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Biomedical subjects

M Dyson

Publications and source records attributed to M Dyson.

At least 55 records · Page 3Linked to original sources
PubMed1989

The significance of membrane changes in the safe and effective use of therapeutic and diagnostic ultrasound.

The cellular changes, such as alterations in motility and the stimulation of synthesis and secretion, induced by relatively low intensities of therapeutic ultrasound (e.g. 500 mW cm-2, SAPA; 100 mW cm-2 SATA) are primarily non-thermal in origin. They appear to be associated with changes in the permeability of the cell (plasma) membrane and in the transport of ions and molecules across it, effects which have been demonstrated in cells irradiated in suspension. In epithelial tissues, both in vitro and in vivo, it has been demonstrated that not only the cellular membrane transport pathways but also the paracellular or intercellular pathways are affected. Although membrane-mediated effects can be of value therapeutically, they could produce adverse effects if they were to occur during development, for the reception and transmission by the membrane of environmental signals are involved in determination of the fate of each cell. Determination is followed by selective gene expression and differentiation, that is, by the progressive increase in structural complexity brought about by the acquisition of specialised characteristics by various cell groups. Most cells of early embryos are ionically coupled via gap junctions which provide an intercellular pathway for electrochemical signalling and the maintenance of the concentration gradients which provide the cells with positional information. Differentiation of the cells varies according to their location with respect to these gradients. Increase in the intracellular concentration of calcium ions, which has been shown to occur after exposure to therapeutic levels of ultrasound, can decrease the permeability of gap junctions and uncouple cells, in the manner which occurs when they differentiate. Ultrasonically induced increases in calcium ion concentration are thus of considerable clinical significance, since they could affect differentiation and consequently histogenesis. Modification of plasma membrane permeability and transport properties, resulting in changes in the availability and activity of second messengers such as free calcium ions, can have profound effects on cell behaviour. Calcium channels appear to be the first channels to develop in the cell membranes of embryos, and internal calcium ion concentration is known to affect the synthesis of fetal proteins. Although generally reversible at intensities of less than 500 mW cm-2, changes in membrane permeability, particularly to calcium ions, could, if prolonged, have undesirable side effects not only on embryogenesis but on late prenatal and postnatal development. It is therefore recommended that the environmental conditions, thresholds, and mechanisms involved in the production of such changes be determined, so that they can be avoided when ultrasound is used diagnostically on sensitive targets such as embryos and fetuses.

Animals↗
PubMed1988

The effect of therapeutic ultrasound on calcium uptake in fibroblasts.

The effect of therapeutic ultrasound on calcium uptake by embryonic chick 3T3 fibroblasts has been studied using calcium-45 radiotracer techniques. Cells were treated while suspended in culture medium at 36 degrees C at intensities from 0.25 W/cm2 SPPA to 1.5 W/cm2 SPPA (1 MHz, pulsed 2 ms on:8 ms off) and for exposure times from 1 min to 20 min. Ultrasound treatment was found to increase calcium uptake for SPPA intensities from 0.5 to 1.0 W/cm2 SPPA, with a maximum increase of 18% after a 5 min exposure. Calcium uptake also increased with increasing exposure time. Measurements performed up to 20 min after treatment showed that the cell was able to reduce this calcium influx, indicating that the membrane did not suffer irreparable damage as a result of the ultrasound exposure.

Animals↗
PubMed1988

Comparison of the effects of moist and dry conditions on dermal repair.

The effects on dermal repair of moist conditions, achieved by covering excised wounds with the adhesive polyurethane dressing OPSITE, and dry conditions, achieved by exposure to air through dry gauze dressings, were compared in full thickness excised wounds on porcine skin during the period from 1 to 21 d after injury. Quantitative studies were made of changes in the populations of neutrophils, macrophages, fibroblasts, and endothelial cells. The number of inflammatory phase cells (neutrophils and macrophages) decreased more rapidly under moist conditions than under dry conditions. There was also a more rapid increase in the number of proliferative phase cells (fibroblasts and endothelial cells) in the moist wounds; by 5 d after injury 66% of the cells of the granulation tissue of the moist wounds were of this type, compared with only 48% of the cells of equivalent areas of the dry wounds. By 21 d after injury the number of fibroblasts in the granulation tissue of the moist wounds had fallen below that in the dry wounds, suggesting that progress from the proliferative into the remodelling phase of repair was more rapid in the moist wounds. It was concluded that there was an acceleration of the inflammatory and proliferative phases of dermal repair in wounds healing under moist conditions when compared with those healing under dry conditions.

Air↗
PubMed1987

The use of ultrasound by physiotherapists in Britain, 1985.

A questionnaire was sent out to physiotherapists in Britain in 1985 requesting information about their use of therapeutic ultrasound. Replies were obtained from National Health Service (NHS) departments and private practitioners. Twenty percent of all physiotherapy treatments in NHS departments involved ultrasound, and 54% of all private treatments. Information was obtained about the range and pattern of ultrasonic frequencies and intensities used. The conditions for which ultrasound is used as a treatment modality are listed, as are the contraindications for its use.

