Biomedical subjects

J Fisher

Publications and source records attributed to J Fisher.

At least 217 records · Page 12Linked to original sources

PubMed1997

Wear of ultra-high molecular weight polyethylene acetabular cups in a physiological hip joint simulator in the anatomical position using bovine serum as a lubricant.

The Leeds physiological anatomical (PA) hip joint simulator was developed to apply three axes of loading and a complex three-dimensional motion so that the forces and motions can reproduce exactly the walking cycles defined by Paul. This paper presents the results of a study using the Leeds PA hip joint simulator to determine the wear of 32 mm ultra-high molecular weight polyethylene (UHMWPE) acetabular cups against stainless steel and zirconia ceramic heads, using bovine serum as lubricant. These results have been compared with the results of a previous study that used water as the lubricant, which led to UHMWPE transfer film being formed on the stainless steel head. Comparisons are also made with clinical results and results from other simulators. The study indicates that it is preferable to use bovine serum in simulator studies. In addition, the results indicate that if the surface roughness of the metallic and femoral heads are similar, and they remain undamaged during the tests, the wear rates of the UHMWPE cups are likely to be similar.

Acetabulum↗

PubMed1997

The wear of ultra-high molecular weight polyethylene sliding on metallic and ceramic counterfaces representative of current femoral surfaces in joint replacement.

A number of studies have investigated the influence of surface roughness on the wear of ultra-high molecular weight polyethylene (UHMWPE) in total joint replacement. The results of these studies have shown that the wear factor is proportional to the counterface roughness raised to a power greater than one. In this laboratory study, the effect of surface finish of several biomaterials on the wear of UHMWPE was studied. The study was conducted using reciprocating pin-on-plate wear tests with bovine serum as a lubricant. The biomaterials investigated as the counterface material included stainless steel, cast cobalt chrome (CoCr), CoCr (ASTM F799), alumina ceramic and zirconia ceramic. The counterface topographies of the wear plates were produced using techniques representative of current manufacturing methods. The surface roughness of the wear plates was varied in the range Ra = 0.005-0.04 micron; this was representative of femoral heads and femoral knee components currently used clinically. Metals and ceramics with a similar surface roughness produced a similar wear rate of UHMWPE. For the limited range of smooth counterfaces used in this study only a moderate correlation was found between the surface roughness and the wear factors. For a change in counterface roughness Ra of 0.005 to 0.04 micron, the wear factor increased from 7.4 +/- 1.6 to 16.5 +/- 2.4 x 10(-9) mm3/N m (mean +/- standard error). This variation in counterface roughness had much less effect in wear than previously reported for rougher counterfaces. For an extended range of counterface roughness, a stronger correlation was found using an exponential function for the regression fit. The exponential function shows the benefits of decreased wear with decreased surface roughness. Although the wear rate decreased less rapidly with decreased counterface roughness for Ra values below 0.05 micron, there were significant advantages to be gained from improved femoral head roughness to below 0.01 micron Ra.

Aluminum Oxide↗

PubMed1997

Friction of composite cushion bearings for total knee joint replacements under adverse lubrication conditions.

Conventional joint replacements consist of a polished metallic or ceramic component articulating against a layer of polyethylene. Although the friction in the contact between these articulating surfaces is low, polyethylene wear is produced as a result of a boundary/mixed lubrication regime. Wear debris is generated by direct asperity contact, abrasion, adhesion and fatigue, and has been shown to cause adverse tissue reactions which can lead to joint failure. The introduction of soft compliant materials, similar in stiffness to articular cartilage, has shown that with cyclic loading and relative motion between the articulating surfaces typical of normal walking, a fluid film can be maintained through combined entraining and squeeze-film actions, and hence wear can be minimized. For 95 per cent of the time, however, we are not walking but standing still or moving slowly. A pendulum simulator has been used in the present study to investigate the effect of adverse tribological conditions which may lead to fluid film breakdown, such as severe cyclic loading, particularly in the swing phase, reduced sliding velocity, reduced stroke length and start-up after a period of constant loading. Friction of a model composite cushion knee bearing, manufactured from a graded modulus (20-1000 MPa) layer of polyurethane, sliding against a polished metal cylinder has been measured for various lubricants and the results have been analysed using a Stribeck assessment. Severe cyclic loading, decreased sliding velocity and decreased stroke length have been found to limit the degree of fluid entrainment previously allowed during the swing phase of normal walking, thus allowing breakdown of fluid films and elevated levels of friction and surface damage. Soft layer joint replacements must therefore be designed to operate with thick elastohydrodynamic fluid films to provide some degree of protection when tribological conditions become severe, or alternatively incorporate alternative boundary or mixed lubrication mechanisms. This study quantifies a potential limitation of the cushion bearing concept.

