Pulsus paradoxus is a drop in blood pressure of more than 10 mmHg (millimeters of mercury) when taking a breath. It’s a very specific sign that can only be adequately recognized when monitoring pressure with an arterial catheter. Pulsus paradoxus is a sign of some other condition and by itself is not a medical condition.
When you breathe in (called inspiration or inhalation), your blood pressure drops a little. However, when the amount of change in blood pressure is big enough, this is called pulsus paradoxus and could be a sign of one of several significant medical conditions.
How much of a drop is too much? A doctor named Adolf Kussmaul arbitrarily picked 10 mmHg over 100 years ago (which translates into 10 points using the standard mercury pressure gauge) and medical professionals have been using that number ever since.
