Carbon sequestration in the subsoil and the time required to stabilize carbon for climate change mitigation

Soils store large quantities of carbon in the subsoil (below 0.2 m depth) that is generally old and believed to be stabilized over centuries to millennia, which suggests that subsoil carbon sequestration (CS) can be used as a strategy for climate change mitigation. In this article, we review the main biophysical processes that contribute to carbon storage in subsoil and the main mathematical models used to represent these processes. Our guiding objective is to review whether a process understanding of soil carbon movement in the vertical profile can help us to assess carbon storage and persistence at timescales relevant for climate change mitigation. Bioturbation, liquid phase transport, belowground carbon inputs, mineral association, and microbial activity are the main processes contributing to the formation of soil carbon profiles, and these processes are represented in models using the diffusion-advection-reaction paradigm. Based on simulation examples and measurements from carbon and radiocarbon profiles across biomes, we found that advective and diffusive transport may only play a secondary role in the formation of soil carbon profiles. The difference between vertical root inputs and decomposition seems to play a primary role in determining the shape of carbon change with depth. Using the transit time of carbon to assess the timescales of carbon storage of new inputs, we show that only small quantities of new carbon inputs travel through the profile and can be stabilized for time horizons longer than 50 years, implying that activities that promote CS in the subsoil must take into consideration the very small quantities that can be stabilized in the long term.

Effect of volume and methylene blue on fluorescence intensity and transit of indocyanine green for sentinel lymph node mapping in a simulated feline tumor model

OBJECTIVE

To compare the effect of volume and solution on transit time and fluorescence intensity (FI) using near-infrared fluorescence imaging (NIRF) in a simulated tumor model in cats. Secondarily, to describe SLN mapping with indocyanine green (ICG) NIRF and report any adverse effects of intradermally injected ICG in cats.

ANIMALS

7 healthy purpose-bred domestic shorthaired male cats.

METHODS

Cats were randomly divided into 2 groups (ICG or ICG + methylene blue [MB]). Transit time and FI were determined for 1 or 2 mL solutions injected intradermally in 4 quadrants around a simulated tumor. Following massage, fluorescence intensity was quantified by calculating the corrected total ROI fluorescence using ImageJ software. Cats were monitored for adverse effects up to 4 weeks post-injection.

RESULTS

A larger solution volume had decreased transit times to the SLN (P = .001). There was no significant difference in transit times between ICG and ICG-MB. ICG demonstrated a greater FI (P = .001) in the SLN compared to ICG-MB. Methylene blue did not percutaneously fluoresce under NIRF. The volume of the solution did not significantly affect FI. No adverse reactions were reported.

CLINICAL RELEVANCE

Increased volume of ICG may aid in rapid percutaneous lymphatic tracking from tumor to SLN. Indocyanine green alone may be preferred over ICG-MB for greater visualization of the SLN. Intradermal injections of ICG and ICG-MB were well-tolerated in healthy cats with no significant complications. Clinical evaluation of this technique in an impaired lymphatic system, as seen in cancer patients, should be assessed in future research.

Gastrointestinal Transit Times in Health as Determined Using Ingestible Capsule Systems: A Systematic Review

BACKGROUND

Ingestible capsule (IC) systems can assess gastrointestinal (GI) transit times as a surrogate for gut motility for extended periods of time within a minimally invasive, radiation-free and ambulatory setting.

METHODS

A literature review of IC systems and a systematic review of studies utilizing IC systems to measure GI transit times in healthy volunteers was performed. Screening for eligible studies, data extraction and bias assessments was performed by two reviewers. A narrative synthesis of the results was performed.

RESULTS

The literature review identified 23 different IC systems. The systematic review found 6892 records, of which 22 studies were eligible. GI transit time data were available from a total of 1885 healthy volunteers. Overall, seventeen included studies reported gastric emptying time (GET) and small intestinal transit time (SITT). Colonic transit time (CTT) was reported in nine studies and whole gut transit time (WGTT) was reported in eleven studies. GI transit times in the included studies ranged between 0.4 and 15.3 h for GET, 3.3-7 h for SITT, 15.9-28.9 h for CTT and 23.0-37.4 h for WGTT. GI transit times, notably GET, were influenced by the study protocol.

CONCLUSIONS

This review provides an up-to-date overview of IC systems and reference ranges for GI transit times. It also highlights the need to standardise protocols to differentiate between normal and pathological function.

Pool dynamics of time-dependent compartmental systems with application to the terrestrial carbon cycle

Compartmental models play an important role to describe the dynamics of systems that involve mass movements between different types of pools. We develop a theory to analyse the average ages of mass in different pools in a linear compartmental system with time-dependent (i.e. non-autonomous) transfer rates, which involves transit times that characterize the average time a particle has spent in a particular pool. We apply our theoretical results to investigate a nine-dimensional compartmental system with time-dependent fluxes between pools modelling the carbon cycle which is a modification of the Carnegie-Ames-Stanford approach model. Knowledge of transit time and mean age allows calculation of carbon storage in a pool as a function of time. The general result that has important implications for understanding and managing carbon storage is that the change in storage in different pools does not change monotonically through time: as rates change monotonically a pool which initially shows a decrease may then show an increase in storage or vice versa. Thus caution is needed in extrapolating even the direction of future changes in storage in carbon storage in different pools with global change.

Gastrointestinal Effects and Tolerance of Nondigestible Carbohydrate Consumption

Nondigestible carbohydrates (NDCs) are food components, including nonstarch polysaccharides and resistant starches. Many NDCs are classified as dietary fibers by the US FDA. Because of their beneficial effects on human health and product development, NDCs are widely used in the food supply. Although there are dietary intake recommendations for total dietary fiber, there are no such recommendations for individual NDCs. NDCs are heterogeneous in their chemical composition and physicochemical properties-characteristics that contribute to their tolerable intake levels. Guidance on tolerable intake levels of different NDCs is needed because overconsumption can lead to undesirable gastrointestinal side effects, further widening the gap between actual and suggested fiber intake levels. In this review, we synthesize the literature on gastrointestinal effects of NDCs that the FDA accepts as dietary fibers (β-glucan, pectin, arabinoxylan, guar gum, alginate, psyllium husk, inulin, fructooligosaccharides and oligofructose, galactooligosaccharides, polydextrose, cellulose, soy fiber, resistant maltodextrin/dextrin) and present tolerable intake dose recommendations for their consumption. We summarized the findings from 103 clinical trials in adults without gastrointestinal disease who reported gastrointestinal effects, including tolerance (e.g., bloating, flatulence, borborygmi/rumbling) and function (e.g., transit time, stool frequency, stool consistency). These studies provided doses ranging from 0.75-160 g/d and lasted for durations ranging from a single-meal tolerance test to 28 wk. Tolerance was NDC specific; thus, recommendations ranged from 3.75 g/d for alginate to 25 g/d for soy fiber. Future studies should address gaps in the literature by testing a wider range of NDC doses and consumption forms (solid compared with liquid). Furthermore, future investigations should also adopt a standard protocol to examine tolerance and functional outcomes across studies consistently.

Younger carbon dominates global soil carbon efflux

Soil carbon (C) is comprised of a continuum of organic compounds with distinct ages (i.e., the time a C atom has experienced in soil since the C atom entered soil). The contribution of different age groups to soil C efflux is critical for understanding soil C stability and persistence, but is poorly understood due to the complexity of soil C pool age structure and potential distinct turnover behaviors of age groups. Here, we build upon the quantification of soil C transit times to infer the age of C atoms in soil C efflux (a_efflux ) from seven sequential soil layer depths down to 2 m at a global scale, and compare this age with radiocarbon-inferred ages of C retained in corresponding soil layers (a_soil ). In the whole 0-2 m soil profile, the mean a_efflux is 194 21 1021 (mean with 5%-95% quantiles) year and is just about one-eighth of a_soil ( 1476 717 2547 year), demonstrating that younger C dominates soil C efflux. With increasing soil depth, both a_efflux and a_soil are increased, but their disparities are markedly narrowed. That is, the proportional contribution of relatively younger soil C to efflux is decreased in deeper layers, demonstrating that C inputs (new and young) stay longer in deeper layers. Across the globe, we find large spatial variability of the contribution of soil C age groups to C efflux. Especially, in deep soil layers of cold regions (e.g., boreal forests and tundra), a_efflux may be older than a_soil , suggesting that older C dominates C efflux only under a limited range of conditions. These results imply that most C inputs may not contribute to long-term soil C storage, particularly in upper layers that hold the majority of new C inputs.

