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Biomedical subjects

M Butterfield

Publications and source records attributed to M Butterfield.

At least 19 recordsLinked to original sources
PubMed2006

Genetic mapping in sugarcane, a high polyploid, using bi-parental progeny: identification of a gene controlling stalk colour and a new rust resistance gene.

Modern sugarcane cultivars (Saccharum spp) are highly polyploïd and aneuploid interspecific hybrids (2n = 100-130). Two genetic maps were constructed using a population of 198 progeny from a cross between R570, a modern cultivar, and MQ76-53, an old Australian clone derived from a cross between Trojan (a modern cultivar) and SES528 (a wild Saccharum spontaneum clone). A total of 1,666 polymorphic markers were produced using 37 AFLP primer combinations, 46 SSRs and 9 RFLP probes. Linkage analysis led to the construction of 86 cosegregation groups for R570 and 105 cosegregation groups for MQ76-53 encompassing 424 and 536 single dose markers, respectively. The cumulative length of the R570 map was 3,144 cM, while that of the MQ76-53 map was 4,329 cM. Here, we integrated mapping information obtained on R570 in this study with that derived from a previous map based on a selfed R570 population. Two new genes controlling Mendelian traits were localized on the MQ76-53 map: a gene controlling the red stalk colour was linked at 6.5 cM to an AFLP marker and a new brown rust resistance gene was linked at 23 cM to an AFLP marker. Besides another previously identified brown rust resistance gene (Bru1), these two genes are the only other major genes to be identified in sugarcane so far.

Basidiomycota↗
PubMed2003

Wear and deformation of ceramic-on-polyethylene total hip replacements with joint laxity and swing phase microseparation.

Wear of polyethylene and the resulting wear debris-induced osteolysis remains a major cause of long-term failure in artificial hip joints. There is interest in understanding engineering and clinical conditions that influence wear rates. Fluoroscopic studies have shown separation of the head and the cup during the swing phase of walking due to joint laxity. In ceramic-on-ceramic hips, joint laxity and microseparation, which leads to contact of the head on the superior rim of the cup, has led to localized damage and increased wear in vivo and in vitro. The aim of this study was to investigate the influence of joint laxity and microseparation on the wear of ceramic on polyethylene artificial hip joints in an in vitro simulator. Microseparation during the swing phase of the walking cycle produced contact of the ceramic head on the rim of the polyethylene acetabular cup that deformed the softer polyethylene cup. No damage to the alumina ceramic femoral head was found. Under standard simulator conditions the volume change of the moderately crosslinked polyethylene cups was 25.6 +/- 5.3 mm3/million cycles and this reduced to 5.6 +/- 4.2 mm3/million cycles under microseparation conditions. Testing under microseparation conditions caused the rim of the polyethylene cup to deform locally, possibly due to creep, and the volume change of the polyethylene cup when the head relocated was substantially reduced, possibly due to improved lubrication. Joint laxity may be caused by poor soft tissue tension or migration and subsidence of components. In ceramic-on-polyethylene acetabular cups wear was decreased with a small degree of joint laxity, while in contrast in hard-on-hard alumina bearings, microseparation accelerated wear. These findings may have significant implications for the choice of fixation systems to be used for different types of bearing couples.

Ceramics↗
PubMed2001

A new design for polyurethane heart valves.

BACKGROUND AND AIM OF THE STUDY: The synthetic flexible tri-leaflet heart valve offers considerable potential for improvement in both hydrodynamic and biomechanical performance of replacement heart valves. To date, success with the synthetic leaflet heart valve has been limited, partly due to limitations in the biostability of the polyurethanes used. With the synthesis of new biostable polyurethanes, the integration of advancing technology, and better knowledge of the functional and biomechanical design requirements necessary to increase the long-term durability of the polyurethane heart valve, novel clinical solutions are now in sight. METHODS: This study describes the design characteristics, hydrodynamic and biomechanical performance of a new design of polyurethane heart valve. The function and durability characteristics of this novel design of heart valve, manufactured using a proven durable non-biostable polyurethane, was compared with that of a single AorTech porcine bioprosthetic heart valve and a single tilting disc mechanical heart valve, the Björk-Shiley Monostrut valve (BSM), of similar size. RESULTS: For equivalent sizes of valve, the new polyurethane heart valve design had significantly lower pressure gradients compared with the porcine valve at all flow rates and to the BSM valve at the higher flow rates. The effective orifice area of the polyurethane valve was greater than the other two valves studied; regurgitation and total energy loss were less. The new polyurethane valve design reached over 360 million cycles in an accelerated durability tester, without failure. CONCLUSION: This new design of polyurethane heart valve showed improved hydrodynamic function in comparison with either the porcine bioprosthetic or the BSM mechanical heart valve. The pulsatile flow results showed a lower total energy loss associated with this valve, indicating improved potential patient benefit. The durability of this new design of polyurethane heart valve was demonstrated when manufactured using a medical-grade polyurethane.

