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Biomedical subjects

M W Collins

Publications and source records attributed to M W Collins.

32 records · Page 2Linked to original sources
PubMed1996

Numerical investigation of steady flow in proximal and distal end-to-side anastomoses.

Steady flow in model proximal and distal end-to-end bypass anastomoses were simulated numerically. The predictions were compared to whole field measurements of the flow in in vitro models, and were shown to match well the general features of the measured flows. The predictions confirmed that the flows in end-to-side anastomoses are complex and three dimensional, and contain areas that could allow long residence times. Careful examination of the predictions revealed certain features of the flows not seen easily in the experiments. Shear stress and pressure on the vessel walls were predicted, and areas known to be prone to intimal hyperplasia were shown to correspond to areas of high spatial gradient of shear stress. Two anastomosis angeles, 30 and 45 deg, were considered, and it was shown that the more acute angle may have some benefit in terms of the levels of shear gradients and the power required to drive the flow through the anastomosis.

Anastomosis, Surgical↗
PubMed1994

Effect of dose and modification of viscous properties of oat gum on plasma glucose and insulin following an oral glucose load.

An extract from oats known as oat gum (OG) is composed mainly of the polysaccharide (1-->3) (1-->4)-beta-D-glucan, which is highly viscous in aqueous solution. Viscous polysaccharides are known to attenuate postprandial plasma glucose and insulin responses. The purposes of this study were to determine the dose-response to OG and establish quantitatively the effect of viscosity on plasma glucose and insulin levels of healthy humans consuming 50 g glucose. Increasing the dose of OG successively reduced the plasma glucose and insulin responses relative to a control without gum. Reduction of the viscosity of OG by acid hydrolysis reduced or eliminated the capacity to decrease postprandial glucose and insulin levels. The ability of OG to modify glycaemic response was unchanged following agglomeration in the presence of maltodextrin. Agglomerated gum dispersed smoothly in a drink without formation of lumps, and development of maximum viscosity was delayed. These properties improve palatability. There was a highly significant linear relationship between log[viscosity] of the mixtures consumed and the glucose and insulin responses. The relationship shows that 79-96% of the changes in plasma glucose and insulin are attributable to viscosity, and that changes occur at relatively low doses and viscosities.

Adult↗
PubMed1994

High beta-glucan oat bran and oat gum reduce postprandial blood glucose and insulin in subjects with and without type 2 diabetes.

The aim of the current study was to characterize the effects of isolated and native sources of beta-glucan, oat gum, and oat bran, respectively, when incorporated into a complete meal. Fasting control subjects and subjects with Type 2 diabetes were fed porridge meals containing either wheat farina, wheat farina plus oat gum or oat bran. Blood samples were collected for 3 h after the test meals and plasma glucose and insulin were measured. Oat bran and wheat farina plus oat gum meals reduced the postprandial plasma glucose excursions and insulin levels when compared with the control wheat farina meal in both control and Type 2 diabetic subjects. This study shows that both the native cell wall fibre of oat bran and isolated oat gum, when incorporated into a meal, act similarly by lowering postprandial plasma glucose and insulin levels. A diet rich in beta-glucan may therefore be of benefit in the regulation of postprandial plasma glucose levels in subjects with Type 2 diabetes.

Adult↗
PubMed1994

Oat beta-glucan reduces blood cholesterol concentration in hypercholesterolemic subjects.

OBJECTIVE: Several studies have indicated that consumption of oat bran lowers blood cholesterol and this effect has been attributed specifically to oat bran's soluble fiber (beta-glucan). This study was designed to test this hypothesis. DESIGN: The purified fibre (oat gum, 80% beta-glucan) was isolated, and agglomerated in the presence of maltodextrin to facilitate dispersion in a drink. Subjects consumed the oat gum (2.9 g beta-glucan), or maltodextrin placebo, twice daily for 4 weeks, in a randomized, cross-over design with a 3 week wash-out between phases. Consumption was equivalent to a daily dose of about 70 g of oat bran. SETTING: The study was with free-living individuals. SUBJECTS: Twenty hypercholesterolemic male and female adults entered, and 19 completed, the study. INTERVENTIONS: Blood lipids from fasting individuals were measured weekly throughout the study. Diet was monitored using 3 day food diaries. RESULTS: There were no significant changes (P > 0.05) in blood lipids during the placebo phase. Mean initial total cholesterol (6.76 +/- 0.13 mmol/l) and low density lipoprotein (LDL) cholesterol (4.59 +/- 0.14 mmol/l) levels fell throughout the oat gum phase, and at week 4 each was reduced 9% relative to initial values (P = 0.0004 and 0.005 respectively). When oat gum was discontinued, total and LDL cholesterol returned to initial levels. There were no significant changes in high density lipoprotein (HDL) cholesterol. Triglyceride levels also remained unchanged except for a singular decrease at week 4 of the oat gum phase relative to the initial value, but not compared to the placebo value. The lowered mean total and LDL cholesterol levels occurred in the absence of any dietary changes. CONCLUSIONS: The main component of the soluble fibre of oats, beta-glucan, significantly reduced the total and LDL cholesterol levels of hypercholesterolemic adults without changing HDL cholesterol.

Adult↗
PubMed1993

Isolation and structure elucidation of a novel product of the acidic degradation of cefaclor.

