Biomedical subjects

E W Abel

Publications and source records attributed to E W Abel.

At least 19 recordsLinked to original sources

PubMed2004

Effect of temperature on the surface free energy of amorphous carbon films.

Diamond-like carbon (DLC) and tetrahedral amorphous carbon (ta-C) have attracted much attention recently for biomedical and antifouling applications due to their excellent biocompatibility and inherent nonstick properties. It has been demonstrated that the solid surface free energy is a dominant factor in cellular or fouling adhesion. However, few data for the surface free energy of DLC and ta-C coatings at temperatures in the range 37-95 degrees C are available. In this study DLC and ta-C coatings on stainless steel 304 sheets were prepared using an unbalanced magnetron sputtering system and a filtered cathodic vacuum arc system, respectively. The contact angles of water, diiodomethane and ethylene glycol on the coated surfaces at temperatures in the range 20-95 degrees C were measured using a Dataphysics OCA-20 contact angle analyzer. The surface free energy of the coatings and their components (e.g., dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the total surface free energy and dispersive surface free energy of the ta-C coatings, DLC coatings, stainless steel 304 and titanium decreased with increasing surface temperature, while the acid-base SFE component increased with increasing temperature.

Journal Article↗

PubMed2003

A study of whole blood platelet and white cell aggregation using a laser flow aggregometer.

Both platelet aggregation and white blood cell aggregation are involved in pathological processes such as thrombosis, atherosclerosis and chronic inflammation. People in older age groups are likely to suffer from cardiovascular diseases and may have increased white cell and platelet aggregation which could contribute to this increased risk. This study aimed to compare white cell and platelet aggregation between different age and gender groups. Whole blood white cell aggregation and platelet aggregation were carried out on healthy volunteers using cytometric techniques. It was found that both white cell and platelet aggregation in the elderly group (white cell aggregation median value, 0.08; range, 0.02-0.14; platelet aggregation median value, 0.32; range, 0.1-0.39) were significantly higher (P = 0.017 for white cell aggregation, P = 0.007 for platelet aggregation) than in the younger group (white cell aggregation median value, 0.05; range, 0.01-0.14; platelet aggregation median value, 0.18; range, 0.07-0.36). No significant differences were found between the gender groups.

Adult↗

PubMed2001

A finite element analysis of hollow stemmed hip prostheses as a means of reducing stress shielding of the femur.

Stress shielding of the femur is known to be a principal factor in aseptic loosening of hip replacements. This paper considers the use of a hollow stemmed hip implant for reducing the effects of stress shielding, while maintaining acceptably low levels of stress in the cement. Using finite element modelling, the stresses in the proximal femur using different shapes of hollow stem were compared with those produced using comparable sizes of solid stem with different values of elastic modulus. A reduction in stress shielding could be achieved with a hollow stem. A cylindrical hollow stem design was then optimised in order to control the maximum allowable stress in the cement, the minimum allowable stresses in the bone, and a combination of the two. The resulting stems achieved an increase in proximal bone stress of about 15% for the first case and 32% for a model using high strength cement, compared with solid stems of the same nominal outside diameter. The gains of these theoretically optimised designs dropped off rapidly further down the stem. Linearly tapered hollow stems reached a 22% gain, which could be a good compromise between acceptable cement stresses and ease of manufacture.

Femur↗

PubMed2001

Effects of draining cochlear fluids on stapes displacement in human middle-ear models.

Displacement-frequency characteristics of the stapes footplate were measured in five human temporal bones before and after draining the vestibule. Measurements were made in the 0.125-8 kHz range at 80 dB input sound pressure level, using a laser Doppler vibrometer. A circuit model was also used to predict stapes displacement. The temporal bone studies show a slight decrease in stapes footplate displacement at low frequency, and little change above 1 kHz. The displacement change is not as great as that found by other investigators or predicted by the model. There is little difference in stapes motion in temporal bones when the inner ear is intact or drained.

Cochlea↗

PubMed2001

In vitro study of a multi-layer piezoelectric crystal attic hearing implant.

We have developed a prototype middle-ear hearing implant which uses a multilayer piezoelectric actuator. In this series of experiments the actuator was attached to the medial wall of the attic so that it makes contact with the body of the incus. Initial in vitro evaluation has been carried out using a laser vibrometer (Polytec CLV) to measure stapes velocity. Stapes displacement is calculated by mathematical integration. The device used in this way is particularly effective at transmitting high frequency sound to the stapes. When switched off the actuator impairs the transmission of sound to the ossicular chain at low frequencies, but this effect is only 7 dB at most. The stapes displacements resulting from the action of the implant have a linear relationship with the voltages used to drive the system. The high capacitance of the present actuator means that its power requirements are higher than that of other comparable devices. An optimal method of coupling the device to the incus has yet to be identified.

