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Biomedical subjects

A J Harrison

Publications and source records attributed to A J Harrison.

At least 19 recordsLinked to original sources
PubMed2006

Seasonal and vertical patterns of egg-laying by the freshwater fish louse Argulus foliaceus (Crustacea: Branchiura).

Argulus foliaceus is a damaging fish ectoparasite for which new control measures are being developed based on egg-removal. In an attempt to develop further understanding of seasonal and vertical egg-laying patterns in this parasite, egg-laying activity was monitored over the period 14 April to 17 November 2003 in 2 rainbow trout Oncorhynchus mykiss fisheries in Northern Ireland, UK. At Site 1, egg-laying was continuous from 21 April to 17 November, when water temperature was above 8 to 10 degrees C. At Site 2, egg-laying was continuous from 4 June to 29 October. In the early months of the season, egg-laying was recorded mainly within the top 1 m of the water column; however, a significant shift to deep water egg-laying was recorded between 7 July and 17 November at Site 1 and between 20 August and 29 October at Site 2. Egg clutches were preferentially laid at depths of up to 8.5 m during this time (Site 2), a feature of egg-laying hitherto unappreciated. Temperature and dissolved oxygen did not differ significantly among depths, but there was an increase in water clarity over time. However, the precise environmental triggers for deep water egg-laying are still unclear. These new insights into the reproductive behaviour of this species will be useful in developing control methods based on egg-removal.

Animals↗
PubMed2002

Dexamethasone and retinoic acid differentially regulate growth and differentiation in an immortalised human clonal bone marrow stromal cell line with osteoblastic characteristics.

Clonogenic immortalised human pre-osteoblastic cell lines provide useful species-specific experimental tools for the study of the regulation of osteoblastic proliferation and differentiation. Steroid hormones are major regulators of bone formation. Although much is known about the effects of dexamethasone on osteoblastic growth and differentiation in vitro, there is less information on the effects of trans-retinoic acid (RA), particularly in human cultures. We have established a clonal adult human cell line (C1) derived from a bone marrow aspirate. The cell line appeared to be bi-potential. The cells were able to differentiate into an adipocytic phenotype under appropriate culture conditions. When grown in osteogenic medium, the cells expressed alkaline phosphatase (ALP) and osteocalcin mRNA. The C1 cells also expressed several other osteoblastic markers such as collagen type 1 (COL 1), PTH/PTH-rp receptor constitutively. Transcripts for the osteoblast transcription factor Cbfa1 was also detected under basal conditions. In addition treatment with 1,25(OH)(2)D(3) (10(-7)M) led to a marked increase in osteocalcin mRNA expression suggesting that this cell line represents a pre-osteoblastic population. We compared the effects of Dex and RA on osteoblastic function. For the assessment of PTH/PTH-rp receptor, osteocalcin and Cbfa1 mRNA expression and PTH-stimulated adenylate cyclase responsiveness, the cells were grown in the presence of Dex and RA and harvested on Days 1, 3, 7 and 14. RA (10(-7)M) had a mitogenic effect on the C1 cells. In contrast, Dex (10(-7)M) inhibited proliferation. A similar effect was observed with primary human bone marrow stromal cultures. Both Dex and RA inhibited COL 1 synthesis and decreased COL1 mRNA. Dex stimulated ALP activity and increased ALP mRNA expression whilst RA had an inhibitory effect. Dex treatment led to an increase in PTH/PTH-rp receptor mRNA and PTH-induced cAMP accumulation with a peak response at 24 h and this effect was sustained for up to 14 days. In contrast, long-term culture with RA resulted in a reduction in the cAMP response to PTH (Days 7 and 14) with no effect on PTH/PTH-rp receptor mRNA expression. Osteocalcin and Cbfa1 mRNA expression did not alter in the presence of Dex and RA at these time points. This study shows that Dex and RA have differential effects on the expression of the phenotypic markers and genes associated with osteoblast maturation. This homogeneous cell line can therefore be used further to elucidate the cellular and molecular mechanisms of action of Dex and RA at the different developmental stages of human osteoblastic differentiation. This cell line may thus provide a useful species-specific in vitro model for the evaluation of key genes and signalling molecules involved in osteogenesis. This would be of help in the design of 'in vivo' studies.

