Mathematical model of calcium exchange during haemodialysis using a citrate containing dialysate

Putative mechanobiological impact of surface texture on cell activity around soft-tissue implants undergoing micromotion

Recent reports of adverse health effects (e.g., capsular contracture, lymphoma) linked to the absence or presence of texture on soft-tissue implants (e.g., breast implants) suggest surface topography may have pathological impact(s). We propose that surface texture influences the transfer of displacements, experienced by an implant undergoing micromotion, to surrounding interfacial extracellular matrix, which in turn impacts the activity of the resident cells and is based on degree of tissue integration. We hypothesize that transfer of displacements due to micromotion promotes interstitial fluid movement that imposes hydrodynamic stresses (pressures, shear stresses) on cells residing in the interfacial tissues and impacts their activity. To address this, we developed a computer simulation to approximate hydrodynamic stresses in the interstitial environment of saturated poroelastic tissues (model soft-tissue implantation sites) generated from oscillatory implant micromotion as a function of the magnitude of translational displacement, direction of motion, degree of tissue integration, and surface roughness of the implant. Highly integrated implants were predicted to generate the highest fluid shear stresses within model tissues, with oscillatory fluid shear stresses up to 80 dyn/cm² for a 20-μm displacement. Notably, application of oscillatory 80 dyn/cm² shear stress to cultured human fibroblasts elicited cell death after 20 h compared to cells maintained under static conditions or exposed to 80 dyn/cm² steady, unidirectional shear. These results indicate that oscillatory interstitial fluid stresses generated by micromotion of an integrated implant may influence the activity of the surrounding cells and play a role in the body's fibrotic response to textured soft-tissue implants.

Using a Human Circulation Mathematical Model to Simulate the Effects of Hemodialysis and Therapeutic Hypothermia

Background: We developed a hemodynamic mathematical model of human circulation coupled to a virtual hemodialyzer. The model was used to explore mechanisms underlying our clinical observations involving hemodialysis. Methods: The model consists of whole body human circulation, baroreflex feedback control, and a hemodialyzer. Four model populations encompassing baseline, dialysed, therapeutic hypothermia treated, and simultaneous dialysed with hypothermia were generated. In all populations atrial fibrillation and renal failure as co-morbidities, and exercise as a treatment were simulated. Clinically relevant measurables were used to quantify the effects of each in silico experiment. Sensitivity analysis was used to uncover the most relevant parameters. Results: Relative to baseline, the modelled dialysis increased the population mean diastolic blood pressure by 5%, large vessel wall shear stress by 6%, and heart rate by 20%. Therapeutic hypothermia increased systolic blood pressure by 3%, reduced large vessel shear stress by 15%, and did not affect heart rate. Therapeutic hypothermia reduced wall shear stress by 15% in the aorta and 6% in the kidneys, suggesting a potential anti-inflammatory benefit. Therapeutic hypothermia reduced cardiac output under atrial fibrillation by 12% and under renal failure by 20%. Therapeutic hypothermia and exercise did not affect dialyser function, but increased water removal by approximately 40%. Conclusions: This study illuminates some mechanisms of the action of therapeutic hypothermia. It also suggests clinical measurables that may be used as surrogates to diagnose underlying diseases such as atrial fibrillation.

Determinants of Hemodialysis Performance: Modeling Fluid and Solute Transport in Hollow-Fiber Dialyzers

Hemodialysis constitutes the lifeline of patients with end stage renal disease, yet the parameters that affect hemodialyzer performance remain incompletely understood. We developed a computational model of mass transfer and solute transport in a hollow-fiber dialyzer to gain greater insight into the determinant factors. The model predicts fluid velocity, pressure, and solute concentration profiles for given geometric characteristics, membrane transport properties, and inlet conditions. We examined the impact of transport and structural parameters on uremic solute clearance by varying parameter values within the constraints of standard clinical practice. The model was validated by comparison with published experimental data. Our results suggest solute clearance can be significantly altered by changes in blood and dialysate flow rates, fiber radius and length, and net ultrafiltration rate. Our model further suggests that the main determinant of the clearance of unreactive solutes is their diffusive permeability. The clearance of protein-bound toxins is also strongly determined by blood hematocrit and plasma protein concentrations. Results from this model may serve to optimize hemodialyzer operating conditions in clinical practice to achieve better clearance of pathogenic uremic solutes.

Impact of the dialysate acid component on haemodialysis mortality rates

BACKGROUND

No prospective study has evaluated the long-term effect on mortality of the new acid concentrates added to bicarbonate dialysate. The aim of this pharmacoepidemiological study was to evaluate the association between hydrochloric or citric acid-based dialysate and mortality on haemodialysis (HD).

METHODS

This study included 117 796 patients with 3 723 887 months on HD recorded in the national French Renal Epidemiology and Information Network registry. Dialysate acid components were retrospectively reconstructed for each facility. All patients on HD were associated each month with an exposure based on that at their facility of treatment. We took each patient's time-varying exposure into account to calculate the monthly mortality rates for each exposure. Incidence rate ratios (IRRs) for mortality were calculated with a Poisson regression, with acetic acid as the reference. Regressions were adjusted for initial clinical characteristics (age, gender, previous cardiovascular events, active malignancy, diabetes, pulmonary disease, mobility), dialysis technique and location (in-centre, outpatient centre, self-care unit) and ESRD vintage, updated monthly.

RESULTS

The crude mortality rate per 1000 patient-months with citric acid {11.5 [95% confidence interval (CI) 11.1-12.0]} was lower than with either acetic acid [12.9 (95% CI 12.8-13.1)] or hydrochloric acid [12.8 (95% CI 12.2-13.5)]. For the 2014-17 period, the IRR for mortality with citric acid [adjusted IRR 0.94 (95% CI 0.90-0.99)] and with hydrochloric acid [adjusted IRR 0.86 (95% CI 0.79-0.94)] were significantly lower than with acetic acid.

CONCLUSION

This post-marketing study of long-term exposure to dialysate acidifiers at the patient level found the use of citric and hydrochloric acid-based dialysates, compared with acetic acid, was associated with lower mortality.