David William Thomas

Analytical formulation for the shielding effectiveness of enclosures with apertures

An analytical formulation has been developed for the shielding effectiveness of a rectangular enclosure with an aperture. Both the magnetic and electric shielding may be calculated as a function of frequency, enclosure dimensions, aperture dimensions and position within the enclosure. Theoretical values of shielding effectiveness are in good agreement with measurements. The theory has been extended to account for circular apertures, multiple apertures, and the effect of the enclosure contents.

Effective dose from cone beam CT examinations in dentistry

Cone beam CT (CBCT) is becoming an increasingly utilized imaging modality for dental examinations in the UK. Previous studies have presented little information on patient dose for the range of fields of view (FOVs) that can be utilized. The purpose of the study was therefore to calculate the effective dose delivered to the patient during a selection of CBCT examinations performed in dentistry. In particular, the i-CAT CBCT scanner was investigated for several imaging protocols commonly used in clinical practice. A Rando phantom containing thermoluminescent dosemeters was scanned. Using both the 1990 and recently approved 2007 International Commission on Radiological Protection recommended tissue weighting factors, effective doses were calculated. The doses (E(1990), E(2007)) were: full FOV head (92.8 microSv, 206.2 microSv); 13 cm scan of the jaws (39.5 microSv, 133.9 microSv); 6 cm high-resolution mandible (47.2 microSv, 188.5 microSv); 6 cm high-resolution maxilla (18.5 microSv, 93.3 microSv); 6 cm standard mandible (23.9 microSv, 96.2 microSv); and 6 cm standard maxilla (9.7 microSv, 58.9 microSv). The doses from CBCT are low compared with conventional CT but significantly higher than conventional dental radiography techniques.

A review of the scientific evidence for biofilms in wounds

Both chronic and acute dermal wounds are susceptible to infection due to sterile loss of the innate barrier function of the skin and dermal appendages, facilitating the development of microbial communities, referred to as biofilms, within the wound environment. Microbial biofilms are implicated in both the infection of wounds and failure of those wounds to heal. The aim of this review is to provide a summary of published papers detailing biofilms in wounds, the effect they have on infection and wound healing, and detailing methods employed for their detection. The studies highlighted within this paper provide evidence that biofilms reside within the chronic wound and represent an important mechanism underlying the observed, delayed healing and infection. The reasons for this include both protease activity and immunological suppression. Furthermore, a lack of responsiveness to an array of antimicrobial agents has been due to the biofilms’ ability to inherently resist antimicrobial agents. It is imperative that effective strategies are developed, tested prospectively, and employed in chronic wounds to support the healing process and to reduce infection rates. It is increasingly apparent that adoption of a biofilm‐based management approach to wound care, utilizing the “antibiofilm tool box” of therapies, to kill and prevent reattachment of microorganisms in the biofilm is producing the most positive clinical outcomes and prevention of infection.

Should paediatric intensive care be centralised? Trent versus Victoria

BACKGROUND The mortality rate is lower among children admitted to specialist paediatric intensive care units (ICUs) than among those admitted to mixed adult and paediatric units in non-tertiary hospitals. In the UK, however, few children receive intensive care in specialist paediatric units. We compared the ICU mortality rate in children from the area the Trent Health Authority, UK, with the rate in children from Victoria, Australia, where paediatric intensive care is highly centralised. METHODS We studied all children under 16 years of age from Trent and Victoria who received intensive care between April 1, 1994, and March 31, 1995. Children younger than 1 month were excluded unless they had cardiac disorders. We developed a logistic regression model that used information gathered at the time of admission to ICU to adjust for risk of mortality. FINDINGS The rates of admission of children to intensive care were similar for Trent and Victoria (1.22 and 1.18 per 1000 children per year), but the mean duration of an ICU stay was 3.93 days for Trent children compared with 2.14 days for children from Victoria. 74 (7.3%) of the 1014 children from Trent died, compared with 60 (5.0%) of the 1194 children from Victoria. With adjustment for severity of illness at the time of admission to ICU, the odds ratio for the risk of death for Trent versus Victoria was 2.09 (95% CI 1.37-3.19, p < 0.0005). There were 31.7 (14.0-50.4) excess deaths in Trent children, which is equivalent to 42.8% of the deaths in ICU, and 11.1% of all deaths in children between the ages of 1 month and 16 years in Trent. INTERPRETATION If Trent is representative of the whole country, there are 453 (200-720) excess deaths a year in the UK that are probably due to suboptimal results from paediatric intensive care. If the ratio of paediatric ICUs to children were the same in the UK as in Victoria, there would be only 12 paediatric ICUs in the country. Our findings suggest that substantial reductions in mortality could be achieved if every UK child who needed endotracheal intubation for more than 12-24 h were admitted to one of 12 large specialist paediatric ICUs.

