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Biomedical subjects

G Hall

Publications and source records attributed to G Hall.

At least 109 records · Page 6Linked to original sources
PubMed1996

Isolation and identification of methanogen-specific DNA from blanket bog peat by PCR amplification and sequence analysis.

The presence of methanogenic bacteria was assessed in peat and soil cores taken from upland moors. The sampling area was largely covered by blanket bog peat together with small areas of red-brown limestone and peaty gley. A 30-cm-deep core of each soil type was taken, and DNA was extracted from 5-cm transverse sections. Purified DNA was subjected to PCR amplification with primers IAf and 1100Ar, which specifically amplify 1.1 kb of the archaeal 16S rRNA gene, and ME1 and ME2, which were designed to amplify a 0.75-kb region of the alpha-subunit gene for methyl coenzyme M reductase (MCR). Amplification with both primer pairs was obtained only with DNA extracted from the two deepest sections of the blanket bog peat core. This is consistent with the notion that anaerobiosis is required for activity and survival of the methanogen population. PCR products from both amplifications were cloned, and the resulting transformants were screened with specific oligonucleotide probes internal to the MCR or archaeal 16S rRNA PCR product. Plasmid DNA was extracted from probe-positive clones of both types and the insert was sequenced. The DNA sequences of 8 MCR clones were identical, as were those of 16 of the 17 16S rRNA clones. One clone showed marked variation from the remainder in specific regions of the sequence. From a comparison of these two different 16S rRNA sequences, an oligonucleotide was synthesized that was 100% homologous to a sequence region of the first 16 clones but had six mismatches with the variant. This probe was used to screen primary populations of PCR clones, and all of those that were probe negative were checked for the presence of inserts, which were then sequenced. By using this strategy, further novel methanogen 16S rRNA variants were identified and analyzed. The sequences recovered from the peat formed two clusters on the end of long branches within the methanogen radiation that are distinct from each other. These cannot be placed directly with sequences from any cultured taxa for which sequence information is available.

Base Sequence↗
PubMed1996

Self-selection, earnings and Chicano migration: differences between return and onward migrants.

"The purpose of this article is to extend the empirical literature on Chicano return migration by examining earnings differentials between return and onward Chicano migrants. Our approach reflects the complexity of estimating such effects in terms of selectivity biases and the interaction between individual and locational attributes. We use data derived from the public use microdata sample (PUMS) of the 1990 U.S. census. After controlling for migration and labor force self-selection, results indicate that Chicano return migrants are not negatively self-selected. Chicano return migrants have smaller earnings profiles largely due to the negative effects of living in areas with higher concentrations of co-ethnics. Apparently, return migrants, at least in the short run, are willing to accept lower earnings for the nonpecuniary benefits of living in the Southwest."

Americas↗
PubMed1996

Short-term recovery from hip and knee arthroplasty.

There are many studies of long-term recovery from major point arthroplasty, but little is known about the first days and weeks after operation. We measured function, emotional state and life evaluation before arthroplasty and at seven and 50 days after in a consecutive series of 40 hip and 23 knee replacements. Pain was relieved significantly at seven days after hip arthroplasty and even more at 50 days. In knee patients, pain relief was modest and was not apparent until 50 days. Functional ability was much improved by 50 days in hip patients, but hardly changed in knee patients. Positive mood and life satisfaction did not improve in either group. Our findings will help with more accurate information for patients before operation and also in judging the rate of recovery.

Aged↗
PubMed1995

Silicon pixel detectors for X-ray diffraction studies at synchrotron sources.

Customized silicon diode detectors are widely used for elementary particle detection for their good spatial resolution. Silicon detectors are also excellent X-ray detectors in the energy range of interest for applications in synchrotron radiation experiments and, with small elements laid out in a two-dimensional array, may provide high performance imaging devices for future diffraction experiments. These pixel detectors are still in the development phase but some are already installed in experiments and within the next few years large area detectors with fast, two-dimensional readout are likely to be available for online acquisition of diffraction patterns. This article describes the technology of silicon pixel detectors and outlines the status of current developments and the performance which could be achieved in a realistic system, indicating the steps required to implement it.

Silicon↗
PubMed1995

Role of stimulus ambiguity in conditional learning.

