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Biomedical subjects

J T Smith

Publications and source records attributed to J T Smith.

At least 55 records · Page 3Linked to original sources
PubMed1997

Towards a generalized model for the primary and secondary contamination of lakes by Chernobyl-derived radiocesium.

As part of the UK Ministry of Agriculture Fisheries and Food Directorate of Fisheries Research (MAFF/DFR) post-Chernobyl monitoring program, a detailed study was carried out of the change over time in dissolved-phase 137Cs concentrations in a number of lakes in Cumbria, UK. These measurements have been combined with published data on 137Cs in Cumbrian and other European lakes in order to develop and test a "double exponential" model for changes in lakewater concentrations: A exp(-k1t) + B exp(-k2t) where the exponential terms correspond, respectively, to the initial fast flush of activity through the system followed by longer-term transfers (timescale, years) from the catchment. Parameter values have been determined for this model by curve-fitting to the set of measurements of post-Chernobyl 137Cs activities in lakes. Values of fitted parameters are shown to be related, in a simple manner, to the physical characteristics of the system, in particular water residence time and mean lake depth. These parameters are generalized to give a simple empirical model for the full set of study lakes. The model is shown to give estimates of 137Cs activity to within a factor of 5 of field data for a period of several years after the fallout. Initial fractional losses of activity from catchment to lake were determined to be within the range 0.44-8.7% per year, declining exponentially with a mean rate constant 0.98 x 10(-3) d(-1).

Biophysical Phenomena↗
PubMed1997

Methods for assessing the effects of drugs on gastrointestinal function in patients and healthy volunteers.

The gastrointestinal tract is a complex organ with many functions. Many diseases affect the way in which the gastrointestinal tract performs these functions. The pharmaceutical industry and academia are putting great effort into the development of treatments for these diseases. As a consequence, there is increasing pressure on the clinical pharmacologist and gastroenterologist to develop methods to measure the effects of drugs on the gastrointestinal tract. This article reviews the methods currently available to assess gastrointestinal function; in particular it focuses on motility and sensitivity.

Digestive System↗
PubMed1996

Mobility of Chernobyl-derived 137Cs in a peatbog system within the catchment of the Pripyat River, Belarus.

The behaviour of Chernobyl-derived 137Cs in a hydrologically isolated bog system in the catchment of the Pripyat River, Belarus was investigated. Measurements were made of 137Cs activities in the solids and pore waters of the bog soils, as well as the variability in activity in water draining from the bog. It was found that the radiocaesium activity of the pore water, and hence the measured distribution coefficient, Kd, was dependent upon the pressure at which the water was removed from the soil. Measured values of Kd were of the order 10(2) l/kg at an extraction pressure of 0.8 MPa, approximately one order of magnitude lower than those measured in a similar system, Devoke Water, in the UK [1]. Results of comparative measurements suggested that this was a result of the different pore water extraction techniques used. The vertical migration of radiocaesium was modelled using a solution of the advection-diffusion equation. Using a mass balance approach, it was estimated that 137Cs was removed from the system at a rate of 0.3% of the catchment inventory per year, approximately 8 years after the Chernobyl accident. It was shown that both vertical migration and removal of 137Cs is best modelled using a Kd based on a measurement of pore water held at low pressure in the soil, approximately 10(3) l/kg. 137Cs activities in soil pore waters and in drainage waters were very strongly related to the aqueous potassium concentration, and both showed concentration minima in drainage water during the spring. It was shown that runoff coefficients of radiocaesium from peat bogs 8 years after the Chernobyl accident were approximately one order of magnitude greater than those from unsaturated soils of higher mineral content.

Cesium Radioisotopes↗
PubMed1996

Gender differences in performance of a selection test using the incremental lifting machine.

The purpose of the study was twofold: (1) to examine any gender differences in the performance of a pre-employment selection test using the incremental lifting machine (ILM); and (2) to formulate recommendations regarding analyses of selection fairness in studies of pre-employment screening tests and devices. Data were collected in a series of studies designed to permit analyses of: (1) dynamic measures derived for a 1.8 m maximum ILM strength test; (2) relationships between ILM test scores and performance of a maximal box-lifting task using three different protocols; (3) the impact of anthropom trie measures on performance of both test and task; (4) prediction of actual task performance; and (5) accuracy of the ILM screening test for three different cut-off standards. Results revealed that females differed significantly from males in their performance of a 1.8 m maximum ILM strength test in terms of timing, displacement, velocity, acceleration, force and power. Maximum ILM scores attained by females were poorly correlated with maximum box-lifting scores, but they were significantly related to body weight. Also, regression analyses based on ILM scores and associated dynamic parameters accounted for twice as much variance in box-lifting scores for males than for females. Furthermore, the use of cut-off standards of 22.7 kg and 27.3 kg produced a percentage of false negative results for females (12% and 32% respectively), but not for males. Also, for the cut-off level of 27.3 kg, female selection rates were only 56% of the selection rates for males. Issues for future investigation are recommended.

