TRANSFER-FUNCTION ANALYSIS OF VENTILATORY INFLUENCE ON SYSTEMIC ARTERIAL-PRESSURE IN THE RAT

We evaluated the hypothesis that fluctuations in systemic arterial pre ssure (SAP) are under the influence of the respiratory pumping mechani sm subjected to a modulatory action by the autonomic nervous system th at is exerted primarily on the heart. Computer-generated broad-band me chanical ventilation (0-3 Hz) was applied to Sprague-Dawley rats that wore anesthetized with ketamine and paralyzed with pancuronium. We obs erved excellent coherence between lung volume and SAP signals at venti latory rates between 0.5 and 2.5 Hz; this coherence was unaffected by phentolamine, propranolol, atropine, bilateral vagotomy, or ventilator y stroke volume at 2-4 ml. Whereas bilateral vagotomy exerted no disce rnible effect, propranolol elicited a significant frequency-dependent (0.5-1.5 Hz) reduction in the magnitude of lung volume-SAP and lung vo lume-pulse pressure transfer functions. There was also a shift toward 0 degrees for the phase of the lung volume-SAP transfer function over the same frequency range. We conclude that the high-frequency componen t (0.8-2.4 Hz) of the SAP spectrum may be generated by the respiratory pumping mechanism. However, the lower-frequency end of this mechanica l influence is subjected to additional amplification by the autonomic nervous system, in which the beta-adrenergic system played a major rol e via its influence on the heart.