Azimuthal instability of the interface in a shear banded flow by direct visual observation.

The stability of the shear banded flow of a Maxwellian fluid is studied from an experimental point of view using rheology and flow visualization with polarized light. We show that the one-layer homogeneous flow cannot sustain shear rates corresponding to the end of the stress plateau. The high shear rate branch is not found and the shear stress oscillates at the end of the plateau. An azimuthal instability appears: the shear induced band becomes unstable and the interface between the two bands undulates in time and space with a period τ, a wavelength λ and a wave vector k parallel to the direction of the tangential velocity.

Tetralogy of Fallot with subpulmonary ventricular septal defect.

Among a total of 608 patients with tetralogy of Fallot, 35 with tetralogy and subpulmonary ventricular septal defect (VSD) have undergone intracardiac repair at the Children's Hospital, Buenos Aires. The crista supraventricular was absent in 62.9% of these patients; it was hypoplastic in 37.1%. Only 3 patients (8.6%) were severely cyanotic and required operation in infancy. The main and left and right pulmonary arteries were relatively large in all but 1 patient. Nevertheless, patch-graft enlargement across the pulmonary valve ring was necessary in 20 (57.1%). We believe that closure of the subpulmonary VSD increase the apparent severity of the pulmonary stenosis and necessitates patch-graft enlargement in patients in whom the appearance of the right ventricular outflow tract before repair would not have suggested its need.

[Sodium transport in red blood cell membranes in essential arterial hypertension]. / Transporte de sodio en membrana de glóbulos rojos en hipertensión arterial esencial.

Several abnormalities in Na metabolism have been implicated in the pathogenesis of essential hypertension. In addition, recent work by several investigators has showed that some Na transport systems in red cell membranes may be altered in those patients. In order to confirm such abnormalities we evaluated simultaneously four different and clearly defined Na transport systems in red cell membranes: the ouabain sensitive Na pump (P) and the Na-K cotransport (Co) in nystatin loaded cells, the maximal rate of Na-Li countertransport (CTT) in lithium loaded cells and the rate constant of Na passive permeability (pp) in 58 normotensive control subjects with no family history of hypertension (N), 19 normotensive subjects with family history of hypertension (NH) and 34 essential hypertensive patients (HE). The mean (mean +/- SEM microns/lc/h) value of the P and pp was found to be comparable in the three groups. Co was found significantly decreased in both HE (241 +/- 28) and in NH (227 +/- 42) when compared to the control group (290 +/- 10). Although NH also showed CTT values (377 +/- 87) higher than controls, the difference did not reach statistical significance. Our results indicate that approximately 90.9% of both HE and NH presented abnormalities in one or more of the various Na transport systems studied. Normotensive patients with a positive family history and alterations in some of the Na transport systems in red cell membranes may prove an interesting experimental model to assess the importance of such alterations for the development of hypertension.

Rheophysical properties of fluorinated nonionic micellar phases.

Micellar phases can be used as templates for the preparation of mesoporous silica materials. Fluorinated and hydrogenated surfactants can provide a large variety of well-defined micellar structures: spherical and cylindrical micelles as well as more complex structures such as lamellar or sponge phases can be formed in various thermodynamic conditions. However, the preparation of ordered mesoporous materials from these organized media is not always successful for a reason not known at the moment. It thus seems of the highest importance to properly characterize the micellar solution prior to the addition of the silica precursor during the material synthesis. In this paper, we describe some rheophysical properties of the micellar phase L(1) prepared with a fluorinated surfactant, the formula of which is C(7)F(15)C(2)H(4)(OC(2)H(4))(8)OH, labeled as R(F)(7)(EO)(8). This surfactant forms micelles in water, and the direct micellar phases have been characterized in a wide range of temperatures and surfactant concentrations. The rheological properties of the L(1) phase have also been studied as a function of temperature and concentration. Under steady and dynamic flow conditions, the solutions behave like Newtonian or shear thinning fluids depending on the temperature and surfactant concentration. A crossover between G' and G" is observed in the solution at the concentration of 20 wt % and at the temperature of 10 °C, suggesting the presence of long entangled micelles in solution at this temperature. When subjected to the action of a shearing device, the 20 wt % solution becomes optically anisotropic and shows flow birefringence, but the average orientation of the micelles quantified by the extinction angle χ shows an unexpected behavior when the shear rate is gradually increased.

'Isolated' pulmonary valve stenosis as part of more widespread cardiovascular disease.

