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Biomedical subjects

P Atkinson

Publications and source records attributed to P Atkinson.

At least 19 recordsLinked to original sources
PubMed2006

A semiconductor source of triggered entangled photon pairs.

Entangled photon pairs are an important resource in quantum optics, and are essential for quantum information applications such as quantum key distribution and controlled quantum logic operations. The radiative decay of biexcitons-that is, states consisting of two bound electron-hole pairs-in a quantum dot has been proposed as a source of triggered polarization-entangled photon pairs. To date, however, experiments have indicated that a splitting of the intermediate exciton energy yields only classically correlated emission. Here we demonstrate triggered photon pair emission from single quantum dots suggestive of polarization entanglement. We achieve this by tuning the splitting to zero, through either application of an in-plane magnetic field or careful control of growth conditions. Entangled photon pairs generated 'on demand' have significant fundamental advantages over other schemes, which can suffer from multiple pair emission, or require post-selection techniques or the use of photon-number discriminating detectors. Furthermore, control over the pair generation time is essential for scaling many quantum information schemes beyond a few gates. Our results suggest that a triggered entangled photon pair source could be implemented by a simple semiconductor light-emitting diode.

Journal Article↗
PubMed2005

Efficient single photon detection by quantum dot resonant tunneling diodes.

We demonstrate that the resonant tunnel current through a double-barrier structure is sensitive to the capture of single photoexcited holes by an adjacent layer of quantum dots. This phenomenon could allow the detection of single photons with low dark count rates and high quantum efficiencies. The magnitude of the sensing current may be controlled via the thickness of the tunnel barriers. Larger currents give improved signal to noise and allow sub-mus photon time resolution.

Journal Article↗
PubMed2005

Should ultrasound guidance be used for central venous catheterisation in the emergency department?

In September 2002, the National Institute of Clinical Excellence (NICE) issued guidelines for England and Wales suggesting that ultrasound guidance should be used for all electives, and should be considered for most emergency, central venous catheterisations.1 These guidelines propose a major change of practice for most clinicians practising in UK Emergency Departments. There are also resource and training implications. In this paper we systematically review the literature to establish what evidence exists for the routine use of ultrasound guidance in the placement of central venous catheters in adult patients attending the Emergency Department, and provide an overview of the practical elements of this procedure.

Adult↗
PubMed2001

Early referral is essential for successful pediatric small bowel transplantation: The Canadian experience.

PURPOSE: The mortality rate for pediatric patients on the waiting list for transplantation has a major impact on the overall effectiveness of pediatric small bowel transplantation. This review was undertaken to determine the fate of Canadian children assessed for small bowel transplant and the outcome of those who undergo transplant in the tacrolimus era. METHODS: The authors reviewed retrospectively all of the pediatric small bowel patients listed since 1988 through the Canadian Organ Replacement Register and all the children referred to our program in its first year. All children who received a small bowel transplant between January 1993 and December 1999 also were reviewed. RESULTS: The mortality rate for pediatric patients on the small bowel transplant list was 53% after an average of 105 days on the list compared with 212 days for those who underwent transplant. Patients who died while on the list were younger and had signs of advanced liver disease at the time of listing. Thirteen Canadian children have received a small bowel transplant with an overall 1-year patient and graft survival rate of 61% and 53%, respectively. Survivors are all independent from total parenteral nutrition. CONCLUSION: Many Canadian children miss their opportunity for a successful small bowel transplant because of late referrals and a shortage of donor organs.

Child↗
PubMed2000

Antagonist activity of meta-chlorophenylpiperazine and partial agonist activity of 8-OH-DPAT at the 5-HT(7) receptor.

This study compared the use of adapter G-proteins to link G(s) coupled G-protein receptors to a Ca(2+) signal, enabling high throughput functional studies using a fluorescent imaging plate reader (FLIPR, Molecular Devices). The pharmacological profile of the human 5-hydroxytryptamine (5-HT(7)) receptor was studied using the adapter G-proteins G(alpha16) and G(qs5) and compared to previously published adenylyl cyclase and receptor binding data. Human embryonic kidney (HEK) 293 cells stably expressing the human 5-HT(7(a)) receptor were transiently transfected with the adapter G-proteins. Changes in intracellular Ca(2+) were monitored using the fluorescent Ca(2+)-indicator Fluo-4.5-Carboxamidotryptamine (5-CT) induced an increase in fluorescence in transfected cells only, which was attenuated by N-ethylmalaeimide and abolished by thapsigargin, consistent with a G-protein mediated mobilisation of intracellular Ca(2+). The pharmacological profile of agonists at the 5-HT(7) receptor was similar using either adapter G-protein. Agonist potency estimates were similar to that reported in binding studies but were greater than that seen in adenylyl cyclase studies. 8-Hydroxy-N, N-dipropylaminotetralin (8-OH-DPAT) and tryptamine acted as partial agonists using the adapter G-proteins, but were full agonists in recombinant systems using adenylyl cyclase. meta-Chlorophenylpiperazine (mCPP) and trifluoro-methylphenyl piperazine (TFMPP) were antagonists on intracellular Ca(2+). Antagonist pharmacological profiles were similar between adapter G-proteins, receptor binding, and adenylyl cyclase studies. These results show that adapter G-proteins can be used to study G(s)-linked receptors using the high throughput FLIPR system measuring changes in intracellular Ca(2+) and provide novel information on mCPP and 8-OH-DPAT.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2000

The carvedilol hibernation reversible ischaemia trial, marker of success (CHRISTMAS) study. Methodology of a randomised, placebo controlled, multicentre study of carvedilol in hibernation and heart failure.

