Effects of drugs on the autonomic control of short-term heart rate variability

The autonomic nervous system links the brain and the heart. Efferent links in the neural control of the heart consist of sympathetic and parasympathet ic (vagal) fibers innervating the sinus node. Because sympathetic and vagal firing alter spontaneous sinus node depolarization, cardiac rate and rhyth m convey information about autonomic influences on the heart. The easy avai lability of ECG rendered possible the assessment of sinus rhythm as an inde x of autonomic outflow. The frequency-domain approach uses non-invasive rec ordings and appears to provide a quantitative evaluation of the: autonomic modulation of cardiovascular function. Spectral profiles resulting from vag al or sympathetic blockades at the cardiac Cor vascular) revel might be use d as references to unravel the mechanism of action of the drug under examin ation. A more comprehensive assessment will be obtained if spectral analysi s is used as a complement to existing techniques applied for describing the neurohumoral status of patients (microneurographic recordings, norepinephr ine spillover). This review also reports some pitfalls encountered in varia bility studies. (C) 2001 Elsevier Science B.V. All rights reserved.