Automated generation of cerebral blood flow and arterial transit time maps from multiple delay arterial spin-labeled MRI

PURPOSE

Develop and evaluate a deep learning approach to estimate cerebral blood flow (CBF) and arterial transit time (ATT) from multiple post-labeling delay (PLD) ASL MRI.

METHODS

ASL MRI were acquired with 6 PLDs on a 1.5T or 3T GE system in adults with and without cognitive impairment (N = 99). Voxel-level CBF and ATT maps were quantified by training models with distinct convolutional neural network architectures: (1) convolutional neural network (CNN) and (2) U-Net. Models were trained and compared via 5-fold cross validation. Performance was evaluated using mean absolute error (MAE). Model outputs were trained on and compared against a reference ASL model fitting after data cleaning. Minimally processed ASL data served as another benchmark. Model output uncertainty was estimated using Monte Carlo dropout. The better-performing neural network was subsequently re-trained on inputs with missing PLDs to investigate generalizability to different PLD schedules.

RESULTS

Relative to the CNN, the U-Net yielded lower MAE on training data. On test data, the U-Net MAE was 8.4 ± 1.4 mL/100 g/min for CBF and 0.22 ± 0.09 s for ATT. A significant association was observed between MAE and Monte Carlo dropout-based uncertainty estimates. Neural network performance remained stable despite systematically reducing the number of input images (i.e., up to 3 missing PLD images). Mean processing time was 10.77 s for the U-Net neural network compared to 10 min 41 s for the reference pipeline.

CONCLUSION

It is feasible to generate CBF and ATT maps from 1.5T and 3T multi-PLD ASL MRI with a fast deep learning image-generation approach.

Toward Precise Nutrient Value of Feed in Growing Pigs: Effect of Meal Size, Frequency and Dietary Fibre on Nutrient Utilisation

Simple Summary

Feed costs are the most important in swine production. Precise determination of nutritional values of pig diets can help reducing feed costs by reducing security margins for nutrients and therefore provide a more sustainable swine production. In commercial farms, pigs have free access to feed and eat with no limitation according to their natural behaviour. In contrast, during digestibility trials, pigs are restricted in their daily intake of feed, which is distributed in a limited number of meals. The number of meals per day and the amount of feed consumed daily can affect the digestibility of the nutrients, the transit time and the metabolism. To reduce feed costs, by-products are frequently added to diets. Most by-products are rich in dietary fibre, which are known to have negative effects on digestibility. Enzymes can be supplemented in the diet to counteract the negative aspects of dietary fibre, but their efficiency can vary depending on the number of meals per day and the amount of feed consumed daily.

Abstract

Nutritional values of ingredients have been and still are the subject of many studies to reduce security margins of nutrients when formulating diets to reduce feed cost. In most studies, pigs are fed a limited amount of feed in a limited number of meals that do not represent how pigs are fed in commercial farm conditions. With free access to feed, pigs follow their intrinsic feeding behaviour. Feed intake is regulated by satiety and satiation signals. Reducing the feed intake level or feeding frequency can affect digestibility and transit time and induce metabolic changes. To reduce feed costs, alternative ingredients that are frequently rich in dietary fibre are added to diets. Fibre acts on the digestion process and transit time by decreasing energy density and causing viscosity. Various analyses of fibre can be realised, and the measured fibre fraction can vary. Exogenous enzymes can be added to counteract the effect of fibre, but digestive tract conditions, influenced by meal size and frequency, can affect the efficiency of supplemented enzymes. In conclusion, the frequency and size of the meals can affect the digestibility of nutrients by modulating gastrointestinal tract conditions (pH and transit time), metabolites (glucose and short-chain fatty acids) and hormones (glucagon-like peptide 1 and peptide tyrosine tyrosine).

Transit Time Measurement in Indicator Dilution Curves: Overcoming the Missing Ground Truth and Quantifying the Error

The vascular function of a vessel can be qualitatively and intraoperatively checked by recording the blood dynamics inside the vessel via fluorescence angiography (FA). Although FA is the state of the art in proving the existence of blood flow during interventions such as bypass surgery, it still lacks a quantitative blood flow measurement that could decrease the recurrence rate and postsurgical mortality. Previous approaches show that the measured flow has a significant deviation compared to the gold standard reference (ultrasonic flow meter). In order to systematically address the possible sources of error, we investigated the error in transit time measurement of an indicator. Obtaining in vivo indicator dilution curves with a known ground truth is complex and often not possible. Further, the error in transit time measurement should be quantified and reduced. To tackle both issues, we first computed many diverse indicator dilution curves using an in silico simulation of the indicator's flow. Second, we post-processed these curves to mimic measured signals. Finally, we fitted mathematical models (parabola, gamma variate, local density random walk, and mono-exponential model) to re-continualize the obtained discrete indicator dilution curves and calculate the time delay of two analytical functions. This re-continualization showed an increase in the temporal accuracy up to a sub-sample accuracy. Thereby, the Local Density Random Walk (LDRW) model performed best using the cross-correlation of the first derivative of both indicator curves with a cutting of the data at 40% of the peak intensity. The error in frames depends on the noise level and is for a signal-to-noise ratio (SNR) of 20 dB and a sampling rate of f_s = 60 Hz at fs-1·0.25(±0.18), so this error is smaller than the distance between two consecutive samples. The accurate determination of the transit time and the quantification of the error allow the calculation of the error propagation onto the flow measurement. Both can assist surgeons as an intraoperative quality check and thereby reduce the recurrence rate and post-surgical mortality.

Machine Learning Analysis of Hydrologic Exchange Flows and Transit Time Distributions in a Large Regulated River

Hydrologic exchange between river channels and adjacent subsurface environments is a key process that influences water quality and ecosystem function in river corridors. High-resolution numerical models were often used to resolve the spatial and temporal variations of exchange flows, which are computationally expensive. In this study, we adopt Random Forest (RF) and Extreme Gradient Boosting (XGB) approaches for deriving reduced order models of hydrologic exchange flows and associated transit time distributions, with integrated field observations (e.g., bathymetry) and hydrodynamic simulation data (e.g., river velocity, depth). The setup allows an improved understanding of the influences of various physical, spatial, and temporal factors on the hydrologic exchange flows and transit times. The predictors also contain those derived using hybrid clustering, leveraging our previous work on river corridor system hydromorphic classification. The machine learning-based predictive models are developed and validated along the Columbia River Corridor, and the results show that the top parameters are the thickness of the top geological formation layer, the flow regime, river velocity, and river depth; the RF and XGB models can achieve 70% to 80% accuracy and therefore are effective alternatives to the computational demanding numerical models of exchange flows and transit time distributions. Each machine learning model with its favorable configuration and setup have been evaluated. The transferability of the models to other river reaches and larger scales, which mostly depends on data availability, is also discussed.

Corn? When did I eat corn? Gastrointestinal transit time in health science students

The objective of this study was to determine gastrointestinal transit time in first-year health science students with a laboratory practical exercise conducted in two cohorts (classes of 2018 and 2019) of first-year health sciences students at the Health Science Campus in Windhoek, Namibia. All first-year health science students undertaking the Physiology course were invited to take part in the laboratory exercise. The primary outcome was the measurement of gastrointestinal transit time from the amount of time taken for ingested whole-kernel sweetcorn to be eliminated, which was calculated as the time period between ingestion of corn and the time of corn first seen in the stool and the time corn was last seen in the stool. The secondary outcome was an association between emotional irritability and/or anxiety and gastrointestinal transit time. The study analyzed responses of 175 students, who reported a median transit time of 29 (1-99) h. There was no difference in gastrointestinal transit time between male and female students. Likewise, there was no difference in the duration of the corn in the bowel between male and female students. Students who reported being worried and irritable during the exercise had more bowel movements before they saw corn in their stool and had slower transit times, respectively. A wider range of transit time was reported in a group of young, healthy students compared with previous studies in the literature. There were no differences between male and female student bowel activity. Anxiety did impact the bowel activity of the participants.

