Pulsus paradoxus

Background

Definition: An exaggerated drop in systemic arterial pressure during inspiration (>10mmHg)

Inspiration is performed by decreasing intrathoracic pressure
Because the heart is in the thorax, this pressure is transmitted to the heart and causes a bigger gradient between the pressure in the veins outside of the thorax and the right atrium/ventricle
As such, with each inhalation, more blood flows into the right side of the heart
When this occurs, the interventricular septum subtly bulges into the LV cavity, lowering LV filling, and therefore lowering systemic stroke volume/BP
Because the ventricle can normally also expand outward, this septal shift is usually small, and the difference in the blood pressure is therefore small between inspiration and expiration (<10 mmHg)
In states in which the ventricle cannot expand outward (e.g. tamponade) or in which the drop in intrathoracic pressure with inspiration is profound (e.g. status asthmaticus), the septal shift is exaggerated and the difference in BP is larger

Intermitent Korotkoff Sounds - All Korotkoff Sounds = Pulsus Pressure (normal = <10mmHg)

Inflate manual BP cuff beyond the point where you hear any Korotkoff sounds
Slowly deflate the cuff until you start hearing any sounds
- At the highest BP when you hear sounds intermittently (rather than with every heart beat), note the blood pressure
- This corresponds to the higher systemic blood pressure which is occurring during expiration
Keep slowly deflating the cuff until you reach the highest BP in which you hear sounds every beat
The difference between *2 and *3 is the "pulsus paradoxus"
- If it is >10 mmHg, it is considered significant.

Severe pulsus paradoxus can be palpated in the pulse as a weakening or disappearance of the pulse during inspiration