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Biomedical subjects

S Paulin

Publications and source records attributed to S Paulin.

At least 19 recordsLinked to original sources
PubMed2001

Unstable step meandering with elastic interactions.

We report on theoretical investigations of the influence of step interactions due to elasticity on unstable step meandering during molecular beam homoepitaxy. It is shown that elasticity causes coarsening of the cellular structure of the meander found in a previous work. The time dependence of step roughness is found to be robust, behaving as t(1/2). The lateral length scale coarsening is shown to be sensitive to the underlying physical mechanisms. In particular, the typical length follows the law t(alpha), with alpha = 1/6 or 1/4 depending on whether line diffusion is negligibly small or not.

Journal Article↗
PubMed1999

Sips, Sops, and SPIs but not stn influence Salmonella enteropathogenesis.

The virulence factors influencing Salmonella-induced enteropathogenesis remain poorly characterised. The interactions of different serotypes of Salmonella with bovine ileal mucosa have been characterised in the ligated ileal loop model. In a quantitative intestinal invasion assay Salmonella dublin, S. choleraesuis, S. gallinarum, and S. abortusovis strains were all recovered from ileal mucosa, either with or without Peyer's patches in similar numbers. This observation suggests that the magnitude and route of intestinal invasion does not mediate Salmonella serotype host specificity. Despite being equally invasive there was a clear hierarchy in the enteropathogenicity of these serotypes. The magnitude of the enteropathogenic responses did not correlate to serotype host specificity. These observations implicate undefined serotype specific factors in influencing enteropathogenicity independently of intestinal invasion. Disruption of genes in Salmonella Pathogenicity Island (SPI) 1 of S. typhimurium and S. dublin blocked the secretion of Salmonella Invasion Proteins (Sips) and Salmonella Outer Proteins (Sops). These mutants were significantly less invasive and enteropathogenic then the wild type strain in ligated ileal loops. Disruption of sopB and sopD significantly reduced enteropathogenesis, but without influencing intestinal invasion. These two genes appear to act in concert. Surprisingly, disruption of stn, the Salmonella enterotoxin gene cloned on the basis of its homology to cholera toxin, did not influence enteropathogenesis. SopB was mapped to the 20 centisome of S. typhimurium and is flanked by 5 genes that are organised in a manner typical of a pathogenicity island, which we have termed SPI-5. Mutation of the other genes in SPI-5 also attenuated enteropathogenesis but not virulence for mice, suggesting SPI-5 is a key locus specifically influencing Salmonella enteropathogenesis.

Animals↗
PubMed1991

First-pass nuclear magnetic resonance imaging studies using gadolinium-DTPA in patients with coronary artery disease.

Nuclear magnetic resonance (NMR) imaging has been shown to accurately portray cardiac anatomy and function. To investigate the potential of NMR imaging for the assessment of coronary stenosis in patients with chest pain, ultrafast NMR imaging in conjunction with a T1 (longitudinal relaxation time) contrast agent was performed in 17 patients with chest pain who had undergone cardiac catheterization. These included 12 patients with significant coronary artery stenoses and 4 who underwent repeat NMR study after myocardial revascularization. Cardiac images at rest were obtained during rapid intravenous injection of gadolinium-DTPA (0.04 mM/kg). Electrocardiographic-gated images were acquired over 380 ms, with repetitive images obtained every 3 to 4 s. After contrast injection, there was pronounced signal enhancement in the right ventricular cavity, followed by enhancement in the left ventricular cavity and myocardium. Regional myocardium perfused by a diseased vessel demonstrated a lower peak signal intensity (p = 0.001) and lower rate of signal increase (p = 0.001) than did myocardium perfused by coronary arteries without stenosis. Repeat NMR study after revascularization showed an increase in peak signal intensity (p less than 0.002). These results demonstrate the clinical potential of dynamic gadolinium-DTPA-enhanced NMR imaging for the assessment of coronary artery disease in patients with chest pain. In combination with anatomic and functional NMR imaging, this technique has the potential to provide a comprehensive noninvasive cardiac evaluation of patients with suspected coronary artery disease.

Adult↗
PubMed1991

Coronary arteries: breath-hold MR angiography.

The authors describe a method for performance of ultrafast magnetic resonance (MR) angiography of coronary arteries with a standard clinical MR system and a body coil. Each image was obtained within a single breath hold by using an electrocardiography-gated, segmented, ultrafast, gradient-echo pulse sequence with an incremental excitation flip angle for the eight phase-encoding steps acquired per segment. By using overlapping 4-mm-thick sections, the coronary arteries were routinely depicted from the coronary ostia distally at MR in healthy subjects. Ultrafast MR angiography of the coronary arteries is feasible with use of a standard body coil. This technique offers considerable potential as an investigational tool and, with further development, may become a clinically useful imaging application.

