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Biomedical subjects

J C Barbenel

Publications and source records attributed to J C Barbenel.

At least 19 recordsLinked to original sources
PubMed1999

A new capillary viscometer for whole blood viscosimetry.

A new capillary system was developed, incorporating infrared sensors, which allowed the determination of whole blood viscosity over a wide range of shear stresses. Flow conditions were defined by the geometry of the capillary and the sample pressure head. Whole blood was considered to be a power law fluid and a modified Mooney's formula was used for the calculation of the related invariants. The new viscometer proved to be very simple in use, requiring one run, had a short measuring time and utilised a small test sample volume. However it can be used for whole blood viscosity measurements only at medium and high shear stresses.

Blood Viscosity↗
PubMed1998

Investigation into the tensile properties of collagen/chondroitin-6-sulphate gels: the effect of crosslinking agents and diamines.

Artificial skin substitutes based on autologous keratinocytes are being developed for grafting onto burns patients. In order to be used successfully in the clinic, these skin substitutes need to have sufficient strength to allow ease of handling. This may be achieved by crosslinking the collagen substratum on which the cells are cultured. The influence of potential crosslinking agents on the tensile properties of acellular collagen gels has been investigated, including the glycosaminoglycan, chondroitin-6-sulphate (Ch6SO4), the water-soluble carbodiimide crosslinking agents 1-ethyl-3-(3-diaminopropyl) carbodiimide (EDAC), and 1,1-carbonyldiimidazole (CDI), and the polyamines, putrescine and diaminohexane. Values for Young's modulus, maximum load, stress, displacement and percentage strain at maximum load were generated by subjecting the samples to a tear propagation test. Incorporation of 20% Ch6SO4 into collagen gels caused a significant increase in the Young's modulus, maximum load and stress at maximum load. Crosslinking treatment with EDAC, CDI or polyamines had little further benefit, and in many cases resulted in a decrease in particular parameters. In terms of mechanical strength, the best crosslinking combination proved to be the combination of CDI and diaminohexane, with results either improved or maintained when compared with the control no treatment variants. However, previous experience suggests that the use of CDI as a crosslinking reagent may inhibit infiltration and proliferation of fibroblasts in the substratum and it may be necessary to reach a compromise to obtain the best combination of biological and mechanical properties for artificial skin substitutes.

Chondroitin Sulfates↗
PubMed1997

A new ambulatory monitoring instrument of posture and mobility related activities.

Long-term ambulatory monitoring of posture and mobility related activities provides useful information about the extent of disability and the outcome of rehabilitation. The aim of this project is developing an instrument which could distinguish between a set of selected mobility-related physical activities and produce parameters characterising the subjects' activity pattern; The selected activities are lying, sitting, standing and walking. A novel activity transducer and a data logger with 1MB memory are employed in the system configuration. Analytical algorithms and program are developed. The subject's whole day activity pattern and the histogram of each activity event are successfully obtained.

Humans↗
PubMed1996

Direct measurement of the optical properties of human breast skin.

The optical properties of thin tissue samples are obtained using goniometric apparatus. Direct measurements of the scattering of 633 nm light by 20-120 microns thick samples of in vitro human breast epidermis and dermis are numerically integrated to obtain values for the scattering and absorption coefficients mu s and mu a, respectively, and the anisotropy parameter g. The total attenuation coefficient mu t is obtained from transmission measurements. The Beer-Lambert law is found to be sufficiently valid for congruent to 100 microns thick samples to be used as the basis of the numerical integration. However, normalisation errors involved with the integration mean that only approximate values of mu a could be obtained. Values of congruent to 40 mm-1 are obtained for mu t and mu s, with the value of mu a estimated as 1 mm-1. The optical properties of human breast epidermis and dermis are found to be similar at 633 nm, and the two could be considered as a single layer for modelling light propagation at this wavelength. Further, the intersubject variability seen in this study suggests that a model that uses a range of values for each optical property may be more useful in a clinical situation.

Adult↗
PubMed1996

Peroneal stimulator; evaluation for the correction of spastic drop foot in hemiplegia.

