Vagal nerve activity and the high frequency peak of the heart rate variability

For the Quality of life (QOL) of patients with an artificial heart system, monitoring an information of the cardiovascular control system may be impor tant. We have been evaluating the autonomic nervous system for that purpose . Recently fluctuations in hemodynamic parameters including heart rate vari ability (HRV) were evaluated by means of spectral analysis and nonlinear ma thematical analysis. Respiratory wavers in HRV were thought ro reflect ongo ing information of the parasympathetic nerve activity. Is it true? In order to confirm this hypothesis, we recorded vagal nerve activity directly in t he chronic animal experiments. Six healthy adult goats were anesthetized wi th Halothene inhalation and thoracotomy were performed by the fourth lib re section during mechanical ventilation. Arterial blood pressure, right and l eft atrial pressures were continuously monitored with the catheter insertio n. Cardiac output was measured by the electromagnetic flowmeter attached to the ascending aorta. After the chest was closed, incision was made to the left neck and left vagal nerve was separated. Stainless steel electrodes we re inserted into the vagal nerve and fixed by the plasticizer. After the in cision was closed, the goats were transferred to the cage and extubated aft er waking. Hemodynamic parameters and vagal nerve activity were measured in the awake condition. The results showed that clear observation of the auto nomic nerve discharges were embodied by this experimental system. The vagal nerve discharges were synchronized with heart beat and respiration. The va gal nerve tonus was significantly influenced by the hemodynamic alteration. However in some condition, the respiratory wave was not always consistent with tonus of the vagal nerve activity, thus suggesting that we should chec k another information to evaluate the parasympathetic tone. We must continu e this study to evaluate an autonomic nerve during artifical heart circulat ion.