In 25 patients aged 6 days to 9 years presenting as 'isolated' pulmonary valve stenosis, histology of the myocardium of right and left ventricles, coronary arteries, and ascending aorta has shown abnormality in one or all these areas. Myocardial necrosis, old and recent, unrelated to coronary occlusion was frequent. Myocardial 'dysplasia' involving both ventricles, and resembling hypertrophic cardiomyopathy (HOCM, ASH) was found in 10 and a relation of this to myocardial injury in the fetus is postulated. Varying degrees of coronary occlusion were frequently seen in both right and left coronary arteries. The histology of the ascending aorta was abnormal showing 'higgledy-piggledy' disorder of smooth muscle components in 12 (48%). In a different series of 53 patients who had pulmonary valvotomy for apparent 'isolated' pulmonary valve stenosis there were 14 with clinical evidence of left ventricular abnormality consistent with the pathological changes described, 2 with the same aortic histological changes, and 2 with macroscopical left ventricular hypertrophy. Two of them developed classical hypertrophic cardiomyopathy years later. It is suggested that when pulmonary valve stenosis presents with a thick tricuspid poorly mobile valve, particularly in infants or in patients with evidence of other congenital stigmata, it may be part of a more widespread cardiovascular abnormality. This should be recognized and considered in the evaluation of surgical patients and late survivors who may show unexpected clinical features.

Towards local rheology of emulsions under Couette flow using Dynamic Light Scattering.

We present local velocity measurements in emulsions under shear using heterodyne Dynamic Light Scattering. Two emulsions are studied: a dilute system of volume fraction phi = 20% and a concentrated system with phi = 75%. Velocity profiles in both systems clearly show the presence of wall slip. We investigate the evolution of slip velocities as a function of shear stress and discuss the validity of the corrections for wall slip classically used in rheology. Focussing on the bulk flow, we show that the dilute system is Newtonian and that the concentrated emulsion is shear-thinning. In the latter case, the curvature of the velocity profiles is compatible with a shear-thinning exponent of 0.4 consistent with global rheological data. However, even if individual profiles can be accounted for by a power law fluid (with or without a yield stress), we could not find a fixed set of parameters that would fit the whole range of applied shear rates. Our data, thus, raise the question of the definition of a global flow curve for such a concentrated system. These results show that local measurements are a crucial complement to standard rheological tools. They are discussed in the light of recent works on soft glassy materials.

Urinary kallikrein in hypertension secondary to hemolytic uremic syndrome: response to diuretic stimulus.

Urinary kallikrein excretion was measured in 43 children, mean age 8 years, who had the hemolytic uremic syndrome (HUS) during the first year of life. Twenty eight were normotensive and fifteen hypertensive. We found no difference in urinary kallikrein excretion between the normotensive and hypertensive groups. Twenty three of these children received a combination of 1 mg/kg/day of hydrochlorothiazide plus amiloride for ten days. 14 of these patients were normotensive and 9 hypertensive. The rate of kallikrein excretion did not change in the hypertensive children whereas normotensive children had a three fold increase following administration of the diuretic. The different behaviour of kallikrein excretion in both groups may reflect a change in the reactive capabilities of the vasodilator system in this form of hypertension.

Small kidney associated with primary vesicoureteral reflux in children. A pathological overhaul.

In this series two quite distinct pathological entities accounted for the small, often deformed, kidney found over a severe primary ureterovesical reflux. One of them is due to dysplastic abnormal metanephric differentiation, and the other is a segmental tubular atrophy with glomerular metamorphosis. In our material there is no evidence to support an inflammatory pathogenesis in these conditions. An abnormal excess vascularization is explained by an arteriovenous fistula present in both. Proper identification of the pathology underlying such cases will assist further studies on the natural history of these two diverse malformations.

Long-term systemic hypertension in children after successful repair of coarctation of the aorta.

The mechanisms responsible for long-term hypertension in children after successful repair of coarctation of the aorta have not yet been determined. We measured plasma renin activity and aldosterone, adrenalin, and noradrenalin concentrations both under basal conditions and in response to standing and treadmill exercise in 24 normal normotensive children, 16 normotensive postcoarctectomy children, eight hypertensive postcoarctectomy children, and seven children with essential hypertension. Exercise-induced changes in plasma renin activity, aldosterone, adrenalin, and noradrenalin were comparable in the four groups in spite of a significantly greater increase in systolic blood pressure in the children with hypertension. In response to standing, the plasma concentration of noradrenalin increased significantly in normotensive but not in hypertensive children. Hyperresponse of blood pressure to exercise in hypertensive postcoarctectomy children and children with essential hypertension is not related to abnormalities in the sympathetic nervous system or the angiotensin-aldosterone axis. Hypertension could be related to primary baroreceptor alterations, to structural changes in the arterial wall, or both. Twenty percent of normotensive postcoarctectomy children had a blood pressure hyperresponse to exercise and an abnormal noradrenalin response to standing similar to that seen in the hypertensive children. Follow-up of children after coarctectomy may elucidate whether these two abnormalities are indicators of an increased risk of developing long-term recurrent hypertension.

Supravalvular mitral stenosis associated with ventricular septal defect.

We describe three patients with supravalvular mitral stenosis caused by a diaphragm located just above the mitral valve and associated with a ventricular septal defect. Two of our three patients also had an associated coarctation of the aorta. The physical signs, ECGs, chest roentgenograms, and cardiac catheterization data are described. Points helpful in the differential diagnosis of this malformation are emphasized. All three patients were treated successfully by surgery.