An automated sensitive approach for measuring whole gut transit time

BACKGROUND

Commonly used methods to measure whole gut transit time in rodents have yet to combine high sensitivity, objectivity, and automation. We have developed a novel method using oral gavage of non-toxic fluorescent dye particles and their detection by fluorescence imaging to enable unbiased automated detection of gut transit time simultaneously in 8 cages.

METHODS

Naïve mice (n = 20) were gavaged with a non-caloric viscous suspension of 4.4% fluorescent dye in 3 groups on 2 occasions. Each group was imaged in 8 cages at 5-minute intervals using blue LEDs for illumination and a Sony full-frame mirrorless camera with a green band-pass emission filter. Custom MATLAB code counted the number of fluorescent boli per cage post hoc and provided graphical and spreadsheet output. Boli counts across a wide range of parameters were compared to blind assessments by an experimenter.

RESULTS

Fluorescent boli were detected with high sensitivity, while unstained boli were readily rejected. All cages showed no fluorescent boli for the first ~20 frames (100 minutes), after which many cages gradually show a rise to 1-6 fluorescent boli. The mean time to first fluorescent bolus in each session was 264 ± 141 and 223 ± 81 minutes post-gavage, with no within subject consistency. There was high correlation between automated scores and that of experimenter (r = .95 ± .02), being robust to parameter changes.

CONCLUSIONS AND INFERENCES

This novel approach provides a reliable, automatic, and low-cost method of measuring gastrointestinal transit time in mice.

Normative values for region-specific colonic and gastrointestinal transit times in 111 healthy volunteers using the 3D-Transit electromagnet tracking system: Influence of age, gender, and body mass index

BACKGROUND

The 3D-Transit electromagnet tracking system (Motilis Medica, SA, Lausanne, Switzerland) is an emerging tool for the ambulatory assessment of gastrointestinal (GI) transit and motility. Using this tool, we aimed to derive normative values for region-specific colonic and GI transit times and to assess the influence of age, gender, and body mass index (BMI).

METHODS

Regional and total colonic transit times (CTT), gastric emptying (GET), small intestinal (SITT), and whole gut (WGTT) transit times were extracted from 111 healthy volunteers from the United Kingdom and Denmark (58 female; median age: 40 years [range: 21-88]). The effects of age, gender, and BMI were assessed using standard statistical methods.

KEY RESULTS

The ascending, transverse, descending, and rectosigmoid colon transit times accounted for 32%, 34%, 17%, and 17% of total CTT in females, and 33%, 25%, 14%, and 28% of total CTT in males. CTT and WGTT were seen to cluster at intervals separated by approximately 24 hours, providing further evidence of the non-continuous nature of these measurements. Increasing age was associated with longer CTT (P = .021), WGTT (P < .001) ascending (P = .004), transverse (P < .001), and total right (P < .001) colon transit times, but shorter rectosigmoid (P = .004) transit time. Female gender was significantly associated with longer transverse (P = .049) and descending (P < .001) colon transit times, but shorter rectosigmoid (P < .001) transit time. Increasing BMI was significantly associated with shorter WGTT (P = .012).

CONCLUSIONS AND INFERENCES

For the first time, normative reference values for region-specific colonic transit have been presented. Age, gender, and BMI were seen to have an effect on transit times.

A Systematic Study on Transit Time and Its Impact on Accuracy of Concentration Measured by Microfluidic Devices

Gating or threshold selection is very important in analyzing data from a microflow cytometer, which is especially critical in analyzing weak signals from particles/cells with small sizes. It has been reported that using the amplitude gating alone may result in false positive events in analyzing data with a poor signal-to-noise ratio. Transit time (τ) can be set as a gating threshold along with side-scattered light or fluorescent light signals in the detection of particles/cells using a microflow cytometer. In this study, transit time of microspheres was studied systematically when the microspheres passed through a laser beam in a microflow cytometer and side-scattered light was detected. A clear linear relationship between the inverse of the average transit time and total flow rate was found. Transit time was used as another gate (other than the amplitude of side-scattering signals) to distinguish real scattering signals from noise. It was shown that the relative difference of the measured microsphere concentration can be reduced significantly from the range of 3.43%-8.77% to the range of 8.42%-111.76% by employing both amplitude and transit time as gates in analysis of collected scattering data. By using optimized transit time and amplitude gate thresholds, a good correlation with the traditional hemocytometer-based particle counting was achieved (R² > 0.94). The obtained results suggest that the transit time could be used as another gate together with the amplitude gate to improve measurement accuracy of particle/cell concentration for microfluidic devices.

Determination of gastrointestinal passage rate using three different markers in laying hens

The titanium dioxide (TiO₂ ) marker technique is currently widely practiced as a method to evaluate gastrointestinal (GI) passage rate in poultry. However, this method requires sacrificing the animal to obtain digesta samples, is labour-intensive and eliminates the possibility of follow-up studies with the same individual. The aim of this study was to evaluate whether the radiographic methods barium-impregnated polyethylene spheres (BIPS) and barium sulphate (BaSO₄ ) suspension are in agreement with the TiO₂ technique and can be used as an alternative method for GI passage rate determination in laying hens. Whole-body radiographs were taken at different time points. Hens of group 3 (n = 55) were orally inoculated with 5 g of feed mixed with 0.15 g TiO₂ , 5 hens per time point sacrificed, and whole gastrointestinal organs (crop, proventriculus, gizzard, small intestine and large intestine) were collected and analysed for TiO₂ content. The average marker passage rate of hens administered BaSO₄ was significantly faster than those administered BIPS (gizzard: 15.2 hr vs. 43.2 hr; small intestine: 15.2 hr vs. 38.4 hr, respectively). A greater percentage of BIPS remained in the crop at 0, 0.5, 2, 3 and 8 hr post-inoculation (p.i.) and in the gizzard at 2, 24, 36 and 48 hr p.i. (all p < 0.05) compared to TiO₂ . In conclusion, the evaluation of the GI transit time is feasible using BIPS, TiO₂ and BaSO₄ . The evaluation of the GI transit time using BIPS and BaSO₄ needs further investigation.

The human microbiome in health and disease: hype or hope

OBJECTIVES

The prognostic, diagnostic, and therapeutic potential of the human gut microbiota is widely recognised. However, translation of microbiome findings to clinical practice is challenging. Here, we discuss current knowledge and applications in the field.

METHODS

We revisit some recent advances in the field of faecal microbiome analyses with a focus on covariate analyses and ecological interpretation.

RESULTS

Population-level characterization of gut microbiota variation among healthy volunteers has allowed identifying microbiome covariates required for clinical studies. Currently, microbiome research is moving from relative to quantitative approaches that will shed a new light on microbiota-host interactions in health and disease.

CONCLUSIONS

Covariate characterization and technical advances increase reproducibility of microbiome research. Targeted in vitro/in vivo intervention studies will accelerate clinical implementation of microbiota findings.

