B

Reasoning: Pulsus paradoxus—the key blood-pressure finding in cardiac tamponade—is defined as a fall in systolic pressure of >10 mm Hg during normal inspiration. To detect this, the cuff is applied while the patient breathes in an unforced, ordinary manner; breath-holding or exaggerated breathing would mask or exaggerate the phenomenon. [Sulzbach, 1989, PMID 2714486; Hamzaoui, 2013, PMID 23222878]