Assessment of autonomic cardiac control by power spectrum of heart rate fluctuations. Effect of neural ablation and suppression of efferent sympathetic nerve traffic

Overview

Heart rate is known to fluctuate at the frequency of respiration as well as at lower frequencies (0.04 Hz and 0.12 Hz). There is strong evidence for a significant role of the autonomic nervous system in mediating these oscillations. The present investigation demonstrates that in an anesthetized dog bilateral cervical vagotomy virtually abolishes heart rate fluctuations above 0.1 Hz and reduces the amplitude of fluctuations in the 0.02-0.1 Hz band by 81%. The residual low-frequency oscillations can be nearly abolished by subsequent abalation of the stellate ganglia. Three of four vagotomized dogs, elimination of negative intrathoracic pressure further reduced the very small remaining respiratory sinus arrhythmia by 82% to 97% suggesting the presence of a very small non-vagal component in the genesis of this arrhythmia Administration of the serotonin precursor 5-hydroxytryptophan has been shown to reduce sympathetic traffic to the heart. In 9 of 11 vagotomized dogs, 5-hydroxytryptophan attenuated low-frequency heart rate fluctuations by 86.7%, probably reflecting reduced activity of the sympathetic nervous system. Two dogs responded with enhanced oscillations. These results confirm the central role of the autonomic nervous system in the regulation of heart rate. The heart rate power spectrum represents a sensitive method to study neural cardiovascular control and the activity of the autonomic nervous system.