ORCID Profile
0000-0002-7198-1446
Current Organisation
The University of Auckland
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: MDPI AG
Date: 16-05-2023
DOI: 10.3390/APP13106092
Abstract: The use of in silico models to improve our understanding of the fluid dynamics within the gastrointestinal tract has increased over the last few decades. Computational fluid dynamics (CFD) is an in silico technique that can be used to characterize and model the fluid mechanics driving the digestion of food and absorption of nutrients. This systematic review outlines the current methodologies used to develop CFD models of the stomach and small intestine, and summarizes the flow and mixing patterns predicted from these models. A literature search was conducted on Scopus, and 15 stomach CFD studies and 15 small intestine CFD studies were included in this review after the literature selection and exclusion process. Two primary flow patterns retropulsive flow and recirculation regions, were identified within the stomach CFD models. The flow patterns within the small intestine were depended on the type of motility pattern present. The shortcomings of the current models are discussed, and considerations for future gastric and intestinal flow modeling are provided.
Publisher: MDPI AG
Date: 17-01-2022
Abstract: We study peristaltic flow in a C-shaped compliant tube representing the first section of the small intestine—the duodenum. A benchtop model comprising of a silicone tube filled with a glycerol-water mixture deformed by a rotating roller was created. Particle image velocimetry (PIV) was used to image flow patterns for deformations approximating conditions in the duodenum (contraction litude of 34% and wave speed 13 mm/s). Reversed flow was present underneath the roller with fluid moving opposite to the direction of the peristaltic wave propagation. Deformations of the tube were imaged and used to construct a computational fluid dynamics (CFD) model of flow with moving boundaries. The PIV and CFD vorticity and velocity fields were qualitatively similar. The vorticity field was integrated over the imaging region to compute the total circulation and there was on average a 22% difference in the total circulation between the experimental and numerical results. Higher shear rates were observed with water compared to the higher viscosity fluids. This model is a useful tool to study the effect of digesta properties, anatomical variations, and peristaltic contraction patterns on mixing and transport in the duodenum in health and disease.
Publisher: Informa UK Limited
Date: 03-05-2016
Publisher: Springer Science and Business Media LLC
Date: 08-04-2016
DOI: 10.1007/S10439-016-1604-8
Abstract: Nasal high flow (NHF) therapy is used to treat a variety of respiratory disorders to improve patient oxygenation. A CO2 washout mechanism is believed to be responsible for the observed increase in oxygenation. In this study, experimentally validated Computational Fluid Dynamics simulations of the CO2 concentration within the upper airway during unassisted and NHF assisted breathing were undertaken with the aim of exploring the existence of this washout mechanism. An anatomically accurate nasal cavity model was generated from a CT scan and breathing was reproduced using a Fourier decomposition of a physiologically measured breath waveform. Time dependent CO2 profiles were obtained at the entrance of the trachea in the experimental model, and were used as simulation boundary conditions. Flow recirculation features were observed in the anterior portion of the nasal cavity upon application of the therapy. This causes the CO2 rich gas to vent from the nostrils reducing the CO2 concentration in the dead space and lowering the inspired CO2 volume. Increasing therapy flow rate increases the penetration depth within the nasal cavity of the low CO2 concentration gas. A 65% decrease in inspired CO2 was observed for therapy flow rates ranging from 0 to 60 L min(-1) supporting the washout mechanism theory.
Publisher: Elsevier BV
Date: 03-2021
Publisher: Elsevier BV
Date: 2019
Publisher: Cold Spring Harbor Laboratory
Date: 30-04-2021
DOI: 10.1101/2021.04.29.441555
Abstract: Facial eczema (FE) in grazing ruminants is a debilitating liver syndrome induced by ingestion of sporidesmin, a toxin belonging to the epipolythiodioxopiperazine class of compounds. Sporidesmin is produced in spores of the fungus Pseudopithomyces chartarum , a microbe which colonises leaf litter in pastures. New Zealand has a high occurrence of FE in comparison to other countries as animals are fed predominantly on ryegrass, a species that supports high levels of Pse. chartarum spores. The climate is also particularly conducive for Pse. chartarum growth. Here, we present the genome of Pse. chartarum and identify the putative sporidesmin gene cluster. The Pse. chartarum genome was sequenced using single molecule real-time sequencing (PacBio) and gene models identified. Loci containing genes with homology to the aspirochlorine, sirodesmin PL and gliotoxin cluster genes of Aspergillus oryzae, Leptosphaeria maculans and Aspergillus fumigatus , respectively, were identified by tBLASTn. We identified and annotated an epipolythiodioxopiperazine cluster at a single locus with all the functionality required to synthesise sporidesmin. The whole genome of Pseudopithomyces chartarum has been sequenced and assembled. The genome is 39.13 Mb, 99% complete, and contains 11,711 protein coding genes. A putative sporidesmin A toxin (cause of facial eczema) gene cluster is described. The genomes of Pse. chartarum and the Leptosphaerulina chartarum teleomorph differ. Comparative genomics is required to further resolve the Pseudopithomyces clade.
Publisher: Elsevier BV
Date: 08-2021
Publisher: IEEE
Date: 07-2020
Publisher: AIP Publishing
Date: 2023
DOI: 10.1063/5.0135070
Abstract: The small intestine is the primary site of enzymatic digestion and nutrient absorption in humans. Intestinal contractions facilitate digesta transport, mixing, and contact with the absorptive surfaces. Previous computational models have been limited to idealized contraction patterns and/or simplified geometries to study digesta transport. This study develops a physiologically realistic model of flow and mixing in the first segment of the small intestine (duodenum) based upon a geometry obtained from the Visible Human Project dataset and contraction patterns derived from electrophysiological simulations of slow wave propagation. Features seen in previous simpler models, such as reversed flow underneath the contracting region, were also present in this model for water, Newtonian liquid digesta, and non-Newtonian (power law) whole digesta. An increase in the contraction litude from 10% to 50% resulted in faster transport with mean speeds over a cycle increasing from 1.7 to 8.7 mm/s. Glucose transport was advection dominated with Peclet numbers greater than 104. A metric of glucose mixing was computed, with 0 representing no mixing and 1 representing perfect mixing. For antegrade contractions at a 50% litude, the metric after 60 s was 0.99 for water, 0.6 for liquid digesta, and 0.19 for whole digesta. Retrograde contractions had a negligible impact on the flow and mixing. Colliding wavefronts resulted in swirling flows and increased the mixing metric by up to 2.6 times relative to antegrade slow wave patterns. The computational framework developed in this study provides new tools for understanding the mixing and nutrient absorption patterns under normal and diseased conditions.
Publisher: Informa UK Limited
Date: 10-2021
DOI: 10.1080/10255842.2021.1984434
Abstract: The ability of the lymphatic network to absorb large molecules and bypass the first-pass liver metabolism makes it appealing as a delivery system for therapeutic substances. In most cases, the drug is injected into the subcutaneous tissue and must negotiate the tissue space, before being drained via the lymphatics. Tracking the transport of drug molecules through this route is challenging, and computational models of lymphatic drainage can play an important role in assessing the efficacy of a proposed delivery strategy. The three-dimensional computational model we present here of the peripheral lymphatic network and surrounding interstitium is informed by anatomical data, and quantifies the degree to which uptake and transit times are affected by drug particle size, physiological flow rates, and specifics of drug injection.
No related grants have been discovered for Vinod Suresh.