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Transit Time (transit + time)
Kinds of Transit Time Selected AbstractsCalculating Ground Water Transit Time of Horizontal Flow through Leaky AquifersGROUND WATER, Issue 1 2008Angelika C. Braunsfurth The calculation of ground water transit times is one important factor in ground water protection. In this paper, we present an analytical solution for the transit time for a Dupuit-type flow system applicable to saturated flow through a horizontal leaky aquifer discharging to a downgradient fixed-head boundary under steady-state conditions. We investigate the influence of leakage when comparing the resulting travel times of our model based on head-dependent leakage with the commonly used model with no leakage and a simplified model with constant leakage. The results show significant differences in the position of the water divide and transit time, suggesting that leakage cannot be ignored. [source] An Analytical Solution for Ground Water Transit Time through Unconfined AquifersGROUND WATER, Issue 4 2005R. Chesnaux An exact, closed-form analytical solution is developed for calculating ground water transit times within Dupuit-type flow systems. The solution applies to steady-state, saturated flow through an unconfined, horizontal aquifer recharged by surface infiltration and discharging to a downgradient fixed-head boundary. The upgradient boundary can represent, using the same equation, a no-flow boundary or a fixed head. The approach is unique for calculating travel times because it makes no a priori assumptions regarding the limit of the water table rise with respect to the minimum saturated aquifer thickness. The computed travel times are verified against a numerical model, and examples are provided, which show that the predicted travel times can be on the order of nine times longer relative to existing analytical solutions. [source] Red Cell Pulmonary Transit Times Through the Healthy Human LungEXPERIMENTAL PHYSIOLOGY, Issue 2 2003G. S. Zavorsky It has previously been postulated that rapid red cell capillary transit through the human lung plays a role in the mechanism of diffusion limitation in some endurance athletes. Methodological limitations currently prevent researchers from directly measuring pulmonary capillary transit times in humans during exercise; however, first pass radionuclide cardiography allows direct measurement of red blood cell (RBC) transit times through the whole lung at various exercise intensities. We examined the relationship between mean whole lung red cell pulmonary transit times (cardiopulmonary transit times or CPTT) and different levels of flow in 88 healthy humans (76 males, 12 females) from several studies (mean age 31 years). The pooled data suggest that the relationship between CPTT and cardiac index (CI), beginning at rest and progressing through to maximum exercise demonstrates that CPTT reaches its minimum value when CI is about 8.1 l m2 min,1 (2.5-3 times the CI value at rest), and does not significantly change with further increases in CI. Cardiopulmonary blood volume (CPBV) index also does not change significantly until CI reaches 2.5 to 3 times the CI value at rest and then increases roughly linearly after that point. Consequently, the systematic increase in CPBV index with increasing pulmonary blood flow between 8.1 and 20 l m2 min,1 displays an adaptive response of the cardiopulmonary system by augmenting CPBV (and perhaps pulmonary capillary blood volume through distension and recruitment) to offset the reduction in CPTT, as no significant difference in mean CPTT is observed between these levels of flow (P > 0.05). Therefore, these data demonstrate that CPBV does not reach maximum capacity during strenuous or maximum exercise. This does not support the principle of quarter-power allometric scaling for flow when explaining modifications during exercise. Therefore, we speculate that the observed relationships between CPTT, CBPV index and flow may prevent mean CPTT (and perhaps mean pulmonary capillary transit times) from decreasing below the threshold time required for oxygenation. [source] Effects of Body Positioning on Swallowing and Esophageal Transit in Healthy DogsJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 4 2009C.M. Bonadio Background: Contrast videofluoroscopy is the imaging technique of choice for evaluating dysphagic dogs. In people, body position alters the outcome of videofluoroscopic assessment of swallowing. Hypothesis/Objective: That esophageal transit in dogs, as measured by a barium esophagram, is not affected by body position. Animals: Healthy dogs (n= 15). Methods: Interventional, experimental study. A restraint device was built to facilitate imaging of dogs in sternal recumbancy. Each dog underwent videofluoroscopy during swallowing of liquid barium and barium-soaked kibble in sternal and lateral recumbancy. Timing of swallowing, pharyngeal constriction ratio, esophageal transit time, and number of esophageal peristaltic waves were compared among body positions. Results: Transit time in the cervical esophagus (cm/s) was significantly delayed when dogs were in lateral recumbency for both liquid (2.58 ± 1.98 versus 7.23 ± 3.11; P= .001) and kibble (4.44 ± 2.02 versus 8.92 ± 4.80; P= .002). In lateral recumbency, 52 ± 22% of liquid and 73 ± 23% of kibble swallows stimulated primary esophageal peristalsis. In sternal recumbency, 77 ± 24% of liquid (P= .01 versus lateral) and 89 ± 16% of kibble (P= .01 versus lateral) swallows stimulated primary esophageal peristalsis. Other variables were not significantly different. Conclusions and Clinical Importance: Lateral body positioning significantly increases cervical esophageal transit time and affects the type of peristaltic wave generated by a swallow. [source] Permanent sacral nerve stimulation for treatment of idiopathic constipationBRITISH JOURNAL OF SURGERY (NOW INCLUDES EUROPEAN JOURNAL OF SURGERY), Issue 7 2002N. J. Kenefick Background: Constipation can usually be managed using conservative therapies. A proportion of patients require more intensive treatment. Surgery provides variable results. This paper describes an alternative approach, in which the neural control of the bowel and pelvic floor is modified, using permanent sacral nerve stimulation. Methods: Four women (aged 27,36 years), underwent temporary