Efficacy of Polydextrose Supplementation on Colonic Transit Time, Bowel Movements, and Gastrointestinal Symptoms in Adults: A Double-Blind, Randomized, Placebo-Controlled Trial

The addition of fiber is one of the most important dietary means to relieve constipation through lifestyle modification. Polydextrose (PDX) has been reported in several studies to increase fecal bulk, soften stools, and increase the number of defecations. However, there are few studies on the effect of PDX on colonic transit time (CTT). Therefore, the aim of this study was to demonstrate the effect of PDX on CTT and other aspects of gastrointestinal function during two weeks (Day 1 to Day 14), preceded by a 2-week run-in period (Day -14 to Day -1). A total of 192 adults who were diagnosed with functional constipation per Rome III criteria were recruited for the study. Participants were randomized equally into 4 groups (12 g, 8 g, or 4 g of PDX or placebo per day). The primary endpoint was CTT, assessed using radio-opaque markers and abdominal X-rays on Day 0, the baseline; and Day 15, the end of the intervention. Secondary outcomes that were measured using inventories were the patient assessment of constipation symptoms and quality of life, bowel function index, relief of constipation, bowel movement frequency (BMF), stool consistency, degree of straining, and proportion of bowel movements. Ancillary parameters and harms were also evaluated. The recruited population was not sufficiently constipated (e.g., baseline values for CTT and BMF of 42 h and 8.7 BMF/week, respectively). Despite this limitation, our results demonstrated an increased number of bowel movements when supplemented with PDX at a dosage of 12 g per day for 2 weeks. This dosage also consistently improved the secondary outcomes that were measured using inventories at Day 15, compared with the baseline. No serious or significant adverse events were reported during the study.

Technical report: Inter- and intra-rater reliability of regional gastrointestinal transit times measured using the 3D-Transit electromagnet tracking system

BACKGROUND

The 3D-Transit electromagnet tracking system is an emerging tool for the ambulatory assessment of gastrointestinal (GI) transit times and motility patterns, based on the anatomical localization of ingestible electromagnetic capsules. Currently, 3D-Transit recordings are manually analyzed to extract GI transit times. As this is a subjective method, there is some inherent variability in the measurements, which may be experience-dependent. We therefore assessed inter- and intra-rater reliability of GI transit times from 3D-Transit recordings.

METHODS

Thirty-six 3D-Transit recordings (17 female; median age: 34 years [range: 21-80]) were analyzed twice by 3 raters with varying experience. Each rater manually identified the timestamps when a capsule progressed from antrum to duodenum, and from ileum to right colon. These timestamps, along with the ingestion and expulsion times, were used to determine whole gut (WGTT), gastric emptying (GET), small intestinal (SITT) and colonic (CTT) transit times. Reliability was determined using interclass correlation coefficients (ICCs).

KEY RESULTS

For capsule progression timestamps, the most and mid-experienced raters had fair to good inter- and excellent intra-rater reliability (ICC_min-max  = 0.61-1.00), whereas the inexperienced rater had poor to fair inter- and poor intra-rater reliability (ICC_min-max  = 0.28-0.55). GET and SITT reliability between the most and mid-experienced raters was fair (ICC_min-max  = 0.61-0.73), while reliability between these raters and the inexperienced rater was poor to fair (ICC_min-max  = 0.28-0.55). CTT reliability was excellent between and within all raters (ICC_min-max  = 0.92-0.99).

CONCLUSIONS & INFERENCES

Inexperienced raters provide the least reliable measurements from 3D-Transit recordings, which confirms requirement for adequate training. Automation may improve the reliability of measurements.

Characterization of ulcerative colitis-associated constipation syndrome (proximal constipation)

BACKGROUND

The syndrome of constipation with other abdominal symptoms ("proximal constipation") in ulcerative colitis (UC) is commonly recognized by practitioners but is poorly described, with no recognized definition and little understanding with regard to prevalence and effect of therapies on disease outcomes. This study aimed to address these issues in a cross-sectional, consecutive series of patients with UC.

METHODS

A working definition of proximal constipation was established. Consecutive patients were recruited, and their disease activity, recent medications, and investigations plus abdominal symptoms were assessed at a study visit. Relevant clinical data were also extracted from medical records.

RESULTS

Of 125 patients with UC, (mean age 47, range 14-84 years, 61 male), 58 (46%) fulfilled the definition of proximal constipation. The main symptoms were reduced stool frequency (69%), hard stools (43%), abdominal pain (40%), excessive flatus (29%), straining (24%), and sensation of incomplete emptying (14%). Proximal constipation was associated with female gender (OR 3.45 [1.45-8.24]), left-sided (OR 2.84 [1.14-7.11]) and concurrently active disease (OR 5.56 [1.96-16.67]), but not age, disease duration or therapy. A total of 88% had an increase in anti-inflammatory therapy, with the use of laxatives or fiber supplements in 63% compared with 1.4% of those without proximal constipation.

CONCLUSIONS

Proximal constipation is common, and its risk increases in active and distal disease, especially in women. Validation of its definition and evaluation of therapeutic strategies are needed. A new term "ulcerative colitis-associated constipation syndrome" is proposed to more accurately depict its nature.

Small Intestinal Permeability and Gut-Transit Time Determined with Low and High Molecular Weight Fluorescein Isothiocyanate-Dextrans in C3H Mice

Protocols for intestinal permeability measurements in mice using 4-kDa fluorescein isothiocyanate-conjugated (FITC) dextran differ considerably among laboratories on the blood-sampling time. To find the optimal point in time for blood sampling, we administered 4-kDa FITC dextran to C3H mice and monitored the marker in plasma over 8 h. We also determined gut-transit time using 70-kDa FITC dextran, which does not cross the intestinal epithelium. The 4-kDa FITC dextran concentration in plasma reached its maximum 45 min after administration. The 70-kDa FITC dextran reached the jejunum after 15 min and passed the entire small intestine within 1 h after its administration, demonstrating that 4-kDa FITC dextran measured in plasma 1 h after its oral application is a marker of small intestinal permeability.

Gastrointestinal Transit Time in Parkinson's Disease Using a Magnetic Tracking System

BACKGROUND

Symptoms from the gastrointestinal tract are highly prevalent in Parkinson's disease (PD), but knowledge of the underlying pathology is incomplete and valid objective markers on regional gastrointestinal function are limited.

OBJECTIVE

The aims were to evaluate gastrointestinal transit time and motility in PD patients and controls.

METHODS

Twenty-two PD patients and 15 controls were included. Gastric-, small intestinal-, and caecum-ascending colonic transit times as well as colonic motility, defined as mass- and fast movements, were performed using the ambulatory 3D-Transit system. Gastrointestinal transit time with radio opaque markers, gastric emptying scintigraphy, and subjective non-motor symptoms were also evaluated.

RESULTS

Using the 3D-Transit system, the patient group displayed significantly longer small intestinal- and caecum-ascending transit times (p = 0.030 and p = 0.0063). No between-group difference was seen in gastric transit time (p = 0.91). Time to first mass- and fast colonic movement were significantly increased in PD (p = 0.023 and p = 0.006). Radio opaque marker gastrointestinal transit time was significantly increased in the patient group (p < 0.0001), whereas no difference was seen in scintigraphic gastric emptying time (p = 0.68). Prevalence of constipation symptoms on the NMSQuest was 41% in PD and 7% in controls.

CONCLUSIONS

Significantly increased small intestinal- and caecum-ascending 3D-Transit times were detected in PD patients. Also, time to first propagating colonic movement was increased. Radio opaque marker gastrointestinal transit time was significantly delayed, but no difference was seen in gastric transit time and gastric emptying time. The present findings highlight widespread intestinal involvement in PD increasing throughout the gastrointestinal tract.

Fecal glucocorticoid metabolites and assay validation: Stress response evaluation in captive brown howler monkeys (Alouatta clamitans)

BACKGROUND

The advent of non-invasive methods provides a powerful alternative to stress studies as the use of stressful handling techniques is no longer needed. However, many factors influence hormone metabolism such as sex, diet, and metabolic rate. Thus, validation should be species- and matrix-specific.

METHODS

To assess stress response in brown howler monkeys Alouatta clamitans, we adopted an ACTH challenge test and parallelism to provide physiological and laboratorial validation. Radioimmunoassay was used to measure fecal levels of corticosterone.

RESULTS AND CONCLUSIONS

All challenged animals presented a peak in fecal glucocorticoids levels the day after the treatment, while control animals did not. There were no significant sex differences, but females with infants had higher levels of corticosterone. Corticosterone levels showed parallelism to the standard curve of the diagnostics kit. Collectively, the data suggest that the method was validated and is useful for monitoring stress, thereby helping in conservation programs both in captivity and in the wild. Transit time information may be coupled with travel distance in seed dispersal studies.

