# What is the Blood Pressure at Different Heights?

• ana111790
In summary, the average man's blood pressure at the level of his feet is 25763 Pa and at the level of his brain when standing is 30213 Pa. When lying down, with his feet and brain at the same height, the blood pressure at both locations is 12103 Pa. The formula for calculating the blood pressure is P = rho*g*h, with h being the height from the heart to the location of interest and the second term being negative if the location is above the heart.
ana111790

## Homework Statement

An average man is 5'9" (1.75 m) tall and his heart is 4'4" (1.32 m) above the ground. If the mean arterial blood pressure at the level of the heart is 91mmHg (12103 Pa) and the density of blood is given as 1.056*10^3 kg/m^3.
a) What is the blood pressure in the man's feet in Pa? In the brain when he is standing up tall?
b) The person now lies down so that his feet and brain are at the same height. When his body returns to hydrostatic equilibrium the mean arterial blood pressure remains the same as above. What is the blood pressure in the feet and brain when he is lying down>

## Homework Equations

P = rho*g*h (Pascal's principle)

## The Attempt at a Solution

I am not sure what the signs should be but for part a)
P = P heart + rho*g*h (where h is the height from the heart to the feet)
P = 12103 + (1.056*10^3) * (9.8) * (1.32 m)
P = 25763 Pa
and
P = P heart + rho*g*h (where h is the height from the heart to the brain)
P = 12103 + (1.056*10^3) * (9.8) * (1.75 m)
P = 30213 Pa

Is this correct at all? I am not sure how to approach part B.
Thanks for any help!

The first calc looks great.
In the second, shouldn't the height difference from heart to head be 1.75 - 1.32? And the second term should be negative; the pressure at the head is less than at the heart.

## 1. What is the definition of pressure?

Pressure is defined as the amount of force per unit area applied on an object or surface. In the context of atmospheric pressure at different heights, it refers to the weight of the air above a given point.

## 2. How does pressure change with height?

The pressure decreases as we move higher in the Earth's atmosphere. This is because the weight of the air above decreases with increasing altitude, resulting in a lower pressure.

## 3. What unit is used to measure pressure?

Pressure can be measured in several units, including Pascals (Pa), atmospheres (atm), and pounds per square inch (psi). In meteorology, pressure is usually measured in hectopascals (hPa) or millibars (mb).

## 4. Why does pressure change with altitude?

The main reason for the change in pressure with altitude is due to the gravitational force of the Earth. The higher we go, the less air there is above us, leading to a decrease in pressure.

## 5. How does pressure affect weather patterns?

Pressure plays a crucial role in determining weather patterns. Areas of high pressure typically indicate clear and dry weather, while low pressure can bring about cloudy and wet conditions. Changes in pressure can also lead to the formation of storms and other severe weather events.

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