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Biomedical subjects

John Allan

Publications and source records attributed to John Allan.

6 recordsLinked to original sources
PubMed2006

A heuristic risk assessment technique for birdstrike management at airports.

Collisions between birds and aircraft (birdstrikes) have caused the loss of at least 88 aircraft and 243 lives in world civil aviation. Conservative estimates suggest that more routine damage and delays following birdstrikes cost the industry and its insurers US$1.2-1.5 billion per year. The majority of strikes happen close to airports and most countries have regulations that require airport managers to control the birdstrike risk on their property. Birdstrike prevention has, however, lagged behind other aspects of flight safety in the development and implementation of risk assessment protocols, possibly because of the inherent difficulty in quantifying the variability in the populations and behavior of the various bird species involved. This article presents a technique that uses both national and airport-specific data to evaluate risk by creating a simple probability-times-severity matrix. It uses the frequency of strikes reported for different bird species at a given airport over the preceding five years as a measure of strike probability, and the proportion of strikes with each species that result in damage to aircraft, in the national birdstrike database, as a measure of likely severity. Action thresholds for risk levels for particular bird species are then defined, above which the airport should take action to reduce the risk further. The assessment is designed for airports where the reporting and collation of birdstrike events is reasonably consistent over time and where a bird hazard management program of some sort is already in place. This risk assessment is designed to measure risk to the airport as a business rather than risk to the traveling passenger individually. It therefore takes no account of aircraft movement rate in the calculations and is aimed at minimizing the number of damaging incidents rather than concentrating on catastrophic events. Once set up at an airport, the technique is simple to implement for nonexperts, and it allows managers to focus bird control resources on the species causing the greatest risk, hence maximizing the return on investment. This protocol is now being successfully used at major airports in the United Kingdom and elsewhere in the world.

Accident Prevention↗
PubMed2005

Comparison of growth rates of fresh and frozen-thawed embryos according to chromosomal status.

PURPOSE: To report a comparison of growth rates between fresh and frozen-thawed embryos on day 3 and 4 according to chromosomal status during PGD. METHODS: Embryos were biopsied on day 3, fluorescent in situ hybridization performed for aneuploidy detection and growth rates monitored. RESULTS: Based on 241 egg pick up-PGD and 133 frozen embryo transfer-PGD cycles. The development rate of embryos despite their chromosomal status was similar on day 3, however, overall, fresh embryos showed a significantly improved development (> or =6 cell stage; 85.7%) compared to frozen embryos (77.0%; p < 0.003). On day 4 fresh embryos showed accelerated development and further developmental improvements were associated with chromosomal normality (56.1% normal vs. 42.2% aneuploid; p < 0.004). CONCLUSIONS: Cryopreservation slows embryo development regardless of the chromosomal status. However, chromosomal status did not influence the chance of embryo implantation which was the same for fresh and thawed embryos.

Cryopreservation↗
PubMed2004

Dilemmas encountered with preimplantation diagnosis of aneuploidy in human embryos.

BACKGROUND: An increased embryo aneuploidy rate is associated with advancing maternal age. Preimplantation genetic diagnosis (PGD) using fluorescence in situ hybridisation (FISH) coupled with in vitro fertilisation (IVF)/embryo biopsy provides a powerful tool to improve the take home baby rates for this poor prognostic group. AIM: To report the preliminary findings of a PGD study for aneuploidy screening and to discuss the dilemmas encountered. METHODS: Preimplantation genetic diagnosis was offered in egg pick up-PGD and frozen embryo transfer-PGD cycles. Embryo biopsy was carried out on day 3 and FISH was used to detect chromosomal abnormalities. RESULTS: The outcome of 75 patients, 100 treatment cycles; 62 egg pick up-PGD and 38 frozen embryo transfer-PGD are presented. The embryo biopsy rate, blastomere survival, presence of nuclei and successful FISH rates for egg pick-up and frozen embryo transfer cycles were similar giving a chromosomal abnormality rate of 57.5 and 51.2% for the respective treatment group. The positive pregnancy, clinical pregnancy and implantation rates were, for egg pick up-PGD 22.7, 13.6 and 21.1% and for frozen embryo transfer-PGD 13.8, 10.3 and 10.0%, respectively. CONCLUSIONS: Preimplantation genetic diagnosis coupled with IVF treatment seems to give satisfactory pregnancy rates. The high embryo aneuploidy rates, chromosomal mosaicism and other issues have presented significant ethical and management dilemmas for our physicians and patients alike. These issues highlight the importance of skillful pretreatment counselling for patients considering PGD.

Aneuploidy↗
PubMed2003

Immunopathogenesis of chlamydia trachomatis infections in women.

OBJECTIVE: To develop a model of pathogenesis by which Chlamydia trachomatis progresses from acute to chronic infection, and finally serious disease (salpingitis, tubal occlusion). DESIGN: Review of current literature located through web-based Medline searches using key words: Chlamydia trachomatis, immunology, cytokines, heat shock protein, infertility. RESULT(S): Cell-mediated immune mechanisms appear to be critical in determining whether acute infection is resolved or progresses into chronicity with pathological outcome. What determines the particular immune pathway depends on a range of determinants-HLA subtype and human genetics, cytokine profile, infectious load, route of infection, and endocrinology. A clearer picture of the natural history of chlamydial pathology may assist in providing better predictors of those women who may go on to develop significant sequelae after infection. CONCLUSION(S): Predicting those who may develop serious disease, including infertility, may contribute to improved management of such persons during earlier stages of infection and assist in prevention.

Chaperonin 60↗