Detection and identification of specific bacteria in wound biofilms using peptide nucleic acid fluorescent in situ hybridization (PNA FISH)

Biofilms provide a reservoir of potentially infectious micro-organisms that are resistant to antimicrobial agents, and their importance in the failure of medical devices and chronic inflammatory conditions is increasingly being recognized. Particular research interest exists in the association of biofilms with wound infection and non-healing, i.e. chronic wounds. In this study, fluorescent in situ hybridization (FISH) was used in combination with confocal laser scanning microscopy (CLSM) to detect and characterize the spatial distribution of biofilm-forming bacteria which predominate within human chronic skin wounds (Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus sp. and Micrococcus sp.). In vitro biofilms were prepared using a constant-depth film fermenter and a reconstituted human epidermis model. In vivo biofilms were also studied using biopsy samples from non-infected chronic venous leg ulcers. The specificity of peptide nucleic acid (PNA) probes for the target organisms was confirmed using mixed preparations of planktonic bacteria and multiplex PNA probing. Identification and location of individual bacterial species within multi-species biofilms demonstrated that P. aeruginosa was predominant. CLSM revealed clustering of individual species within mixed-species biofilms. FISH analysis of archive chronic wound biopsy sections showed bacterial presence and allowed bacterial load to be determined. The application of this standardized procedure makes available an assay for identification of single- or multi-species bacterial populations in tissue biopsies. The technique provides a reliable tool to study bacterial biofilm formation and offers an approach to assess targeted biofilm disruption strategies in vivo.

Generalized material models in TLM .I. Materials with frequency-dependent properties

This paper presents the fundamentals of a unified approach for the treatment of general material properties in time-domain simulation based on transmission-line modeling (TLM). Linear frequency-dependent isotropic materials are dealt with in the first instance. The iteration schemes for one-dimensional (1-D) and three-dimensional (3-D) models are developed from Maxwells curl equations and the constitutive relations. Results are presented showing the accuracy of this approach.

A prospective study of the microbiology of chronic venous leg ulcers to reevaluate the clinical predictive value of tissue biopsies and swabs

This study determined whether comprehensive microbiological analysis offered real predictive value in terms of healing outcome, and assessed the clinical usefulness of surface swabs vs. tissue biopsies for clinically noninfected leg wounds. The wound microflora of 70 patients with chronic venous leg ulcers was quantified after sampling by swabbing and biopsy. A highly significant association between wound surface area at 4 weeks and eventual healing at 6 months was found (p<0.001), although initial wound size, sex, height, and weight were not significant predictors of outcome (p>0.1). A significant association between healing and bacterial diversity in the wound as assessed by swab (p=0.023) was demonstrated. Furthermore, the bacterial density of wound surface area by swab (CFU/mL; p=0.018) or biopsy (CFU/g tissue; p=0.038) were shown to be independent predictors of nonhealing. Logistic regression showed that microbiological analysis of biopsies provided no additional prognostic information when compared with analysis of the surface microflora (p=0.27). Hence, if biopsies do not contribute significantly to patient management, their use should be discouraged in clinically noninfected wounds. Furthermore, independent predictors of healing, such as wound surface microbial diversity and density, could identify patients likely to have an unfavorable outcome and to whom resources should be targeted.

Use of 16S Ribosomal DNA PCR and Denaturing Gradient Gel Electrophoresis for Analysis of the Microfloras of Healing and Nonhealing Chronic Venous Leg Ulcers

ABSTRACT The bacterial microfloras of 8 healing and 10 nonhealing chronic venous leg ulcers were compared by using a combination of cultural analysis and denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene products. Cultural analysis of the microflora revealed that the majority of both wound types carried the aerobes Staphylococcus and Pseudomonas spp. (89 and 80%, respectively). Sequencing of 16S ribosomal DNAs selected on the basis of DGGE profiling allowed the identification of strains not detected by cultural means. Of considerable interest was the finding that more than 40% of the sequences represented organisms not cultured from the wound from which they were amplified. DGGE profiles also revealed that all of the wounds possessed one apparently common band, identified by sequencing as Pseudomonas sp. The intensity of this PCR signal suggested that the bacterial load of nonhealing wounds was much higher for pseudomonads compared to healing wounds and that it may have been significantly underestimated by cultural analysis. Hence, the present study shows that DGGE could give valuable additional information about chronic wound microflora that is not apparent from cultural analysis alone.

Epidermal growth factor therapy and wound healing — past, present and future perspectives

The role ofepidermal growth factor (EGF) has been extensively investigated in normal and pathological wound healing. It is implicated in keratinocyte migration, fibroblast function and the formation of granulation tissue. Since the discovery of EGF, the first growth factor to be isolated, over 45 years ago, growth factor therapy has progressed into clinical practice in the treatment ofwounds. The investigation EGF in wound healing has progressed from the treatment of acute wounds, to its limited effect in chronic wounds. EGF is readily degraded in the chronic wound environment, but with the recent focus of research in new drug delivery systems that are able to protect and stabilise the protein, the potential healing effects of EGF are at the forefront of research. In this review, the history of EGF and wound healing research is considered, as are current and future therapeutic options.

Cell biology: Non-thermal heat-shock response to microwaves

Exposure limits set for microwave radiation assume that any biological effects result from tissue heating: non-thermal effects have been reported but remain controversial. We show here that prolonged exposure to low-intensity microwave fields can induce heat-shock responses in the soil nematode Caenorhabditis elegans. This effect appears to be non-thermal, suggesting that current exposure limits set for microwave equipment may need to be reconsidered.