What is pulses paradoxus?

Pulsus Paradoxus: Definition, Measurement, and Clinical Significance

Pulsus paradoxus is defined as an abnormal decrease in systolic blood pressure exceeding 10 mmHg during inspiration while diastolic blood pressure remains unchanged. 1, 2

Definition and Pathophysiology

Pulsus paradoxus represents an exaggeration of the normal physiological decrease in systolic blood pressure that occurs during inspiration. While a slight decrease (typically <10 mmHg) is normal during respiration, a drop greater than 10 mmHg is considered abnormal and clinically significant.

The key characteristics of pulsus paradoxus include:

• Inspiratory decrease in systolic blood pressure >10 mmHg
• Diastolic blood pressure remains unchanged
• The pulse becomes weaker or may disappear during inspiration (hence the term "paradoxical")

Measurement Technique

According to the European Society of Cardiology guidelines, pulsus paradoxus is measured as follows 1:

1. Inflate the blood pressure cuff above the patient's systolic pressure
2. During slow deflation, note when the first Korotkoff sounds appear (only during expiration)
3. Continue deflation until sounds are heard throughout the respiratory cycle
4. The difference between these two pressure points is the measure of pulsus paradoxus

This can also be detected clinically by feeling the pulse, which becomes noticeably weaker during inspiration in patients with significant pulsus paradoxus.

Clinical Significance

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

1. Cardiac Tamponade

• Most significant association - a key diagnostic finding 1
• Results from increased pericardial pressure causing exaggerated ventricular interdependence
• The magnitude correlates with the severity of hemodynamic compromise

2. Constrictive Pericarditis

• Can be present due to similar hemodynamic effects as tamponade

3. Respiratory Conditions

• Severe asthma or COPD exacerbations
• Results from exaggerated intrathoracic pressure swings during respiration

4. Superior Vena Cava Thrombosis

• Can produce pulsus paradoxus due to impaired right heart filling 2

Pathophysiological Mechanisms

The mechanisms underlying pulsus paradoxus involve:

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

2. Intrathoracic Pressure Changes: Negative intrathoracic pressure during inspiration increases right ventricular filling while simultaneously decreasing left ventricular filling

3. Fixed Cardiac Volume: In conditions like cardiac tamponade, the total cardiac volume becomes fixed, making ventricular interdependence more pronounced

Clinical Applications

Pulsus paradoxus is valuable in:

• Diagnosing cardiac tamponade - a key clinical sign that should prompt urgent evaluation 1
• Assessing severity of acute asthma and response to therapy
• Monitoring patients with pericardial effusions for development of tamponade physiology

Important Caveats

• Pulsus paradoxus may be absent in cardiac tamponade when certain conditions coexist (e.g., left ventricular dysfunction, atrial septal defect) 1
• It can be present in conditions other than cardiac tamponade
• The magnitude correlates with the severity of the underlying condition
• Modern echocardiography provides additional diagnostic information that complements the finding of pulsus paradoxus

Understanding pulsus paradoxus and its proper measurement remains an important clinical skill, particularly in emergency settings where rapid diagnosis of conditions like cardiac tamponade can be life-saving.