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Frequent Measurements (frequent + measurement)

Distribution by Scientific Domains

Medical Sciences	75%

Selected Abstracts

Analysis of hepatitis B viral load decline under potent therapy: Complex decay profiles observed

HEPATOLOGY, Issue 5 2001
Sharon R. Lewin
We used a new real-time polymerase chain reaction (PCR)-based assay that is sensitive, has a wide dynamic linear range, and is highly reproducible to quantify hepatitis B virus (HBV) DNA in the serum of infected individuals undergoing potent antiviral therapy. In addition, we made frequent measurements of viral load after initiation of treatment and maintained follow-up to about 12 weeks. To analyze the data we used a new model of HBV decay, which takes into account that existing drug treatments do not completely block de novo infection and the possibility of noncytolytic loss of infected cells. On initiation of therapy, there was a mean delay of 1.6 days followed by a biphasic or muliphasic decay of plasma HBV DNA. The slope of the first phase varied considerably, with one individual having rapid decay, corresponding to a virion half-life of 1 hour, but others showing half-lives of up to 92 hours. Individuals either had a slow second-phase decline (t½ = 7.2 ± 1.2 days) or a flat second phase. Some individuals exhibited a complex "staircase pattern" of decay, with further phases of viral DNA decline and phases with little change in viral load. [source]

Winter streamflow variability, Yukon Territory, Canada

HYDROLOGICAL PROCESSES, Issue 4 2002
R. D. Moore
Abstract Knowledge of winter streamflow regimes is required in northern catchments to evaluate water supply and to assess the vulnerability of aquatic habitat. The objective of this study was to explore the nature and causes of winter streamflow variability in northern rivers through examination of a limited number of case studies involving intensive field measurements, as well as a synoptic analysis of winter streamflow measurements archived by Water Survey of Canada for rivers in Yukon Territory, Canada. Evidence was found for an abrupt decrease in discharge at freeze-up in one of the case studies and for 10 of the 25 stations in the synoptic analysis that had measurements within 30 days of freeze-up (an additional 12 stations had no measurements within 30 days of freeze-up). However, given the paucity of measurements in the early winter, the magnitude, duration and frequency of these events cannot be specified. The case studies indicate that, even where a coherent depression does not occur, discharge can fluctuate around a smooth recession trend for about the first 30 days after the onset of ice effects, probably as a result of transient storage and release of water behind ice jams. A storage-depletion model that represents streamflow as outflow from two parallel linear reservoirs provided a reasonable fit to most of the observed measurements (excluding those in the first 30 days following freeze-up), with model fit deteriorating with increasing latitude and decreasing catchment size. The effect of latitude could relate to abstraction of flow by ice production, which would cause deviations from a storage-depletion trend. Northern catchments also tended to have steeper late-winter recessions, which could reflect a lack of extensive, deep aquifers to maintain late-winter discharge. The tendency to poorer model fit in smaller catchments could reflect a problem with data reliability, since it is more difficult to find good winter gauging sections in smaller streams. Some evidence for temperature-related discharge fluctuations was found in both the case studies and synoptic analyses. However, the magnitude of these effects appears to be about ±10 to 15%, at most, and not to be consistent between winters. Further advances in understanding winter streamflow variability will require frequent measurements on a range of streams over a number of winters. Copyright © 2002 John Wiley & Sons, Ltd. [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]

Increased insulin sensitivity in young, growth hormone deficient children

CLINICAL ENDOCRINOLOGY, Issue 1 2001
Sandra Husbands
OBJECTIVE Although growth hormone (GH) has well documented insulin antagonistic effects, GH deficient adults often demonstrate insulin resistance. In young GH deficient children, increased susceptibility to hypoglycaemia might indicate increased insulin sensitivity; however, this has not been documented. We therefore determined insulin sensitivity in GH deficient and GH sufficient children. DESIGN AND PATIENTS Prospective study of children undergoing insulin tolerance tests for clinical investigation of GH or cortisol secretion at a regional Paediatric Endocrine/Growth Clinic between October 1986 and December 1997. Ninety-one tests were performed in children with GH deficiency and 142 tests in children with normal GH response to insulin (peak GH , 20 IU/l). MEASUREMENTS The standard insulin tolerance test was modified to permit frequent measurements of glucose (0, 5, 10, 15, 20, 30, 45, 60 and 90 minutes). Rate of log glucose disappearance in the first 15 minutes was calculated as a direct measure of insulin sensitivity. RESULTS GH deficient children were more insulin sensitive than GH sufficient children (P = 0·004) and had lower glucose nadirs post-insulin (P = 0·005). Subgroup analysis revealed that these differences were greater in younger (< 12 years old) or pre/early pubertal children. In 14 prepubertal children, exogenous sex steroid priming resulted in lower insulin sensitivity (P < 0·05) compared to nonprimed tests. CONCLUSIONS Young GH deficient children were more insulin sensitive than children with normal GH secretion. This difference attenuated with age and puberty, possibly secondary to pubertal sex steroids; however, insulin resistance as reported in GH deficient adults, was not observed in adolescents. [source]