Three experiments using rats and the conditioned emotional response procedure examined the notion that when a conditioned stimulus (CS) is paired with a reinforcer (US), that CS must be ambiguous if the CS-US association is to become the target of conditional control. CS ambiguity was manipulated by varying whether the CS had been preexposed prior to conditioning. In Experiments 1 and 2, it was demonstrated that a cue that accompanied pairings of a CS and shock acquired conditional control over the CS-shock association when that CS had been preexposed, but not when it was novel. The measure of conditional control in Experiments 1 and 2 was the ability of the (conditional) cue to enhance responding to the target CS. Experiment 3 used a blocking procedure to show that this enhancement reflected an amplification of the target CS's effective associative strength. These findings extend existing knowledge of the conditions required for conditional cue formation.

Animals↗
PubMed1995

Enhancement of latent inhibition in rats with electrolytic lesions of the hippocampus.

Two groups of rats--1 with electrolytic lesions of the hippocampus and 1 consisting of sham-operated controls--received flavor-aversion conditioning with 2 flavors. All subjects had received prior nonreinforced exposure to Flavor A. Latent inhibition was apparent in slower acquisition of the aversion to Flavor A than to Flavor B. Hippocampal lesions had no effect on acquisition to the nonpreexposed Flavor B but produced a marked enhancement of the latent inhibition effect. The contrast between this result and previous findings of an attenuation of latent inhibition in subjects with hippocampal lesions is discussed.

Animals↗
PubMed1995

Experimental Legionnaires' disease in SCID-Beige mice reconstituted with human leucocytes.

A new small animal model of experimental Legionnaires' disease is described in which the reconstitution of SCID-Beige mice with human peripheral blood leucocytes permits the in-vivo growth of Legionella pneumophila in the lungs of aerosol-challenged mice. Following infection, viable bacterial counts within the lungs of mice increased from 10(5) cfu/lung at the time of inoculation to a maximum of 10(10) cfu/lung by 48 h post-inoculation. Two types of disease were detected in the lungs of infected SCID-Beige mice. An acute exudative bronchiolitis and bronchopneumonia were seen in the most severely affected mice and, in the less severely affected mice, lesions of subacute or chronic disease were seen with thickening of alveolar walls and consolidation of lung tissue. Human cells did not appear to be involved directly in the pathology but were required for the establishment of infection. Immunohistological staining of lung tissue revealed substantial amounts of bacterial antigen distributed in a pattern similar to that seen in human Legionnaires' disease.

Aerosols↗
PubMed1995

Confidential unit exclusion: the North London Blood Transfusion Centre's experience.

A 'Confidential AIDS Questionnaire' has been used at North London Blood Transfusion Centre (NLBTC) donor sessions since July, 1985. The aim of the questionnaire is to encourage self-exclusion by those donors whose behaviour puts them at risk of HIV infection. In a situation where such individuals cannot avoid donating they can indicate, in confidence, that their blood should not be used for transfusion. Since the introduction of this procedure, an average of 10 donors per month, who admitted relevant risk behaviour, have been permanently excluded and a number of prospective donors have excluded themselves when faced with the questionnaire. We have found the questionnaire to be well accepted by donors. It is a useful adjunct to routine donor selection and microbiological testing of donations in our efforts to minimize transfusion-transmitted infection.

Acquired Immunodeficiency Syndrome↗
PubMed1994

The cost of intensive care: a comparison on one unit between 1988 and 1991.

OBJECTIVE: To assess the changes in cost of intensive care in one unit after a 3 year period and to evaluate the relative costs of an integrated high dependency unit. DESIGN: Combined retrospective and prospective audit of all expenditure incurred in an intensive care/high dependency unit over two periods: April 1988-February 1989 and January-July 1991. SETTING: Combined 13-bedded intensive care/high dependency unit of a central London teaching hospital. RESULTS: The overall cost rose by 50%. Hidden costs such as infrastructure maintenance, capital assets, pathology and radiology services accounted for nearly a quarter of total expenditure. Pharmacy and supplies each accounted for some 10% of total expenditure whereas staff costs exceeded 50%. The cost of the intensive care section rose by 14% of 1149 pounds per patient day as increased bed occupancy offset increases in nurse: patient ratios and expenditure on consumables. However, the cost of the high dependency unit section rose by 87% to 437.83 pounds. This was due to a lower bed occupancy (through increased patient turnover), improved staffing ratios, and increased utilisation of equipment and supplies. CONCLUSIONS: Intensive care is an increasingly expensive speciality, the costs for which are rising over and above the rate of general inflation. Staff costs are by far the largest single item of expenditure. Large reductions in spending on drugs and consumables are unlikely to provide considerable savings on the total budget. Hidden costs account for a high proportion of the budget and should be taken into account when evaluating cost. The significantly lower cost of high dependency care should encourage studies into its cost-effectiveness.

