Which finding indicates cardiac tamponade during inspiration?

The indicator of cardiac tamponade during inspiration is characterized by a drop of greater than 10 mm Hg in systolic blood pressure, a phenomenon known as pulsus paradoxus. This occurs due to the impaired filling of the heart's chambers during inspiration; as intrathoracic pressure decreases, venous return to the right side of the heart increases, which can limit left ventricular filling and subsequently lower the systolic blood pressure. This drop is significant in the context of cardiac tamponade, where the pericardial fluid accumulation restricts the heart's ability to expand and fill properly.

In conditions like cardiac tamponade, monitoring blood pressure can reveal this critical hemodynamic change. Hence, recognizing this drop in blood pressure during inspiration serves as an important clinical sign for diagnosing cardiac tamponade.