Maximum size of drops levitated by an air cushion

Liquid drops can be kept from touching a plane solid surface by a gas stream entering from underneath, as it is observed for water drops on a heated plate, kept aloft by a stream of water vapor. We investigate the limit of small flow rates, for which the size of the gap between the drop and the substrate becomes very small, to obtain a full analytical description of stationary drop states and their stability. Above a critical drop radius no stationary drops can exist, below the critical radius two solutions coexist. However, only the solution with the smaller gap width is stable, the other is unstable. We compare to experimental data and use boundary integral simulations to show that unstable drops develop a gas "chimney" that breaks the drop in its middle.

Contact allergies in haemodialysis patients: a prospective study of 75 patients

BACKGROUND

Haemodialysis exposes patients to many potentially sensitizing allergens.

OBJECTIVES

The primary objective of this study was to evaluate the prevalence of delayed hypersensitivity in a population of haemodialysis patients. Secondary objectives were to identify the possible risk factors for contact sensitization and to propose a series of skin tests adapted to haemodialysis patients.

METHODS

A prospective monocentric study was carried out in a nonselected population of haemodialysis patients. For each patient, medical history of atopy and allergic contact dermatitis, ongoing treatments (including topical ones), presence of eczema at the site of vascular access for haemodialysis were recorded. Allergological investigation included delayed hypersensitivity tests (European Environmental and Contact Dermatitis Research Group battery, tests GERDA, additional list and a battery of antiseptics and other dialysis-specific allergens) and latex skin prick test.

RESULTS

Seventy-five patients (41 men, 34 women, mean age of 65 years old), with a mean 3.8 years under dialysis, were included. Nineteen patients (25%) had at least one positive skin test and 13 (17%) a positive patch test to at least one allergen relative to dialysis process including eight tests to lidocaine-prilocaine cream and three to povidone-iodine. Tests results seemed clinically relevant since nine patients had localized pruritus at the fistula site and six patients active eczema around it.

CONCLUSION

Contact sensitizations are frequent in haemodialysis patients and are linked to vascular access conditioning especially the use of lidocaine-prilocaine cream. Designing a specific test battery could help to diagnose the potential allergens and subsequently to give advice to avoid contact with sensitizing agents.

[Position statements regarding usage of biosimilars of Epoetins. Position paper of the Société de néphrologie, Société francophone de dialyse, and Société de néphrologie pédiatrique]

The European patents for epoetin alpha recently expired. Biosimilars (i.e. "a medicine which is similar to a biological medicine that has already been authorized" [EMEA 2007]) of epoetins have thus been released on the market in Europe. Because of the complexity of the processes that are required to produce medicinal products containing biotechnology-derived proteins as active substances and to characterize the physicochemical properties of these compounds, the guidelines that have been developed for generic drugs cannot be used for approval of biosimilar products. The EMEA guidelines do not answer all questions that have been raised for the development of biosimilars, and in some cases, decisions will have to be taken at a national level. This is why the Society of Nephrology (Société de néphrologie), the French-speaking Society of Dialysis (Société francophone de dialyse) and the Pediatric Society of Nephrology (Société de néphrologie pédiatrique) established guidelines for the usage of biosimilar epoetins concerning approval, identification, substitution of an innovator drug, post-marketing surveillance, extension of indication and pharmacovigilance plan.

Extreme resistance of superhydrophobic surfaces to impalement: reversible electrowetting related to the impacting/bouncing drop test

The paper reports on the comparison of the wetting properties of superhydrophobic silicon nanowires (NWs), using drop impact impalement and electrowetting (EW) experiments. A correlation between the resistance to impalement on both EW and drop impact is shown. From the results, it is evident that when increasing the length and density of NWs (i) the thresholds for drop impact and EW irreversibility increase and (ii) the contact-angle hysteresis after impalement decreases. This suggests that the structure of the NW network could allow for partial impalement, hence preserving the reversibility, and that EW acts the same way as an external pressure. The most robust of our surfaces shows a threshold to impalement higher than 35 kPa, while most of the superhydrophobic surfaces tested so far have impalement thresholds smaller than 10 kPa.

Pharmacodynamics of unfractionated heparin during and after a hemodialysis session

BACKGROUND

Anti-Xa activity is used as a clinical guide to anticoagulation with heparin, but heparin dosing regimens for hemodialysis were established before anti-Xa assays were developed; thus, the optimal regimen for heparin dosing was not determined. The aim is to confirm the interesting characteristics of unfractionated heparin pharmacokinetics for hemodialysis anticoagulation, provide insight into the hemorrhagic risk of hemodialysis patients, and determine the dose of unfractionated heparin and its adequate mode of administration.

