Growth and shape of a laboratory alluvial fan.

Using laboratory experiments, we investigate the influence of water and sediment discharges on the morphology of an alluvial fan. In our flume, a single-thread laminar river deposits corundum sand into a conical fan. We record the fan progradation with top-view images and measure its shape using the deformation of a Moiré pattern. The fan remains virtually self-affine as it grows, with a nearly constant slope. We find that, when the sediment discharge is small, the longitudinal slope of the fan remains close to that of a river at the threshold for sediment transport. Consequently the slope depends on the water discharge only. A higher sediment discharge causes the fan's slope to depart from the threshold value. Due to the downstream decrease of the sediment load, this slope gets shallower towards the fan's toe. This mechanism generates a concave fan profile. This suggests that we could infer the sediment flux that feeds a fan based on its proximal slope.

Estimating ecosystem metabolism from continuous multi-sensor measurements in the Seine River.

Large rivers are important components of the global C cycle. While they are facing an overall degradation of their water quality, little remains known about the dynamics of their metabolism. In the present study, we used continuous multi-sensors measurements to assess the temporal variability of gross primary production (GPP) and ecosystem respiration (ER) rates of the anthropized Seine River over an annual cycle. Downstream from the Paris urban area, the Seine River is net heterotrophic at the annual scale (-226 gO2 m-2 year-1 or -264 gC m-2 year-1). Yet, it displays a net autotrophy at the daily and seasonal scales during phytoplankton blooms occurring from late winter to early summer. Multivariate analyses were performed to identify the drivers of river metabolism. Daily GPP is best predicted by chlorophyll a (Chla), water temperature (T), light, and rainfalls, and the coupling of daily GPP and Chla allows for the estimation of the productivity rates of the different phytoplankton communities. ER rates are mainly controlled by T and, to a lesser extent, by Chla. The increase of combined sewer overflows related to storm events during the second half of the year stimulates ER and the net heterotrophy of the river. River metabolism is, thus, controlled at different timescales by factors that are affected by human pressures. Continuous monitoring of river metabolism must, therefore, be pursued to deepen our understanding about the responses of ecosystem processes to changing human pressures and climate.

[Arterial hypertension, chronic renal insufficiency and dialysis]. / Hypertension arterielle, insuffisance renale chronique et dialyse.

The principal characteristic of hypertension in chronic kidney disease (CKD), especially at CKD stage 5. Is an increased systolic pressure, with normal or even low diastolic pressure. This isolated systolic hypertension is also characterized by ab abnormal increase in pulse pressure which is by itself an independent cardiovascular risk factor. The principal reason for these abnormalities is accelerated ageing of arterial system, principally the aorta and large central arteries. This ageing is characterized by stiffening of arteritis whose natural history is not clearly understood. One of the principal pathogenic factor associated with stiffening is extensive calcification of arterial walls, mainly the medial layer (media-calcinosis). Mineral metabolism disorders such as hyperphosphatemia, play a major role in pathophysiology of calcifications. Arterial stiffness is characterized by very steep volume-pressure relationship and for this reason is associated with hemodynamic instability. Small blood volume increase producing abnormally high pressure while small decrease in blood volume could be associated with deep hypotension.

Contributive factors to cardiovascular hypertrophy in renal failure.

Cardiovascular diseases are the leading cause of morbidity and mortality among end-stage renal disease (ESRD) patients. This is related to the accumulation of nonspecific cardiovascular risk factors in this population, aggravated by some specific features, proper to chronic uremia. The principal abnormalities observed in ESRD patients, with no history of cardiovascular disease, consist in an increased left ventricular mass and a chronic left ventricular dilation. The enlargement of the ventricular cavities is due to a chronic flow overload in which the anemia and dialysis arteriovenous fistula play a dominant role. The increase in ventricular mass is usually less pronounced than the ventricular dilation and for a given arterial pressure the ventricular mass-to-volume ratio is inadequately low. The "inadequate" cardiac hypertrophy is more frequently observed in patients with severe secondary hyperparathyroidism and results in a chronic increase in ventricular stress and oxygen consumption. On the other hand, ESRD patients with aluminum overload exhibit an increased ventricular mass which compensates for ventricular dilation. The echocardiographic indices of ventricular systolic function are normal, contrasting with a pronounced impairment of diastolic properties. The impairment of ventricular filling is in part related to the increased left ventricular mass.

Parathyroid hormone and cardiovascular effects of dihydropyridines in chronic renal failure.

