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Biomedical subjects

R Wytch

Publications and source records attributed to R Wytch.

At least 19 recordsLinked to original sources
PubMed1995

Stiffening effects of cortical bone on vertebral cancellous bone in situ.

STUDY DESIGN: This study tested a theory about vertebral cancellous bone stiffness by performing experimental tests and comparing the results with the theoretical predictions. OBJECTIVES: To test experimentally a theoretical prediction that vertebral cancellous bone appears stiffer than would be expected from isolated tests because of the constraining effects of the cortical bone, to measure the magnitude of this strengthening effect and its dependency on tissue composition and density. SUMMARY OF BACKGROUND DATA: Vertebral bodies are composed mainly of cancellous bone surrounded by a thin shell of much stronger cortical bone. Little is known of the ways in which these two materials function synergistically to produce strong but light structures and why sometimes extensive damage to the cancellous bone has apparently little outward effect on vertebral body strength. METHODS: Cancellous bone from 45 lumbar vertebrae from a homogeneous group of pigs was tested in compression both in situ in the vertebral body and as an excised cylinder. The density and composition of the bone were then measured and correlation tested with both of the stiffness measurements. RESULTS: The cancellous bone in situ appears much stiffer than when isolated by a factor of about 4 (range, 1.6-12). No correlation was found between stiffness, either in situ or in isolation, and density, although density is predicted entirely by the volume fractions of water, organic, and mineral phases. CONCLUSIONS: Combining low density cancellous bone with stiffer, more dense cortical bone leads to a lightweight structure that is much stronger than might be expected from the isolated properties of its components.

Animals↗
PubMed1995

Validation of a computer model of haemorrhage and transcapillary refill.

A computer model is described which uses blood volume deficit and its duration to simulate the first two hours of haemorrhage, including an estimation of the blood volume added by Starlings transcapillary refill mechanism. Computer prediction of the haematocrit was compared with published data on haemorrhage in animals. There was close correlation with data on the haemodilution caused by Starling's transcapillary refill mechanism in conscious swine (r = 0.84).

Animals↗
PubMed1994

Electrical impedance tomography: a review of current literature.

Electrical impedance tomography (EIT) is a relatively new imaging technique that has been developed during the past decade. The electrical properties of tissues are imaged by injecting small currents and measuring the resultant voltages. These voltages are then converted into a tomographic image using a reconstructing algorithm. The method has no known hazards and is relatively inexpensive. There are many possible clinical applications of this technique but apart from gastric emptying, most are still at the research stage as there are various technical and practical problems to be overcome. This paper describes the basic principles of EIT and reviews the English literature to try to assess its potential in clinical imaging.

Algorithms↗
PubMed1992

Glass fibre versus non-glass fibre splinting bandages.

We have assessed the current range of synthetic splinting bandages, comparing glass with non-glass fabrics and plaster-of-Paris. Physical and mechanical tests have been carried out and the opinions of patients, volunteers and orthopaedic staff were recorded. Modern bandages have some better properties than standard plaster bandage but do not conform as well, are more expensive and potentially more hazardous. However, non-glass bandages are lighter, less brittle, more radiolucent and less hazardous than glass fibre bandages and are preferred by both patients and applicators.

Attitude to Health↗
PubMed1991

On immediate functional bracing of Colles' fracture.

A prospective randomized trial was carried out in 60 consecutive patients with Colles' fractures requiring manipulation. They were treated by either a standard Colles' plaster (control group) or in a functional plaster brace applied immediately after reduction of the fracture. The brace extended from the proximal radius and ulna to the level of the radial styloid and allowed a full range of movement at the radiocarpal joint. Both groups comprised 30 patients and were matched for age, sex and dominance of hand. There was no significant difference in initial severity of fracture or the quality of reduction. Radiological results on cast removal (35-42 days) were significantly better in the brace group compared with those treated with a below-elbow cast (P less than 0.05). Wrist function was also significantly better in the brace treated group at 12 weeks after fracture (P less than 0.05). This brace has a number of advantages over standard plaster treatment, but requires a degree of skill and experience in its application. A prefabricated brace has now been developed with a similar 'built in' three-point loading which will be easier for inexperienced staff to apply.

Adult↗
PubMed1991

Intracast pressure measurements in Colles' fractures.

Intracast pressures were recorded in conventional plaster-of-Paris below-elbow casts and compared with a new prefabricated brace for the functional treatment of Colles' fractures. Interface pressures were consistently higher in the brace than in the conventional plaster cast throughout the treatment period, and demonstrated more specific loading to the fracture site.

Adolescent↗
PubMed1991

Radiographic assessment of splinting bandages.

The physical attenuation of X-rays by a variety of splinting bandages was measured and compared with the subjective opinion of nine radiologists. The radiolucency of the bandages and their interference with the interpretation of bony detail on radiographs (using a radiographic knee phantom) was assessed. Plaster-of-Paris (POP) bandages produced the greatest attenuation of X-rays and the greatest interference with interpretation of bony detail. All the polyurethane resin impregnated fabric bandages produced less attenuation than POP, but variations occurred due to the fabric type and knit of the bandage. The lowest attenuation occurred in those bandages using cotton, polyester or polypropylene fabric, and in all but one instance these caused least interference in radiographic interpretation. The exception was the polyester bandage, where the coarse knit of the fabric produced a large difference in X-ray beam absorption between the air spaces and the bandage. The distracting mesh pattern on the radiograph interfered with radiographic visualization. The glass fibre bandages caused intermediate attenuation, being better than POP but not as radiolucent as the non-glass fabrics.

