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Biomedical subjects

J A Dixon

Publications and source records attributed to J A Dixon.

At least 19 recordsLinked to original sources
PubMed1998

Detection of canine distemper virus in 100% of Paget's disease samples by in situ-reverse transcriptase-polymerase chain reaction.

Previous evidence implicating paramyxoviruses in the aetiopathology of Paget's disease of bone has been controversial. While several groups have demonstrated the presence of paramyxoviruses using electron microscopy, immunohistochemistry, and molecular biological techniques, others have found no evidence of viruses using reverse transcriptase-polymerase chain reaction (RT-PCR). We have previously provided evidence that canine distemper virus (CDV) is present in approximately 65% of samples of pagetic bone, using in situ hybridization and RT-PCR; however, these results have been criticized. To further investigate the possible Role of CDV, we have now developed the technique of in situ-RT-PCR (IS-RT-PCR) to examine for the presence of CDV-nucleocapsid (CDV-N) ribonucleic acid (RNA) in pagetic bone. Control samples consisted of uninvolved sites from patients with the disease, normal bone, and several active remodeling states. IS-RT-PCR was optimized to detect CDV-N using distemper-infected vero cells. The specificity of the technique was confirmed using vero cells infected with CDV, which showed amplified signal following IS-RT-PCR, and cells infected with measles virus (MV), in which no positive signal for CDV was detected by IS-RT-PCR. Following conventional in situ hybridization, CDV-N was detectable in 10 of 15 pagetic bone samples. However, after five, and particularly 10, cycles of IS-RT-PCR, CDV-N was found in all 15 samples. There was no evidence of CDV in four samples from uninvolved sites from pagetic patients, or in any of the other control samples. In this study, using the novel technique of IS-RT-PCR, CDV was found to be present in 100% of pagetic samples examined. There was no evidence of the virus in any of the control samples, including samples of bone from uninvolved sites from patients with Paget's disease. These results provide additional proof that CDV is present within pagetic bone and further support the hypothesis that paramyxoviruses are involved in the etiopathology of Paget's disease.

Animals↗
PubMed1998

Developmental ordering, scale types, and strong inference.

Developmental ordering, 1 item preceding another in development, is a primary piece of evidence in developmental research. However, testing developmental ordering hypotheses is remarkably difficult; the problem is that researchers rarely have absolute measures (ratio scales). Therefore, directly comparing 2 measures is often not sensible. This article demonstrates that, depending on the type of scale, the observed data pattern is constrained by the underlying relationship. Although the observed data pattern may not reflect the exact relationship, it does limit the possible relationships. Researchers can use this information to reject potential underlying relationships. An application of the method of strong inference (J. R. Platt, 1964) is outlined whereby researchers can use observed data patterns to systematically reject competing developmental ordering hypotheses. The approach requires only standard statistical methods and assumptions.

Age Factors↗
PubMed1997

Gender and hedging: from sex differences to situated practice.

In a reanalysis of women's language, Holmes (1995) has argued that women's use of hedges expresses interpersonal warmth and not, as many researchers have maintained, linguistic tentativeness. It is typically men, she suggests, who employ hedges to convey imprecision and incertitude. In this study, we investigated the use of the hedges sort of and you know in a sample of South African students. Holmes's method of analysis was applied to hedging behavior in 52 dyadic conversations. The study consisted of a 2 (Speaker Gender: Male/Female) x 2 (Audience Gender: Male/Female) x 2 (CONDITION: Competitive/Noncompetitive) between-subjects experimental design. The results showed that contextual influences eclipsed the effects of gender: in fact, no main effects were found for speaker gender. Fewer hedges were deployed in the competitive condition than in the noncompetitive condition. Moreover, perhaps reflecting differences in social status, both sexes used sort of to express tentativeness more frequently when talking to male addressees. When speaking to female addressees, on the other hand, men deployed facilitative you know hedges more readily than women.

Adolescent↗
PubMed1997

Characterizing the intuitive representation in problem solving: evidence from evaluating mathematical strategies.

Two experiments were conducted to investigate the nature of the intuitive problem representation used in evaluating mathematical strategies. The first experiment tested between two representations: a representation composed of principles and an integrated representation. Subjects judged the correctness of unseen math strategies based only on the answers they produced for a set of temperature mixture problems. The distance of the given answers from the correct answers and whether the answers violated one of the principles of temperature mixture were manipulated. The results supported the principle representation hypothesis. In the second experiment we manipulated subjects' understanding of an acid mixture task with a brief paragraph of instruction on one of the principles. Subjects then completed an estimation task intended to measure their understanding of the problem domain. The evaluation task from the first experiment was then presented, but with acid mixture instead of temperature mixture. The results showed that intuitive understanding of the domain mediates the effect of instruction on evaluating problems. Additionally, the results supported the hypothesis that subjects perform a mapping process between their intuitive understanding and math strategies.

