Direct measurement of arterial blood pressure is impractical because the required apparatus would have to be about how tall?

Direct measurement of arterial blood pressure is impractical because the required apparatus would have to be about how tall?

• A. Two meters
• B. One meter
• C. Ten centimeters
• D. Five meters

Answer: (A)

Direct arterial pressure measurement with a column of liquid works by balancing the arterial pressure against the hydrostatic pressure of a vertical fluid column. The height needed depends on the pressure magnitude and the liquid’s density: P = ρ g h. Arterial pressure is about 100–120 mmHg (roughly 13–16 kPa). Using water (ρ ≈ 1000 kg/m³, g ≈ 9.8 m/s²), the required height is h ≈ P/(ρ g) ≈ 16,000 Pa / (1000 × 9.8) ≈ 1.6 meters. So you’d need a water column around 1.6–2 meters tall to balance the pressure. That makes direct measurement with such a setup impractical in clinical practice, hence the reliance on indirect or noninvasive methods. Shorter heights like one meter or ten centimeters wouldn’t balance the arterial pressure, and five meters would far exceed what is needed.

Direct arterial pressure measurement with a column of liquid works by balancing the arterial pressure against the hydrostatic pressure of a vertical fluid column. The height needed depends on the pressure magnitude and the liquid’s density: P = ρ g h. Arterial pressure is about 100–120 mmHg (roughly 13–16 kPa). Using water (ρ ≈ 1000 kg/m³, g ≈ 9.8 m/s²), the required height is h ≈ P/(ρ g) ≈ 16,000 Pa / (1000 × 9.8) ≈ 1.6 meters. So you’d need a water column around 1.6–2 meters tall to balance the pressure. That makes direct measurement with such a setup impractical in clinical practice, hence the reliance on indirect or noninvasive methods. Shorter heights like one meter or ten centimeters wouldn’t balance the arterial pressure, and five meters would far exceed what is needed.