OBJECTIVE: The objective of the study was to assess the orthotic and therapeutic value of the peroneal stimulator (PS) for adult hemiplegic patients. DESIGN: This was a two-period crossover study lasting 11 weeks. After recruitment each patient had a 4-week control period followed by a 4-week treatment period. The patients were assessed before the control period, after the control period, and after the treatment period. SETTING: Nineteen patients were recruited from physiotherapy departments in the Glasgow area; 2 subsequently dropped out before the treatment period. PATIENTS: All patients had hemiplegia as a result of cerebrovascular accident (CVA) and were greater than 3 months but less than 36 months post-CVA. Average time since stroke was 7 months. MAIN OUTCOME MEASURES: The patients' gait was assessed over smooth linoleum, carpet, and uneven ground. Gait was evaluated using a switch-based portable system. Outcome measures were the temporal gait parameters of speed, symmetry, heel strike, and foot inversion during stance. The gait evaluation was repeated on 5 separate days at each assessment. The Barthel Index was applied to each session. RESULTS: There was a significant orthotic improvement in inversion on all surfaces and for symmetry on linoleum (AN-OVA, p = .05). There was no significant improvement in patients' gait when not using the PS. There was a significant improvement in the Barthel Index over the treatment period (Wilcoxon, p = .05). CONCLUSION: Use of the PS an an orthotic device late in the rehabilitation program would be appropriate for a selected subpopulation of patients.

Adaptation, Physiological↗
PubMed1995

A body-worn gait analysis system for evaluating hemiplegic gait.

This paper describes a system for measuring the temporal parameters of hemiplegic gait. This system uses shoe insoles with sensors, acting as switches, placed under the heel, head of the first metatarsal, head of the fifth metatarsal and the big toe. This system is able to monitor gait for up to 10 min and can be used by the patient over any surface. Parameters for evaluating hemiplegic gait are defined, including scuffing during swing and the degree of inversion during stance.

Cerebrovascular Disorders↗
PubMed1995

Poly(vinyl chloride) formulations: acute toxicity to cultured human cell lines.

Two quantitative cytotoxicity assay methods (cytoplasmic retention of carboxyfluorescein and mitochondrial cleavage of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT)) have been used to evaluate the response of two cultured human cell lines; HepG2 (hepatoma) and W138va13 (transformed lung fibroblasts) to extracts of a range of poly(vinyl chloride) (PVC) formulations. Two plasticizers; di(2-ethylhexyl)phthalate (DEHP) and di-isooctyl phthalate and a range of tin and non-tin stabilizers were incorporated in the study. Only those formulations containing both a plasticizer and a tin-based stabilizer produced extracts which were toxic. Extracts of those formulations which contained both plasticizer and dibutyl tin dimaleate stabilizer were toxic to both cell lines in both assay methods. Extracts of a formulation containing plasticizer and a dioctyl tin mercaptide were toxic to both cell lines in the carboxyfluorescein assay but were only toxic to the WI38va13 cells in the MTT assay. The WI38va13 cells were generally more sensitive to the extracts than the HepG2 cells. When serial dilutions of the extracts were evaluated, the carboxyfluorescein assay proved to be the more sensitive of the two. The acute toxicity of extracts of these PVC formulations cannot be directly attributed to the plasticizers or to the tin stabilizers. It is likely that a synergistic mechanism, such as plasticizer facilitated extraction of the tin stabilizer, exists.

Carcinoma, Hepatocellular↗
PubMed1995

Improvements in bandaging technique following training.

Effective compression bandaging is critical for leg ulcer care. The bandaging technique of 18 nurses was assessed using a pressure monitor and the assessment repeated after training with feedback from the monitor. The use of a bandage marked with a tension indicator resulted in a small, insignificant improvement in bandaging technique. The combination of training and feedback significantly improved the nurses' bandaging technique. This improvement was sustained on retesting two weeks later.

Bandages↗
PubMed1994

Anisotropic elasticity and strength of glutaraldehyde fixed bovine pericardium for use in pericardial bioprosthetic valves.

Uniaxial tensile tests were performed on glutaraldehyde fixed bovine pericardial strips prepared from chemically modified pericardial samples. These samples originated from an area which demonstrated anisotropic mechanical properties in the native material and which is suitable for the construction of leaflets for pericardial bioprostheses. After glutaraldehyde fixation the tissue had retained its anisotropicity in stiffness and strength in two orthogonal directions. In the range of the functional stresses for a heart valve leaflet (< 1 MPa) the unconstrained fixation regime had modified the initial anisotropic elastic behavior into a more isotropic one. The implications of these findings are that leaflets manufactured from bovine pericardium can be made to resemble, to a degree, the well known anisotropy found in two orthogonal directions in natural human heart valve leaflets, or porcine bioprosthetic heart valve leaflets.

