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Biomedical subjects

R Curtis

Publications and source records attributed to R Curtis.

At least 19 recordsLinked to original sources
PubMed2006

Augmentation of implant purchase with bone cements: an in vitro study of injectability and dough distribution.

Vertebroplasty is widely used to treat (augment) osteoporotic fractures of the spine. This technique--with or without metallic implants--might have more widespread indications, if the mechanics of the injection and distribution of the cement dough through cannulated instruments and implants were better understood. This study was performed to investigate injectability of calcium phosphate and acrylic bone cements through implant prototypes, which featured different perforated sleeve designs. Using a custom-made capillary rheometer, the forces needed to inject 10 mL of the cement dough through standard cannulas were measured in the first series of experiments. In the second series, plastic sleeves were attached to the rheometer, simulating the implant. In both series, the dough was injected into ambient laboratory atmosphere, and in the second series, cement distribution was analyzed by means of an optical system. Injection of cement dough through the cannulas required forces between 50 and 400 N in the case of acrylic cements and between 40 and 500 N in case of the calcium phosphate cements. Using different sleeves did not have a significant influence on the distribution of the cement dough around the sleeve. The amount of cement dough injected was reduced when a perforated implant was attached to the cannula. More material was delivered through the proximal holes of the implant, leading to a V-shaped distribution of the cement dough. Among topics to be investigated in future studies is determination of the injectability of cement dough into trabecular bone or bone-like structures.

Biocompatible Materials↗
PubMed2006

Augmentation of osteoporotic bone: effect of pulsed jet-lavage on injection forces, cement distribution, and push-out strength of implants.

Demographic change in the population leads to higher incidence of fragility fractures. Fracture fixation with standard implants may lead to implant cut-out due to reduced purchase. Augmentation of the bone stock with bone cements might overcome this problem. However, cancellous bone infiltration with the viscous cement dough reveals problems of fat embolism or high pressures during application of the cement. This study investigates the improved quality of bovine cancellous bone augmentation when pulsed jet-lavage is used for fat and marrow removal. Parameters such as injection forces, cement dough distribution through cannulated implants and mechanical strength of the fixation were applied for quantification. Injection of 5 mL of acrylic bone cement required significantly lower forces in the lavaged as compared to the untreated bone (50 N vs. > 300 N). Cement distribution was much more homogeneous and push-out forces significantly higher in the pretreated bone group (8.33 +/- 1.41 kN vs. 1.66 +/- 0.63 kN). The application of pulsed jet-lavage for fat removal prior to acrylic cement augmentation led to much more controlled outcomes of the augmentation. This seems to be a relevant step towards safe and efficient injection of bone cements into cancellous bone structures.

Bone Cements↗
PubMed2006

Reducing transfer times for coronary angiography in patients with acute coronary syndromes: one solution to a national problem.

BACKGROUND: Patients with acute coronary syndrome (ACS) are at high risk of further cardiac events and benefit from early intervention, as reflected by international guidelines recommending early transfer to interventional centres. The current average waiting time of up to 21 days contravenes evidence based early intervention, creates geographical inequity of access, wastes bed days, and is unsatisfactory for patients. METHODS: A regional transfer unit (RTU) was created to expatriate access of ACS patients referred from other centres to the revascularisation service. By redesigning the care pathway patients arriving on the RTU undergo angiography within 24 hours, and then leave the RTU the following day, allowing other ACS patients to be treated. RESULTS: During the first six months of the RTU, the mean waiting time from referral to procedure decreased from 20 (SD 15) days (range 0-51) to 8 (SD 3) days (range 0-21) for 365 patients transferred from a district general hospital. Ninety seven per cent of patients underwent angiography within 24 hours, 61% having undergone percutaneous coronary intervention at the same sitting, and 78% were discharged home within 24 hours. CONCLUSIONS: Delivering standards laid out in the National Service Framework, reducing inequalities of care across the region, and facilitating evidence based strategies of care represents a challenging and complex issue. For high risk patients suffering ACS who need early invasive investigation, a coordinated network wide approach together with the creation of an RTU resulted in a 62% reduction in waiting times for no extra resources. Further improvements can be expected through increased capacity of this verified strategy.

