Search PubMed⌕ Search

Biomedical subjects

V Wynn

Publications and source records attributed to V Wynn.

At least 19 recordsLinked to original sources
PubMed1996

Lipid and carbohydrate metabolic risk markers for coronary heart disease and blood pressure in healthy non-obese premenopausal women of different racial origins in the United Kingdom.

Metabolic risk markers for coronary heart disease (CHD) were determined in apparently healthy females of differing racial origins residing in the United Kingdom. The females were of black (n=122), Oriental (n=144), South Asian (n=128), and white (n=271) origin, premenopausal, non-obese, and aged 16-45 years. In comparison to whites, South Asians had lower serum high-density lipoprotein (HDL) cholesterol and HDL2 cholesterol and higher fasting and oral glucose tolerance test plasma insulin responses. Black females had higher fasting plasma and oral glucose tolerance test insulin and lower serum triglyceride and glucose compared with white females. Orientals differed from whites in having higher fasting and oral glucose tolerance test insulin concentrations. Resting systolic or diastolic blood pressures, total serum cholesterol, HDL3 cholesterol, and low-density lipoprotein (LDL) cholesterol did not differ between groups. Whereas previous studies have demonstrated similar differences in representative samples from different ethnic communities, our results clearly demonstrate that differences also exist in young healthy females, individuals considered to have the least risk of CHD.

Adult↗
PubMed1996

Group aggregates and individual reliability: the case of verbal short-term memory.

Two experiments examined the generalizability of the effects of word length and phonological similarity with visual and auditory presentation in immediate verbal serial ordered recall. In Experiment 1, data were collected from 251 adult volunteers drawn from a broad cross-section of the normal population. Word length and phonological similarity in both presentation modes significantly influenced the group means. However, 43% of the subjects failed to show at least one of the effects, and the likelihood that effects appeared was highly correlated with verbal memory span. In Experiment 2, 40 subjects of the original sample were retested, 20 of whom had failed to show one or more effects in Experiment 1. Whether or not an effect had appeared for individual subjects on the first test session was a poor predictor of whether the effect would appear on retest. Finally, an analysis of subject reports demonstrated that the patterns of experimental data could be accounted for in part by the strategies that subjects reported using, and the effect of strategy was independent of the effect of span. The implications of these findings for theories of verbal short-term memory are discussed.

Acoustic Stimulation↗
PubMed1995

Relationships between blood pressure, oral contraceptive use and metabolic risk markers for cardiovascular disease.

Data from a previous study, designed to compare metabolic risk markers for cardiovascular disease in non-users and oral contraceptive (OC) users, were analysed to evaluate the influence of OC composition on blood pressure. Healthy, female volunteers (1189 women) either not using OC (non-users) or currently using one of six different combined formulations (users) were compared. Combinations studied contained 30-40 micrograms ethinyl estradiol combined with the progestins levonorgestrel, norethindrone (at two and three different doses, respectively) or desogestrel. After statistical standardisation to account for the significantly greater age of the non-users and longer duration of OC use amongst the levonorgestrel combination users, mean blood pressure was higher, compared with non-users, in users of monophasic or triphasic levonorgestrel combinations (systolic: +4.3 mmHg (p < 0.001) and +2.7 mmHg (p < 0.001), respectively; diastolic: +2.6 mmHg (p < 0.001) and +2.3 mmHg (p < 0.05), respectively). Blood pressures in users of monophasic norethindrone and desogestrel combinations were not significantly raised and there was no increase in the proportion of women with abnormal values. Diastolic and systolic blood pressures were positively associated with oral glucose tolerance test insulin response (r = 0.11 (p < 0.01) and r = 0.15 (p < 0.001), respectively) in users but not in non-users. Currently used OC containing norethindrone or desogestrel progestins have little impact on blood pressure. Their correlated reduction in impact on insulin concentrations, though small, suggests common mechanisms through which OC affect blood pressure and insulin.

Adolescent↗
PubMed1994

Cardiologists rebuked.

Explore the source record for details and available documents.

Attitude of Health Personnel↗
PubMed1994

Associations between insulin sensitivity, and free fatty acid and triglyceride metabolism independent of uncomplicated obesity.