STUDY DESIGN

Cross-sectional study of the pharmacokinetics of unfractionated heparin performed during and after a 4-hour midweek hemodialysis session.

SETTING & PARTICIPANTS

35 long-term hemodialysis patients at the Sainte-Marguerite Unit of the Marseille University Hospital, Marseille, France.

PREDICTOR

Hemodialysis anticoagulation with continuous unfractionated heparin infusion at a dose of 50 IU/kg/session (25 IU/kg/h during the first hour, 12.5 IU/kg during the second and third hours, and stop during the last hour).

OUTCOME & MEASUREMENTS

Anti-Xa activity was monitored during the 10 hours after the beginning of the hemodialysis session. Levels of 0.3 to 0.7 IU/mL are considered sufficient for anticoagulation. Pharmacokinetics was determined by using a population approach (nonlinear mixed-effects modeling). The final model and corresponding parameter values (including interindividual and residual variability) were used to simulate 1,000 replicates.

RESULTS

No case of clotting was recorded. A pharmacokinetic model with 1 compartment and first-order elimination best fitted the data. Terminal half-life was 54 minutes. Median anti-Xa activities were 0.55 IU/mL at peak, 0.25 IU/mL at end of the 4-hour session, and less than 0.1 IU/mL at 90 minutes after the session. We simulated a continuous infusion of the dose of 50 IU/kg for 1, 2, 3, and 4 hours. Peak values were 1.1, 0.8, 0.6, and 0.5 IU/mL, respectively. Values at the end of the session were 0.12, 0.18, 0.3, and 0.5 IU/mL, respectively. Values became less than 0.1 IU/mL at 15, 60, 105, and 120 minutes after the session, respectively.

LIMITATIONS

Interindividual variability in unfractionated heparin pharmacokinetics.

CONCLUSIONS

Unfractionated heparin administered by means of a 3-hour continuous infusion for hemodialysis anticoagulation provided an efficient and safe effect that quickly disappeared after the end of the session.

A bench to bedside view of uremic toxins

Reviewing the current picture of uremic toxicity reveals its complexity. Focusing on cardiovascular damage as a model of uremic effects resulting in substantial morbidity and mortality, most molecules with potential to affect the function of a variety of cell types within the vascular system are difficult to remove by dialysis. Examples are the larger middle molecular weight molecules and protein-bound molecules. Recent clinical studies suggest that enhancing the removal of these compounds is beneficial for survival. Future therapeutic options are discussed, including improved removal of toxins and the search for pharmacologic strategies blocking responsible pathophysiologic pathways.

Natural killer cell alterations correlate with loss of renal function and dialysis duration in uraemic patients

BACKGROUND

Natural killer (NK) cells provide a first line of immune defence towards infections and tumours, and participate in atherosclerosis and pregnancy diseases, of which there is a higher incidence in uraemic patients. Still, their relative contribution to the immunodeficient state associated with renal failure is poorly documented.

METHODS

A multivariate and comparative analysis of lymphocyte subsets in haemodialysed (HD) and undialysed (UD) uraemic patients in comparison to healthy donors (HC) is provided in this article. NK-mediated cytotoxicity, degranulation and interferon secretion were compared in HD and HC.

RESULTS

Evaluation of NK cells in 210 HD patients concluded with a decrease in NK cell counts in comparison to HC. Multivariate analysis associated lowered NK cell counts in UD patients with decreased renal clearance and higher NK counts HD with male gender and age. The 32% NK cell count decrease observed in sex- and age-matched groups (n = 88) was associated with B- and CD8(+)T-lymphocyte defects. NK cell functions were similar in subgroups of HD and HC matched for NK cell counts. Longer dialysis duration was associated with improved NK cytototoxic activity. While the expression of receptors modulating NK cytotoxicity were not modified, expression of the activation markers CD69 and NKp44, CD94 and chemokine receptors CX3CR1 and CXCR4 was altered in HD.

CONCLUSIONS

This study is the first to associate decrease in renal function with selective fading of NK cell number and identify haemodialysis duration as a factor influencing NK cell function. It further shows that lower cell counts rather than intrinsic NK cell dysfunction per se characterize immune disorders in HD.

