Pulsus Paradoxus: Definition, common cause, Pathology and Clinical relevance

Definition

Pulsus paradoxus is an exaggerated fall in systolic blood pressure (>10 mmHg) during inspiration.

Normally, systolic BP falls slightly during inspiration (<10 mmHg).
When the drop is >10 mmHg, it is called pulsus paradoxus.

Despite the name “paradoxus”, the pulse does not actually disappear; it only becomes weaker or unpalpable during inspiration.

Normal Physiology

During inspiration:

Intrathoracic pressure decreases
Venous return to the right ventricle increases
RV expands
Interventricular septum shifts slightly toward the left ventricle
LV filling decreases slightly
Systolic BP falls by <10 mmHg

Mechanism of Pulsus Paradoxus

In certain conditions:

Excess RV filling or external compression
RV expansion pushes interventricular septum toward LV
LV filling markedly decreases
LV stroke volume falls
Systolic BP drops >10 mmHg during inspiration

Causes of Pulsus Paradoxus

Cardiac Causes

Cardiac Tamponade (classic cause)
Constrictive Pericarditis
Large pericardial effusion

Respiratory Causes

Severe Asthma
Chronic Obstructive Pulmonary Disease exacerbation

Other Causes

Tension Pneumothorax
Massive pulmonary embolism
Severe hypovolemia
Upper airway obstruction

How to Measure Pulsus Paradoxus

Using a sphygmomanometer:

Inflate cuff above systolic pressure.
Slowly deflate.
Note two pressures:

First pressure: Korotkoff sounds heard only during expiration
Second pressure: Sounds heard throughout inspiration and expiration

Difference between the two = Pulsus paradoxus

Example:

Expiration only = 120 mmHg
Throughout respiration = 105 mmHg

Pulsus paradoxus = 15 mmHg

Clinical Significance

A pulsus paradoxus >10 mmHg suggests serious cardiopulmonary disease, especially:

Cardiac tamponade
Severe asthma attack

Reverse Pulsus Paradoxus

Reverse pulsus paradoxus is a rare cardiovascular finding in which systolic blood pressure increases during inspiration, opposite to the normal drop seen in typical pulsus paradoxus. It is most commonly associated with conditions that alter intrathoracic pressure dynamics or ventricular interaction, such as positive pressure ventilation, hypertrophic obstructive cardiomyopathy (HOCM), isovolumetric ventricular pacing, and sometimes aortic regurgitation.

The mechanism usually involves enhanced left ventricular filling or reduced afterload during inspiration, leading to a paradoxical rise in systolic pressure. Clinically, it is less frequently encountered than classic pulsus paradoxus and is often identified in intensive care settings where patients are mechanically ventilated. Recognition of reverse pulsus paradoxus is important because it can provide clues about underlying cardiac physiology and ventilatory influences rather than indicating conditions like cardiac tamponade, which are linked to the traditional form.