Pulsus paradoxus is a characteristic feature of -

Pulsus paradoxus (PP), also paradoxic pulse or paradoxical pulse, is an abnormally large decrease in systolic blood pressure and pulse wave amplitude during inspiration . The normal fall in pressure is less than 10 mm hg . When the drop is more than 10 mm Hg, it is referred to as pulsus paradoxus. Pulsus paradoxus is not related to pulse rate or hea rate and it is not a paradoxical rise in systolic pressure. 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). Ref Harrison 20th edition pg 1734