Adult↗
PubMed1987

Intracoronary thallium-201 scintigraphy after thrombolytic therapy for acute myocardial infarction compared with 10 and 100 day intravenous thallium-201 scintigraphy.

Thallium-201 imaging has been utilized to estimate myocardial salvage after thrombolytic therapy for acute myocardial infarction. However, results from recent animal studies have suggested that as a result of reactive hyperemia and delayed necrosis, thallium-201 imaging may overestimate myocardial salvage. To determine whether early overestimation of salvage occurs in humans, intracoronary thallium-201 scans 1 hour after thrombolytic therapy were compared with intravenous thallium-201 scans obtained approximately 10 and 100 days after myocardial infarction in 29 patients. In 10 patients with angiographic evidence of coronary reperfusion, immediate improvement in thallium defects and no interim clinical events, there was no change in imaging in the follow-up studies. Of nine patients with coronary reperfusion but no initial improvement of perfusion defects, none showed worsening of defects in the follow-up images. Six of these patients demonstrated subsequent improvement at either 10 or 100 days after infarction. Seven of 10 patients with neither early evidence of reperfusion nor improvement in perfusion defects had improvement of infarct-related perfusion defects, and none showed worsening. In conclusion, serial scanning at 10 and 100 days after infarction in patients with no subsequent clinical events showed no worsening of the perfusion image compared with images obtained in acute studies. Therefore, there is no evidence that thallium-201 imaging performed early in patients with acute myocardial infarction overestimates improvement.

Acute Disease↗
PubMed1987

MR imaging of the aortic root and proximal coronary arteries.

Six patients who had recently undergone selective coronary and left ventricular angiography were prospectively examined with MR to show the aortic root and proximal coronary arteries. The examinations were performed with a superconductive 1.5-T instrument with spin-echo sequences and ECG-gated multiple slices of 5-mm thickness. The location and plane direction of the scan were guided by findings on initial coronary MR scout scans and by a review of the angiograms. In four of the six patients both coronary orifices and the proximal centimeters of both coronary arteries were identified. In the remaining two, only the left proximal coronary artery was seen. Although segments of more peripherally located portions of the main coronary arteries and branches were detectable, a prospective and conclusive identification without knowledge of the angiographic anatomy would have been extremely difficult. Differential diagnostic problems, such as erroneous interpretation of pericardial recesses and coronary veins, were observed. Unsuccessful demonstration of the right coronary artery orifice in two cases coincided with more peripherally located occlusion of the vessels on the angiogram. MR with spin-echo sequences appears to be unsatisfactory for diagnosis of coronary arteriosclerotic disease, but it may be useful in other conditions that result in significant coronary dilatation, such as fistulae and aneurysms.

Aged↗
PubMed1985

Uptake of hematoporphyrin derivative by valvular vegetations in experimental infective endocarditis.

Drugs that localize in valvular vegetations may be useful in the diagnosis and treatment of infective endocarditis. We therefore tested the hypothesis that parenterally injected hematoporphyrin derivative (HPD), which is concentrated in tumors and atherosclerotic plaques, localizes in the vegetations of experimental infective endocarditis. In 14 rabbits, various bacteria were given intra-arterially immediately after injury to the aortic valve. In 12 additional rabbits, sterile vegetations on the aortic valve were produced by the trauma caused by an indwelling catheter that had been in place over a long period. HPD, 2.5 mg/kg, was injected intravenously 1 to 2 days before the animals were killed in six rabbits with sterile vegetations and in seven rabbits with infected vegetations. In all rabbits, multiple vegetations on the aortic valve leaflets were identified. On exposure to ultraviolet light, strong porphyrin fluorescence of all vegetations, whether sterile or infected, was observed only in rabbits given HPD. In two rabbits given HPD 10 weeks after catheter implantation across the aortic valve, however, only mild fluorescence could be detected in healing endocardial vegetations. In frozen sections of HPD-laden lesions, a patchy distribution of fluorescence was observed that was similar to the pattern of HPD localization in atheromatous plaques. Since vegetations in experimental infective endocarditis selectively concentrate HPD, porphyrins could be useful in the diagnosis and treatment of infective endocarditis.

Animals↗