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Biomedical subjects

P Flaud

Publications and source records attributed to P Flaud.

At least 19 recordsLinked to original sources

Intramuscular pressure and surface EMG in voluntary ankle dorsal flexion: Influence of elastic compressive stockings.

Intramuscular pressure (IMP) is of major importance in blood flow and is often taken as a good estimate of muscular tension. However, its measurement remains invasive. The aims of the present work were: (1) to re-examine the possibility of evaluating IMP and muscular tension changes by means of surface electromyographic recordings, and (2) to clarify the influence of elastic compressive stockings (ECS). Surface EMG of muscles tibialis anterior (TA), soleus, gastrocnemius, and IMP from the anterior tibial compartment (ATC), deep posterior compartment (DPC), superficial posterior compartment (SPC) of the right leg, were simultaneously recorded in nine healthy subjects. Subjects performed series of voluntary concentric TA contractions (right ankle dorsal flexions) and TA isometric contractions, with or without elastic ECS, in a decubitus posture. Rest IMP mean values, measured over 60 s, ranged between 12.3 and 26.6 mmHg, i.e. in the range or slightly higher than those reported in the literature. When ECS were applied, mean IMP increase was 6.4 mmHg in ATC, 8.7 mmHg in DPC and 21.0 mmHg in SPC, while the corresponding EMG amplitude decreased. In ankle dorsal flexion movements, instantaneous values of TA-EMG amplitudes were linearly correlated to ATC-IMP instantaneous values, over the whole of the EMG rising part of every movement. When ECS were applied, the relationships between TA-EMG amplitude and ATC-IMP amplitude remained linear but where shifted towards higher IMP, in agreement with the increase in rest IMP. Because of antagonist co-contractions, IMP from DPC and SPC were also linearly correlated with ATC-IMP but with low coefficients of proportionality. As in TA concentric contractions, TA-EMG amplitudes were linearly correlated to ATC-IMP instantaneous values in isometric contractions, but the slopes of the latter were always greater. This result is explained by the relationship between muscle tension and shortening velocity. Al the results showed that: (1) instantaneous changes in surface EMG amplitude may provide a good estimate of IMP changes during the rising part of isometric, but also of concentric voluntary contractions; (2) elastic compressive stockings do not impair subjects relaxation capacity but actually increase the ratio IMP/muscle activation. As a consequence, ECS may actually increase the venous return during voluntary contractions.

Adaptation, Physiological↗

Experimental evidence of a potentially increased thrombo-embolic disease risk by domestic electromagnetic field exposure.

We have used the EaHy926 endothelial cell line, able to secrete both pro and anti-aggregant platelet agents, as a model for thrombo-embolic diseases. We experimentally established, by comparing these two secretions with or without a Faraday cage, that the environmental electromagnetic field significantly increases the thrombo-embolic risks in this endothelial cell line.

6-Ketoprostaglandin F1 alpha↗

A digital model for the venous junctions.

The venous network in the lower limbs is composed of a considerable number of confluent junctions. Each of these singularities introduces some blood flow disturbances. Each physiological junction is unique, in terms of its geometry as well as the blood flow rate. In order to account for this great variability, we developed a numerical model based on the use of the N3S code (a software package for solving Navier-Stokes equations). To test the validity of the model, one of the numerical simulations is compared with the data obtained in the corresponding experimental configuration. The velocity measurements were carried out with an ultrasonic pulsed Doppler velocimeter. We also measured pressure differences using differential sensors. The numerical computations were then used to obtain the values of the flow variables at any point, with various geometrical and flow configurations. As far as the velocity field is concerned, a very marked three-dimensional pattern with swirls was observed. The pressure evolution was also strongly disturbed, with a non-linear decrease. All these data indicate that confluence effects cannot be neglected when evaluating pressure decreases. With a tool of this kind, it is possible to accurately predict the disturbances associated with any geometrical configuration or any flow rate.

Blood Flow Velocity↗

Non-linear analysis of the arterial pulsatile flow: assessment of a model allowing a non-invasive ultrasonic functional exploration.