Bandages↗
PubMed1991

Imaging microbubbles and tissues using a linear focussed scanner operating at 20 MHz: possible implications for the detection of cavitation thresholds.

B-Scan images have been used as a means of detecting the onset of cavitation in tissues. New echoes appearing during simultaneous sonication with therapeutic ultrasound have often been attributed to bubble formation. In this study temperature rises up to 15 degrees C W-1 cm2 in guinea pig leg (post-mortem) were found, which would itself increase the rate of growth of gas bubbles. It is also hypothesized that a temperature dependent attenuation coefficient predicted by Bamber and Hill may, at least in part, account for new echoes appearing in tissues. Possible artefactual echoes in the B-scan images arising from acoustically induced gas bubbles in the coupling medium are also discussed.

Animals↗
PubMed1991

Modern splinting bandages.

We have assessed the current range of synthetic splinting bandages, using physical and mechanical tests and the subjective opinions of patients, volunteers and orthopaedic staff. Modern bandages have some better properties than standard plaster bandage but do not conform as well, are more expensive, and potentially more hazardous.

Bandages↗
PubMed1990

A microcomputer-based video vector system for clinical gait analysis.

A microcomputer-based video vector system has been developed to display the resultant ground reaction force vector on a television image of the subject in real-time. For each television field the force platform signals are acquired and processed and the resultant force vector superimposed on the video image of the walking subject. The force platform results are stored on disc and the composite video signals recorded on video tape for further analysis. The system is easy to set up and use and the results can be readily interpreted. The external moments produced at the joint centers by the ground reaction forces can be observed visually and, if required, quantification of the external moments can be achieved following data collection. The spatial resolution of the system is 0.342% vertically and 0.156% horizontally. The force vector visualization technique has routine applications in orthotics and prosthetics. It is also a useful technique for the teaching of biomechanics.

Calibration↗
PubMed1988

Flammability of modern synthetic bandages.

The potential fire hazard associated with polyurethane impregnated fibreglass bandages has been investigated. Tests have been carried out in accordance with the most appropriate British Standard (BS5438:1976). Results of these tests show that polyurethane impregnated fibreglass bandages do not represent a serious risk to a wearer as the rate of heat transfer through the casts is sufficiently rapid to alert the wearer of the proximity of a heat source before the cast ignites.

Bandages↗
PubMed1988

Dust emission during cutting of polyurethane-impregnated bandages.

The airborne dust generated when cutting splinting bandages represents a potential respiratory hazard, particularly to those who regularly remove casts with a power saw. Plaster of Paris (POP) dust is already classified by the Health and Safety Executive as a nuisance dust. This paper reports on a study to determine the nature, size and concentration of dust produced when cutting polyurethane (PU) impregnated bandages using a power saw. It has been shown that, under severe conditions PU bandages produce lower airborne dust concentrations than POP bandage but that all of the bandages tested produced particles small enough to reach the final divisions of the lung. It is therefore recommended that a dust extraction unit be used when cutting all types of bandage.

Air Pollutants, Occupational↗
PubMed1987

Mechanical assessment of polyurethane impregnated fibreglass bandages for splinting.

The introduction of polyurethane (PU) resin impregnated fibreglass bandages is likely to have a significant effect on modern orthopaedic practice. The manufacturers of these products claim many improved properties compared to plaster of Paris bandages, such as , high strength to weight ratio, rapid setting time and high radiolucency. This paper reports on a series of mechanical tests designed to assess the strength, flexibility, working time and wear properties of the current range of fibreglass bandages and to compare them with plaster of Paris bandages. The results have clearly demonstrated that the fibreglass bandages are mechanically superior and offer numerous advantages over plaster of Paris for use as the definitive casting material for both weight-bearing and non-weight-bearing casts.

Bandages↗
PubMed1987

New splinting materials.

Plaster of Paris (P.o.P.) bandage has been the pre-eminent external splinting material for over 150 years and from time to time synthetic alternatives have been tried. So far none has seriously challenged the dominance of P.o.P. as a primary or secondary material in the management of fractures. The recent introduction of Polyurethane coated fibreglass bandage appears to offer a more serious challenge than previous contenders. This technical note reviews bandage type splinting materials and explains some of the properties of the PU materials.

Bandages↗
PubMed1985

Exposure treatment of the burned patient--a computer simulation of the thermal environment and its effect on evaporation and heat loss.

The influence of the thermal environment on evaporation and heat loss from burned tissue has been studied in order to optimise conditions for treatment of severely burned patients. Diffusion resistances have been defined to describe movement of water vapour through the skin and away from the body surface. These have been evaluated from experiments on a water phantom and from data on evaporation rates from burned tissue and normal skin. Results show that the diffusion resistance for burned tissue is less than one tenth of that for normal skin, but changes substantially during the development of an eschar. Evaporation is promoted by a high skin temperature and a low relative humidity, but not by raising the ambient air temperature. Blowing warm dry air over a burn wound will enhance evaporation and reduce heat loss, encouraging the rapid formation of a dry eschar to provide a barrier against infection. Selective irradiation of burned tissue with low levels of radiant energy can be used to compensate for local heat losses, and allow the air temperature in the treatment room to be kept at a level comfortable for the patient and nursing staff.

Body Temperature Regulation↗