We studied the influence of parathyroid gland activity on cardiovascular response to dihydropyridines (nicardipine (NIC), 80 mg/day for 4 weeks) in 20 hypertensive patients with end-stage renal failure (ESRF). Before the treatment hyperparathyroidism (HPTH) was estimated on the basis of serum parathormone (PTH), and bone histomorphometry (osteoclastic resorption surfaces (ORS), and number of osteoclasts (NO]. NIC induced a significant decrease in systolic (SAP) and diastolic (DAP) arterial blood pressure, but did not significantly change the heart rate (HR) or the SAP X HR (myocardial oxygen consumption estimate). Changes in SAP and DAP were correlated to baseline serum PTH (P less than .001), to ORS (P less than .01) and to NO (P less than .01). Furthermore, a significant decrease in blood pressure was observed only in patients with histological signs of hyperparathyroidism (ORS greater than 1%). In this subset of patients NIC induced a significant decrease in SAP X HR (P less than .02) which was correlated to PTH and histomorphometric indexes of HPTH (P less than .01). The results of the present study show that blood pressure response to dihydropyridines in ESRF is associated with parathyroid activity as judged from serum PTH and bone histomorphometry.

Cardiac hypertrophy and arterial alterations in end-stage renal disease: hemodynamic factors.

Left ventricular (LV) hypertrophy is the most common cardiovascular alteration observed in end-stage renal disease patients. LV hypertrophy results from chronic flow and pressure overload and combines features of concentric and eccentric hypertrophy. The causes of chronic flow overload are the presence of AV shunt, salt and water overload, and anemia. The pressure overload is related to alterations of physical properties of large arteries characterized by an increased arterial and aortic stiffness. The systolic function of hypertrophied ventricle is preserved, but the diastolic filling is impaired. The ventricular hypertrophy progresses over the time on hemodialysis together with a progressive worsening of both systolic and diastolic functions.

Effects of antihypertensive agents on carotid pulse contour in humans.

The aim of this study was to assess the influence of antihypertensive agents on arterial wave reflections (AWR) and carotid pulse pressure (PP) in humans. Twenty patients with hypertension (predominantly systolic) were studied. After one month of placebo therapy they were randomly assigned to atenolol (At) 50 mg/day or to nitrendipine (Ni) 40 mg/day. Carotid pressure waveform was recorded noninvasively by applanation tonometry using a Millar micromanometer-tipped probe. Arterial wave reflections were quantified as the ratio of the height of the late systolic peak (delta P) to the total height of carotid pulse pressure wave as an augmentation index (delta P/PP). Travel time of the reflected wave (delta tp) was timed from the foot of the pressure wave to the foot of the late systolic peak. Atenolol and Ni were equally effective in reducing sphygmomanometric brachial artery blood pressure (BP). Whereas At (p < 0.05) and Ni (p < 0.01) reduced the carotid PP, Ni (p < 0.01) but not At significantly reduced delta P/PP. Both agents increased the delta tp (p < 0.01) and decreased aortic PWV (p < 0.01). Nitrendipine was associated with a decrease in left ventricular ejection time (LVET) (p < 0.01), while At increased heart period (p < 0.01) and LVET. The LVET/delta tp ratio decreased after Ni (from 3.25 +/- 0.77 to 2.42 +/- 0.73; p < 0.01) but did not change after At. The study shows, that for the same effect on peripheral BP, Ni has a more pronounced effect on pressure wave in central arteries, resulting from an improvement in the timing between the ventricular ejection and AWRs.

Iodine-131 ablation therapy for a patient receiving peritoneal dialysis.

The authors describe a patient with follicular thyroid carcinoma who was receiving continuous ambulatory peritoneal dialysis to manage end-stage renal disease. To deliver radioiodine therapy to ablate thyroid remnants safely and under optimal conditions, the behavior of 37 MBq (1 mCi) I-131 was followed daily for 3 days. Blood activity and total body count decreased with a half-life of 100 hours (4.17 days). The daily iodide removal rate, estimated as a percentage of the total administrated activity, was low: 5.3% to 8.6% in peritoneal dialysate and 1.3% to 2.2% in urine. The thyroid uptake, measured using a probe, was 2.4% to 2.1% from day 1 to day 3 and 1.9% later at day 8. The volume of thyroid remnants was determined by ultrasonography to be 0.6 g. The patient received a reduced ablative I-131 dose of 814 MBq (22 mCi). Radiation emitted from the patient after I-131 therapy, monitored using a radiation monitor probe located at a distance of 1 meter, decreased with an effective half-life of 70 hours (2.9 days). The integration of the curve from t = 0 showed a level always less than 25 microSv/hour as early as 24 hours after treatment. Because the iodine removal rate is continuous but low in a case of peritoneal dialysis, smaller therapeutic doses must be administered to deliver maximal radiation to residual thyroid tissue while minimizing excessive radiation exposure to patients, their families, and medical staff.