BACKGROUND: Carvedilol reduces mortality and improves symptoms and ejection fraction in ischemic heart failure, but its mode of action is not well defined and not all patients respond to treatment. The aim of the CHRISTMAS (Carvedilol Hibernation Reversible Ischaemia Trial, Marker of Success) study is to examine whether hibernation may be a significant factor determining this response. This paper describes the methodology and the rationale for the choice of the nuclear cardiology and echocardiography imaging techniques used in the study. METHODS AND RESULTS: The CHRISTMAS study is a double-blind, randomised, parallel group, multinational study of oral carvedilol versus placebo in patients with chronic stable heart failure due to left ventricular systolic dysfunction from coronary artery disease. The study aims to randomise 400 patients who are on optimal treatment. Two parallel groups will be randomised to carvedilol or placebo, namely 200 with hibernating myocardium at baseline and 200 matched patients without. The presence of hibernation is defined from a mismatch between regional contractile function and regional viability, measured by echocardiography (severe segmental asynergy) and nitrate prepared resting Tc99m-MIBI myocardial perfusion imaging (segmental activity >60%). The primary treatment-related end-point of the study is the comparison of the mean change, from baseline to the final visit, in radionuclide-determined left ventricular ejection fraction in patients on placebo with those on carvedilol, between the groups designated as hibernating and non-hibernating. Other end-points being examined include the prevalence of hibernation in heart failure, the relationship between the volume of hibernating myocardium and the ejection fraction response, the prevalence of reversible ischemia in heart failure, and the comparison of echo with gated SPECT. To date, 303 patients have been screened and 251 patients randomised in the study. The study aims to report in 2000. CONCLUSIONS: The CHRISTMAS study addresses the issue of whether the presence of hibernation is a predictor of the ejection fraction response to carvedilol in heart failure. It also examines the potential role of medical therapy in hibernation as well as a number of other end-points. The study may potentially lead to an important new role for nuclear cardiology in heart failure, and demonstrates important synergy between cardiac imaging and the pharmaceutical industry.

Adrenergic beta-Antagonists↗
PubMed2000

Knee injuries in motor vehicle collisions: a study of the National Accident Sampling System database for the years 1979-1995.

A detailed study of knee injuries recorded in the 1979-1995 National Accident Sampling System database maintained by the National Highway Traffic Safety Administration was conducted. Injuries to other body regions were also considered in order to illustrate the relative frequency of knee injuries. This study demonstrated that knee injuries constitute approximately 10% of all injuries recorded every year. However, the majority of these injuries were of low severity (i.e. contusions, abrasions, lacerations) with an abbreviated injury score (AIS) of 1. Most knee injuries occurred following a frontal collision with no intrusion. The study also indicated most knee fractures occur in crashes where the vehicle velocity differences (deltaVs) were less than 45 kmph, with some occurring at deltaVs as low as 10 kmph. Serious non-fracture knee injuries (i.e. ligament tears) rated AIS 2 accounted for 20 out of every 1000 injuries and predominantly occurred at deltaVs below 25 kmph. In this study it was noted that women were more likely to experience a knee contusion than men. This study further suggests that knee impact scenarios have remained relatively constant over the years as the knee injury rates showed little variation. The rate of lap and shoulder belt use was lower in occupants who experienced a knee injury vs. the rate in the overall database and airbags were present in only a small number of cases. As this study largely included only vehicles without airbags it provides a good baseline for analysis of the influence of the airbag on knee injury trends in the future.

Accidents, Traffic↗
PubMed2000

Oral administration of adrafinil improves discrimination learning in aged beagle dogs.

Aged beagle dogs were trained on either a size or intensity discrimination task 2 h following treatment with either 20 mg/kg of adrafinil or a placebo control. Training continued until the dogs reached a predetermined criterion level of performance, or failed to acquire the task after 40 sessions. The treatments and tasks were then reversed, with both the test order and treatment order counterbalanced. Thus, half of the animals were first tested on the intensity discrimination, and half of these were first tested under adrafinil. Treatment with adrafinil produced significant improvement in learning, as indicated by a decrease in both errors and trials to criterion. An effect of adrafinil on motivation may partially account for these findings; however, adrafinil did not significantly affect response latency. Adrafinil is believed to serve as an alpha-1 adrenoceptor agonist. The improved learning may also result from enhancement of vigilance due to facilitation of noradrenergic transmission in the central nervous system.

Administration, Oral↗
PubMed2000

Use of a delayed non-matching to position task to model age-dependent cognitive decline in the dog.

Spatial learning and memory in young and old dogs was studied in a series of experiments using a delayed non-matching to position (DNMP) paradigm. Past research from our laboratory has suggested that aged dogs perform more poorly on a version of the DNMP task compared to young dogs [Head et al., Spatial learning and memory as a function of age in the dog, Behav. Neurosci. 1995;109(5):851-585]. We have now extended these findings by testing a large number of dogs on three different variations of the DNMP paradigm to evaluate different aspects of spatial learning and memory. Our results indicate that: (1) aged dogs show impaired spatial learning compared to young dogs, (2) aged dogs display spatial working memory deficits compared to young dogs, (3) young dogs have a greater maximum working spatial memory capacity than old dogs and (4) we can use the DNMP paradigm to cognitively categorize different subsets of aged dogs. These data indicate that the DNMP paradigm can serve as a valuable tool to evaluate age-dependent cognitive dysfunction in the canine.

Age Factors↗