Acoustic Stimulation↗

PubMed2000

An anatomically shaped incus prosthesis for reconstruction of the ossicular chain.

An anatomically shaped incus replica prosthesis has been designed to reconstruct the ossicular chain. A series of in vitro studies on human temporal bones evaluated the acoustic performance of this prosthesis and compared it with a Causse partial ossicular replacement prosthesis (PORP). Pure tones in the frequency range 0. 125-8 kHz stimulated the tympanic membrane at sound pressure levels of 80, 90 and 100 dB. Measurements of the stapes footplate velocity were made with a laser interferometer. The acoustic function of the ossicular chain reconstructed with the incus replica prosthesis was found to be within 10 dB of that of the original intact ossicular chain, when both the upper and lower joints of the implant were rigidly fixed in place. It was shown that a rigid mechanical contact between the ossicular prosthesis and ossicles is a prerequisite for effective sound transmission. The anatomically shaped incus prosthesis gave a 15-dB improvement on the PORP at frequencies below 1.5 kHz.

Acoustic Stimulation↗

PubMed2000

Mean platelet volume is a useful parameter: a reproducible routine method using a modified Coulter thrombocytometer.

The principal physiological function of platelets is to promote haemostasis but they also contribute to thrombosis and atherogenesis. Platelet volume is a marker and possibly a determinant of platelet function in that large platelets are more active than normal sized platelets. Mean platelet volume (MPV), a measure of platelet size, reflects changes in either the level of platelet stimulation or the rate of platelet production. For these reasons, we have developed a sensitive instrument to measure platelet volume, which we believe is more reliable and specific than previously used instruments. It is based on a computer-interfaced Coulter Thrombocytometer and a pulse analyser including a high-speed baseline restorer. We have developed a reproducible method to assay MPV and from the histogram derived the median (MED) and the skewness (SK) values. We have looked at the effects of anticoagulant used and time elapse prior to assay. A normal range has been established for MPV which correlates directly with MED and inversely with SK. The MPV decreases with age but there is no difference between genders. We have demonstrated a negative correlation between whole blood platelet number and MPV and MED, and a direct relationship with the SK of the histogram of the platelet volume.

Adolescent↗

PubMed2000

The development and validation of an algorithm for real-time computerised fetal heart rate monitoring in labour.

OBJECTIVE: To develop and validate a computerised algorithm for the interpretation of the characteristics of fetal heart rate monitoring in labour. DESIGN: Prospective observational study. SETTING: Labour ward in a tertiary hospital. SAMPLE: Intrapartum cardiotocograms from 24 pregnancies. METHODS: A computerised algorithm was developed to assess the fetal heart baseline rate, variability, the number of accelerations and the number of decelerations. Twenty five minute segments of cardiotocograms were interpreted by the algorithm and also by seven expert reviewers independently. The reviewers were unaware of the outcome of labour. The reliability of the characteristics of cardiotocography and the validity of the computerised algorithm were assessed using the intraclass correlation coefficient and weighted kappa statistic for continuous and ordinal variables respectively. RESULTS: The inter rater reliability of the baseline fetal heart rate and the number and type of decelerations was good (intraclass correlation coefficient 0.93, 0.93 and 0.79, respectively). The reliability of baseline variability (kappa = 0.27) and accelerations (intraclass correlation coefficient = 0.27) was poor. The computerised algorithm had good agreement with the reviewers for the baseline fetal heart rate (intraclass correlation coefficient 0.91 to 0.98) and the number of decelerations (intraclass correlation coefficient 0.82 to 0.91), but was less valid as regards the number of late decelerations (intraclass correlation coefficient 0.68 to 0.85) and the number of accelerations (intraclass correlation coefficient 0.06 to 0.80), and was invalid as regards baseline variability (kappa 0.00 to 0.34). CONCLUSIONS: The high level of validity of the computerised algorithm for the estimation of the baseline fetal heart rate and the number of decelerations justifies its further technical development.

Adolescent↗

PubMed2000

Bone mineral density of the radius in patients with Colles' fracture.

To ascertain whether patients with Colles' fracture should be investigated for osteoporosis and the risk of future fractures, we measured the bone mineral density of the distal radius of the other arm in 31 women patients and compared the results with those of a control group of 289 normal women. We divided the patients into two groups, those younger than 66 years and those older. In 25 patients we found values for bone mineral density which were lower than one standard deviation below the mean value for their age. Younger patients had a deficit greater than that expected for their ages. We believe that women with Colles' fracture should be evaluated routinely for osteoporosis, particularly if they are under 66 years of age.

Adult↗

PubMed1998

Mechanical evaluation of a new minimum-contact plate for internal fracture fixation.