Ultrasonic measurements and modelling of blood flow in large vessels allows non-invasive evaluation of clinically interesting hemodynamic variables. To this aim, a non-linear mathematical model for the pulsatile arterial flow is proposed using the approximation of "local flow" theory. The model requires only measurements of instantaneous radius and centre-line blood velocity, and the knowledge of the tube distensibility to calculate blood velocity profiles, pressure gradient and wall shear stress. Evaluation of the proposed model using experimental data obtained from the literature proved that it can provide reliable results. In addition, as shown by assessing significance of various non-linear terms, results did not significantly change when a linear pressure-radius relationship was used instead of a non-linear relationship. Also, the model was found to be moderately sensitive to arterial tapering. Thus, the proposed model is suitable for a non-invasive clinical arterial exploration since it only requires three measurements which can be easily and precisely obtained in vivo using ultrasonic methods: the instantaneous radius, the centre-line velocity and the mean pulse wave velocity, this last variable characterizing the tube distensibility when assuming a linear pressure-radius relationship.

Arteries↗

Modeling of the deformation of flexible tubes using a single law: application to veins of the lower limb in man.

The topic of this study mainly concerns a representative model of the behavior of flexible ducts such as elastic tubes or veins. This model is based on a phenomenological approach of the inflation and collapse of the tube. It leads to a single "universal" analytical expression of the tube law, valid fir a wide range of' positive and negative transmural pressures, which presents a significant improvement compared to previous theoretical studies defined with different expressions on restricted ranges of pressure. Moreover, the theoretical approaches most often require simplif'ing hypotheses--no longitudinal tension, no surrounding tissues--which are quite unrealistic both in the physiological case and in the experimental setup. These theoretical models can therefore be expected only roughly to describe the actual behavior of such vessels. The representative model, on the contrary, allows one to account for the deformation--inflating as well as collapse--of elastic tubes or veins with better accuracy. The tube law is a function of six parameters chosen in order to fit the experimental data. A comparison between results obtained in our laboratory using silicone tubes and representative models is presented. The model is then applied to physiological data obtained in vivo on human leg veins.

Elasticity↗

Hemorheology in asymptomatic HIV-infected patients.

Although cardiac and vascular complications have been recognized among patients infected with the Human Immunodeficiency Virus-1 (HIV-1), their vascular biology and rheology have not been studied. Rheology of red blood cells (RBC) was assessed with an erythroaggregometer in 22 HIV-1 infected asymptomatic patients (pts) and 17 healthy HIV negative controls (C). All participants were normotensive, nondiabetics, had normal lipid levels and had an hematocrit ranging from 37 to 44% and hemoglobin levels > or = 12 g/100 ml. Patients had a shorter RBC aggregation characteristic time than controls (1.49 +/- 0.17 vs. 2.04 +/- 0.41 s, p = 0.001) and an increased disaggregation shear rate (166 +/- 34.9 vs. 122 +/- 25.4 s(-1), p = 0.001). This hyperaggregation tendancy was associated with increased gamma-globulin (18.3 +/- 3.3 vs. 13.7 +/- 1.9 g/l, p = 0.01) and fibrinogen (3.52 +/- 0.57 vs 3.03 +/- 0.48 g/l, p = 0.003) levels and with an increased erythrocyte sedimentation rate (ESR) (25 +/- 14.3 vs. 12.3 +/- 7.5 mm, p = 0.02). Even in patients with ESRs ranging within normal values (< or = 20 mm), the aggregation characteristic time was found lower in patients than in controls (p = 0.004). There was no correlation between these rheological changes and the CD4+ T-cell count. The 17 patients receiving an antiviral therapy had lower CD4+ T-cell counts than their 5 untreated counterparts (244.7 +/- 167 vs. 410 +/- 106/mm3, p = 0.025), and a higher disaggregation shear rate (177.4 +/- 38.2 vs. 127 +/- 25.4, p = 0.01). Thus, an impairment of rheological characteristics is observed in asymptomatic HIV-I infected patients in association with changes in plasma proteins.

Adult↗

Deconvolution process in measurement of arterial velocity profiles via an ultrasonic pulsed Doppler velocimeter for evaluation of the wall shear rate.

