Tamponade Physiology and Pulsus Paradoxus

Pulsus Paradoxus = > 10 mmHg fall in systolic BP during inspiration.  To actually measure, inflate the cuff like normal, slowly deflate until your hear the Korotkoff sounds first during expiration.  Then deflate until the Korotkoff sounds are heard during the entire respiratory cycle.  If > 10 mmHg difference between the two, this is pulsus paradoxus which has >80% sensitivity for tamponade.

During normal inspiration, a little bit of pulsus paradoxus is normal, due to negative intrathoracic pressure leading to increased venous return to the right heart.  The right ventricle then bulges into the LV leading to a slight decrease in stroke volume.   However, this effect is minimal because the RV can also bulge outwards towards the pericardium.

In tamponade, however, the RV cannot bulge outwards because it is limited by the pericardial effusion, and the increase in R heart volume with inspiration can only be accommodated by bowing of the interventricular septum towards the left, leading to a decrease in LV stroke volume --> decreased cardiac output and BP.

Click here to learn more about how to measure pulsus paradoxus.

(Chanu Rhee MD, 10/19/10)