England↗
PubMed1987

Acoustic cavitation generated by an extracorporeal shockwave lithotripter.

Evidence is presented of acoustic cavitation generated by a Dornier extracorporeal shockwave lithotripter. Using x-ray film, thin aluminum sheets, and relatively thick metal plates as targets, evidence of liquid jet impacts associated with cavitation bubble collapse was observed. The jet impact was violent enough to puncture thin foils and deform metal plates. Furthermore, numerous jet impacts were generated over a volume of greater than 200 cm3. It is likely that such violent cavitation will also occur in tissue, and observed biological effects (e.g. renal calculus disintegration and tissue trauma) may be related to cavitation damage.

Lithotripsy↗
PubMed1987

Ultrasonically induced gas bubble production in agar based gels: Part I. Experimental investigation.

Macroscopically visible gas bubbles can be produced in an agar based gel by irradiation with either continuous or pulsed ultrasound at frequencies from 0.75 to 3.0 MHz. The variation in the number of bubbles formed with frequency, acoustic pressure, pulse length, duty cycle, and temperature closely resembles that seen in vivo. Furthermore, the acoustic pressure required to initiate bubble formation is also close to that required in vivo. It has been observed that alterations in the concentration and pH of the gels can have a profound effect on the nature and quantity of bubbles. This suggests that not only is this gel model suitable for the representation of the macroscopic features of bubble formation in vivo, but can be used to gain information about the preexisting bubble nuclei. Based on the experimental results obtained it can be suggested that for peak negative acoustic pressures of up 1 MPa (equivalent, for a plane travelling sinusoidal wave, to a time averaged intensity of 30 W/cm2) bubble formation can be avoided by the use of high frequencies, short pulse lengths and long duty cycles.

Agar↗
PubMed1987

Ultrasonically induced gas bubble production in agar based gels: Part II. Theoretical analysis.

Visible size gas bubbles can be produced in an agar based gel when irradiated with either continuous wave (CW) or pulsed ultrasound. It is shown that many aspects of the production of these bubbles can be explained in a qualitative manner by a theoretical model based upon growth of a cavitation nucleus by rectified diffusion. Quantitative predictions for the number of bubbles produced as a function of various parameters tend to be different from measured values by less than an order of magnitude. The results given here provide a useful theoretical basis for the explanation of earlier measurements of ultrasonically induced bubbles in vivo.

Agar↗
PubMed1987

Type I and III collagen content and fibre distribution in normal human skin during ageing.

The content of type I and III collagen in normal human skin from subjects of different ages was studied by means of a new high performance liquid chromatography method and by SDS-polyacrylamide gel electrophoresis and scanning electron microscopy. The ratio of types I and III collagen in covered skin remained constant throughout childhood and young adult life and the proportion of type III was shown to be the same as previously reported. However, in the elderly, the proportion of type III collagen in the dermis increased to a variable degree. Scanning electron microscopic examination showed a decrease in the number of collagen fibre bundles with age. Average bundle width varied significantly with age. These results may reflect an impaired synthesis of type I collagen in aged skin.

Adolescent↗
PubMed1987

Endocardial fibroelastosis: possible X linked inheritance.

We report a pedigree in which six males died of cardiac failure within the first eight months of life. These males were related through healthy females, as with X linked recessive inheritance. There was no consanguinity. None of the affected boys had an anatomical cardiac abnormality. In two affected brothers, histological evidence for endomyocardial fibroelastosis was documented, and in one of these electron microscopy demonstrated abnormalities of the mitochondria as found in mitochondrial cytopathy. A review of published reports revealed five similar X linked pedigrees, and in two of these mitochondrial abnormalities were found. We suggest that these families may show an X linked recessive cardiomyopathy with mitochondrial abnormalities.

Endocardial Fibroelastosis↗
PubMed1987

Free radical production in amniotic fluid and blood plasma by medical ultrasound.

Evidence is reported that continuous wave and long pulse ultrasonic systems can induce relatively large amounts of free radicals in biological fluids in vitro under conditions similar to those currently in use for therapeutic applications. The operating conditions and approximate threshold intensities under which these instruments can produce free radicals are described.

Amniotic Fluid↗
PubMed1985

The diagnostic value of synovial biopsy in patients with arthritis of unknown cause.

Synovial biopsy of a knee joint was performed in 59 patients with arthritis of unknown cause. Light microscopy revealed a diagnosis in three. A cause became apparent in only a further 23 over a prolonged period of follow-up. Neither light microscopy, immunofluorescence nor electron microscopy discriminated between te principal diagnostic groups. Synovial fluid analysis was better than synovial biopsy at predicting osteoarthritis. Five men with giant effusions developed osteoarthritis and these might represent an entity. Synovial inflammatory changes were less pronounced in those with longer histories. Disease duration and activity may have more influence on synovial characteristics than the nature of the disorder.