and then permanent stimulation. All had idiopathic constipation, resistant to maximal therapy, with symptoms for 8,32 years. Clinical evaluation, bowel diary, Wexner constipation score, symptom analogue score, quality of life questionnaire and anorectal physiology were completed. Results: There was a marked improvement in all patients with temporary, and in three with permanent, stimulation. Median follow-up was 8 (range 1,11) months. Bowel frequency increased from 1,6 to 6,28 evacuations per 3 weeks. Improvement occurred, at longest,follow,up, in median (range) evacuation score (4 (0,4) versus 1 (0,4)), time with abdominal pain (98 (95,100) versus 12 (0,100) per cent), time with bloating (100 (95,100) versus 12 (5,100) per cent), Wexner score (21 (20,22) versus 9 (1,20)), analogue score (22 (16,32) versus 80 (20,98)) and quality of life. Maximum anal resting and squeeze pressures increased. Rectal sensation was altered. Transit time normalized in one patient. Conclusion: Permanent sacral nerve stimulation can be used to treat patients with resistant idiopathic constipation. © 2002 British Journal of Surgery Society Ltd [source] Dynamics of water transport and storage in conifers studied with deuterium and heat tracing techniquesPLANT CELL & ENVIRONMENT, Issue 1 2006F. C. MEINZER ABSTRACT The volume and complexity of their vascular systems make the dynamics of long-distance water transport in large trees difficult to study. We used heat and deuterated water (D2O) as tracers to characterize whole-tree water transport and storage properties in individual trees belonging to the coniferous species Pseudotsuga menziesii (Mirb.) Franco and Tsuga heterophylla (Raf.) Sarg. The trees used in this study spanned a broad range of height (13.5,58 m) and diameter (0.14,1.43 m). Sap flow was monitored continuously with heat dissipation probes near the base of the trunk prior to, during and following injection of D2O. The transit time for D2O transport from the base of the trunk to the upper crown and the tracer residence time were determined by measuring hydrogen isotope ratios in water extracted from leaves sampled at regular intervals. Transit times for arrival of D2O in the upper crown ranged from 2.5 to 21 d and residence times ranged from 36 to 79 d. Estimates of maximum sap velocity derived from tracer transit times and path length ranged from 2.4 to 5.4 m d,1. Tracer residence time and half-life increased as tree diameter increased, independent of species. Species-independent scaling of tracer velocity with sapwood-specific conductivity was also observed. When data from this study were combined with similar data from an earlier study of four tropical angiosperm trees, species-independent scaling of tracer velocity and residence time with sapwood hydraulic capacitance was observed. Sapwood capacitance is an intrinsic tissue-level property that appears to govern whole-tree water transport in a similar manner among both tracheid- and vessel-bearing species. [source] Lymantria dispar herbivory induces rapid changes in carbon transport and partitioning in Populus nigraENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 1 2008Benjamin A. Babst Abstract We tested for rapid changes in photosynthate transport and partitioning in response to Lymantria dispar (L.) (Lepidoptera: Lymantriidae) (gypsy moth) herbivory in Populus nigra L. (Salicaceae). Transport and partitioning of [11C]-photosynthate from young mature leaves were measured in vivo before and 18 h after leaf chewing by gypsy moth larvae, which were caged on three older leaves. Following herbivory, there was an increase in export speed of recently fixed carbon from younger mature leaves. The increased export speed was due to a quicker transit time of 11C through the leaf, rather than a change in transport speed through the phloem. Additionally, basipetal partitioning of [11C]-photosynthate was increased following herbivory. Neither of these changes was observed in control plants. This enhancement of export occurs even though herbivores are well known to induce increases in carbon allocation to secondary metabolites within leaves. Our results demonstrate that the use of non-destructive imaging of 11C tracer is a powerful tool for examining plant responses to herbivory. Although the mechanisms underlying the rapid increase in carbon flux to stems and roots remain to be elucidated, our results raise the possibility of a coordinated whole plant response to herbivory. Thus, even when the herbivore specializes on only one plant tissue type, a whole plant approach may be key to understanding how plants respond to herbivory. [source] Aminoguanidine prevents arterial stiffening in a new rat model of type 2 diabetesEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 8 2006K.-C. Chang Abstract Background, Formation of advanced glycation end-products (AGEs) on collagen within the arterial wall may be responsible for the development of diabetic vascular injury. This study focused on investigating the role of aminoguanidine (AG), an inhibitor of AGE formation, in the prevention of noninsulin-dependent diabetes mellitus (NIDDM)-derived arterial stiffening and cardiac hypertrophy in rats. Materials and methods, The NIDDM was induced in male Wistar rats, which were administered intraperitoneally with 180 mg kg,1 nicotinamide (NA) 30 min before an intravenous injection of 50 mg kg,1 streptozotocin (STZ). After induction of diabetes mellitus type 2, animals receiving daily peritoneal injections with 50 mg kg,1 AG for 8 weeks were compared with the age-matched, untreated, diabetic controls. Results, After exposure to AG, the STZ-NA diabetic rats had improved aortic distensibility, as evidenced by 18·8% reduction of aortic characteristic impedance (P < 0·05). Treatment of the experimental syndrome with AG also resulted in a significant increase in wave transit time (+23·7%, P < 0·05) and a decrease in wave reflection factor (,26·6%, P < 0·05), suggesting that AG may prevent the NIDDM-induced augmentation in systolic load of the left ventricle. Also, the glycation-derived modification on aortic collagen was found to be retarded by AG. The diminished ratio of left ventricular weight to body weight suggested that prevention of the diabetes-related cardiac hypertrophy by AG may correspond to the drug-induced decline in aortic stiffening. Conclusions, Long-term administration of AG to the STZ-NA diabetic rats imparts significant protection against the NIDDM-derived impairment in vascular dynamics, at least partly through inhibition of the AGE accumulation on collagen in the arterial wall. [source] Arterial stiffening and cardiac hypertrophy in a new rat model of type 2 diabetesEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 1 2006K.