomized, crossover trial. SETTING: Clinical research unit. PARTICIPANTS: Nine adult men. INTERVENTIONS: On 2 separate days, volunteers ingested approximately 75 mg/kg of ibuprofen. In treatment 1, 30 minutes after ingestion of ibuprofen, a 3-L WBI at 2 L/h was begun. This procedure was repeated in treatment 2 with an 8-L. WBI administered at 2 L/h. Fourteen timed serum samples were collected prior to and after drug ingestion for a 24-hour period and analyzed for ibuprofen concentration. The peak serum concentration, time to peak concentration, total area under the serum concentration-time curve (AUC), clearance, and volume of distribution were compared. RESULTS: The mean +/- SD AUCs did not differ between the 3-L (1185.3 +/- 216.9 mg.h/L) and 8-L (1153.5 +/- 251.5 mg.h/L) treatments (p = 0.710). Time to peak serum concentration, peak serum concentration, clearance, and volume of distribution were comparable for the 2 treatments (p > 0.05). CONCLUSIONS: These data indicated that a total WBI volume of 3 L would be expected to perform as well as 8 L administered at the same rate. We recommend that further research define the optimal dose of WBI in acute ingestion of toxins.

Adult↗