In standing, how does leg BP typically compare to arm BP, and what explains this difference?

In standing, how does leg BP typically compare to arm BP, and what explains this difference?

• A. Leg BP is lower due to hydrostatic pressure
• B. Leg BP is higher due to hydrostatic pressure
• C. Leg BP is the same as arm BP at all times
• D. Leg BP cannot be measured standing

Answer: (B)

In standing, gravity creates a hydrostatic pressure gradient along the vertical axis of the body. The leg is substantially below the heart, so the arterial pressure there must rise to push blood up against gravity. This hydrostatic column adds pressure to the leg arteries, making leg blood pressure higher than arm blood pressure when standing. The difference reflects the weight of the blood column from heart to the leg and is roughly in the tens of millimeters of mercury range for the gradient, explaining why the leg shows higher pressures while the arm remains closer to the heart level. When lying down, this gradient disappears because the heart and measurement sites are at about the same level.

In standing, gravity creates a hydrostatic pressure gradient along the vertical axis of the body. The leg is substantially below the heart, so the arterial pressure there must rise to push blood up against gravity. This hydrostatic column adds pressure to the leg arteries, making leg blood pressure higher than arm blood pressure when standing. The difference reflects the weight of the blood column from heart to the leg and is roughly in the tens of millimeters of mercury range for the gradient, explaining why the leg shows higher pressures while the arm remains closer to the heart level. When lying down, this gradient disappears because the heart and measurement sites are at about the same level.