-C. Chang Abstract Background, We determined the effects of NIDDM on haemodynamic parameters describing arterial wall elasticity and cardiac hypertrophy in rats administered streptozotocin (STZ) and nicotinamide (NA), using the aortic impedance analysis. Methods, Male Wistar rats at 2 months were administered intraperitoneally 180 mg kg,1 of NA, 30 min before an intravenous injection of 50 mg kg,1 STZ, to induce type 2 diabetes. The STZ-NA rats were divided into two groups, 4 weeks and 8 weeks after induction of diabetes, and compared with untreated age-matched controls. Pulsatile aortic pressure and flow signals were measured by a high-fidelity pressure sensor and electromagnetic flow probe, respectively, and were then subjected to Fourier transformation for the analysis of aortic input impedance. Results, In each diabetic group, the experimental syndrome was characterized by a moderate and stable hyperglycaemia and a relative deficiency of insulin secretion. However, the 8-week but not the 4-week STZ-NA diabetic rats showed a decrease in cardiac output in the absence of any significant changes in mean aortic pressure, having increased total peripheral resistance. The diabetic syndrome at 8 weeks also contributed to an increase in aortic characteristic impedance, from 1·49 ± 0·33 (mean ± SD) to 1·95 ± 0·28 mmHg s mL,1 (P < 0·05), suggesting a detriment to the aortic distensibility in NIDDM. Meanwhile, the STZ-NA diabetic animals after 8 weeks had an increased wave reflection factor (0·46 ± 0·09 vs. 0·61 ± 0·13, P < 0·05) and decreased wave transit time (25·8 ± 3·8 vs. 20·6 ± 2·8 ms, P < 0·05). Ratio of the left ventricular weight to body weight was also enhanced in the 8-week STZ-NA diabetic rats. Conclusion, The heavy intensity with early return of the pulse wave reflection may augment systolic load of the left ventricle coupled to the arterial system, leading to cardiac hypertrophy in the rats at 8 weeks after following STZ and NA administration. [source] Lactose intolerance: analysis of underlying factorsEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 1 2003R. J. Vonk Abstract Background We studied the degree of lactose digestion and orocecal transit time (OCTT) as possible causes for the variability of symptoms of lactose intolerance (LI) in a sample of a population with genetically determined low lactase activity. Methods Lactose digestion index (LDI) was measured by the recently developed 13C-lactose/2H-glucose test. The OCTT was determined using the breath hydrogen test. Based on a 6-h symptom score (SSC) after a challenge dose of 25 g of lactose the subjects were divided into a tolerant group (T: n= 15; SSC = 0) and an intolerant group (IT: n= 28; SSC 1,40). The intolerant group was subdivided according to the severity of symptoms: group ITa (n = 17; mild symptoms without diarrhoea) and group ITb (n = 11; with diarrhoea). Results The LDI was lower in the intolerant group (0·34 ± 0·14) (mean ± SD) than in the tolerant group (0·47 ± 0·14) (P = 0·008). The OCTT of group IT (60, 30,90 min) (median, quartiles) was significantly shorter than that of group T (105, 60,120 min) (P = 0·003) and was positively correlated with the LDI (P = 0·050). In groups ITa and ITb the OCTT (60, 30,90 min; 60, 26,83 min) and LDI (0·30 ± 0·14; 0·39 ± 0·14) were similar. Conclusions Lactose digestion capacity, which is determined by small intestinal lactase activity as well as by OCTT, affects the occurrence of lactose intolerance. However, the major difference in intolerance symptoms is caused by differences in the colonic processing of maldigested lactose. [source] Acute Hypervolaemia Improves Arterial Oxygen Pressure in Athletes with Exercise-Induced HypoxaemiaEXPERIMENTAL PHYSIOLOGY, Issue 4 2003Gerald S. Zavorsky The aim of this study was to determine the effect of acute plasma volume expansion on arterial blood-gas status during 6.5 min strenuous cycling exercise comparing six athletes with and six athletes without exercise-induced arterial hypoxaemia (EIAH). We hypothesized that plasma volume expansion could improve arterial oxygen pressure in a homogeneous sample of athletes - those with EIAH. In this paper we have extended the analysis and results of our recently published surprising findings that lengthening cardiopulmonary transit time did not improve arterial blood-gas status in a heterogeneous sample of endurance cyclists. One 500 ml bag of 10% Pentastarch (infusion condition) or 60 ml 0.9% saline (placebo) was infused prior to exercise in a randomized, double-blind fashion on two different days. Power output, cardiac output, oxygen consumption and arterial blood gases were measured during strenuous exercise. Cardiac output and oxygen consumption were not affected by acute hypervolaemia. There were group × condition interaction effects for arterial oxygen pressure and alveolar-arterial oxygen pressure difference, suggesting that those with hypoxaemia experienced improved arterial oxygen pressure (+4 mmHg) and lower alveolar-arterial oxygen pressure difference (-2 mmHg) with infusion. In conclusion, acute hypervolaemia improves blood-gas status in athletes with EIAH. The impairment of gas exchange occurs within the first minute of exercise, and is not impaired further throughout the remaining duration of exercise. This suggests that arterial oxygen pressure is only minimally mediated by cardiac output. [source] Variations in Hole Injection due to Fast and Slow Interfacial Traps in Polymer Light-Emitting Diodes with InterlayersADVANCED FUNCTIONAL MATERIALS, Issue 1 2010M. James Harding Abstract Detailed studies on the effect of placing a thin (10,nm) solution-processable interlayer between a light-emitting polymer (LEP) layer and a poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic)-acid-coated indium tin oxide anode is reported; particular attention is directed at the effects on the hole injection into three different LEPs. All three different interlayer polymers have low ionization