Analysis of Variance↗
PubMed1996

rel-(1R,6S,7S,8R,9S)-9-methyl-8-phenyl-6-[(1s,2R)-(2-phenylcyclohexyl) oxy]-4-aza-3,5-dioxatricyclo[5.2.1.0(4,9)]decane.

The structure of the title compound, C26H31NO3, was determined by X-ray crystallography. It was found to be a unique bridged tricyclic nitroso acetal. Notable features include a chair conformation of the tetrahydro-1,2-oxazine ring and a highly pyramidalized N atom [sigma angles = 314.2 (6) degrees]. The configurations of the five contiguous stereogenic centers in the nitroso acetal establish that the tandem cycloaddition sequence proceeded via an exo-[4 + 2] endo-[3 + 2] pathway.

Crystallography, X-Ray↗
PubMed1994

Physical knowledge of sugar water solutions: cross-cultural data.

Children's understanding of sugar water solutions may progress through universal stages: from nonpreservation to preservation to liquefaction to atomism. This claim was investigated in the current study; the claim was originally prefigured in the work of Piaget and Inhelder (1974) and more recently consolidated by Slone (1987). Our sample consisted of 270 South African children drawn from three cultural groups and ranging in age from 4 to 14 years. Children watched a demonstration in which a sugar lump was dissolved in water. Then, using structured interviews, we explored their understanding of this phenomenon. The results generally confirmed the hypothesized developmental sequence. Moreover, because the sequence was consistent across cultural groups, the claim that physical knowledge evolves through universal stages also was supported. Perhaps significantly, however, the progression of knowledge development did not unequivocally lead to the concept of atomism. Developmental implications of these findings are discussed.

Adolescent↗
PubMed1994

Evaluation of sensibility in leprosy--comparison of various clinical methods.

In order to determine whether various sensibility tests, not in common use at our hospital, are appropriate for the neurological screening of leprosy patients, an extended nerve function assessment (NFA) was done on 50 in- and outpatients who had been diagnosed as suffering from leprosy (100 hands and feet). The nerve function assessment battery consisted of Semmes-Weinstein monofilament testing (SWMT), moving 2-point discrimination (M2PD). Pinprick (PP), position sense (PS), vibration sense (VS) and voluntary muscle testing (VMT). In addition the SWMT was performed on 637 hands and 634 feet of field patients' in order to get a better indication of the prevalence of sensory impairment as measured with the SWMT. The SWMT has been shown to be a sensitive test of peripheral nerve function, therefore the other tests were compared with the SWMT. Results are reported separately for the ulnar, median and posterior tibial nerve. Test sites were the pulp of the distal phalanx of the index finger, the little finger and the big toe. Correlation between the SWMT and each of the other tests proved statistically significant; the closest correlations were between the SWMT, M2PD and PP for both ulnar and median nerves (r > 0.7, F test > 100, p < 0.0001). It is argued that the first tests to show nerve function impairment (NFI) are the M2PD and the SWMT. VS and PS were also absent in a significant proportion of patients. Arguments are presented that this may indicate advanced NFI. Results are compared with other data currently available in the literature.

Adolescent↗
PubMed1991

Application of charge-coupled device technology for measurement of laser light and fluorescence distribution in tumors for photodynamic therapy.

Laser and fluorescence light distributions with applications for photodynamic therapy were measured in mouse tumors using a non-invasive electronic optical imaging system. The system consists of a liquid-nitrogen-cooled, charge-coupled-device (CCD) array camera under computer control with 576 x 384 detection elements having dimensions of 23 microns x 23 microns. The available dynamic range of the array is approx. 10(3), and the effective wavelength range is 400-1000 nm. An interstitially placed cylindrical diffusing optical fiber was used to provide tumor illumination. The light distribution pattern from the fiber was determined by immersing the cylindrical diffusing tip in a fluorescing solution and recording the emission image. Fluorescence imaging facilitates an accurate measurement of light intensity distribution while avoiding problems associated with the directional nature of other detection methods used with diffusing fibers. Radiation-induced fibrosarcoma tumors on C3H mice were grown to about 1 cm diameter for in vivo recording of light distribution from the tumor volume and for determination of effective light penetration distance at 18 wavelengths in the range 458-995 nm. Endogenous tumor fluorescence and Photofrin II fluorescence intensity were measured over the wavelength range 585-725 nm to investigate the possible application of CCD imaging technology for drug distribution measurements. Model experiments were begun to evaluate the relative importance of potential distortions of light distribution measurements using this approach.

