EFFECT OF SYMPATHETIC MODULATION AND SYMPATHOVAGAL INTERACTION ON HEART-RATE-VARIABILITY IN ANESTHETIZED DOGS

Changes in the function of the autonomic nervous system underlying cha nges in heart rate variability are not fully understood. Furthermore, decreased heart rate variability has been found to be related to poor prognosis, for example, in patients with coronary artery disease. Our aim was to study how modulation in sympathetic stimulation at various frequencies is transferred into heart rate variation, and how the inte raction between sympathetic and parasympathetic inputs can affect the high-frequency component of heart rate variability. We stimulated elec trically cardiac sympathetic and vagal nerves in anaesthetized, vagoto mized, spinal anaesthetized dogs. We controlled the frequency and magn itude of the modulation in programmed stimulation patterns and analyse d the resulting changes in heart rate variability by power spectral an alysis. We found that modulations in sympathetic stimulation were refl ected in the high-frequency component of heart rate variability, as we ll as in the low- and medium-frequency components. In addition, a nove l finding was that sympathetic stimulation reduced the magnitude of th e high-frequency variations caused by vagal stimulation. This suggests that, although the high-frequency component of heart rate variability is mainly under parasympathetic regulation, it may also be influenced by the sympathetic nervous system.