Changes in autonomic nerve activity during acute pericardial tamponade.

Acute experimental pericardial tamponade in anesthetized mongrel dogs produces marked alterations of autonomic reflex mechanisms. Afferent nerve activity from left ventricular receptors is inhibited during tamponade, whereas pericardial receptors are excited. Sympathetic efferent nerve activity traversing the ansae subclaviae is markedly increased during tamponade by the carotid sinus baroreceptor reflex and also by other undefined mechanisms. The increase in sympathetic activity produces a transient tachycardia and inotropic effect. A paradoxical increase vagal efferent nerve activity occurs during the period of maximal hypotension and appears to override the normal baroreceptor reflexes. This increase in vagal efferent activity corresponds to the development of a marked bradycardia during cardiac tamponade.