Effects of lumen volume transit time and pressure on loop of Henle function

1979 ◽  
Vol 237 (3) ◽  
pp. F196-F203 ◽  
Author(s):  
A. D. Baines ◽  
D. Basmadjian ◽  
B. C. Wang
Keyword(s):  
Transit Time ◽  
Distal Tubule ◽  
Salt Transport ◽  
Perfusion Rate ◽  
Luminal Diameter ◽  
Lumen Volume ◽  
Unstirred Layers ◽  
Transit Times ◽  
Two Samples ◽  
In Transit

Experiments on Henle's loops were designed to demonstrate the relationships of absorption to distal pressure, transit time, and luminal diameter. Loops of superficial nephrons in hydropenic rats, isolated from the rest of the nephron by oil or solid paraffin blocks, were microperfused at 13.6--20 nl/min. Two samples of fluid were collected from the early distal tubule--one with suction in order to lower distal pressure and reduce luminal volume, the other without suction so that the lumen was distended. Transit times were 30 +/- 2 s without and 19 +/- 2 s with suction. Proximal tubule pressure and perfusion rate were not altered by collection with suction. Absolute absorption, however, descreased from 10.6 +/- 0.4 to 8.4 +/- 0.4 nl/min (P less than 0.001). When salt transport was inhibited by 10(-4) M furosemide in the perfusate, water absorption was 7.8 +/- 0.7 nl/min without suction and 6.1 +/- 0.8 nl/min with suction (P less than 0.01). Computer simulation of Henle's loop shows that these observations cannot be explained by changes in transit time, hydrostatic pressure, or unstirred layers. The observations are simulated when radial fluxes depend on wall thickness and surface area in the descending thin limb.

Transit time dispersion in the pulmonary arterial tree

1998 ◽  
Vol 85 (2) ◽  
pp. 565-574 ◽  
Author(s):  
Anne V. Clough ◽  
Steven T. Haworth ◽  
Christopher C. Hanger ◽  
Jerri Wang ◽  
David L. Roerig ◽  
...  
Keyword(s):  
Transit Time ◽  
Mean Transit Time ◽  
Arterial Tree ◽  
Lung Lobe ◽  
Transit Times ◽  
Pulmonary Capillary ◽  
Time Dispersion ◽  
Pulmonary Arterial ◽  
The Difference ◽  
In Transit

Knowledge of the contributions of arterial and venous transit time dispersion to the pulmonary vascular transit time distribution is important for understanding lung function and for interpreting various kinds of data containing information about pulmonary function. Thus, to determine the dispersion of blood transit times occurring within the pulmonary arterial and venous trees, images of a bolus of contrast medium passing through the vasculature of pump-perfused dog lung lobes were acquired by using an X-ray microfocal angiography system. Time-absorbance curves from the lobar artery and vein and from selected locations within the intrapulmonary arterial tree were measured from the images. Overall dispersion within the lung lobe was determined from the difference in the first and second moments (mean transit time and variance, respectively) of the inlet arterial and outlet venous time-absorbance curves. Moments at selected locations within the arterial tree were also calculated and compared with those of the lobar artery curve. Transit times for the arterial pathways upstream from the smallest measured arteries (200-μm diameter) were less than ∼20% of the total lung lobe mean transit time. Transit time variance among these arterial pathways (interpathway dispersion) was less than ∼5% of the total variance imparted on the bolus as it passed through the lung lobe. On average, the dispersion that occurred along a given pathway (intrapathway dispersion) was negligible. Similar results were obtained for the venous tree. Taken together, the results suggest that most of the variation in transit time in the intrapulmonary vasculature occurs within the pulmonary capillary bed rather than in conducting arteries or veins.

scholarly journals The effect of age, sex and level of intake of dietary fibre from wheat on large-bowel function in thirty healthy subjects

1986 ◽  
Vol 56 (2) ◽  
pp. 349-361 ◽  
Author(s):  
Alison M. Stephen ◽  
H. S. Wiggins ◽  
H. N. Englyst ◽  
T. J. Cole ◽  
B. J. Wayman ◽  
...  
Keyword(s):  
Transit Time ◽  
Basal Diet ◽  
Bowel Function ◽  
White Bread ◽  
Stool Weight ◽  
Transit Times ◽  
Slow Transit ◽  
In Transit ◽  
Effect Of Age ◽  
Faecal Ph