potentials, which are similar to those of the LEPs, so the observed changes in hole injection are not due to variations in injection barrier height. It is instead shown that changes are due to variations in hole trapping at the injecting interface, which is responsible for varying the hole current by up to two orders of magnitude. Transient measurements show the presence of very fast interfacial traps, which fill the moment charge is injected from the anode. These can be considered as injection pathway dead-ends, effectively reducing the active contact surface area. This is followed by slower interfacial traps, which fill on timescales longer than the carrier transit time across the device, further reducing the total current. The interlayers may increase or decrease the trap densities depending on the particular LEP involved, indicating the dominant role of interfacial chain morphology in injection. Penetration of the interlayer into the LEP layer can also occur, resulting in additional changes in the bulk LEP transport properties. [source] Limited ability of Palestine Sunbirds Nectarinia osea to cope with pyridine alkaloids in nectar of Tree Tobacco Nicotiana glaucaFUNCTIONAL ECOLOGY, Issue 6 2004H. TADMOR-MELAMED Summary 1Secondary compounds are common in floral nectar but their relative effects on nectar consumption and utilization in nectarivorous birds are unclear. 2We studied the effect of two pyridine alkaloids, nicotine and anabasine, present in Tree Tobacco (Nicotiana glauca) nectar, on food consumption, gut transit time and sugar assimilation efficiency of the Palestine Sunbird (Nectarinia osea), a pollinator of N. glauca in east Mediterranean ecosystems. 3Sunbirds demonstrated dose-dependent deterrence; they were not deterred by the lowest natural concentrations of these alkaloids in nectar (0·1 ppm nicotine and 0·6 ppm anabasine) but they were significantly deterred by the average concentrations detected in nectar (0·5 ppm nicotine and 5 ppm anabasine). 4The two pyridine alkaloids reduced gut transit time (by 30,42%) and sugar assimilation efficiency (by 9,17%) compared with the control alkaloid-free diet. 5Sunbirds are able to cope with low, but not average, concentrations of nicotine and anabasine in N. glauca nectar. If sunbirds are efficient pollinators of N. glauca they may induce selection on it to reduce pyridine alkaloid production in the nectar. Alternatively, high concentrations in some N. glauca plants may lead the birds to visit more plants with lower alkaloid concentrations. Hence, they will be more efficient pollinators, especially if other nectar-producing plants are scarce. [source] Drug metabolism and disposition in childrenFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 3 2003M. Strolin Benedetti Abstract Key factors undergoing maturational changes accounting for differences in drug metabolism and disposition in the pediatric population compared with adults are reviewed. Gastric and duodenal pH, gastric emptying time, intestinal transit time, bacterial colonization and probably P-glycoprotein are important factors for drug absorption, whereas key factors explaining differences in drug distribution between the pediatric population and adults are membrane permeability, plasma protein concentration and plasma protein characteristics, endogenous substances in plasma, total body and extracellular water, fat content, regional blood flow and probably P-glycoprotein, mainly that present in the gut, liver and brain. As far as drug metabolism is concerned, important differences have been found in the pediatric population compared with adults both for phase I enzymes [oxidative (e.g. cytochrome CYP3A7 vs. CYP3A4 and CYP1A2), reductive and hydrolytic enzymes] and phase II enzymes (e.g. N -methyltransferases and glucuronosyltransferases). Finally, key factors undergoing maturational changes accounting for differences in renal excretion in the pediatric population compared with adults are glomerular filtration and tubular secretion. It would be important to generate information on the developmental aspects of renal P-glycoprotein and of other renal transporters as done and still being done with the different isozymes involved in drug metabolism. [source] Geodetic observations of ice flow velocities over the southern part of subglacial Lake Vostok, Antarctica, and their glaciological implicationsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006Jens Wendt SUMMARY In the austral summer seasons 2001/02 and 2002/03, Global Positioning System (GPS) data were collected in the vicinity of Vostok Station to determine ice flow velocities over Lake Vostok. Ten GPS sites are located within a radius of 30 km around Vostok Station on floating ice as well as on grounded ice to the east and to the west of the lake. Additionally, a local deformation network around the ice core drilling site 5G-1 was installed. The derived ice flow velocity for Vostok Station is 2.00 m a,1± 0.01 m a,1. Along the flowline of Vostok Station an extension rate of about 10,5 a,1 (equivalent to 1 cm km,1 a,1) was determined. This significant velocity gradient results in a new estimate of 28 700 years for the transit time of an ice particle along the Vostok flowline from the bedrock ridge in the southwest of the lake to the eastern shoreline. With these lower velocities compared to earlier studies and, hence, larger transit times the basal accretion rate is estimated to be 4 mm a,1 along a portion of the Vostok flowline. An assessment of the local accretion rate at Vostok Station using the observed geodetic quantities yields an accretion rate in the same order of magnitude. Furthermore, the comparison of our geodetic observations with results inferred from ice-penetrating radar data indicates that the ice flow may not have changed significantly for several thousand years. [source] Calculating Ground Water Transit Time of Horizontal Flow through Leaky AquifersGROUND WATER, Issue 1 2008Angelika C. Braunsfurth The calculation of ground water transit times is one important factor in ground water protection. In this paper, we present an analytical solution for the transit time for a Dupuit-type flow system applicable to saturated flow through a horizontal leaky aquifer discharging to a downgradient fixed-head boundary under steady-state conditions. We investigate the influence of leakage when