PubMed Health⌕ Search

Biomedical subjects

P Swann

Publications and source records attributed to P Swann.

11 recordsLinked to original sources
PubMed2006

Functional loss in early age-related maculopathy: the ischaemia postreceptoral hypothesis.

We review proposed models and psychophysical and electrophysiological tests performed in many studies for early age-related maculopathy (ARM). We suggest that ischaemia is the trigger for impaired retinal pigment epithelium function causing imbalance of secretion of vascular growth factors, reduced disc degradation capability and reduced metabolic activity and possible inflammatory response. This results in increased deposition of cell debris, such as drusen and thickens Bruch's membrane causing even more ischaemia of the overlying neurosensory retina. The photoreceptors are more resistant to ischaemia given their proximity to the choroid. Furthermore, being 'upstream' from the inner retinal layers, they act as an oxygen sink depriving retinal layers further from the choroid. Postreceptoral cell layers and especially parts of the inner nuclear layer that are located in the watershed zone between two sources of blood supply are preferentially vulnerable to ischaemia. Based on psychophysical and electrophysiological findings we propose that most of the function impairment in early ARM starts postreceptorally.

Electroretinography↗
PubMed2005

Cone- and rod-mediated multifocal electroretinogram in early age-related maculopathy.

PURPOSE: To investigate the cone- and rod-mediated multifocal electroretinograms (mfERG) in early age-related maculopathy (early ARM). METHODS AND SUBJECTS: We investigated the cone- and rod-mediated mfERG in 17 eyes of 17 subjects with early ARM and 16 eyes of 16 age-matched control subjects with normal fundi. All subjects had a visual acuity of 6/12 or better. We divided the ARM subjects into two groups based on drusen size and retinal pigment epithelium abnormalities-a less advanced (ARM1) and a more advanced (ARM2) group. The mfERG data were compared to templates derived from the control group. We analysed the mfERG results for the central and peripheral fields (CP method) and the superior and inferior fields (SI method). RESULTS: While the mean cone results showed no statistically significant difference between the groups, the rods showed significantly delayed responses in the ARM1 group for the CP and the SI methods, but not in the ARM2 group, although there was a trend of longer latencies compared to the control group. CONCLUSION: Our results show a functional impairment of the rods in early ARM subjects. As there is histopathological evidence showing earlier rod than cone impairment in early ARM, following the rod function with the mfERG might be helpful in diagnosis or for monitoring the progression of early ARM.

Aged↗
PubMed2005

Monitoring retinal function in early age-related maculopathy: visual performance after 1 year.

PURPOSE: To monitor visual performance in early age-related maculopathy (ARM). METHODS: We measured monocular visual function-high-contrast visual acuity (HC-VA), central visual fields (mean sensitivity, MS), colour vision (desaturated Panel D-15), Pelli-Robson (P-R), and cone- and rod-mediated multifocal electroretinograms (mfERG) in 13 ARM subjects and 13 age-matched control subjects with normal fundi at baseline and after 1 year. All had visual acuity of 6/12 or better. The mfERG data were compared to templates derived from the control group at baseline. We analysed the mfERG results by averaging the central and peripheral fields and the superior and inferior fields (CP and SI methods) and by calculating the local responses. RESULTS: The mean rod-mediated responses were significantly delayed in the ARM group for the CP (P=0.04) and the SI methods (P=0.03) at baseline compared to the control group. This did not change significantly after 1 year, whereas the mean cone-mediated responses were within the normal range at both times. Although the local analysis revealed lower amplitudes for the cone- and rod-mediated responses at baseline this was not found after 1 year and only the local rod-mediated latencies were delayed at both times (P<0.01). HC-VA, desaturated Panel D-15 and P-R were significantly worse in the ARM group (P< or =0.01) at baseline but did not show further significant deterioration. Progressive fundus changes were found in only two subjects (18%). CONCLUSION: Although there was significant impairment of retinal function in early ARM at baseline no further deterioration was evident after 1 year.

Aged↗
PubMed2004

The effects of dexamphetamine on simulated driving performance.