Animals↗
PubMed1990

The development of perspective taking: understanding differences in information and weighting.

2 separate aspects of perspective taking are that judgments attributed to another should depend on the information available to the other (Information effect) and on how the other's use of information differs from one's own (Weighting effect). These 2 aspects of perspective taking were studied in a moral judgment task with preschoolers, and second and fifth graders. Subjects were read a series of stories about a little boy transgressing and asked to make judgments from both their own perspective and that of a mother character in the stories. The mother story character had either the same information as the subject or only partial information. Valence of intention and consequence and the amount of mother's knowledge varied factorially. Subjects were clustered using scores derived from the judgements. 3 clusters were found that showed different levels of perspective-taking ability. There was a developmental progression in the 3 levels of perspective taking. Subjects in the Harshness cluster attributed harsher judgments to the mother perspective. Subjects in the Weighting cluster weighted information differently depending on the perspective from which they judged. Subjects in the Information-and-Weighting cluster weighted information differently depending on perspective, and also considered the amount of information available to the mother character in attributing judgments. The findings are compared to current theory on the development of perspective taking. Future research and theory need to consider the influence of both information and weighting differences on performance in perspective-taking tasks.

Affect↗
PubMed1989

Anterior lesser curvature laser seromyotomy with posterior truncal vagotomy: a potential treatment of peptic ulcer disease.

Anterior lesser curvature seromyotomy combined with posterior truncal vagotomy has been suggested as an alternative to proximal gastric vagotomy in the treatment of peptic ulcer. The argon laser may be an ideal instrument for performing seromyotomy. This study compares anterior lesser curvature argon laser seromyotomy/posterior or truncal vagotomy with anterior proximal gastric vagotomy/posterior truncal vagotomy in a canine preparation. Six dogs underwent anterior lesser curvature argon laser seromyotomy/posterior truncal vagotomy and six others underwent anterior proximal gastric vagotomy/posterior truncal vagotomy. Gastric emptying and acid secretion studies were performed preoperatively and at 1 and 6 months postoperatively. Operating time and blood loss were determined. Anterior lesser curvature argon laser seromyotomy was performed with the argon laser at 10 W, continuous, delivered through a 600 micron unsheathed quartz fibre. Anterior proximal gastric vagotomy and posterior truncal vagotomy were performed in the standard fashion. Solid phase gastric emptying was slowed with both operations (P less than 0.05) but this was not manifest clinically. Blood loss (millilitres) was less following anterior lesser curvature argon laser seromyotomy/posterior truncal vagotomy than following anterior proximal gastric vagotomy/posterior truncal vagotomy (21(6.8) versus 95(28.1), mean (s.e.m.), P less than 0.05) but operating time was not significantly different between the groups. Mean basal acid secretion was reduced by 64 per cent 6 months after anterior lesser, curvature argon laser seromyotomy/posterior truncal vagotomy (P less than 0.05) and by 53 per cent after anterior proximal gastric vagotomy/posterior truncal vagotomy (not significant). Mean stimulated acid secretion was reduced by 41 per cent 6 months after anterior lesser curvature argon laser seromyotomy/posterior truncal vagotomy (P less than 0.05) and by 24 per cent after anterior proximal gastric vagotomy/posterior truncal vagotomy (not significant). We conclude that anterior lesser curvature argon laser seromyotomy/posterior truncal vagotomy is an acceptable alternative to anterior proximal gastric vagotomy/posterior truncal vagotomy and may provide superior parietal cell denervation with less operative blood loss.

Animals↗
PubMed1989

Catheter-directed neodymium:YAG laser injury of the left ventricle for arrhythmia ablation: dosimetry and hemodynamic, hematologic, and electrophysiologic effects.

