Image du mois. Syncope vasovagale en direct.

in Revue Médicale de Liège (1997), 52(5), 315

Modelling the Arterial Wall by Finite Elements

in Archives Internationales de Physiologie, de Biochimie et de Biophysique (1993), 101(3, May-Jun), 185-91

The mechanical behaviour of the arterial wall was determined theoretically utilizing some parameters of blood flow measured in vivo. Continuous experimental measurements of pressure and diameter were ... [more ▼]

The mechanical behaviour of the arterial wall was determined theoretically utilizing some parameters of blood flow measured in vivo. Continuous experimental measurements of pressure and diameter were recorded in anesthetized dogs on the thoracic ascending and midabdominal aorta. The pressure was measured by using a catheter, and the diameter firstly, at the same site, by a plethysmograph with mercury gauge and secondly, by a sonomicrometer with ferroelectric ceramic transducers. The unstressed radius and thickness were measured at the end of each experiment in situ. Considering that the viscous component is not important relatively to the nonlinear component of the elasticity and utilizing several equations for Young modulus calculation (thick and thin wall circular cylindrical tube formulas and Bergel's equation) the following values were obtained for this parameter: 0.6 MPa-2 MPa in midabdominal aorta and 2 MPa-6.5 MPa in thoracic ascending aorta. The behaviour of the aorta wall was modelled considering an elastic law and using the finite element program "Lagamine" working in large deformations. The discretized equilibrium equations are non-linear and a unique axi-symmetric, iso-parametric element of 1 cm in length with 8 knots was used for this bi-dimensional problem. The theoretical estimation of radius vessel, utilizing a constant 5 MPa Young modulus and also a variable one, are in good agreement with the experimental results, showing that this finite element model can be applied to study mechanical properties of the arteries in physiological and pathological conditions. [less ▲]

Contribution of Peripheral Blood Pooling to Central Hemodynamic Disturbances During Endotoxin Insult in Intact Dogs

in Critical Care Medicine (1989), 17(12), 1314-9

The aim of the present study was to determine possible effects of Escherichia coli endotoxin on peripheral vascular compliance and relate them to concomitant central hemodynamic disturbances. Endotoxin ... [more ▼]

The aim of the present study was to determine possible effects of Escherichia coli endotoxin on peripheral vascular compliance and relate them to concomitant central hemodynamic disturbances. Endotoxin was infused at 0.25 micrograms/kg.min during 2 h in six anesthetized dogs, while six additional animals served as controls. Vascular compliance of the systemic circulation was calculated in intact animals from the changes in CVP after known changes in systemic blood volume. In control dogs, vascular compliance averaged 2.3 ml/mm Hg.kg body weight. During slow endotoxin infusion, cardiovascular effects were measurable only after a certain period of time had elapsed from the start of endotoxin insult and consisted of hypotension associated with systemic vasodilation. Systemic BP decreased gradually from 124 to 68 mm Hg while vascular compliance was finally increased by 100%, when compared to control values. This latter rise was responsible for a reduction in the cardiac preloads. Pulmonary wedge pressure and CVP were decreased from 7.1 to 3.4 and from 4.5 to 2.6 mm Hg, respectively. However, parallel to the decrease in left ventricular preload, endotoxin induced a progressive decrease in left ventricular afterload. Because of the balance in ventricular loading, cardiac output remained almost unchanged. After volume loading (dextran 30 ml/kg), cardiac output was remarkably increased from 3.28 to 6.24 L/min.m2 while peripheral vasodilation was not affected by this maneuver. It is concluded that low dose endotoxin infusion induces in dogs a hemodynamic pattern similar to human sepsis. The left ventricular loading changes are related to an enhanced systemic vascular compliance from 2.3 to 4.5 ml/mm Hg.kg. High flow shock state is encountered provided peripheral blood pooling is compensated by adequate volume replacement. [less ▲]

Critical analysis of the "anaerobic threshold" during exercise at constant workloads.

in European Journal of Applied Physiology and Occupational Physiology (1981), 46(4), 367-77

The method described by Wasserman for anaerobic threshold (AT) determination, based on the recording of ventilatory parameters, was supported by the simultaneous appearance of hyperlactacidemia and ... [more ▼]

The method described by Wasserman for anaerobic threshold (AT) determination, based on the recording of ventilatory parameters, was supported by the simultaneous appearance of hyperlactacidemia and hyperventilation during a standardized incremental work test. Our study aimed at testing the AT in another profile of exercise, viz., during exercises at constant workloads. A homogenous population of 66 healthy subjects performed on a treadmill a total of 100 exercises of 20 min duration at constant workloads (43, 48, 52, 57, 63, and 71% VO2 max). The VO2, V, and venous plasma lactic acid (LA) were determined every minute. LA showed an initial transient increase at 43% VO2 max and a steady-state elevated level above 48% VO2 max. In contrast, the hyperventilation threshold (HVT) was only observed above 57% VO2 max, simultaneously with a delayed steady-state VO2 and with a sustained increase of lactate until the end of exercise. The meaning of the simultaneity of these three events must still be studied. However, the dissociation between both early and steady-state lactate thresholds and HVT is not in keeping with the concept of AT. In these conditions, there is no evidence that HVT necessarily represents an AT, viz., a critical intensity of exercise inducing an insufficient oxygen delivery to the muscles. This conclusion does not imply that the measurement of HVT should be rejected as an empirical test of physical fitness. [less ▲]

Independance du seuil d'hyperlactacidemie et du seuil d'hyperventilation dans l'exercice rectangulaire chez l'homme.

in Comptes Rendus des Séances de la Société de Biologie et de ses Filiales (1980), 174(6), 977-82

During exercises at constant workload, the hyperlactatemia threshold (continuous lactate production during the whole exercise) (48% VO2 max) and the hyperventilation threshold (57% VO2 max) are not ... [more ▼]

During exercises at constant workload, the hyperlactatemia threshold (continuous lactate production during the whole exercise) (48% VO2 max) and the hyperventilation threshold (57% VO2 max) are not simultaneous. This finding demonstrates that the hyperventilation threshold could not be regarded as an "anaerobic threshold". [less ▲]

Determinisme de la derive lente de la frequence cardiaque pendant l'exercise musculaire.

in Comptes Rendus des Séances de la Société de Biologie et de ses Filiales (1978), 172(3), 569-74

The slow increase in heart rate which is observed in normal man submitted to heavy muscular exercise is due for a part to an activation of orthosympathetic cardiac activity which is blocked by beta ... [more ▼]

The slow increase in heart rate which is observed in normal man submitted to heavy muscular exercise is due for a part to an activation of orthosympathetic cardiac activity which is blocked by beta antagonists. It is also explained by direct action of hyperthermia on the heart. [less ▲]

Influence de l'etat d'alimentation sur l'hyperlactacidemie d'exercice

in Comptes Rendus des Séances de la Société de Biologie et de ses Filiales (1976), 170(1), 223-6

In normal man, food ingested two hours before the beginning of physical exercise increases the lactacidemia (+ 27%).