Variations in transit-time-based ultrasonic velocity estimates in human calcaneus due to frequency-dependent attenuation and dispersion

2000 ◽  
Author(s):  
Keith A. Wear
Keyword(s):  
Ultrasonic Velocity ◽  
Transit Time ◽  
Frequency Dependent ◽  
In Transit ◽  
Attenuation And Dispersion

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.

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.

scholarly journals Short-Term Daily Intake of Polydextrose Fiber Does Not Shorten Intestinal Transit Time in Constipated Adults: A Randomized Controlled Trial

Nutrients ◽  
2018 ◽  
Vol 10 (7) ◽  
pp. 920 ◽  
Author(s):  
Peter Duncan ◽  
Catherine Enters-Weijnen ◽  
Nashmil Emami ◽  
Peter McLean ◽  
Tiago Nunes ◽  
...  
Keyword(s):  
Transit Time ◽  
Controlled Trial ◽  
Daily Intake ◽  
Intestinal Transit ◽  
Double Blind ◽  
Intestinal Transit Time ◽  
Gi Symptoms ◽  
Marker Distribution ◽  
Clinical Measures ◽  
In Transit

Chronic constipation (CC) remains a common gastrointestinal (GI) disorder that conveys a substantial healthcare burden. Expert guidelines recommend increasing fiber intake, yet the clinical evidence to support this needs strengthening for specific fibers. The aim was to evaluate changes in intestinal transit time and GI symptoms in CC patients who consumed polydextrose. In a randomized, double-blind, placebo-controlled trial, 128 adults with CC received 8 g or 12 g polydextrose, or placebo, daily for 4 weeks. Transit time, as primary outcome, was assessed by radiopaque marker distribution after 2-weeks intervention. Bowel habits, GI symptoms and quality of life (QOL) were assessed by questionnaire, including the Patient-Assessment of Constipation (PAC) Symptoms (SYM), and PAC-QOL. Following 2-weeks intervention, no reduction was seen in transit time in any group and following 2- or 4-weeks intervention, no improvements were seen in stool frequency or consistency in any group. After 2-weeks intervention with 8 g/day polydextrose an improvement was seen in the PAC-SYM rectal score (p = 0.041). After 4-weeks intervention both rectal (p = 0.049) and stool (p = 0.029) scores improved while improvement in the QOL satisfaction score did not reach significance (p = 0.071). Overall, the results suggest that 2-weeks consumption of 8 or 12 g/day polydextrose does not significantly improve physiological measures of gut function in CC adults. Longer term consumption may improve clinical measures, but further studies will be required to substantiate this.

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.

scholarly journals Ultrasonic Parameters of Some Ternary Liquid Mixture

2021 ◽  
Vol 16 (2) ◽  
Author(s):  
H K Semwal ◽  
S C Bhatt ◽  
S C Nautiyal
Keyword(s):  
Relaxation Time ◽  
Ultrasonic Velocity ◽  
Room Temperature ◽  
Liquid Mixture ◽  
Liquid Mixtures ◽  
Frequency Dependent ◽  
Ultrasonic Interferometer ◽  
Ultrasonic Parameters

At different composition and frequeny ultrasonic velocity has been measured in some ternary liquid mixtures at room temperature with the help of ultrasonic interferometer. Composition and frequency dependent variation of relaxation time (τ) have been shown in Figs. And analyzed for these ternary liquid mixtures.

scholarly journals Technical note: Transit time distributions are not L-shaped

2017 ◽  
Author(s):  
Earl Bardsley
Keyword(s):  
Probability Density ◽  
Transit Time ◽  
Technical Note ◽  
Probability Density Functions ◽  
Density Functions ◽  
Entry And Exit ◽  
Exponential Distributions ◽  
Tracer Particles ◽  
In Transit ◽  
Zero Time

Abstract. A probability density function f(t) with origin at t = 0 is defined here as being "L-shaped" if f'(t) ≤ 0 for t ≥ 0. L-shaped probability density functions, especially exponential distributions, are often assumed as transit time distributions in hydrological studies. However, L-shaped transit time distributions are not possible. This is because the transit time of a particle must always be with reference to a store, the transit time being some finite duration of time between particle entry and exit. Tracer particles cannot transit through any part of a store in zero time so transit time distributions have the property f(0) = 0, which is incompatible with L-shaped probability density functions. This is a fundamental constraint on the form of transit time distributions, which must possess at least one mode at t > 0. Some L-shaped probability density functions may well approximate actual transit time distributions, but they are of different form to the true distributions. A call is therefore made for L-shaped probability density functions to be no longer employed in transit time modelling.

Sign in / Sign up

Export Citation Format

Share Document