Pulsus paradoxus.

Abstract

Pulsus paradoxus is an increased inspiratory decline of systemic systolic blood pressure. The mechanism of pulsus paradoxus in cardiac tamponade was studied in closed-chest dogs. Superior and inferior caval flow, measured by electromagnetic flowmeter, increased during inspiration in control animals and during cardiac tamponade. Transpericardial pressure and pulmonary arterial flow increased with inspiration during cardiac tamponade. When systemic venous return was held constant, no degree of cardiac tamponade could produce a parodoxical pulse. With constant venous return, respiratory variations of intrathoracic pressure were faithfully transmitted into the pericardial space during the control state and during tamponade. Inspiratory fall in systemic systolic blood pressure during cardiac tamponade appeared to depend on three factors: increase in right ventricular output during the preceding expiration; inspiratory decline in intrathoracic pressure; inspiratory rise in intrapericardial pressure produced by increased right heart filling. In these experiments, inspiratory diaphragmatic stretch of the pericardium and failure of transmission of negative intrathoracic pressure into the pericardium did not seem to be important factors in the production of a paradoxical pulse.