Simultaneous identification of static and dynamic vagosympathetic interactions in regulating heart rate

We earlier reported that stimulation of either one of the sympathetic and v agal nerves augments the dynamic heart rate (HR) response to concurrent sti mulation of its counterpart. We explained this phenomenon by assuming a sig moidal static relationship between nerve activity and HR. To confirm this a ssumption, we stimulated the sympathetic and/or vagal nerve in anesthetized rabbits using large-amplitude Gaussian white noise and determined the stat ic and dynamic characteristics of HR regulation by a neural network analysi s. The static characteristics approximated a sigmoidal relationship between the Linearly predicted and the measured HRs (response range: 212.4 +/- 46. 3 beats/min, minimum HR: 96.0 +/- 28.4 beats/min, midpoint of operation: 19 6.7 +/- 31.3 beats/min, maximum slope: 1.65 +/- 0.51). The maximum step res ponses determined from the dynamic characteristics were 7.9 +/- 2.9 and -14 .0 +/- 4.9 beats.min(-1).Hz(-1) for the sympathetic and the vagal system, r espectively. Because of these characteristics, changes in sympathetic or va gal tone alone can alter the dynamic HR response to stimulation of the othe r nerve.