Biomechanical Phenomena↗
PubMed2001

The influence of ventricular input impedance on the hydrodynamic performance of bioprosthetic aortic roots in vitro.

BACKGROUND AND AIM OF THE STUDY: Hydrodynamic function testing using pulsatile flow simulators provides a valuable means of comparative assessment of heart valves in vitro. The majority of pulsatile flow simulators consist of modular rigid chambers and a positive displacement pump with an infinite input impedance, in which the inertia of the test fluid results in pressure oscillations when the valves under test are opening and closing. For mechanical and stented bioprosthetic valves these pressure oscillations decay quickly. However, due to the highly compliant nature of tissue roots, the resulting pressure and flow oscillations are extreme and extend throughout systole. With increasing interest in the use of free-sewn roots and valves it is most desirable to improve this hydrodynamic model. The aim of this study was to investigate the influence in changes in ventricular input impedance on the hydrodynamic characteristics of free-sewn aortic roots and stented valves. METHODS: The Leeds pulsatile flow simulator was modified to incorporate additional compliance chambers in the form of a viscoelastic impedance adaptor (VIA) at the pump/ventricular interface. Six 23 mm bioprosthetic aortic roots fixed with 0.5% buffered glutaraldehyde at zero pressure, and a size 23 mm stented porcine aortic bioprosthesis were tested in this modified simulator, at the conditions of maximum and minimum input compliance. RESULTS: The pressure and flow waveforms for the fixed aortic roots showed considerable differences at the conditions of maximum and minimum input compliance. Indeed, the extreme pressure oscillations observed at minimum compliance (infinite input impedance) were not present at maximum compliance, and the forward flow waveform was much smoother. In contrast, for the stented valve, the differences in the pressure and flow waveforms between maximum and minimum input compliance were minimal, but this was expected due to the lack of compliance in the stented valve itself. In addition, the flow and pressure waveforms at maximum compliance in the VIA were comparable for the fixed aortic roots and the stented bioprosthesis, thus allowing direct comparison of the characteristics of these two different devices. Using test conditions of maximum input compliance, effective orifice area for the roots was 1.69 cm2 compared with 1.47 cm2 for the stented valve. CONCLUSION: An appropriate physiological model for the hydrodynamic testing of compliant tissue roots has been established.

Aortic Valve↗
PubMed2000

Atomic quadrupolar photoemission asymmetry parameters from a solid state measurement

A method for measuring the asymmetry parameter gamma arising from dipole-quadrupole interference in core-level photoemission is proposed which is based on condensed thin films and exploits the influence of this asymmetry in photoemission monitoring of x-ray standing wave field absorption. The high density of material in this method offers some advantages over a conventional gas-phase measurement. Results are presented for C, O, and F 1s photoemission at photon energies around 3 keV. The combined nondipole asymmetry factor (delta+gamma/3) for non- s-states can be determined in a similar way.

Journal Article↗
PubMed2000

Relation of regional fat distribution to insulin sensitivity in postmenopausal women.

OBJECTIVE: To examine the relation between insulin sensitivity and total and regional body fat in nonobese postmenopausal women. DESIGN: Cross-sectional study. SETTING: A clinical research center. PATIENT(S): Twenty-seven women in the early postmenopausal period, with a mean (+/-SD) age of 50.8 +/- 4.1 years, who had had their last menstrual period 6 months to 3 years before the study. None were taking hormone replacement therapy, and all had an FSH level of >35 mIU/mL, a body mass index of <30 kg/m2, and a waist circumference of <94 cm. INTERVENTION(S): Computed tomography scans at the L4-5 vertebral disk space, dual-photon x-ray absorptiometry scans, and euglycemic hyperinsulinemic clamps were performed. MAIN OUTCOME MEASURE(S): Intraabdominal fat, subcutaneous abdominal fat, sagittal diameter, total body fat, percent body fat, and insulin sensitivity. RESULT(S): The natural log of insulin sensitivity correlated significantly with intraabdominal fat (r = -.39), subcutaneous fat (r = -.43), and sagittal diameter (r = -.48). After adjusting for total fat, sagittal diameter remained significantly related to insulin sensitivity. CONCLUSION(S): Central abdominal fat is inversely and independently related to insulin sensitivity after adjusting for total fat in women in the early postmenopausal period. Efforts to reduce either subcutaneous abdominal fat or intraabdominal fat should be helpful in reducing the risk of noninsulin-dependent diabetes mellitus in postmenopausal women.