1. To evaluate the effect of age, sex and level of intake on the colonic response to wheat fibre, thirty healthy volunteers aged 17–62 years (nineteen men, eleven women) recruited from a local industry, were divided into four groups and given a controlled diet for two 3-week periods. The diet contained white bread during one period or one of four different amounts of bran-enriched wholemeal bread during the other (30, 60, 110, 170 g/d).2. Wide variation was observed between subjects in stool weight on the basal diet and in response to wheat fibre. Stepwise regression analysis showed that the variation in stool weight was significantly related to sex (t4.0, P <0.001) but not to age, height, weight or energy:fibre intakes on the basal diet. Stool weight in men (162(SE 11) g/d) was approximately double that in women (83(SE 11) g/d). Transit time and stool weight were closely related and the effect of sex on stool weight could be explained entirely by differences in transit.4. Faecal carbohydrate excretion increased with the addition of bran mainly due to increased amounts of cellulose and pentose (arabinose+xylose), whilst digestibility of dietary non-starch polysaccharide fell from 77.6 (SE 2.3)% on the white bread diet to 65.6 (SE 2.4)% with the added bran (t 7.4, P < 0.01, n26).5. Faecal pH was more acid in men than in women and was related to methane production. Methane producers had higher faecal pH than non-producers (7.06 (SE 0.1 1) v. 6.65 (SE O.1)), lower stool weight (g/d; 93 (SE 12) v. 156 (SE 13)) and slower transit times (h; 84.6 (SE 11.7) v. 48.6 (SE 6.6)).6. These studies show that, when on similar diets, women have much lower stool weights and slower transit times than men. Furthermore, within the range of amounts of wheat fibre used in this and other published work, stool weight increases in linear proportion to the dose of fibre added to the diet. Methane excretion in breath is associated in this group of subjects with slow transit time and high faecal pH.

The Influence of Red Cell Mechanical Properties on Flow Through Single Capillary-Sized Pores

1988 ◽  
Vol 110 (2) ◽  
pp. 155-160 ◽  
Author(s):  
R. S. Frank ◽  
R. M. Hochmuth
Keyword(s):  
Mechanical Properties ◽  
Transit Time ◽  
Shear Viscosity ◽  
Fold Increase ◽  
Red Cell ◽  
Geometric Properties ◽  
Transit Times ◽  
Percent Increase ◽  
Flow Through ◽  
In Transit

The resistive pulse technique was used to study the influence of specific mechanical properties of the red cell on its ability to enter and flow through single capillary-sized pores with diameters of 3.6, 5.0 and 6.3 μm and lengths of 11 μm. A two-fold increase in membrane shear elasticity resulted in a 40 percent increase in the cell’s transit time through a 3.6 μm pore but produced no change in transit time through a 6.3 μm pore. A two-fold increase in membrane shear viscosity produced a 40 percent increase in transit time through the 3.6 μm pore and small but significant increases in transit times through the larger pores. Osmotically dehydrated cells showed no increase in transit time through a 6.3 μm pore, but showed increases in transit times of 50 to 70 percent through 5.0 and 3.6 μm pores. Dense red cells showed increased transit times through both 5.0 μm and 6.0 μm pores. These results indicate that for cells with normal geometric properties, the membrane’s shear viscosity and elasticity only influence the cell’s transit through pores of 5 μm or less in diameter. However, alterations in the cell’s geometric properties can extend the influence of membrane shear properties to larger diameter pores.