OBJECTIVE: To determine whether the mechanical properties (stiffness and strength) of a new design of internal fixation plate, with reduced bone-to-plate contact area for reducing disturbance to the bone blood supply at the fracture site, are comparable with those of commonly used fracture fixation plates. DESIGN: Four-point bending and torsion tests were conducted to compare the new minimum contact plate (MCP) with two established internal fixation plates: the dynamic compression plate (DCP) and the limited contact dynamic compression plate (LC-DCP). The bending stiffness and strength were determined according to the International Standards Organization bending test for bone plates, and the torsional stiffness and torque to failure were calculated from torsional loading data with the plates attached to synthetic bones. RESULTS: The new MCP plate was significantly stiffer than the other two plates and stronger than the DCP plate in bending (p < 0.01). In torsion, the MCP plate was marginally stiffer (p < 0.11) and significantly stronger (p < 0.01) than the LC-DCP plate and not as stiff and strong as the DCP plate (p < 0.01). CONCLUSIONS: Mechanically, the MCP plate has adequate stiffness and strength for clinical application because it is at least as stiff and strong as one of the commonly used plates under both bending and torsional loading conditions.

Animals↗

PubMed1998

Mechanical performance of an axially mobile plate for fracture fixation.

BACKGROUND: Emphasis of the advantages of secondary bone healing over primary bone healing has led to a trend of moving from rigid fixation to less-rigid fixation. A reduction in axial stiffness of fixators has been shown to be beneficial to bone healing, and many external fixators have been designed that incorporate axial dynamization. METHODS AND RESULTS: A new axially mobile plate has been designed for long-bone fracture fixation, to give the bone fragments a degree of axial mobility while maintaining bending and torsional stability after fixation. Mechanical bending and torsion tests have been conducted on the axially mobile plate and also on the conventional dynamic compression plate and the limited-contact dynamic compression plate. The results have shown that the new plate is stiffer and stronger in both bending and torsion than at least one of these conventional plates. CONCLUSION: The axially mobile plate has adequate mechanical properties and can be taken forward to clinical trails.

Biomechanical Phenomena↗

PubMed1997

A high-speed gated baseline restorer and its implementation in a blood cell volume analyser.

Accurate measurement of the height of individual pulses in a signal that is a.c.-coupled is dependent upon correcting a changing baseline to a constant value. A new fast baseline restorer, using internally triggered gated feedback with gain, has been designed and a version optimized for Gaussian-shaped pulses. Performance is dependent on the magnitudes of both the forward and the feedback gains. The design presented can achieve a 0.5% accuracy in pulse height for a minimum pulse width of 2.5 microseconds or for 5 microseconds overlapping pulses as long as the overlap is less than 50%. Typical applications for the baseline restorer include blood cell volume measurement systems, scintillation counters and radiation spectroscopy.

Biomedical Engineering↗

PubMed1997

Evaluation of cancellous structure in the distal radius using spectral analysis.

A preliminary study was conducted to analyze trabecular patterns in digitized wrist radiographic images from 68 patients (31 males and 37 females), aged from 7 to 93 years. The fast Fourier transform was used to perform the spectral analysis of the distal radius. Three indices were defined to permit quantification of the cancellous structure in terms of the spacing and orientation of bone trabeculae (periodicity): a spectral trabecular index, a longitudinal trabecular index, and a transverse trabecular index. The spectral trabecular index reflects the periodicity of the trabeculae (spacing and orientation), while the other 2 selectively reflect the periodicity of longitudinally and transversely oriented ones. The ratio of the longitudinal and transverse trabecular indices was also studied. The shape of the high magnitude frequencies in the spectrum was crosslike for all patients, implying a preferentially orthogonal 2-dimensional structure for the cancellous bone in the distal end of the radius. The variation of the defined trabecular bone indices with age corresponded with the formation of bone through infancy and adolescence, reaching a peak in adulthood and gradual loss thereafter. This quantification detects structural changes that occur with aging and may therefore be useful in the study of osteoporosis.

Adolescent↗

PubMed1996

Neural network analysis of the EMG interference pattern.

This paper investigates the performance of artificial neural networks for analysing and classifying EMG signals from healthy subjects and patients with myopathic and neuropathic disorders. EMG interference patterns (IP) were recorded under maximum voluntary contraction from the right biceps of a total of 50 subjects. Parameters were obtained from the signals using recognized quantification techniques including turns analysis, small segments analysis and frequency analysis. Supervised networks examined were an improved backpropagation network (IBPN), a radial basis network (RBN), and a learning vector quantization network (INQ). Supervised networks using different combinations of parameters from turns analysis and small segments analysis gave diagnostic yields of 60-80%. Combinations using frequency analysis parameters produced similar results. The performance of unsupervised Self-Organising Feature Maps (SOFM) was generally lower than that of the supervised networks. Including personal data (sex and age) did not improve the overall performance.