A 3D-printed passive ultrasound phase-interference compensator for reduced wave degradation in cancellous bone - an experimental study in replica models

The current ‘active’ solution to overcome the impediment of ultrasound wave degradation associated with transit-time variation in complex tissue structures, such as the skull, is to vary the transmission delay of ultrasound pulses from individual transducer elements. This article considers a novel ‘passive’ solution in which constant transit time is achieved by propagating through an additional material layer positioned between the ultrasound transducer and the test sample. To test the concept, replica models based on four cancellous bone natural tissue samples and their corresponding passive ultrasound phase-interference compensator were 3D-printed. Normalised broadband ultrasound attenuation was used as a quantitative measure of wave degradation, performed in transmission mode at a frequency of 1 MHz and yielding a reduction ranging from 57% to 74% when the ultrasound phase-interference compensator was incorporated. It is suggested that the passive compensator offers a broad utility and, hence, it may be applied to any ultrasound transducer, of any complexity (single element or array), frequency and dimension.

Diagnostic value of OMOM capsule endoscopy for small bowel diseases in adults

The present study aimed to determine the diagnostic yield of OMOM capsule endoscopy for small bowel diseases in adults. A total of 89 patients, including 45 cases of obscure abdominal pain, 22 of chronic diarrhea, 18 of obscure gastrointestinal bleeding and 4 of obscure anemia were enrolled in the present study. The transit time of the endoscopy capsule in the digestive tract was recorded and the testing results were analyzed. All detections were completed except for four capsule retentions and the completion rate was 95.51%. The average transit time of the endoscopy capsule in the esophagus, stomach and small intestine was 62.18±64.23 sec, 67.46±63.13 and 346.53±102.81 min, respectively. Of the 89 patients, 54 (60.67%) were found to have lesions, among which 19 had mucosal erosion (21.35%), 15 had anabrosis (16.85%), 9 were diagnosed with polyps (10.11%), 5 with angiodysplasia (5.62%); furthermore, tumors were identified in 5 patients (5.62%) and ancylostomiasis in 1 patient (1.12%). The results confirmed the feasibility and validity of OMOM capsule endoscopy for diagnosing small bowel diseases in adults.

Transit-time and age distributions for nonlinear time-dependent compartmental systems

Many processes in nature are modeled using compartmental systems (reservoir/pool/box systems). Usually, they are expressed as a set of first-order differential equations describing the transfer of matter across a network of compartments. The concepts of age of matter in compartments and the time required for particles to transit the system are important diagnostics of these models with applications to a wide range of scientific questions. Until now, explicit formulas for transit-time and age distributions of nonlinear time-dependent compartmental systems were not available. We compute densities for these types of systems under the assumption of well-mixed compartments. Assuming that a solution of the nonlinear system is available at least numerically, we show how to construct a linear time-dependent system with the same solution trajectory. We demonstrate how to exploit this solution to compute transit-time and age distributions in dependence on given start values and initial age distributions. Furthermore, we derive equations for the time evolution of quantiles and moments of the age distributions. Our results generalize available density formulas for the linear time-independent case and mean-age formulas for the linear time-dependent case. As an example, we apply our formulas to a nonlinear and a linear version of a simple global carbon cycle model driven by a time-dependent input signal which represents fossil fuel additions. We derive time-dependent age distributions for all compartments and calculate the time it takes to remove fossil carbon in a business-as-usual scenario.

Analysis of Radiopaque Gastrointestinal Foreign Bodies Expelled by Spontaneous Passage in Children: A 15-Year Single-Center Study

Background: Most ingested foreign bodies (FBs) pass spontaneously through the gastrointestinal (GI) tract, but only limited data on transit time are available. We evaluated the relationship of FB size and shape with transit time. Methods: We retrospectively reviewed medical records collected over 15 years (January 2001 to December 2015) on pediatric patients with radiopaque FBs in the GI tract. We categorized the FBs as regularly (round or spherical) or irregularly shaped (ovoid, long, flake-like, or projecting) and measured their sizes radiographically. The diameter of regularly shaped FBs and the length of irregularly shaped FBs were correlated with transit time. Results: In total, 484 patients with GI FBs were surveyed, and 267 (55.1%) FBs were radiopaque. Among the 267 radiopaque FBs, 88 (33.1%) required endoscopic removal and 7 (2.6%) underwent surgical intervention. Eighty-seven patients with single FBs in the GI tract for whom precise details of transit time were enrolled into the analysis of transit time; their mean age was 3.48 ± 2.21 years. Of the 87 FBs, 61 (70.1%) were regularly shaped, and 26 (29.9%) were irregularly shaped. The diameter of regularly shaped FBs was positively associated with transit time, as revealed by Mann-Whitney U test; diameters >1.5 and >2 cm were significantly correlated with longer transit times (both p = 0.003). A trend toward an increased transit time for long irregularly shaped FBs was also apparent; the p-values for lengths of 1.5, 2, and 2.5 cm were 0.824, 0.153, and 0.055, respectively. Under receiver operating characteristic (ROC) curve analysis, the optimal cutoff diameter for regularly shaped FBs, and length for irregularly shaped FBs, to predict a transit time of longer than 72 h were 1.95 and 2.25 cm, respectively. Conclusions: The passage rate of ingested radiopaque FBs is 64.4%. Small FBs that have passed the duodenal curve should be managed conservatively via clinical observation and radiographic surveillance. Our results indicate that the larger an FB is, the longer the transit time will be.

Intracranial contrast transit times on digital subtraction angiography decrease more in patients with delayed intraparenchymal hemorrhage after Pipeline

Background Pipeline embolization devices (PEDs) are used for endovascular treatment of cerebral aneurysms but can be associated with delayed ipsilateral intraparenchymal hemorrhage (DIPH). Changes in intracranial hemodynamics after PED are poorly understood. Objective Here, we assess hemodynamic changes after PED in patients and compare these changes in patients with and without DIPH (DIPH+ and DIPH-). Methods Records of patients with distal internal carotid artery (ICA) aneurysms treated with PED at our institution between 2012 and 2017 were retrospectively reviewed. Regions of interest were selected proximally to PED over the cavernous ICA and distally over the middle cerebral artery (MCA), and then transit times were determined using syngo iFlow software (Siemens). Ratio of MCA to ICA transit time was compared before, after treatment, and at follow-up. Ratios were also compared between DIPH+ and DIPH- subgroups. Correlations between aneurysm size, age, and ratios were investigated. Results Fifty-three patients were included. The ratio of MCA to ICA transit time decreased significantly after PED deployment (1.13 vs. 1.22, p < 0.01). The ratio in the DIPH + subgroup ( n = 4) was significantly lower (1.00 vs. 1.14, p = 0.01) and decreased significantly more (21% vs. 4.4%, p = 0.02) compared to the DIPH- subgroup ( n = 49). The ratio tended to be higher in larger aneurysms at baseline ( r = 0.25, p = 0.07) but not after PED treatment ( r = 0.11, p = 0.15). Age did not correlate with ratio. Conclusion The ratio of MCA to ICA transit time decreases following PED treatment and decreases more in patients with DIPH. These contrast transit time changes can be detected in real time immediately after PED deployment.

Effects of probiotic-containing products on stool frequency and intestinal transit in constipated adults: systematic review and meta-analysis of randomized controlled trials

Background:

Probiotics are commonly recommended for the alleviation of constipation symptoms. The aim of this research was to determine the effects of probiotic-containing products on stool frequency and intestinal transit time (ITT) in constipated adults and to determine the factors that influence the efficacy of these products.

Methods:

We conducted a systematic review of randomized controlled trials that measured weekly stool frequency or ITT in constipated adults receiving probiotic-containing supplements. A random effects meta-analysis was performed; stool frequency was summarized by the mean difference statistic and ITT was summarized by the standardized mean difference (SMD) statistic. Meta-regression and diagnostic model performance testing were used to identify publication bias and sources of heterogeneity.