comparing the resulting travel times of our model based on head-dependent leakage with the commonly used model with no leakage and a simplified model with constant leakage. The results show significant differences in the position of the water divide and transit time, suggesting that leakage cannot be ignored. [source] Secretin activation of the apical Na+ -dependent bile acid transporter is associated with cholehepatic shunting in rats,HEPATOLOGY, Issue 5 2005Gianfranco Alpini The role of the cholangiocyte apical Na+ -dependent bile acid transporter (ASBT) in bile formation is unknown. Bile acid absorption by bile ducts results in cholehepatic shunting, a pathway that amplifies the canalicular osmotic effects of bile acids. We tested in isolated cholangiocytes if secretin enhances ASBT translocation to the apical membrane from latent preexisting intracellular stores. In vivo, in bile duct,ligated rats, we tested if increased ASBT activity (induced by secretin pretreatment) results in cholehepatic shunting of bile acids. We determined the increment in taurocholate-dependent bile flow and biliary lipid secretion and taurocholate (TC) biliary transit time during high ASBT activity. Secretin stimulated colchicine-sensitive ASBT translocation to the cholangiocyte plasma membrane and 3H-TC uptake in purified cholangiocytes. Consistent with increased ASBT promoting cholehepatic shunting, with secretin pretreatment, we found TC induced greater-than-expected biliary lipid secretion and bile flow and there was a prolongation of the TC biliary transit time. Colchicine ablated secretin pretreatment-dependent bile acid,induced choleresis, increased biliary lipid secretion, and the prolongation of the TC biliary transit. In conclusion, secretin stimulates cholehepatic shunting of conjugated bile acids and is associated with increased cholangiocyte apical membrane ASBT. Bile acid transport by cholangiocyte ASBT can contribute to hepatobiliary secretion in vivo. (HEPATOLOGY 2005.) [source] Baseflow and peakflow chemical responses to experimental applications of ammonium sulphate to forested watersheds in north-central West Virginia, USA,HYDROLOGICAL PROCESSES, Issue 12 2002Pamela J. Edwards Abstract Stream water was analysed to determine how induced watershed acidification changed the chemistry of peakflow and baseflow and to compare the relative timing of these changes. Two watersheds in north-central West Virginia, WS3 and WS9, were subjected to three applications of ammonium sulphate fertilizer per year to induce acidification. A third watershed, WS4, was the control. Samples were collected for 8 years from WS9 and for 9 years from WS3. Prior to analyses, concentration data were flow adjusted, and the influence of natural background changes was removed by accounting for the chemical responses measured from WS4. This yielded residual values that were evaluated using robust locally weighted regression and Mann,Kendall tests. On WS3, analyte responses during baseflow and peakflow were similar, although peakflow responses occurred soon after the first treatment whereas baseflow responses lagged 1,2 years. This lag in baseflow responses corresponded well with the mean transit time of baseflow on WS3. Anion adsorption on WS3 apparently delayed increases in SO4 leaching, but resulted in enhanced early leaching losses of Cl and NO3. Leaching of Ca and Mg was strongly tied, both by timing and stoichiometrically, to NO3 and SO4 leaching. F -factors for WS3 baseflow and peakflow indicated that the catchment was insensitive to acid neutralizing capacity reductions both before and during treatment, although NO3 played a large role in reducing the treatment period F -factor. By contrast, the addition of fertilizer to WS9 created an acid sensitive system in both baseflow and peakflow. On WS9, baseflow and peakflow responses also were similar to each other, but there was no time lag after treatment for baseflow. Changes in concentrations generally were not as great on WS9 as on WS3, and several ions showed no significant changes, particularly for peakflow. The lesser response to treatment on WS9 is attributed to the past abusive farming and site preparation before larch planting that resulted in poor soil fertility, erosion, and consequently, physical and chemical similarities between upper and lower soil layers. Even with fertilizer-induced NO3 and SO4 leaching increases, base cations were in low supplies and, therefore, unavailable to leach via charge pairing. The absence of a time lag in treatment responses for WS9 baseflow indicates that it has substantially different flow paths than WS3. The different hydrologies on these nearby watersheds illustrates the importance of understanding watershed hydrology when establishing a monitoring programme to detect ecosystem change. Published in 2002 by John Wiley & Sons, Ltd. [source] Clinical application of wireless capsule endoscopyJOURNAL OF DIGESTIVE DISEASES, Issue 2 2003Zhi Zheng GE BACKGROUND: Diagnostic modalities for identifying lesions within the small bowel have been quite limited. Wireless capsule endoscopy (WCE) is a new, innovative technique that can detect very small mucosal lesions in the entire small bowel and can be used in the outpatient setting. The present study explored the diagnostic value, tolerance and safety of WCE in the identification of small bowel pathology that was not detected with conventional small bowel imaging studies. METHODS: From May through September 2002, 15 patients with suspected small bowel diseases were prospectively examined, Of them, 12 presented with persistent obscure gastrointestinal bleeding and negative findings on upper endoscopy, colonoscopy, small bowel radiography, and bleeding-scan scintig-raphy or mesenteric angiography. RESULTS: Wireless capsule endoscopy identified pathologic small bowel findings in 11 of the 15 patients (73%): angioectasias, Dieulafoy's lesion, polypoid lesion, submucosal mass, Crohn's disease, carcinoid tumor, lipoma, aphthous ulcer, and hemorrhagic gastritis; four of the patients had two lesions. The images displayed were considered to be good. The capsule endoscopes remained in the stomach for an average of 82 min (range 6,311 min) and the mean transit time in the small bowel was 248 min (range 104,396 min). The mean time of recording was 7 h 29 min (from 5 h to 8 h 30 min). The