THE MECHANISM OF PULSUS PARADOXUS DURING ACUTE PERICARDIAL TAMPONADE *

A small fall in systemic arterial pressure during inspiration has been observed to occur in normal individuals. The term "pulsus paradoxus " has been applied to an accentuation of this phenome-non as it occurs in patients with pericardial tam-ponade. The mechanism for this increased re-spiratory variation of systemic arterial pressure during pericardial tamponade has interested many observers. Several explanations, based on ob-servations in experimental animals and man, have been proposed to explain the hemodynamic altera-tions responsible for pulsus paradoxus. Wood (1) has suggested that with the descent of the diaphragm during inspiration, traction is applied to the pericardium, raising intrapericardial pres-sure and interfering with left ventricular filling. Dornhorst, Howard, and Leathart (2), using an experimental model, claimed that filling of the right ventricle during inspiration raised intra-pericardial pressure, which then interfered with left ventricular filling. Much earlier, Katz and Gauchat (3) demonstrated a decrease in the pres-sure gradient between superior vena cava and right atrium during inspiration. On the basis of this observation, they postulated that a similar mechanism on the left side could explain the paradoxical pulse in pericardial tamponade. Recently, Sharp and co-workers (4) had an op-portunity to perform an acute tamponade experi-ment in a man who required permanent cannula-tion of the pericardial sac. Their data, not based on actual measurement of pulmonary venous and left atrial pressures, indicated that the mechanism suggested by Katz and Gauchat (3) for the ex