Question

To keep blood from pooling in their lower legs on plane trips, some people wear compression socks. These socks are sold by the pressure they apply; a typical rating is 20 mmHg.

Over what vertical distance can this pressure move the blood?

Express your answer with the appropriate units.

Answer 1

SI unit of pressure is Pascal but use of mm/cm of Hg is also popular.

pressure = , where h = height, = density of Hg (say 13600 kg/m³ and g= acceleration due to gravity

hence,

20 mm of Hg =0.02*13600*9.8 = 2665.6 Pa

so, lets assume density of blood to be 1060 kg/m³

thus, = 2665.6 Pa

or, h = 2665.6/(1060*9.8) = 25.6 cm

hence, the sock rating 20 mm of Hg can move blood up to 25.6 cm.