Abdomen↗
PubMed2000

Fatigue analysis of clinical bioprosthetic heart valves manufactured using photooxidized bovine pericardium.

BACKGROUND AND AIM OF THE STUDY: Recent reports have given details of early clinical failures of bioprosthetic heart valves manufactured using dye-mediated photooxidized bovine pericardium. These failures were attributed to abrasion of the inflow surface of the leaflets against the cloth-covered inner face of the outer valve frame. These failures had not been detected during preclinical testing of such valves. The aim of this study was to determine if such failure modes could be replicated during fatigue testing of the photooxidized valves, and whether lining of the inflow face of the outer frame with pericardium could eliminate these failures. METHODS: The fatigue properties of six lined and six unlined PhotoFix(R) alpha valves was determined using two Rowan Ash fatigue testers which were cycled at 15 Hz for a maximum of 210 million cycles. The closing pressure within in each chamber was 110+/-10 mm Hg. Each valve was inspected every 40 million cycles for any signs of fatigue failure. All valves were tested to at least 210 million cycles. RESULTS: In all six lined PhotoFix alpha valves there was no evidence that wear, tear or abrasion of the inflow aspect of the leaflets adjacent to the inflow face of the outer frame had occurred. Only one unlined valve showed any signs of damage adjacent to the outer frame, as evidenced by loss of loose connective tissue, but this did not have the imprint of the cloth covering, which would have suggested actual wear. Effectively, after 200 million cycles, no fatigue failures of either the lined or the unlined PhotoFix alpha valves had occurred. Moreover, the leaflet tears that had been observed clinically were not replicated in this study. CONCLUSION: Previous studies have shown a good qualitative, quantitative association between fatigue failure in Rowan Ash accelerated fatigue testers, and clinical experience in glutaraldehyde-treated bovine pericardial valves. The accelerated fatigue tester did not provide an adequate model for the prediction of clinical failure for the photooxidized pericardial valves.

Bioprosthesis↗
PubMed1998

The reported training and experience of editors in chief of specialist clinical medical journals.

CONTEXT: The majority of the peer-reviewed clinical literature is edited by editors whose training in editorial matters may be limited or nonexistent. We suspect that editors are selected for their clinical or academic rather than editorial ability. OBJECTIVE: To test the hypothesis that editors of medical specialist clinical journals were recruited from active clinicians rather than those with evident ability or training as editors. DESIGN, SETTING, AND SUBJECTS: Anonymous mail survey to editors of the 262 peer-reviewed clinical journals that had received at least 1000 citations in the 1994 Science Citation Index. MAIN OUTCOME MEASURES: Training and editorial practices of editors. RESULTS: Replies were received from 191 editors (73%): in 1994 the journals they edited had 6060 (27300/1000 [maximum/minimum]) citations, 234 (740/31) source items, and an impact factor of 2.10 (18.3/0.2); nonresponders' journals had similar characteristics. Of the responding editors, 181 (95%) were part-time, 132 (69%) treated patients, and 164 (86%) were recruited by one of the following methods: election by a scientific society (49 [30%]), nomination by the previous editor (41 [25%]), or response to an advertisement (29 [18%]). There was no strong association between method of recruitment or formal editorial training and the status of the journal. Only 9% of editors in the United States send at least half of the papers to reviewers outside their own country, compared with 41% of editors in the United Kingdom and 73% in other countries, and 69% do not feel bound to follow the advice they receive concerning acceptance of papers. CONCLUSIONS: Clinical journals are usually edited by practicing clinicians who are self-taught part-time editors, but willing to accept further training. They usually consult 2 reviewers, but exercise independent judgment on the acceptability of papers.

Peer Review↗
PubMed1996

Why the Urgency for Earlier Diagnosis of HIV Infection in Women?

