Changes in Heart Period, Heart Period Variability, and a Spectral Analysis Estimate of Respiratory Sinus Arrhythmias During Aortic Nerve Stimulation in Rabbits

ABSTRACT Changes in heart period, heart period variance (HPV), and the respiratory component of HPV were examined during enhanced negative chronotropic influences on the heart produced by aortic depressor nerve (ADN) stimulation in urethane anesthetized rabbits. Spectral analysis was used to quantify the respiratory component of HPV, respiratory sinus arrhythmia (RSA). The statistic derived from spectral analysis which describes RSA, V̂, has been proposed to be sensitive to vagal influences on the heart. Stimulation of the ADN significantly increased V̂, heart period, and HPV. However, unlike V̂ and heart period, HPV values remained elevated following the end of stimulation. Propranolol administration did not alter the magnitude of the evoked increase in V̂, heart period, or HPV. In contrast, administration of atropine abolished the increases due to stimulation in all three measures. Heart period exhibited a monotonic relationship with stimulation current intensity. This relationship disappeared after propranolol administration suggesting sympathetic mediation. The results suggest that V̂ is sensitive to manipulations of vagal influences on the heart. In addition, V̂ often responds in a different manner from heart period and HPV.