Results:

A total of 21 studies (23 comparisons) comprising 2656 subjects were included. All studies utilized probiotics containing Lactobacillus or Bifidobacterium species. Probiotic-containing products resulted in a mean increase in weekly stool frequency of 0.83 (95% confidence interval [CI] 0.53-1.14, P<0.001). There was high heterogeneity among the studies (I²=85%, P<0.001) and evidence of significant publication bias (Egger’s P-value <0.01). After adjustment for publication bias, the mean difference in weekly stool frequency was reduced from 0.83 to 0.30. The effects on stool frequency were greater in studies where functional constipation was diagnosed using Rome III (P<0.01), or Rome II or III criteria (P<0.05), compared to non-Rome diagnosis techniques. Probiotic-containing products were also efficacious in reducing ITT (SMD=0.65, 95%CI 0.33-0.97, P<0.001). There was high heterogeneity among studies (I²=66%, P<0.01), but no evidence of publication bias (Egger’s P-value=0.52). A larger total sample size was associated with greater efficacy as regards ITT (P=0.03). The probiotic species, the number of probiotic strains and the daily probiotic dosage had no influence on the outcomes.

Conclusion:

Supplementation with products containing Lactobacillus or Bifidobacterium species increases stool frequency and reduces ITT in constipated adults. However, since significant heterogeneity in outcomes was detected among the studies analyzed, the results should be interpreted with caution.

Established and emerging methods for assessment of small and large intestinal motility

BACKGROUND

Gastrointestinal symptoms are common in the general population and may originate from disturbances in gut motility. However, fundamental mechanistic understanding of motility remains inadequate, especially of the less accessible regions of the small bowel and colon. Hence, refinement and validation of objective methods to evaluate motility of the whole gut is important. Such techniques may be applied in clinical settings as diagnostic tools, in research to elucidate underlying mechanisms of diseases, and to evaluate how the gut responds to various drugs. A wide array of such methods exists; however, a limited number are used universally due to drawbacks like radiation exposure, lack of standardization, and difficulties interpreting data. In recent years, several new methods such as the 3D-Transit system and magnetic resonance imaging assessments on small bowel and colonic motility have emerged, with the advantages that they are less invasive, use no radiation, and provide much more detailed information.

PURPOSE

This review outlines well-established and emerging methods to evaluate small bowel and colonic motility in clinical settings and in research. The latter include the 3D-Transit system, magnetic resonance imaging assessments, and high-resolution manometry. Procedures, indications, and the relative strengths and weaknesses of each method are summarized.

Changes in contrast transit times on digital subtraction angiography post-Pipeline Embolization Device deployment

It is postulated that hemodynamic changes occur in the distal vascular bed post-deployment of Pipeline Embolization Devices (PEDs). In this paper, we evaluate changes in the contrast transit times (TTs) on digital subtraction angiography (DSA) post-PED interventions. DSA films were analyzed using custom-made software for the time-density relationship at baseline and compared to post-PED deployment. All analyses were performed within the middle cerebral artery (MCA) M1 segment. Analyses included TT10%-100% (time needed for the contrast to change from 10% image intensity to 100%), TT100%-10%, and TT25%-25%. Forty-four patients were included. We found a significant decrease in TT10%-100% (2.79 to 2.24 seconds, p < 0.001) post-PED. There was a significant correlation between the percentage change in TT100%-10% and aneurysm size ( p = 0.02). There was also a significant decrease in TT25%-25% (7.07 to 6.41 seconds, p = 0.02) post-PED. Moreover, there was a significant correlation between the absolute or percentage changes in TT25%-25% and aneurysm size (rho = 0.54, p = 0.05 and rho = 0.29, p = 0.05, respectively). Statistically significant distal intracranial hemodynamic changes occur post-PED deployment. These hemodynamic changes appear to be more pronounced with large and giant aneurysms.

[Evaluation of oro-cecal transit time in patients with irritable bowel syndrome with cereal products intolerance]

The main symptoms of irritable bowel syndrome (IBS) include abnormal frequency of bowel movements. On this basis, three main clinical types of the disease have been distinguished, i.e.: constipation (IBSC), diarrhea (IBS-D) and mixed-type (IBS-M) in accordance with the Rome III criteria. These disorders mainly affect the colon, but symptoms related to upper gastrointestinal tract are also often observed.

AIM

The aim of the study was to assess the oro-caecal transit time in patients with irritable bowel syndrome with IgG-dependent hypersensitivity to cereal products.

MATERIALS AND METHODS

The study was performed in three 30-person groups, aged 27-48 years (38.3 ± 10.4), in whom three types of IBS were diagnosed basing on the Rome III criteria . The control group consisted of 30 subjects without gastrointestinal symptoms. Orocaecal transit time was measured by hydrogen breath test using lactulose and Gastro + Gastrolyzer (Bedfont).

RESULTS

The mean oro-caecal transit time was respectively in the groups: controls - 86,3 ± 5,95 min., IBS-C - 95,8 ±10,9 min. (p<0,05), IBS-D - 77,8 ± 8,21 min (p<0,01) and IBS-M - 80,6 ± 14,2 (p>0,05). There was a positive correlation between the transit time and disorder severity in IBS-C (p=0,05) group and negative in IBS-D (p<0,001) group. No significant correlation was found in IBS-M group (p=0,864).

CONCLUSIONS

Disturbed digestic passage in the upper gastrointestinal tract may affect the clinical manifestation of irritable bowel syndrome.

Effect of electrical forepaw stimulation on capillary transit-time heterogeneity (CTH)

Functional hyperemia reduces oxygen extraction efficacy unless counteracted by a reduction of capillary transit-time heterogeneity of blood. We adapted a bolus tracking approach to capillary transit-time heterogeneity estimation for two-photon microscopy and then quantified changes in plasma mean transit time and capillary transit-time heterogeneity during forepaw stimulation in anesthetized mice (C57BL/6NTac). In addition, we analyzed transit time coefficient of variance = capillary transit-time heterogeneity/mean transit time, which we expect to remain constant in passive, compliant microvascular networks. Electrical forepaw stimulation reduced, both mean transit time (11.3% ± 1.3%) and capillary transit-time heterogeneity (24.1% ± 3.3%), consistent with earlier literature and model predictions. We observed a coefficient of variance reduction (14.3% ± 3.5%) during functional activation, especially for the arteriolar-to-venular passage. Such coefficient of variance reduction during functional activation suggests homogenization of capillary flows beyond that expected as a passive response to increased blood flow by other stimuli. This finding is consistent with an active neurocapillary coupling mechanism, for example via pericyte dilation. Mean transit time and capillary transit-time heterogeneity reductions were consistent with the relative change inferred from capillary hemodynamics (cell velocity and flux). Our findings support the important role of capillary transit-time heterogeneity in flow-metabolism coupling during functional activation.

Constipation in parkinson's disease: Subjective symptoms, objective markers, and new perspectives

Constipation is among the first nonmotor symptoms to develop in the prodromal phase of PD. Pathological alpha-synuclein deposition is present throughout the gastrointestinal tract up to 20 years preceding diagnosis. Nevertheless, constipation in the context of PD remains ill defined and poorly understood. In this review, we summarize current knowledge of subjective symptoms and objective measures of constipation in PD. More than 10 different definitions of constipation have been used in the PD literature, making generalizations difficult. When pooling results from the most homogeneous studies in PD, a median constipation prevalence of 40% to 50% emerges, but with large variation across individual studies. Also, constipation prevalence tends to increase with disease progression. A similar prevalence is observed among patients with idiopathic rapid eye movement sleep behavior disorder. Interestingly, we detected a correlation between constipation prevalence in PD patients and healthy control groups in individual studies, raising concerns about how various constipation questionnaires are implemented across study populations. More than 80% of PD patients exhibit prolonged colonic transit time, and the same is probably true for de novo PD patients. Thus, the prevalence of objective colonic dysfunction exceeds the prevalence of subjective constipation. Colonic transit time measures are simple, widely available, and hold promise as a useful biomarker in manifest PD. More research is needed to elucidate the role of gastrointestinal dysfunction in disease progression of PD. Moreover, colonic transit measures may have utility as a more accurate risk factor for predicting PD in the prodromal phase. © 2016 International Parkinson and Movement Disorder Society.

