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Biomedical subjects

J Sykes

Publications and source records attributed to J Sykes.

At least 37 records · Page 2Linked to original sources
PubMed1999

Assessment of myocardial viability using MRI during a constant infusion of Gd-DTPA: further studies at early and late periods of reperfusion.

It was previously shown in a canine model of ischemia/reperfusion injury that the partition coefficient of gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA) (lambda) increases in infarcted tissue. That previous study used a non-magnetic resonance imaging (MRI) method to measure lambda and only investigated reperfusion times from 2 hr to 3 weeks. This study presents evidence suggesting that lambda starts to increase as early as 1 min after reperfusion of a 2 hr occlusion and continues to rise for up to 2 hr or more; lambda stays increased as late as 8 weeks, reaching peak values at 1-11 days and subsequently decreasing. It was also demonstrated that lambda can be accurately measured in vivo using a saturation recovery turbo fast low-angle shot (FLASH) sequence. The results of this study show that MRI during a constant infusion of Gd-DTPA has great potential for the non-invasive determination of myocardial viability as early as 1 min to as late as 8 weeks following reperfusion of acute myocardial infarction.

Animals↗
PubMed1998

Noninvasive assessment of pharmaceutical intervention during myocardial ischemia-reperfusion in a canine model using two-dimensional 31P chemical shift imaging.

The metabolic effects during myocardial ischemia and sustained reperfusion of the antianginal agents diltiazem (n = 10) and propranolol (n = 10) were monitored with noninvasive phosphorus nuclear magnetic resonance spectroscopy to establish any correlation between metabolic changes and infarct size. Spectroscopy followed changes in high-energy phosphate concentrations and myocardial intracellular pH during 2 h of left anterior descending coronary artery occlusion and 3 subsequent weeks of reperfusion, in a closed chest canine infarct model. Gadolinium-DTPA enhanced magnetic resonance imaging was used to assess the extent of myocardial injury (infarct size). Microspheres were used to document the zone at risk and the success of reperfusion. Whereas diltiazem appeared to reduce the derangement in high-energy phosphates during coronary occlusion, there was no significant change in infarct size when compared with a previously studied control group. Propranolol, which produced a lesser decline in pH during occlusion and smaller pH changes during early reperfusion, was associated with a significant reduction in the degree of tissue necrosis (compared with controls). There was an inverse correlation (r = -0.51) between the change in myocardial pH (occlusion end to immediate reperfusion) and the recovery index (an index of myocardial salvage). By 1 h into reperfusion, there was a stronger inverse correlation between pH and infarct size (r = -0.75), implying a protective effect of delaying pH recovery during early reperfusion and indicating the potential use of this parameter as a predictor of tissue viability.

Adenosine Triphosphate↗
PubMed1998

A multi-centre, general practice comparison of ispaghula husk with lactulose and other laxatives in the treatment of simple constipation.

An open, multi-centre study in general practice compared with efficacy, speed of action and acceptability of ispaghula husk (Fybogel Orange, Reckitt & Colman Products, UK), lactulose and other laxatives in the treatment of patients with simple constipation. A total of 65 GPs recruited 394 patients, of whom 224 (56.9%) were assigned to treatment with ispaghula and 170 (43.1%) to other laxatives (mainly lactulose) for up to four weeks. Thirteen patients withdrew before treatment started, so that 381 entered the study. Patients were assessed by their GP before entry and after two and four weeks of treatment. Patients also kept daily records of their bowel movements. After four weeks' treatment, ispaghula husk was assessed by the GPs to be superior to the other treatments in improving bowel function and in overall effectiveness, palatability and acceptability. Patients' reports of time to first bowel movement showed little difference between the treatments. Over 60% of patients in each treatment group passed a first motion within 24 hours, and over 80% within 36 hours. Ispaghula husk produced a higher percentage of normal, well-formed stools and fewer hard stools than other laxatives. Incidences of soiling, diarrhoea and abdominal pain were lower in the group receiving ispaghula husk. Overall, ispaghula husk was an effective treatment for simple constipation, and was associated with better stool consistency and a lower incidence of adverse events compared with lactulose or with other laxatives.

Adult↗
PubMed1997

Controlled reperfusion after myocardial ischemia in a canine model monitored by two-dimensional phosphorus 31 chemical shift spectroscopic imaging.