As our perspective of AIDS changes from a disease that affects homosexual men and intravenous drug abusers to one that spreads increasingly through heterosexual contact, greater numbers of women are being diagnosed with HIV infection. Because clinicians still may perceive AIDS to be primarily a "male" disease and may maintain a low level of suspicion of it in their female patients, HIV infection is believed to be underdiagnosed and go unrecognized for longer periods in women than in men. Early reports in the 1980s that showed a worse prognosis and shorter median survival for women than for men are now explained by factors such as later presentation and diagnosis, disparity in access to care, and reluctance of clinicians to prescribe zidovudine to pregnant patients. Recent studies show that, with early identification of infection and subsequent treatment and prophylactic therapy, there are no differences in disease progression or survival in women compared with men. Moreover, from a public health standpoint, earlier diagnosis can decrease incidence of both sexual and vertical transmission. Women may choose to undergo tubal ligation to prevent future vertical transmission; additionally, zidovudine now is used in pregnant women and has been demonstrated to decrease transmission rates from 25% to 8%

Journal Article↗
PubMed1995

Information on marketed drugs for doctors and patients. Experience in six European countries.

This article describes a project that looked at the availability of information on marketed pharmaceutical products to doctors and patients in six European countries. It examines the legal status of the drug compendia published in each country and reports on the implementation of EC Directive 92/27/EEC on labeling and packaging. A small survey showed that it is hard to compare patient information because it is difficult to obtain copies of pack inserts available in each country. However, a limited analysis revealed some differences in the content and presentation of data for doctors and patients.

Drug Industry↗
PubMed1993

Geometry of homograft valve leaflets: effect of dilation of the aorta and the aortic root.

With the increasing interest in aortic homografts as either a free-sewn valve or whole-root replacement, the effect of internal pressure and dilation of the aorta and aortic root on valve leaflet geometry has been studied. Seven aortic homograft roots were studied, six that had been stored in antibiotics and one that had been cryopreserved. The diameter of the aorta was determined as a function of internal pressure and correlated with the stress-strain characteristics of the aortic wall. Three-dimensional leaflet surface geometry was measured in the "neutral" position, and the leaflet was characterized by its radius of curvature and angle of inclination, using a cylindrical model. The diameter of the aorta increased by between 30% and 50% as the dilation pressure increased from 0 to 120 mm Hg. This was consistent with the stress-strain data obtained from strips of the aortic wall in the circumferential direction. The angle of inclination of the leaflet increased from 20 to 80 degrees and the radius of curvature increased from 4 to 17 mm as the internal pressure increased from 0 to 80 mm Hg. The open leaflet configuration showed a triangular orifice with low bending strains for a dilated root, but increased bending strains with reduced dilation pressure. These are important considerations when implanting a free-sewn homograft into the aortic root.

Adult↗
PubMed1993

Frame-mounted porcine valve bioprostheses: preparation during aortic-root dilation. Biomechanics and design considerations.

The leaflet geometry and function of frame-mounted porcine bioprostheses prepared with dilation of the aortic root during frame mounting was investigated. The diameter of the porcine aortic root increased by 47% when dilated with a pressure of 120 mm Hg. In the absence of pressure dilation, the ratio of circumferential leaflet length to the radius of the aortic root (S/RA) was 2.7 +/- 0.1, and the angle of inclination of the leaflet to the base of the valve was 17 +/- 4.3 degrees. In this condition, the leaflet geometry was similar to that of some second-generation porcine bioprostheses, which demonstrated high open-leaflet bending strains at the commissures. Dilation of the porcine root with 120 mm Hg reduced the value of S/RA to 1.84 and produced a triangular open-leaflet configuration with minimum open-leaflet bending strains. Open-leaflet bending strains were also reduced in two prototype frame-mounted valves prepared with partial dilation of the aortic root, which had an S/RA ratio of less than 2.3 and a leaflet angle greater than 27 degrees. The study indicates that the next generation of porcine bioprostheses should be prepared with at least 17% dilation of the aortic root during frame mounting and with zero pressure difference across the leaflets during fixation. This can be achieved by applying an equal hydrostatic pressure to both sides of the valve leaflets during fixation and frame mounting.

Animals↗
PubMed1992

Carbomedics and St. Jude Medical bileaflet valves: an in vitro and in vivo comparison.

The hydrodynamic and haemodynamic function of 29 mm mitral and 23 mm aortic St Jude Medical (SJM) and CarboMedics (CM) heart valves have been compared in a pulsatile flow simulator in the laboratory and by doppler ultrasound in vivo. The laboratory studies showed that there was no significant difference in the pressure drop across the valves. The valves also had similar regurgitant volumes. Doppler ultrasound confirmed these results with a mean pressure drop of 12.9 +/- 5.5 mmHg across the CM aortic valves and 12.6 +/- 5.5 mmHg for the SJM aortic valves. The mean mitral diastolic pressure drops were 3.8 +/- 1.8 and 4.6 +/- 1.4 mmHg for the CM and SJM valves, respectively. Mild aortic regurgitation was detected in 5 of 14 patients in the CM group and 1 out of 6 patients in the SJM group, though none of the cases were clinically significant. Both the in vitro and in vivo results show these valves to have acceptable and comparable function.