Effects of Cereal, Fruit and Vegetable Fibers on Human Fecal Weight and Transit Time: A Comprehensive Review of Intervention Trials

Cereal fibers are known to increase fecal weight and speed transit time, but far less data are available on the effects of fruits and vegetable fibers on regularity. This study provides a comprehensive review of the impact of these three fiber sources on regularity in healthy humans. We identified English-language intervention studies on dietary fibers and regularity and performed weighted linear regression analyses for fecal weight and transit time. Cereal and vegetable fiber groups had comparable effects on fecal weight; both contributed to it more than fruit fibers. Less fermentable fibers increased fecal weight to a greater degree than more fermentable fibers. Dietary fiber did not change transit time in those with an initial time of <48 h. In those with an initial transit time ≥48 h, transit time was reduced by approximately 30 min per gram of cereal, fruit or vegetable fibers, regardless of fermentability. Cereal fibers have been studied more than any other kind in relation to regularity. This is the first comprehensive review comparing the effects of the three major food sources of fiber on bowel function and regularity since 1993.

Pilot study trialling a new ambulatory method for the clinical assessment of regional gastrointestinal transit using multiple electromagnetic capsules

BACKGROUND

Gastrointestinal (GI) motor disorders often involve several regions of the GI tract. Therefore, easy and safe assessment of whole gut and regional motility is valuable for more precise diagnosis. 3D-Transit is a novel method for ambulatory evaluation of total and regional gastrointestinal transit times (GITT) based on the anatomical localization of ingestible electromagnetic capsules. The main purpose of this study was to test the performance of the 3D-Transit system.

METHODS

Twenty healthy volunteers each ingested three electromagnetic capsules over a period of two consecutive days. Standard radio-opaque markers (ROM) were also ingested to assess the agreement between total GITT obtained with both methods.

KEY RESULTS

Investigations were well-tolerated and three capsules could be tracked simultaneously with minimal data loss (Capsule 1: median: 0.2% of time (range 0-25.3%). Region specific contraction patterns were identified and used for computation of total and regional GITT in all subjects. Inter-observer agreement was 100% for total GITT (median variation 0%) but less for regional GITT. Day-to-day and diurnal variations were significant for total and regional GITT. Total GITT assessed by 3D-Transit capsules were moderately well-correlated to those assessed with standard ROM (Spearman's rho = 0.7).

CONCLUSIONS & INFERENCES

3D-transit is a well-tolerated and minimal invasive ambulatory method for assessment of GI motility. By providing both total and regional transit times, the 3D-Transit system holds great promise for future clinical studies of GI function in health and disease.

Investigation of pH and Temperature Profiles in the GI Tract of Fasted Human Subjects Using the Intellicap(®) System

Gastrointestinal (GI) pH and temperature profiles under fasted-state conditions were investigated in two studies with each 10 healthy human subjects using the IntelliCap(®) system. This telemetric drug delivery device enabled the determination of gastric emptying time, small bowel transit time, and colon arrival time by significant pH and temperature changes. The study results revealed high variability of GI pH and transit times. The gastric transit of IntelliCap(®) was characterized by high fluctuations of the pH with mean values ranging from pH 1.7 to pH 4.7. Gastric emptying was observed after 7-202 min (median: 30 min). During small bowel transit, which had a duration of 67-532 min (median: 247 min), pH values increased slightly from pH 5.9-6.3 in proximal parts to pH 7.4-7.8 in distal parts. Colonic pH conditions were characterized by values fluctuating mainly between pH 5 and pH 8. The pH profiles and transit times described in this work are highly relevant for the comprehension of drug delivery of solid oral dosage forms comprising ionizable drugs and excipients with pH-dependent solubility.

Novel MRI tests of orocecal transit time and whole gut transit time: studies in normal subjects

BACKGROUND

Colonic transit tests are used to manage patients with Functional Gastrointestinal Disorders. Some tests used expose patients to ionizing radiation. The aim of this study was to compare novel magnetic resonance imaging (MRI) tests for measuring orocecal transit time (OCTT) and whole gut transit time (WGT), which also provide data on colonic volumes.

METHODS

21 healthy volunteers participated. Study 1: OCTT was determined from the arrival of the head of a meal into the cecum using MRI and the Lactose Ureide breath test (LUBT), performed concurrently. Study 2: WGT was assessed using novel MRI marker capsules and radio-opaque markers (ROMs), taken on the same morning. Studies were repeated 1 week later.

KEY RESULTS

OCTT measured using MRI and LUBT was 225 min (IQR 180-270) and 225 min (IQR 165-278), respectively, correlation r(s) = 0.28 (ns). WGT measured using MRI marker capsules and ROMs was 28 h (IQR 4-50) and 31 h ± 3 (SEM), respectively, correlation r(s) = 0.85 (p < 0.0001). Repeatability assessed using the intraclass correlation coefficient (ICC) was 0.45 (p = 0.017) and 0.35 (p = 0.058) for MRI and LUBT OCTT tests. Better repeatability was observed for the WGT tests, ICC being 0.61 for the MRI marker capsules (p = 0.001) and 0.69 for the ROM method (p < 0.001) respectively.

CONCLUSIONS & INFERENCES

The MRI WGT method is simple, convenient, does not use X-ray and compares well with the widely used ROM method. Both OCTT measurements showed modest reproducibility and the MRI method showed modest inter-observer agreement.

Effect of prolonged general anesthesia with sevoflurane and laparoscopic surgery on gastric and small bowel propulsive motility and pH in dogs

OBJECTIVE

To determine if general anesthesia with sevoflurane and laparoscopic surgery changed gastric and small bowel propulsive motility or pH in dogs.

STUDY DESIGN

Prospective, controlled trial.

ANIMALS

Twelve, 19-24 months old, female, Treeing Walker Hound dogs, weighing 23-30 kg.

METHODS

Dogs were anesthetized for a median of 8.5 hours during another study to determine the minimum alveolar concentration of sevoflurane using a visceral stimulus. Gastric and small bowel motility were determined using a sensor capsule that measures pressure, pH and temperature. Gastric transit time and motility index were calculated. For 8/12 dogs, gastric motility, pH and transit time were measured. In 4/12 dogs, small bowel motility and pH were measured.

RESULTS

Anesthesia decreased gastric and small bowel motility but did not change luminal pH. Mean gastric contraction force decreased from median (range) 11 (8-20) to 3 (1-10) mmHg (p < 0.01) and gastric motility index decreased from 0.63 (0-1.58) to 0 (0-0.31; p = 0.01). Frequency of contractions did not change, 3.7 (1.6-4.4) versus 2.8 (0.1-5.1) contractions minute(-1) (p = 0.1). Gastric motility returned to normal 12-15 hours following anesthesia. Gastric emptying was prolonged from 12 (5.3-16) to 49 (9.75-56.25) hours (p < 0.01). Mean small bowel contraction force decreased from 34 (24-37) to 3 (0.9-17) mmHg (p < 0.02) and motility index decreased from 3.75 (1-4.56) to 0 (0-1.53; p = 0.02). Frequency of contractions did not change, 0.5 (0.3-1.4) versus 1.4 (0.3-4.6) contractions minute(-1) (p = 0.11). Small bowel motility returned within 2 hours after anesthesia. Laparoscopy did not result in changes to gastric or small bowel parameters beyond those produced by general anesthesia.

CONCLUSIONS AND CLINICAL RELEVANCE

The force of gastric and small bowel contractions decreased during sevoflurane anesthesia for laparoscopy. Although gastric motility returned to normal within 12-15 hours the impairment of gastric emptying lasted 30-40 hours, predisposing dogs to postoperative ileus.

Robust estimation of pulse wave transit time using group delay

PURPOSE

To evaluate the efficiency of a novel transit time (Δt) estimation method from cardiovascular magnetic resonance flow curves.

