Mathematical Model to Characterize Internal Filtration

The course of hematocrit value along the length of a dialyzer's fiber: Hemoconcentration modeling and validation methods

OBJECTIVES

Contemporary therapies for chronic kidney disease patients encompass a wide range of hemodialysis treatments, most of which rely greatly on dialyzers and hemofilters. The filtration process taking place in these devices with respect to the hemodynamic characteristics of the flow, has not yet been fully investigated. This study aims at improving the understanding of hemodynamics in a dialyzer by employing experimental methods and mathematical models.

METHODS

A semiempirical model has been formulated based on the principles of hemodynamics, considering the dominant phenomena of filtration-backfiltration and the corresponding driving forces. An in vitro hemodialysis circuit was accordingly assembled for experimental data acquisition, and subsequently for model validation. The circuit consisted of two dialyzers arranged in sequential order, in pursuance of increasing the number of sampling points. Fresh, heparinized porcine blood was used throughout the course of this study. Pressure and flow data obtained from in vitro investigations with the hemodialysis circuit were used as an input for the semiempirical model.

FINDINGS

The model predicted a substantial divergence in the course of hematocrit value along the length of the hollow fibers, which is corroborated by the experimental data. Particularly in certain operational conditions, hematocrit rose from 25% at the inlet to 65% halfway along the dialyzers' length, to end at 30% at the outlet.

CONCLUSION

Validation of the model's predictions with experimental data demonstrated a very good agreement, confirming the model's accuracy. Potential implementation of the model in clinical practice in the future might contribute greatly to an improved hemodialysis experience.

Relative importance of residual renal function and convection in determining beta-2-microglobulin levels in high-flux haemodialysis and on-line haemodiafiltration

BACKGROUND

Convective blood purification improves beta(2)-microglobulin (beta(2)M) removal and may delay the onset of dialysis-related amyloidosis. We assessed the differential effects of high-flux haemodialysis (HD) and on-line haemodiafiltration (HDF) on plasma beta(2)M levels, given the enhanced convective capability of HDF.

METHODS

We measured pre-dialysis beta(2)M levels in 297 patients in a programme employing both high-flux HD and HDF, then analysed the relationship of beta(2)M to modality and other variables.

RESULTS

Independent determinants of plasma beta(2)M levels were residual renal function, age, HD vintage, and C-reactive protein load, but not the patient's predominant modality (high-flux HD or HDF). Patients with KRU levels <0.5 ml/min had significantly higher beta(2)M levels than patients with KRU between 0.5 and 1 ml/min.

CONCLUSIONS

Residual renal function is of overriding importance as a determinant of beta(2)M levels in HD patients and may supersede enhanced convective clearance by HDF. Beneficial effects extend to very low levels of residual renal function.