Angioplasty, Balloon, Coronary↗
PubMed2004

Fixation principles in metaphyseal bone--a patent based review.

Osteoporotic changes start in cancellous bone due to the underlying pathophysiology. Consequently, the metaphyses are at a higher risk of "osteoporotic" fracture than the diaphysis. Furthermore, implant purchase to fix these fractures is also affected by the poor bone quality. In general, researchers and developers have worked on three different approaches to address the problem of fractures to osteoporotic bone: adapted anchoring techniques, improved load distribution as well as transfer with angular stable screws, and augmentation techniques using bone substitutes. A patent-based review was performed to evaluate which ideas were utilized to improve fixation in osteoporotic, metaphyseal bone, especially in the proximal femur, and to analyze whether the concept had entered clinical use. Anchoring devices that are either extramedullary or intramedullary have a long clinical history. However, demanding surgical techniques and complications, especially in poor quality bone, are justification that such implants and their corresponding surgical techniques need to be improved upon. Expanding elements have been evaluated in the laboratory. The results are promising and the potential of this approach has yet to be fully exploited in the clinics. Internal fixators with angular stable screws open the door for many new anchorage ideas and have great potential for further optimization of load distribution and transfer. Augmentation techniques may improve anchorage in osteoporotic bone. However, the properties of bone substitute materials will need to be modified and improved upon in order to meet the demanding requirements. If we summarise the development process and the clinical use of implants to date, we have to clearly state that more factors than simply biomechanical advantage will determine the clinical success of a new fixation principle or a new implant. Instead, fracture treatment of patients with osteoporosis really needs an interdisciplinary approach!

Bone Nails↗
PubMed2004

The role of perceived and actual disease status in adjustment to rheumatoid arthritis.

OBJECTIVES: To examine the role and relative impact of illness perceptions, coping strategies and clinical disease indicators on adjustment in patients with rheumatoid arthritis. METHOD: Participants were 75 women with rheumatoid arthritis. The Illness Perception Questionnaire (IPQ), the COPE questionnaire and the Arthritis Impact Measurement Scale (AIMS) were administered during a semistructured interview. Disease status was indicated by physician ratings of joint involvement and by the laboratory indices of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). RESULTS: Statistically significant correlations (P<0.01) were in the expected direction. Various aspects of adjustment (good physical function, low pain and depression) were associated with perceptions of low illness identity, high control/cure, more serious illness consequences and long illness timeline. Low disease activity was related to good physical function. Depression was associated with high use of coping by denial and with less frequent use of five COPE strategies: active coping, planning, seeking instrumental social support, positive reinterpretation and growth, and acceptance. In hierarchical regression analysis, disease status explained variance in physical function (15%). Illness perceptions accounted for variance in all three adjustment outcomes, ranging from 22 to 27%. Coping variables did not add to the explanation of variance on adjustment. CONCLUSIONS: Illness perceptions have significant implications for adaptation to illness and they outweigh the impact of medical disease status on depression, physical function and pain. Health interventions based on understanding and modifying perceptions of illness may prove useful in facilitating patient well-being.

Adaptation, Psychological↗
PubMed2004

The potential signalling pathways which regulate surface changes induced by phytohormones in the potato cyst nematode (Globodera rostochiensis).

