Pulsus paradoxus
Synonyms and keywords:  PP; paradoxic pulse; paradoxical pulse

# Overview
Pulsus paradoxus  is an exaggeration of the normal variation in the pulse and drop of systolic blood pressure during the inspiratory phase of respiration, in which the pulse becomes weaker as one inhales and stronger as one exhales. It is a sign that is indicative of several conditions including cardiac tamponade and lung diseases (e.g. asthma, COPD).

# Mechanism of Reduced Blood Pressure During Inspiration in Normal Conditions
During inspiration, systolic blood pressure decreases, and pulse rate goes up. This is because the intrathoracic pressure becomes more negative relative to atmospheric pressure.  This increases systemic venous return, so more blood flows into the right side of the heart. However, the decrease in intrathoracic pressure also expands the compliant pulmonary vasculature. This increase in pulmonary capacitance pools the blood in the lungs, and decreases pulmonary venous return, so flow is reduced to the left side of the heart. Reduced left-heart filling leads to a reduced stroke volume which manifests as a decrease in systolic blood pressure.  The decrease in systolic blood pressure leads to a faster heart rate due to the baroreceptor reflex, which stimulates sympathetic outflow to the heart.

# Mechanism of Reduced Blood Pressure During Inspiration in Pulsus Paradoxus
A decrease in blood pressure and increase in pulse rate is normally seen with inspiration. As explained above, this is seen normally as a result of increased pulmonary venous capacitance during inspiration, that in turn leads to decrease in blood from lungs to left ventricle resulting in drop of blood pressure and increase in pulse rate during inspiration. Normally the drop in blood pressure is 10 mmHg) on inspiration. The reason for the increased fall in blood pressure is the limitation on outward expansion of the right ventricle  in tamponade and other conditions. The right ventricular increased pressure during inspiration results in bulging of the interventricular septum into the left ventricle, leading to a large reduction in left ventricular filling that contributes to a large decrease in stroke volume. The paradox in pulsus paradoxus is that, on clinical examination, one can detect extra beats on cardiac auscultation, during inspiration, when compared to the radial pulse.  It results from an accentuated decrease of the blood pressure, which leads to the (radial) pulse not being palpable and may be accompanied by an increase in the jugular venous pressure height (Kussmaul sign).  As is usual with inspiration, the heart rate is increased, due to increased venous return.

# Measurement of Pulsus Paradoxus
PP is quantified using a blood pressure cuff and stethoscope, by measuring the variation of the pressure in systole with respiration. Normal systolic blood pressure variation (with respiration) is considered to be 10 mmHg.  Pulsus paradoxus is an inspiratory reduction in systolic pressure >10 mmHg. Pulsus paradoxus can also be measured by listening to Korotkoff sounds and hearing the actual sound of the systolic beat. If the pressure gradient is >10mmHg, it can be classified as pulsus paradoxus and shifting of the atrial septum.

# Predictive Value for Tamponade
PP has been shown to be predictive of the severity of cardiac tamponade.

# Causes

## Common Causes
Pulsus paradoxus can be caused by several physiologic mechanisms.  Anatomically, these can be grouped into:
- Decreased right heart functional reserve, e.g. myocardial infarction and tamponade,
- Right ventricular inflow or outflow obstruction, e.g. superior vena cava obstruction and pulmonary embolism, and
- Decreased blood to the left heart due to pulmonary vasodilation/hyperinflation, e.g. asthma, COPD and anaphylactic shock.

## Causes by Organ System
Cardiac:
- Cardiac tamponade
- Pericardial effusion
- Pulmonary embolism
- Cardiogenic shock
- Adhesive pericarditis
- Constrictive pericarditis
- Endocardial fibrosis
- Mitral stenosis with right heart failure
- Myocardial amyloidosis
- Tricuspid stenosis
Pulmonary:
- Tension pneumothorax
- Asthma
- Pulmonary embolism
Non-pulmonary and non-cardiac:
- Anaphylactic shock
- Cytarabine
- Superior vena cava obstruction
- Hypovolemia
- Scleroderma

## Causes in Alphabetical Order
- Adhesive pericarditis
- Cardiac Tamponade
- Cytarabine
- Constrictive pericarditis
- Endocardial fibrosis
- Hypovolemia
- Mitral stenosis with right heart failure
- Myocardial amyloidosis
- Paramediastinal effusion
- Pericardial effusion
- Pulmonary embolism
- Pulmonary emphysema
- Scleroderma
- Severe asthma
- Tricuspid stenosis

# Related Chapters
- Precordial exam
- Pulsus alternans
- Cardiac tamponade