EFFECTS OF CONSTANT CARDIAC AUTONOMIC NERVE-STIMULATION ON HEART-RATE-VARIABILITY

Heart rate variability is used to assess cardiac autonomic tone. We so ught to determine the relationship of graded direct stimulation of eff erent cardiac autonomic nerves on heart rate variability in an anesthe tized canine model. Time and frequency domain variables were measured at denervated baseline and during electrical stimulation of the vagi a nd ansae subclaviae over a wide range of frequencies. Vagal and ansae stimuli produced significant changes in heart rate that correlated wit h the intensity of stimulation. Vagal stimulation resulted in small in creases in time domain indexes of heart rate variability and in the po wer spectrum from 0.04 to 0.40 Hz, but with no correlation between sti mulus intensity and changes in these indexes. By contrast, ansae stimu lation had no effect on time or frequency domain measures. In the abse nce of central modulation of autonomic outflow, indexes of heart rate variability reflect the presence of vagal input but do not correlate w ith the level of vagal tone and are unaffected by changes in mean symp athetic tone.