What is pulsus paradoxus and what are its respiratory causes?

 Pulsus paradoxus is an exaggerated fall in systolic blood pressure during inspiration.

Normally during inspiration, systolic BP falls slightly (≤10 mmHg).

In pulsus paradoxus, the fall is >10 mmHg.

Despite the name, there is no true paradox. The “paradox” refers to the fact that:

Heart sounds may still be heard,

But the peripheral pulse becomes weak or disappears during inspiration.

Mechanism

During inspiration:

More venous blood enters the right ventricle.

In conditions with limited cardiac space/filling (e.g., tamponade), the RV expands at the expense of the LV.

LV filling decreases → stroke volume falls → systolic BP drops markedly.

Conditions causing pulsus paradoxus

Cardiac causes

Cardiac tamponade (classic)

Constrictive pericarditis (less common)

Severe heart failure

Respiratory causes

Severe asthma

Severe COPD exacerbation

Tension pneumothorax

Massive pulmonary embolism