Transfer function analysis of ventilatory influence on systemic arterial pressure in the rat

We evaluated the hypothesis that fluctuations in systemic arterial pressure (SAP) are under the influence of the respiratory pumping mechanism subjected to a modulatory action by the autonomic nervous system that is exerted primarily on the heart. Computer-generated broad-band mechanical ventilation (0-3 Hz) was applied to Sprague-Dawley rats that were anesthetized with ketamine and paralyzed with pancuronium. We observed excellent coherence between lung volume and SAP signals at ventilatory rates between 0.5 and 2.5 Hz; this coherence was unaffected by phentolamine, propranolol, atropine, bilateral vagotomy, or ventilatory stroke volume at 2- 4 ml. Whereas bilateral vagotomy exerted no discernible effect, propranolol elicited a significant frequency-dependent (0.5-1.5 Hz) reduction in the magnitude of lung volume-SAP and lung volume-pulse pressure transfer functions. There was also a shift toward 0° for the phase of the lung volume-SAP transfer function over the same frequency range. We conclude that the high-frequency component 10.8-2.4 Hz) of the SAP spectrum may be generated by the respiratory pumping mechanism. However, the lower-frequency end of this mechanical influence is subjected to additional amplification by the autonomic nervous system, in which the β-adrenergic system played a major role via its influence on the heart.