Influence of parathyroidectomy on mortality in hemodialysis patients: a prospective observational study

BACKGROUND

In hemodialysis patients, the relationships between serum PTH and phosphorus levels and mortality are debated because both high and low turnover bone diseases increase the risk of vascular calcifications. Furthermore, the prevalence of hypoparathyroidism is increasing, and there is a fear that this state is associated with an increase in bone fractures.

METHODS

We performed a cross-sectional study to determine the prevalence and the causes of hypoparathyroidism (defined as basal and post-hypocalcemic-challenge serum PTH levels < 55 pg/mL) in 97 patients undergoing chronic hemodialysis treatment in our unit. We then prospectively observed patients with low PTH levels (< 55 pg/mL, n = 26) and those with hyperparathyroidism defined as a PTH levels > 200 pg/mL (n = 25) during eight years for all causes of mortality and bone fractures. Kaplan-Meyer survival curves were adjusted for age and sex.

RESULTS

Hypoparathyroidism was present in 30% of our patients. The main causes of hypoparathyroidism were parathyroidectomy (77%) and aluminium and iron overload. Survival did not differ between patients with hypoparathyroidism and hyperparathyroidism and between patients with serum phosphorus < or > 2 mmol/L. Parathyroidectomy was associated with better survival (p < 0.01). Similarly, incidence of bone fractures did not differ for the two groups.

CONCLUSIONS

Parathyroidectomy is the main cause of hypoparathyroidism in hemodialysis patients and is associated with a lower mortality risk. This result suggests that a more aggressive treatment of secondary hyperparathyroidism could decrease mortality in this high-risk population.

Vibration-induced climbing of drops

We report an experimental study of liquid drops moving against gravity, when placed on a vertically vibrating inclined plate, which is partially wetted by the drop. The frequency of vibrations ranges from 30 to 200 Hz, and, above a threshold in vibration acceleration, drops experience an upward motion. We attribute this surprising motion to the deformations of the drop, as a consequence of an up or down symmetry breaking induced by the presence of the substrate. We relate the direction of motion to contact angle measurements. This phenomenon can be used to move a drop along an arbitrary path in a plane, without special surface treatments or localized forcing.

Cardiac troponins I and T in hemodialysis patients without acute coronary syndrome

BACKGROUND

There is a reluctance to use cardiac troponins (cTn) for the monitoring of acute coronary syndrome (ACS) in hemodialysis (HD) patients because renal failure per se is thought to lead to increased cTn levels. The aim of this study was to analyse the proportion of patients with increased cTn levels in HD patients without ACS.

METHODS

cTnI was measured with the AccuTnI(trade mark) from Beckman (cTnI-B) and Troponin I Stat(trade mark) from Dade Behring (cTnI-DB) assays; cTnT was measured with the third generation assay from Roche. The study included 105 HD patients. The clinical outcomes were determined after 2.5 years.

RESULTS

Considering the receiver operator characteristic (ROC) cutoff, the proportion of patients with elevated cTnI-B, cTnI-DB and cTnT levels was respectively 2%, 3% and 27%. The proportion of patients with abnormal cTn values increased when a lower cutoff value was considered, based on the 99th percentile of a reference population with a coefficient of variation of less than 10% (99th percentile-10% CV cutoff). The proportion of patients with elevated values did not differ before and after the HD session. The 2.5 years mortality was associated with increased levels of cTnT but not with increased levels of cTnI.

CONCLUSIONS

When the ROC cutoff is applied, cTnI assays are suitable for the monitoring of ACS in HD patients. cTnT could lead to false positive diagnosis of myocardial infarction, however it is predictive of long-term mortality. The 99th percentile-10% CV cutoff does not seem appropriate in HD patients.

Stabilized Kuramoto-Sivashinsky equation: a useful model for secondary instabilities and related dynamics of experimental one-dimensional cellular flows

We report numerical simulations of one-dimensional cellular solutions of the stabilized Kuramoto-Sivashinsky equation. This equation offers a range of generic behavior in pattern-forming instabilities of moving interfaces, such as a host of secondary instabilities or transition toward disorder. We compare some of these collective behaviors to those observed in experiments. In particular, destabilization scenarios of bifurcated states are studied in a spatially semi-extended situation, which is common in realistic patterns, but has been barely explored so far.

