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Time-dependent Variations (time-dependent + variation)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

Time-dependent Variations in Ischemia-modified Albumin Levels in Mesenteric Ischemia

ACADEMIC EMERGENCY MEDICINE, Issue 6 2009
Abdulkadir Gunduz MD
Abstract Objectives:, The objective was to determine the value of ischemia-modified albumin (IMA) in the diagnosis of mesenteric embolism. The authors investigated whether or not plasma IMA levels rose in the acute period in a rat model of mesenteric ischemia and the related time-dependent changes. Methods:, In this randomized, controlled, nonblinded trial, 36 mature female Wistar rats were divided into six groups: three control (Groups I, III, and V) and three ischemia (Groups II, IV, and VI). In the control groups, blood was sampled at 30 minutes (Group I), 2 hours (Group III), and 6 hours (Group V) following a simple laparotomy. In the ischemia groups, following laparotomy, the superior mesenteric artery (SMA) was clamped using a bulldog clamp, and blood samples were taken at 30 minutes (Group II), 2 hours (Group IV), and 6 hours (Group VI). Results:, Plasma IMA levels in the ischemia groups were significantly higher compared to those of the control groups (p < 0.004). In addition, levels were higher in the 6-hour blood samples of the ischemia group than in the 2-hour and 30-minute samples (p < 0.001). Serum IMA was also higher in the 2-hour blood samples of the ischemia group than in the 30-minute samples (p < 0.001). Conclusions:, These preliminary findings suggest that serum IMA levels may represent a significant parameter in the early diagnosis of acute mesenteric ischemia and that further studies are necessary. [source]

Influence of estradiol on cortisol secretion in ovariectomized cynomolgus macaques (Macaca fascicularis)

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 1 2003
R.C. Stavisky
Abstract In an investigation of cortisol secretion in fully mature, ovariectomized cynomolgus monkeys (Macaca fascicularis), we compared monkeys that were given either placebo (OVX, n = 26) or 17, estradiol (E2 ) (EST, n = 26) in a daily oral dose. Serum cortisol concentrations were measured prior to the experimental manipulation and 3, 6, 9, and 12 months following initiation of treatment. Pretreatment cortisol values did not differ between groups. Assessment of the treatment period values revealed that cortisol concentrations were significantly higher (,10%) in the EST than in the OVX monkeys. Cortisol also varied significantly across periods of sampling. This time-dependent variation was attributable to elevations in months 6 and 9 (when daylight was generally long), relative to months 3 and 12 (when daylight was relatively short). The modest stimulatory effect of estrogen on corticosteroid production observed in this study is consistent with what has been seen in women, and contrasts with the more robust effects observed in New World monkeys. The possible relationship between season and cortisol secretion observed here has not been previously described in monkeys. Am. J. Primatol. 60:17,22, 2003. © 2003 Wiley-Liss, Inc. [source]

Improved tomographic reconstructions using adaptive time-dependent intensity normalization

JOURNAL OF SYNCHROTRON RADIATION, Issue 5 2010
Valeriy Titarenko
The first processing step in synchrotron-based micro-tomography is the normalization of the projection images against the background, also referred to as a white field. Owing to time-dependent variations in illumination and defects in detection sensitivity, the white field is different from the projection background. In this case standard normalization methods introduce ring and wave artefacts into the resulting three-dimensional reconstruction. In this paper the authors propose a new adaptive technique accounting for these variations and allowing one to obtain cleaner normalized data and to suppress ring and wave artefacts. The background is modelled by the product of two time-dependent terms representing the illumination and detection stages. These terms are written as unknown functions, one scaled and shifted along a fixed direction (describing the illumination term) and one translated by an unknown two-dimensional vector (describing the detection term). The proposed method is applied to two sets (a stem Salix variegata and a zebrafish Danio rerio) acquired at the parallel beam of the micro-tomography station 2-BM at the Advanced Photon Source showing significant reductions in both ring and wave artefacts. In principle the method could be used to correct for time-dependent phenomena that affect other tomographic imaging geometries such as cone beam laboratory X-ray computed tomography. [source]

A Computer-Based Method for Determination of the Cell-Free Layer Width in Microcirculation

MICROCIRCULATION, Issue 3 2006
SANGHO KIM
ABSTRACT Objectives: The cell-free layer between the erythrocyte column and the vessel wall is an important determinant of hydrodynamic resistance in microcirculatory vessels. The authors report a method for continuous measurement of the width of this layer. Methods: The light intensity of a linear array of pixels perpendicular to the vessel axis is continuously determined from a video image of a microcirculatory vessel. A threshold level based on Otsu's method is used to establish the interface between the cell-free layer and the erythrocyte column. To test the method, video images at 750,4500 frames/s were obtained from venules and arterioles in rat spinotrapezius muscle at normal and reduced arterial pressures before and after induction of erythrocyte aggregation with Dextran 500. The current measurements were compared to manual measurements of the same images. Results: Values obtained by the manual and the new methods were in agreement within the 95% confidence limit by the Bland-Altman analysis and within 90,95% range by the correlation coefficient (R2). The more frequent measurements reveal substantial, rapid variations in cell-free layer width and changes in mean values with alteration of arterial pressure and red cell aggregability. Conclusions: A new, computer-based technique has been developed that provides measurements of rapid, time-dependent variations in the width of the cell-free layer in the microcirculation. [source]