A numerically based simulation of pulsed Doppler ultrasound convolution and deconvolution of theoretical hemodynamic velocity profiles yields two major conclusions on performing a deconvolution process. First, the most important parameter to be accounted for is the size of the sample volume. Second, a deconvolution process with an overestimated sample volume size is revealed by high-frequency noise on the resulting profile. A deconvolution process is presented for in vivo arterial velocity profiles, which has the advantage of being systematic and not needing experimental testing for determining the size or the shape of the sample volume. It is also independent of the observation angle. Finally, an example of an application to in vivo human velocity profiles is given. Evaluation of the wall shear rate from the corrected deconvolved profiles shows a noticeable improvement with respect to that using the directly convolved Doppler profiles.

Arteries↗

In vitro study of haemodynamics in a giant saccular aneurysm model: influence of flow dynamics in the parent vessel and effects of coil embolisation.

The purpose of this study was to investigate the influence of flow dynamics in the parent vessel and of intra-aneurysmal coil embolisation on flow pattern and pressure in an in vitro model of giant aneurysm. A pulsatile perfusion with a glycerol aqueous solution was installed in a silicone model of a lateral giant aneurysm. Flow visualization and pressure measurements were performed while modifying the flow rate, the pulsatility and the pulse rate in the parent vessel, and after partial coil embolisation. Vortices were formed during systole at the downstream lip of the aneurysm and circulated around the aneurysm. The centre and dome of the aneurysm were areas of fluid stagnation. Flow rate and pulsatility were the main factors which varied the pattern of flow within the aneurysm. Partial coil embolisation induced major flow disturbances in the aneurysm, in particular fluid stagnation at the dome. Pressure measurements were similar in the aneurysm and in the parent vessel. It was concluded that the pulsatility of flow is an important as the flow rate when considering the haemodynamics in a giant aneurysm. In the clinical context, this could explain the efficacy of vertebral artery occlusion in thrombosing giant vertebrobasilar aneurysms. Studies with intra-aneurysmal coil embolisation showed early fluid stagnation at the dome. This could result in embolic migration during endovascular treatment. Partial coil embolisation may prevent early rebleeding; however, it may induce additional mural stresses resulting from new haemodynamic forces and compliance mismatch.

Blood Flow Velocity↗

[In vitro evaluation of Dibie-Musset vena caval filter].

The Dibie-Musset (DM) vena caval filter was evaluated on a hydraulic test bench reproducing flow conditions in the inferior vena cava: pressure, flow, viscosity, diameter and elasticity of the conduit. The results were compared with those obtained with the Greenfield filter (GF). In addition to classical measurements (captation and loss of load) we measured the velocity profile with a Doppler ultrasonic probe proximal and distal to the filter to study flow conditions before and after embolisation of clots. In order to circumvent the difficulties encountered with the use of real thrombi, chemical gels with visco-elastic properties, evaluated by viscosimetry, similar to those of blood clots, were used. Clots 45 mm long and 4 mm diameter were injected in several series of measurements. The DM filter was stable and did not migrate. In the horizontal position (flexible conduit) the DM filter was significantly more effective than the GF for less than 5 clots injected successively. The filtration capacity of both filters decreased with the number of clots captured. In the vertical position (rigid conduit), when there are less than 5 clots injected the two devices were perfectly effective. There was no significant difference between the two filters when 10 clots were injected. The loss of load resulting from the presence of the filter and clots was greater with the DM filter because of the greater captation capacity. However, the velocity profile distal to the filter was less disturbed with the DM filter because there was a more uniform distribution of the clots captured over the surface of the filter.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Viscosity↗

Comparative effects of diabetes mellitus and hypertension on physical properties of human large arteries.

