Effect of respiration on venous return and stroke volume in cardiac tamponade

Measurements have been made of pressure and blood velocity in venae cavae and aorta in a patient with severe cardiac tamponade in whom there was pulsus paradoxus. The characteristic pressure changes of pulsus paradoxus were associated with variations in peak blood velocity in the ascending aorta and stroke output. Maximum filling of the right side of the heart occurred during inspiration, and was associated in time with minimum left ventricular stroke volume. These findings point to competition for space by the ventricles in the distended pericardial sac as being the major factor in the production of pulsus paradoxus.