How It Works: This simulation shows what would happen to blood pressure if ONLY vessel diameter changed, keeping cardiac output constant at 5 L/min.

Notice: When the vessel widens, resistance drops dramatically because of the radius-to-the-fourth-power relationship. This means even small changes in diameter cause huge changes in resistance!

The Mystery: If vessel diameter alone worked this way, Carlos' blood pressure should have DROPPED during exercise when his artery widened. But his actual BP went UP to 142/88 mmHg! What's the missing piece? (Hint: What else increases during exercise?)