It has been demonstrated that the surface lipophilicity of the plant-parasitic nematode Globodera rostochiensis decreases when infective larvae are exposed to the phytohormones indole-3-acetic acid (auxin) or kinetin (cytokinin). In the present study, it was shown that inhibition of phospholipase C (PLC) or phosphatidylinositol 3 kinase (PI3-kinase) reversed the effect of phytohormones on surface lipophilicity. The signalling pathway(s) involved in surface modification were investigated using 'caged' signalling molecules and stimulators or inhibitors of different signalling enzymes. Photolysis of the 'caged' signalling molecules, NPE-caged Ins 1,4,5-P3, NITR-5/AM or caged-cAMP to liberate IP3, Ca2+ or cAMP respectively, decreased the surface lipophilicity. Activation of adenylate cyclase also decreased the surface lipophilicity. In contrast, inhibition of PI3-kinase using Wortmannin, LY-294002 or Quercetin, and inhibition of PLC using U-73122 all increased the surface lipophilicity. Two possible signalling pathways involved in phytohormone-induced surface modification are proposed.

Adenine↗
PubMed2004

A comparative study of the static and kinetic frictional resistance of titanium molybdenum alloy archwires in stainless steel brackets.

This ex vivo study compared the static and kinetic frictional resistance of eight different archwires tested in a single, stainless steel, zero base 0.022 x 0.028 inch (0.56 x 0.711 mm) slot standard edgewise bracket. The archwires evaluated were 0.019 x 0.025 inch (0.483 x 0.636 mm) in dimension, manufactured from the following alloys: beta titanium (TMA), 'low friction' coloured beta titanium (aqua, honeydew, purple and violet), ion-implanted beta titanium, Timolium and a stainless steel control. Prior to friction testing, bracket and archwire dimensions were measured by direct digital imaging via a desktop computer linked to a binocular light microscope. Frictional force was evaluated using an Instron universal testing machine. All experiments were carried out at room temperature, with no ligation, in the dry state with 20 degrees of added torque. The results demonstrated that static and kinetic friction were statistically significant (P < 0.001) for all archwire types. Ion-implanted and standard TMA archwires were found to have no significant advantage over stainless steel. The archwire alloys may be ranked as follows: stainless steel produced the lowest frictional resistance followed by honeydew, ion-implanted TMA and Timolium, with aqua, purple and violet producing frictional resistance values as high as standard TMA. It was also found that the percentage difference between the archwire and bracket slot dimensions claimed by the manufacturers and those measured in this experiment produced tolerances ranging from +5.37 to -6.67 per cent.

Analysis of Variance↗
PubMed2002

Monoclonal antibodies reactive with secreted-excreted products from the amphids and the cuticle surface of Globodera pallida affect nematode movement and delay invasion of potato roots.

This paper describes Excreted-secreted proteins (ES) proteins that were immunolocalised in the cuticle, amphids and subventral glands of second stage juveniles of the two species of potato cyst nematodes (Globodera pallida and Globodera rostochiensis). Monoclonal antibodies reactive with these ES proteins were used in a bioassay to investigate their effect on nematode movement and on their ability to invade potato roots. Antibodies recognising the nematode cuticle surface and the amphids affected nematode movement and delayed nematode penetration of roots. These effects were temporary, since the nematodes were able to recover and infect potato roots. Movement of second stage juveniles treated with the antibodies was impaired for the first 30 min after inoculation: the juveniles remained close to the point of introduction and moved slowly and abnormally. They recovered normal movement after 1-2 h, possibly because the turnover rate of the secreted proteins meant that they were no longer blocked by the monoclonal antibodies. No effect was observed on second stage juveniles treated with an antibody reactive with secretions from the oesophageal glands. Nematodes treated with antibodies reactive with the nematode cuticle surface were notably more affected than those treated with other antibodies; nematodes failed to recover movement when in continuous contact with the antibodies. It is possible that the physical presence of the antibodies on the nematode surface affected their motility. Nematodes treated with antibodies reactive with secretions from the amphids were temporarily unable to move towards potato roots and their exploratory behaviour was greatly affected by the antibody treatment. Whether these antibodies were able to inhibit temporarily the function of the amphids or this effect was due to physical presence of the antibodies blocking the amphidial pore remains to be determined.

Animals↗
PubMed2002

Effects of phytohormones on the surfaces of plant-parasitic nematodes.