MATERIALS AND METHODS

Flow curves were estimated from phase contrast images of 30 patients. Our method (TT-GD: transit time group delay) operates in the frequency domain and models the ascending aortic waveform as an input passing through a discrete-component "filter," producing the observed descending aortic waveform. The GD of the filter represents the average time delay (Δt) across individual frequency bands of the input. This method was compared with two previously described time-domain methods: TT-point using the half-maximum of the curves and TT-wave using cross-correlation. High temporal resolution flow images were studied at multiple downsampling rates to study the impact of differences in temporal resolution.

RESULTS

Mean Δts obtained with the three methods were comparable. The TT-GD method was the most robust to reduced temporal resolution. While the TT-GD and the TT-wave produced comparable results for velocity and flow waveforms, the TT-point resulted in significant shorter Δts when calculated from velocity waveforms (difference: 1.8±2.7 msec; coefficient of variability: 8.7%). The TT-GD method was the most reproducible, with an intraobserver variability of 3.4% and an interobserver variability of 3.7%.

CONCLUSION

Compared to the traditional TT-point and TT-wave methods, the TT-GD approach was more robust to the choice of temporal resolution, waveform type, and observer.

Obliteration of gastric varices improves the arrival time of ultrasound contrast agents in hepatic artery and vein

BACKGROUND AND AIM

Liver cirrhosis (LC) is accompanied by hepatic arterializations, intrahepatic shunts, and hyperdynamic circulations. These changes shorten the arrival time (AT) of ultrasound contrast agents to the hepatic vein (HV). Whether treatment of gastric fundal varices (GVs) by balloon-occluded transvenous obliteration (B-RTO) improves the AT in LC patients was prospectively investigated.

METHODS

A total of 32 LC patients with GVs and 10 normal controls (NCs) were enrolled. This study was approved by the clinical research ethics committee. Images of hepatic artery (HA), portal vein (PV), and HV were monitored after an injection of a contrast agent using quantification software. The AT before and after B-RTO in LC patients and that in NCs were compared.

RESULTS

All GVs were treated effectively, and indocyanine green retention rate was improved (P < 0.0001). The mean values of the HA, PV, and HV ATs in the NCs were 21.9 ± 3.3, 28.2 ± 2.0, and 40.5 ± 2.1 s, respectively. Those in LC patients were 17.4 ± 4.4, 21.9 ± 5.6, and 26.3 ± 6.7, respectively, which were shorter than those in NCs (P < 0.01, P < 0.002, P < 0.0001, respectively). However, these ATs were significantly prolonged 1 week after B-RTO, with mean values of 18.7 ± 4.8, 23.8 ± 6.0, and 30.0 ± 7.2 s (P = 0.043, P < 0.01, P < 0.001).

CONCLUSION

Obliteration of GVs shifted the AT in LC patients to the normalization, raising the possibility of improvement of arterialization and intrahepatic shunt.

Evaluation of regional and whole gut motility using the wireless motility capsule: relevance in clinical practice

The wireless motility capsule (WMC) is an ambulatory noninvasive and nonradioactive diagnostic sensor that continuously samples intraluminal pH, temperature, and pressure as it moves through the gastrointestinal (GI) tract. This review summarizes the data obtained in clinical trials with the WMC and discusses its role in clinical practice. The United States Food and Drug Administration has approved the SmartPill GI monitoring system for the evaluation of gastric emptying time in patients with suspected gastroparesis, the evaluation of colonic transit time in patients with suspected chronic constipation, and for the characterization of pressure profiles from the antrum and duodenum. Clinical studies have shown that WMC-measured GI transit times can distinguish patients with motility abnormalities similarly to conventional testing. However, the WMC offers the advantage of providing a full GI-tract profile, enabling the detection of multiregional GI transit abnormalities in patients with suspected upper or lower GI dysmotility. The WMC also characterizes pressure profiles of the GI tract and impaired pressure profile limits are reported for the antrum and duodenum. In comparison with manometry, interpretations of pressure measurements obtained by the WMC are limited by an inability to detect a peristaltic pressure wave front, and further investigation is required to develop clinical applications. Clinical studies with the WMC indicated that it should be considered for the evaluation of regional and whole gut transit time in patients with suspected upper or lower dysmotility, particularly if there are concerns about multiregional dysmotility.

Effects of adlay, buckwheat, and barley on transit time and the antioxidative system in obesity induced rats

In the present study, we examined whether four grains including adlay (AD), buckwheat (BW), glutinous barley (GB), and white rice (WR) affect the duration of food residence in the gastrointestinal tract and hepatic enzyme activities in rats fed different combinations of the grains. The rats were raised for 4 weeks on a high fat diet based on the American Institute of Nutrition-93 (AIN-93G) diets containing 1% cholesterol and 20% dietary lipids. Forty male rats were divided into four groups and raised for 4 weeks with a diet containing one of the grains. Corresponding to the dietary fiber contents of the experimental grains, gut transit time was shortest in the rats fed GB and increased in the order of BW, AD, and WR. In addition, the accumulated shortest transit time occurred in the GB group. Gut transit time affected weight gain and major organ weight, as it was closely related to the absorption of nutrients. The level of thiobarbituric acid reactive substance (TBARS) in liver was higher in rats fed WR, AD, BW, and GB, indicating that the other grains decreased oxidative stress in vivo more than WR. Glutathione, glutathione peroxidase, and glutathione S-transferase levels in the AD, BW, and GB groups were significantly higher than those in the WR group. In conclusion, reduced colonic transit time has been implicated in reducing the incidence of colon cancer, as evidenced by populations consuming diets rich in fiber. Whole grains such as AD, BW, and GB may contribute to a significant supply of antioxidants to prevent oxidative stress if they are consumed in large amounts.

Sub-100 nm channel length graphene transistors

Here we report high-performance sub-100 nm channel length graphene transistors fabricated using a self-aligned approach. The graphene transistors are fabricated using a highly doped GaN nanowire as the local gate with the source and drain electrodes defined through a self-aligned process and the channel length defined by the nanowire size. This fabrication approach allows the preservation of the high carrier mobility in graphene and ensures nearly perfect alignment between source, drain, and gate electrodes. It therefore affords transistor performance not previously possible. Graphene transistors with 45-100 nm channel lengths have been fabricated with the scaled transconductance exceeding 2 mS/μm, comparable to the best performed high electron mobility transistors with similar channel lengths. Analysis of and the device characteristics gives a transit time of 120-220 fs and the projected intrinsic cutoff frequency (f(T)) reaching 700-1400 GHz. This study demonstrates the exciting potential of graphene based electronics in terahertz electronics.

The gastrointestinal absorption of drugs in man: a review of current concepts and methods of investigation

The various mechanisms which have been advanced to explain drug absorption are critically reviewed and the limitations of current theories are discussed. Various techniques for investigating drug absorption and transit through the gut are presented, and the results obtained with metoprolol are briefly considered to illustrate the potential of some of these methods.

A transfer function analysis of coronary and renal circulation calculated from upstream and downstream indicator-dilution curves

A method has been developed for computing the distribution of blood transit times (transfer function) from indicator-dilution curves recorded from upstream (aorta) and downstream (pulmonary artery, renal vein and coronary sinus) circulator sites in mongrel dogs. The method employs a Fourier series transformation of the upstream and downstream curves and yields a time-domain transfer function which is independent of recirculating dye particles. Discontinuities, created in the upstream and downstream indicator curves by the termination of sampling (120 sec postinjection), are removed by a tail terminating procedure which employs normal and lagged normal density distributions. The transfer functions computed for the trans-renal and trans-coronary circulations and their relationship to the systemic circulation dispersion patterns are shown under control conditions (pentobarbital anesthesia) and during intra-aortic infusion of angiotensin, acetylcholine and adenosine triphosphate. These distribution patterns reflect the response of the vascular system to the drugs and demonstrate, to a limited extent, the role which different vascular beds have in the cardiovascular mixing process.