Pulsus paradoxus is one in which, during inspiration, the pulse becomes feeble or imperceptible. Since the time of Griesenger and Kussmaul pulsus paradoxus has been observed in a variety of pathologic conditions. F. Rigel1 classifies these conditions as follows:
Mechanical interference with the large veins and aorta, as in Kussmaul's case. Here the heart is unaffected.
Obstructions in the air passage, causing an increased negative intra-thoracic pressure, which inhibits the heart's action.
Lowered activity of the heart.
Pulsus paradoxus is a distinct variation from the normal, consequently it is pathologic and must have a cause. As pulsus paradoxus has been observed in a variety of conditions, its causes must vary, but in each condition this cause should be constant. From a clinical point of view pulsus paradoxus should be a sign of the existence of its cause, and the importance of this sign must depend on the nature of
CALVERT WJ. PULSUS PARADOXUS IN PERICARDITIS WITH EFFUSION.. JAMA. 1907;XLVIII(14):1168-1171. doi:10.1001/jama.1907.25220400020001f