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Heart rate response to hemodialysis-induced changes in potassium and calcium levels.

BACKGROUND
It is well known that hemodialysis affects cardiovascular functions, mainly because of excess body water removal. Conversely, the role of hemodialysis-induced modifications in body fluid characteristics is not yet well-grounded. In particular, the impact of modifications in plasma electrolytes on the pacemaking rhythm of the sinus node has not yet been evaluated.


METHODS
Eight patients on regular hemodialysis treatment were studied along a two-hour diffusive dialysis study session without fluid removal. Biochemical (metabolic and hormonal) as well as hemodynamic parameters were measured during the treatment. A computer model of the sinus node cell electrical activity was used to analyse the experimental data. The measured changes in electrolyte concentrations and pH were imposed as model inputs and the model-computed heart rate changes were validated against the measured ones. After validation, numerical simulation was used to obtain a quantitative evaluation of the comparative weight of calcium and potassium on heart rate changes, by simulating treatments leading to different changes in plasma concentrations of such electrolytes.


RESULTS
A significant heart rate increase (11%) was obtained following potassium, calcium and pH changes, with no significant variations in indices of autonomic activity. Simulation results revealed that calcium load and potassium removal both accelerate sinoatrial pacemaker beating. Concurrent changes in these electrolyte concentrations may cause heart rate to increase up to 30% at the end of hemodialysis. Heart rate sensitivity to extracellular potassium changes appears to be strictly dependent upon calcium concentration.


CONCLUSIONS
Hemodialysis-induced changes in calcium and potassium concentrations may greatly affect the rhythm of the sinus node pacemaker.