Estimating Heart Power Output for Humans Standing/Lying Down

In summary, the task is to estimate the change in power output of the heart in a standing and lying down position, using conservation of energy and the equation P = W/t. The potential energy of the body is calculated using mgh, and the work done by the blood can be calculated by considering the mass of blood involved and the height it is lifted. It may be helpful to consider the effects of siphoning and the fact that blood may be lifted or fall back to the heart.
  • #1
gunster
7
0

Homework Statement



Humans have about v = 60 cm3
of blood per kilogram of body mass and blood makes a
complete circuit in t = 20 s seconds. For a
human body of thickness 0.2 m and height
1.8 m, estimate the change in power output of
the heart when the body is standing up on a
horizontal surface compared to when the body
is lying down on the same surface. Assume
that the density of blood is ρ = 0.001 kg/cm3
and the mass of the human body is 66 kg. Use
g = 9.8 m/s

Homework Equations


P = W/t

Conservation of energy


The Attempt at a Solution



Completely clueless really. I assume that I need to use conservation of energy to find the work.

I set mgh as the PE of the body for both cases when h = 1.8 (standing horizontal) and h=0.3 (lying down)

however, I have no idea how I could find the work that the blood does. Can anyone explain to me how I can go about doing that?
 
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  • #2
Do you know how to calculate the work needed to lift mass m to height h? You could use work done = potential energy gained, so W = mgh.
It will be a bit tricky to see what mass of blood is involved and how much it is lifted in each case.

Or is it lifted? You could argue that siphoning of the blood means there is no real lift involved at all. Oh, I shouldn't have mentioned that this thought - clearly you are asked to calculate lifting to a height so don't think about siphoning. Blood that initially falls down will have to be lifted back up to the heart while blood that is initially lifted will then fall back to the heart, so maybe a factor of 1/2 involved.
 

FAQ: Estimating Heart Power Output for Humans Standing/Lying Down

1. How is heart power output calculated for humans?

Heart power output is typically calculated by multiplying the stroke volume (the amount of blood pumped by the heart per beat) by the heart rate (the number of beats per minute). This gives the amount of blood pumped by the heart in one minute, which is equivalent to the power output of the heart.

2. Does heart power output differ between standing and lying down?

Yes, heart power output is affected by body position. When standing, the heart has to work against gravity to pump blood to the upper body, resulting in a higher power output. When lying down, the heart doesn't have to work as hard, so the power output is lower.

3. Can heart power output be measured directly?

No, heart power output cannot be measured directly. It is estimated based on the stroke volume and heart rate, which can be measured using various methods such as echocardiography, electrocardiography, or pulse oximetry.

4. What factors can affect heart power output?

Several factors can affect heart power output, including age, physical fitness, body position, and overall health. For example, a younger and physically fit person may have a higher heart power output compared to an older and less fit person.

5. Why is it important to estimate heart power output?

Estimating heart power output can provide valuable information about the functioning of the heart and overall cardiovascular health. It can also help in diagnosing and monitoring certain heart conditions, such as heart failure, and can be used to track improvements in physical fitness.

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