Adipocytes↗
PubMed2001

Motor development and gender effects on stretch-shortening cycle performance.

A substantial part of human movement such as jumping, hopping, leaping and other bounding movements are improved by making a counter-movement. These activities are often described as stretch shortening cycle (SSC) movements. The aim of this study was to determine whether the SSC affects performance in vertical jump in children to the same extent as it does in adults. Comparisons were made between counter-movement jump (CMJ) and squat jump (SJ) performance in children and adults. The ratio of take-off velocity between jumps was used to measure performance of the SSC. Two groups of subjects comprising of 22 adults and 20 children performed three CMJ's and three SJ's from a force platform. Impulse, take-off velocity and power were obtained by numerical integration of the force n time traces. Performance was calculated from the velocity at take off. Both groups jumped significantly higher in the CMJ but there was a higher degree of variability in the performance of the children. The results indicated that children could utilise a SSC to enhance jumping performance. Variability in the take-off velocities in children, particularly in the SJ suggests the children performed this jump non-optimally.

Adult↗
PubMed2000

Schemes for the identification of tissue types and boundaries at the tool point for surgical needles.

Precise control of automated invasive surgical tools requires real-time identification of tissue types and their deformation. At the focus of this paper is the epidural puncture, for which it is shown that the tissue type and deformation can respectively be determined from laser-based spectroscopy and the change in force required to push the needle through the various tissues. Studies have shown that physiological variations from one patient to another are too great to allow absolute values to be reliably used to indicate the position of the needle tip. However, the pattern of force variation during penetration is shown to be similar between specimens. Interpretation of this information in conjunction with spectroscopic techniques can be used to discriminate between tissues and tissue structure at the needle tip. This paper describes results from an investigation on automatic techniques for interpreting the type and deformation of tissues under tool action.

Adipose Tissue↗
PubMed2000

A moment-based technique for the automatic spatial alignment of plantar pressure data.

Plantar pressure measurements have many potential clinical applications in the field of orthopaedics. However, the only current routine clinical application of pedobarography is for the identification of high pressure zones in diabetic patients with neuropathy who are at risk from foot ulceration. For pedobarography to become a routine clinical tool in orthopaedics, a thorough knowledge of normal plantar pressure distributions would be required. To date, no large scale studies to define population norms have been conducted, probably because of the high cost associated with analysing large quantities of plantar pressure data. Plantar pressure distributions display a high step-to-step variation and, therefore, it is necessary to conduct multiple trials. Comparison between these trials is difficult, somewhat subjective, and slow, because it must be conducted manually. The present authors have developed a technique to align automatically the spatial components of a series of datasets. The technique then allows predefined parameters to be automatically extracted from the data, hence greatly reducing analysis time. The authors believe that not only does the technique make large scale studies economically viable but that it could also form the basis for expert systems for the diagnosis of foot pathologies and the prescription of orthoses.

Automation↗
PubMed1998

The yielding of tensioned fine wires in the Ilizarov frame.

The Ilizarov frame uses tensioned fine wires to support bone fragments. The objective of this study was to determine whether these wires deformed plastically under functional load bearing and to determine the significance of such deformation on the long-term performance of frames used for treating lower limb conditions. The mechanical characteristics of the wires were determined by means of destructive tensile tests and used in the construction of a series of finite element models replicating typical frame configurations. Each model was then subjected to a single load cycle representing a single step and the residual displacement (i.e. plastic deformation) was determined. In each case a residual displacement of between 0.26 and 0.42 mm was observed giving a corresponding reduction in wire tension of between 8.3 and 32.8 per cent. These reductions in wire tension reduce the frame's overall stiffness and so compromise its ability to inhibit high-amplitude axial and shear motions at the fracture site which are deleterious to the healing outcome.

Biomechanical Phenomena↗
PubMed1997

Postural instability in diabetic neuropathic patients at risk of foot ulceration.

