• It refers to the decrease in the systolic blood pressure by more than 10mm Hg during inspiration
• Seen in
  • cardiac tamponade
  • constrictive pericarditis
  • obstructive pulmonary disease

The reason for the decrease in systolic blood pressure during inspiration is explained in this article : Inspiratory decrease in systolic blood pressure and pulse volume – Mechanism

Mechanism of pulsus paradoxus:

1. In cardiac tamponade
   • Tense fluid in the pericardial sac impairs ventricular filling
   • Also, the negative intrathoracic pressure is not well transmitted to the pericardial sac
   • Fall in pulmonary venous pressure is more than the fall in left atrial pressure
   • Hence filling of the left atrium and in turn the left ventricle is decreased resulting in decrease in stroke volume more than normal
2. In obstructive pulmonary disease
   • There is exaggeration of the inspiratory decrease in intrathoracic pressure
   • Hence the fall in stroke volume and blood pressure is more

What is the paradox?
Pulsus paradoxus is an exaggeration of the normal variation in the systolic blood pressure and hence it is not truly paradoxical.

1. Inspiratory decrease in systolic blood pressure and pulse volume – Mechanism
2. Frusemide in left ventricular failure
3. Reverse Bernheim effect
4. Pericardial fluid