Biomedical subjects

Alice V Stanton

Publications and source records attributed to Alice V Stanton.

5 recordsLinked to original sources

PubMed2003

Silent myocardial ischaemia in treated hypertensives with and without left ventricular hypertrophy.

BACKGROUND: Silent ischaemia has been reported to be associated with an increased risk of myocardial infarction and sudden death in a wide range of patient groups. The aim of this study was to examine the prevalence of silent ischaemia in hypertensive patients with and without left ventricular hypertrophy (LVH). METHODS: Twenty hypertensive patients participating in the Anglo-Scandinavian Cardiac Outcomes Trial with echocardiographic LVH (11 males, nine females), and 20 age, sex, blood pressure, and drug treatment-matched hypertensive patients without LVH underwent 24-h combined ambulatory blood pressure and electrocardiographic (ECG) monitoring. Ischaemic events were defined by the 'rule of 3 x 1'-asymptomatic ST-depression >/= 1 mm (0.1 mV), lasting at least 1 min, and with a duration of at least 1 min between two events. RESULTS: Thirteen patients with LVH had ischaemic events, whilst only four without LVH demonstrated ischaemia. Median numbers of events (seven versus zero; P < 0.01) and median total ischaemic area (0.25 versus 0 mV*min/day; P < 0.01) were significantly increased amongst hypertensive patients with LVH by comparison to those without LVH. CONCLUSION: Despite similar levels of established risk factors for atherosclerotic coronary artery disease, the prevalence of silent ischaemia was markedly increased amongst hypertensive patients with LVH by comparison to those with normal left ventricular dimensions. Ambulatory ECG monitoring may have a use in the identification of those at greatest risk of cardiovascular complications and sudden death, amongst hypertensive patients with persistent cardiac hypertrophy despite anti-hypertensive therapy.

Adult↗

PubMed2002

Ethnic differences in carotid and left ventricular hypertrophy.

OBJECTIVES: Afro-Caribbean subjects have a higher prevalence of hypertension, a lower prevalence of ischaemic heart disease and a higher premature mortality compared to White Europeans. Left ventricular hypertrophy (LVH) is also more prevalent in Afro-Caribbeans even at similar levels of blood pressure. It is widely believed that carotid artery intima-media thickening (IMT) represents an early marker for the development of atheroma, and carotid IMT and LVH are associated in White populations. Whether the relationship between carotid IMT and LVH is similar in Black subjects is unknown. METHODS: Thirty-eight subjects were studied using carotid and femoral ultrasonography and echocardiography; 19 Afro-Caribbean and 19 White European subjects were matched for age, sex and mean 24 h systolic blood pressure. RESULTS: The Afro-Caribbean group had a significantly greater left ventricular mass index (LVMI) compared to the White European: 136.4 +/- 6.1 versus 112.4 +/- 6.2 g/m2, P < 0.01. However, carotid IMT, carotid diameter, femoral IMT and femoral diameter were similar between the groups: 0.75 +/- 0.02 versus 0.77 +/- 0.04 mm, 6.54 +/- 0.15 versus 6.56 +/- 0.16 mm, 0.66 +/- 0.03 versus 0.68 +/- 0.03 mm and 8.40 +/- 0.33 versus 8.25 +/- 0.23 mm, respectively. CONCLUSIONS: Afro-Caribbean subjects with similar blood pressures have similar mean carotid and femoral IMTs compared to White Europeans, in spite of marked differences in LVMI. Whether this reflects a discrepancy in the degree of cardiovascular risk for similar levels of LVMI or whether this is a reflection of an altered pattern of target organ damage associated with hypertension in Afro-Caribbean subjects is unclear.

Adult↗

PubMed2002

Retinal vascular tree morphology: a semi-automatic quantification.