Review on uraemic solutes II--variability in reported concentrations: causes and consequences

The aim of this manuscript is to initiate a constructive discussion about deviations in measured concentrations of uraemic solutes; these deviations, if not perceived or handled appropriately, may lead to incorrect interpretations of the pathophysiological role of uraemic solutes and/or to erroneous therapeutic decisions. To come to an objective approach towards this problem, variability analysis of reported concentrations may be of help. Striking outliers should either be discarded or considered together with other values which are more consistent with the majority of reported data.

The uremic solute indoxyl sulfate induces oxidative stress in endothelial cells

BACKGROUND

Endothelial dysfunction and oxidative stress are matters of concern in patients with chronic renal failure (CRF). Uremic solutes retained in these patients could be involved in these processes. Notably, the protein-bound uremic solute indoxyl sulfate induces endothelial dysfunction in vitro, and has shown pro-oxidant effects.

OBJECTIVE

To demonstrate that indoxyl sulfate is a potential mediator of oxidative stress in endothelial cells in vitro.

METHODS

Indoxyl sulfate-induced oxidative stress in human umbilical vein endothelial cells (HUVEC) was studied by measuring reactive oxygen specie (ROS) production by cytofluorimetry, by analyzing the involvement of the pro-oxidative enzymes NAD(P)H oxidase, xanthine oxidase, and NO synthase, and by measuring the levels of the non-enzymatic antioxidant glutathione.

RESULTS

We showed that indoxyl sulfate induced a significant production of ROS in HUVEC, with or without human serum albumin. We then investigated the role of pro-oxidative enzymes and measured the levels of the antioxidant glutathione. The NAD(P)H oxidase inhibitors, DPI, and apocynin, inhibited ROS production, whereas inhibitors of xanthine oxidase, NO synthase, and mitochondrial ROS had no effect. Interestingly, indoxyl sulfate strongly decreased the levels of glutathione, one of the most active antioxidant systems of the cell. In addition, the ROS production mediated by indoxyl sulfate was inhibited by the antioxidants vitamin C, vitamin E, and NAC.

CONCLUSION

The uremic solute indoxyl sulfate enhances ROS production, increases NAD(P)H oxidase activity, and decreases glutathione levels in endothelial cells. Thus, indoxyl sulfate induces oxidative stress by modifying the balance between pro- and antioxidant mechanisms in endothelial cells.

Relationship between A2A Adenosine Receptor Expression and Intradialytic Hypotension during Hemodialysis

BACKGROUND

Intradialytic hypotension (IDH) is a common complication of hemodialysis sessions (HDSs). Adenosine may contribute to the drop in blood pressure during IDH events because it has hypotensive effects. As A(2A) adenosine receptor expression is essential for blood pressure control, we compared the expression of A(2A) receptors (Bmax, K(D), and messenger ribonucleic acid [mRNA] levels) in peripheral blood mononuclear cells from IDH and non-IDH patients and from controls. We also evaluated adenosine plasma levels (APLs).

METHODS

We included 10 hemodialyzed patients with at least three IDH events per month. We also included 11 hemodialyzed patients with no history of IDH events and 10 healthy subjects as controls.

RESULTS

IDH patients had higher Bmax values than non-IDH patients (mean before HDS, +86%; after HDS, +112%), whereas non-IDH patients had lower Bmax values than controls (mean -72%). K(D) values were not significantly different between patients and controls. The levels of mRNA increased significantly during HDS but without an increase in receptor expression on the cell membranes. APLs were higher in hemodialyzed patients than in controls.

CONCLUSION

We found that A(2A) receptors are more expressed in IDH patients than in non-IDH patients, whereas APL was high in all patients. Both high APL and a relative increase in A(2A) receptor expression may favor IDH events.

Population pharmacokinetics of ceftriaxone and pharmacodynamic considerations in haemodialysed patients

OBJECTIVES

To determine the pharmacokinetic parameters of ceftriaxone following an infusion in haemodialysed outpatients and to use these parameters for an optimisation of dosing based on pharmacodynamic indices.

METHODS

Fifty haemodialysed patients were enrolled in a single-centre, prospective, open-label study. They received short intravenous infusions of ceftriaxone 1 or 2 g every 48 hours for bronchopneumonia immediately after the dialysis session. Total plasma concentrations of ceftriaxone were analysed with a population pharmacokinetic approach using nonlinear mixed-effects modelling. Free drug concentrations were derived from published binding parameters in order to estimate the time when they exceed the minimum inhibitory concentration (MIC).

