Grey's Anatomy, Season 7

Meredith:
[voiceover] The human body is a highly pressurized system, the blood pressure measures the force of blood pulsating through the arteries. It's important to keep this pressure regulated, low or inadequate pressure can cause weakness or failure. It's when the pressure gets too high that problems really occur. If the pressure continues to increase, a closer examination is called for because it's the best indicator that something is going terribly wrong.