PULSUS PARADOXUS

- Definition:-

  Inspiratory decline in systolic pressure greater than 10mm of Hg.

- Measurement :-

 Step 1 : inflate blood pressure cuff until no sounds are heard.

Step 2  : slowly decrease the pressure until systolic sound are heard during expiration but not during inspiration. Note this pressure

Step 3 : decrease the pressure further until sounds are heard through out the respiratory cycle. Note this pressure.

Step 4 : if pressure difference between the two is greater than 10mm Hg, it is called as Pulsus Paradoxus.

- Seen in :-

Acute severe Asthma.

Cardiac tamponade.

Pericardial constriction.

- Mechanism :-

Normally, during inspiration, there is a decrease in intra thoracic pressure which results in increased venous return. This causes increased right ventricular filling and stroke volume, but the left ventricular stroke volume falls slightly.

But in Cardiac tamponade and pericardial constriction, the increased inspiratory right ventricular stroke volume reduces the left ventricular compliance, resulting in pronounced fall in systolic pressure during the inspiration.   

In case of acute severe asthma, the negative pleural pressure increasing the afterload and thereby impedance to left ventricular filling.