Insulin resistance is associated with hypertriglyceridemia and elevated free fatty acid (FFA) concentrations in obese and diabetic individuals, but it is unclear to what extent this relationship is independent of obesity and is present in healthy individuals. We studied 92 healthy middle-aged males selected from the top, middle, and lowest quintiles of the insulin sensitivity index (Si) determined in a group of 182 men using the minimal model of glucose disappearance. Plasma FFA, triglyceride, glucose, insulin, and C-peptide concentrations were measured during a 3-hour intravenous glucose tolerance test (IVGTT). The low-Si (most insulin-resistant) group had more central body fat distribution (subscapular/triceps skinfold thickness) and a higher median body mass index (BMI) of 26.8 (range, 21.1 to 41.1) kg.m-2 compared with the middle- and high-Si groups with BMIs of 24.9 (19.1 to 31.5) and 23.7 (18.8 to 33.2) kg.m-2 (P < .05). Relatively minor glucose intolerance in the low-Si group was no longer significant when central adiposity was accounted for. Glucose tolerance was maintained by increased insulin secretion, leading to IVGTT insulin responses twofold and fourfold higher in the middle- and low-Si groups, respectively, compared with the high-Si group (P < .01). Fasting FFA and triglyceride concentrations were increased in the low-Si group relative to the other groups independent of BMI or central adiposity (P < .01). During the IVGTT, FFA decreased to similar minimum concentrations in all three groups. Triglyceride concentrations during the IVGTT increased above their minimum levels, particularly in the low-Si group (P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Counting on working memory in arithmetic problem solving.

Mental calculation is an important everyday skill involving access to well-learned procedures, problem solving, and working memory. Although there is an active literature on acquiring concepts and procedures for mental arithmetic, relatively little is known about the role of working memory in this task. This paper reports two experiments in which dual-task methodology is used to study the role of components of working memory in mental addition. In Experiment 1, mental addition of auditorily presented two-digit numbers was significantly disrupted by concurrent random letter generation and, to a lesser extent, by concurrent articulatory suppression, but was unimpaired by concurrent hand movement or by presentation of irrelevant pictures. Although the number of errors increased with two of the dual tasks, the incorrect responses tended to be quite close to the correct answer. In Experiment 2, the numbers for addition were presented visually. Here again, random generation produced the largest disruption of mental arithmetic performance, while a smaller amount of disruption was observed for articulatory suppression, hand movement, and unattended auditorily presented two-digit numbers. The overall levels of performance were better and the absolute size of the disruptive effects shown with visual presentation was very small compared with those found for auditory presentation. This pattern of results is consistent with a role for a central executive component of working memory in performing the calculations required for mental addition and in producing approximately correct answers. Visuospatial resources in working memory may also be involved in approximations. The data support the view that the subvocal rehearsal component of working memory provides a means of maintaining accuracy in mental arithmetic, and this matches a similar conclusion derived from previous work on counting. The general implications for the role of working memory in arithmetic problem solving will be discussed.

Adolescent↗
PubMed1994

Methodological issues in the application of the minimal model: effects of glucose dose, basal glucose concentration, test duration and modelling constraint.

An intravenous glucose tolerance test (IVGTT) glucose dose of 0.3 g/kg has been adopted for measurement of insulin sensitivity using the minimal model. Traditionally, however, a dose of 0.5 g/kg has been used, which might be expected to improve the IVGTT insulin response and hence the effectiveness of minimal model analysis. In a preliminary study of 5 subjects given 0.3 and 0.5 g/kg IVGTTs, each lasting 120 minutes, we found a 53% increase in IVGTT insulin response at the higher dose, but there was a marked discrepancy in the difference between fasting and final glucose concentrations (-0.17 mmol.l-1 at 0.3 g/kg and -1.01 mmol.l-1 at 0.5 g/kg). Good agreement obtained between estimates of Si derived from 0.3 and 0.5 g/kg IVGTTs (mean Si: 0.3 g/kg test = 6.0 min-1.microU-1.ml, 0.5 g/kg test = 5.8 min-1.microU-1.ml: r = 0.97, p < 0.001) providing the final IVGTT glucose concentration rather than the fasting concentration was taken as the basal level for modelling analysis. These findings were confirmed and extended in two further studies; firstly in an analysis of the effects of choice of basal glucose concentration and the application of various modelling constraints in a cross-section of 66 subjects with a wide range of insulin sensitivities; then in a further study in which seven subjects were each given two 0.3 g/kg IVGTTs and one 0.5 g/kg IVGTT, with each test being prolonged to 300 minutes. Agreement between estimates of Si at the two different doses was again only achieved by taking the final IVGTT glucose concentration as basal (mean Si: 0.3 g/kg test = 4.7 min-1.microU-1.ml, 0.5 g/kg test = 3.8 min-1.microU-1.ml: r = 0.75, p < 0.05), although one anomalous test required that a constraint be applied to the modelling process for this agreement to obtain. Closest agreement between the 300 minute 0.3 and 0.5 g/kg IVGTTs was found when tests were modelled up to 180 minutes. An IVGTT duration of 180 minutes appears to be optimum for re-establishing the basal concentration necessary for effective modelling analysis. Application of constraints can markedly affect certain analyses and may introduce some bias; their use should be carefully monitored, although their effect on large datasets is likely to be small.