mean time to reach the cecum was 336 min (180,470 min). The average number of the images transmitted by the capsule was 57 919 and the average time the physician took to review the images transmitted by the capsule was 82 min (range 30,120 min). The average time of elimination of the capsule was 33 h (range 24,48 h). All 15 patients reported that the capsule was easy to swallow, painless, and preferable to conventional endoscopy. No complications were observed. CONCLUSIONS: Wireless capsule endoscopy is safe, well tolerated, and useful for identifying occult lesions of the small bowel, especially in patients who present with obscure gastrointestinal bleeding. [source] Study on functional constipation and constipation-predominant irritable bowel syndrome by using the colonic transit test and anorectal manometryJOURNAL OF DIGESTIVE DISEASES, Issue 4 2002Li Xing ZHAN OBJECTIVE: To investigate the visceral perception, anorectal pressure and colonic transit time (CTT) in patients with functional constipation and constipation-predominant irritable bowel syndrome (C-IBS), and to study the manometric abnormalities of these two conditions. METHODS: The CTT in patients with functional constipation and C-IBS was studied by using radiopaque markers. Rectal visceral perception thresholds, rectal compliance and anorectal pressure were examined by electric barostat. RESULTS: The CTT in both groups of constipated patients was abnormal. A lot of radiopaque markers remained in the right colon in C-IBS patients, whereas in patients with functional constipation, the radiopaque markers remained in each segment of the colon. The anorectal resting pressure, squeezing pressure and relaxation pressure were normal in both groups. Rectal compliance and defecation thresholds were much higher compared with controls, and the rectal visceral perception of functional constipation was also abnormal. CONCLUSIONS: The motility abnormalities of functional constipation and C-IBS occurred in different colonic segments. Results suggest that CTT measurement and anorectal manometry could be helpful in the differential diagnosis of these two conditions. [source] Food choice in Siganus fuscescens: influence of macrophyte nutrient content and availabilityJOURNAL OF FISH BIOLOGY, Issue 2 2004R. D. Pillans Using multiple-choice feeding experiments, the selection of six species of macrophytes by the herbivorous rabbitfish Siganus fuscescens was examined. The rabbitfish showed distinct food choice in the laboratory; however, selection of macrophytes by S. fuscescens was not related to their absolute nutrient content (nitrogen, carbon, energy and ash free dry mass). Nutrient assimilation estimates showed that the macrophytes which were most preferred were those that S. fuscescens assimilated best. In S. fuscescens, the macrophytes that were preferred passed through the gut significantly faster than the less preferred species. Gut transit time had a significant effect on the absolute value of a food item in terms of net nutrient gain per unit time. This study showed that food value could be inferred from the absolute nutrient content of the macrophytes. Thus both the ability to assimilate nutrients as well as the absolute nutrient content of macrophytes must be quantified when assessing food value. [source] Evaluation of gut motility in type II diabetes by the radiopaque marker methodJOURNAL OF GASTROENTEROLOGY AND HEPATOLOGY, Issue 4 2000Motoyuki Iida Abstract Background: The clinical usefulness of the radiopaque marker method for detecting diabetic gastrointestinal motility disturbances, was evaluated by examining 21 type II diabetes subjects who did not have any neuropathic symptoms. Methods: After administration of a Sitzmark capsule®, markers were located using plain abdominal radiographs, and the transit time of the markers through seven areas of digestive tract was calculated by Arhan's methods. The plasma concentration of acetaminophen at 45 min after oral administration was measured to evaluate gastric emptying time. The coefficient of variation of R-R intervals on the electrocardiograms (CVR-R) was measured to evaluate parasympathetic autonomic function. Results: In the diabetics, the average (± SD) transit time through upper digestive tracts was slightly but not significantly elongated compared with control subjects (14.4 ± 8.3 vs 9.9 ± 6.1 h). Significant elongation was observed in transit time through the lower digestive tracts or the whole gut (44.6 ± 20.9 and 57.9 ± 22.3 h, respectively) compared with control subjects (23.3 ± 8.5 and 33.2 ± 11.0 h). The transit time of the markers from stomach to small intestine was highly correlated (r = 0.693) with plasma concentration of acetaminophen. The transit time through either the whole colon (r = 0.564) or the whole gut (r = 0.630) was highly correlated with CVR-R. Conclusions: These findings suggest that the radiopaque marker method is a useful tool for detecting the sections of the digestive tract responsible for gut motility disturbances. In type II diabetics with no neuropathic symptoms, the lower digestive tracts may deteriorate prior to the impairment of upper digestive tracts. [source] Perfusion parameters derived from bolus-tracking perfusion imaging are immune to tracer recirculation,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2010Jayme Cameron Kosior PhD Abstract Purpose: To investigate the impact of tracer recirculation on estimates of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). Materials and Methods: The theoretical model used to derive CBF, CBV, and MTT was examined. CBF and CBV estimates with and without tracer recirculation were compared in computer simulations to examine the effects of tracer recirculation. Results: The equations used to derive CBF, CBV, and MTT assume that the arterial input function and tissue tracer signals define the input and output signals, respectively, of a linear time-invariant system. As a result of the principle of superposition, these perfusion parameters are immune to tracer recirculation, which was confirmed by computer simulation. However, limited acquisition durations can lead to CBV and CBF errors of up to 50%. Conclusion: Tracer recirculation does not impact estimation of CBF, CBV, or MTT. However, previous approaches used to remove recirculation effects may be beneficial when used to compensate