Journal Article↗
PubMed1996

Benign soft-tissue lesions in children.

This article is a review of the common benign soft-tissue lesions of the spine and extremities. Reviewed are the pathophysiology, natural history, appropriate work-up, and treatment options. A recommendation is given to consider the diagnosis as possible malignancy and approach such lesions with caution.

Blood Vessels↗
PubMed1996

Influence of temperature on mutational resistance to 4-quinolones.

Minimum inhibitory concentration (MIC) values of ciprofloxacin (CAS 85721-33-1), ofloxacin (CAS 82419-36-1) or levofloxacin (CAS 100986-85-4) against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Staphylococcus epidermidis were determined at 37, 30 and 25 degrees C on nutrient agar. With E. coli and S. aureus, reducing the incubation temperature from 37 to 30 to 25 degrees C decreased the MIC values for each drug. With P. aeruginosa, temperature reduction also decreased the MIC values for ciprofloxacin but increased the MICs for ofloxacin or levofloxacin. With S. epidermidis, temperature reduction increased the MICs for ciprofloxacin and ofloxacin but with levofloxacin the MICs were identical at 37 or 25 degrees C but higher at 30 degrees C. Mutants of these bacterial species were selected on nutrient agar containing five times their respective MICs of the 4-quinolones at 37, 30 and 25 degrees C. with S. epidermidis, temperature reduction always reduced its mutation frequency to resist 4-quinolones, whereas with the other three species the effect of temperature was more variable, and in some instances even elevated their mutation rates.

4-Quinolones↗
PubMed1995

Rapid determination of logarithmic partition coefficients between n-octanol and water using micellar electrokinetic capillary chromatography.

Micellar electrokinetic capillary chromatography (MECC) was evaluated as a rapid screening tool for the determination of logarithmic partition coefficients between n-octanol-water (log P(OW)). The technique is performed by electrochromatographing a mixture of standards of known log P(OW). The logarithmic capacity factor of each standard was plotted against its log P(OW) to form a linear calibration curve for a given set of chromatographic conditions. The log P(OW) of an unknown is calculated by using its chromatographically determined capacity factor and extracting the log P(OW) value from the calibration curve. The method was evaluated with a set of model compounds with known log P(OW). The accuracy of the method was examined and found to be within the limits required for screening purposes. The correlation of log P(OW) values determined using HPLC and MECC for some novel compounds was examined. This technique allows the screening of log P(OW) at a rate of four samples per hour with minimal sample requirements (< microgram) and with extremely small solvent waste generated.

1-Octanol↗
PubMed1995

An investigation of the effects of water velocity on inorganic phosphorus influx to a sediment.

Measurements of the net influx of soluble reactive phosphorus (SRP), to a river bed-sediment, illustrate the importance of the water velocity and hydrodynamics in controlling the transfer rates. Experiments are reported using a characterised bed-sediment, with associated fauna, contained in a flowing-water channel. The results show a systematic increase in the net influx of SRP with increasing water velocity. A mathematical description of the influx was sought by modelling the experimental results using the Elovich equation, a boundary-layer model and a parabolic rate equation. In fact all three kinetic equations produce a good representation of the experimental data and it is concluded that further research is needed, in well-defined hydrodynamic conditions, to distinguish between the boundary-layer model and the parabolic equation. The boundary-layer model leads to an inverse relationship between the boundary-layer thickness (z/microm), and the water velocity (v/cm s(-1), viz z approximately 2500/v). In comparison, the parabolic equation of the form: influx of SRP (mol m(-2) = kp [SRP-EPC0]2, where EPC0 is the concentration at which the influx is zero prior to the sorption of phosphorus by the sediment and kp is the rate constant which leads to a velocity dependence, kp* = 0.714v + 1 where kp* is the reduced rate constant, kp* = kp(v)/kp(0). The semi-empirical Elovich equation in the form: influx of SRP (mol m(-2)) = (1/b) ln(1 + abt) where a and b are the Elovich parameters and t the time, gives a convenient description of the net influx of SRP to bed-sediments downstream of a point-source of pollution. The parameters calculated from the results obtained from the experimental channel are used to estimate the SRP flux to the sediment for a distance of up to 5 km downstream of a point-input of SRP.

Journal Article↗
PubMed1995

Bactericidal activity of the new 4-quinolones DU-6859a and DV-7751a.