Animals↗
PubMed1994

Mechanics of native bovine pericardium. I. The multiangular behaviour of strength and stiffness of the tissue.

Native bovine pericardial samples have recently been reported to be mechanically anisotropic in both biaxial and uniaxial tests. We present results of multiangular tensile tests conducted on strips from native pericardial samples. These tests were needed in order to establish the nature of the anisotropy, in other words identify the class of the material symmetry. We also examine the possibility of describing the multiangular behaviour of the ultimate tensile stress and stiffness of the tissue by using a theory pertinent to composite structures comprised of linear elastic elements. This application was in general successful and should contribute towards a better understanding of the mechanics and deformations of natural materials with a woven fabric (structure).

Animals↗
PubMed1994

Mechanics of native bovine pericardium. II. A structure based model for the anisotropic mechanical behaviour of the tissue.

A constitutive law to describe the mechanical behaviour of native bovine pericardial samples is proposed. The model is based upon an idealization of the tissue structure and in particular makes use of the preferential orientation of the collagen and elastin fibres in the plane of the tissue along a mechanically predominant direction. This non-axisymmetric layout of the tissue fibres has been shown in the past to cause a systematic variation of the tensile strength and the stiffness with the angle of orientation. The proposed constitutive relation provided a very good fit for results collected along two orthogonal principal directions in the past in uniaxial and biaxial tensile testing modes. It also allowed a better understanding of the interaction of the various load bearing elements and was able to describe some strange features of the tissue's anisotropic mechanical behaviour.

Animals↗
PubMed1994

External fixation of the distal radius. A biomechanical study.

External fixation is a useful method of treating unstable fractures of the distal radius. There is a lack of information regarding the behaviour of mini-fixation systems, particularly under cyclical loading, which would be expected to occur at the wrist. This laboratory study was designed to investigate the mechanical characteristics of nine current fixation systems. A programme of loading was devised to mimic forces acting on the distal radius. Wooden dowel was used to mount the fixator. Distraction and compression forces were applied in an Instron rig. Displacement was monitored throughout the load programme. No fixator failed at the loads tested. The small Hoffman rectangular frame proved stiffest in compression and extension, but was heavier than other devices. A trend of progressive, permanent deformation became apparent in those fixators which contain plastic or composite materials. This feature has implications for loss of fracture reduction in the clinical setting.

Biomechanical Phenomena↗
PubMed1993

Foot microcirculation and blood rheology in diabetes.

Diabetes mellitus is associated with circulatory abnormalities. The blood flow in the skin of the dorsum of the foot and haemorheological variables were measured in 36 subjects. They were divided into three equal groups of diabetic patients: those with neuropathy, and both age and sex matched non-diabetic subjects; all were characterized by age, duration of diabetes and blood biochemistry. High and low shear rate blood viscosities were measured; aggregation was characterized using a Myrerene Aggregometer. The microcirculation in the skin of the dorsum of the foot was measured using a laser Doppler flowmeter. Measurements were made at room temperature with the subjects supine with the leg horizontal, and then with the lower leg vertical; the measurements were repeated at 42 degrees C. Both diabetic groups had significantly increased low shear whole blood viscosity compared with normal subjects. The aggregation index was significantly greater in diabetic neuropaths than normal subjects. There were significant differences in the depth of vasomotor activity between the three groups, with the diabetic neuropaths commonly showing no motor activity at room temperature. The only significant correlations were between equilibrium laser Doppler values with the limb horizontal and both the low and high shear whole blood viscosities.

Blood Viscosity↗
PubMed1993

Abnormal thermal hyperaemia in the skin in paraplegia.

Surface insulation, together with laser Doppler flowmetry, was used to assess the skin microcirculation of paraplegic patients. Two control groups of five male and five female subjects were used to establish the response of normals with which to compare the results obtained from six paraplegic subjects. No significant sex related difference was revealed from this study. It was found that in normal subjects, surface insulation resulted in a significant increase in both skin temperature and skin blood flow. In paraplegic patients, the temperature increase was significantly less than in the normal subjects and there was no significant thermally induced hyperaemia after surface insulation.

Adult↗