The direct effects of phytohormones (auxin and kinetin) and root diffusates on the surface lipophilicity of the plant parasitic nematodes Globodera rostochiensis and Meloidogyne incognita were investigated. The fluorescent lipid probe AF18 (5-N(octodecanoyl) aminofluorescein) was used to detect surface changes. Root diffusates increased AF18 uptake by G. rostochiensis while it had no effect on M. incognita. Kinetin and auxin decreased AF18 uptake in G. rostochiensis, while they had the opposite effect on M. incognita. Auxin/kinetin ratio was also found to be important in triggering the surface changes, especially at high concentrations. Whether plant nematodes have auxin and/or kinetin binding proteins is discussed as well as the mechanism behind the surface lipophilicity changes due to root diffusates and phytohormones.

Adenine↗
PubMed2002

Consistent condom use among drug-using youth in a high HIV-risk neighbourhood.

The objectives of this study were to determine predictors of consistent condom use in heterosexual relationships of young adults who use hard drugs in a neighbourhood with widespread drug-use-connected HIV. We interviewed 196 18-24 year olds who injected drugs or used heroin, cocaine or crack in the prior year and lived in the Bushwick neighbourhood of New York City. Interviews covered sociodemographics, substance use and sexual networks. The unit of analysis is the relationship; the dependent variable measures consistent condom use over the prior 30 days in a given relationship. Consistent condom use was reported in 26% of 377 non-commercial relationships and in all of 22 commercial relationships. Using multiple logistic regression, consistent condom use in non-commercial relationships was more likely in relationships that are not 'very close'; for men (but not women) with peers whose norms are more favourable to condom use; and for subjects who had concurrent sex partners in the last 12 months. In conclusion, we found that: (1) the lack of relationship between the peer norms of drug-using women and their condom use suggests they may have little control over condom use in their relationships-programmes should attempt to empower young women drug users and to develop ways for their peers to influence the men in their lives; (2) epidemiologically, the positive association of concurrency to consistent condom use suggests that condom use may be restricting HIV spread through the community-the presence of consistent condom use in all of the commercial sexual relationships also may restrict HIV spread; (3) prevention efforts should attempt to change peer cultures as a way to develop self-sustaining risk reduction. These changes should include changes in gender roles and power relations.

Adult↗
PubMed2001

Prevalence and correlates of anal sex with men among young adult women in an inner city minority neighborhood.

In a population-representative sample of 202 18-24-year-old women in a neighborhood with widespread injection of drugs and HIV, 14% reported unprotected anal sex with men in the past year. Independent significant predictors were illegal drug use, having a main partner who takes the lead in deciding what to do during sex, and less self-deception. Having ever had anal sex was associated with having ever been infected with hepatitis B.

Adolescent↗
PubMed2001

The quality and isolation of habitat patches both determine where butterflies persist in fragmented landscapes.

Habitat quality and metapopulation effects are the main hypotheses that currently explain the disproportionate decline of insects in cultivated Holarctic landscapes. The former assumes a degradation in habitat quality for insects within surviving ecosystems, the latter that too few, small or isolated islands of ecosystem remain in landscapes for populations to persist. These hypotheses are often treated as alternatives, and this can lead to serious conflict in the interpretations of conservationists. We present the first empirical demonstration that habitat quality and site isolation are both important determinants of where populations persist in modern landscapes. We described the precise habitat requirements of Melitaea cinxia, Polyommatus bellargus and Thymelicus acteon, and quantified the variation in carrying capacity within each butterfly's niche. We then made detailed surveys to compare the distribution and density of every population of each species with the size, distance apart and quality of their specific habitats in all their potential habitat patches in three UK landscapes. In each case, within-site variation in habitat quality explained which patches supported a species' population two to three times better than site isolation. Site area and occupancy were not correlated in any species. Instead of representing alternative paradigms, habitat quality and spatial effects operate at different hierarchical levels within the same process: habitat quality is the missing third parameter in metapopulation dynamics, contributing more to species persistence, on the basis of these results, than site area or isolation. A reorientation in conservation priorities is recommended.

