a) Under normal conditions the human heart exerts a pressure of 110 mmHg on the

Question

a) Under normal conditions the human heart exerts a pressure of 110 mmHg on the arterial blood. What is the arterial blood pressure in the feet of a man standing upright? What is the blood pressure in the brain? The feet are 140 cm below the level of the heart; the brain is 40 cm above the level of the heart; the density of human blood is 1055 kg/m3. Neglect the speed of flow of the blood, i.e., pretend it is at rest.

(b) Under conditions of stress the human heart can exert a pressure of up to 190 mmHg. Suppose that an astronaut were to land on the surface of a large planet where the acceleration of gravity is 61 m/s2. Could the astronaut's heart maintain a positive blood pressure in his brain while he is standing upright? Could the astronaut survive?

Explanation / Answer

110mm-Hg = 1.47x104 N/m2 (pascal)

p = p(o) - g(density)(z)

p(feet) = 1.47x104 + (9.81)(1055)(1.4)
p(feet) = 2.92x104

p(brain) = 1.47x104 - (9.81)(1055)(0.4)
p(brain) = 1.06x104

(b)

p = p(o) - g(density)(z)
p(brain) = 1.47x104 - (61.0)(1055)(0.4)

p(brain) = 1.47x104 - 2.47x104
p(brain) = -1.1 x 104

no, no

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