for limited acquisition durations in which the passage of the bolus is not adequately captured. J. Magn. Reson. Imaging 2010;31:753,756. © 2010 Wiley-Liss, Inc. [source] Assessing normal pulse wave velocity in the proximal pulmonary arteries using transit time: A feasibility, repeatability, and observer reproducibility study by cardiovascular magnetic resonanceJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2007MRCP, William M. Bradlow BM Abstract Purpose To calculate pulse wave velocity (PWV) in the proximal pulmonary arteries (PAs) by cardiovascular magnetic resonance (CMR) using the transit-time method, and address respiratory variation, repeatability, and observer reproducibility. Materials and Methods A 1.9-msec interleaved phase velocity sequence was repeated three times consecutively in 10 normal subjects. Pulse wave (PW) arrival times (ATs) were determined for the main and branch PAs. The PWV was calculated by dividing the path length traveled by the difference in ATs. Respiratory variation was considered by comparing acquisitions with and without respiratory gating. Results For navigated data the mean PWVs for the left PA (LPA) and right PA (RPA) were 2.09 ± 0.64 m/second and 2.33 ± 0.44 m/second, respectively. For non-navigated data the mean PWVs for the LPA and RPA were 2.14 ± 0.41 m/second and 2.31 ± 0.49 m/second, respectively. No statistically significant difference was found between respiratory non-navigated data and navigated data. Repeated on-table measurements were consistent (LPA non-navigated P = 0.95, RPA non-navigated P = 0.91, LPA navigated P = 0.96, RPA navigated P = 0.51). The coefficients of variation (CVs) were 12.2% and 12.5% for intra- and interobserver assessments, respectively. Conclusion One can measure PWV in the proximal PAs using transit-time in a reproducible manner without respiratory gating. J. Magn. Reson. Imaging 2007;25:974,981. © 2007 Wiley-Liss, Inc. [source] Calculation of cerebral perfusion parameters using regional arterial input functions identified by factor analysisJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2006Linda Knutsson MS Abstract Purpose To calculate regional cerebral blood volume (rCBV), regional cerebral blood flow (rCBF), and regional mean transit time (rMTT) accurately, an arterial input function (AIF) is required. In this study we identified a number of AIFs using factor analysis of dynamic studies (FADS), and performed the cerebral perfusion calculation pixel by pixel using the AIF that was located geometrically closest to a certain voxel. Materials and Methods To verify the robustness of the method, simulated images were generated in which dispersion or delay was added in some arteries and in the corresponding cerebral gray matter (GM), white matter (WM), and ischemic tissue. Thereafter, AIFs were determined using the FADS method and simulations were performed using different signal-to-noise ratios (SNRs). Simulations were also carried out using an AIF from a single pixel that was manually selected. In vivo results were obtained from normal volunteers and patients. Results The FADS method reduced the underestimation of rCBF due to dispersion or delay that often occurs when only one AIF represents the entire brain. Conclusion This study indicates that the use of FADS and the nearest-AIF method is preferable to manual selection of one single AIF. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Magnetic resonance brain perfusion imaging with voxel-specific arterial input functionsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2006Renate Grüner MSc Abstract Purpose To propose an automatic method for estimating voxel-specific arterial input functions (AIFs) in dynamic contrast brain perfusion imaging. Materials and Methods Voxel-specific AIFs were estimated blindly using the theory of homomorphic transformations and complex cepstrum analysis. Wiener filtering was used in the subsequent deconvolution. The method was verified using simulated data and evaluated in 10 healthy adults. Results Computer simulations accurately estimated differently shaped, normalized AIFs. Simple Wiener filtering resulted in underestimation of flow values. Preliminary in vivo results showed comparable cerebral flow value ratios between gray matter (GM) and white matter (WM) when using blindly estimated voxel-specific AIFs or a single manually selected AIF. Significant differences (P , 0.0125) in mean transit time (MTT) and time-to-peak (TTP) in GM compared to WM was seen with the new method. Conclusion Initial results suggest that the proposed method can replace the tedious and difficult task of manually selecting an AIF, while simultaneously providing better differentiation between time-dependent hemodynamic parameters. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Susceptibility Contrast and Arterial Spin Labeled Perfusion MRI in Cerebrovascular DiseaseJOURNAL OF NEUROIMAGING, Issue 1 2003Ronald L. Wolf MD ABSTRACT Purpose. To directly compare dynamic susceptibility contrast (DSC) and continuous arterial spin labeled (CASL) magnetic resonance (MR) perfusion techniques in patients with known cerebrovascular disease, with the goals of identifying possible pitfalls in interpretation and determining potential for a complementary role in this setting. Methods. DSC and CASL MR perfusion studies were performed and compared in 11 patients with acute and/or chronic cerebrovascular disease. Using an automated segmentation technique, Pearson correlation coefficients were generated for CASL perfusion measurements compared to DSC perfusion maps (time-to-peak [TTP], relative cerebral blood volume [rCBV], cerebral blood flow [rCBF], and mean transit time [MTT]) by hemisphere and vascular territory. Results. TTP maps obtained using DSC perfusion MR correlated best both subjectively and objectively with CASL perfusion MRmeasurements when all patients studied were considered. If patients with a major transit delay were excluded, DSC rCBF correlated best with CASL CBF measurements. Conclusion. There may be a complementary role for CASL and DSC perfusion MR methods in cerebrovascular disease, especially in the setting of a marked transit delay. [source] Relationship between faecal character and intestinal transit time in normal dogs and diet-sensitive dogsJOURNAL OF SMALL ANIMAL PRACTICE, Issue 7 2002V. E. Rolfe The relationship