Neural effects on SA node action potential and interbeat interval-a model study

Cardiac sinoatrial (SA) node activity is known to be influenced by the sympathetic and parasympathetic branches of the autonomic nervous system. The two branches connect to the SA node cells via different synapses, and affect differently their action potential (AP) shape and timing. The authors describe a model constructed to study these interactions. The model contains several linear as well as nonlinear subsystems, which have been reported to model the physiological processes involved. The model produces under steady state conditions, with no neural activity, AP sequences with intervals of about 360 ms. Under step increases of either [NE] or [ACh], nonlinear cycle length changes occur-some 30% decrease from control for sympathetic activity, and some 81% increase for parasympathetic activity. The simulation results, when stimulating the model with either of the two input signals, are in general agreement with the experimental findings that the system behaves as a low-pass filter