Pulmonary transit time and diffusing capacity in mammals

1984 ◽  
Vol 246 (3) ◽  
pp. R384-R388 ◽  
Author(s):  
S. L. Lindstedt
Keyword(s):  
Oxygen Consumption ◽  
Body Mass ◽  
Transit Time ◽  
Time Course ◽  
Physical And Mechanical Properties ◽  
Oxygen Binding ◽  
Diffusing Capacity ◽  
Transit Times ◽  
Mammalian Lung ◽  
In Transit

Allometry is used as a tool to explain the apparent mismatch of oxygen consumption and diffusing capacity in the mammalian lung. By combining equations for pulmonary capillary volume and cardiac output, it is apparent that erythrocyte transit time through the lung must scale disproportionately to body mass. This inequality is a consequence of physical and mechanical properties setting optimal cardiac and respiratory frequencies. Because of much shorter transit times, the mean alveolar-capillary oxygen pressure difference increases as body size decreases. The time course of oxygen binding to hemoglobin may limit maximum oxygen consumption in the smallest mammals. To assure carbon dioxide diffusion equilibrium, levels of carbonic anhydrase are much higher in small than in large mammals. Because of the differences in transit time, the pulmonary diffusing capacity must scale linearly to body mass to assure adequate oxygen delivery in all mammals.

Intercontinental and transcontinental mail transit times from Europe to Berkeley, 1892 to 1941

1986 ◽  
Vol 13 (2) ◽  
pp. 141-154 ◽  
Author(s):  
RUDOLF SCHMID
Keyword(s):  
Transit Times ◽  
In Transit

SUMMARY Mail transit times from Germany to Berkeley, California, are computed for issues of the current awareness journals Botanisches Centralblatt (1880–1945) and the interdisciplinary Naturae Novitates (1879–1944). Issues of the former for 1892 to 1902 averaged 29.3 days (31.2 days if abnormal times are included) in transit from Kassel to Berkeley, with many issues (92) requiring only 20 to 25 days for intercontinental and transcontinental transit. Mail transit of Naturae Novitates from Berlin to Berkeley averaged 40.7 days (42 if abnormal times are included) per issue for 1903 to 1916 and 44 days (51.1 days) per issue for 1922 to 1941 (cumulatively averaging 42 days, or 45.9 days for abnormal times), with some issues in 1906 requiring only 11-12 days for intercontinental and transcontinental transit. A smaller sampling for Nature for 1923 and 1930 gave averages of, respectively, 21.5 and 22.4 days, with a minimum of 14 days in both years. These times are consistent with known transatlantic and transcontinental, ship and rail, mail transit times for these periods, as tabulated from various sources. For perspective, early intercontinental and transcontinental air transit times and pre-1892 intercontinental ship transit times are also tabulated.

scholarly journals Simulating a Ground Truth for Transit Time Analysis of Indicator Dilution Curves

2020 ◽  
Vol 6 (3) ◽  
pp. 268-271
Author(s):  
Michael Reiß ◽  
Ady Naber ◽  
Werner Nahm
Keyword(s):  
Transit Time ◽  
Sampling Rate ◽  
Ground Truth ◽  
Indicator Dilution ◽  
Cross Sectional ◽  
In Vivo Measurements ◽  
Multiple Indicator Dilution ◽  
Transit Times ◽  
Dilution Curves

AbstractTransit times of a bolus through an organ can provide valuable information for researchers, technicians and clinicians. Therefore, an indicator is injected and the temporal propagation is monitored at two distinct locations. The transit time extracted from two indicator dilution curves can be used to calculate for example blood flow and thus provide the surgeon with important diagnostic information. However, the performance of methods to determine the transit time Δt cannot be assessed quantitatively due to the lack of a sufficient and trustworthy ground truth derived from in vivo measurements. Therefore, we propose a method to obtain an in silico generated dataset of differently subsampled indicator dilution curves with a ground truth of the transit time. This method allows variations on shape, sampling rate and noise while being accurate and easily configurable. COMSOL Multiphysics is used to simulate a laminar flow through a pipe containing blood analogue. The indicator is modelled as a rectangular function of concentration in a segment of the pipe. Afterwards, a flow is applied and the rectangular function will be diluted. Shape varying dilution curves are obtained by discrete-time measurement of the average dye concentration over different cross-sectional areas of the pipe. One dataset is obtained by duplicating one curve followed by subsampling, delaying and applying noise. Multiple indicator dilution curves were simulated, which are qualitatively matching in vivo measurements. The curves temporal resolution, delay and noise level can be chosen according to the requirements of the field of research. Various datasets, each containing two corresponding dilution curves with an existing ground truth transit time, are now available. With additional knowledge or assumptions regarding the detection-specific transfer function, realistic signal characteristics can be simulated. The accuracy of methods for the assessment of Δt can now be quantitatively compared and their sensitivity to noise evaluated.

