Electrical stimulation of the autonomic nervous system has been applied to modulate various physiologic functions. One example is the modulation of cardiac functions and hemodynamic performance using neural stimulation. The myocardium is innervated with sympathetic and parasympathetic nerves. Activities in these nerves, including artificially applied electrical stimuli, modulate the heart rate and contractility (strength of the myocardial contractions). Electrical stimulation applied to the parasympathetic nerves, such as the cardiac branch of the vagus nerve, is known to decrease the heart rate and the contractility, lengthen the systolic phase of a cardiac cycle, and shorten the diastolic phase of the cardiac cycle. Electrical stimulation applied to the sympathetic nerves is known to have essentially the opposite effects.
The ability of the electrical stimulation of the autonomic nerves in modulating the heart rate and contractility is utilized to treat abnormal cardiac conditions, such as to improve hemodynamic performance for heart failure patients and to control myocardial remodeling and prevent arrhythmias following myocardial infarction. However, the autonomic nervous system regulates functions of many organs of the body. Neural stimulation pulses delivered to the autonomic nervous system to treat a cardiac disorder may unintentionally modulate various other physiologic functions. Therefore, there is a need to prevent or control unintended, potentially adverse effects when neural stimulation is applied to the autonomic nervous system.