Elasticity↗

PubMed1997

Adverse psychological impact of operative obstetric interventions: a prospective longitudinal study.

OBJECTIVE: This paper reports the findings of a prospective longitudinal study of 272 nulliparous pregnant women, which investigated as one of its objectives the psychological sequelae of obstetric procedures. METHOD: Participants completed structured interviews and standardised, published psychometric questionnaires, including the Rosenberg Self-Esteem Scale and the Profile of Mood States late in pregnancy and again early in the postpartum period. RESULTS: Little evidence was found to support the notion that the total number of obstetric interventions was linked to a deterioration in postpartum mood. Significant adverse psychological effects were associated with the mode of delivery. Those women who had spontaneous vaginal deliveries were most likely to experience a marked improvement in mood and an elevation in self-esteem across the late pregnancy to early postpartum interval. In contrast, women who had Caesarean deliveries were significantly more likely to experience a deterioration in mood and a diminution in self-esteem. The group who experienced instrumental intervention in vaginal deliveries fell midway between the other two groups, reporting neither an improvement nor a deterioration in mood and self-esteem. CONCLUSIONS: The findings of this study suggest that operative intervention in first childbirth carries significant psychological risks rendering those who experience these procedures vulnerable to a grief reaction or to posttraumatic distress and depression.

Adult↗

PubMed1997

A study of the combined effects of shelf ageing following irradiation in air and counterface roughness on the wear of UHMWPE.

Damage to polished femoral heads in vivo can cause increased wear of acetabular cups. Oxidation and ageing after sterilisation by gamma irradiation in air, can also change the mechanical properties and wear resistance of ultra high molecular weight polyethylene (UHMWPE). This study investigated the combined effect of these changes in material properties on the wear of UHMWPE for different counterface roughnesses, representative of new femoral heads and those damaged in vivo. Wear rates were studied on a tri-pin-on-disc tribometer in a protein-containing solution. A comparison was made of the wear, using three different counterface roughnesses, of specimens that were manufactured from polyethylene acetabular cups of different shelf ages (3-120 months) after gamma irradiation in air but never implanted. These were compared to the wear of control specimens that were manufactured from cups that had not been sterilised. The wear surfaces were tested 1 mm below the initial articulating surface of the cup, the position of high degradation. The wear rate of UHMWPE which had been sterilised by gamma irradiation in air was shown to increase significantly with ageing time on the shelf for all counterface conditions. The wear rate of all materials increased markedly as the counterface roughness increased, but to different extents depending on the age of the material. The combined effect of ageing and increase in counterface roughness had a dramatic effect (as high as 2000 fold increase) on the wear rate. Both ageing of the polymer and damage to the femoral head have been cited as causing increased wear in vivo. The results of this study demonstrate that these variables can act synergistically to markedly effect UHMWPE wear rate.

Air↗

PubMed1997

Material optimisation of the femoral component of a hip prosthesis based on the fatigue notch fatigue approach.

Previous studies have optimised the shape of a cemented stainless steel stem in order to minimise the fatigue notch factor Kf in the cement whilst at the same time maximising Kt in the proximal medial bone to prevent bone resorption [1]. The present study firstly describes the effect of changes in the modulus of elasticity of the stem material for both the original Charnley stem and the optimised shape on Kf as predicted by a 2D finite element (FE) model of the implanted prosthesis. The paper further describes a method for parametric optimisation to determine the best material properties of a layered composite femoral stem consisting of a core material (stainless steel) and an outer layer of a different material, the elastic modulus of which is used as a design variable. The overall objective of the optimisation was to maximise Kf in the proximal bone whilst at the same time constraining Kf at all cement interfaces to be no greater than its initial value. The results of the first study suggest that Young's moduli of about 145 and 210 GPa are optimal for the monolithic Charnley and optimised stems, respectively. A composite prosthesis with a layer of modulus 31 GPa added to the optimised stainless steel stem in the proximal region only was found to significantly increase the stresses in the proximal bone and reduce Kf in the cement whilst retaining the advantages of an outer stem profile very similar to that of the original Charnley prosthesis.