The acidic aqueous degradation of cefaclor, an orally administered cephalosporin antibiotic, has been investigated. The most prominent peak in the high-performance liquid chromatography profile of a degraded solution of cefaclor was isolated by preparative high-performance liquid chromatography. Mechanistically, the formation of this degradent from cefaclor involves a condensation of two cefaclor degradation products in which both products have undergone contraction from a six-membered cephem ring to a five-membered thiazole ring, presumably via a common episulfonium ion intermediate.

Cefaclor↗
PubMed1993

Aqueous acidic degradation of the carbacephalosporin loracarbef.

The aqueous degradation of the carbacephalosporin loracarbef under moderately acidic conditions (pH range, 2.7-4.3) is described. Structures of a total of 10 compounds isolated by preparative reversed-phase HPLC have been proposed. Five of these 10 degradation compounds arose from hydrolysis of the beta-lactam ring followed by structural changes in the six-membered heterocyclic ring. Four compounds form from intermolecular reactions of loracarbef to form dimeric structures with peptide linkages. The remaining compound resulted from oxidation of the primary amine to a hydroxylamine. Pathways for the formation of these compounds from the parent loracarbef are proposed.

Cefaclor↗
PubMed1992

Flow studies in canine artery bifurcations using a numerical simulation method.

Three-dimensional flows through canine femoral bifurcation models were predicted under physiological flow conditions by solving numerically the time-dependent three-dimensional Navier-stokes equations. In the calculations, two models were assumed for the blood, those of (a) a Newtonian fluid, and (b) a non-Newtonian fluid obeying the power law. The blood vessel wall was assumed to be rigid this being the only approximation to the prediction model. The numerical procedure utilized a finite volume approach on a finite element mesh to discretize the equations, and the code used (ASTEC) incorporated the SIMPLE velocity-pressure algorithm in performing the calculations. The predicted velocity profiles were in good qualitative agreement with the in vivo measurements recently obtained by Jones et al. The non-Newtonian effects on the bifurcation flow field were also investigated, and no great differences in velocity profiles were observed. This indicated that the non-Newtonian characteristics of the blood might not be an important factor in determining the general flow patterns for these bifurcations, but could have local significance. Current work involves modeling wall distensibility in an empirically valid manner. Predictions accommodating these will permit a true quantitative comparison with experiment.

Animals↗
PubMed1992

Glutathione peroxidase activity in a healthy Canadian population. Effects of age, smoking and drinking habits, exercise and oral contraceptive use.

The activity of the enzyme glutathione peroxidase (SeGSHPx) has been suggested as an indicator of selenium status. The purpose of this study was to measure the activity of this enzyme in a large sample of healthy, free-living Canadians to determine normal distributions and the effects of age, smoking, and drinking habits, exercise, and the use of oral contraceptives (OCs) or estrogen replacement therapy. The population consisted of 386 self-selected subjects between the ages of 24 and 75. Erythrocyte SeGSHPx activity was 21.5 +or- 7 (Mean +or- SD) and 33.6 +or- 8U/g Hb and plasma activity was 226 +or- 31 and 214 +or- 38 U/L for males (n=239) and females (n=147), respectively. Erythrocyte activity was significantly higher in females and males (p0.01). The Se form of GSHPx accounted for 76% and 54% of total activity in plasma and erythrocytes, respectively. No differences due to age were seen in males, although plasma SeGSHPx, non-SeGSHPx, and total GSHPx activities were elevated in females 65 years of age and older. Cigarette smoking significantly elevated erythrocyte SeGSHPx and total activity in male subjects. This elevation did not vary with the amount smoked and was not seen in ex-smokers. Drinking elevated erythrocyte non-SeGSHPx and total activity in male subjects with the highest activity seen in drinkers who also smoked. No significant differences were seen with level of exercise except for a slight elevation with vigorous exercise. Estrogen use significantly elevated erythrocyte SeGSHPx, non-SeGSHPx, and total activities in both pre- and postmenopausal women. These data suggest that some lifestyle factors can have small but significant effects of GSHPx activity and must be controlled for when population-based surveys are being conducted.

Americas↗
PubMed1991

Oat gum lowers glucose and insulin after an oral glucose load.

Foods containing soluble dietary fibers delay glucose absorption and lower postprandial plasma glucose. This effect of oat bran has been attributed to oat gum (80% beta-glucan). However, purified oat gum has previously not been available for human studies. In this study the glucose and insulin responses to consuming 14.5 g of specifically prepared oat gum with 50 g glucose were compared with the response to guar gum with glucose and to glucose alone in nine healthy, fasting subjects. Plasma glucose and insulin increases after the glucose drink were greater than after both gum meals between 20 and 60 min (P less than 0.01). The responses to the two gum meals were nearly identical. These results establish that the more palatable oat gum lowers postprandial plasma glucose and insulin concentrations in humans and may be comparable with or of greater benefit than guar gum.

Adult↗
PubMed1990

A review of the numerical analysis of blood flow in arterial bifurcations.

Arterial bifurcation flow has been of special interest for some years because of its important role in the formation of atherosclerotic plaques and thrombi. To investigate the flow phenomena analytically, four major factors need to be accommodated--the three-dimensionality of a general bifurcation, the pulsatile nature of the laminar flow, the distensibility of the arterial wall and the non-Newtonian character of the blood. In this review, both engineering and medical aspects of each factor are carefully surveyed. It is demonstrated that the latest generation of computational fluid dynamics codes can treat this problem area and that it is both feasible and desirable to investigate the effects of each independent factor.

Arteries↗