Why are blood pressure values commonly reported in mmHg?

Why are blood pressure values commonly reported in mmHg?

• A. Mercury is about 13.5 times heavier than water for the same volume
• B. Water density is too low
• C. The unit mmHg is easier to interpret color changes
• D. The cuff uses metal mercury to calibrate

Answer: (A)

Measuring pressure in millimeters of mercury comes from using a column of mercury to balance arterial pressure. Mercury is extremely dense, about 13.5 times heavier than water for the same volume, so a relatively short column of mercury is enough to balance the pressures produced by the arteries. That makes readings easy to read: a systolic pressure around 120 mmHg means about a 120‑millimeter tall mercury column. If water were used instead, the column would have to be much taller—unwieldy and hard to read. Today, some devices aren’t mercury-based, but the unit mmHg remains as a standard because of historical calibration and widespread continuity. The other options don’t explain why the unit is used: water’s density being lower isn’t about readability of the unit itself, color changes aren’t involved, and cuff calibration isn’t universally done with mercury in modern devices.

Measuring pressure in millimeters of mercury comes from using a column of mercury to balance arterial pressure. Mercury is extremely dense, about 13.5 times heavier than water for the same volume, so a relatively short column of mercury is enough to balance the pressures produced by the arteries. That makes readings easy to read: a systolic pressure around 120 mmHg means about a 120‑millimeter tall mercury column. If water were used instead, the column would have to be much taller—unwieldy and hard to read. Today, some devices aren’t mercury-based, but the unit mmHg remains as a standard because of historical calibration and widespread continuity. The other options don’t explain why the unit is used: water’s density being lower isn’t about readability of the unit itself, color changes aren’t involved, and cuff calibration isn’t universally done with mercury in modern devices.