Pulsus paradoxus

Background

• Definition: An exaggerated drop in systemic arterial pressure during inspiration (>10mmHg)

Physiology

• Inspiration is performed by decreasing intrathoracic pressure
• Because the heart is in the thorax, this pressure is transmitted to the heart and causes a bigger gradient between the pressure in the veins outside of the thorax and the right atrium/ventricle
• As such, with each inhalation, more blood flows into the right side of the heart
• When this occurs, the interventricular septum subtly bulges into the LV cavity, lowering LV filling, and therefore lowering systemic stroke volume/BP
• Because the ventricle can normally also expand outward, this septal shift is usually small, and the difference in the blood pressure is therefore small between inspiration and expiration (<10 mmHg)
• In states in which the ventricle cannot expand outward (e.g. tamponade) or in which the drop in intrathoracic pressure with inspiration is profound (e.g. status asthmaticus), the septal shift is exaggerated and the difference in BP is larger

Differential Diagnosis

Causes of pulsus paradoxus

• Moderate to severe cardiac tamponade
• Constrictive pericarditis
• Active COPD/asthma exacerbation

Evaluation

Measurement

Intermitent Korotkoff Sounds - All Korotkoff Sounds = Pulsus Pressure (normal = <10mmHg)

• Inflate manual BP cuff until Korotkoff sounds disappear
• Slowly deflate the cuff until Korotkoff sounds re-appear
  • At the highest BP when you hear sounds intermittently (rather than with every heart beat), note the blood pressure
  • This corresponds to the systemic blood pressure occurring during expiration
• Keep slowly deflating the cuff until you reach the highest BP when you hear sounds with every beat (no longer intermittent)
  • This corresponds to the systemic blood pressure during inspiration
• The difference between two pressures is the "pulsus paradoxus"
  • >10 mmH is considered significant

• Severe pulsus paradoxus can be palpated in the pulse as a weakening or disappearance of the pulse during inspiration

Evaluation

• Abnormal = >10mmHg
• Tamponade
  • Sensitivty = 80%
  • +LR = 3.3
  • -LR = 0.03

Management

• Treat underlying cause

See Also

• Cardiac Tamponade

References

• Stanford 25 Medical Blog (http://stanfordmedicine25.stanford.edu/the25/bppp.html)