Health Services Research↗
PubMed1994

Discriminative inhibition is specific to the response-reinforcer association but not to the discriminative stimulus.

In 4 experiments an instrumental contingency between a response and a reinforcer was introduced in the presence of a discriminative stimulus. Then a discriminative inhibitor (S delta) was established that signaled that the instrumental contingency would no longer operate in the presence of that discriminative stimulus, so that the S delta suppressed operant responding. The degree to which the S delta, s inhibitory properties transferred to different discriminative stimuli and different response-reinforcer associations was then explored. In Experiments 1 and 2 the S delta, s effects transferred perfectly to a 2nd discriminative stimulus, whereas the results of Experiments 3 and 4 were consistent with the hypothesis that the S delta, s inhibitory properties were specific to the original response-reinforcer association. The theoretical implications of these findings are discussed.

Animals↗
PubMed1994

Hemodynamic effects of manual hyperinflation in critically ill mechanically ventilated patients.

SUBJECT OBJECTIVE: To assess the hemodynamic effects of manual lung hyperinflation in mechanically ventilated patients and to measure the different inspiratory pressures and tidal volumes generated by different operators. DESIGN: Measurements of aortic blood flow (by esophageal Doppler ultrasonography), systemic blood pressure, tidal volumes (by respirometry), and inspiratory pressures in the ventilator circuit were measured on the ventilator, during six intended manual hyperinflations (tidal volume > 150% that delivered by ventilator) using a 2-L rebreathing bag, and at 1, 5, 10, and 15 min after reconnection to the ventilator. SETTING: Intensive care unit. PATIENTS: Eighteen mechanically ventilated patients with normovolemia and stable circulatory status were assessed on a total of 20 occasions. INTERVENTIONS: Patients were disconnected from the ventilator to enable six manual hyperinflations to be given. Measurements were made before and at 5-min intervals until no further hemodynamic changes were seen. MEASUREMENTS AND RESULTS: Hyperinflation (50% increase in tidal volume) was achieved only in 10 of 20 studies. Large variations were seen in percentage change in peak inspiratory pressure (-30% to +250%) and tidal volume (-33% to +127%) generated. Falls in cardiac output correlated to the increase in tidal volume but not to the increase in peak inspiratory pressure and took up to 15 min to recover to baseline values. Changes in cardiac output were independent of lung compliance and concurrent vasoactive drug support. No consistent change was noted in either blood pressure or heart rate. CONCLUSIONS: Lung hyperinflation is frequently not achieved by the manual technique. Significant changes in cardiac output can occur and appear to be related to the tidal volume rather than pressure generated.

Adult↗
PubMed1994

Effect of low level energy laser irradiation on wound healing. An experimental study in rats.

In this randomized experimental study the wound healing process in rats was investigated after treatment with low level energy laser. In the caudal area of the back of 38 rats, standardized full thickness wounds were punched out bilaterally. The animals were randomly divided into two groups, A and B with 19 rats in each group. Group A was laser irradiated on one side wound (A1), leaving the contralateral side as a control of possible systemic effects (A2). Group B was given placebo irradiation (ordinary light) on one side (B1) and the contralateral side was left without treatment (B2). Two animals from each group were sacrificed continuously every second day from day 3. Neither the clinical nor the microscopical examination of the wound healing process revealed any differences between group A1, A2, B1 and B2, during the observation period. This study did not confirm that low level energy laser treatment would affect the wound healing process.

Animals↗
PubMed1994

Occasion-setting training renders stimuli more similar: acquired equivalence between the targets of feature-positive discriminations.

In two experiments rats received training on two concurrent appetitive feature-positive discriminations. A preliminary test in Experiment 1 confirmed previous demonstrations of the transfer of occasion-setting properties--the feature from one of these discriminations was better able to facilitate responding to the occasion-set target CS from the second discrimination than to a control stimulus that had not been the subject of occasion-setting. The source of this transfer was investigated in a second phase of training, and in Experiment 2. In both experiments one of the occasion-set CSs was paired with food, and generalization of appetitive conditioned responding from this stimulus to the second occasion-set CS, and to a control cue, was examined. There was more generalization from the first occasion-set CS to the second CS that had also been occasion-set than to the control cue. This is taken as evidence that occasion-set CSs are rendered more similar as a result of their common training history. The implications of these findings for explaining transfer of occasion setting are discussed.

Animals↗