OBJECTIVES: The effects of hypertension and diabetes on the physical properties of large arteries were compared in men. BACKGROUND: Although these two diseases are linked to vascular stiffening, no study has analyzed whether the arterial rigidity in diabetes is as substantial as in hypertension. METHODS: Noninvasive measurements of brachial artery mean pressure, diameter (pulsed Doppler study) and compliance (pulse wave velocity) were obtained in 29 men: 11 control subjects, 9 hypertensive nondiabetic patients and 9 diabetic normotensive patients. Individual diameter- and compliance-pressure curves extrapolated from the measured diameter and mean pressure point with a logarithmic elastic model permitted calculation of isobaric diameter and compliance at the same pressure in each subject. RESULTS: Compared with control subjects, hypertensive patients had a larger brachial artery measured diameter and isobaric diameter (p < 0.01) and lower measured and isobaric compliance (p < 0.001, p < 0.01). Compared with control subjects, diabetic patients had lower measured and isobaric compliance (p < 0.01). Comparison of diabetic and hypertensive patients showed that measured diameter and isobaric diameter were decreased in the former (p < 0.01). In the control and hypertensive groups, mean pressure correlated positively with measured diameter and isobaric diameter (p < 0.01) and negatively with measured and isobaric compliance (p < 0.001 and p < 0.01, respectively). In the control and diabetic groups, fasting glucose correlated negatively with measured and isobaric compliance (p < 0.01, p < 0.05). CONCLUSIONS: Intrinsic alterations of the large artery independent of a stretching pressure effect reduce arterial elasticity similarly in those with hypertension or diabetes. The loss of compliance is related to the chronic elevation of blood pressure in hypertension and to that of glycemia in diabetes and is associated with a relative large artery vasoconstriction in diabetic patients as compared with patients with hypertension.

Adult↗

[Intrinsic (isobaric) effect of essential hypertension on visco-elastic properties of the brachial artery].

The purpose of this study was to estimate the effect of hypertension on the visco-elastic properties of the brachial artery in man. Seventy-five subjects including 23 with normal blood pressure (group N, PN = 95 +/- 7 mmHg, P designates the arterial mean pressure, P = DBP + (SBP-DBP)/3) and 52 with essential hypertension (group H, PH = 122 +/- 12 mmHg) participated to this study. We measured the diameter of the brachial artery (D) by the pulsed Doppler method, the brachial-radial pulse wave velocity (PWV) by the mecanographic method, and calculated the arterial compliance (C) by the Bramwell-Hill formula. A nonlinear model was used to calculate compliance and pression at any given pressure, in particular at PN or PH. We obtained the following results: [table; see text] Passive (pressure-induced) effect was obtained by comparing D(PH) to D(PN) and C(PH) to C(PN). Isobaric effect of hypertension was estimated by comparing D(PH) and C(PN) between the N and H groups. We concluded that hypertension actually induces a decrease in compliance. However, arterial diameter is increased in hypertension. The increase in diameter appears as a compensatory effect, without which the reduction in compliance would be more nocive to the circulatory system.

Adult↗

A new geometric procedure for in vivo pulsed Doppler evaluation of velocity distribution inside the diametrical section of large arteries in humans.

A new geometric procedure determination of velocity profiles inside large human arteries, such as the brachial and femoral, has been developed. The procedure requires the use of two crystal element Doppler probes and a highly precise micromanipulator with three degrees of freedom. Precise positioning is needed to obtain the required high degree of parallelism between the vessel axis and the plane containing the two crystal elements. Once the appropriate degree of parallelism is achieved, a controlled translation of the probe, perpendicular to the ultrasonic beam plane, allows velocity waveforms to be recorded at sequential radial positions across the measured artery. Velocity profiles obtained with this geometric procedure depended on the type of artery investigated. The profiles measured with the geometric procedure were more symmetrical than those found using the electronic range-gated time system of reception. While the geometric and electronic methods were almost identical in determining the diameter values of the three arteries measured, the geometric procedure enabled greater accuracy for detailed analysis of velocity profiles in the peripheral large arteries in humans. Although the present methodology is not applicable in clinical practice due to prolonged data acquisition time (approximately 45 s) it is expected that future equipment improvements will reduce this time significantly.

Adult↗

Pulsatile flow and oscillating wall shear stress in the brachial artery of normotensive and hypertensive subjects.

