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Biomedical subjects

P Flaud

Publications and source records attributed to P Flaud.

25 records · Page 2Linked to original sources
PubMed1989

[Non invasive evaluation of endothelial shearing phenomena in human arteries. Application to essential hypertension].

Pulsatile wall shear conditions close to the brachial artery were evaluated in 11 normotensive and in 19 hypertensive patients of similar age by determining arterial diameter and centerline blood velocity with a pulsed Doppler and blood viscosity at 96 sec-1 with a coaxial cylinder viscometer. A Womersley model of intraluminal distribution of blood velocities enabled to determine from unsteadiness parameter alpha of Womersley, arterial diameter and maximal minimal and pulse (maximal-minimal) values of centerline velocity, the maximal minimal and pulse shear rate and shear stress (product between shear rate and viscosity) close to the endothelium. Compared to normotensives hypertenvises had higher arterial diameter (p less than 0.001), lower maximal minimal and pulse centerline velocities (p less than 0.001, p less than 0.01, p less than 0.001) higher blood viscosity (p less than 0.001), lower maximal, minimal and pulse wall shear rate (p less than 0.001, p less than 0.05, p less than 0.001) and lower maximal minimal and pulse shear stress (p less than 0.01). In the overall normotensive and hypertensive group, mean blood pressure negatively correlated to maximal minimal and pulse shear rates (r = -0.65; r = -0.45, r = -0.63) and to maximal, minimal and pulse shear stress (r = -0.46; r = -0.37, r = -0.48). Thus, hypertension is associated with a reduction of oscillating shear conditions in the viscosity of the brachial artery wall which might in long term influence structural and/or functional response to the endothelium.

Adult↗
PubMed1989

[Blood viscosity is a chronic adjustment factor of arterial vasodilatation in humans].

Arteriolar geometry and blood viscosity, the two main factors determining vascular resistance were studied in 44 normotensive subjects and 106 hypertensive patients at the brachial circulation level. Vascular resistance was calculated as the ratio between mean blood pressure and mean arterial flow determined by pulsed Doppler. Blood viscosity at 240 sec-1 was measured with a coaxial cylinder viscometer: Compared to controls, hypertensive patients had higher vascular resistance (161 + 8 vs 124 + 9 mmHg.ml-1.sec, P less than 0.05) and higher viscosity (4.75 + 0.05 vs 4.50 + 0.07 mPasec, P less than 0.01). Vascular resistance was negatively correlated to blood viscosity both in control (r = 0.48; P less than 0.001) and in hypertensive (r - 0.39, P less than 0.001) groups. Arteriolar equivalent radius (a) calculated from Poiseuille's equation from the relation a = (8 mu/pi R) 1/4 was positively correlated to viscosity in the two regressions were statistically different (P less than 0.001) indicating that at higher viscosity levels, arteriolar equivalent radius had lesser increase in normotensive than in hypertensive groups. Thus chronic increase in blood viscosity is accompanied by a small vessels vasodilatory phenomenon which seems less efficient in normotensive than in hypertensive subjects and might contribute in part to the mechanisms of vascular resistance elevation observed in hypertension.

Adult↗
PubMed1989

[Paradoxal diminution of resistance of the large arteries in human essential hypertension].

Segmental pressure drop and longitudinal resistance of brachial artery were evaluated in 11 normotensive (NT) and 19 hypertensive (HT) subjects of similar age by measuring arterial diameter (D), blood velocity (V) and flow (Q) with pulsed Doppler and blood viscosity (mu) at 96 sec-1 with a coaxial cylinder viscometer. Mean pressure drop (delta P) per unit of length of artery was calculated according to the relation delta P = 4 tau/D, where tau is the mean wall shear stress evaluated on the basis of a Poiseuille velocity profile by the formula: r = vV/D. Brachial artery resistance per unit of length was deduced as the (delta P/Q) ratio. (table; see text) In the overall normotensive and hypertensive group, (n = 30), pressure drop (delta P) was negatively correlated with mean blood pressure (r = -0.55, P less than 0.01). Despite increased viscosity hypertensive patients have a decreased resistance of large arteries whose mechanisms include a reduction in shear stress close to the endothelium and a dilation of the conduit artery; these two abnormalities contribute to decrease the viscous force of the circulating blood column against the arterial wall.

Adult↗
PubMed1988

A structural viscoelastic model of soft tissues.

A non-linear elastic model taking into account the microscopic structure of biological soft tissues is briefly presented and extended to quasi linear viscoelasticity. The modelling of the rheological behavior for near zero stress values is then discussed.

Connective Tissue↗
PubMed1976

[Wall rheology and arterial hydrodynamics: theoretical and hydromechanical models (author's transl)].

Recent results in research on transport of macromolecules between blood and the arterial wall have shown that endothelial cells are very sensitive to mechanical events localised in the flow boundary layer. Cardiac pressure waves of finite amplitude are characterized by non linear propagation phenomena in which the fluid-wall interaction plays an important role through the wall rheology. Different models of the mechanical behavior of arterial wall have been studied and their influence on blood flow field have been analysed.

Animals↗
PubMedDate not supplied

Collagen vascular grafts: a step towards improved compliance in small-calibre bypass surgery; preliminary report.

This study assesses the static compliance of a 4-mm-calibre collagen vascular graft. The graft was prepared by extrusion from a gel of collagen obtained from the skin of grown calves. To allow easy surgical handling, the prosthesis was reinforced by embedding a polyester mesh between two concentric tubes of collagen. Compliance was determined in vitro by filling the graft with increasing volumes of saline while intraluminal pressure and longitudinal stretching were simultaneously recorded. A 4-mm polytetrafluoroethylene prosthesis and a freshly-harvested human saphenous vein served as references. In the range of physiological pressures (100 to 200 mmHg), the collagen graft was only half as stiff as the polytetrafluoroethylene graft (5.6 vs 2.7 mm3/mb/m) and, in spite of its reinforcement, yet slightly more compliant than the vein itself (4.5 mm3/mb/m). Thus, from a mechanical viewpoint, a collagen prosthesis seems to be a valuable alternative for small-vessel bypass grafting, but further studies of its flow-surface characteristics are now warranted to assess its potential usefulness in the clinical setting.

Blood Vessel Prosthesis↗