Phosphorus 31 magnetic resonance spectroscopy at 2 T was used to monitor high-energy phosphate metabolism over a 3-week period in a canine model of myocardial infarction and reperfusion. Twenty animals were divided into two groups: group 1 (n = 11) received intravenous nitroglycerin beginning at the onset of coronary occlusion; group 2 (n = 9) received a 105-minute infusion of superoxide dismutase (SOD) beginning at the onset of reperfusion. A metabolic protective effect was observed (vs controls) with both agents, manifested by a reduction in the degree of pH decline from baseline values and preservation of the adenosine triphosphate/total phosphate ratio during occlusion and reperfusion. Further, both treatments, compared with controls, produced a lower infarct/zone at risk ratio: controls, 1.5 +/- 1.2; nitroglycerin, 0.52 +/- 0.50; and SOD, 0.64 +/- 0.40. The technique of 31P magnetic resonance spectroscopy demonstrated its use for the noninvasive assessment of myocardial metabolism in response to therapeutic intervention.

Adenosine Triphosphate↗
PubMed1997

High refresh rate and oculomotor adaptation facilitate reading from video displays.

Reading from a video display terminal (VDT) was tested at screen refresh rates of 500 Hz and 60 Hz. Reading was initially 8 words/min (3.05%) faster at 500 Hz. A hypothesis that reading rate on VDTs is limited by stimulus availability accounts for the difference. When the eye reaches a new fixation position, it 'parks' until a sample of text appears at the fovea. Then processing resumes in the normal way. This idea, combined with the 500-Hz reading data, can predict reading rate at any refresh rate, and is quantitatively confirmed by the reading rate at 60 Hz. The difference in reading rates disappeared for the second half of the text, as a result of differences between frequencies of eye movements in the two refresh conditions. From the first half to the second, subjects at 60 Hz made more large forward saccades and fewer small reverse saccades. Both changes make sampling of the text more sparse, compensating for the dead time between samples. Subjects were unaware of refresh conditions, differences in their reading rates, and types of eye movements they generated. Reading from a continuously illuminated active-matrix display is slightly faster than from a comparable VDT.

Adaptation, Ocular↗
PubMed1997

Comparative bioavailability of aspirin and paracetamol following single dose administration of soluble and plain tablets.

In this study, the bioavailability of aspirin and paracetamol was compared in plain and soluble combination formulations in fasting, healthy volunteers. Blood samples were taken and Cmax, Tmax and AUC measured at various times following administration of single doses of the two formulations in 12 subjects. The rapidity of uptake of aspirin following administration of a soluble formulation suggests significant absorption from the stomach. There was no significant difference in the pharmacokinetic parameters of paracetamol derived from a soluble or plain formulation. A comparison of the uptake of aspirin from the soluble aspirin formulation with paracetamol from either plain or soluble tablets showed that aspirin entered the plasma and achieved peak levels significantly more quickly. However, the half life of paracetamol was significantly longer than that of aspirin. These findings suggest that onset of analgesia should be more rapid following dosing with soluble aspirin, a conclusion supported by comparative efficacy studies conducted with differing formulations of aspirin.

Acetaminophen↗
PubMed1996

The determination of myocardial viability using Gd-DTPA in a canine model of acute myocardial ischemia and reperfusion.

The partition coefficient of Gd-DTPA was thought to vary with the amount of cellular membrane damage after an acute myocardial infarction. The relationship between the partition coefficient of Gd-DTPA (lambda) and the uptake of 201Tl (as a marker of tissue viability) was studied 2 h to 3 weeks after reperfusion of a 2-h occlusion to the left anterior descending coronary artery in a canine model. Gd-DTPA was infused as a bolus followed by a prolonged constant infusion, and this infusion protocol was optimized such that the concentration of Gd-DTPA was directly related to lambda. After this infusion, MR images of excised hearts showed regions of increased signal intensity corresponding to increased Gd-DTPA concentration. At all time points, lambda and 201Tl uptake were strongly negatively correlated indicating that lambda is an accurate indicator of myocardial viability. Furthermore, lambda in the infarcted regions was increased relative to normal regions after 2 h of reperfusion and stayed elevated up to 3 weeks. At all time points, lambda in the infarcted and normal regions were significantly different. As well, this data showed a trend that lambda in infarcted regions decreased monotonically from 1 day to 3 weeks. This trend was confirmed with MR imaging by examining the change in signal intensity of in vivo images from 4 days to 3 weeks in two animals. These results suggest that MRI with Gd-DTPA could be used to measure the extent of myocardial damage after an acute myocardial infarction.

Animals↗
PubMed1995

A report on the use of technician ophthalmoscopy combined with the use of the Canon non-mydriatic camera in screening for diabetic retinopathy in the community.