[Allogeneic immune response after blood transfusion in patients awaiting renal transplantation]. / Réponse immune allogénique après transfusion sanguine chez des malades en attente de transplantation rénale.

To investigate the mechanisms of the beneficial effect of blood transfusions (BT) on subsequent kidney transplant survival, we studied the influence of 3 planned BT on lymphocyte reactivity and on lymphocytotoxic antibody (LT) production in previously non-transfused uremic patients. A sustained and non-specific decrease in mixed lymphocyte reactivity (MLR) was observed in approximately 60% of the cases, whereas other patients had only a transient decrease but otherwise normal or even increased responses. Neither the pre-BT degree of immune responsiveness nor the clinical status of the patients had any influence on this phenomenon. Similarly, hepatitis B seroprophylaxy or vaccination did not interfere with this BT effect. Anti-HLA, LT, which are potentially harmful for the transplant, were noted in 13% of cases, while 13% additional cases displayed "cold" anti-B lymphocyte LT which do not have the same prognostic value. In some instances, suppression of cellular reactivity developed concurrently with LT production, which indicates that there is no interaction between cellular and humoral responses induced by BT.

[Is ligation of the remaining native ureter at the time of renal transplantation always harmless?]. / La ligature de l'uretère propre restant, lors des transplantations rénales, est-elle toujours anodine?

Three cases of nephrectomy after transplantation with uretero-ureteral anastomosis are presented: this anastomosis in transplantation looks to be anodyne when the transplant keeps normal function. Complications become when appears a degradation of the renal function.

[Cardiovascular repercussions of chronic hemodialysis]. / Retentissement cardio-vasculaire de l'hémodialyse chronique.

Coronary disease and left ventricular failure are the two main causes of death in haemodialysis patients. In these particular patients it is the accumulation of several risk factors rather than accelerated atherogenesis which seems to be the responsible for the frequent manifestations of a coronary disease which is sometimes difficult to diagnose. Independently of any cardiovascular history, the so-called "uraemic cardiopathy" is characterized by left ventricular dilatation associated with an increased myocardial mass but with a low mass/volume ratio. The systolic function is preserved whereas the ventricular diastolic compliance is altered due to the left ventricular hypertrophy.

Body height as a determinant of carotid pulse contour in humans.

AIM: The aim of this study was to assess the effect of body height on arterial wave reflections and the carotid pulse pressure contour in humans. METHODS: In 85 men, the carotid pulse wave and arterial wave reflections were determined from the common carotid artery pulse contour as recorded by applanation tonometry using a Millar micromanometer-tipped probe. The arterial wave reflection was calculated as the ratio of the height of the late systolic peak to the total height of the carotid pulse wave. The reflected wave was timed from the foot of the pressure wave to the foot of the late systolic peak. RESULTS: Multiple regression analysis showed that body height and aortic pulse wave velocity were the principal determinants of travel time of the reflected wave and of arterial wave reflections (P < 0.0001), short stature being associated with a short travel time and increased reflections (P < 0.0001). CONCLUSIONS: Body height is a determinant of arterial wave reflections and peak systolic blood pressure in humans.

Laboratory alluvial fans in one dimension.

When they reach a flat plain, rivers often deposit their sediment load into a cone-shaped structure called alluvial fan. We present a simplified experimental setup that reproduces, in one dimension, basic features of alluvial fans. A mixture of water and glycerol transports and deposits glass beads between two transparent panels separated by a narrow gap. As the beads, which mimic natural sediments, get deposited in this gap, they form an almost one-dimensional fan. At a moderate sediment discharge, the fan grows quasistatically and maintains its slope just above the threshold for sediment transport. The water discharge determines this critical slope. At leading order, the sediment discharge only controls the velocity at which the fan grows. A more detailed analysis reveals a slight curvature of the fan profile, which relates directly to the rate at which sediments are transported.

Width of laminar laboratory rivers.

A viscous fluid flowing over plastic grains spontaneously generates single-thread channels. With time, these laminar analogues of alluvial rivers reach a reproducible steady state, showing a well-defined width and cross section. In the absence of sediment transport, their shape conforms with the threshold hypothesis which states that, at equilibrium, the combined effects of gravity and flow-induced stress maintain the bed surface at the threshold of motion. This theory explains how the channel selects its size and slope for a given discharge. In this light, laboratory rivers illustrate the similarity between the avalanche angle of granular materials and Shields's criterion for sediment transport.