If the blood pressure in your brain is 120 mm when you are lying down, what would it be when you stand up? Assume that your brain is 40 cm from your heart and that rho = 1060 kg/m3 for your blood. Note: Normally, your blood vessels constrict and expand to keep your brain blood pressure stable when you change your posture.

The correct answer is 88.84 mmHg.

Explanation:

The pressure differential between the brain and the heart while standing up will be 120 - rho * g (gravity) * h, here h is the distance from the brain to the heart. The h is 40 cm or 0.4 m.

rho*g*h = 1060 kg/m³*9.8 m/s²*0.4m

= 4155 Pa

Now converting Pa to mmHg we get:

4155 Pa * 760 mmHg / 1.01325 * 10⁵ Pa

= 31.16 mmHg

Thus, the pressure in the brain now is 120 - 31.16

= 88.84 mmHg (hypotension)