Flow Method (flow + method)

Distribution by Scientific Domains

Selected Abstracts

Determination of in-plane permeability of fiber preforms by the gas flow method using pressure measurements

Sun K. Kim
A method is described for measuring the in-plane permeability of orthotropic fibrous preforms using gas flow. The method is based on an optimization process between computed and measured pressures at various locations in the mold during steady state gas flow through the enclosed preform. The computed pressure is obtained by the control volume finite element method (CVFEM). This method was demonstrated by using a specially designed mold with multiple ports for gas injection and pressure measurement and it was shown that it can be implemented easily and yields consistent and reliable results. [source]

The Influence of Cannulation Technique on Blood Flow to the Brain in Rats Undergoing Cardiopulmonary Bypass: A Cautionary "Tail"

Terence Gourlay
Abstract Recently, there has been an increase in the use of rat models of cardiopulmonary bypass (CPB) for research purposes. Much of this work has focused on cerebral injury associated with CPB. Many of these studies employ a peripheral cannulation approach, often utilizing the caudal artery and internal or external jugular vein. The aim of the present study was to establish whether there is any alteration in blood flow to the brain associated with the use of different cannulation routes. Twenty-four adult male Sprague Dawley rats were allocated to one of three study groups: Group 1,caudal artery return, Group 2,open-chest aortic return, and Group 3,nonbypass control group. Colored microspheres were injected into all animals at four time points (postinduction, initiation of bypass, midbypass, and end bypass). After the termination of each experiment, the brains were excised, the tissue was digested, the microspheres were harvested, and the global blood flow to the brain was assessed using the reference flow method. There was a significant reduction in blood flow to the brain between both bypass groups and the control group. Additionally, cerebral blood flow was significantly lower in the caudal return group than in the aortic return group. There is a significant drop in blood flow to the brain associated with the initiation and continuation of CPB when compared to non-CPB controls. These results also confirm a considerable cerebral hypoperfusion associated with the peripheral cannulation technique, and suggest that peripheral bypass may exaggerate the influence CPB has on cerebral injury. This technique must therefore be employed with caution. [source]

ECL Cell Histamine Mobilization Studied byGastric Submucosal Microdialysis in Awake Rats:Methodological Considerations

Peter Ericsson
They secrete histamine in response to circulating gastrin. Gastric submucosal microdialysis has been used to study ECL-cell histamine mobilization in awake rats. In the present study we assess the usefulness and limitations of the technique. Microdialysis probes were implanted in the gastric submucosa. Histological analysis of the stomach wall around the probe revealed a moderate, local inflammatory reaction 1,2 days after implantation; the inflammation persisted for at least 10 days. Experiments were conducted 3 days after the implantation. The "true" submucosal histamine concentration was determined by perfusing at different rates (the zero flow method) or with different concentrations of histamine at a constant rate (the no-net-flux method): in fasted rats it was calculated to be 87±5 (means±S.E.M.) nmol/l and 76±9 nmol/l, respectively. The corresponding histamine concentrations in fed rats were 93±5 and 102±8 nmol/l, respectively. With a perfusion rate of 74 ,l/hr the recovery of submucosal histamine was 49%, at 34 ,l/hr the recovery increased to 83%. At a perfusion rate below 20 ,l/hr the microdialysate histamine concentration was close to the actual concentration in the submucosa. The ECL-cell histamine mobilization was independent of the concentrations of Ca2+ in the perfusion medium (0,3.4 mmol/l Ca2+). In one experiment, histamine mobilization in response to gastrin (10 nmol/kg/hr subcutaneously) was monitored in rats pretreated with prednisolone (60 mg/kg) or indomethacin (15 mg/kg). The two antiinflammatory agents failed to affect the concentration of histamine in the microdialysate either before or during the gastrin challenge, which was in accord with the observation that the inflammatory reaction was modest and that inflammatory cells were relatively few around the probe and in the wall of the probe. In another experiment, rats were given aminoguanidine (10 mg/kg) or metoprine (10 mg/kg) 4 hr before the start of gastrin infusion (5 nmol/kg/hr intravenously). Metoprine (inhibitor of histamine N-methyl transferase) did not affect the microdialysate histamine concentration, while aminoguanidine (inhibitor of diamine oxidase) raised both basal and gastrin-stimulated histamine concentrations. We conclude that microdialysis can be used to monitor changes in the concentration of histamine in the submucosa of the stomach, and that the inflammatory reaction to the probe is moderate and does not affect the submucosal histamine mobilization. [source]

Body temperature measurement in VLBW infants by continuous skin measurement is a good or even better alternative than continuous rectal measurement

RDG Van Der Spek
Abstract Background: An inadequate body temperature in preterm infants influences morbidity and mortality. Continuous rectal measurement is a reliable method to measure body temperature but might have adverse effects and is even contra-indicated in case of low platelets or necrotising enterocolitis. A save and non-invasive method to measure body temperature is the transcutaneous ,zero heat flow' method. Aim: We hypothesised that for monitoring body temperature in very low birth weight (VLBW) infants, central measurement of temperature by way of the zero heat flow principle is just as reliable as rectal temperature. Methods: Twenty-six infants, birth weight between 520 g and 1250 g, gestational age 25.28,32.28 weeks were provided with an insulated continuous skin probe with ,zero heat flow' and a continuous rectal probe. Both measurements were registered every hour over a period of 48 h. The sample size was calculated to detect a difference of less than or equal to 0.20°C. Results: 1205 of the 1248 temperature measurements were analysed. At any moment, skin temperature was higher or equal when compared to rectal temperature. Mean skin temperature was 0.13°C (SD 0.33) higher than mean rectal temperature (t -test, p < 0.001). Correlation between rectal and skin temperature was 0.82 (p , 0.05). Conclusion: In VLBW infants, temperature measurement by ,zero heat flow' method is just as reliable as by rectal method. [source]