Adolescent↗
PubMed1984

Chromatin associated protease from calf thymus.

We have identified and purified a chromatin bound protease from calf thymus. The purified enzyme cleaves histone H1 when whole histone is used as substrate. The enzyme is inhibited by Soya bean trypsin inhibitor, but not by PMSF, EDTA, pepstatin or Ellman's reagent. Further studies have shown that H1(0) and histone H5 are also cleaved by this enzyme, and that when HMG 1 and 2 are used as substrate HMG1 alone is degraded to give specific degradation products. We have also shown that the enzyme co-isolates with whole histone prepared by acid extraction of calf thymus nuclei, but interestingly it is not present in whole histone samples prepared in the same manner from pig thymus. A second chromatin bound protease which specifically cleaves histone H3 when whole histone is used as substrate has also been identified during the course of this work.

Animals↗
PubMed1983

Chronic arthritis associated with the presence of intrasynovial rubella virus.

In this report we present 21 instances in which live rubella virus was isolated from synovial fluid obtained from 6 cases of inflammatory oligoarthritis or polyarthritis over a period of 2 years in the absence of firm clinical evidence of rubella. In 3 cases (cases 1, 2, 6,) a persistent oligoarthritis predominantly affecting the knee joints occurred in 2 adult women and one man, lasting to date 27, 29, and 18 months respectively, and in one of these cases virions were found in cells of the synovial membrane. In case 3 a boy of 9 presented with an illness indistinguishable from the systemic variety of juvenile chronic arthritis (Still's disease). In case 4 a young man with persistent monoarthritis was found to have ankylosing spondylitis, and in case 5 a progressive erosive polyarthritis developed 5 years after an attack of rubella complicated by rubella arthritis. The virus was identified by a variety of virological techniques and infection confirmed by immunofluorescence and (in one case) electron microscopy.

Adult↗
PubMed1983

Stimulation of bone repair by ultrasound.

The repair of fibular fractures has been accelerated and modified by treatment with ultrasound. Complete bilateral transverse fibular fractures were made in adult female Wistar rats. Twelve were maintained as untreated controls. In seventy rats, one fracture was treated with ultrasound and the other mock-irradiated. Ultrasound was delivered at an intensity of 0.5 W cm-2 (spatial average, temporal peak), pulsed 2 ms on, 8 ms off for 5 minutes on 4 consecutive days during each week of treatment. The effects of treatment for different combinations of weeks, and at frequencies of 1.5 MHz and 3.0 MHz, were compared microradiographically and histologically. Ultrasonic therapy was most effective when given during the first two weeks after injury, that is, during the inflammatory and early proliferative phases of healing (before hard callus formation). Bone repair tended to be of the juvenile type, involving rapid ossification with little cartilage production when treatment was limited to this period.

Animals↗
PubMed1982

Non-thermal cellular effects of ultrasound.

The cellular effects of ultrasound can be grouped into those which are predominantly thermal in origin and those which are, at least in part, non-thermal. Cellular effects of ultrasound generally acknowledged to be essentially non-thermal include changes associated with standing waves, acoustic streaming, microstreaming and cavitation; they have been demonstrated in vitro and may, in many instances, also occur in vivo. While some stimulate cell activity and can be exploited in ultrasonic therapy, others are potentially hazardous and must be avoided. Examples of experimentally-demonstrated cellular effects in which non-thermal, ultrasonically-induced events are involved are described, together with the mechanisms considered to be involved in producing them. The relevance of such effects to the safe and beneficial use of ultrasound in diagnosis and therapy is considered.

Biophysical Phenomena↗
PubMed1981

Synovial histopathology of behçet's syndrome.

Synovial tissue obtained from 7 patients with Behçet's syndrome and 7 patients with early rheumatoid arthritis could not be distinguished under ordinary light microscopy when examined blind. A wide spectrum of features was seen in both diseases, and it is suggested that these may reflect severity and duration as much as the nature of the arthritis. Electron microscopy also failed to illustrate any distinct features of Behçet's syndrome, but immunofluorescent studies indicated consistent deposition of IgG.

Adult↗
PubMed1980

The role of ultrasound-induced cavitation in the 'in vitro' stimulation of collagen synthesis in human fibroblasts.

Collagen synthesis by human embryonic fibroblasts in vitro was estimated using a collagenase-sensitivity assay. Collagen synthesis was stimulated by irradiation with ultrasound at a frequency of 3 MHz, a space-time peak intensity of 0.5 Wcm-2, pulsed at a mark-space ratio of 2:8 ms for 5 min at ambient pressure. This stimulation was suppressed by the application of a positive pressure of 2 atmospheres during irradiation of the cells. Increasing the pressure in the absence of ultrasound had no effect on the rate of collagen synthesis in control cells. This stimulation, therefore, appears to be due to ultrasound-induced cavitation, since it is unlikely that increasing the pressure could modify any other ultrasonic parameter. Collagen synthesis is apparently stimulated to the same extent as general protein synthesis.

Acoustic Stimulation↗