between stool character and whole gut transit time (WGTT), which is the average time for the passage of material through the lumen of the alimentary tract from ingestion to defecation, was studied in eight control dogs and 12 dogs with nonspecific dietary sensitivity. Dogs were fed four diets in a cross-over design, and faecal quality was assessed daily and WGTT determined using plastic pellets. Faecal quality was unaffected by diet in the control dogs. Dogs with dietary sensitivity produced looser faeces compared with the control dogs, and this was significant for two of the diets. There was no significant effect of diet on mean WGTT within or between groups. Minimum WGTT, which was the interval to the first appearance of markers in faeces, was shorter in sensitive dogs compared with controls, and this was significant for two of the four diets. There were significant, inverse relationships between minimum WGTT and both mean faeces score and percentage unacceptable defecations. These data suggest that rapid transit of certain dietary components may impact negatively on stool quality and contribute to loose faeces in dogs with non-specific dietary sensitivity. [source] Origins and Applications of London Dispersion Forces and Hamaker Constants in CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2000Roger H. French The London dispersion forces, along with the Debye and Keesom forces, constitute the long-range van der Waals forces. London's and Hamaker's work on the point-to-point dispersion interaction and Lifshitz's development of the continuum theory of dispersion are the foundations of our understanding of dispersion forces. Dispersion forces are present for all materials and are intrinsically related to the optical properties and the underlying interband electronic structures of materials. The force law scaling constant of the dispersion force, known as the Hamaker constant, can be determined from spectral or parametric optical properties of materials, combined with knowledge of the configuration of the materials. With recent access to new experimental and ab initio tools for determination of optical properties of materials, dispersion force research has new opportunities for detailed studies. Opportunities include development of improved index approximations and parametric representations of the optical properties for estimation of Hamaker constants. Expanded databases of London dispersion spectra of materials will permit accurate estimation of both nonretarded and retarded dispersion forces in complex configurations. Development of solutions for generalized multilayer configurations of materials are needed for the treatment of more-complex problems, such as graded interfaces. Dispersion forces can play a critical role in materials applications. Typically, they are a component with other forces in a force balance, and it is this balance that dictates the resulting behavior. The ubiquitous nature of the London dispersion forces makes them a factor in a wide spectrum of problems; they have been in evidence since the pioneering work of Young and Laplace on wetting, contact angles, and surface energies. Additional applications include the interparticle forces that can be measured by direct techniques, such as atomic force microscopy. London dispersion forces are important in both adhesion and in sintering, where the detailed shape at the crack tip and at the sintering neck can be controlled by the dispersion forces. Dispersion forces have an important role in the properties of numerous ceramics that contain intergranular films, and here the opportunity exists for the development of an integrated understanding of intergranular films that encompasses dispersion forces, segregation, multilayer adsorption, and structure. The intrinsic length scale at which there is a transition from the continuum perspective (dispersion forces) to the atomistic perspective (encompassing interatomic bonds) is critical in many materials problems, and the relationship of dispersion forces and intergranular films may represent an important opportunity to probe this topic. The London dispersion force is retarded at large separations, where the transit time of the electromagnetic interaction must be considered explicitly. Novel phenomena, such as equilibrium surficial films and bimodal wetting/dewetting, can result in materials systems when the characteristic wavelengths of the interatomic bonds and the physical interlayer thicknesses lead to a change in the sign of the dispersion force. Use of these novel phenomena in future materials applications provides interesting opportunities in materials design. [source] Effects of Body Positioning on Swallowing and Esophageal Transit in Healthy DogsJOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 4 2009C.M. Bonadio Background: Contrast videofluoroscopy is the imaging technique of choice for evaluating dysphagic dogs. In people, body position alters the outcome of videofluoroscopic assessment of swallowing. Hypothesis/Objective: That esophageal transit in dogs, as measured by a barium esophagram, is not affected by body position. Animals: Healthy dogs (n= 15). Methods: Interventional, experimental study. A restraint device was built to facilitate imaging of dogs in sternal recumbancy. Each dog underwent videofluoroscopy during swallowing of liquid barium and barium-soaked kibble in sternal and lateral recumbancy. Timing of swallowing, pharyngeal constriction ratio, esophageal transit time, and number of esophageal peristaltic waves were compared among body positions. Results: Transit time in the cervical esophagus (cm/s) was significantly delayed when dogs were in lateral recumbency for both liquid (2.58 ± 1.98 versus 7.23 ± 3.11; P= .001) and kibble (4.44 ± 2.02 versus 8.92 ± 4.80; P= .002). In lateral recumbency, 52 ± 22% of liquid and 73 ± 23% of kibble swallows stimulated primary esophageal peristalsis. In sternal recumbency, 77 ± 24% of liquid (P= .01 versus lateral) and 89 ± 16% of kibble (P= .01 versus lateral) swallows stimulated primary esophageal peristalsis. Other variables were not significantly different. Conclusions and Clinical Importance: Lateral body positioning significantly increases cervical esophageal transit time and affects the type of peristaltic wave generated by a swallow. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||