Pulsus Paradoxus: Pathogenesis and Clinical Findings Inspiration: Diaphragm and intercostal muscles contract
Author: Yan Yu, Victória Silva, Layla Al-Yasiri Reviewers: Sean Spence, Laura Craig, Juliette Hall, Raafi Ali, George Tadros. Shahab Marzoughi Nanette Alvarez* * MD at time of publication
Vascular pathology (rare)
Thoracic cavity expands
Lungs expand and intrathoracic pressure ↓
Physiologic:
↑ Venous return to right (R) heart
↑ R heart preload (volume of blood inside the ventricle right before it contracts)
↑ Blood pools in the right side of the heart
Obstructive lung diseases (e.g., COPD**, asthma**)
Hyperinflated lungs
↑ Stretching of pulmonary vessels at rest
On inspiration, ↑↑ stretching of pulmonary vessels
↑↑ Blood pools within pulmonary vasculature
↓↓ Flow to L heart
Pathologic: Constrictive pathologies (e.g., cardiac
tamponade**, constrictive pericarditis**) Decreased pericardial compliance
Constriction of ventricles
On inspiration, ↑ venous return to R heart (normal)
R ventricle unable to fully expand due to ↓ compliance
Septum bows into L ventricle
L ventricle unable to fully expand ↓↓ Filling of L heart
↓↓ L ventricular end diastolic volume
↓↓ L heart stroke volume ↓↓ Cardiac output Pulsus Paradoxus
Exaggerated ↓in systolic BP on inspiration (>10mmHg)
Air flows into the lungs
Pulmonary vessels are physically stretched/pulled
↑ Blood pools in pulmonary vessels
↓ Return of blood to left (L) heart
↓ L heart preload
↓ L heart stroke volume
↓ Cardiac output
Obstruction of superior or inferior vena cava (e.g., clot)
↓↓ Venous return to R heart at rest
↓↓ Right heart filling
↓↓ Blood flow to pulmonary arteries
Pulmonary embolism**
Clot occludes pulmonary arteries/ arterioles
↓↓ Flow to pulmonary veins
At rest, ↓↓ flow to L heart
On inspiration, ↓↓↓ flow to L heart
↓ Systolic blood pressure (BP) of < 10mmHg on inspiration BP = cardiac output x systemic vascular resistance **See corresponding Calgary Guide slides Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published Jan 21, 2013; updated Dec 3, 2024 on www.thecalgaryguide.com