RATIONALE: The number of road fatalities related to the presence of amphetamines in drivers has been relatively constant over the past 10 years. However, there remains uncertainty as to the extent that these drugs induce driving impairment, and whether any such impairments translate to an increase in road fatalities. OBJECTIVES: To examine the acute effects of 0.42 mg/kg dexamphetamine on simulated driving performance, and to establish which, if any, simulated driving abilities become impaired following dexamphetamine administration. METHODS: A repeated-measures, counter-balanced, double-blind, placebo-controlled design was employed. Twenty healthy volunteers completed two treatment conditions-0.42 mg/kg dexamphetamine and placebo. Performance was assessed using a driving simulator task. Blood and saliva samples were obtained prior to the driving tasks and immediately after task completion (120 min and 170 min post-drug administration, respectively). RESULTS: Mean dexamphetamine blood concentrations were 83 ng/ml and 98 ng/ml at 120 min and 170 min, respectively. Results indicated a decrease in overall simulated driving ability following dexamphetamine administration during the day-time but not the night-time scenario tasks. Contributing to this performance reduction, "incorrect signalling", "failing to stop at a red traffic light" and "slow reaction times" were the behaviours most strongly affected by dexamphetamine. CONCLUSIONS: The decrease in simulated driving ability observed during the day-time driving tasks are consistent with the perceptual narrowing or tunnel vision that is associated with dexamphetamine consumption.

Adult↗
PubMed1997

A phantom for evaluating bone mineral density of the hand by dual-energy x-ray absorptiometry.

Dual-energy x-ray absorptiometry (DXA) is a precise, widely used method for measuring bone mineral density (BMD), usually of the lumbar spine and femoral neck. Recent developments, such as a lower x-ray tube current and pixel by pixel analysis, enable smaller bones and thinner tissues volumes, as in the hand, to be measured. Measurements of hand bone mineral content (BMC) and BMD could be useful in assessing disease severity in early rheumatoid arthritis and in monitoring disease progression and response to therapeutic intervention. A phantom is required for evaluating the software, measuring long-term precision and comparing with other DXA methods. This note describes the design and evaluation of a hand phantom for use on a Lunar DPX-L dual-energy x-ray absorptiometer. The phantom consists of three sections representing the metacarpals, and proximal and distal phalanges, using aluminum and Perspex as the bone and lean tissue equivalents respectively. The BMD of the three sections is approximately 1.0, 0.6 and 0.3 g cm-2. The phantom demonstrates limitations in the potential accuracy of BMD determination at low densities using the Small Animal Software on the Lunar DPX-L. Improved recognition of low-density regions was obtained with the Lunar EXPERT with precision values of 0.9, 1.1 and 2.0% for the three sections of the phantom respectively.

Absorptiometry, Photon↗
PubMed1991

Stress management for irritable bowel syndrome: a controlled trial.

Thirty-five patients with irritable bowel syndrome were randomized to receive treatment in a stress management programme or conventional therapy which included the antispasmodic Colpermin. The stress management programme involved a median of six 40-min sessions with a physiotherapist during which patients were helped to understand the nature of their symptoms, their relationship to stress and were taught relaxation exercises. Two thirds of those in the stress management programme found the programme effective in relieving symptoms and experienced fewer attacks of less severity. This benefit was maintained for at least 12 months. Few of those given conventional management had any benefit. A stress management programme would appear to be of value for patients with irritable bowel syndrome.

Adult↗
PubMed1984

Mycoplasmal pneumonia. Three severe cases of a common infection.

Mycoplasma pneumoniae is one of the most common causes of community-acquired pneumonia. Infection is usually self-limited, but fulminant pneumonia and extrapulmonary complications can supervene. Usually, unilateral confluent, patchy, or nodular infiltrates of the lower lobe are seen on roentgenograms. Diagnosis is achieved by isolation of the organism or by serologic methods. Treatment with either erythromycin or tetracycline is effective, although organisms can be recovered during therapy. In the three cases of mycoplasmal pneumonia reported here, infection was resistant to initial therapy but patients recovered when appropriate antimicrobial therapy was instituted.

Adult↗
PubMed1984

A controllable artificial afterload for isolated heart studies.

This paper presents an artificial afterload, based on the Westerhof model, for use in isolated heart preparations. The system has adjustable elements representing peripheral resistance and total arterial compliance, together with a fixed element representing aortic impedance. It is controlled by a computer in a manner which incorporates feed forward and feedback techniques. The system maintains constant 'arterial' pressure in the face of large excursions of the flow through it. It can be programmed to change this pressure in a dynamic fashion. The time taken to recover from large changes in flow and to reset the pressure is at most 3 S. Absolute values of peripheral resistance are easily obtained without any knowledge of the actual flow being required. Tests of the system demonstrate its stability and rapid transient characteristics.

Biomedical Engineering↗