A semi-automatic method to measure and quantify geometrical and topological properties of continuous vascular trees in clinical fundus images is described. Measurements are made from binary images obtained with a previously described segmentation process. The skeletons of the segmented trees are produced by thinning,ff branch and crossing points are identified and segments of the trees are labeled and stored as a chain code. The operator selects a tree to be measured and decides if it is an arterial or venous tree. An automatic process then measures the lengths, areas and angles of the individual segments of the tree. Geometrical data and the connectivity information between branches from continuous retinal vessel trees are tabulated. A number of geometrical properties and topological indexes are derived. Vessel diameters and branching angles are validated against manual measurements and several derived geometrical and topological properties are extracted from red-free fundus images of ten normotensive and ten age- and sex-matched hypertensive subjects and compared with previously reported results.

Adult↗

PubMed2002

Measurement of hemodynamics in human carotid artery using ultrasound and computational fluid dynamics.

The objective of the study was to investigate the feasibility of using computational fluid dynamic modeling (CFD) with noninvasive ultrasound measurements to determine time-variant three-dimensional (3D) carotid arterial hemodynamics in humans in vivo. The effects of hyperoxia and hypoxic hypercapnia on carotid artery local hemodynamics were examined by use of this approach. Six normotensive volunteers followed a double-blind randomized crossover design. Blood pressure, heart rate, and carotid blood flow were measured while subjects breathed normal air, a mixture of 5% CO(2) and 15% O(2) (hypoxic hypercapnia), and 100% O(2) (hyperoxia). Carotid artery geometry was reconstructed on the basis of B-mode ultrasound images by using purpose-built image processing software. Time-variant 3D carotid hemodynamics were estimated by using finite volume-based CFD. Systemic blood pressure was not significantly affected by hyperoxia or hypoxic hypercapnia, but heart rate decreased significantly with hyperoxia. There was an increase in diastolic flow velocity in the external carotid artery after hypoxic hypercapnia, but otherwise carotid blood flow velocities did not change significantly. Compared with normal air, hyperoxic conditions were associated with a decrease in the width of the region of flow separation in the external carotid artery. During hyperoxia, there was also an increase in the minimum and a decrease in maximum shear stress in the bifurcation and hence a reduction in cyclic variation in shear stress. Hypoxic hypercapnia was associated with a reduced duration of flow separation in the external carotid artery and an increase in the minimum shear stress without affecting the cyclic variation in shear stress. This study demonstrates the feasibility of using noninvasive ultrasound techniques in conjunction with CFD to describe time-variant 3D hemodynamics in the human carotid arterial bifurcation in vivo.

Adult↗

PubMed2002

Is carotid artery intima-media thickening a reliable marker of early atherosclerosis?

BACKGROUND: It is widely believed that carotid artery intima-media thickening represents an early marker for the development of atheroma. However, carotid intima-media thickening might also be expected to occur in response to an increased tensile stress and decreased wall shear stress which may accompany physical exercise. DESIGN, METHODS, AND RESULTS: In order to test this hypothesis 24 athletes (professional footballers) were compared to 14 age and sex matched control subjects. Each subject underwent carotid and femoral ultrasonography and echocardiography. The athletes had a greater left ventricular mass index compared with the controls: 135 (127-143) vs. 104 (91-116) g/m2, p < 0.001. In addition, they had a greater carotid intima-media thickness (IMT): 0.55 (0.52-0.57) vs. 0.51 (0.48-0.54) mm, p < 0.05. However, carotid artery diameters, femoral IMT and femoral artery diameters were similar: 6.0 (5.9-6.2) vs. 5.8 (5.6-6.1) mm, 0.43 (0.42-0.45) vs. 0.43 (0.41-0.45) mm and 8.3 (8.0-8.6) vs. 8.4 (8.0-8.7) mm, respectively. CONCLUSIONS: The increased carotid IMT of the athletes may result from intermittent exposure to markedly elevated systemic arterial pressures during exercise, resulting in intermittent elevations in carotid wall tensile stress. The lack of a disparity between athletes and controls for femoral IMT may be explained by the intermittent elevation of femoral wall tensile stress being accompanied by increased femoral artery blood flow and wall shear stress, which would tend to reduce any wall thickening. This is an important observation, since it suggests that an increased carotid IMT cannot be relied on solely as a marker of early atherosclerosis.

Adolescent↗