STUDY OBJECTIVE - The aim of the study was to examine oscillating arterial wall shear stress in hypertension. DESIGN - Pulsatile flow and oscillating wall shear stress were measured in brachial artery in hypertensive v normotensive subjects using pulsed Doppler apparatus. Methods were tested in four subjects using a micrometric procedure of Doppler probe displacement providing instantaneous real time velocity profiles. SUBJECTS - 19 ambulatory male patients with mild to moderate hypertension (diastolic blood pressure 95-114 mm Hg) and 11 normotensive male controls of similar age were studied. All were non-smokers. MEASUREMENTS and RESULTS - Arterial diameter and pulsatile centreline blood velocity were determined with pulsed Doppler, and blood viscosity was measured with a coaxial cylinder viscometer. Shear rates corresponding to maximum (gamma Vmax), minimum (gamma Vmin), and pulse (gamma Vpulse) velocities were evaluated with a simplified method of computation of Womersley equations. Corresponding shear stresses (tau Vmax, tau Vmin, tau Vpulse) were calculated as the product between shear rate and viscosity. The differences in wall shear rates obtained with the Womersley method and with the micrometric procedure were less than 10%. Compared to normotensives, hypertensives had greater arterial diameter [0.508(SEM0.006) v 0.446(0.014), p less than 0.001], lower maximum velocity [36.2(1.5) v 46.3(2.4) cm.s-1, p less than 0.001], lower absolute value of minimum velocity [-8.3(1.2) v -14.3(2.3) cm.s-1, p less than 0.01], lower pulse velocity [44.5(2.2) v 61.2(3.9) cm.s-1, p less than 0.001], and higher blood viscosity [4.77(0.08) v 4.28(0.09) mPa.s, p less than 0.001]. gamma and tau Vmax, Vmin and Vpulse were all lower in absolute value in hypertensives. Overall mean blood pressure in all subjects was negatively correlated to gamma Vmax (r = -0.65), tau Vmax (r = -0.46), gamma Vmin (r = -0.45), tau Vmin (r = -0.37), gamma Vpulse (r = -0.63), and tau Vpulse (r = -0.48). In hypertensives, age was correlated negatively to gamma Vmax (r = -0.44), tau Vmax (r = -0.46), gamma Vmin (r = -0.57), tau Vmin (r = -0.57), gamma Vpulse (r = -0.58), and tau Vpulse (r = -0.58). In normotensives, age was not correlated with shear parameters, except for tau Vmax (r = -0.60) and tau Vpulse (r = -0.66). CONCLUSIONS - The hypertensive state is associated with a reduction in oscillating wall shear in large arteries despite an increase in blood viscosity. Age in combination with hypertension also decreases wall shear conditions.

Adult↗

Non-invasive evaluation of segmental pressure drop and resistance in large arteries in humans based on a Poiseuille model of intra-arterial velocity distribution.

STUDY OBJECTIVE: The aim of the study was to evaluate in hypertensive subjects the longitudinal pressure drop and segmental resistance in a large artery in relation to shearing forces of the circulating blood column at the arterial wall. DESIGN: Arterial diameter, blood velocity, and flow were measured in the brachial artery using pulsed Doppler apparatus. Blood viscosity was measured at 96 s-1 with a low shear viscometer. Segmental resistance per unit arterial length was calculated using the basic Poiseuille resistance expression from the ratio between blood viscosity and the fourth power of arterial diameter. Longitudinal pressure drop was deduced as the product between segmental resistance and blood flow. The Poiseuille model of velocity distribution also enabled wall shear rate and stress to be calculated from the ratio between blood velocity and arterial diameter and from the product between shear rate and blood viscosity respectively. PATIENTS: 19 ambulatory male patients with mild to moderate hypertension and 11 normotensive male controls of similar age were studied. RESULTS: Compared to controls, hypertensive patients had higher arterial diameter (p less than 0.001) lower blood velocity (p less than 0.05), higher blood viscosity (p less than 0.01), lower segmental resistance and pressure drop (p less than 0.001, p less than 0.01) and lower shear rate and stress (p less than 0.01, p less than 0.05). A negative correlation existed in the overall normotensive and hypertensive population between pressure drop and mean blood pressure (r = -0.55, p less than 0.01). CONCLUSION: The hypertensive state is associated with a clear reduction in large artery segmental resistance and longitudinal pressure drop concomitantly with a decrease in shear conditions at the arterial wall. The mechanisms of reduced resistance and pressure drop are related to decreased wall shear and increased diameter of the artery, both of which reduce the frictional forces at the blood-arterial wall interface.

Adult↗

Blood viscosity as a chronic contributing factor of vasodilatation in humans.