Bone Cements↗

PubMed1997

The influence of sizing and method of fixation on the hydrodynamic function of stentless, free-hand inserted porcine bioprosthesis: an in vitro study.

BACKGROUND AND AIMS OF THE STUDY: There is increasing interest in the use of stentless porcine bioprostheses implanted by the free-hand suturing technique. However, preservation of normal valve geometry and function is a matter of concern. This in vitro study was conducted to investigate the influence of sizing and method of fixation in glutaraldehyde on the hydrodynamic function of stentless, free-hand inserted porcine bioprosthetic valves in the aortic position. METHODS: Three sets of porcine aortic roots were used, with six specimens in each set. Group A comprised 2-3 mm larger aortic valve (oversizing) fixed in glutaraldehyde under zero pressure inserted by free-hand suturing technique in fresh aortic roots; group B comprised size-for-size placement of aortic valve fixed in glutaraldehyde under zero pressure inserted by free-hand suturing technique in fresh aortic roots; and group C comprised size-for-size placement of aortic valve fixed in glutaraldehyde under zero pressure with permanent predilatation before fixation inserted by free-hand suturing technique in fresh aortic roots (undersizing). Hydrodynamic function and leaflet bending deformations were analyzed in a modified pulsatile flow simulator which incorporated the elastic aortic roots. RESULTS: The hydraulic effective orifice area (EOA) of the valve (derived from flow and pressure measurements) was divided by actual orifice area of the annulus to determine the performance index. Although statistically non-significant, the performance index of 0.50 in group A (oversizing) was higher than that of size-for-size placement in group B (0.39). The performance index in group C of 0.41, following use of a permanent predilatation technique, was again not significantly different. The mean pressure difference during peak flow followed a correspondingly reversed order, with 11.4 mmHg in group B, 8.86 mmHg in group C, and 7.75 mmHg in group A. No significant difference was observed between the groups in terms of open leaflet bending deformations, nor was there any inter-group difference in regurgitation. CONCLUSIONS: No beneficial effect was seen to suggest that size-for-size placement was superior to the currently followed practice of over-sizing. In contrast to previous studies of whole root replacement, permanent predilatation and fixation was also not shown to have any additional advantages in a stentless scalloped free-hand inserted porcine valve.

Animals↗

PubMed1996

Retinal degeneration in mice lacking the gamma subunit of the rod cGMP phosphodiesterase.

The retinal cyclic guanosine 3',5'-monophosphate (cGMP) phosphodiesterase (PDE) is a key regulator of phototransduction in the vertebrate visual system. PDE consists of a catalytic core of alpha and beta subunits associated with two inhibitory gamma subunits. A gene-targeting approach was used to disrupt the mouse PDEgamma gene. This mutation resulted in a rapid retinal degeneration resembling human retinitis pigmentosa. In homozygous mutant mice, reduced rather than increased PDE activity was apparent; the PDEalphabeta dimer was formed but lacked hydrolytic activity. Thus, the inhibitory gamma subunit appears to be necessary for integrity of the photoreceptors and expression of PDE activity in vivo.

3',5'-Cyclic-GMP Phosphodiesterases↗

PubMed1996

Study on pharmacokinetics of radioactive labelled defibrotide after oral or intravenous administration in rats.

Defibrotide (D) was labelled with 125I or with 32P. The radiolabelled compounds ([125I]-Defibrotide ([125I]-D), [32P]-Defibrotide ([32P]-D) retained the same profibrinolytic activity, in vitro, as the parent drug, suggesting that the labelling procedures had not modified the pharmacological properties of D and hence that its chemical structure was not affected significantly. After single intravenous or oral administration of [125I]-D or [32P]-D the pharmacokinetic parameters for the two labels were generally in good agreement (75%). t 1/2 alpha was in the range of minutes while t 1/2 beta was in the range of hours. Bioavailability, following single oral administration of [125I]-D or [32P]-D, was in the range of 58-70%. These data suggest that D, in spite of its macromolecular nature, is absorbed, after oral administration, fairly well.

Administration, Oral↗

PubMed1996

Delayed repair: the role of glutathione in a rat incisional wound model.

