What is Pulsus paradoxus?

Pulsus Paradoxus

Pulsus paradoxus is defined as an abnormal decrease in systolic blood pressure exceeding 10 mmHg during inspiration while diastolic blood pressure remains unchanged. 1

Definition and Measurement

• Pulsus paradoxus represents an exaggeration of the normal inspiratory decrease in systolic blood pressure that occurs during respiration
• While a slight decrease in systolic pressure during inspiration is physiological, a drop greater than 10 mmHg is considered pathological 1, 2
• Measurement technique:
  • Inflate blood pressure cuff above the patient's systolic pressure
  • Note when the first Korotkoff sounds appear during expiration
  • Continue deflating until sounds are heard throughout the respiratory cycle
  • The difference between these two pressure points is the measure of pulsus paradoxus 1

Mechanisms

The pathophysiology of pulsus paradoxus involves several interrelated mechanisms:

1. Ventricular interdependence: During inspiration, increased venous return to the right ventricle causes the interventricular septum to shift leftward, reducing left ventricular filling and stroke volume 1

2. Intrathoracic pressure changes: Inspiration creates negative intrathoracic pressure, which increases right ventricular filling while simultaneously decreasing left ventricular filling

3. Fixed cardiac volume: In conditions like cardiac tamponade, the total cardiac volume is fixed by the pericardial effusion, exaggerating the competition between ventricles for space 1

Clinical Significance and Associated Conditions

Pulsus paradoxus is an important clinical sign associated with several conditions:

• Cardiac tamponade: A key diagnostic finding requiring urgent evaluation 1
• Severe asthma or COPD exacerbations: The magnitude correlates with severity 2
• Constrictive pericarditis: Can present with pulsus paradoxus 3
• SVC obstruction: May cause pulsus paradoxus due to impaired right heart filling 1

Important Considerations

• The magnitude of pulsus paradoxus correlates with the severity of hemodynamic compromise 1
• Pulsus paradoxus may be absent in cardiac tamponade when certain conditions coexist, such as:
  • Left ventricular dysfunction
  • Atrial septal defect 1, 4
• In mechanically ventilated patients, the pattern is reversed: systolic BP is higher during inspiration than expiration 5

Diagnostic Value

• Valuable for diagnosing cardiac tamponade
• Useful in assessing severity of acute asthma and response to therapy
• Important for monitoring patients with pericardial effusions for development of tamponade physiology 1
• Modern echocardiography provides additional diagnostic information that complements the finding of pulsus paradoxus 1

Historical Perspective

The term has an interesting history:

• First described by Richard Lower in 1669 as a reduction in pulse volume during inspiration
• Described in bronchial asthma by Floyer in 1850
• The term "pulsus paradoxus" was coined by Adolf Kussmaul in 1873 in patients with constrictive pericarditis 3

The term "paradoxus" refers to the paradoxical disappearance of the pulse during inspiration while heart sounds remain audible, which seemed contradictory to early physicians 6.