Animals↗
PubMed2001

Sodium channel beta1 and beta3 subunits associate with neurofascin through their extracellular immunoglobulin-like domain.

Sequence homology predicts that the extracellular domain of the sodium channel beta1 subunit forms an immunoglobulin (Ig) fold and functions as a cell adhesion molecule. We show here that beta1 subunits associate with neurofascin, a neuronal cell adhesion molecule that plays a key role in the assembly of nodes of Ranvier. The first Ig-like domain and second fibronectin type III-like domain of neurofascin mediate the interaction with the extracellular Ig-like domain of beta1, confirming the proposed function of this domain as a cell adhesion molecule. beta1 subunits localize to nodes of Ranvier with neurofascin in sciatic nerve axons, and beta1 and neurofascin are associated as early as postnatal day 5, during the period that nodes of Ranvier are forming. This association of beta1 subunit extracellular domains with neurofascin in developing axons may facilitate recruitment and concentration of sodium channel complexes at nodes of Ranvier.

Aging↗
PubMed2001

Differential modulation of sodium channel gating and persistent sodium currents by the beta1, beta2, and beta3 subunits.

Brain sodium channels are complexes of a pore-forming alpha subunit with auxiliary beta subunits, which are transmembrane proteins that modulate alpha subunit function. The newly cloned beta3 subunit is shown to be expressed broadly in neurons in the central and peripheral nervous systems, but not in glia and most nonneuronal cells. Beta1, beta2, and beta3 subunits are coexpressed in many neuronal cell types, but are differentially expressed in ventromedial nucleus of the thalamus, brain stem nuclei, cerebellar Purkinje cells, and dorsal root ganglion cells. Coexpression of beta1, beta2, and beta3 subunits with Na(v)1.2a alpha subunits in the tsA-201 subclone of HEK293 cells shifts sodium channel activation and inactivation to more positive membrane potentials. However, beta3 is unique in causing increased persistent sodium currents. Because persistent sodium currents are thought to amplify summation of synaptic inputs, expression of this subunit would increase the excitability of specific groups of neurons to all of their inputs.

Animals↗
PubMed2001

Consistent condom use in the heterosexual relationships of young adults who live in a high-HIV-risk neighbourhood and do not use "hard drugs".

This study was set up to determine the predictors of condom use in the heterosexual non-commercial sexual relationships of young adults who neither inject drugs nor use cocaine, heroin or crack, in a neighbourhood with widespread drug-use-connected HIV. The analytic sample is 279 young adults, aged 18-24, who have never injected drugs and who have not used heroin, cocaine or crack in the last year. They were recruited in the Bushwick neighbourhood of New York City, July 1997 to September 1999. A face-to-face interview included items about their sociodemographic background, substance use and sexual networks. Sexual relationship and self-reported consistent (100%) condom use over the prior year with the partner in a given relationship was examined. Subjects had 337 heterosexual non-commercial relationships. Consistent condom use was reported in 32% of these relationships. In multiple logistic regression, consistent condom use was more likely in relationships that are not 'very close' (odds ratio = 3.92; 95% confidence interval = 2.08, 7.52); in the relationships of subjects whose peer norms support condom use (OR = 1.94; 95% CI = 1.43, 2.69), who are not problem drinkers (OR = 8.70; 95% CI = 2.22, 58.8), and (perhaps as a result of measurement issues) who are men (OR = 1.95; 95% CI = 1.04, 3.68). In conclusion, consistent condom use remains uncommon among youth in this high-risk neighbourhood. It is thus important to keep HIV from entering the sexual networks of youth in communities like this through programmes aimed at drug injectors and their sexual partners. Programmes to increase condom use among young adults should focus on strengthening norms that promote safer sex to protect oneself and others. In addition, assistance should be provided to youth who are problem drinkers.

Adolescent↗