The study evaluated catheter-directed laser injury of the left ventricular myocardium in a canine model as a potential method for treatment of resistant ventricular tachycardia. The relationship between laser energy delivered, the laser delivery characteristics, and the lesion size was evaluated both in vitro and in vivo. The effect of laser injury on several hematologic and hemodynamic parameters was studied. Programmed electrical stimulation studies were performed to assess the proarrhythmia potential of laser injury of the myocardium. The results showed the depth and diameter of myocardial injury to be directly related to total laser energy applied. Both depth and diameter of injury were increased by multiple applications of laser energy to the same myocardial location. One-half to full thickness left ventricular injury was produced without perforation or embolization. Endocardial vaporization occurred only with laser powers higher than necessary to produce full-thickness injury. There was no sustained effect on the hemodynamic or hematologic variables studied, nor were proarrhythmia effects identified. The laser injury produced in these studies was of smaller magnitude than might be necessary for clinical arrhythmia ablation, and the lack of sustained hemodynamic effects and pro-arrhythmia potential needs to be verified in subsequent studies with larger laser lesions. The results support continued evaluation of catheter-directed laser injury of the myocardium as a potential method for elimination of life-threatening ventricular arrhythmias.

Animals↗
PubMed1989

Superficial malignant schwannoma on the face: a case for early radical surgery.

A case of superficial epithelioid schwannoma is presented. The lesion arose as a skin papule in the infra-orbital region and recurring repeatedly over a five-year period, caused significant local morbidity without metastasis. Radical surgery was delayed in the hope of preserving binocular vision. The similarity of this tumour with a rare variant of malignant melanoma, the neurotropic melanoma, is discussed.

Facial Neoplasms↗
PubMed1989

Spontaneous external carotid artery occlusion.

The case of a 64-year-old man who presented with severe left sided facial pain and cyanosis of the left ear, preauricular region and tongue is described. Digital subtraction angiography confirmed complete occlusion of the left external carotid artery. The patient was anticoagulated and his symptoms resolved over the following month, presumably due to improvement of collateral blood supply to the ischaemic areas. The literature on the clinical manifestations of external carotid ischaemia is reviewed and the relationship between facial pain, internal and external carotid atherosclerosis is emphasised.

Carotid Artery Thrombosis↗
PubMed1988

Plasma and synovial fluid meclofenamic acid concentrations in patients with rheumatoid arthritis of the knee.

We have measured plasma and synovial fluid concentrations of meclofenamic acid at 2, 4, 8, and 12 h during steady-state administration (100 mg three times daily for 4-7 days). Paired plasma and synovial samples were obtained pre-treatment and at one of the above times in twelve patients with a diagnosis of rheumatoid arthritis. In addition, the extent of protein binding of meclofenamic acid was assessed in vitro in the pre-treatment plasma and synovial fluid specimens. Peak total concentrations of 1.73 and 0.86 micrograms.ml-1 were observed in plasma (at 2 h) and synovial fluid (at 4 h) respectively. The extent of protein binding was 99.7 and 99.6% (not significantly different) in plasma and synovial fluid respectively. The results of this study are compared to those from similar reported studies of other nonsteroidal anti-inflamatory compounds.

Arthritis, Rheumatoid↗
PubMed1988

Copper vapor laser fragmentation of gallstones: in vitro measurements of wall heat transmission.

Laser fragmentation is a promising new modality in management of retained CBD stones. Recent reports demonstrate the feasibility of lasers for this, but few studies have evaluated their safety (e.g., thermal injury may occur at greater than 43 degrees C). This study was conducted to measure heat transmission from lased bilirubinate and mixed stones to a simulated CBD wall. Four welded thermocouples were passed to the inside wall of 6-mm polyvinyl tubing 90 degrees apart to surround the lumen stone. The thermocouples were interfaced to a computer and temperatures were recorded every 270 msec. The tubing was submerged in a 37 degrees C water bath for all lasing work. A copper vapor laser (wavelength, 510 nm; 5.6 W; 5 kHz; pulse length, 30 ns) was attached to a 650-micron quartz fiber. A stone was "impacted" in the tubing and the laser fiber was pushed against the stone while making multiple passes to fragment it. Thirty mixed gallstones (mean size, 6.9 X 5.1 mm) and 20 bilirubinate gallstones (mean size, 7.1 X 5.2 mm) were fragmented during the study. Maximum temperature (Tmax), duration of Tmax (TmaxD), interval to stone piercing (TiP), and interval to fragmentation (TiF) were measured and comparisons were carried out with the SPSS statistical package using the t test procedure. The Tmax generated during fragmentation of bilirubinate stones (43.4 +/- 1.7 degrees C) was significantly less (P less than 0.002) than the Tmax for mixed stones (54.0 +/- 2.7 degrees C) but both Tmax values represented potentially injurious temperature levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholelithiasis↗