Effect of electrolyte and pH changes on the sinus node pacemaking in humans.

The importance of plasma electrolytes and pH levels in determining heart rate is not yet well grounded. Hemodynamic and biochemical data were collected during 8 purely diffusive hemodialysis, which allowed changes in extracellular fluid to be achieved without eliciting notable changes in the autonomic control of heart rate. A significant heart rate increase was obtained after potassium decrease and calcium and pH increase, with no significant variations in indices of autonomic activity. Model-based computer simulations were then used to separate the effects of each ionic species and pH on sinus node cell pacemaker activity. This analysis revealed that changes in physiological range of potassium, calcium, and pH could cause large heart rate variations from 60 to 90 bpm. Nonlinear heart rate dependence on potassium was also recognized. It was concluded that electrolyte and pH changes in physiological range have an important, complex, impact on the pacemaking rhythm independently of autonomic outflow.