Glutathione is a low molecular weight tripeptide that is a major intracellular antioxidant, modulates DNA synthesis, and may regulate signal transduction mechanisms. Our previous studies in rats suggested that intracellular stores of glutathione were sensitive to skin ischemia and, therefore, may regulate the early temporal course of wound healing. A 4-cm incision was placed on a rat's back and in vivo wound strength was measured over time. Animals were depleted of glutathione using L-buthionine-(S,R)-sulfoximine (BSO), an inhibitor of the enzyme gamma-glutamylcysteine synthetase. Some animals were treated in combination with allopurinol/BSO or with allopurinol alone. The data demonstrated at 4 days that BSO treatment produced a fourfold reduction in glutathione (3.51 +/- 1.78) over baseline (16.15 +/- 2.18) levels and twofold reduction (5.0 +/- 1.1) over untreated sham controls (11.1 +/- 2.3) (P < 0.05). Allopurinol provided no protection to glutathione levels. BSO treatment alone reduced wound burst strength compared to the other groups (P < 0.05). Allopurinol treatment enhanced wound strength over sham controls and BSO groups at 9 days after wounding (P < 0.05). Hydroxyproline content in wounds accumulated faster by Day 4 in the BSO-treatment groups compared to sham controls (P < 0.05), whereas the BSO-treatment groups had lower hydroxyproline levels measured at Day 6 (P < 0.05). These data provide the first evidence that wound healing is related to the temporal course of glutathione metabolism. The effect may not be related to oxidant stress since allopurinol provided enhanced wound burst strength without protecting wound glutathione levels.

Allopurinol↗

PubMed1996

RNA packaging.

Explore the source record for details and available documents.

Amino Acid Sequence↗

PubMed1996

A three-dimensional, time-dependent analysis of flow through a bileaflet mechanical heart valve: comparison of experimental and numerical results.

The flow through a bileaflet mechanical heart valve during the first half of systole was predicted using computational fluid dynamics (CFD). A three-dimensional model of the geometry of the ventricle, valve, sinus and aorta was developed. Flow through the valve was assumed to be Newtonian and laminar. The peak systolic Reynolds number was 1500 based on the aortic radius and the mean aortic velocity. Flow visualisation and laser Doppler anemometry (LDA) experiments were performed and the results were compared to the CFD model. Good agreement between the LDA measurements and CFD predictions was found in the jets through the major orifices of the valve. The global flow fields predicted by the CFD showed reasonable agreement with the flow visualisation. A starting vortex was shed from the valve leaflets of the CarboMedics valve and the prototype valve. As systole progressed the two major orifice jets were directed towards the aortic wall and a weaker central jet was seen in both the experimental and CFD models. Large vortices were present on either side of the central orifice jet in the sinus area of both models. The three-dimensional time-dependent CFD model was considered to give a reasonable indication of the dominant flow patterns downstream of the bileaflet heart valve and has the potential to be an extremely useful tool to analyse the different designs of existing and future bileaflet valves.

Aorta↗

PubMed1996

A method for shape optimization of a hip prosthesis to maximize the fatigue life of the cement.

The long term success of total joint replacement can be limited by fatigue failure of the acrylic cement and the resulting disruption of the bone-cement interface. The incidence of such problems may be diminished by reduction of the fatigue notch factor in the cement, so that stress concentrations are avoided and the fatigue crack initiation time maximized. This study describes a method for numerical shape optimization whereby the finite element method is used to determine an optimal shape for the femoral stem of a hip prosthesis in order to minimize the fatigue notch factor in the cement layer and at interfaces with the bone and stem. A two-dimensional model of the proximal end of a femur fitted with a total hip prosthesis was used which was equivalent to a simplified three-dimensional axisymmetric model. Software was developed to calculate the fatigue notch factor in the cement along the cement/stem and cement/bone interfaces and in the proximal bone. The fatigue notch factor in the cement at the cement/stem interface was then minimized using the ANSYS finite element program while constraining the fatigue notch factor at the cement/bone interface at or below its initial level and maintaining levels of stress in the proximal bone to prevent stress shielding. The results were compared with those from other optimization studies.

Algorithms↗

PubMed1996

Molecular evidence for a common leukaemic progenitor in acute mixed lymphoid and myeloid leukaemia.

De novo acute leukaemia presenting with a mixed lymphoid and myeloid leukaemic population has rarely been described. We have used the consensus Ig heavy chain primers and DNA isolated from these two distinct populations of cells in polymerase chain reactions. We demonstrated that both populations of cells exhibited Ig heavy chain gene rearrangements. Cloning and subsequent DNA sequencing of the amplified products showed a common V-D-J junctional nucleotide sequence. This work therefore provides the first evidence that the leukaemic cells in de novo acute leukaemia with a mixed lymphoid and myeloid population are derived from a common progenitor clone and may offer an explanation for the poor prognosis in these patients.

