From the Guidelines

Pulsus paradoxus is defined as a drop in systolic blood pressure >10 mmHg during inspiration, while diastolic blood pressure remains unchanged.

Pulsus paradoxus is a key diagnostic finding in cardiac tamponade, a life-threatening condition characterized by the accumulation of fluid in the pericardial space, leading to compression of the heart 1.
The magnitude of pulsus paradoxus is evaluated by sphygmomanometry, and a difference of >10 mmHg between the systolic blood pressure during expiration and inspiration is considered significant 1.
Pulsus paradoxus is due to exaggerated ventricular interdependence, which occurs when the overall volume of cardiac chambers becomes fixed, and any change in the volume of one side of the heart causes opposite changes in the other side 1.

Pulsus paradoxus can be detected by feeling the pulse, and its presence is apparent when the patient is breathing normally 1.
Echocardiography is a useful diagnostic tool to identify pericardial effusion and estimate its size, location, and degree of hemodynamic impact, and can also guide pericardiocentesis 1.
Other diagnostic tools, such as ECG, chest X-ray, and cardiac catheterization, may also be used to diagnose cardiac tamponade and pulsus paradoxus 1.

The treatment of cardiac tamponade involves drainage of the pericardial fluid, preferably by needle pericardiocentesis, with the use of echocardiographic or fluoroscopic guidance, and should be performed without delay in unstable patients 1.
Key points to remember are that pulsus paradoxus is a significant finding in cardiac tamponade, and its diagnosis and treatment require a multidisciplinary approach, including echocardiography, cardiac catheterization, and pericardiocentesis 1.

From the Research

Pulsus paradoxus is defined as an exaggerated fall in systolic blood pressure with inspiration, typically greater than 10 mmHg 2, 3, 4, 5.
It is characterized by a decline in systemic systolic blood pressure by more than 10 mmHg during inspiration 3.

Pulsus paradoxus is a valuable clinical sign that can occur in conditions such as cardiac tamponade, constrictive pericarditis, asthma, and other clinical conditions 2, 3, 5.
The predictive value of a present or absent pulsus paradoxus is rather limited in certain situations, such as inflow obstruction into the heart or extreme respiratory variations in intrathoracal pressure 3.
Pulsus paradoxus can be measured using various methods, including palpation, cuff sphygmomanometry, and arterial wave formation 4.
The phenomenon of pulsus paradoxus can be altered in mechanically ventilated patients, with the pattern of changes observed in pulsus paradoxus being reversed 6.

Inspiratory increases in right heart filling and output are necessary for pulsus paradoxus to occur, causing increases in right ventricular dimensions and pulmonic and tricuspid velocities, and decreases in left ventricular dimensions and aortic and mitral velocities and left ventricular diastolic compliance 2.
Doppler studies of pulmonary venous inflow confirm that an inspiratory fall in left atrial filling is necessary for pulsus paradoxus 2.
Echocardiography has aided in understanding the mechanisms underlying pulsus paradoxus and its presence in other conditions 2.