In medicine, a pulsus paradoxus (PP), also paradoxic pulse or paradoxical pulse, is defined as an abnormally large decrease in systolic blood pressure and pulse wave amplitude during inspiration. The normal fall in pressure is less than 10 mmHg or 10 torr. When the drop is more than 10mm Hg, it is referred to as pulsus paradoxus. Pulsus paradoxus has nothing to do with pulse rate or heart rate. The normal variation of blood pressure during breathing/respiration is a decline in blood pressure during inhalation and an increase during exhalation. Pulsus paradoxus is a sign that is indicative of several conditions, including cardiac tamponade, pericarditis, chronic sleep apnea, croup, and obstructive lung disease (e.g. asthma, COPD).
The paradox in pulsus paradoxus is that, on clinical examination, one can detect beats on cardiac auscultation during inspiration that cannot be palpated at 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's sign). As is usual with inspiration, the heart rate is slightly increased, due to decreased left ventricular output.
Read more about Pulsus Paradoxus: Mechanism of Reduced Blood Pressure During Inspiration in Normal Conditions and In Tamponade, Measurement of PP, Predictive Value For Tamponade, Causes, See Also