This paper describes a general practice based diabetic retinopathy screening service employing a technician trained in direct and indirect ophthalmoscopy and taking photographs with a Canon CR3 45 NM non-mydriatic polaroid camera analysed by a consultant ophthalmologist to provide a comparison with the screener's opinion. Prospective data is presented from the first 1050 patients screened for diabetic retinopathy in the Exeter Health Authority area. Analysis of data collected showed a prevalence of diabetic retinopathy in the screened population of 27%, 14% previously undetected with a 0.5% prevalence of sight-threatening retinopathy. There was almost complete agreement between ophthalmoscopy findings and the consultant analysis of photographs. Screening costs were calculated at 10.38 pounds per patient screened. A specially trained non-medically qualified technician can provide a good quality cost-effective screening service for diabetic retinopathy within a primary care setting.

Adolescent↗
PubMed1986

A Monte Carlo program to calculate the exposure rate from airborne radioactive gases inside a nuclear reactor containment building.

A program was developed to calculate the exposure rate resulting from airborne gases inside a reactor containment building. The calculations were performed at the location of a wall-mounted area radiation monitor. The program uses Monte Carlo techniques and accounts for both the direct and scattered components of the radiation field at the detector. The scattered component was found to contribute about 30% of the total exposure rate at 50 keV and dropped to about 7% at 2000 keV. The results of the calculations were normalized to unit activity per unit volume of air in the containment. This allows the exposure rate readings of the area monitor to be used to estimate the airborne activity in containment in the early phases of an accident. Such estimates, coupled with containment leak rates, provide a method to obtain a release rate for use in offsite dose projection calculations.

Accidents↗
PubMed1985

Experimental evaluation of a method for performing personnel beta dosimetry using multi-element thermoluminescent dosimeters.

Two multi-element thermoluminescent (TL) dosimeter designs were calibrated in a gamma field and then exposed to beta sources emitting different beta spectra. The TL readouts from the dosimeters were analyzed using an algorithm designed to enable calculation of the beta doses from the dosimeter readings without performing any beta calibrations. The results suggest that the method is promising for application in personnel beta dosimetry.

Beta Particles↗
PubMed1985

The precise midline forehead flap in reconstruction of the nose.

The midline forehead flap has been a preferred choice for nasal repair in our practice for over 20 years, with no significant complication ever having developed (Figs. 9 to 11). The abundance and length of tissue it provides is remarkable, given the inconspicuous defect remaining in the forehead area. Its use is economical of tissue, time, and expense to the patient. Most importantly, the midline flap provides superior aesthetic and reconstructive repair in a relatively short period of time without resorting to more complicated, and therefore more risky, flap designs.

Adult↗
PubMed1983

The effect of ionic and temperature shifts used for in vitro ribosome subunit reconstitution upon the large molecular weight ribosomal ribonucleic acids.

The behaviour of purified, intact preparations of 16 S and 23 S rRNAs has been studied in their respective ribosome subunit reconstitution systems by means of sedimentation and electrophoretic analysis. Both species undergo profound conformation changes to more compact species at the temperatures and ionic conditions commonly agreed for their reconstitution into ribosome subunits. The 16 S rRNA undergoes a complete conformation change over the input range of concentration used, whereas the change for 23 S rRNA is incomplete for inputs above 1.5 mg X ml-1. Intact 23 S rRNA is also required and some preparations recommended for r-protein binding studies do not meet this requirement for reconstitution. These observations are discussed in relation to the overall effectiveness of ribosome subunit reconstitution systems.

Escherichia coli↗
PubMed1979

The pools of ribosomal proteins and ribosomal ribonucleic acids during relaxed control of Escherichia coli A19 (Hfr, rel met rns).

The soluble fraction extracted from Escherichia coli A19 (Hfr, rel met rns) during early and late times of phenotypic and genotypic induced relaxed control have been examined for the possible accumulation of ribosomal proteins (r-proteins) and rRNA species during this time of unbalanced macromolecular synthesis. Ribosomal proteins and rRNA species were not found to accumulate within the soluble fraction at any time during this period of relaxed control; even after the typical rRNA accumulation had ceased, r-proteins did not accumulate. It is concluded, from these and related observations, that the r-proteins and rRNA species known to be produced during relaxation must immediately associate to form the unusual ribonucleoprotein particles (e.g. 'relaxed particles' and 'chloramphenicol particles') characteristic of periods of relaxed control. Since r-proteins do not accumulate even when net RNA accumulation halts, it appears that some elements of the normal, basic co-ordination between rRNA and r-protein synthesis/stability persist even during relaxed control.

Centrifugation, Density Gradient↗