Aortic Valve↗
PubMed1992

The hydrodynamic function and leaflet dynamics of aortic and pulmonary roots and valves: an in vitro study.

Fresh homograft aortic and pulmonary roots were tested in a pulsatile flow simulator to assess their hydrodynamic function and leaflet opening characteristics. Simultaneous flow and pressure measurements were obtained for a range of cardiac outputs. The effective orifice area and regurgitant volumes were calculated. The mean pressure difference across the pulmonary roots was obtained under both left and right side pressures. A video recording of valve leaflet function was also obtained for each valve. A comparison was made with four porcine bioprosthetic heart valves (21 and 23 mm). The mean pressure difference with respect to flow for the 21 mm Hancock II and Intact porcine bioprostheses was significantly higher than that for all aortic roots tested. The 24 mm aortic root showed significantly lower pressure drop compared to all porcine valves tested. The mean pressure difference across each pulmonary root at pulmonary pressures was significantly greater than at systemic pressures. At systemic pressures the fully open leaflets had a triangular orifice with low leaflet open bending strains at the commissures. At the lower internal pressures, with reduced dilation of the root, higher bending strains were noted. These were not as severe as seen in porcine valves.

Adult↗
PubMed1992

A model of the geometrical changes in aortic valve leaflets in response to leaflet extension and variable boundary conditions.

The function, deformation and performance of heart valve leaflets are dependent on the material properties and the geometry of the leaflet. As the leaflet acts as a constrained membrane the geometry is dependent on the boundary condition applied to the leaflet and any permanent extension of the leaflet. Both of these factors are varied during the preparation of frame-mounted porcine bioprosthetic heart valves and surgical insertion of free-sewn valves. This can result in abnormal geometry and function. A mathematical model has been developed which describes these changes in geometry of a cylindrical leaflet as a function of the diameter of the aortic root (boundary conditions) and the length (or permanent extension) of the leaflet. Both the angle of inclination and the radius of curvature of the cylindrical leaflet were reduced with increased leaflet length or decreased aortic diameter. Agreement was found between the model predictions and experimental observations in porcine bioprosthetic heart valves, where abnormal leaflet geometries are produced by non-physiological boundary conditions and permanent set of the leaflets by fixation with glutaraldehyde. The general solutions developed in this model allow leaflet geometries to be predicted for a range of conditions in free-sewn and frame-mounted valves.

Animals↗
PubMed1991

Comparative study of the hydrodynamic function of the CarboMedics valve.

The hydrodynamic function of each size of the CarboMedics valve was assessed in a pulsatile flow simulator. The mean pressure difference with respect to forward flow, regurgitant volumes, and total energy loss across each valve were analyzed. The results for the 23-mm aortic and 29-mm mitral CarboMedics valves were compared with those for the St. Jude Medical and Björk-Shiley Monostrut valves. Results showed good hydrodynamic function for each CarboMedics valve, although the pressure difference and total energy loss across the 19-mm aortic valve was high. The hydrodynamic function of the CarboMedics valve was comparable with that of the St. Jude Medical valve. Both valves showed similar leakage volumes, which were significantly larger than that for the Björk-Shiley Monostrut valve. On account of this the total energy loss in the Björk-Shiley valve was significantly less than that for the bileaflet valves in the aortic position. Concern remains for the continuing presence of high closed-valve regurgitation in the bileaflet valves.

Aortic Valve↗
PubMed1991

Leaflet geometry and function in porcine bioprostheses.

The leaflet geometry and hydrodynamic function of five porcine bioprostheses have been studied and compared to a fresh tissue porcine valve. The neutral leaflet geometries in two high pressure fixed valves (Carpentier Edwards and Hancock) and two low pressure fixed valves (Carpentier Edwards Supra-Annular and Hancock 2) had been modified during fixation and mounting. The leaflets were extended or displaced downwards towards the base of the valve, producing a higher ratio of circumferential leaflet length to inter-commissural spacing than in the fresh tissue valve. This produced high bending strains in the commissural area of the open leaflet in hydrodynamic tests. The leaflet geometry of the fresh tissue porcine valve studied was defined by a cylindrical shell inclined at approximately 27 degrees to the base of the valve and showed reduced open leaflet bending strains. Leaflet opening at low flows was dependent on leaflet geometry. Geometrical changes which are induced during mounting and fixation produced higher bending strains in the commissural area of the open leaflets. These may be contributing factors to tissue degeneration and calcification in this area.

Bioprosthesis↗