Since resistance to flow is theoretically determined by arteriolar geometry and blood viscosity, we studied these two factors in 44 normal and 106 hypertensive subjects. Brachial bed vascular resistance was calculated as the ratio between mean pressure and brachial artery flow. Systemic blood viscosity in vitro was determined at 96 per s, while microvessel blood viscosity in vivo was estimated from the haematocrit-viscosity relationship at 240 per s. A resistive radius index was calculated which was only related to the microvessel viscosity: resistance ratio. Compared to normal subjects, hypertensive subjects had higher systemic in vitro blood viscosity (4.75 +/- 0.47 versus 4.50 +/- 0.43 mPa.s; P less than 0.005) and microvessel blood viscosity (2.60 +/- 0.21 versus 2.43 +/- 0.16 mPa.s; P less than 0.001). Hypertensive subjects also had a higher brachial vascular resistance (161 +/- 89 versus 124 +/- 58 mmHg/ml per s; P less than 0.01), but showed a similar resistive radius index (2.47 +/- 0.36 versus 2.57 +/- 0.35) compared to normal subjects. There was a positive correlation between systemic viscosity and brachial artery diameter and a negative correlation between microvessel viscosity and vascular resistance in the normotensive (P less than 0.05 and P less than 0.001, respectively) and hypertensive groups (P less than 0.001 and P less than 0.005, respectively). The resistive radius index was positively related to viscosity in normal and in hypertensive groups (P less than 0.001) but these relationships were significantly different (P less than 0.001), showing that, at the highest viscosities, arterial radius increased less in hypertensive than in normal subjects. Thus, the level of blood viscosity might influence arterial diameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

[Contrary effects of hypertension and cigarette smoking on the conditions of wall shear in large arteries].

Systolic wall shear conditions were studied in the brachial artery of 4 groups of subjects including 11 non-smokers normotensives (NSNT), 25 non smokers hypertensives (NSHT), 21 smokers normotensives (SNT) and 10 smokers hypertensives (SHT). Brachial artery diameter (D) and systolic centerline blood velocity (VCLS) were measured with a pulsed Doppler device and blood viscosity at 96 sec-1 was measured with a coaxial cylinder viscometer. The wall shear rate (gamma S) corresponding to systolic velocity was calculated using a Womersley model of pulsatile flow according to the formula: alpha = (D/2) (omega/mu) 1/2, omega being the angular pulse frequency and mu the kinematic viscosity. The wall shear stress was then calculated as the product between wall shear rate and viscosity. The analysis of results in the 4 groups showed that both hypertension and smoking increased blood viscosity bu their effects on wall shear were opposite since hypertension decreased shear and stress while smoking did not change it. However, in hypertensive patients, smoking induced a clear elevation in wall shear rate and stress, whereas in smokers hypertension did not change shear conditions. Thus, opposite and interactive effects of hypertension and smokers exist on large artery wall shear phenomena which could induce differences in response of functional and structural endothelial cells to these two vascular risk factors.

Adult↗

[A new hemodynamic endothelial approach using non-invasive evaluation of instantaneous wall shear in human arteries. Application in arterial hypertension].

A new non-invasive methodology of measurement of pulsatile wall shear in superficial large arteries in man is presented from simple determinations of internal diameter of large artery and centerline instantaneous blood velocity (pulsed Doppler apparatus) and asymptotic blood viscosity (coaxial cylinder viscometer). Pulsatile distribution of velocity across the arterial lumen has been represented by a Womersley model enabling to define and calculate wall shear rate as the slope at the wall to the velocity profile at each cardiac time. These complex mathematical calculations have been performed on micro-computer by means of appropriate programmation according to the following steps (1) Digitization and processing of instantaneous centerline blood velocity (2) Decomposition of velocity signal into Fourier series as a sum of elementary velocity sinusoids of increasing frequency (3) computation of velocity profile and slope at the wall to the profile for each harmonic (4) Resynthetization of instantaneous wall shear rate as function in time (5) calculation of wall shear stress by multiplying wall shear rate by blood viscosity. Taking the brachial artery as model of peripheral large artery, pulsatile wall shear rate and stress curves were determined in individual subjects and analysed by means of several characteristic indices including: maximum, minimum and mean values; time of systolic increase and time of systolic relaxation; and oscillating index defined from the positive and negative surfaces of the shear curve. This original methodology open new way for studying hemodynamical conditions at the interface between blood and endothelium surface of large arteries and might be applied to the physiopharmacological approach of vascular disease such as hypertension.

Adult↗