Adult↗

PubMed1996

Transmission of full-length echocardiographic images over ISDN for diagnosing congenital heart disease.

OBJECTIVES: To study the feasibility of transmitting full-length diagnostic-quality echocardiograms with video conferencing systems linked by ISDN. METHODS: Forty-three previously video-recorded full-length echocardiograms (22 complete two-dimensional Doppler studies, 21 separate M-mode studies) were transmitted from a site 30 miles distant using desktop video conferencing systems linked with one ISDN line (128 kbps). Blinded interpretations of the original recorded and transmitted studies were made by two pediatric cardiologists (two-dimensional Doppler) and a pediatric sonographer (M-mode). RESULTS: Diagnoses of normal (N = 12) and abnormal (N = 10) conditions were made from the original tapes; the same interpretations were made from the transmitted studies. Twenty-one specific abnormalities in the 10 abnormal studies were seen on both original and transmitted videotapes. These abnormalities ranged from simple congenital heart defects, including ventricular septal defect, atrial septal defect, and patent ductus arteriosus, to complex ones, such as coronary artery fistula, double-outlet right ventricle, and complete atrioventricular canal. Qualitatively, there was mild degradation in gray scale, brightness, and contrast of the images. Six M-mode variables from the transmitted images had excellent concordance with the original tracings (P = 0.506 to 0.838; r = 0.86 to 0.97). CONCLUSIONS: Although our sample size was small, this preliminary experience indicates that video conferencing equipment utilizing ISDN technology is a reliable method for transmitting full-length diagnostic-quality echocardiographic studies from remote sites. This technology may have a significant impact on the management of pediatric patients with suspected heart disease. Further evaluation is warranted.

Child↗

PubMed1996

Donor-to-host transmission of Mycoplasma hominis in lung allograft recipients.

Mycoplasma hominis is a significant pathogen in immunocompromised hosts, particularly organ transplant recipients. We describe two recipients of lung allografts from the same donor who had M. hominis pleuropulmonary infection during the immediate postoperative period. The most likely source of infection in these cases was the donor's respiratory tract. The slow-growing pinpoint colonies formed by M. hominis on routine bacterial culture medium may be easily overlooked and should be subcultured to mycoplasmal medium for definitive identification. The recommended management of this infection consists of drainage and antimicrobial therapy with tetracycline, clindamycin, or a fluoroquinolone. This report highlights the potential for M. hominis to be transmitted from donor to recipient during organ transplantation.

Adult↗

PubMed1996

Treatment of penile fibrosis with prosthetic implantation and flap advancement with tissue debulking.

PURPOSE: Even after successful penile prosthesis implantation in patients with extensive penile fibrosis, a subset will have insufficient penile length for satisfactory sexual intercourse. We report a combined surgical approach to gain additional functional length in these patients. MATERIALS AND METHODS: During the last 18 months 11 patients with extensive cavernous fibrosis underwent penile prosthesis implantation with a modified suprapubic V-Y advancement flap and lower abdominal tissue debulking. RESULTS: After prosthesis implantation the accompanying procedures allowed these patients to gain an additional 3.5 to 6.5 cm. in functional length. All patients had a functional device after a mean followup of 12 months. No prosthesis became infected and no patient required an additional flap procedure. CONCLUSIONS: This surgical approach allows patients to gain additional functional length for satisfactory intercourse after treatment of extensive penile fibrosis.

Aged↗

PubMed1996

Violence and remote area nursing.

The Federal government and others have accepted that violence is a problem in rural and remote communities across Australia. The issue of personal safety for Remote Area Nurses (RANs) living in remote areas has been mentioned in a number of State and Regional reports. However, to the knowledge of this research group, no systematic attempt to gather data on the incidence of violence experienced by RANs and other remote health workers has occurred. This study aims to redress the lack of data on the experience and description of violence against remote area nurses. Results indicate that remote area nurses are living with frequent threats to their personal safety while on duty, on call and off duty, and that violent incidents are often handled badly by employers, the community and remote area nurses themselves. Twenty-four-hour call is an employment requirement for 82% of respondents. Those required to be on call 24 hours experience episodes of violence more frequently. Despite nearly all of the respondents experiencing episodes of violence within the 12 months prior to the study, there was a tendency for remote area nurses, except in the case of physical violence, to perceive both the frequency and the severity of their experiences with violence as low and not personally directed.

Community Health Nursing↗