Validation of cerebral arteriovenous malformation hemodynamics assessed by DSA using quantitative magnetic resonance angiography: preliminary study

2017 ◽  
Vol 10 (2) ◽  
pp. 156-161 ◽  
Author(s):  
Sophia F Shakur ◽  
Denise Brunozzi ◽  
Ahmed E Hussein ◽  
Andreas Linninger ◽  
Chih-Yang Hsu ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Magnetic Resonance Angiography ◽  
Transit Time ◽  
Internal Carotid ◽  
Flow Measurements ◽  
Quantitative Magnetic Resonance ◽  
Transit Times ◽  
Before And After ◽  
Preliminary Study ◽  
The Difference

BackgroundThe hemodynamic evaluation of cerebral arteriovenous malformations (AVMs) using DSA has not been validated against true flow measurements.ObjectiveTo validate AVM hemodynamics assessed by DSA using quantitative magnetic resonance angiography (QMRA).Materials and methodsPatients seen at our institution between 2007 and 2016 with a supratentorial AVM and DSA and QMRA obtained before any treatment were retrospectively reviewed. DSA assessment of AVM flow comprised AVM arterial-to-venous time (A-Vt) and iFlow transit time. A-Vt was defined as the difference between peak contrast intensity in the cavernous internal carotid artery and peak contrast intensity in the draining vein. iFlow transit times were determined using syngo iFlow software. A-Vt and iFlow transit times were correlated with total AVM flow measured using QMRA and AVM angioarchitectural and clinical features.Results33 patients (mean age 33 years) were included. Nine patients presented with hemorrhage. Mean AVM volume was 9.8 mL (range 0.3–57.7 mL). Both A-Vt (r=−0.47, p=0.01) and iFlow (r=−0.44, p=0.01) correlated significantly with total AVM flow. iFlow transit time was significantly shorter in patients who presented with seizure but A-Vt and iFlow did not vary with other AVM angioarchitectural features such as venous stenosis or hemorrhagic presentation.ConclusionsA-Vt and iFlow transit times on DSA correlate with cerebral AVM flow measured using QMRA. Thus, these parameters may be used to indirectly estimate AVM flow before and after embolization during angiography in real time.

Stability of maternal serum free β-hCG following whole blood sample transit: First trimester Down’s syndrome screening in Scotland

2021 ◽  
pp. 000456322110452
Author(s):  
Angela Ballantyne ◽  
Lorna Rashid ◽  
Rebecca Pattenden
Keyword(s):  
Transit Time ◽  
Down's Syndrome ◽  
Down’S Syndrome ◽  
First Trimester ◽  
Maternal Serum ◽  
Dependent Manner ◽  
Serum Free ◽  
Β Hcg ◽  
In Transit ◽  
The Impact

Background Maternal serum free beta human chorionic gonadotrophin (free β-hCG) is used as a biomarker in first trimester screening for fetal Down’s syndrome. Production of free β-hCG can occur in vitro in a time- and temperature-dependent manner; thus, the current Scottish screening protocol states samples must be received by the laboratory within 72 h. To assess the validity of the protocol, an audit was conducted to determine the impact of transit time on maternal serum free β-hCG multiple of median (MoM) values in the Scottish screened population. Methods Corrected MoM values from antenatal screening carried out over one year (April 2017 to March 2018) were stratified according to sample transit time and compared. To investigate possible environmental temperature effects, the data were split according to season and maternal serum free β-hCG concentrations from summer and winter compared. Results Of the 28,368 samples included in the study, 24,368 were received on the day of phlebotomy or after one day in transit. Only 1.5% of samples were received after 3 days in transit. The difference in maternal serum free β-hCG MoM values due to transit time was not significant. No statistical difference was found between maternal serum free β-hCG concentrations from samples collected in summer and winter months. Conclusion The current sample receipt protocol in use by the Scottish Down’s syndrome screening programme is fit for purpose.

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