RESULTS

The pharmacokinetics were best described by a two-compartment model. None of the covariates tested (age, bodyweight, height, sex, body mass index, albumin) influenced the pharmacokinetic parameters. The estimated population pharmacokinetic parameters (interindividual variability [percentage of coefficient of variation]) were clearance 0.36 L/h (48%), volume of distribution of the central compartment 4.53 L (47%), intercompartmental clearance 10.8 L/h and volume of distribution of the peripheral compartment 9.54 L (63%). The terminal elimination half-life (t(1/2)beta) from plasma was 27.5 hours. The mean (range) times when the free drug concentration exceeded the MIC (T>MIC) following ceftriaxone 1 g infusion were 60.3 (53.0-67.7) hours and 2.5 (1.0-3.9) hours for the breakpoints 1 and 8 mg/L (based on free drug concentration), respectively. After administration of ceftriaxone 2 g, the T>MIC was 88.5 (78.8-98.3) hours and 17.7 (13.3-22.0) hours for the breakpoints 1 and 8 mg/L, respectively. The simulated free drug concentrations (median, first and third quartile) for 48 and 72 hours following the first dose of ceftriaxone 1g were 1.11, 0.63 and 1.89 mg/L, and 0.63, 0.28 and 1.18 mg/L, respectively. For ceftriaxone 2g infusion, the simulated free concentrations (median, first and third quartile) at 48 and 72 hours were 2.50, 1.40 and 4.52 mg/L, and 1.37, 0.60 and 2.70 mg/L, respectively.

CONCLUSIONS

On the basis of decreased clearance in haemodialysed patients, it can be argued that the dose of ceftriaxone should be decreased or the delay between doses should be increased. However, taking into account pharmacodynamic considerations, this study showed that following intravenous administration of ceftriaxone 1 g after each dialysis session, some patients were at risk of achieving a concentration below the MIC (1 mg/L), particularly if the second administration occurred 72 hours after the first dosing. Thus, a dose of ceftriaxone 2 g intravenously is recommended immediately following dialysis, particularly in patients with severe infections or when the dosing interval will be higher than 48 hours.

The uremic solute p-cresol decreases leukocyte transendothelial migration in vitro

Chronic renal failure (CRF) patients display an immunodeficiency state, and uremic solutes that accumulate during CRF may be involved in this immunodeficiency. In this study, we examined whether the uremic solute para-cresol (p-cresol), at concentrations similar to those found in patients, alters leukocyte transmigration in vitro. We found that p-cresol significantly inhibited monocyte THP-1 cell line and PBMCs transmigration across IL-1beta-stimulated human umbilical vein endothelial cell (HUVEC) in a static two-compartment model. This inhibitory effect of p-cresol persisted in the presence of a physiologic concentration of human serum albumin. In order to investigate the mechanism involved, expression of endothelial chemokines, fractalkine, monocyte chemoattractant protein 1 (MCP-1) and IL-8 and membrane expression of junctional adhesion molecule A (JAM-A or JAM-1) were studied. We found that p-cresol decreased mRNA expression of the chemokine fractalkine in IL-1beta-stimulated HUVEC, without modifying mRNA expression of MCP-1 and IL-8. In addition, p-cresol decreased IL-1beta-induced expression of membrane-bound and soluble forms of fractalkine and impaired the membrane expression of JAM-A. Taken together, these results suggest that p-cresol, by impairing leukocyte transendothelial migration, plays a role in the immune dysfunction of uremic patients.

Propagating wave pattern on a falling liquid curtain

A regular pattern of surface waves is observed on a liquid curtain falling from a horizontal, wetted tube, maintained between two vertical wires. Since the upper boundary is not constrained in the transverse direction, the top of the curtain enters a pendulum-like motion, when the flow rate is progressively reduced, coupled to the propagation of curtain undulations, structured as a checkerboard. This structure is formed by two patterns of propagating waves. In some sense, these propagating patterns replace the stationary pattern of liquid columns observed at a lower flow rate. Measurements of phase velocity, frequency, and wavelength are reported. The data are in agreement with a simple dimensional argument suggesting that the wave velocity is proportional to the surface tension divided by the mass flux of liquid per unit length. This scaling is also that followed by the fluid velocity at the so-called transonic point, i.e., the point where the fluid velocity equals that of sinuous waves. We finally discuss the implications of these results for the global stability of liquid curtains.