Pulsus Paradoxus: Causes and Clinical Significance

Introduction

Pulsus paradoxus is a medical sign characterized by an exaggerated drop in systolic blood pressure during inspiration (greater than 10 mmHg). Under normal conditions, there is a slight decrease in blood pressure during inhalation, but when this drop is excessive, it indicates an underlying pathology.

Causes of Pulsus Paradoxus

Pulsus paradoxus is most commonly associated with conditions that affect heart function or alter intrathoracic pressure. The major causes include:

1. Cardiac Causes

• Cardiac tamponade : The most classic cause. Fluid accumulation in the pericardial sac compresses the heart, limiting diastolic filling, which is further exacerbated during inspiration.
• Constrictive pericarditis : The rigid pericardium prevents normal heart expansion, leading to hemodynamic compromise.

2. Pulmonary Causes

• Severe asthma or chronic obstructive pulmonary disease (COPD) : Hyperinflation of the lungs increases negative intrathoracic pressure, exaggerating the normal drop in systolic blood pressure.
• Pulmonary embolism : Large emboli can impair right ventricular filling and consequently affect left ventricular output.

3. Hypovolemic Shock

• Reduced preload due to severe hypovolemia (e.g., from hemorrhage or dehydration) can mimic pulsus paradoxus by diminishing stroke volume further during inspiration.

4. Other Causes

• Tension pneumothorax : Increased intrathoracic pressure impairs venous return and heart function.
• Obstructive sleep apnea : Repeated inspiratory effort against an obstructed airway can create large swings in intrathoracic pressure.
• Severe anaphylaxis : Increased airway resistance and systemic hypotension contribute to hemodynamic instability.

Why is Pulsus Paradoxus Clinically Important?

Recognition of pulsus paradoxus can provide a critical clue for diagnosing life-threatening conditions such as cardiac tamponade or a severe asthma attack. Measuring it in clinical practice can aid in early intervention and appropriate management.

How is it Measured?

Pulsus paradoxus is assessed using a sphygmomanometer: 1. Inflate the cuff above systolic pressure. 2. Gradually deflate while listening for Korotkoff sounds. 3. Note the pressure at which sounds appear only during expiration. 4. Note the pressure at which sounds appear during both inspiration and expiration. 5. The difference between these two pressures gives the pulsus paradoxus value.

A drop >10 mmHg is considered significant.

Conclusion

Pulsus paradoxus is a key clinical sign seen in serious cardiac and pulmonary conditions. Understanding its causes helps in rapid diagnosis and treatment, particularly in emergencies like cardiac tamponade and severe asthma.

Source recommendations

1. American Heart Association Guidelines on Cardiac Tamponade

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2. European Society of Cardiology Guidelines on Pericardial Diseases

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3. Global Initiative for Asthma (GINA) Guidelines

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4. American Thoracic Society Guidelines on COPD

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