Biomedical Engineering↗

PubMed1994

Determination of the depth of cure for VLC composites by nuclear magnetic resonance microimaging.

OBJECTIVES: The purpose of this study was to evaluate the potential of nuclear magnetic resonance microimaging (NMRM) for investigating the depth of cure for visible light curing of dental composite materials. METHODS: Cylindrical composite specimens were light-cured within the NMRM instrument for predetermined times. Vertical slice, mid-resolution, spin-echo images were acquired using a Bruker AM300WB instrument with a Bruker microimaging attachment. Images were digitized and intensity profiles generated using deuterium oxide/water as a reference intensity. Separate specimens were made to obtain Vickers microhardness values as a function of depth to compare an established method for determining depth of cure with NMRM. RESULTS: A difference in NMR image intensity between uncured and cured composite resin has been detected. Values for integrated intensities were obtained at 150 microns intervals over the mid-fifth of the total image width. An abrupt transition was not seen at the cure front which advances with cumulative exposure time. NMRM produced similar data trends to microhardness measurement. SIGNIFICANCE: NMRM produces three-dimensional images of "mobile" hydrogen nuclei to a resolution of 10(-5) mm3. It is non-invasive, non-destructive and able to selectively image protons in different chemical environments. It can be used to investigate depth of cure for light curing materials, but must be regarded as a research technique and not one for routine measurement. Refinement is necessary, possible, and in progress to improve resolution from the present 10(-2) mm3 towards the limit, and to reduce noise.

Composite Resins↗

PubMed1993

A technique for the tensile testing of demineralised bone.

The purpose of this study was to devise a method for the tensile testing of the organic component of demineralised bone. It was hoped that the method could be applied to determine whether an observed reduction in the strength of bone in copper-deficient rats could be attributed to a reduction in the cross-linking of collagen. Tensile testing of a fully demineralised specimen proved impossible to perform because of the difficulty in gripping the material, which tended to slide out of its holding clamps. The technique devised involved the demineralisation of only the diaphysis of the bone, leaving the bone ends intact. This enabled the bone to be gripped firmly at both ends in an Instron tensile testing machine. Elongation under loading of the demineralised diaphysis was measured by the Instron and a video recording was made of the elongation of the central portion. The strain was found to be uniform. Tensile strength was found to correlate with copper levels in the liver (r = 0.54, p < 0.05), although no significant differences were found between the strength, the stiffness, or the strain to failure for bone from the copper-deficient animals and bone from the normal controls. The test method itself should be useful in other studies in which the tensile properties of the organic phase of bone need to be measured.

Animals↗

PubMed1993

Impaired mechanical strength of bone in experimental copper deficiency.

Copper, through its role as cofactor for lysyl oxidase, is essential for intra- and inter-molecular cross-links in collagen. Copper deficiency, in man and in animals, is associated with bone fragility ascribed to defective cross-links. To assess bone strength in copper-deficient animals, we designed a sensitive torsion-testing apparatus according to biomechanical considerations. Femora from 7 copper-deficient rats and from their pair-fed controls were tested in torsional loading until fracture. Significant decreases in the maximal sustained torque (t = 2.93, p < 0.05), in the ultimate angular deformation (t = 2.52, p < 0.05) and in the toughness (t = 2.88, p < 0.05) were demonstrated. In a complementary study, it was shown that the ash weight and the calcium content of the femora from the copper-deficient animals did not differ from those of the controls. It was likely, therefore, that the impaired mechanical strength was related to defects in the collagen component of bone.

Animals↗

PubMed1993

Finite element analysis of poor distal contact of the femoral component of a cementless hip endoprosthesis.

The difficulty of achieving good distal contact between a cementless hip endoprosthesis and the femur is well established. This finite element study investigates the effect on the stress distribution within the femur due to varying lengths of distal gap. Three-dimensional anatomical models of two different sized femurs were generated, based upon computer tomograph scans of two cadaveric specimens. A further six models were derived from each original model, with distal gaps varying from 10 to 60 mm in length. The resulting stress distributions within these were compared to the uniform contact models. The extent to which femoral geometry was an influencing factor on the stress distribution within the bone was also studied. Lack of distal contact with the prosthesis was found not to affect the proximal stress distribution within the femur, for distal gap lengths of up to 60 mm. In the region of no distal contact, the stress within the femur was at normal physiological levels associated with the applied loading and boundary conditions. The femoral geometry was found to have little influence on the stress distribution within the cortical bone. Although localized variations were noted, both femurs exhibited the same general stress distribution pattern.

Biomechanical Phenomena↗