Adult↗
PubMed1993

Insulin resistance, secretion, and elimination in postmenopausal women receiving oral or transdermal hormone replacement therapy.

Estrogen/progestin steroid combinations adversely affect glucose tolerance and insulin resistance, but their effects in combined hormone replacement therapy (HRT) have rarely been evaluated. We studied 61 untreated symptomatic postmenopausal women randomized to receive oral (conjugated equine estrogens, 0.625 mg/d continuous + levonorgestrel, 0.075 mg/d for 12 days of each 28-day cycle) or transdermal therapy (estradiol 17 beta, 0.05 mg/d continuous + norethindrone acetate, 0.25 mg/d for 14 days of each 28-day cycle). An untreated control group of 30 postmenopausal women not seeking HRT was also studied. Intravenous glucose tolerance tests (IVGTT) were performed at baseline and 3, 6, and 18 months later. Mathematical modeling analysis of plasma glucose, insulin, and C-peptide concentration profiles provided measures of insulin resistance, secretion, and elimination. There were no changes in glucose or insulin concentrations with transdermal therapy. Oral therapy caused a deterioration of glucose tolerance and an increased overall plasma insulin response, apparently due to a reduction in the immediate plasma insulin response to glucose. This may have resulted from increased hepatic insulin uptake, uncompensated for by an increase in first-phase pancreatic insulin secretion. Neither treatment caused significant insulin resistance compared with baseline, but with the oral treatment insulin resistance was greater during the combined phase compared with the estrogen-only phase. Thus the oral regimen affected both insulin delivery and insulin resistance. The transdermal regimen had relatively few effects on insulin metabolism.

Administration, Cutaneous↗
PubMed1993

Venous blood arterialization and parameters from the minimal models of glucose disappearance and post-hepatic insulin delivery.

1. Modelling analysis of intravenous glucose tolerance test glucose and insulin concentrations can provide measures of insulin sensitivity and metabolism from a single straightforward procedure. However, little is known of the effects of blood arterialization on model-derived parameters. 2. Intravenous glucose tolerance tests were carried out on 18 subjects, with measurement of glucose and insulin concentrations in simultaneously sampled non-arterialized and arterialized blood. Blood oxygen saturation, partial pressure of CO2 and pH were measured on both non-arterialized and arterialized blood during the intravenous glucose tolerance test. Using the minimal models of glucose disappearance and post-hepatic insulin delivery, measures of insulin sensitivity, glucose-dependent glucose disposal, first- and second-phase post-hepatic insulin responsiveness to glucose and plasma insulin elimination rate were derived from intravenous glucose tolerance test glucose and insulin concentrations in both arterialized and non-arterialized blood. 3. During the intravenous glucose tolerance test mean blood oxygen saturation was 6.7% higher, partial pressure of CO2 was 0.3 kPa lower and pH was 0.015 higher in arterialized than non-arterialized blood. Mean parameter values did not differ when derived from measurements made on non-arterialized and arterialized blood. Model-derived parameters were not related to the degree of arterialization, although there was some consistent variation with sampling site for parameters of glucose-dependent glucose disposal (Sg), first-phase post-hepatic insulin responsiveness (phi 1) and insulin elimination (ni). 4. Measurements made on non-arterialized blood are suitable for analyses employing the minimal models of glucose disappearance and post-hepatic insulin delivery. Imprecision in some parameters may be diminished by adherence to a single sampling site.

Adult↗
PubMed1993

The effects of the menopause on insulin sensitivity, secretion and elimination in non-obese, healthy women.

