Very low-frequency heart rate variability wave amplitude and sympathetic stimulation--characterization and modeling.

The purpose of this study was to assess the relationship between very low-frequency heart rate variability (LFHR) wave amplitude and the degree of sympathetic stimulation. We developed a computerized system for the controlled increase of heart rate (HR) by isoproterenol (ISP), with which we obtained a series of stabilized HR levels in conscious freely moving rats. We found that LFHR amplitude rises gradually as a function of the average HR for each level until it reaches a point where additional increases in average HR are associated with gradual decrease in LFHR amplitude. We successfully built and fitted a model of LFHR amplitude to the experimental results. The fact that our model fits the experimental data well may suggest a possible relationship between our LFHR amplitude findings and the basic physiologic properties of the HR-ISP system inherent in our model.