Which statement accurately describes the unit in which blood pressure is reported in clinical practice?

• A. Atmospheres (atm)
• B. Pascals (Pa)
• C. Millimeters of mercury (mmHg)
• D. Torr

Answer: (C)

Blood pressure is reported in millimeters of mercury because the measurement originally came from the height of a mercury column in a sphygmomanometer. The pressure in the arteries is balanced by that mercury column, so the pressure is directly reflected by the height in millimeters. This unit makes the typical blood pressure numbers—like around 120 over 80—easy to grasp and remember, since they fall within a convenient, familiar range. Using pascals would yield numbers around 16,000 Pa for 120 mmHg, which is less intuitive for daily clinical use. Atmospheres would compress these readings into very small fractions of an atmosphere, making themselves impractical for routine reporting. Torr is essentially the same magnitude as millimeters of mercury, but the standard clinical convention is to use millimeters of mercury.