We have carried out intravenous glucose tolerance tests with measurement of plasma glucose, insulin and C-peptide concentrations on 66 premenopausal and 92 postmenopausal non-obese caucasian women. After adjustment for the effects of a number of possible confounding variables, including age and body mass index, there was little difference between pre and postmenopausal women in glucose and insulin concentrations either fasting or in response to intravenous glucose. Mathematical modelling analysis of the resultant plasma concentration profiles was used to obtain measures of insulin sensitivity, secretion and elimination, and non-insulin dependent glucose disposal. We found reciprocal differences in mean insulin sensitivity (increased by 50%) and non-insulin dependent glucose disposal (decreased by 30%). Plasma C-peptide response and pancreatic insulin secretion were markedly lower in the postmenopausal group (-35% and -51% respectively). However, the rate constant for insulin elimination was also lower in these women. As a result, intravenous glucose tolerance test plasma insulin concentrations were not significantly different between the two groups. We conclude that, despite the occurrence of little or no variation in plasma glucose and insulin concentrations, the menopause is associated with significant changes in insulin metabolism.

Adult↗
PubMed1993

Working memory and strategies in syllogistic-reasoning tasks.

It has often been asserted that working-memory limitations are a major factor contributing to problem difficulty; for example, Johnson-Laird's (1983) mental-models theory appeals to working-memory limitations to explain the difficulty of syllogistic reasoning. However, few studies have directly explored working memory in problem solving in general or syllogistic reasoning in particular. This paper reports two studies. In the first, working-memory load was varied by presenting syllogistic tasks either verbally or visually (so that the premises were continuously available for inspection). A significant effect of memory load was obtained. In the second study, premises were presented visually for a subject-determined time. Dual-task methods were used to assess the role of working-memory components, as identified in Baddeley's (1986) model. Syllogistic performance was disrupted by concurrent random-number generation but not by concurrent articulatory suppression or by concurrent tapping in a preset pattern. Furthermore, the concurrent syllogism task interfered with random generation and to a lesser extent with articulatory suppression, but not with tapping. We conclude that while the central-executive component of working memory played a major role in the syllogistic-task performance reported here, the articulatory loop had a lesser role, and the visuospatial scratch pad was not involved.

Adult↗
PubMed1992

Effect of simvastatin on high density lipoprotein subfractions and apolipoproteins in type IIa hypercholesterolemia.

Changes in plasma concentrations of high density lipoproteins (HDL) and triglycerides may partly explain the ability of cholesterol-lowering drugs to decrease the incidence of coronary heart disease. We measured the response of fasting plasma lipids, lipoproteins, and apolipoproteins in 46 subjects with Type IIa hypercholesterolemia treated with simvastatin for 3 months. The initial dose of simvastatin (10 mg/day) was subsequently increased up to 40 mg/day if the plasma cholesterol concentration had not fallen below 5.2 mmol/l. Plasma concentrations of HDL cholesterol and of the apolipoproteins AI and AII were increased by simvastatin. The increase in HDL cholesterol (9%) was due to increases in both subfractions (HDL2 17%; HDL3 7%), changes that would be consistent with a beneficial effect on cardiovascular risk. Simvastatin decreased plasma triglyceride concentrations by 25%. Plasma total cholesterol concentrations fell by 35% after 3 months of treatment; this fall was proportional to the initial concentration and was due almost entirely to a 45% fall in low density lipoprotein cholesterol. In contrast, plasma concentrations of lipoprotein Lp(a) were not affected by simvastatin.

Anticholesteremic Agents↗
PubMed1992

Insulin resistance--modelling studies.

Elevated insulin concentrations are independent predictors of coronary heart disease (CHD) and are related to high blood pressure, low serum HDL-cholesterol and elevated serum triglyceride. Insulin resistance is a major determinant of the plasma insulin concentration. Computer modelling of plasma glucose, insulin and C-peptide concentrations during an intravenous glucose tolerance test enables quantification of the determinants of plasma insulin concentration. The association between risk markers of CHD and model-derived measures of determinants of plasma insulin concentration in a group of healthy males has been investigated. In univariate linear regression analysis of the glucose, insulin and C-peptide data, the incremental insulin area during the second phase (10-180 min.) was found to be the strongest predictor of lipid, lipoprotein and blood pressure variables. Variations in insulin sensitivity and hepatic insulin throughput contribute to variation in the insulin response and may be secondary correlates of lipids, lipoproteins and blood pressure.

Adult↗