Diabetic peripheral neuropathy is believed to cause postural instability due to abnormal proprioception. We assessed body sway in four groups, each of 20 subjects, matched for age, sex, and BMI: non-diabetic controls, non-neuropathic diabetic controls, subjects with diabetic neuropathy and no history of foot ulceration, and subjects with diabetic neuropathy and a history of foot ulceration. Postural sway was assessed on a Kistler force plate using the Romberg test, measuring the standard deviation of the centre of pressure in both sagittal (antero-posterior movement) and frontal (side to side movement) planes with eyes open and closed. The Romberg test results were log transformed and then analysed using analysis of variance followed by Newman-Keuls test. There was no significant difference in body sway between the two control groups and the first group of subjects with diabetic neuropathy. However, in patients with a history of ulceration, values were significantly higher (p < 0.05) compared to all other groups in both planes and conditions studied. These results are suggestive of a relationship between impaired body sway control and foot ulceration. Postural instability may have clinical significance and increase the risk of minor trauma and ulceration in patients with diabetic neuropathy.

Analysis of Variance↗
PubMed1997

Hospitals in England: impact of the 1990 National Health Service reforms.

OBJECTIVES: This article aims to describe recent changes in English hospitals, with particular reference to the impact of the National Health Service (NHS) and Community Care Act of 1990. METHODS: Significant policies that have affected the functioning of the hospital sector of the British NHS are reviewed. Data from the NHS Department of Health are used to describe trends in utilization. RESULTS: The NHS and Community Care Act of 1990 radically changed the financial and organizational framework within which hospitals operate. By creating separate purchasing organizations, the act opened the way for competition between hospitals. In practice, such competition has been very limited. Central directives aimed at reducing waiting times for nonurgent admissions, as well as at raising the volume of work done relative to the finances available have been more significant influences. These changes, combined with rising numbers of emergency admissions, have put the physical and human resources of English hospitals under intense pressure. Admissions have risen, lengths of stay have fallen across all age groups, and ambulatory care has grown rapidly. CONCLUSIONS: There is little consensus on the future direction regarding the role and structure of acute-care hospitals. There is evidence, though, that improvements in the process and outcomes of care are possible within the current financial and organizational framework of the hospital sector.

England↗
PubMed1997

Simulation of resistance forces acting on surgical needles.

High precision in the manual control of needles and biopsy probes in medical treatment requires high skill and dexterity levels. In anaesthesia, force sensation is an important feedback mechanism, and the practitioner needs to refresh or develop skills to improve on the interpretation of needle progress towards the target site. This paper describes an experimental tactile force simulator for uniaxial needle action for which the force resisting progress of the needle is derived from measured data. As an example, the approach taken to develop the simulation of the insertion of epidural needles is described. Adaptation to other procedures would be possible by adopting new reference models based on appropriate measured force data.

Animals↗
PubMed1992

Ipratropium bromide delivered orally by metered dose inhaler does not decrease salivary flow in normal subjects.

A randomised placebo-controlled cross-over group study was conducted to ascertain the occurrence and duration of xerostomia induced by 240 micrograms (high dose) and 120 micrograms (low dose) of ipratropium bromide (IPB) delivered by metered dose inhaler (MDI) into the mouth in normal subjects. Salivary output was higher with both doses of IPB than with placebo though the differences were not statistically significant. IPB was less palatable than placebo as indicated on visual analogue scale (VAS) and the taste of the drug may have caused a reflex increase in salivary output from the major salivary glands which would have masked any possible local effect of the drug on the smaller submucosal glands of the mouth. IPB delivered into the oral cavity by MDI is therefore not a suitable treatment for hypersalivation.

Administration, Inhalation↗
PubMed1977

Attempts to immunize monkeys against Plasmodium knowlesi by using heat-stable, serum-soluble antigens.

Thirty-six Macaca mulatta monkeys were immunized with different concentrations and regimens of heat-stable, serum-soluble (S-) antigens of Plasmodium knowlesi prior to challenge with the homologous parasite via sporozoite inoculation. Fewer deaths and reduced maximum parasitemias occurred in those animals inoculated with 10 to 40 mg of S-antigen compared to nonimmunized monkeys or those receiving only Freund's adjuvant. Protection was incomplete, however, suggesting that atibodies to S-antigens may have a limited role in protection of hosts to malarial infection.

Animals↗