pulsus paradoxus

Pulsus paradoxus is an exaggerated fall in blood pressure each time a person breathes in. Normally the systolic pressure dips by only a small amount with inspiration; when that dip exceeds about 10 millimetres of mercury, it is called pulsus paradoxus, and the pulse may even seem to fade away at the wrist during a deep breath.

The name is a little misleading: it is not truly paradoxical but an exaggeration of normal physiology. With inspiration, more blood is drawn into the right side of the heart. When the heart is confined, as in cardiac tamponade, the filling right ventricle bulges against the septum and crowds the left ventricle, which then ejects less blood, dropping the systolic pressure during inhalation.

It is a classic and important sign of cardiac tamponade and is therefore actively sought when an effusion is suspected. It is not unique to tamponade, however; it also appears in severe asthma, chronic lung disease, constrictive pericarditis, and large pulmonary embolism, so it must be interpreted in context. It is measured at the bedside with a blood-pressure cuff.