Measurement of pulsus paradoxus and pulse pressure variation ultimately both reflect cardiac filling status.

1. What does each measure?

2. What main hemodynamic element does both of these measurements use to reveal it's respective clinical finding?

3. Diagnoses aside, what is the single distinguishing circumstance in how these two things are measured? In other words, if this circumstance exists, one
cannot be measured but the other one can, and if it does not exist, the converse is true.