Pulsus paradoxus is defined as a fall in systolic blood pressure by more than 10 mm Hg during which phase of respiration?

• A. Inspiration
• B. Expiration
• C. Both inspiration and expiration
• D. At rest

Answer: (A)

Pulsus paradoxus is an exaggerated drop in systolic blood pressure during inspiration. The best phase is inspiration, because with each breath in the intrathoracic pressure becomes more negative and venous return to the right heart increases. In conditions like cardiac tamponade, the rigid pericardium prevents the heart from accommodating that extra filling, causing the right ventricle to bulge outward and shift the interventricular septum toward the left ventricle. This reduces left ventricular filling and stroke volume, so systolic pressure falls by more than 10 mm Hg. During expiration, this shift reverses and systolic pressure returns toward baseline, so the abnormal drop is specifically seen with inspiration.