The bactericidal activity of two new 4-quinolones, DU-6859a and DV-7751a, was investigated against strains of Escherichia coli, Staphylococcus aureus, S. epidermidis, Streptococcus pneumoniae and Enterococcus faecalis. DU-6859a and DV-7751a were more bactericidal than any 4-quinolone tested previously. Furthermore, DU-6859a was unique among 4-quinolones in being able to kill Ent. faecalis after incubation for only 3 h in nutrient broth. The bactericidal mechanisms of DV-7551a were similar to those of other 4-quinolones, but, uniquely, DU-6859a possessed additional bactericidal mechanisms against both Str. pneumoniae and Ent. faecalis. This may explain the unusually potent bactericidal activity of this agent against these species. These results show that DU-6859a is a unique extended-spectrum 4-quinolone, which should prove to be superior to established 4-quinolones.

Anti-Infective Agents↗
PubMed1995

Validity of newborn oscillometric blood pressure.

The objective of this study was to determine the validity of oscillometric blood pressure in relation to arterial blood pressure. Thirty-one newborns were studied. Clinical characteristics, complications, and treatment interventions were documented. Arterial pressure (every 2 sec) and oscillometric pressure (every 3 min) were concurrently recorded for 1-2 h. Serial observations of oscillometric pressure followed the trend of arterial pressure in the individual newborn. However, the study averaged oscillometric pressures were lower than the arterial pressures: systolic, by 1 mmHg; mean, by 5.3 mmHg (p < 0.0001); and diastolic, by 4.6 mmHg (p < 0.0001). The variance of individual, 15-min averaged, and 1-h averaged observations of oscillometric pressure in relation to arterial pressure was examined. Variance for individual observations may be large. The least variance of oscillometric pressure was in the 1-h averaged mean pressure, in which the difference was +/- 2 mmHg in 77% and +/- 4 mmHg in 95% of observations. Clinical characteristics, with the exception of birth weight and treatment interventions, did not affect the variance of oscillometric pressure. This study implies that the offset in relation to arterial pressure should be established for each oscillometric pressure monitoring system. Hourly averaged mean oscillometric pressure is satisfactory for many newborn assessments and management circumstances. However, arterial pressure may be necessary to accurately document transient hypertension or hypotension or an unstable blood pressure.

Birth Weight↗
PubMed1994

Micellar electrokinetic capillary chromatography with in situ charged micelles: 3. Evaluation of alkylglucoside surfactants as anionic butylboronate complexes.

This article represents an extension to a new approach introduced very recently by our laboratory for the control of the surface charge density as well as the hydrophobic character of micellar phases used in micellar electrokinetic capillary chromatography (MECC). The approach is based on the complexation of polyolic surfactants, e.g., alkylglucosides, with butylboronate to form in situ branched, anionic surfactants. The butylboronate can also incorporate into the micelle via its alkyl tail and acts as a "class I" organic additive that mainly modifies the micelle by decreasing the critical micellar concentration, i.e., increasing the hydrophobic character of the micelle, while exhibiting little influence on the aqueous phase. The net result is an in situ charged micellar entity whose hydrophobic character is dynamically altered. The alkylglucoside-butylboronate micellar phases yielded high separation efficiencies and proved useful in the separation of charged and neutral herbicides as well as the chiral separations of medicarpins and precursors, and dansylated D and L-amino acids in the presence of native or modified cyclodextrin chiral selectors.

Amino Acids↗
PubMed1994

Comparative pharmacokinetics of bismuth from ranitidine bismuth citrate (GR122311X), a novel anti-ulcerant and tripotassium dicitrato bismuthate (TDB).

GR122311X (ranitidine bismuth citrate, Glaxo Group Research Ltd.) is a salt of ranitidine with a complex of bismuth and citric acid which is being developed for the treatment of peptic ulceration. In this study, 4 groups of 12 healthy male subjects were dosed for 10 days with either GR122311X 500 mg bid (301 mg bismuth per day), GR122311X 1.0 g bid (602 mg bismuth per day), tripotassium dicitrato bismuthate (TDB, DeNoltab, Gist Brocades Ltd., Weybridge, England) 240 mg bid (431 mg bismuth per day) or placebo. After the last dose the geometric mean for Cmax for 500 mg bid of GR122311X was 5 ng.g-1, for 1.0 g bid GR122311X it was 12 ng.g-1 and it was 21 ng.g-1 for 240 mg TDB bid. The corresponding trough plasma levels were 2 ng.g-1, 4 ng.g-1 and 4 ng.g-1, respectively. The AUC over a dosing interval after the last dose (AUC tau) were 34 ng.h.g-1, 71 ng.h.g-1 and 79 ng.h.g-1, respectively. The bismuth urinary recoveries over the last dosing interval (Ae tau) were 97 micrograms, 227 micrograms and 309 micrograms, respectively, which is less than 1% of the administered doses. The renal clearance of bismuth was less than the glomerular filtration rate. After adjustment for bismuth dose, the Cmax for GR122311X 500 mg was 35% that of TDB, while for GR122311X 1.0 g the Cmax was 42% that of TDB. Similar differences were observed for Ae tau. In conclusion bismuth pharmacokinetics after oral administration of GR1223311X exhibited lower Ae tau and Cmax, with a much narrower Cmax range than those observed for TDB.

Adolescent↗
PubMed1994

Ranitidine bismuth citrate and ranitidine do not affect gastric emptying of a radio-labelled liquid meal.

Ranitidine bismuth citrate, a new chemical entity which is a salt complex of ranitidine and bismuth citrate, is being developed for the treatment of relapse of benign gastric and duodenal ulcer and eradication of Helicobacter pylori. The aim of the present study was to establish whether ranitidine bismuth citrate (800 mg) or ranitidine hydrochloride (300 mg) have any effect on gastric emptying of a liquid meal using gamma scintigraphy. On three separate occasions, each of twelve subjects received a single oral tablet of 800 mg ranitidine bismuth citrate, 300 mg ranitidine hydrochloride or placebo in random order. Thirty minutes after dosing each subject was given 375 ml of 99mTc-DTPA (diethylene triaminepentaacetic acid) labelled Clinifeed-ISO. The primary endpoint was the time to 50% gastric emptying (t50%). The proportion of the meal remaining was summarised by weighted mean proportion of the meal remaining in the stomach over 0-60 min and 0-180 min, separately. No differences were observed for t50%, weighted mean 0-60 min, and weighted mean 0-180 min between any two treatments. In man, we have detected no significant effect of single oral doses of ranitidine bismuth citrate 800 mg or ranitidine hydrochloride 300 mg on the rate of gastric emptying of a liquid meal when compared with placebo.

Adult↗
PubMed1994

Development of physical fitness standards for Canadian Armed Forces older personnel.

The purpose of the study was to develop a minimum physical fitness standard for Canadian Forces personnel, 35 years and older, based on common criteria for physically demanding tasks. A random sample of 100 men and 76 women performed the Exercise Prescription (EXPRES) test and five physically demanding tasks that simulate common military tasks, while restricted, for safety reasons, to 90% maximal predicted heart rate. Results indicated poor predictive power, as variances ranged from 5 to 55% between EXPRES fitness scores and task performance. With approval from an expert panel, the 75th percentile score for each task was selected as the cutting criterion. The passing-group data were converted to Z-scores in order to determine the 5th percentile from each EXPRES item: these scores became the EXPRES fitness standard. The minimum fitness standard had a greater impact on women than on men but was representative of the passing groups for both sexes.

Adult↗
PubMed1994

Activity of 4-quinolones against Pseudomonas aeruginosa.

The minimum inhibitory concentrations (MICs), bactericidal activities and mechanisms of action of ofloxacin (CAS 82419-36-1), levofloxacin (CAS 100986-85-4) and ciprofloxacin (CAS 86393-32-0) were investigated against Pseudomonas aeruginosa. All three 4-quinolones were found to possess higher MICs against Pseudomonas aeruginosa than against other Gram-negative bacteria. Despite this, however, all three drugs were more rapidly bactericidal and produced a greater level of kill against Pseudomonas aeruginosa than against any other bacterial species previously tested. Thus MIC tests cannot be used to predict the bactericidal activity of 4-quinolones. Furthermore, MIC tests showed ciprofloxacin to be more potent than ofloxacin or levofloxacin against Pseudomonas aeruginosa. However, bactericidal tests showed levofloxacin to be about 10 times more bactericidal than either ciprofloxacin or ofloxacin. Thus MIC tests cannot predict the relative bactericidal potency of 4-quinolones against Pseudomonas aeruginosa. Therefore, MIC tests should not be used as the sole measure for the efficacy of 4-quinolones, as is often the case. Surprisingly, the characteristic biphasic dose response curve, normally shown by 4-quinolones against other bacteria, was absent when Pseudomonas aeruginosa was tested. This unusual effect was explained by the presence of bactericidal mechanism B associated with the unique loss of bactericidal mechanism A at high 4-quinolone concentrations. This loss of bactericidal mechanism A may explain the recent high incidences of chromosomally-mediated 4-quinolone resistance with Pseudomonas aeruginosa because it may be easier for Pseudomonas aeruginosa to mutate to resist one mechanism of action than to mutate to resist two or more mechanisms of action.

Anti-Infective Agents↗